@article{smirnov_kokorin_kovaleva_2023, title={Magnetic Resonance in Molecular Biology, Biophysics and Biochemistry}, volume={2}, ISSN={["1613-7507"]}, DOI={10.1007/s00723-023-01527-w}, journal={APPLIED MAGNETIC RESONANCE}, author={Smirnov, Alex I. I. and Kokorin, Alexander I. I. and Kovaleva, Elena G. G.}, year={2023}, month={Feb} }
 @article{nunn_milikisiyants_danilov_torelli_dei cas_zaitsev_shenderova_smirnov_shames_2022, title={Electron irradiation-induced paramagnetic and fluorescent defects in type Ib high pressure-high temperature microcrystalline diamonds and their evolution upon annealing}, volume={132}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0103313}, DOI={10.1063/5.0103313}, abstractNote={Defects introduced to synthetic type Ib diamond micrometer-size particles by electron-beam irradiation were studied by electron paramagnetic resonance and photoluminescence (PL) spectroscopy as a function of e-beam fluence and post-irradiation thermal annealing. Increasing electron-beam fluence causes a substantial reduction of the substitutional nitrogen (P1) content, accompanied by progressively higher concentrations of paramagnetic negatively charged vacancies (V − ) and triplet interstitials (R1/R2). Annealing results in a drastic decrease in the V − and R1/R2 content and an increase in the negatively charged nitrogen-vacancies (NV − or W15). Analysis of PL spectra allows for identification of color centers in the irradiated diamond samples and following their evolution after annealing. These data facilitate understanding of different factors contributing to the formation of color centers in diamond and promote efforts toward controlled engineering of optical centers in fluorescent diamond particles.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Nunn, Nicholas and Milikisiyants, Sergey and Danilov, Evgeny O. and Torelli, Marco D. and Dei Cas, Laura and Zaitsev, Alexander and Shenderova, Olga and Smirnov, Alex I. and Shames, Alexander I.}, year={2022}, month={Aug} }
 @article{nevzorov_marek_milikisiyants_smirnov_2021, title={Characterization of photonic band resonators for DNP NMR of thin film samples at 7 T magnetic field}, volume={323}, ISSN={["1096-0856"]}, DOI={10.1016/j.jmr.2020.106893}, abstractNote={Polarization of nuclear spins via Dynamic Nuclear Polarization (DNP) relies on generating sufficiently high mm-wave B1e fields over the sample, which could be achieved by developing suitable resonance structures. Recently, we have introduced one-dimensional photonic band gap (1D PBG) resonators for DNP and reported on prototype devices operating at ca. 200 GHz electron resonance frequency. Here we systematically compare the performance of five (5) PBG resonators constructed from various alternating dielectric layers by monitoring the DNP effect on natural-abundance 13C spins in synthetic diamond microparticles embedded into a commercial polyester-based lapping film of just 3 mil (76 μm) thickness. An odd-numbered configuration of dielectric layers for 1D PBG resonator was introduced to achieve further B1e enhancements. Among the PBG configurations tested, combinations of high-ε perovskite LiTaO3 together with AlN as well as AlN with optical quartz wafers have resulted in ca. 40 to over 50- fold gains in the average mm-wave power over the sample vs. the mirror-only configuration. The results are rationalized in terms of the electromagnetic energy distribution inside the resonators obtained analytically and from COMSOL simulations. It was found that average of B1e2 over the sample strongly depends on the arrangement of the dielectric layers that are the closest to the sample, which favors odd-numbered PBG resonator configurations for their use in DNP.}, journal={JOURNAL OF MAGNETIC RESONANCE}, author={Nevzorov, Alexander A. and Marek, Antonin and Milikisiyants, Sergey and Smirnov, Alex I.}, year={2021}, month={Feb} }
 @article{voinov_smirnova_smirnov_2021, title={EPR Oximetry with Nitroxides: Effects of Molecular Structure, pH, and Electrolyte Concentration}, volume={11}, ISSN={["1613-7507"]}, url={https://doi.org/10.1007/s00723-021-01446-8}, DOI={10.1007/s00723-021-01446-8}, journal={APPLIED MAGNETIC RESONANCE}, author={Voinov, Maxim A. and Smirnova, Tatyana I and Smirnov, Alex I}, year={2021}, month={Nov} }
 @article{chestnut_milikisiyants_chatterjee_kern_smirnov_2021, title={Electronic Structure of the Primary Electron Donor P-700(+center dot) in Photosystem I Studied by Multifrequency HYSCORE Spectroscopy at X- and Q-Band}, volume={125}, ISSN={["1520-5207"]}, url={https://doi.org/10.1021/acs.jpcb.0c09000}, DOI={10.1021/acs.jpcb.0c09000}, abstractNote={The primary electron donor P700 of the photosystem I (PSI) is a heterodimer consisting of two chlorophyll molecules. A series of electron-transfer events immediately following the initial light excitation leads to a stabilization of the positive charge by its cation radical form, P700+•. The electronic structure of P700+• and, in particular, its asymmetry with respect to the two chlorophyll monomers is of fundamental interest and is not fully understood up to this date. Here, we apply multifrequency X- (9 GHz) and Q-band (35 GHz) hyperfine sublevel correlation (HYSCORE) spectroscopy to investigate the electron spin density distribution in the cation radical P700+• of PSI from a thermophilic cyanobacterium Thermosynechococcus elongatus. Six 14N and two 1H distinct nuclei have been resolved in the HYSCORE spectra and parameters of the corresponding nuclear hyperfine and quadrupolar hyperfine interactions were obtained by combining the analysis of HYSCORE spectral features with direct numerical simulations. Based on a close similarity of the nuclear quadrupole tensor parameters, all of the resolved 14N nuclei were assigned to six out of total eight available pyrrole ring nitrogen atoms (i.e., four in each of the chlorophylls), providing direct evidence of spin density delocalization over the both monomers in the heterodimer. Using the obtained experimental values of the 14N electron-nuclear hyperfine interaction parameters, the upper limit of the electron spin density asymmetry parameter is estimated as RA/Bupper = 7.7 ± 0.5, while a tentative assignment of 14N observed in the HYSCORE spectra yields RB/A = 3.1 ± 0.5.}, number={1}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, publisher={American Chemical Society (ACS)}, author={Chestnut, Melanie M. and Milikisiyants, Sergey and Chatterjee, Ruchira and Kern, Jan and Smirnov, Alex I}, year={2021}, month={Jan}, pages={36–48} }
 @article{zhang_chung_ke_lin_mebrahtu_smirnov_finkelstein_baranger_2021, title={Nonequilibrium quantum critical steady state: Transport through a dissipative resonant level}, volume={3}, ISSN={["2643-1564"]}, DOI={10.1103/PhysRevResearch.3.013136}, abstractNote={Nonequilibrium properties of correlated quantum matter are being intensively investigated because of the rich interplay between external driving and the many-body correlations. Of particular interest is the nonequilibrium behavior near a quantum critical point (QCP), where the system is delicately balanced between different ground states. We present both an analytical calculation of the nonequilibrium steady-state current in a critical system and experimental results to which the theory is compared. The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an Ohmic dissipative environment. A two-channel Kondo-like QCP occurs when the level is on resonance and symmetrically coupled to the leads, conditions achieved by fine tuning using electrostatic gates. We calculate and measure the nonlinear current as a function of bias (I−V curve) at the critical values of the gate voltages corresponding to the QCP. The quantitative agreement between the experimental data and the theory, with no fitting parameter, is excellent. As our system is fully accessible to both theory and experiment, it provides an ideal setting for addressing nonequilibrium phenomena in correlated quantum matter.Received 16 October 2020Revised 16 January 2021Accepted 21 January 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.013136Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCoulomb blockadeQuantum criticalityTransport phenomenaPhysical SystemsNanotubesQuantum dotsCondensed Matter, Materials & Applied PhysicsGeneral Physics}, number={1}, journal={PHYSICAL REVIEW RESEARCH}, author={Zhang, Gu and Chung, Chung-Hou and Ke, Chung-Ting and Lin, Chao-Yun and Mebrahtu, Henok and Smirnov, Alex I and Finkelstein, Gleb and Baranger, Harold U.}, year={2021}, month={Feb} }
 @article{seed_acharya_perelygin_smirnov_krim_2021, title={Tribotronic control and cyclic voltammetry of platinum interfaces with metal oxide nanofluids}, volume={566}, ISSN={["1873-5584"]}, DOI={10.1016/j.apsusc.2021.150675}, abstractNote={Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are reported for aqueous suspensions of positively charged Al2O3 and negatively charged TiO2 nanoparticles, employing Quartz Crystal Microbalance (QCM) and cyclic voltammetry (CV) techniques. Tribotronic methods were employed to adjust the nanoparticles’ positions relative to Pt surface electrodes, and both voltammetry and tribological performance measures were observed to be highly sensitive to the adjustments. Interfacial friction levels were observed to be higher for both types of nanoparticles when electrostatically driven towards the surface. For electric fields of sufficient amplitude and duration, the TiO2 nanosuspension exhibited properties consistent with reversible electrophoretic deposition of the nanoparticles, accompanied by changes in the electrochemical attributes of the electrode itself. Overall, the study suggests a method for active tribological control and optimization of device performance in applications where suspensions of charged nanoparticles are present and can be exposed to external fields.}, journal={APPLIED SURFACE SCIENCE}, author={Seed, C. M. and Acharya, B. and Perelygin, V and Smirnov, A. and Krim, J.}, year={2021}, month={Nov} }
 @article{cha_milikisiyants_davidson_xue_smirnova_smirnov_guo_chang_2020, title={Alternative Reactivity of Leucine 5-Hydroxylase Using an Olefin-Containing Substrate to Construct a Substituted Piperidine Ring}, volume={59}, ISSN={["0006-2960"]}, url={https://doi.org/10.1021/acs.biochem.0c00289}, DOI={10.1021/acs.biochem.0c00289}, abstractNote={Applying enzymatic reactions to produce useful molecules is a central focus of chemical biology. Iron and 2-oxoglutarate (Fe/2OG) enzymes are found in all kingdoms of life and catalyze a broad array of oxidative transformations. Herein, we demonstrate that the activity of an Fe/2OG enzyme can be redirected when changing the targeted carbon hybridization from sp3 to sp2. During leucine 5-hydroxylase catalysis, installation of an olefin group onto the substrate redirects the Fe(IV)-oxo species reactivity from hydroxylation to asymmetric epoxidation. The resulting epoxide subsequently undergoes intramolecular cyclization to form the substituted piperidine, 2S,5S-hydroxypipecolic acid.}, number={21}, journal={BIOCHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Cha, Lide and Milikisiyants, Sergey and Davidson, Madison and Xue, Shan and Smirnova, Tatyana I and Smirnov, Alex I and Guo, Yisong and Chang, Wei-Chen}, year={2020}, month={Jun}, pages={1961–1965} }
 @article{kovaleva_molochnikov_tambasova_marek_chestnut_osipova_antonov_kirilyuk_smirnov_2020, title={Electrostatic properties of inner nanopore surfaces of anodic aluminum oxide membranes upon high temperature annealing revealed by EPR of pH-sensitive spin probes and labels}, volume={604}, ISSN={["1873-3123"]}, url={https://doi.org/10.1016/j.memsci.2020.118084}, DOI={10.1016/j.memsci.2020.118084}, abstractNote={Anodic aluminum oxide (AAO) membranes are versatile nanomaterials that combine the chemically stable and mechanically robust properties of ceramics with homogeneous nanoscale organization that can be tuned to desirable pore diameters and lengths. The AAO substrates feature high surface area that is readily accessible to large and small molecules, making these nanostructures uniquely suited for many possible applications. Examples include templated self-assembly of macroscopically aligned biological membranes and substrates for heterogeneous catalysis. For further development of such applications, one would like to characterize and tune the electrostatic properties of the inner pore surface as well as the local acidity within the nanochannels. Here, we employed electron paramagnetic resonance (EPR) spectroscopy of a small molecule – ionizable nitroxide – as a reporter of the average local acidity in the nanochannels and the local electrostatic potential in the immediate vicinity of the pore surface. The former was achieved by measuring EPR spectra of this molecular probe diffusing in an aqueous phase confined in the AAO nanochannels while for the latter the nitroxide was covalently attached to the hydroxyl group of the alumina surface. We show that the local acidity within the nanochannels is increased by as much as ≈1.48 pH units vs. the pH of bulk solution by decreasing the pore diameter down to ca. 31 nm. Furthermore, the positive surface charge of the as-prepared AAO could be decreased and even switched to a negative surface charge upon annealing the membranes first to 700 °C and then to 1200 °C. For as-prepared AAO, the local electrostatic potential reaches ψ= (163 ± 5) mV for the nitroxide label covalently attached to AAO and located about 0.5 nm away from the surface. Overall, we demonstrate that the acid-based properties of the aqueous volume confined by the AAO nanopores pores can be tuned by either changing the pore diameter from ca. 71 to 31 nm or by thermal annealing to switch the sign of the surface charge. These observations provide a simple and robust means to tailor these versatile high-surface-area nanomaterials for specific applications that depend on acid-base equilibria.}, journal={JOURNAL OF MEMBRANE SCIENCE}, publisher={Elsevier BV}, author={Kovaleva, Elena G. and Molochnikov, Leonid S. and Tambasova, Daria and Marek, Antonin and Chestnut, Melanie and Osipova, Victoria A. and Antonov, Denis O. and Kirilyuk, Igor A. and Smirnov, Alex I}, year={2020}, month={Jun} }
 @book{smirnov_2020, title={Spectroscopic Tools for Food Analysis}, ISBN={["978-0-7503-2322-2"]}, DOI={10.1088/2053-2563/ab4428}, abstractNote={Food quality analysis is an area of interest that has always attracted the attention of everyone, and making suitable tools for food analysis is especially important. This volume presents such techniques and their state-of-the-art applications.}, journal={SPECTROSCOPIC TOOLS FOR FOOD ANALYSIS}, author={Smirnov, Alex I.}, year={2020}, pages={1–87} }
 @article{good_voinov_bolton_ward_sergeyev_caporini_scheffer_lo_rosay_marek_et al._2019, title={A biradical-tagged phospholipid as a polarizing agent for solid-state MAS Dynamic Nuclear Polarization NMR of membrane proteins}, volume={100}, ISSN={0926-2040}, url={http://dx.doi.org/10.1016/J.SSNMR.2019.04.003}, DOI={10.1016/j.ssnmr.2019.04.003}, abstractNote={A novel Dynamic Nuclear Polarization (DNP) NMR polarizing agent ToSMTSL-PTE representing a phospholipid with a biradical TOTAPOL tethered to the polar head group has been synthesized, characterized, and employed to enhance solid-state Nuclear Magnetic Resonance (SSNMR) signal of a lipid-reconstituted integral membrane protein proteorhodopsin (PR). A matrix-free PR formulation for DNP improved the absolute sensitivity of NMR signal by a factor of ca. 4 compared to a conventional preparation with TOTAPOL dispersed in a glassy glycerol/water matrix. DNP enhancements measured at 400 MHz/263 GHz and 600 MHz/395 GHz showed a strong field dependence but remained moderate at both fields, and comparable to those obtained for PR covalently modified with ToSMTSL. Additional continuous wave (CW) X-band electron paramagnetic resonance (EPR) experiments with ToSMTSL-PTE in solutions and in lipid bilayers revealed that an unfavorable conformational change of the linker connecting mononitroxides could be one of the reasons for moderate DNP enhancements. Further, differential scanning calorimetry (DSC) and CW EPR experiments indicated an inhomogeneous distribution and/or a possibility of a partial aggregation of ToSMTSL-PTE in DMPC:DMPA bilayers when the concentration of the polarizing agent was increased to 20 mol% to maximize the DNP enhancement. Thus, conformational changes and an inhomogeneous distribution of the lipid-based biradicals in lipid bilayers emerged as important factors to consider for further development of this matrix-free approach for DNP of membrane proteins.}, journal={Solid State Nuclear Magnetic Resonance}, publisher={Elsevier BV}, author={Good, Daryl B. and Voinov, Maxim A. and Bolton, David and Ward, Meaghan E. and Sergeyev, Ivan V. and Caporini, Marc and Scheffer, Peter and Lo, Andy and Rosay, Melanie and Marek, Antonin and et al.}, year={2019}, month={Aug}, pages={92–101} }
 @article{perelygin_voinov_marek_ou_krim_brenner_smirnova_smirnov_2019, title={Dielectric and Electrostatic Properties of the Silica Nanoparticle-Water Interface by EPR of pH-Sensitive Spin Probes}, volume={123}, ISSN={["1932-7455"]}, url={https://doi.org/10.1021/acs.jpcc.9b08007}, DOI={10.1021/acs.jpcc.9b08007}, abstractNote={Interfacial electrostatic properties of monodisperse silica nanoparticles (SiNPs) in aqueous suspensions as a function of bulk pH were characterized by spin labeling EPR of two ionizable nitroxides...}, number={49}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, publisher={American Chemical Society (ACS)}, author={Perelygin, Vladislav and Voinov, Maxim A. and Marek, Antonin and Ou, Erkang and Krim, Jacqueline and Brenner, Donald and Smirnova, Tatyana I and Smirnov, Alex I}, year={2019}, month={Dec}, pages={29972–29985} }
 @article{smirnova_smirnov_2019, title={EPR studies of bionanomaterials}, volume={50}, ISBN={["978-0-12-814024-6"]}, ISSN={["1079-4042"]}, DOI={10.1016/B978-0-12-814024-6.00007-8}, journal={ELECTRON MAGNETIC RESONANCE - APPLICATIONS IN PHYSICAL SCIENCES AND BIOLOGY}, author={Smirnova, Tatyana I. and Smirnov, Alex I.}, year={2019}, pages={129–159} }
 @article{milikisiyants_voinov_marek_jafarabadi_liu_han_wang_smirnov_2019, title={Enhancing sensitivity of Double Electron-Electron Resonance (DEER) by using Relaxation-Optimized Acquisition Length Distribution (RELOAD) scheme}, volume={298}, ISSN={1090-7807}, url={http://dx.doi.org/10.1016/J.JMR.2018.12.004}, DOI={10.1016/j.jmr.2018.12.004}, abstractNote={Over the past decades pulsed electron-electron double resonance (PELDOR), often called double electron-electron resonance (DEER), became one of the major spectroscopic tools for measurements of nanometer-scale distances and distance distributions in non-crystalline biological and chemical systems. The method is based on detecting the amplitude of the primary (3-pulse DEER) or refocused (4-pulse DEER) spin echo for the so-called spins when the other spins coupled to the former by a dipolar interaction are flipped by a pulse at another EPR frequency. While the timing of the pump pulse is varied in steps, the positions of the observer pulses are typically fixed. For such a detection scheme the total length of the observer pulse train and the electron spin memory time determine the amplitude of the detected echo signal. Usually, the distance range considerations in DEER experiments dictate the total length of the observer pulse train to exceed the phase memory time by a factor of few and this leads to a dramatic loss of the signal-to-noise ratio (SNR). While the acquisition of the DEER signal seems to be irrational under such conditions, it is currently the preferred way to conduct DEER because of an effective filtering out of all other unwanted interactions. Here we propose a novel albeit simple approach to improve DEER sensitivity and decrease data acquisition time by introducing the signal acquisition scheme based on RELaxation Optimized Acquisition (Length) Distribution (DEER-RELOAD). In DEER-RELOAD the dipolar phase evolution signal is acquired in multiple segments in which the observer pulses are fixed at the positions to optimize SNR just for that specific segment. The length of the segment is chosen to maximize the signal acquisition efficiency according the phase relaxation properties of the spin system. The total DEER trace is then obtained by stitching the multiple segments into a one continuous trace. The utility of the DEER-RELOAD acquisition scheme has been demonstrated on an example of the standard 4-pulse DEER sequence applied to two membrane protein complexes labeled with nitroxides. While theoretical gains from the DEER-RELOAD scheme increase with the number of stitched segments, in practice, even dividing the acquisition of the DEER trace into two segments may improve SNR by a factor of >3, as it has been demonstrated for one of these two membrane proteins.}, journal={Journal of Magnetic Resonance}, publisher={Elsevier BV}, author={Milikisiyants, Sergey and Voinov, Maxim A. and Marek, Antonin and Jafarabadi, Morteza and Liu, Jing and Han, Rong and Wang, Shenlin and Smirnov, Alex I.}, year={2019}, month={Jan}, pages={115–126} }
 @article{ma_lin_kim_ko_kim_oh_sun_gorman_voinov_smirnov_et al._2019, title={Liquid Metal Nanoparticles as Initiators for Radical Polymerization of Vinyl Monomers}, volume={8}, ISSN={["2161-1653"]}, url={https://doi.org/10.1021/acsmacrolett.9b00783}, DOI={10.1021/acsmacrolett.9b00783}, abstractNote={Sonication of gallium or gallium-based liquid metals in an aqueous solution of vinyl monomers leads to rapid free radical polymerization (FRP), without the need for conventional molecular initiators. Under ambient conditions, a passivating native oxide separates these metals from solution and renders the metal effectively inert. However, sonication generates liquid metal nanoparticles (LMNPs) of ∼100 nm diameter and thereby increases the surface area of the metal. The exposed metal initiates polymerization, which proceeds via a FRP mechanism and yields high molecular weight polymers that can form physical gels. Spin trapping EPR reveals the generation of free radicals. Time-of-flight secondary ion mass spectrometry measurements confirm direct polymer bonding to gallium, verifying the formation of surface-anchored polymer grafts. The grafted polymers can modify the interfacial properties, that is, the preference of the metal particles to disperse in aqueous versus organic phases. The polymer can also be degrafted and isolated from the particles using strong acid or base. The concept of physically disrupting passivated metal surfaces offers new routes for surface-initiated polymerization and has implications for surface modification, reduction reactions, and fabrication of mechanically responsive materials.}, number={11}, journal={ACS MACRO LETTERS}, publisher={American Chemical Society (ACS)}, author={Ma, Jinwoo and Lin, Yiliang and Kim, Yong-Woo and Ko, Yeongun and Kim, Jongbeom and Oh, Kyu Hwan and Sun, Jeong-Yun and Gorman, Christopher B. and Voinov, Maxim A. and Smirnov, Alex I. and et al.}, year={2019}, month={Nov}, pages={1522–1527} }
 @article{acharya_pardue_su_smirnov_brenner_krim_2019, title={Nanotribological Performance Factors for Aqueous Suspensions of Oxide Nanoparticles and Their Relation to Macroscale Lubricity}, volume={7}, ISSN={["2075-4442"]}, url={https://doi.org/10.3390/lubricants7060049}, DOI={10.3390/lubricants7060049}, abstractNote={Quartz crystal microbalance (QCM) measurements of nanotribological properties of statistically diverse materials combinations of nanoparticles and substrate electrodes in aqueous suspensions are reported and compared to macroscale measurements of the same materials combinations for a subset of the nanoparticle combinations. Four ceramic nanoparticles, TiO2, SiO2, Al2O3, and maghemite (γ-Fe2O3) and ten substrate materials (Au, Al, Cr, Cu, Mo, Ni, Pt, SiO2, Al2O3, and SS304) were studied. The QCM technique was employed to measure frequency and motional resistance changes upon introduction of nanoparticles into the water surrounding its liquid-facing electrode. This series of experiments expanded prior studies that were often limited to a single nanoparticle - solid liquid combination. The variations in QCM response from one nanoparticle to another are observed to be far greater than the variation from one substrate to another, indicating that the nanoparticles play a larger role than the substrates in determining the frictional drag force levels. The results were categorized according to the direction of the frequency and motional resistance changes and candidate statistical performance factors for the datasets were generated. The performance factors were employed to identify associations between the QCM atomic scale results and the macroscale friction coefficient measurements. Macroscale measurements of friction coefficients for selected systems document that reductions (increases) in motional resistance to shear, as measured by the QCM, are linked to decreases (increases) in macroscale friction coefficients. The performance factors identified in the initial study therefore appear applicable to a broader set of statistically diverse samples. The results facilitate full statistical analyses of the data for identification of candidate materials properties or materials genomes that underlie the performance of nanoparticle systems as lubricants.}, number={6}, journal={LUBRICANTS}, publisher={MDPI AG}, author={Acharya, Biplav and Pardue, Tyler N. and Su, Liangliang and Smirnov, Alex I. and Brenner, Donald W. and Krim, Jacqueline}, year={2019}, month={Jun} }
 @article{acharya_seed_brenner_smirnov_krim_2019, title={Tuning friction and slip at solid-nanoparticle suspension interfaces by electric fields}, volume={9}, ISSN={["2045-2322"]}, url={http://dx.doi.org/10.1038/s41598-019-54515-1}, DOI={10.1038/s41598-019-54515-1}, abstractNote={Abstract We report an experimental Quartz Crystal Microbalance (QCM) study of tuning interfacial friction and slip lengths for aqueous suspensions of TiO 2 and Al 2 O 3 nanoparticles on planar platinum surfaces by external electric fields. Data were analyzed within theoretical frameworks that incorporate slippage at the QCM surface electrode or alternatively at the surface of adsorbed particles, yielding values for the slip lengths between 0 and 30 nm. Measurements were performed for negatively charged TiO 2 and positively charged Al 2 O 3 nanoparticles in both the absence and presence of external electric fields. Without the field the slip lengths inferred for the TiO 2 suspensions were higher than those for the Al 2 O 3 suspensions, a result that was consistent with contact angle measurements also performed on the samples. Attraction and retraction of particles perpendicular to the surface by means of an externally applied field resulted in increased and decreased interfacial friction levels and slip lengths. The variation was observed to be non-monotonic, with a profile attributed to the physical properties of interstitial water layers present between the nanoparticles and the platinum substrate.}, journal={SCIENTIFIC REPORTS}, author={Acharya, B. and Seed, C. M. and Brenner, D. W. and Smirnov, A. I. and Krim, J.}, year={2019}, month={Dec} }
 @inproceedings{smirnov_soldatov_petrenko_takata_kida_hagiwara_zhitomirsky_shapiro_2018, title={Competition between dynamic and structural disorder in a doped triangular antiferromagnet RbFe(MoO<inf>4</inf>)<inf>2</inf>}, volume={969}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85046082725&partnerID=MN8TOARS}, DOI={10.1088/1742-6596/969/1/012115}, abstractNote={Magnetisation measurements and electron spin resonance (ESR) spectra of a doped quasi two dimensional (2D) antiferromagnet on a triangular lattice Rb1-xKxFe(MoO4)(2) reveal a crucial change of the ground state spin configuration and a disappearance of a characteristic 1/3-magnetisation plateau at x = 0.15. According to theory for triangular antiferromagnets with a weak random modulation of the exchange bonds, this is a result of the competition between the structural and dynamic disorders. The dynamic zero-point or thermal fluctuations are known to lift the degeneracy of the mean field ground state of a triangular antiferromagnet and cause the spin configuration to be the most collinear, while the static disorder provides another selection of the ground state, with the least collinear structure. Low-level doping (x <= 0.15) was found to decrease the Neel temperature and saturation field by only few percent, while the magnetisation plateau disappears completely and the spin configuration is drastically changed. ESR spectra confirm an impurity-induced change of the so-called Y-type structure to an inverted Y-structure for x = 0.15. For x = 0.075 the intermediate regime with the decrease of width and weakening of flattening of 1/3-plateau was found.}, number={1}, booktitle={Journal of Physics: Conference Series}, author={Smirnov, A.I. and Soldatov, T.A. and Petrenko, O.A. and Takata, A. and Kida, T. and Hagiwara, M. and Zhitomirsky, M.E. and Shapiro, A.Y.}, year={2018} }
 @article{yu_tang_cha_milikisiyants_smirnova_smirnov_guo_chang_2018, title={Elucidating the Reaction Pathway of Decarboxylation-Assisted Olefination Catalyzed by a Mononuclear Non-Heme Iron Enzyme}, volume={140}, ISSN={["1520-5126"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85056414780&partnerID=MN8TOARS}, DOI={10.1021/jacs.8b10077}, abstractNote={Installation of olefins into molecules is a key transformation in organic synthesis. The recently discovered decarboxylation-assisted olefination in the biosynthesis of rhabduscin by a mononuclear non-heme iron enzyme ( P.IsnB) represents a novel approach in olefin construction. This method is commonly employed in natural product biosynthesis. Herein, we demonstrate that a ferryl intermediate is used for C-H activation at the benzylic position of the substrate. We further establish that P.IsnB reactivity can be switched from olefination to hydroxylation using electron-withdrawing groups appended on the phenyl moiety of the analogues. These experimental observations imply that a pathway involving an initial C-H activation followed by a benzylic carbocation species or by electron transfer coupled β-scission is likely utilized to complete C═C bond formation.}, number={45}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Yu, Cheng-Ping and Tang, Yijie and Cha, Lide and Milikisiyants, Sergey and Smirnova, Tatyana I. and Smirnov, Alex I. and Guo, Yisong and Chang, Wei-chen}, year={2018}, month={Nov}, pages={15190–15193} }
 @article{nevzorov_milikisiyants_marek_smirnov_2018, title={Multi-resonant photonic band-gap/saddle coil DNP probehead for static solid state NMR of microliter volume samples}, volume={297}, ISSN={["1096-0856"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85055585775&partnerID=MN8TOARS}, DOI={10.1016/j.jmr.2018.10.010}, abstractNote={The most critical condition for performing Dynamic Nuclear Polarization (DNP) NMR experiments is achieving sufficiently high electronic B1e fields over the sample at the matched EPR frequencies, which for modern high-resolution NMR instruments fall into the millimeter wave (mmW) range. Typically, mmWs are generated by powerful gyrotrons and/or extended interaction klystrons (EIKs) sources and then focused onto the sample by dielectric lenses. However, further development of DNP methods including new DNP pulse sequences may require B1e fields higher than one could achieve with the current mmW technology. In order to address the challenge of significantly enhancing the mmW field at the sample, we have constructed and tested one-dimensional photonic band-gap (PBG) mmW resonator that was incorporated inside a double-tuned radiofrequency (rf) NMR saddle coil. The photonic crystal is formed by stacking ceramic discs with alternating high and low dielectric constants and thicknesses of λ/4 or 3λ/4, where λ is the wavelength of the incident mmW field in the corresponding dielectric material. When the mmW frequency is within the band gap of the photonic crystal, a defect created in the middle of the crystal confines the mmW energy, thus forming a resonant structure. An aluminum mirror in the middle of the defect has been used to substitute one-half of the structure with its mirror image in order to reduce the resonator size and simplify its tuning. The latter is achieved by adjusting the width of the defect by moving the aluminum mirror with respect to the dielectric stack using a gear mechanism. The 1D PBG resonator was the key element for constructing a multi-resonant integrated DNP/NMR probehead operating at 190–199 GHz EPR/300 MHz 1H/75.5 MHz 13C NMR frequencies. Initial tests of the multi-resonant DNP/NMR probehead were carried out using a quasioptical mmW bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz 1H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 and ca. 199 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3 × 0.3 × 3.0 mm3) demonstrated dramatic 1500-fold enhancement of 13C natural abundance NMR signal at full incident mmW power. Significant 13C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as <100 μW. Further tests of the resonator performance have been carried out with a thin (ca. 100 μm thickness) composite polystyrene-microdiamond film by controlling the average mmW power at the optimal DNP conditions via a gated mode of operation. From these experiments, the PBG resonator with loaded Q ≃ 250 and finesse F≈75 provides up to 12-fold or 11 db gain in the average mmW power vs. the non-resonant probehead configuration employing only a reflective mirror.}, journal={JOURNAL OF MAGNETIC RESONANCE}, author={Nevzorov, Alexander A. and Milikisiyants, Sergey and Marek, Antonin N. and Smirnov, Alex I.}, year={2018}, month={Dec}, pages={113–123} }
 @article{smirnov_2018, title={Nanopore-Confined Bilayers: A Model of Biomembranes with Defined Curvature and a Tool for Oriented Sample Magnetic Resonance}, volume={114}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2017.11.2230}, DOI={10.1016/J.BPJ.2017.11.2230}, abstractNote={It is well established that biological function of cellular membranes is determined by both membrane proteins and the membrane biochemical composition. Moreover, the membrane shape/local curvature may also play a role in modulating membrane properties and the proteins’ function. While specific biomembrane compositions are more readily replicated in biophysical bench experiments, formation of bilayers of specific shapes and curvature represents a more challenging task. Macroscopic alignment of such membranes – an important prerequisite of high resolution magnetic resonance and other studies – is even more difficult especially over a broad range of experimental conditions such pH, ionic strength, and temperature. Here we describe methods for forming self-assembled lipid nanotubular bilayers inside cylindrical nanopores composed of anodic aluminum oxide (AAO). Such hybrid nanostructures, named lipid nanotube arrays, represent a new type of substrate-supported and macroscopically-aligned lipid bilayers of defined curvature that have many attractive features for both membrane biophysics and structure-function protein studies by spectroscopic techniques. Optical properties of AAO allow for assessing the integrity of membrane protein complexes by UV-vis while high density of the deposited lipids and proteins enable examination by other biophysical methods, including DSC, QCM, and magnetic resonance. The latter studies have shown that the individual lipids in such nanopore-confined structures maintain fast uniaxial diffusion and a high degree of macroscopic alignment. The macroscopic alignment enables detailed studies of effects of lipid composition on structure of integral membrane proteins by solid state oriented sample NMR, EPR and DEER. Accessibility of either both or mainly inner leaflet of the nanotubular bilayers to water-soluble species provides for studies of protein, peptides, and drug binding. Supported by DE-FG02-02ER15354 to AIS.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Smirnov, Alex I.}, year={2018}, month={Feb}, pages={402a} }
 @article{milikisiyants_nevzorov_smirnov_2018, title={Photonic band-gap resonators for high-field/high-frequency EPR of microliter-volume liquid aqueous samples}, volume={296}, ISSN={["1096-0856"]}, url={https://doi.org/10.1016/j.jmr.2018.09.006}, DOI={10.1016/j.jmr.2018.09.006}, abstractNote={High-field EPR provides significant advantages for studying structure and dynamics of molecular systems possessing an unpaired electronic spin. However, routine use of high-field EPR in biophysical research, especially for aqueous biological samples, is still facing substantial technical difficulties stemming from high dielectric millimeter wave (mmW) losses associated with non-resonant absorption by water and other polar molecules. The strong absorbance of mmW's by water also limits the penetration depth to just fractions of mm or even less, thus making fabrication of suitable sample containers rather challenging. Here we describe a radically new line of high Q-factor mmW resonators that are based on forming lattice defects in one-dimensional photonic band-gap (PBG) structures composed of low-loss ceramic discs of λ/4 in thickness and having alternating dielectric constants. A sample (either liquid or solid) is placed within the E = 0 node of the standing mm wave confined within the defect. A resonator prototype has been built and tested at 94.3 GHz. The resonator performance is enhanced by employing ceramic nanoporous membranes as flat sample holders of controllable thickness and tunable effective dielectric constant. The experimental Q-factor of an empty resonator was ≈ 420. The Q-factor decreased slightly to ≈ 370 when loaded with a water-containing nanoporous disc of 50 μm in thickness. The resonator has been tested with a number of liquid biological samples and demonstrated about tenfold gain in concentration sensitivity vs. a high-Q cylindrical TE012-type cavity. Detailed HFSS Ansys simulations have shown that the resonator structure could be further optimized by properly choosing the thickness of the aqueous sample and employing metallized surfaces. The PBG resonator design is readily scalable to higher mmW frequencies and is capable of accommodating significantly larger sample volumes than previously achieved with either Fabry-Perot or cylindrical resonators.}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Milikisiyants, Sergey and Nevzorov, Alexander A. and Smirnov, Alex I}, year={2018}, month={Nov}, pages={152–164} }
 @article{kovaleva_molochnikov_antonov_stepanova_hartmann_tsmokalyuk_marek_smirnov_2018, title={Proton Activity in Nanochannels Revealed by Electron Paramagnetic Resonance of Ionizable Nitroxides: A Test of the Poisson-Boltzmann Double Layer Theory}, volume={122}, ISSN={["1932-7447"]}, url={https://doi.org/10.1021/acs.jpcc.8b04938}, DOI={10.1021/acs.jpcc.8b04938}, abstractNote={Chemical and physical processes occurring within the nanochannels of mesoporous materials are known to be determined by both the chemical nature of the solution inside the pores/channels as well as the channel surface properties, including surface electrostatic potential. Such properties are important for numerous practical applications such as heterogeneous catalysis and chemical adsorption including chromatography. However, for solute molecules diffusing inside the pores, the surface potential is expected to be effectively screened by counter ions for the distances exceeding the Debye length. Here, we employed electron paramagnetic resonance spectroscopy of ionizable nitroxide spin probes to experimentally examine the conditions for the efficient electrostatic surface potential screening inside the nanochannels of chemically similar silica-based mesoporous molecular sieves (MMS) filled with water at ambient conditions and a moderate ionic strength of 0.1 M. Three silica MMS having average channel diamet...}, number={35}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, publisher={American Chemical Society (ACS)}, author={Kovaleva, Elena G. and Molochnikov, Leonid S. and Antonov, Denis O. and Stepanova, Darya P. Tambasova and Hartmann, Martin and Tsmokalyuk, Anton N. and Marek, Antonin and Smirnov, Alex I.}, year={2018}, month={Sep}, pages={20527–20538} }
 @article{ou_voinov_smirnov_smirnova_2018, title={Silica-Supported Lipid Bilayers: Electrostatic Effects at Lipid Interfaces as Reported by Spin-Labeling EPR}, volume={114}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2017.11.565}, DOI={10.1016/J.BPJ.2017.11.565}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Ou, Erkang and Voinov, Maxim A. and Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2018}, month={Feb}, pages={96a} }
 @article{chestnut_milikisiyants_koolivand_voynov_smirnova_smirnov_2018, title={Using Hyscore Spectroscopy of Nitroxides to Profile Water Content of Lipid Bilayers with 2 Å Spatial Resolution}, volume={114}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2017.11.130}, DOI={10.1016/J.BPJ.2017.11.130}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Chestnut, Melanie and Milikisiyants, Sergey and Koolivand, Amir and Voynov, Maxim A. and Smirnova, Tatyana I. and Smirnov, Alex I.}, year={2018}, month={Feb}, pages={16a} }
 @article{milikisiyants_voinov_smirnov_2018, title={efocused  ut- f- ase (ROOPh) DEER: A pulse scheme for suppressing an unmodulated background in double electron-electron resonance experiments}, volume={293}, ISSN={1090-7807}, url={http://dx.doi.org/10.1016/J.JMR.2018.05.007}, DOI={10.1016/J.JMR.2018.05.007}, abstractNote={EPR pulsed dipolar spectroscopy (PDS) is indispensable for measurements of nm-scale distances between electronic spins in biological and other systems. While several useful modifications and pulse sequences for PDS have been developed in recent years, DEER experiments utilizing pump and observer pulses at two different frequencies remain the most popular for practical applications. One of the major drawbacks of all the available DEER approaches is the presence of a significant unmodulated fraction in the detected signal that arises from an incomplete inversion of the coupled spins by the pump pulse. The latter fraction is perceived as one of the major sources of error for the reconstructed distance distributions. We describe an alternative detection scheme – a Refocused Out-Of-Phase DEER (ROOPh-DEER) – to acquire only the modulated fraction of the dipolar DEER signal. When Zeeman splitting is small compared to the temperature, the out-of-phase magnetization components cancel each other and are not observed in 4-pulse DEER experiment. In ROOPh-DEER these components are refocused by an additional pump pulse while the in-phase component containing an unmodulated background is filtered out by a pulse at the observed frequency applied right at the position of the refocused echo. Experimental implementation of the ROOPh-DEER detection scheme requires at least three additional pulses as was demonstrated on an example of a 7-pulse sequence. The application of 7-pulse ROOPh-DEER sequence to a model biradical yielded the interspin distance of 1.94 ± 0.07 nm identical to the one obtained with the conventional 4-pulse DEER, however, without the unmodulated background present as a dominant fraction in the latter signal.}, journal={Journal of Magnetic Resonance}, publisher={Elsevier BV}, author={Milikisiyants, Sergey and Voinov, Maxim A. and Smirnov, Alex I.}, year={2018}, month={Aug}, pages={9–18} }
 @article{acharya_chestnut_marek_smirnov_krim_2017, title={A Combined QCM and AFM Study Exploring the Nanoscale Lubrication Mechanism of Silica Nanoparticles in Aqueous Suspension}, volume={65}, ISSN={["1573-2711"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85026840191&partnerID=MN8TOARS}, DOI={10.1007/s11249-017-0898-5}, number={3}, journal={TRIBOLOGY LETTERS}, author={Acharya, B. and Chestnut, M. and Marek, A. and Smirnov, A. I. and Krim, J.}, year={2017}, month={Sep} }
 @article{curtis_marek_smirnov_krim_2017, title={A comparative study of the nanoscale and macroscale tribological attributes of alumina and stainless steel surfaces immersed in aqueous suspensions of positively or negatively charged nanodiamonds}, volume={8}, journal={Beilstein Journal of Nanotechnology}, author={Curtis, C. K. and Marek, A. and Smirnov, A. I. and Krim, J.}, year={2017}, pages={2045–2059} }
 @article{curtis_marek_smirnov_krim_2017, title={A comparative study of the nanoscale and macroscale tribological attributes of alumina and stainless steel surfaces immersed in aqueous suspensions of positively or negatively charged nanodiamonds}, volume={8}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85031433523&partnerID=MN8TOARS}, DOI={10.3762/bjnano.8.205}, abstractNote={This article reports a comparative study of the nanoscale and macroscale tribological attributes of alumina and stainless steel surfaces immersed in aqueous suspensions of positively (hydroxylated) or negatively (carboxylated) charged nanodiamonds (ND). Immersion in −ND suspensions resulted in a decrease in the macroscopic friction coefficients to values in the range 0.05–0.1 for both stainless steel and alumina, while +ND suspensions yielded an increase in friction for stainless steel contacts but little to no increase for alumina contacts. Quartz crystal microbalance (QCM), atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements were employed to assess nanoparticle uptake, surface polishing, and resistance to solid–liquid interfacial shear motion. The QCM studies revealed abrupt changes to the surfaces of both alumina and stainless steel upon injection of –ND into the surrounding water environment that are consistent with strong attachment of NDs and/or chemical changes to the surfaces. AFM images of the surfaces indicated slight increases in the surface roughness upon an exposure to both +ND and −ND suspensions. A suggested mechanism for these observations is that carboxylated −NDs from aqueous suspensions are forming robust lubricious deposits on stainless and alumina surfaces that enable gliding of the surfaces through the −ND suspensions with relatively low resistance to shear. In contrast, +ND suspensions are failing to improve tribological performance for either of the surfaces and may have abraded existing protective boundary layers in the case of stainless steel contacts. This study therefore reveals atomic scale details associated with systems that exhibit starkly different macroscale tribological properties, enabling future efforts to predict and design complex lubricant interfaces.}, number={1}, journal={Beilstein Journal of Nanotechnology}, author={Curtis, C.K. and Marek, A. and Smirnov, Alex I. and Krim, J.}, year={2017}, pages={2045–2059} }
 @inbook{smirnov_2017, title={Chapter 6 - Electron Paramagnetic Resonance Spectroscopy to Study Liquid Food and Beverages }, url={http://www.sciencedirect.com/science/article/pii/B9780128054284000064}, DOI={http://dx.doi.org/10.1016/B978-0-12-805428-4.00006-4}, abstractNote={Food spoilage by chemical oxidation represents one of the major problems for society. Typically, an exposure of a food or beverage to oxygen would trigger a chain of chemical reactions involving proteins, pigments, fatty acids, and lipids, producing other compounds with undesirable biochemical properties including toxicity, as well as undesirable taste, smell, and color. Many of these processes occur via free radical mechanisms and involve chain reactions. This chapter reviews current progress in the use of electron paramagnetic resonance (EPR) spectroscopy to characterize endogenous free radicals and paramagnetic metal ion complexes in liquid food and beverages, as well as reactive radical species directly involved in chemical reactions leading to food degradation. This field has experienced enormous growth over the last two decades. We also review the expanding use of EPR to characterize antioxidants present in food, and commercial applications of EPR methods to predict the shelf life of beer. The remaining problems, potential solutions, and future directions for using this powerful and informative spectroscopic method in characterizing liquid food and beverages are also discussed.}, booktitle={Electron Spin Resonance in Food Science}, publisher={Academic Press}, author={Smirnov, A.I.}, editor={Shukla, Ashutosh KumarEditor}, year={2017}, pages={83–109} }
 @article{margita_voinov_smirnov_2017, title={Effect of Solution Ionic Strength on the pKa of the Nitroxide pH EPR Probe 2,2,3,4,5,5-Hexamethylimidazolidin-1-oxyl}, volume={75}, ISSN={1085-9195 1559-0283}, url={http://dx.doi.org/10.1007/S12013-017-0780-Y}, DOI={10.1007/s12013-017-0780-y}, number={2}, journal={Cell Biochemistry and Biophysics}, publisher={Springer Nature}, author={Margita, Kaleigh and Voinov, Maxim A. and Smirnov, Alex I.}, year={2017}, month={Feb}, pages={185–193} }
 @article{ou_voinov_smirnov_smirnova_2017, title={Effects of Silica Support on Dynamics of Transmembrane Peptides and Effective p K a of Ionisable Sidechains}, volume={112}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2016.11.967}, DOI={10.1016/J.BPJ.2016.11.967}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Ou, Erkang and Voinov, Maxim and Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2017}, month={Feb}, pages={175a} }
 @book{smirnov_2017, title={Electron Paramagnetic Resonance Spectroscopy to Study Liquid Food and Beverages}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85024402756&partnerID=MN8TOARS}, DOI={10.1016/B978-0-12-805428-4.00006-4}, abstractNote={Food spoilage by chemical oxidation represents one of the major problems for society. Typically, an exposure of a food or beverage to oxygen would trigger a chain of chemical reactions involving proteins, pigments, fatty acids, and lipids, producing other compounds with undesirable biochemical properties including toxicity, as well as undesirable taste, smell, and color. Many of these processes occur via free radical mechanisms and involve chain reactions. This chapter reviews current progress in the use of electron paramagnetic resonance (EPR) spectroscopy to characterize endogenous free radicals and paramagnetic metal ion complexes in liquid food and beverages, as well as reactive radical species directly involved in chemical reactions leading to food degradation. This field has experienced enormous growth over the last two decades. We also review the expanding use of EPR to characterize antioxidants present in food, and commercial applications of EPR methods to predict the shelf life of beer. The remaining problems, potential solutions, and future directions for using this powerful and informative spectroscopic method in characterizing liquid food and beverages are also discussed.}, journal={Electron Spin Resonance in Food Science}, author={Smirnov, A.I.}, year={2017}, pages={83–109} }
 @article{shames_smirnov_milikisiyants_danilov_nunn_mcguire_torelli_shenderova_2017, title={Fluence-Dependent Evolution of Paramagnetic Triplet Centers in e-Beam Irradiated Microcrystalline lb Type HPHT Diamond}, volume={121}, ISSN={["1932-7447"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85031327261&partnerID=MN8TOARS}, DOI={10.1021/acs.jpcc.7b06514}, abstractNote={Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type high-pressure high-temperature (HPHT) diamonds were studied by continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy at X-band (9.4 GHz), pulsed EPR at X- and Q-bands (34 GHz), and fluorescence spectroscopies as a function of radiation fluences up to 5 × 1019 e–/cm2. EPR spectra of mostly “forbidden” Δms = 2 electronic spin transitions observed at g ≈ 4 (i.e., so-called half-field EPR spectra) reveal the presence of the main W15 triplet defects associated with the fluorescent negatively charged nitrogen-vacancy (NV–) centers as well as additional triplet spin centers identified as W16, W17, W18, and W33 that appear upon increasing the e-beam fluence. Consequent annealing at 1,400 °C significantly reduces the content of W17, W18, and W33 but not W15 and W16 defects. The efficacy of NV– center fabrication as a function of fluence dependent e-beam irradiation is also reported.}, number={40}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Shames, Alexander I. and Smirnov, Alex I. and Milikisiyants, Sergey and Danilov, Evgeny O. and Nunn, Nicholas and McGuire, Gary and Torelli, Marco D. and Shenderova, Olga}, year={2017}, month={Oct}, pages={22335–22346} }
 @article{mitra_gao_zheng_wu_voinov_smirnov_smirnova_wang_chavala_han_2017, title={Glycol Chitosan Engineered Autoregenerative Antioxidant Significantly Attenuates Pathological Damages in Models of Age-Related Macular Degeneration}, volume={11}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/ACSNANO.7B00429}, DOI={10.1021/acsnano.7b00429}, abstractNote={Age-related macular degeneration (AMD) is the foremost cause of irreversible blindness in people over the age of 65 especially in developing countries. Therefore, an exploration of effective and alternative therapeutic interventions is an unmet medical need. It has been established that oxidative stress plays a key role in the pathogenesis of AMD, and hence, neutralizing oxidative stress is an effective therapeutic strategy for treatment of this serious disorder. Owing to autoregenerative properties, nanoceria has been widely used as a nonenzymatic antioxidant in the treatment of oxidative stress related disorders. Yet, its potential clinical implementation has been greatly hampered by its poor water solubility and lack of reliable tracking methodologies/processes and hence poor absorption, distribution, and targeted delivery. The water solubility and surface engineering of a drug with biocompatible motifs are fundamental to pharmaceutical products and precision medicine. Here, we report an engineered water-soluble, biocompatible, trackable nanoceria with enriched antioxidant activity to scavenge intracellular reactive oxygen species (ROS). Experimental studies with in vitro and in vivo models demonstrated that this antioxidant is autoregenerative and more active in inhibiting laser-induced choroidal neovascularization by decreasing ROS-induced pro-angiogenic vascular endothelial growth factor (VEGF) expression, cumulative oxidative damage, and recruitment of endothelial precursor cells without exhibiting any toxicity. This advanced formulation may offer a superior therapeutic effect to deal with oxidative stress induced pathogeneses, such as AMD.}, number={5}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Mitra, Rajendra N. and Gao, Ruijuan and Zheng, Min and Wu, Ming-Jing and Voinov, Maxim A. and Smirnov, Alex I. and Smirnova, Tatyana I. and Wang, Kai and Chavala, Sai and Han, Zongchao}, year={2017}, month={May}, pages={4669–4685} }
 @article{voinov_scheid_kirilyuk_trofimov_smirnov_2017, title={IKMTSL-PTE, a Phospholipid-Based EPR Probe for Surface Electrostatic Potential of Biological Interfaces at Neutral pH: Effects of Temperature and Effective Dielectric Constant of the Solvent}, volume={121}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/ACS.JPCB.7B00592}, DOI={10.1021/acs.jpcb.7b00592}, abstractNote={The synthesis and characterization of a lipidlike electrostatic spin probe, (S)-2,3-bis(palmitoyloxy)propyl 2-((4-(4-(dimethylamino)-2-ethyl-1-oxyl-5,5-dimethyl-2,5-dihydro-1H-imidazol-2-yl)benzyl)disulfanyl)ethyl phosphate (IKMTSL-PTE), are being reported. The intrinsic pKa0 of IKMTSL-PTE was determined by X-band (9.5 GHz) electron paramagnetic resonance (EPR) titration of a water-soluble model compound, 4-(dimethylamino)-2-ethyl-2-(4-(((2-hydroxyethyl)disulfanyl)methyl)phenyl)-5,5-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl (IKMTSL-ME), an adduct of methanethiosulfonate spin label IKMTSL and 2-mercaptoethanol. The pKa0 of IKMTSL-ME in bulk aqueous solutions was found to be significantly higher than that of 4-(((2-hydroxyethyl)disulfanyl)methyl)-2,2,3,5,5-pentamethylimidazolidin-1-oxyl (IMTSL-ME), an adduct of the corresponding methanethiosulfonate spin label IMTSL and 2-mercaptoethanol (17 °C, pKa0 = 6.16 ± 0.03 vs 20 °C, pKa0 = 3.33 ± 0.03, respectively). A series of EPR titration experiments with IKMTSL-ME in aqueous solutions containing 0-60% v/v isopropanol have been carried out at 17 and 48 °C to determine the effects of temperature and bulk dielectric permittivity constant, ε, on the probe pKa. A linear relationship between the probe pKa and ε has been established and found to be essentially the same at 17 and 48 °C. The polarity term contributing to the pKa of IKMTSL-PTE at an uncharged lipidlike interface was determined by incorporating the probe into electrically neutral micelles formed from nonionic detergent Triton X-100, and it was found, similar to IMTSL-PTE, to be negative. In negatively charged DMPG lipid bilayers, IKMTSL-PTE exhibits ionization transitions with significantly higher pKa values than those previously reported for IMTSL-PTE (e.g., at 17 °C, pKai = 7.80 ± 0.03 vs pKa0 = 5.70 ± 0.05). The surface electrostatic potentials of DMPG lipid bilayers calculated using IKMTSL-PTE titration data were found to be somewhat lower than those calculated using IMTSL-PTE. The lower values measured by IKMTSL-PTE are the likely consequences of the structure of the linker that positions the reporter nitroxide further away from the bilayer plane into aqueous phase. Overall, the ionization transitions of IKMTSL-PTE with pKa values close to the neutral pH range make this lipidlike molecule a valuable spectroscopic EPR probe for studying the electrostatic phenomena at biological interfaces, including lipid bilayer/membrane protein systems, that could be unstable in the acidic pH range accessible by the previously available probes.}, number={11}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Scheid, Christina T. and Kirilyuk, Igor A. and Trofimov, Dmitrii G. and Smirnov, Alex I.}, year={2017}, month={Mar}, pages={2443–2453} }
 @article{kovaleva_molochnikov_stepanova_pestov_trofimov_kirilyuk_smirnov_2017, title={Interfacial Electrostatic Properties of Hydrated Mesoporous and Nanostructured Alumina Powders by Spin Labeling EPR}, volume={75}, ISSN={["1559-0283"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994323104&partnerID=MN8TOARS}, DOI={10.1007/s12013-016-0767-0}, number={2}, journal={CELL BIOCHEMISTRY AND BIOPHYSICS}, author={Kovaleva, Elena G. and Molochnikov, Leonid S. and Stepanova, Darya P. and Pestov, Alexander V. and Trofimov, Dmitrii G. and Kirilyuk, Igor A. and Smirnov, Alex I.}, year={2017}, month={Jun}, pages={159–170} }
 @article{smirnov_berliner_2017, title={Nitroxide Radicals: Synthesis and Functional Bio-/Nanomaterials - an Introduction}, volume={75}, ISSN={["1559-0283"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85015658211&partnerID=MN8TOARS}, DOI={10.1007/s12013-017-0788-3}, number={2}, journal={CELL BIOCHEMISTRY AND BIOPHYSICS}, author={Smirnov, Alex I. and Berliner, Lawrence J.}, year={2017}, month={Jun}, pages={149–150} }
 @article{milikisiyants_wang_munro_donohue_ward_bolton_brown_smirnova_ladizhansky_smirnov_2017, title={Oligomeric Structure of Anabaena Sensory Rhodopsin in a Lipid Bilayer Environment by Combining Solid-State NMR and Long-range DEER Constraints}, volume={429}, ISSN={["1089-8638"]}, url={https://doi.org/10.1016/j.jmb.2017.05.005}, DOI={10.1016/j.jmb.2017.05.005}, abstractNote={Oligomerization of membrane proteins is common in nature. Here, we combine spin-labeling double electron-electron resonance (DEER) and solid-state NMR (ssNMR) spectroscopy to refine the structure of an oligomeric integral membrane protein, Anabaena sensory rhodopsin (ASR), reconstituted in a lipid environment. An essential feature of such a combined approach is that it provides structural distance restraints spanning a range of ca 3-60Å while using the same sample preparation (i.e., mutations, paramagnetic labeling, and reconstitution in lipid bilayers) for both ssNMR and DEER. Direct modeling of the multispin effects on DEER signal allowed for the determination of the oligomeric order and for obtaining long-range DEER distance restraints between the ASR trimer subunits that were used to refine the ssNMR structure of ASR. The improved structure of the ASR trimer revealed a more compact packing of helices and side chains at the intermonomer interface, compared to the structure determined using the ssNMR data alone. The extent of the refinement is significant when compared with typical helix movements observed for the active states of homologous proteins. Our combined approach of using complementary DEER and NMR measurements for the determination of oligomeric structures would be widely applicable to membrane proteins where paramagnetic tags can be introduced. Such a method could be used to study the effects of the lipid membrane composition on protein oligomerization and to observe structural changes in protein oligomers upon drug, substrate, and co-factor binding.}, number={12}, journal={JOURNAL OF MOLECULAR BIOLOGY}, publisher={Elsevier BV}, author={Milikisiyants, Sergey and Wang, Shenlin and Munro, Rachel A. and Donohue, Matthew and Ward, Meaghan E. and Bolton, David and Brown, Leonid S. and Smirnova, Tatyana I. and Ladizhansky, Vladimir and Smirnov, Alex I.}, year={2017}, month={Jun}, pages={1903–1920} }
 @article{smirnov_soldatov_petrenko_takata_kida_hagiwara_shapiro_zhitomirsky_2017, title={Order by Quenched Disorder in the Model Triangular Antiferromagnet RbFe (MoO4)2}, volume={119}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85026456796&partnerID=MN8TOARS}, DOI={10.1103/PhysRevLett.119.047204}, abstractNote={We observe a disappearance of the 1/3 magnetization plateau and a striking change of the magnetic configuration under a moderate doping of the model triangular antiferromagnet RbFe(MoO4)2. The reason is an effective lifting of degeneracy of mean-field ground states by a random potential of impurities, which compensates, in the low temperature limit, the fluctuation contribution to free energy. These results provide a direct experimental confirmation of the fluctuation origin of the ground state in a real frustrated system. The change of the ground state to a least collinear configuration reveals an effective positive biquadratic exchange provided by the structural disorder. On heating, doped samples regain the structure of a pure compound thus allowing for an investigation of the remarkable competition between thermal and structural disorder.}, number={4}, journal={Physical Review Letters}, author={Smirnov, A.I. and Soldatov, T.A. and Petrenko, O.A. and Takata, A. and Kida, T. and Hagiwara, M. and Shapiro, A.Y. and Zhitomirsky, M.E.}, year={2017} }
 @article{marek_voinov_smirnov_2017, title={Spin Probe Multi-Frequency EPR Study of Unprocessed Cotton Fibers}, volume={75}, ISSN={1085-9195 1559-0283}, url={http://dx.doi.org/10.1007/S12013-017-0787-4}, DOI={10.1007/s12013-017-0787-4}, number={2}, journal={Cell Biochemistry and Biophysics}, publisher={Springer Nature}, author={Marek, Antonin and Voinov, Maxim A. and Smirnov, Alex I.}, year={2017}, month={Mar}, pages={211–226} }
 @article{nevzorov_jafarabadi_marek_smirnov_2017, title={Structure and Dynamics of Nanopore-Confined Membrane Proteins are Affected by Bilayer Lipid Composition}, volume={112}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2016.11.2109}, DOI={10.1016/J.BPJ.2016.11.2109}, abstractNote={Self-assembled nanotubular lipid bilayers confined within macroscopically aligned high-density homogeneous nanopore array structure of anodic aluminum oxide (AAO) membranes exhibit a high degree of macroscopic alignment that facilitates their studies by oriented sample solid state (OS SS) NMR and spin-labeling EPR methods. The principal advantages of the lipid nanotube arrays are in the applicability of this method to essentially any lipid composition and a tolerance of the macroscopic alignment to a wide range of environmental conditions such as, e.g., temperature, pH, and ionic strength. Here we describe 1) a recent progress in reconstructing small pore-forming and transmembrane peptides as well as large membrane protein complexes, such as photosynthetic reaction center (RC) protein in inorganic nanopores and 2) utilization of this technology to study lipid-induced changes in protein conformations by magnetic resonance methods. Specifically, by using OS SS NMR we have shown that the tilt and α-helix kink angles of Pf1 coat protein are affected by the bilayer composition on example of DOPC, POPC and DMPC bilayers. Effects of unsaturated lipids on Pf1 dynamics as evidenced by the changes in the linewidths in the Pf1 spectra are also reported. We relate these changes to the bilayer fluidity and its effects on the uniaxial rotational diffusion of the protein within the membrane. Further, we demonstrate the use of DEER spectroscopy to obtain long-range distance constraints for membrane protein systems incorporated into lipid nanotubes. The improved nanopore alignment technique described here provides a general method for studying lipid-induced structural conformations of membrane proteins under physiologically relevant conditions by magnetic resonance. Supported by U.S. DOE contract No. DE-FG02-02ER15354 to A.I.S. and NSF MRI 1229547 to A.A.N.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Nevzorov, Alexander A. and Jafarabadi, Morteza and Marek, Antonin and Smirnov, Alex I.}, year={2017}, month={Feb}, pages={388a} }
 @article{kovaleva_molochnikov_venkatesan_marek_stepanova_kozhikhova_mironov_smirnov_2016, title={Acid-Base Properties of Nanoconfined Volumes of Anodic Aluminum Oxide Pores by EPR of pH-Sensitive Spin Probes}, volume={120}, ISSN={["1932-7447"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84958092831&partnerID=MN8TOARS}, DOI={10.1021/acs.jpcc.5b10241}, abstractNote={Anodic aluminum oxide (AAO) ceramic membranes with macroscopically aligned and hexagonally packed nanopore architecture are attractive substrates for forming nanotubular lipid bilayers as well as sorption and catalytic media because of a tunable pore diameter, robust pore structure, and low fabrication cost. Here we employed continuous wave X-band (9 GHz) EPR of two pH-sensitive nitroxide radicals to assess acid–base properties AAO membranes prepared from low-cost commercial grade aluminum and compared those with commercial Anodisc membranes from Whatman, Ltd. The AAO membranes with pore diameters ≥58 ± 8 nm showed essentially the same pH inside the pores, pHint, as the bulk external solution, pHext, over the 0.1–3.0 M range of ionic strength. However, the apparent pKa of nitroxide probes inside the pores deviated from the bulk values for the nanopores of smaller diameters of ca. 29 and 18 nm. Specifically, for the latter nanopores the values of pHint were found to be 0.5–0.8 pH unit lower than the bulk p...}, number={5}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, publisher={American Chemical Society (ACS)}, author={Kovaleva, Elena G. and Molochnikov, Leonid S. and Venkatesan, Umamaheswari and Marek, Antonin and Stepanova, Darya P. and Kozhikhova, Ksenia V. and Mironov, Maxim A. and Smirnov, Alex I.}, year={2016}, month={Feb}, pages={2703–2711} }
 @article{jafarabadi_marek_koolivand_acharya_nevzorov_krim_smirnov_2016, title={Interactions of Antibacterial Peptides with Nanotubular Lipid Bilayers: Binding Kinetics and Distortions of the Bilayer Structure}, volume={110}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2015.11.488}, DOI={10.1016/J.BPJ.2015.11.488}, abstractNote={Interactions of peptides with membranes are central for understanding key cellular processes involving membrane proteins such as folding, signaling, transport, energy conversion, and immune response. These interactions also determine efficiency of antibacterial and cytotoxic peptides in disrupting the barrier function of cellular membranes. We employed macroscopically aligned tubular lipid bilayers confined inside cylindrical nanopores of anodic aluminum oxide (AAO) as a versatile nanotechnology platform to study membrane interactions of antibacterial peptides of melittin and alamecitin. Kinetics of peptide binding to lipid nanotubes and the eventual lipid removal/lysis (for melittin) were observed by quartz crystal microbalance (QCM) using a crystal with an in-house fabricated nanostructured surface while the structural changes in bilayers were monitored by solid state oriented sample NMR. Specifically, using 78 nm nanopores we have achieved exceptionally narrow (100-140 Hz or <1 ppm) 31P resonances of the lipid phosphate groups of macroscopically aligned nanotubular bilayers that indicated <1-2o mosaic spread in the lipid alignment in the absence of bioreactive peptides. 31P resonances broadened and shifted towards the isotropic values upon interacting with melittin with some lysis of lipids observed after several hours of exposure. The binding and lipid lysis from bilayers confined in essentially the same nanopores albeit at much smaller lipid quantity were further quantified by real-time QCM for bilayers of various lipid compositions. Taken together, the data relate peptide binding and lysis kinetics to structural changes in lipid bilayers, thus, shedding the light on the underlying multistep mechanism. The main advantage of the lipid nanotube AAO platform is in its versatile applicability to various biophysical methods such QCM and NMR under essentially the same environmental conditions such as pH, ionic strength, temperature, etc. and exceptionally broad range of lipid bilayer compositions.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Jafarabadi, Morteza and Marek, Antonin and Koolivand, Amir and Acharya, Biplav and Nevzorov, Alexander A. and Krim, Jacqueline and Smirnov, Alex I.}, year={2016}, month={Feb}, pages={79a} }
 @article{smirnov_2016, title={Magnetic resonance of spinons in quantum magnets}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84987665903&partnerID=MN8TOARS}, DOI={10.3367/UFNe.2016.02.037757}, abstractNote={A study is made of the spinon continuum fine structure which is observed to occur in the spin-liquid phases of chain- and triangular-lattice magnets at small wave vectors due to the action of a uniform Dzyaloshinsky–Moriya interaction. An ordered phase with a strongly quantum-reduced order parameter is found to exhibit the coexistence of magnon and spin type excitations, the former crossing over to the latter when the excitation energy exceeds that of the exchange interaction.}, number={6}, journal={Physics-Uspekhi}, author={Smirnov, A.I.}, year={2016}, pages={564–570} }
 @article{nellutla_nori_singamaneni_prater_narayan_smirnov_2016, title={Multi-frequency ferromagnetic resonance investigation of nickel nanocubes encapsulated in diamagnetic magnesium oxide matrix}, volume={120}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4971869}, DOI={10.1063/1.4971869}, abstractNote={Partially aligned nickel nanocubes were grown epitaxially in a diamagnetic magnesium oxide (MgO:Ni) host and studied by a continuous wave ferromagnetic resonance (FMR) spectroscopy at the X-band (9.5 GHz) from ca. 117 to 458 K and then at room temperature for multiple external magnetic fields/resonant frequencies from 9.5 to 330 GHz. In contrast to conventional magnetic susceptibility studies that provided data on the bulk magnetization, the FMR spectra revealed the presence of three different types of magnetic Ni nanocubes in the sample. Specifically, three different ferromagnetic resonances were observed in the X-band spectra: a line 1 assigned to large nickel nanocubes, a line 2 corresponding to the nanocubes exhibiting saturated magnetization even at ca. 0.3 T field, and a high field line 3 (geff ∼ 6.2) tentatively assigned to small nickel nanocubes likely having their hard magnetization axis aligned along or close to the direction of the external magnetic field. Based on the analysis of FMR data, the latter nanocubes possess an anisotropic internal magnetic field of at least ∼1.0 T in magnitude.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Nellutla, Saritha and Nori, Sudhakar and Singamaneni, Srinivasa R. and Prater, John T. and Narayan, Jagdish and Smirnov, Alex I.}, year={2016}, month={Dec}, pages={223902} }
 @article{basso_jafarabadi_smirnov_costa-filho_2016, title={Ordering Effect Induced by SARS-CoV Fusion Peptides on Membranes Containing Negatively Charged Lipids Might be Important to Membrane Fusion}, volume={110}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2015.11.2261}, DOI={10.1016/J.BPJ.2015.11.2261}, abstractNote={The S2 subunit of the spike glycoprotein from SARS coronavirus (CoV) contains internal membranotropic domains that play important roles to the viral and host cell membrane fusion. These functional domains, which include a so-called fusion peptide (FP) and an internal FP, are exposed to membrane interactions upon a specific trigger. Although membrane fusion has been broadly studied in recent years, many aspects of the molecular mechanism behind the virus-host cell membrane fusion remain unknown, including conformational changes of the lipid bilayers during peptide-membrane interactions.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Basso, Luis G.M. and Jafarabadi, Morteza and Smirnov, Alex I. and Costa-Filho, Antonio J.}, year={2016}, month={Feb}, pages={418a} }
 @article{voinov_good_ward_milikisiyants_marek_caporini_rosay_munro_ljumovic_brown_et al._2015, title={Cysteine-Specific Labeling of Proteins with a Nitroxide Biradical for Dynamic Nuclear Polarization NMR}, volume={119}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/ACS.JPCB.5B05230}, DOI={10.1021/acs.jpcb.5b05230}, abstractNote={Dynamic nuclear polarization (DNP) enhances the signal in solid-state NMR of proteins by transferring polarization from electronic spins to the nuclear spins of interest. Typically, both the protein and an exogenous source of electronic spins, such as a biradical, are either codissolved or suspended and then frozen in a glycerol/water glassy matrix to achieve a homogeneous distribution. While the use of such a matrix protects the protein upon freezing, it also reduces the available sample volume (by ca. a factor of 4 in our experiments) and causes proportional NMR signal loss. Here we demonstrate an alternative approach that does not rely on dispersing the DNP agent in a glassy matrix. We synthesize a new biradical, ToSMTSL, which is based on the known DNP agent TOTAPOL, but also contains a thiol-specific methanethiosulfonate group to allow for incorporating this biradical into a protein in a site-directed manner. ToSMTSL was characterized by EPR and tested for DNP of a heptahelical transmembrane protein, Anabaena sensory rhodopsin (ASR), by covalent modification of solvent-exposed cysteine residues in two (15)N-labeled ASR mutants. DNP enhancements were measured at 400 MHz/263 GHz NMR/EPR frequencies for a series of samples prepared in deuterated and protonated buffers and with varied biradical/protein ratios. While the maximum DNP enhancement of 15 obtained in these samples is comparable to that observed for an ASR sample cosuspended with ~17 mM TOTAPOL in a glycerol-d8/D2O/H2O matrix, the achievable sensitivity would be 4-fold greater due to the gain in the filling factor. We anticipate that the DNP enhancements could be further improved by optimizing the biradical structure. The use of covalently attached biradicals would broaden the applicability of DNP NMR to structural studies of proteins.}, number={32}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Good, Daryl B. and Ward, Meaghan E. and Milikisiyants, Sergey and Marek, Antonin and Caporini, Marc A. and Rosay, Melanie and Munro, Rachel A. and Ljumovic, Milena and Brown, Leonid S. and et al.}, year={2015}, month={Jul}, pages={10180–10190} }
 @article{milikisiyants_wang_munro_donohue_brown_smirnova_ladizhansky_smirnov_2015, title={Determining Oligomeric Order of a Membrane Protein by Double Electron-Electron Resonance Spectroscopy}, volume={108}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2014.11.541}, DOI={10.1016/J.BPJ.2014.11.541}, abstractNote={Many different classes of membrane proteins are known to form oligomers in cellular membranes in order to carry out specific cellular functions. Detection and detailed structural characterization of protein oligomers in lipid milieu is by no means a trivial task. Here we demonstrate the use of spin-labeling and Double Electron-Electron Resonance (DEER) spectroscopy to determine the oligomeric order of a membrane protein. Specifically, we investigate oligomerization of a seven-helical membrane photoreceptor Anabaena Sensory Rhodopsin (ASR) from Anabaena sp. PCC7120. Recently, ASR structure has been solved by both x-ray protein crystallography (Science 2004, 306, 1390) and solid-state NMR (Nat Methods 2013, 10, 1007). Here we show that the same spin-labeling sites we employed for paramagnetic relaxation enhancement (PRE) NMR can also be used for DEER experiments. The results demonstrate that DEER restraints can not only differentiate between the dimer (x-ray) and trimer (ssNMR) models that have very different interfaces, but further rule out hypothetical tetramer and other higher order polygon models. The crux of our DEER-based approach relies on taking advantage of the multi-spin effects and analyzing experimental DEER traces by direct fitting to the multispin models. Overall, the observed profound effect of higher order spin correlations on the DEER trace allows for a reliable differentiation between oligomer models. In the specific case of ASR, the DEER trace modeling allowed us to unambiguously discard all but the trimer model. Furthermore, the addition of DEER electron-electron distances to the NMR restraints in the structure calculation protocol improves local RMSD, and allows for refinement of the orientation of helices. Supported by U.S. DOE Contract DE-FG02-02ER15354 to AIS and NSERC Discovery Grants RGPIN-2014-04547 to VL and RGPIN-2013-250202 to LSB.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Milikisiyants, Sergey and Wang, Shenlin and Munro, Rachel and Donohue, Matthew and Brown, Leonid S. and Smirnova, Tatyana I. and Ladizhansky, Vladimir and Smirnov, Alex I.}, year={2015}, month={Jan}, pages={93a} }
 @article{voinov_smirnov_2015, title={Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR}, volume={564}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84944354832&partnerID=MN8TOARS}, DOI={10.1016/bs.mie.2015.08.007}, abstractNote={Electrostatic interactions are known to play a major role in the myriad of biochemical and biophysical processes. Here, we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that are based on an observation of reversible protonation of nitroxides by electron paramagnetic resonance (EPR). Two types of probes are described: (1) methanethiosulfonate derivatives of protonatable nitroxides for highly specific covalent modification of the cysteine's sulfhydryl groups and (2) spin-labeled phospholipids with a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and degree of rotational averaging, thus, allowing the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, the local electrostatic potential to be determined. Due to their small molecular volume, these probes cause a minimal perturbation to the protein or lipid system. Covalent attachment secures the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR, and also the methods to analyze the EPR spectra by simulations are outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide range of ca. 2.5-7.0 pH units, making them suitable to study a broad range of biophysical phenomena, especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for probe calibration, and examples of lipid bilayer surface potential studies, are also described.}, journal={Electron Paramagnetic Resonance Investigations of Biological Systems by Using Spin Labels, Spin Probes, and Intrinsic Metal Ions, Part B}, publisher={Elsevier BV}, author={Voinov, Maxim A. and Smirnov, Alex I.}, year={2015}, pages={191–217} }
 @article{nevzorov_smirnov_2015, title={Line Narrowing in Oriented-Sample NMR of Membrane Proteins}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84955112839&partnerID=MN8TOARS}, DOI={10.1007/978-1-4899-7621-5_5}, abstractNote={The growing need for structure determination of membrane proteins incorporated within their native bilayers calls for the development of novel experimental methods and membrane mimetics for the structure-function studies of these important biological constituents. Solid-state NMR of macroscopically aligned samples has emerged as a powerful tool that enables studies of membrane proteins under their native-like conditions. Here we present an alternative alignment method based on anodic aluminum oxide nanopores, which are capable of incorporating a broad repertoire of lipids. Moreover, the temperature and pH stability of lipid bilayers within the nanopores enable solid-state NMR experiments under a wider range of conditions than ever before. Uniaxial motional averaging by rotational diffusion of membrane proteins ensures the line narrowing of experimental NMR linewidths, thus, providing structural and dynamic information for the lipid-embedded proteins.}, journal={Protein NMR}, publisher={Springer Science \mathplus Business Media}, author={Nevzorov, Alexander A. and Smirnov, Alex I.}, year={2015}, pages={159–185} }
 @article{nevzorov_smirnov_2015, title={Line narrowing in oriented-sample NMR of membrane proteins}, volume={32}, journal={Protein nmr: modern techniques and biomedical applications}, author={Nevzorov, A. A. and Smirnov, A. I.}, year={2015}, pages={159–185} }
 @article{marek_tang_milikisiyants_nevzorov_smirnov_2015, title={Nanotube Array Method for Studying Lipid-Induced Conformational Changes of a Membrane Protein by Solid-State NMR}, volume={108}, ISSN={["1542-0086"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84921058848&partnerID=MN8TOARS}, DOI={10.1016/j.bpj.2014.11.011}, abstractNote={Anodic aluminum oxide substrates with macroscopically aligned homogeneous nanopores of 80 nm in diameter enable two-dimensional, solid-state nuclear magnetic resonance studies of lipid-induced conformational changes of uniformly (15)N-labeled Pf1 coat protein in native-like bilayers. The Pf1 helix tilt angles in bilayers composed of two different lipids are not entirely governed by the membrane thickness but could be rationalized by hydrophobic interactions of lysines at the bilayer interface. The anodic aluminum oxide alignment method is applicable to a broader repertoire of lipids versus bicelle bilayer mimetics currently employed in solid-state nuclear magnetic resonance of oriented samples, thus allowing for elucidation of the role played by lipids in shaping membrane proteins.}, number={1}, journal={BIOPHYSICAL JOURNAL}, publisher={Elsevier BV}, author={Marek, Antonin and Tang, Wenxing and Milikisiyants, Sergey and Nevzorov, Alexander A. and Smirnov, Alex I.}, year={2015}, month={Jan}, pages={5–9} }
 @article{smirnova_smirnov_2015, title={Peptide-Membrane Interactions by Spin-Labeling EPR.}, volume={564}, url={http://europepmc.org/abstract/med/26477253}, DOI={10.1016/bs.mie.2015.08.018}, abstractNote={Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy is a well-established method that has recently grown in popularity as an experimental technique, with multiple applications in protein and peptide science. The growth is driven by development of labeling strategies, as well as by considerable technical advances in the field, that are paralleled by an increased availability of EPR instrumentation. While the method requires an introduction of a paramagnetic probe at a well-defined position in a peptide sequence, it has been shown to be minimally destructive to the peptide structure and energetics of the peptide-membrane interactions. In this chapter, we describe basic approaches for using SDSL EPR spectroscopy to study interactions between small peptides and biological membranes or membrane mimetic systems. We focus on experimental approaches to quantify peptide-membrane binding, topology of bound peptides, and characterize peptide aggregation. Sample preparation protocols including spin-labeling methods and preparation of membrane mimetic systems are also described.}, journal={Methods in Enzymology}, author={Smirnova, TI and Smirnov, AI}, year={2015}, pages={219–258} }
 @article{liu_leininger_koolivand_smirnov_shenderova_brenner_krim_2015, title={Tribological properties of nanodiamonds in aqueous suspensions: effect of the surface charge}, volume={5}, ISSN={["2046-2069"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84942156290&partnerID=MN8TOARS}, DOI={10.1039/c5ra14151f}, abstractNote={The sign of nanodiamond surface charge is discovered to profoundly impact friction at both nanometer and macroscopic scales.}, number={96}, journal={RSC ADVANCES}, author={Liu, Zijian and Leininger, Dustin and Koolivand, Amir and Smirnov, Alex I. and Shenderova, Olga and Brenner, Donald W. and Krim, Jacqueline}, year={2015}, pages={78933–78940} }
 @article{donohue_voynov_milikisiyants_smirnov_smirnova_2015, title={“Snorkeling” of the Charged Sidechain of a Transmembrane Peptide as Directly Observed by Double Electron-Electron Resonance Experiment}, volume={108}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2014.11.1120}, DOI={10.1016/J.BPJ.2014.11.1120}, abstractNote={While hydrophobic amino acids constitute the bulk of transmembrane protein domains, polar and even charged amino acids are not uncommon and often play significant roles in membrane protein function. Positioning a polar residue within the bilayer core is highly unfavorable thermodynamically; however, the free energy penalty could be minimized by “stretching” the side chain of the amino acid to bring the charged moiety closer to the bilayer surface while keeping the rest of the side chain inside the hydrophobic core. This biophysical phenomenon is known as “snorkeling”. Here we report experimental observations of “snorkeling” for nitroxide-modified side-chains upon protonation, its dependence upon the location along the transmembrane peptide helix, and how this snorkeling is affected by the membrane electrostatic surface potential. pH sensitive spin labels, either IMTSL or IKMTSL (JPCB 2009, 113, 3453) were attached to two cysteine residues positioned equidistant from the center of the WALP peptide so that the primary sequence of each peptide is palindromic, thus, ensuring symmetric location of the labels with respect to the bilayer. The change in protonation states of the nitroxide was directly observed from EPR spectra. The distance between two nitroxide moieties was measured by Q-band double electron-electron resonance (DEER) experiment. Upon protonation, the distance between the two IMTSL probes increased compared to that of the neutral forms, by approximately 3 A indicating displacements of the charged nitroxide sidechain towards the polar head region. The “snorkeling” of the label was observed to be depth dependent - no changes in the positioning of the sidechain upon protonation was observed for labels located within 10-8 A from the center of the bilayer. Supported by NSF-0843632 to TIS.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Donohue, Matthew and Voynov, Maxim and Milikisiyants, Sergey and Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2015}, month={Jan}, pages={203a} }
 @article{marek_koolivand_song_voinov_smirnov_2014, title={Curved Lipid Bilayers: Structure, Dynamics, Phase Properties and Surface Electrostatics}, volume={106}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2013.11.1296}, DOI={10.1016/J.BPJ.2013.11.1296}, abstractNote={A growing body of experimental data suggests that at least some of membrane-anchored and membrane-associated proteins are capable of sensing the membrane curvature. Further, highly curved lipid bilayers and small vesicles are involved in such important cellular processes as membrane fusion, endo- and exocytosis, and tubules' formation. Finally, Golgi apparatus represents an example of highly curved lipid structure. While significance of membrane curvature in cellular regulatory processes is emerging, limited data exist on biophysical properties of highly curved lipid bilayers. Here we summarize results of differential scanning calorimetry and spin labeling EPR studies of unilamellar vesicles (SUV) with average diameter ranging from 200 to 30 nm. Analysis of DSC data at multiple scan rates revealed broadening and shifts of the main phase transition of DMPC from ca. 22.9 to 23.6 oC. This observation is consistent with bilayer compression and an increase in local order parameter reveled by EPR and oxygen accessibility measurements. To assess the surface electrostatics of lipid vesicles we employed EPR of a recently introduced phospholipid (IMTSL-PTE) bearing a pH-sensitive nitroxide covalently attached to the lipid head group (Biophys. J. 2013, 104: 106). The magnitude of the negative surface electrostatic potential, Ψ, for POPG increased from −137 to −167 mV upon decrease in the vesicle diameter from 107 to 31 nm even though zeta-potentials were identical. This effect could be again rationalized by increase in lipid packing upon increase in curvature for the bilayer in fluid phase. However, the effect vanished for the gel phase. We conclude that biologically relevant fluid bilayer phase allows for a larger variability in the lipid packing density in the lipid polar head group region than a more ordered gel phase. Supported by U.S. DOE Contract DE-FG02-02ER15354.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Marek, Antonin and Koolivand, Amir and Song, David and Voinov, Maxim A. and Smirnov, Alex I.}, year={2014}, month={Jan}, pages={221a} }
 @article{rao_lee_prater_smirnov_narayan_2014, title={Laser annealing induced ferromagnetism in SrTiO3 single crystal}, volume={105}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4891184}, DOI={10.1063/1.4891184}, abstractNote={The appearance of ferromagnetic order up to 400 K upon KrF (248 nm) laser irradiation is reported in un-doped SrTiO3 (STO) single crystal. The high resolution x-ray photo emission spectroscopy (XPS) measurements reveal a strong shift of Sr-, Ti-, and O-related peaks. X-ray diffraction of laser annealed STO does not reveal a signature of either secondary magnetic or amorphous phases. 300 K X-band (∼9.543 GHz) angle-dependent electron paramagnetic resonance (EPR) measurements showed no evidence of additional magnetic peaks upon laser irradiation. XPS and EPR data did not provide a strong evidence of Ti3+ formation upon laser annealing. No differences in the visible 300 K Raman spectra of pristine and laser annealed STO are noticed. Interestingly, the magnetic moment is decreased by almost 10-fold upon oxygen annealing of laser annealed STO, inferring that oxygen vacancies play an important role in establishing the observed ferromagnetism.}, number={4}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Rao, S. S. and Lee, Y. F. and Prater, J. T. and Smirnov, A. I. and Narayan, J.}, year={2014}, month={Jul}, pages={042403} }
 @article{donohue_voynov_smirnov_smirnova_2014, title={Profiling the Dielectric Constant at the Membrane-Peptide Interface using Ionizable EPR Probes}, volume={106}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2013.11.2841}, DOI={10.1016/J.BPJ.2013.11.2841}, abstractNote={Polarity, electric potentials, and hydration are the major physico-chemical characteristics of lipid membranes that govern membrane-protein and protein-protein interactions as well as small molecules transport. Insertion of transmembrane proteins perturbs membrane structure altering local dielectric environment and hydration at the membrane-protein interface. The significance of distorting local membrane structure at the lipid-protein interface for modulating protein-protein interactions should not be overlooked. In this work we report on employing pH-sensitive ionizable EPR labels to profile a heterogeneous dielectric environment along the α-helix of a WALP peptide integrated in a lipid bilayer. Labels were attached to two cysteine residues positioned equidistant from the center of the peptide so that the primary sequence of each peptide is palindromic, thus insuring symmetric location of the labels with respect to the bilayer center. The change in protonation state of the nitroxide was directly observed by EPR. Q-band double electron-electron resonance (DEER) experiments were carried out to determine the distance between spin labels when imbedded in lipid bilayers to provide information about the label location. Thus, for the first time measurements of local electrostatics at peptide-bilayer interface were based on direct distance measurements rather than on assumptions on the probe location. Two pH sensitive spin labels, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethyl-imidazolidin-4-ylmethyl) ester (IMTSL) and S-4-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-1-oxyl-2,5-dihydro-1H-imidazol-2-yl) benzylmethanethiosulfonate (IKMTSL), with intrinsic pKa's differing by approximately 2 pH units were used to expand the pH range of the titration experiments. This provided the opportunity to vary the lipid composition in order to investigate effect of the surface charge on dielectric profile at peptide-membrane interface. Water penetration at the peptide-membrane interface was assessed by hyperfine sublevel correlation spectroscopy (HYSCORE) experiment in which the hyperfine coupling between the nitroxide and hydrogen/deuterium atom of water is measured. Supported by NSF-0843632 to TIS.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Donohue, Matthew and Voynov, Maxim A. and Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2014}, month={Jan}, pages={508a} }
 @article{lagerstedt_petrlova_hilt_marek_chung_sriram_budamagunta_desreux_thonon_jue_et al._2013, title={EPR assessment of protein sites for incorporation of Gd(III) MRI contrast labels}, volume={8}, ISSN={["1555-4309"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84876786430&partnerID=MN8TOARS}, DOI={10.1002/cmmi.1518}, abstractNote={We have engineered apolipoprotein A-I (apoA-I), a major protein constituent of high-density lipoprotein (HDL), to contain DOTA-chelated Gd(III) as an MRI contrast agent for the purpose of imaging reconstituted HDL (rHDL) biodistribution, metabolism and regulation in vivo. This protein contrast agent was obtained by attaching the thiol-reactive Gd[MTS-ADO3A] label at Cys residues replaced at four distinct positions (52, 55, 76 and 80) in apoA-I. MRI of infused mice previously showed that the Gd-labeled apoA-I migrates to both the liver and the kidney, the organs responsible for HDL catabolism; however, the contrast properties of apoA-I are superior when the ADO3A moiety is located at position 55, compared with the protein labeled at positions 52, 76 or 80. It is shown here that continuous wave X-band (9 GHz) electron paramagnetic resonance (EPR) spectroscopy is capable of detecting differences in the Gd(III) signal when comparing the labeled protein in the lipid-free with the rHDL state. Furthermore, the values of NMR relaxivity obtained for labeled variants in both the lipid-free and rHDL states correlate to the product of the X-band Gd(III) spectral width and the collision frequency between a nitroxide spin label and a polar relaxation agent. Consistent with its superior relaxivity measured by NMR, the rHDL-associated apoA-I containing the Gd[MTS-ADO3A] probe attached to position 55 displays favorable dynamic and water accessibility properties as determined by X-band EPR. While room temperature EPR requires >1 m m Gd(III)-labeled and only >10 µ m nitroxide-labeled protein to resolve the spectrum, the volume requirement is exceptionally low (~5 µl). Thus, X-band EPR provides a practical assessment for the suitability of imaging candidates containing the site-directed ADO3A contrast probe.}, number={3}, journal={CONTRAST MEDIA & MOLECULAR IMAGING}, publisher={Wiley-Blackwell}, author={Lagerstedt, Jens O. and Petrlova, Jitka and Hilt, Silvia and Marek, Antonin and Chung, Youngran and Sriram, Renuka and Budamagunta, Madhu S. and Desreux, Jean F. and Thonon, David and Jue, Thomas and et al.}, year={2013}, pages={252–264} }
 @article{donohue_voynov_smirnov_smirnova_2013, title={Molecular pH Probes at a Protein-Lipid Interface: Assessment of Local Dielectric Environment for Transmembrane Peptide}, volume={104}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2012.11.2073}, DOI={10.1016/j.bpj.2012.11.2073}, abstractNote={Spin-labeling EPR spectroscopy has found many applications in studying structure and dynamics of proteins and biological membranes. Recently, there has been substantial interest in utilizing EPR to characterize local effects of polarity and hydrogen bonding in these systems. Here we report on employing an pH-sensitive EPR probe IMSTL (S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester) to profile heterogeneous dielectric environments along the α-helix of a WALP peptide integrated in a lipid bilayer. A series of symmetrically positioned double cysteine mutants were labeled with a pH-sensitive nitroxide and the protonation state of IMTSL was directly observed by EPR. Q-band DEER experiments with double-labeled WALPs were employed to derive nitroxide-nitroxide distances of nitroxides before and after the protonation and, therefore, the positions of pH probes with respect to lipid bialyer. Thus, for the first time measurements of local electrostatics at peptide-bilayer interface were based on direct distance measurements rather than on assumptions on the probe location. For double-labeled WALP consecutive protonation of symmetrically positioned nitroxide tags was observed. The difference in observable pKa values was interpreted in terms of electrostatic interaction energy between titratable probes allowing us to estimate effective dielectric constant. Supported by NSF-0843632 to TIS.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Donohue, Matthew and Voynov, Maxim A. and Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2013}, month={Jan}, pages={373a} }
 @article{mebrahtu_borzenets_zheng_bomze_smirnov_florens_baranger_finkelstein_2013, title={Observation of Majorana quantum critical behaviour in a resonant level coupled to a dissipative environment}, volume={9}, ISSN={["1745-2481"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84887225371&partnerID=MN8TOARS}, DOI={10.1038/nphys2735}, abstractNote={We investigate experimentally an exotic state of electronic matter obtained by fine-tuning to a quantum critical point (QCP), realized in a spin-polarized resonant level coupled to strongly dissipative electrodes. Several transport scaling laws near and far from equilibrium are measured, and then accounted for theoretically. Our analysis reveals a splitting of the resonant level into two quasi-independent Majorana modes, one strongly hybridized to the leads, and the other tightly bound to the quantum dot. Residual interactions involving these Majorana fermions result in the observation of a striking quasi-linear non-Fermi liquid scattering rate at the QCP. Our devices constitute a viable alternative to topological superconductors as a platform for studying strong correlation effects within Majorana physics.}, number={11}, journal={NATURE PHYSICS}, author={Mebrahtu, H. T. and Borzenets, I. V. and Zheng, H. and Bomze, Y. V. and Smirnov, A. I. and Florens, S. and Baranger, H. U. and Finkelstein, G.}, year={2013}, month={Nov}, pages={732–737} }
 @article{borzenets_coskun_mebrahtu_bomze_smirnov_finkelstein_2013, title={Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures}, volume={111}, ISSN={["1079-7114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84880100049&partnerID=MN8TOARS}, DOI={10.1103/physrevlett.111.027001}, abstractNote={We examine the nature of the transitions between the normal and the superconducting branches of superconductor-graphene-superconductor Josephson junctions. We attribute the hysteresis between the switching (superconducting to normal) and retrapping (normal to superconducting) transitions to electron overheating. In particular, we demonstrate that the retrapping current corresponds to the critical current at an elevated temperature, where the heating is caused by the retrapping current itself. The superconducting gap in the leads suppresses the hot electron outflow, allowing us to further study electron thermalization by phonons at low temperatures ($T \lesssim 1$K). The relationship between the applied power and the electron temperature was found to be $P\propto T^3$, which we argue is consistent with cooling due to electron-phonon interactions.}, number={2}, journal={PHYSICAL REVIEW LETTERS}, author={Borzenets, I. V. and Coskun, U. C. and Mebrahtu, H. T. and Bomze, Yu. V. and Smirnov, A. I. and Finkelstein, G.}, year={2013}, month={Jul} }
 @article{voinov_marek_kett_smirnov_2013, title={Surface Electrostatics and Peptide Binding to Lipid Bilayer of Defined Curvature}, volume={104}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2012.11.579}, DOI={10.1016/j.bpj.2012.11.579}, abstractNote={Many proteins are known to have strong binding preferences for curved lipid bilayer surfaces. This property of proteins to sense membrane curvature has a number of implications in cellular processes including endocytosis, exocytosis, and vesicle trafficking as well as pathogenic processes associated with viral infections or protein aggregation disorders. Here we employ small unilamellar vesicles (SUVs) that are sized by extrusion through nanoporous filters as a model of convex membranes with accessible outer surface. For concave structures we developed nanopore-confined tubular lipid bilayers with tunable curvature radii ranging from ca. 40 to 250 nm. The nanotubular bilayers are formed by lipid self-assembly inside cylindrical nanopores of anodic aluminum oxide (AAO). These systems impose essentially no restrictions on the lipid composition and have the inner surface of negative curvature accessible for solute molecules and peptide binding. Using these model structures we show that the surface electrostatic potential of lipid bilayers is affected by the curvature to a rather large degree. For example, for SUVs composed of negatively charged lipids the magnitude of the surface potential increased with bilayer bending from ca. −106 mV for 100 nm SUV to −166 mV for 30 nm SUVs. These measurements were carried out by spin probe EPR method using recently synthesized lipids having pH-reporting nitroxides covalently tethered to the lipid polar head. EPR titration experiments were followed by the measurement of the lipid vesicle electrophoretic mobility and peptide binding. Overall, the data indicate that the bilayer bending affects the local electrostatic potential in a rather large degree providing a likely biophysical mechanism for affecting protein binding to lipid membranes without adjusting lipid composition. Supported by U.S. DOE Contract DE-FG02-02ER15354.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Voinov, Maxim A. and Marek, Antonin and Kett, Peter and Smirnov, Alex I.}, year={2013}, month={Jan}, pages={98a} }
 @article{voinov_rivera-rivera_smirnov_2013, title={Surface Electrostatics of Lipid Bilayers by EPR of a pH-Sensitive Spin-Labeled Lipid}, volume={104}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2012.11.3806}, DOI={10.1016/j.bpj.2012.11.3806}, abstractNote={Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids’ polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes.}, number={1}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Voinov, Maxim A. and Rivera-Rivera, Izarys and Smirnov, Alex I.}, year={2013}, month={Jan}, pages={106–116} }
 @article{young_donohue_smirnova_smirnov_zhou_2013, title={The UDP-diacylglucosamine Pyrophosphohydrolase LpxH in Lipid A Biosynthesis Utilizes Mn2+ Cluster for Catalysis}, volume={288}, ISSN={["1083-351X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84884550173&partnerID=MN8TOARS}, DOI={10.1074/jbc.m113.497636}, abstractNote={In Escherichia coli and the majority of β- and γ-proteobacteria, the fourth step of lipid A biosynthesis, i.e. cleavage of the pyrophosphate group of UDP-2,3-diacyl-GlcN, is carried out by LpxH. LpxH has been previously suggested to contain signature motifs found in the calcineurin-like phosphoesterase (CLP) family of metalloenzymes; however, it cleaves a pyrophosphate bond instead of a phosphoester bond, and its substrate contains nucleoside diphosphate moieties more common to the Nudix family rather than to the CLP family. Furthermore, the extent of biochemical data fails to demonstrate a significant level of metal activation in enzymatic assays, which is inconsistent with the behavior of a metalloenzyme. Here, we report cloning, purification, and detailed enzymatic characterization of Haemophilus influenzae LpxH (HiLpxH). HiLpxH shows over 600-fold stimulation of hydrolase activity in the presence of Mn2+. EPR studies reveal the presence of a Mn2+ cluster in LpxH. Finally, point mutants of residues in the conserved metal-binding motifs of the CLP family greatly inhibit HiLpxH activity, highlighting their importance in enzyme function. Contrary to previous analyses of LpxH, we find HiLpxH does not obey surface dilution kinetics. Overall, our work unambiguously establishes LpxH as a calcineurin-like phosphoesterase containing a Mn2+ cluster coordinated by conserved residues. These results set the scene for further structural investigation of the enzyme and for design of novel antibiotics targeting lipid A biosynthesis.Background: LpxH is a novel pyrophosphate hydrolase in lipid A biosynthesis.Results: Enzymatic and EPR studies reveal a catalytically important Mn2+ cluster within LpxH.Conclusion: LpxH is a Mn2+-dependent lipid A enzyme with an active site similar to calcineurin-like phosphatases, not Nudix family hydrolases.Significance: Unmasking the true nature of LpxH catalysis represents an important step toward structural characterization and development of antibiotics. In Escherichia coli and the majority of β- and γ-proteobacteria, the fourth step of lipid A biosynthesis, i.e. cleavage of the pyrophosphate group of UDP-2,3-diacyl-GlcN, is carried out by LpxH. LpxH has been previously suggested to contain signature motifs found in the calcineurin-like phosphoesterase (CLP) family of metalloenzymes; however, it cleaves a pyrophosphate bond instead of a phosphoester bond, and its substrate contains nucleoside diphosphate moieties more common to the Nudix family rather than to the CLP family. Furthermore, the extent of biochemical data fails to demonstrate a significant level of metal activation in enzymatic assays, which is inconsistent with the behavior of a metalloenzyme. Here, we report cloning, purification, and detailed enzymatic characterization of Haemophilus influenzae LpxH (HiLpxH). HiLpxH shows over 600-fold stimulation of hydrolase activity in the presence of Mn2+. EPR studies reveal the presence of a Mn2+ cluster in LpxH. Finally, point mutants of residues in the conserved metal-binding motifs of the CLP family greatly inhibit HiLpxH activity, highlighting their importance in enzyme function. Contrary to previous analyses of LpxH, we find HiLpxH does not obey surface dilution kinetics. Overall, our work unambiguously establishes LpxH as a calcineurin-like phosphoesterase containing a Mn2+ cluster coordinated by conserved residues. These results set the scene for further structural investigation of the enzyme and for design of novel antibiotics targeting lipid A biosynthesis. Background: LpxH is a novel pyrophosphate hydrolase in lipid A biosynthesis. Results: Enzymatic and EPR studies reveal a catalytically important Mn2+ cluster within LpxH. Conclusion: LpxH is a Mn2+-dependent lipid A enzyme with an active site similar to calcineurin-like phosphatases, not Nudix family hydrolases. Significance: Unmasking the true nature of LpxH catalysis represents an important step toward structural characterization and development of antibiotics. The outer membrane of Gram-negative bacteria is arranged into an asymmetric bilayer with the inner leaflet consisting of phospholipids such as phosphatidylglycerol and phosphatidylethanolamine and the outer leaflet containing lipopolysaccharide (LPS). LPS serves to shield bacteria from external damage caused by detergents and antibiotics (1Raetz C.R. Whitfield C. Lipopolysaccharide endotoxins.Annu. Rev. Biochem. 2002; 71: 635-700Crossref PubMed Scopus (3358) Google Scholar) and is anchored into the bacterial outer membrane via a hexacylated saccharolipid called lipid A (1Raetz C.R. Whitfield C. Lipopolysaccharide endotoxins.Annu. Rev. Biochem. 2002; 71: 635-700Crossref PubMed Scopus (3358) Google Scholar, 2Raetz C.R. Reynolds C.M. Trent M.S. Bishop R.E. Lipid A modification systems in Gram-negative bacteria.Annu. Rev. Biochem. 2007; 76: 295-329Crossref PubMed Scopus (924) Google Scholar). In addition to serving as a membrane anchor, lipid A also has a critical role in host response to bacterial infection, as it can be recognized by the TLR-4·MD2 complex, leading to activation of the NF-κB pathway, secretion of cytokines, and subsequent clearance of infection (3Park B.S. Song D.H. Kim H.M. Choi B.S. Lee H. Lee J.O. The structural basis of lipopolysaccharide recognition by the TLR4-MD-2 complex.Nature. 2009; 458: 1191-1195Crossref PubMed Scopus (1591) Google Scholar, 4Rietschel E.T. Kirikae T. Schade F.U. Mamat U. Schmidt G. Loppnow H. Ulmer A.J. Zähringer U. Seydel U. Di Padova F. Bacterial endotoxin: molecular relationships of structure to activity and function.FASEB J. 1994; 8: 217-225Crossref PubMed Scopus (1322) Google Scholar). However, overactivation of the immune system by lipid A can result in the potentially fatal condition of sepsis (5Russell J.A. Management of sepsis.N. Engl. J. Med. 2006; 355: 1699-1713Crossref PubMed Scopus (897) Google Scholar). Lipid A is required for the growth and survival of most Gram-negative bacteria, making its biosynthesis an attractive target for novel antibiotics (1Raetz C.R. Whitfield C. Lipopolysaccharide endotoxins.Annu. Rev. Biochem. 2002; 71: 635-700Crossref PubMed Scopus (3358) Google Scholar, 2Raetz C.R. Reynolds C.M. Trent M.S. Bishop R.E. Lipid A modification systems in Gram-negative bacteria.Annu. Rev. Biochem. 2007; 76: 295-329Crossref PubMed Scopus (924) Google Scholar, 6Barb A.W. Zhou P. Mechanism and inhibition of LpxC: an essential zinc-dependent deacetylase of bacterial lipid A synthesis.Curr. Pharm. Biotechnol. 2008; 9: 9-15Crossref PubMed Scopus (113) Google Scholar). In Escherichia coli, the pathway for lipid A biosynthesis consists of nine enzymes, each of which catalyzes a separate step (1Raetz C.R. Whitfield C. Lipopolysaccharide endotoxins.Annu. Rev. Biochem. 2002; 71: 635-700Crossref PubMed Scopus (3358) Google Scholar). Nearly all of these nine enzymes are highly conserved throughout Gram-negative bacteria (7Opiyo S.O. Pardy R.L. Moriyama H. Moriyama E.N. Evolution of the Kdo2-lipid A biosynthesis in bacteria.BMC Evol. Biol. 2010; 10: 362Crossref PubMed Scopus (31) Google Scholar). However, an exception to the universal nature of the pathway is the fourth step that involves the hydrolysis of UDP-2,3-diacylglucosamine (UDP-DAGn) 2The abbreviations used are: UDP-DAGn, UDP-2,3-diacylglucosamine; CLP, calcineurin-like phosphoesterase; EcLpxH, E. coli LpxH; HiLpxH, H. influenzae LpxH; IPTG, isopropyl β-d-1-thiogalactopyranoside; Lipid X, 2,3-diacylglucosamine 1-phosphate; TEV protease, tobacco etch virus protease; Ni-NTA, nickel-nitrilotriacetic acid. to yield UMP and 2,3-diacylglucosamine 1-phosphate (more commonly known as lipid X) (Fig. 1). This reaction, thought to be the first membrane-associating step of the pathway, can be carried out by either LpxH (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar, 9Babinski K.J. Kanjilal S.J. Raetz C.R. Accumulation of the lipid A precursor UDP-2,3-diacylglucosamine in an Escherichia coli mutant lacking the lpxH gene.J. Biol. Chem. 2002; 277: 25947-25956Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar) or LpxI (10Metzger 4th, L.E. Raetz C.R. An alternative route for UDP-diacylglucosamine hydrolysis in bacterial lipid A biosynthesis.Biochemistry. 2010; 49: 6715-6726Crossref PubMed Scopus (41) Google Scholar). These two enzymes share no sequence similarity, are never found in the same organism, and attack different phosphates in their catalysis of UDP-DAGn hydrolysis (10Metzger 4th, L.E. Raetz C.R. An alternative route for UDP-diacylglucosamine hydrolysis in bacterial lipid A biosynthesis.Biochemistry. 2010; 49: 6715-6726Crossref PubMed Scopus (41) Google Scholar). Despite these differences, lpxI can complement an lpxH knock-out in E. coli (10Metzger 4th, L.E. Raetz C.R. An alternative route for UDP-diacylglucosamine hydrolysis in bacterial lipid A biosynthesis.Biochemistry. 2010; 49: 6715-6726Crossref PubMed Scopus (41) Google Scholar), indicating that LpxI and LpxH have the same function within the context of the lipid A pathway. The gene encoding LpxH was first discovered in E. coli, and sequence analysis of LpxH orthologs revealed a DXH(X)∼25GDXXDR(X)∼25GNH(D/E) (where X is any residue) motif that is found in the calcineurin-like phosphoesterase (CLP) superfamily (Pfam00149). These enzymes perform catalysis using an ordered shell of water molecules and divalent or trivalent metal cofactors coordinated by conserved residues of the metallophosphoesterase motif (11Mitić N. Smith S.J. Neves A. Guddat L.W. Gahan L.R. Schenk G. The catalytic mechanisms of binuclear metallohydrolases.Chem. Rev. 2006; 106: 3338-3363Crossref PubMed Scopus (362) Google Scholar, 12Cleland W.W. Hengge A.C. Enzymatic mechanisms of phosphate and sulfate transfer.Chem. Rev. 2006; 106: 3252-3278Crossref PubMed Scopus (363) Google Scholar). It has been postulated that the metal ions serve to bridge an oxide that performs a nucleophilic attack, to stabilize the formation of a phosphorane intermediate, and to coordinate a nucleophilic hydroxyl group to allow for deprotonation (12Cleland W.W. Hengge A.C. Enzymatic mechanisms of phosphate and sulfate transfer.Chem. Rev. 2006; 106: 3252-3278Crossref PubMed Scopus (363) Google Scholar, 13White D.J. Reiter N.J. Sikkink R.A. Yu L. Rusnak F. Identification of the high affinity Mn2+-binding site of bacteriophage λ phosphoprotein phosphatase: effects of metal ligand mutations on electron paramagnetic resonance spectra and phosphatase activities.Biochemistry. 2001; 40: 8918-8929Crossref PubMed Scopus (29) Google Scholar). Besides calcineurin, enzymes of the CLP superfamily also include protein serine/threonine phosphatases (14Zhuo S. Clemens J.C. Stone R.L. Dixon J.E. Mutational analysis of a Ser/Thr phosphatase. Identification of residues important in phosphoesterase substrate binding and catalysis.J. Biol. Chem. 1994; 269: 26234-26238Abstract Full Text PDF PubMed Google Scholar), purple acid phosphatases (15Battistuzzi G. Dietrich M. Löcke R. Witzel H. Evidence for a conserved binding motif of the dinuclear metal site in mammalian and plant purple acid phosphatases: 1H NMR studies of the di-iron derivative of the Fe(III)Zn(II) enzyme from kidney bean.Biochem. J. 1997; 323: 593-596Crossref PubMed Scopus (12) Google Scholar), nucleotidases, sphingomyelin phosphodiesterases (16Ago H. Oda M. Takahashi M. Tsuge H. Ochi S. Katunuma N. Miyano M. Sakurai J. Structural basis of the sphingomyelin phosphodiesterase activity in neutral sphingomyelinase from Bacillus cereus.J. Biol. Chem. 2006; 281: 16157-16167Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar), exonucleases, and cyclic nucleotide phosphodiesterases (11Mitić N. Smith S.J. Neves A. Guddat L.W. Gahan L.R. Schenk G. The catalytic mechanisms of binuclear metallohydrolases.Chem. Rev. 2006; 106: 3338-3363Crossref PubMed Scopus (362) Google Scholar). These enzymes have broad functions but are thought to have evolved from the same ancestor (17Koonin E.V. Conserved sequence pattern in a wide variety of phosphoesterases.Protein Sci. 1994; 3: 356-358Crossref PubMed Scopus (106) Google Scholar). Compared with other enzymes of this family, LpxH hydrolyzes a unique substrate containing both lipid and nucleotide moieties and does so by breaking a pyrophosphate bond, a type of chemistry that to our knowledge has not been previously reported for CLP enzymes (11Mitić N. Smith S.J. Neves A. Guddat L.W. Gahan L.R. Schenk G. The catalytic mechanisms of binuclear metallohydrolases.Chem. Rev. 2006; 106: 3338-3363Crossref PubMed Scopus (362) Google Scholar). Additionally, no metal dependence of LpxH has been reported (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar), adding to the mystery of whether the enzyme functions like other members of the CLP family. Here, we report cloning, overexpression, and purification of an LpxH ortholog from Haemophilus influenzae (HiLpxH) to near homogeneity (>95%). Using an optimized autoradiographic assay, we have carried out detailed enzymatic characterization of HiLpxH. We show that HiLpxH activity is stimulated over 600-fold by Mn2+, and our EPR studies reveal a Mn2+ cluster that serves to facilitate catalysis. Mutagenesis studies indicate the functional importance of the predicted Mn2+-binding residues in the conserved metallophosphoesterase motif. This work sheds new insights into LpxH catalysis that were previously disguised by enzyme impurity, less-than-optimal assay conditions, and low enzymatic activity. These new observations highlight a strong mechanistic similarity of LpxH to members of the CLP family and set the scene for structural studies of LpxH. Reagents for bacterial growth included yeast extract, tryptone, and Bacto agar, and were purchased from Difco. The HEPES, phosphate-buffered saline (PBS) components, HCl, salts, ampicillin, isopropyl β-d-thiogalactoside (IPTG), fatty acid-free bovine serum albumin (BSA), EDTA, and DTT were purchased from Sigma. Methanol, chloroform, pyridine, and acetic acid were obtained from EMD Science (Gibbstown, NJ). Radioactive γ-32Pi was purchased from PerkinElmer Life Sciences. The plasmids used in this study were purified using Qiagen Mini-Prep kits (Qiagen, Valencia, CA) according to the manufacturer's protocol. DNA fragments were purified using QIAquick spin kits. Sequencing was carried out by Eton Bioscience, Inc. (Research Triangle Park, NC). Unless otherwise noted, protein concentration was determined either by the bicinchoninic acid assay or Bradford assay (Thermo Scientific, Waltham, MA) depending on compatibility with buffer components. Both of these methods were carried out as described by the manufacturer. Amplification of lpxH (HI0375) from H. influenzae genomic DNA (ATCC, Manassas, VA) was accomplished using PCR with primers 50 bp upstream and downstream of lpxH. To facilitate eventual ligation of the gene product into an expression vector, we used primers (Integrated DNA Technologies, Coralville, IA) that allowed for the incorporation of NdeI and XhoI restriction sites to the 5′ and 3′ ends of lpxH and the elimination of the stop codon at the end of the gene. The PCR was carried out using a Mastercycler Gradient Thermocycler (Eppendorf, Hamburg, Germany) with the reagents and protocol of the KOD hot start kit (EMD Chemicals, Gibbstown, NJ); the reaction was additionally supplemented with 3% (w/v) dimethyl sulfoxide. Sequencing of the resulting product using the original primers was used to ensure proper amplification. To generate an expression vector with a C-terminal His10 tag that was cleavable by tobacco etch virus (TEV) protease, 33 additional nucleotides were added to pET21b (Novagen/EMD Chemicals) to encode for the seven amino acids of the protease site (ENLYFQG) (18Lucast L.J. Batey R.T. Doudna J.A. Large-scale purification of a stable form of recombinant tobacco etch virus protease.BioTechniques. 2001; 30: 544-546Crossref PubMed Scopus (108) Google Scholar) and the four additional histidine residues needed to elongate the affinity tag. This was accomplished using QuikChange (Stratagene, La Jolla, CA) mutagenesis with primers (Integrated DNA Technologies) that were designed to insert the additional nucleotides 3′ to the XhoI restriction site in pET21b. The reaction was carried out using the manufacturer's protocol with an additional supplement of 3% (w/v) dimethyl sulfoxide and 1 m betaine. Following nucleotide insertion, the resulting plasmid, p21t10, was confirmed by sequencing and transformed into chemically competent DH5α cells (Invitrogen). Additionally, p21t10 was transformed into chemically competent E. coli C41(DE3) to create the vector control expression strain VC_T10. Insertion of amplified H. influenza lpxH into p21t10 was accomplished by digestion of both the PCR fragment and the vector with NdeI and XhoI (New England Biolabs) under conditions described by the manufacturer. After treatment of p21t10 with antarctic phosphatase (New England Biolabs) under conditions described by the manufacturer, digested lpxH was inserted into the plasmid with T4 ligase (Invitrogen) as directed by the manufacturer. The ligation product, pHiHt10, was transformed into chemically competent C41(DE3) E. coli to generate the expression strain HiH_t10. Sequencing with T7 forward and reverse primers confirmed the appropriate insertion of H. influenzae lpxH into p21t10. Two samples of cell-free extract from HiH_t10 (obtained as described below with cell debris removed after centrifugation at 10,000 × g) corresponding to 6 mg of total protein were brought to a volume of 1 ml with the appropriate stock solutions to yield final solution concentrations of 200 mm NaCl, 20 mm HEPES, pH 8.0, and either 0 or 1.5% w/v of Triton X-100. These samples were then incubated for 1 h at 4 °C and then subjected to ultracentrifugation at 100,000 × g for 45 min. Resulting supernatants were collected as cytosolic fractions, and pellets were resuspended in 200 mm NaCl and 20 mm HEPES, pH 8.0, to obtain membrane fractions. The fractions were analyzed for the presence of HiLpxH by both SDS-PAGE and the optimized UDP-DAGn hydrolase activity assay, as described below. A typical preparation of HiLpxH began with inoculating an overnight culture of LB with a single colony of HiH_t10. This overnight culture was subsequently used to inoculate 3 liters of LB (10 g of tryptone, 5 g of yeast extract, 10 g of NaCl per liter) supplemented with 100 μg/ml ampicillin to an A600 of 0.02. Cultures were incubated at 30 °C with aeration at 220 rpm until they reached A600 of 0.7–0.8 and then were induced for expression by the addition of 1 mm IPTG and grown for an additional 4–5 h until the A600 reached ∼4. Cells from the growths were pelleted by centrifugation at 5,000 × g, washed with 140 ml of cold PBS, and then stored at −80 °C. For lysis, the frozen pellet was thawed, resuspended in 80 ml of ice-cold 20 mm HEPES, pH 8.0, and passed twice through a French pressure cell (SIM-AMINCO; Spectronic Instruments) at 18,000 p.s.i. The debris from the resulting lysate was removed by centrifugation at 10,000 × g, and the subsequent supernatant was collected as a cell-free extract and stored at −80 °C. Cell-free extract was thawed and diluted to 5 mg/ml with 20 mm HEPES, pH 8.0. A stock solution of 10% (w/v) Triton X-100 (Thermo Scientific) was used to bring the cell-free extract to a final detergent concentration of 1.5% (w/v). All subsequent steps were carried out at 4 °C. The resulting solution was then mixed by inversion for 1 h and then subjected to ultracentrifugation at 100,000 × g for 45 min. The supernatant was removed and diluted with the appropriate stocks to make a 450-ml solution of ∼3 mg/ml protein, 20 mm HEPES, pH 8.0, 200 mm NaCl, 20 mm imidazole, and 0.5% Triton X-100. This solution was then loaded by gravity onto a packed column of 20 ml of Ni-NTA resin (Qiagen) that had been pre-equilibrated in 20 column volumes of load buffer (20 mm HEPES, pH 8.0, 200 mm NaCl, 20 mm imidazole, 0.1% Triton X-100). The loaded column was next washed with an additional 10 column volumes of load buffer followed by a 15-column volume wash with load buffer supplemented with 30 mm imidazole (final imidazole concentration 50 mm). To exchange HiLpxH out of detergent, the column was subjected to a 50 column volume wash with a solution of 20 mm HEPES, pH 8.0, 200 mm NaCl. Elution of the protein was accomplished by a 7 column volume wash with a solution of 20 mm HEPES, pH 8.0, 200 mm NaCl, and 400 mm imidazole. Samples from each wash of the column were analyzed by SDS-PAGE to ensure proper fractionation. After elution, a TEV protease reaction was used to cleave the C-terminal His10 tag. The eluted protein was diluted to a volume of 200 ml with the appropriate stock solutions to yield a sample with final concentrations of 2 mm DTT, 2 mm EDTA, 20 mm HEPES, pH 8.0, 200 mm NaCl, 300 mm imidazole, and ∼0.015 mg/ml (∼1:50 of the HiLpxH concentration) of TEV protease. The protease used was prepared as described in the literature (18Lucast L.J. Batey R.T. Doudna J.A. Large-scale purification of a stable form of recombinant tobacco etch virus protease.BioTechniques. 2001; 30: 544-546Crossref PubMed Scopus (108) Google Scholar), and cleavage was monitored using SDS-PAGE. After overnight incubation, the reaction was concentrated to a final volume of 50 ml using 15 ml of Amicon Ultra 10K molecular weight cutoff centrifuge concentrators (Millipore, Billerica, MA) and then dialyzed overnight against 8 liters of 20 mm HEPES, pH 8.0, and 200 mm NaCl. The remaining TEV protease and any uncleaved HiLpxH was removed from the sample by passage over a 5-ml Ni-NTA column pre-equilibrated with 20 column volumes of a solution containing 20 mm HEPES, pH 8.0, 200 mm NaCl, and 20 mm imidazole. The flowthrough was collected and then concentrated using Millipore conical spin concentrations to a final concentration of ∼8 mg/ml. The final protein sample, which contained HiLpxH followed by the residual TEV cleavage site residues of ENLYFQ, was analyzed by SDS-PAGE to confirm purity and stored at −80 °C in 15-μl aliquots. QuikChange (Stratagene) mutagenesis was used to make alanine point mutants of conserved residues within HiLpxH. The method was carried out as described above, with pHiHt10 serving as template DNA. Specific primers (Integrated DNA Technologies) were created for each desired alanine substitution, and sequencing with T7 forward and reverse primers was used to confirm the mutations. The mutated pHiHt10 vectors were transformed into chemically competent E. coli C41(DE3) to create respective expression strains. These strains, along with wild-type HiH_t10, were grown under conditions described for HiLpxH purification except that the culture volume was 250 ml. Cells from each of the growths were centrifuged at 5,000 × g, and collected pellets were washed with 30 ml of cold PBS and then stored at −80 °C. For lysis, the frozen pellet from each mutant strain and the wild-type strain was thawed, resuspended in 8 ml of ice-cold 20 mm HEPES, pH 8.0, and passed twice through a French pressure cell (Sim-Aminco, Spectronic Instruments) at 18,000 p.s.i. The debris from the resulting lysate was removed by centrifugation at 10,000 × g, and the subsequent supernatant was collected as cell-free extract and stored at −80 °C. Purification of the protein from these growths was the same as HiLpxH but adjusted to account for the smaller culture size. The cell-free extract was thawed, diluted, and solubilized as described for HiLpxH. Following the centrifugation step after detergent incubation, the supernatant was removed and diluted with the appropriate stocks to make a 20-ml solution of ∼3 mg/ml protein, 20 mm HEPES, pH 8.0, 200 mm NaCl, 20 mm imidazole, and 0.5% Triton X-100. This solution from each strain was then loaded by gravity onto separate columns of 1 ml of Ni-NTA resin (Qiagen) that had been pre-equilibrated in 20 column volumes of the load buffer described above. Washing, detergent exchange, and elution were carried out as outlined for HiLpxH. Samples from each wash of the column were analyzed by SDS-PAGE to ensure proper fractionation. Following elution, the samples were each concentrated to 3 ml using 5 ml of Amicon Ultra 10K molecular weight cutoff centrifuge concentrators (Millipore) and then dialyzed overnight against 1 liter of 20 mm HEPES, pH 8.0, 200 mm NaCl. Resulting protein solutions from each mutant and the wild-type sample were further concentrated to 500 μl and stored in −80 °C. 32P-Labeled UDP-DAGn was prepared as described previously (10Metzger 4th, L.E. Raetz C.R. An alternative route for UDP-diacylglucosamine hydrolysis in bacterial lipid A biosynthesis.Biochemistry. 2010; 49: 6715-6726Crossref PubMed Scopus (41) Google Scholar) with some modifications. First, 50 μl of 0.2 m 1H-tetrazole in acetonitrile in the morpholidate reaction was replaced with 20 μl of 0.1 m dicyanoimidazole in acetonitrile (Sigma). Second, after the product of the morpholidate reaction was dried under N2, it was extracted with a single phase Bligh-Dyer (19Bligh E.G. Dyer W.J. A rapid method of total lipid extraction and purification.Can. J. Biochem. Physiol. 1959; 37: 911-917Crossref PubMed Scopus (42694) Google Scholar) with volumes of 0.5 ml of methanol, 0.25 ml of chloroform, and 0.2 ml of PBS. The mixture was centrifuged to pellet debris, and the supernatant was transferred to a 2-ml polypropylene tube and dried under N2. The radioactive substrate was then resuspended in 100–170 μl of 20 mm HEPES, pH 8.0, containing 0.02% Triton X-100 and sonicated for 2 min. One final centrifugation step was used to pellet any insoluble material. The supernatant containing the final [β-32P]UDP-DAGn was transferred to a new tube and stored at −20 °C. These extra extraction steps removed contaminating impurities that interfered with the linearity of our assays. General autoradiographic assays for hydrolase activity were similar to that previously described (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar) with optimized modifications. Reactions mixtures were a final volume of 15 μl in 0.6-ml polypropylene tubes and contained 20 mm HEPES, pH 8.0, 0.5% (w/v) BSA, 0.05% (w/v) Triton X-100, 1 mm MnCl2, 100 μm UDP-DAGn (prepared as described previously (20Radika K. Raetz C.R. Purification and properties of lipid A disaccharide synthase of Escherichia coli.J. Biol. Chem. 1988; 263: 14859-14867Abstract Full Text PDF PubMed Google Scholar)), 1,000 cpm/μl [β-32P]UDP-DAGn, and enzyme. Previous studies of E. coli LpxH reported a small enhancement in enzyme stability and activity when the protein was purified with MnCl2 (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar); therefore, MnCl2 was incorporated into the assay. All reaction components besides the enzyme were mixed to a volume of 12 μl and equilibrated at 30 °C for 10 min, after which 3 μl of enzyme was added to start the reaction. Unless otherwise noted, enzyme samples were diluted in a buffer identical to the assay mixture but lacking any lipid substrate. Aliquots of 1.5 μl were taken from the reactions at various time intervals and spotted onto 20 × 20-cm glass-backed silica gel thin layer chromatography (TLC) plates (EMD Chemicals, Darmstadt, Germany). These plates were developed in a 25:15:4:2 chloroform/methanol/water/acetic acid tank system, dried, exposed to phosphoscreens, scanned, and quantified as described previously (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). To assess the effectiveness of the optimized in vitro assay, E. coli LpxH (EcLpxH) cell-free extract, HiLpxH cell-free extract, and purified HiLpxH were analyzed for activity under both the original and the improved assay conditions. To prepare the EcLpxH cell-free extract, E. coli C41(DE3) was transformed with pKJB2 (8Babinski K.J. Ribeiro A.A. Raetz C.R. The Escherichia coli gene encoding the UDP-2,3-diacylglucosamine pyrophosphatase of lipid A biosynthesis.J. Biol. Chem. 2002; 277: 25937-25946Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar), a pET21a+ plasmid containing E. coli lpxH. A 250-ml culture of the resulting strain was grown at 30 °C in LB media and induced for expression with IPTG at mid-log phase. After 5 h, cells were harvested and lysed to generate cell-free extract using the method described above. The same procedure was carried out in parallel with strain HiH_t10 to prepare the HiLpxH cell-free extract. Purified HiLpxH was isolated by the aforementioned technique. Activity assessment under original conditions was conducted as reported previously with the final protein concentrations in the assay for EcLpxH cell-free extract, HiLpxH cell-free extract, and HiLpxH being 1.8, 4.5, and 8.5 μg/ml respectively. Samples were also tested under the optimized in vitro conditions with protein concentrations of 45 ng/ml EcLpxH cell-free extract, 110 ng/ml HiLpxH cell-free extract, and 1.7 ng/m}, number={38}, journal={JOURNAL OF BIOLOGICAL CHEMISTRY}, publisher={American Society for Biochemistry & Molecular Biology (ASBMB)}, author={Young, Hayley E. and Donohue, Matthew P. and Smirnova, Tatyana I. and Smirnov, Alex I. and Zhou, Pei}, year={2013}, month={Sep}, pages={26987–27001} }
 @article{li_voinov_smirnov_2012, title={Chaperon and Lipid Composition Requirements for Transmembrane Insertion of CesA Helices 4 and 5}, volume={102}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2011.11.2411}, DOI={10.1016/j.bpj.2011.11.2411}, abstractNote={Folding of proteins with large transmembrane domains such as cellulose synthase CesA occurs in a highly heterogeneous environment of cellular membranes. Currently, detailed biophysical understanding of these processes is missing with only few examples of membrane proteins allowing for reversible folding found in the literature. Recently, in the course of ongoing investigation of the transmembrane structure of selected CesA helices, we have determined that both transmembrane helices (TMH) 4 and 5 would not insert properly into lipid bilayers and form aggregates unless specific requirements for lipid composition and/or chaperones are satisfied.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Li, Le and Voinov, Maxim A. and Smirnov, Alex I.}, year={2012}, month={Jan}, pages={440a} }
 @article{smirnov_2012, title={ChemInform Abstract: EPR Studies of Nanomaterials}, volume={43}, DOI={10.1002/chin.201206212}, abstractNote={Review: 39 refs.}, number={6}, journal={ChemInform}, publisher={Wiley-Blackwell}, author={Smirnov, Alex}, year={2012}, month={Jan}, pages={no-no} }
 @inproceedings{smirnov_povarov_starykh_shapiro_petrov_2012, title={Low energy dynamics in spin-liquid and ordered phases of S=1/2 antiferromagnet Cs<inf>2</inf>CuCl<inf>4</inf>}, volume={400}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873636295&partnerID=MN8TOARS}, DOI={10.1088/1742-6596/400/3/032091}, abstractNote={Cs2CuCl4 realizes spin-1/2 quantum antiferromagnet on a distorted triangular lattice. It remains in a quantum spin-liquid state far below Curie-Weiss temperature 4 K and exhibits an incommensurate spin ordering at TN=0.6 K. We studied Cs2CuCl4 by means of electron spin resonance (ESR) at temperatures down to 0.05 K in the frequency range 9 60 GHz, we observe that the above spinon-type ESR survives deep in the ordered phase. These novel phenomena are consequences of fractionalized spinon excitations of spin chains, which are effectively decoupled in Cs2CuCl4 due to strong geometric frustration.}, number={PART 3}, booktitle={Journal of Physics: Conference Series}, author={Smirnov, A.I. and Povarov, K.Yu. and Starykh, O.A. and Shapiro, A.Ya. and Petrov, S.V.}, year={2012} }
 @article{smirnova_voynov_poluektov_smirnov_2012, title={Probing Dielectric and Hydrogen Bonding Gradients in Biological Membranes}, volume={102}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2011.11.2262}, DOI={10.1016/j.bpj.2011.11.2262}, abstractNote={Nitroxide spin-labeling in combination with EPR spectroscopy has found many applications in studying structure and dynamics of proteins and biological membranes. Recently, there has been a substantial interest in utilizing EPR to characterize local effects of polarity and hydrogen bonding in proteins and biological membrane systems. Here we report on employing an arsenal of advanced spin-labeling EPR methods to profile heterogeneous dielectric and hydrogen bonding environment along the α-helical chain of an alanine-rich WALP peptide that is anchored in a lipid bilayer in a transmembrane orientation. A series of WALP cysteine mutants was labeled with a pH-sensitive nitroxide IMSTL (S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester) that is similar in molecular volume to phenylalanine. The protonation state of this nitroxide could be directly observed by EPR allowing us to follow proton gradient across the membrane in the vicinity of the WALP α-helix, and, thus, to reconstruct the gradient in the effective dielectric constant. These experiments were complemented by assessing local polarity from characteristic changes in EPR spectra that were enhanced by the use of perdeuterated and 15N-substituted nitroxides and high field EPR at 130 GHz (D-band). Formation of hydrogen bonds between the nitroxides and membrane-penetrating water molecules was observed directly in HYSCORE X-band experiments. Such measurements allowed us to derive experimental profiles of heterogeneous dielectric and hydrogen bonding environment along a typical transmembrane α-helix. Supported by: NSF-0843632 to TIS and NIH 1R01GM072897 to AIS.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Smirnova, Tatyana I. and Voynov, Maxim A. and Poluektov, Oleg G. and Smirnov, Alex I.}, year={2012}, month={Jan}, pages={414a} }
 @article{mebrahtu_borzenets_liu_zheng_bomze_smirnov_baranger_finkelstein_2012, title={Quantum phase transition in a resonant level coupled to interacting leads}, volume={488}, ISSN={["0028-0836"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84864433651&partnerID=MN8TOARS}, DOI={10.1038/nature11265}, abstractNote={An interacting one-dimensional electron system, the Luttinger liquid, is distinct from the "conventional" Fermi liquids formed by interacting electrons in two and three dimensions. Some of its most spectacular properties are revealed in the process of electron tunneling: as a function of the applied bias or temperature the tunneling current demonstrates a non-trivial power-law suppression. Here, we create a system which emulates tunneling in a Luttinger liquid, by controlling the interaction of the tunneling electron with its environment. We further replace a single tunneling barrier with a double-barrier resonant level structure and investigate resonant tunneling between Luttinger liquids. For the first time, we observe perfect transparency of the resonant level embedded in the interacting environment, while the width of the resonance tends to zero. We argue that this unique behavior results from many-body physics of interacting electrons and signals the presence of a quantum phase transition (QPT). In our samples many parameters, including the interaction strength, can be precisely controlled; thus, we have created an attractive model system for studying quantum critical phenomena in general. Our work therefore has broadly reaching implications for understanding QPTs in more complex systems, such as cold atoms and strongly correlated bulk materials.}, number={7409}, journal={NATURE}, publisher={Nature Publishing Group}, author={Mebrahtu, Henok T. and Borzenets, Ivan V. and Liu, Dong E. and Zheng, Huaixiu and Bomze, Yuriy V. and Smirnov, Alex I. and Baranger, Harold U. and Finkelstein, Gleb}, year={2012}, month={Aug}, pages={61–64} }
 @article{zhao_nellutla_son_vaughn_ye_smith_caignaert_lufaso_pekarek_smirnov_et al._2011, title={Ba4KFe3O9: A Novel Ferrite Containing Discrete 6-Membered Rings of Corner-Sharing FeO4 Tetrahedra}, volume={50}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80053934262&partnerID=MN8TOARS}, DOI={10.1021/ic201374g}, abstractNote={Single crystals of a new iron-containing oxide, Ba4KFe3O9, were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO4 tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe3+ coordination environments. The observed magnetic moment (∼3.9 μB) at 400 K is significantly lower than the calculated spin-only (∼5.2 μB) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe3+ sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ∼200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba4KFe3O9 calculated from χT data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ∼ 2.01 that is characteristic of Fe3+ ions in a tetrahedral environment, thus confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe6 magnetic species with an intensity ratio of ∼1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (δBpp). The line-width ratio δBpp(major)/δBpp(minor) ∼ 3.6 correlates well with the ratio of the Weiss constants, θminor/θmajor ∼ 4.}, number={20}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Zhao, Qingbiao and Nellutla, Saritha and Son, Won-Joon and Vaughn, Shae A. and Ye, Longfei and Smith, Mark D. and Caignaert, Vincent and Lufaso, Michael and Pekarek, Thomas M. and Smirnov, Alex I. and et al.}, year={2011}, month={Oct}, pages={10310–10318} }
 @article{smirnov_2011, title={EPR Studies of Nanomaterials}, url={http://dx.doi.org/10.1002/9783527633531.ch20}, DOI={10.1002/9783527633531.ch20}, abstractNote={Abstract Nanotechnology is broadly defined as the practical applications of nanoscale objects having dimensions from ca. 1 to 100 nm. At such atomic scale small clusters of atoms and molecules are exhibiting some rather intriguing physical, chemical, and biological properties that are absent in bulk materials of the same composition and the surface interactions become the dominant factors. Furthermore, one can combine manmade nanoobjects with genetically programmed self-assembled biomacromolecules to produce bionanomaterials – a fruitful avenue of research and technology development. The growth in bionanomaterials’ research creates additional demands for spectroscopic and analytical methods capable of characterizing the nanoscale objects and especially interfacial phenomena in a non-destructive way. Electron paramagnetic resonance (EPR) is one of the techniques that could meet this challenge. This chapter discusses some recent applications of EPR in studies bionanomaterials with particular emphasis on the interfacial properties of the nanoobjects and their interactions with biomacromolecules.}, journal={Multifrequency Electron Paramagnetic Resonance}, publisher={Wiley-Blackwell}, author={Smirnov, Alex}, year={2011}, month={Apr}, pages={825–843} }
 @article{jin_aggarwal_wei_nori_kumar_ponarin_smirnov_narayan_narayan_2011, title={Intrinsic Room-Temperature Ferromagnetic Properties of Ni-Doped ZnO Thin Films}, volume={42}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/S11661-010-0479-9}, DOI={10.1007/s11661-010-0479-9}, number={11}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Jin, C. and Aggarwal, R. and Wei, W. and Nori, S. and Kumar, D. and Ponarin, D. and Smirnov, A. I. and Narayan, J. and Narayan, R. J.}, year={2011}, month={Nov}, pages={3250–3254} }
 @article{smirnova_chadwick_bankaitis_schaaf_poluektov_smirnov_2011, title={Role of Electrostatic and Hydrogen Bonding Environment in Sequestering Lipids from Membranes Into the Sec14 Protein Cavity}, volume={100}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2010.12.3215}, DOI={10.1016/j.bpj.2010.12.3215}, abstractNote={Sec14p is a major yeast phosphatidylinositol/phosophatidylcholine (PtdIns/PtdCho) transfer protein that promotes transfer of PtdIns or PtdCho between lipid bilayers in vitro in energy-independent manner. The exact biophysical mechanism of such a process is unknown at this moment. Here we report on employing an arsenal of advanced spin-labeling EPR methods to probe local electrostatic and hydrogen bonding environment that govern binding of lipids by Sec14 protein. n-doxyl PtdCho (where n=5,7,10,12, and 16 reflects position of nitroxide along the acyl chain) were used as EPR active probes. The local polarity and hydrogen bonding profile inside the lipid binding cavity of Sec14p were assessed from characteristic changes in high field EPR at 130 GHz (D-band). The data indicate that the phospholipid-binding cavity of Sec14p with the likely sequestered water molecules provides a close match for the polarity profile along the bound PtdCho molecule and the one determined for membrane bilayers. This polarity match rationalizes the efficient energy-independent partitioning of a lipid molecule from a bilayer into the Sec14p phospholipid-binding pocket. Further, we have developed a direct method for observing formation of a hydrogen bond between sequestered water molecules and a spin-labeled site by applying pulsed Hyperfine Sub-level Correlation (HYSCORE) spectroscopy. Funded by: NSF-0843632 to TIS and NIH 1R01GM072897 to AIS.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Smirnova, Tatyana I. and Chadwick, Thomas G. and Bankaitis, Vytas A. and Schaaf, Gabriel and Poluektov, Oleg G. and Smirnov, Alex I.}, year={2011}, month={Feb}, pages={552a–553a} }
 @book{voinov_smirnov_2011, title={Spin labels and spin probes for measurements of local pH and electrostatics by EPR}, volume={22}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84876733821&partnerID=MN8TOARS}, DOI={10.1039/9781849730877-00071}, abstractNote={We dedicate this review to the memory of Prof. Leonid Volodarsky – the true pioneer of the synthesis and applications of pH-sensitive nitroxides.}, number={1}, journal={Electron Paramagnetic Resonance}, publisher={Royal Society of Chemistry (RSC)}, author={Voinov, Maxim A. and Smirnov, Alex I.}, year={2011}, pages={71–106} }
 @article{voinov_marek_li_smirnov_2011, title={Surface Electrostatics Associated with Lipid Bilayer Curvature}, volume={100}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2010.12.2956}, DOI={10.1016/j.bpj.2010.12.2956}, abstractNote={Spontaneous lipid bilayer bending and related curvature are being recognized as an essential mechanism associated with many cellular functions. Experimental observations indicate that tubular vesicles of just 50 to 100 nm in diameter are commonly formed within the Golgi body and also between the endoplasmic reticulum and the Golgi. While changes in various conditions may promote the tubulation of the Golgi membrane, detailed understanding of basic biophysical processes beyond the bilayer bending are missing in the literature and so are convenient models of highly curved lipid tubules. Here we report a systematic study of a surface potential for both small unilamellar monodisperse lipid vesicles (SUMV) with diameters ranging from 30 to 100 nm and also lipid tubules that are stabilized by confining these structures within rigid homogeneous nanopores of similar diameters. For example, for SUMVs composed of negatively charged lipids the magnitude of the surface potential increased with bilayer bending from ca. −106 mV for 100 nm SUMV to −166 mV for 30 nm SUMV. These measurements were carried out by spin probe EPR method using recently synthesized lipids having pH-reporting nitroxides covalently tethered to the lipid polar head. Parallel differential scanning calorimetry experiments indicated the presence of at least two components within the lipid phase. These phase components were characterized by measurably different phase transition temperatures and correlation times of the lipid thermal relaxation. Overall, the data indicate that the bilayer bending affects the local electrostatic potential and lipid fluctuation properties in a rather large degree and is likely associated with a mechanism for cellular machinery function. Supported by U.S. DOE Contract DE-FG02-02ER15354.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Voinov, Maxim A. and Marek, Antonin and Li, Le and Smirnov, Alex I.}, year={2011}, month={Feb}, pages={505a} }
 @article{voinov_pagán jason o. sosa_morrison_smirnova_smirnov_2011, title={Surface-Mediated Production of Hydroxyl Radicals as a Mechanism of Iron Oxide Nanoparticle Biotoxicity}, volume={133}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja104683w}, DOI={10.1021/ja104683w}, abstractNote={Emerging applications of nanosized iron oxides in nanotechnology introduce vast quantities of nanomaterials into the human environment, thus raising some concerns. Here we report that the surface of γ-Fe(2)O(3) nanoparticles 20-40 nm in diameter mediates production of highly reactive hydroxyl radicals (OH(•)) under conditions of the biologically relevant superoxide-driven Fenton reaction. By conducting comparative spin-trapping EPR experiments, we show that the free radical production is attributed primarily to the catalytic reactions at the nanoparticles' surface rather than being caused by the dissolved metal ions released by the nanoparticles as previously thought. Moreover, the catalytic centers on the nanoparticle surface were found to be at least 50-fold more effective in OH(•) radical production than the dissolved Fe(3+) ions. Conventional surface modification methods such as passivating the nanoparticles' surface with up to 935 molecules of oleate or up to 18 molecules of bovine serum albumin per iron oxide core were found to be rather ineffective in suppressing production of the hydroxyl radicals. The experimental protocols developed in this study could be used as one of the approaches for developing analytical assays for assessing the free radical generating activity of a variety of nanomaterials that is potentially related to their biotoxicity.}, number={1}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Pagán Jason O. Sosa and Morrison, Erin and Smirnova, Tatyana I. and Smirnov, Alex I.}, year={2011}, month={Jan}, pages={35–41} }
 @inproceedings{smirnov_svistov_prozorova_zheludev_lumsden_ressouche_petrenko_hagiwara_kimura_nishikawa_et al._2010, title={Coexistance of spiral and commensurate structures in a triangular antiferromagnet KFe(MoO<inf>4</inf>)<inf>2</inf>}, volume={200}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77957161748&partnerID=MN8TOARS}, DOI={10.1088/1742-6596/200/3/032068}, abstractNote={Magnetization, specific heat, magnetic resonance and neutron diffraction measurements are used to study the magnetic structure of KFe(MoO4)2. This stacked triangular antiferromagnet (TN=2.5 K) demonstrates an unusual breaking of the spin system into two intercalated and almost independent 2D subsystems. One is a collinear antiferromagnet with a simple spin-flop behavior. The other is a spiral magnet. The spin structure may be explained assuming two types of inequivalent magnetic planes with distorted triangular lattices of Fe3+(S=5/2) ions.}, number={SECTION 3}, booktitle={Journal of Physics: Conference Series}, author={Smirnov, A.I. and Svistov, L.E. and Prozorova, L.A. and Zheludev, A. and Lumsden, M.D. and Ressouche, E. and Petrenko, O.A. and Hagiwara, M. and Kimura, S. and Nishikawa, K. and et al.}, year={2010} }
 @article{banerjee_moeller_smirnov_grebel_2010, title={Graphenated IR Screens}, volume={10}, ISSN={["1558-1748"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77649100489&partnerID=MN8TOARS}, DOI={10.1109/jsen.2009.2037356}, abstractNote={Metallo-dielectric screens have been investigated from the visible to the terahertz spectral region for astronomy and remote sensing applications. These screens are made of periodic structures, which are at resonance with the wavelength of interest. A standing wave of surface wave is formed at resonance conditions, which then enables transmission or reflection of certain bands. Graphene is a monolayer thick 2-D crystal of carbon. Graphene is chemically inert and exhibits very large mobility. Recently, we succeeded in fabricating monolayer and a few layered graphene into films on solid and perforated substrates. By combining the resonance properties of IR screens with the unique properties of graphene, we were able to fabricate a new spectroscopic platform, which enhanced IR and Raman signals of molecules, and specifically, biospecies.}, number={3}, journal={IEEE SENSORS JOURNAL}, publisher={Institute of Electrical & Electronics Engineers (IEEE)}, author={Banerjee, Amrita and Moeller, Dieter and Smirnov, Alex I. and Grebel, Haim}, year={2010}, month={Mar}, pages={419–422} }
 @article{smirnova_voynov_poluektov_smirnov_2010, title={Heterogeneous Dielectric and Hydrogen Bonding Environment of Transmembrane Peptides}, volume={98}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2009.12.494}, DOI={10.1016/j.bpj.2009.12.494}, abstractNote={A complex set of hydrogen bonding and hydrophobic interactions between the protein side chains and cellular membrane components is primary responsible for such important biophysical processes as initial protein binding/docking to cellular membranes, membrane insertion, folding, and the final adaptation of the correct transmembrane position. Although general concepts of membrane protein folding and thermodynamic stability are beginning to emerge, the experimental data on the transmembrane profile of the effective dielectric constant and the local hydrogen bond network formed by membrane protein side chains remain severely limited.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Smirnova, Tatyana I. and Voynov, Maxim A. and Poluektov, Oleg G. and Smirnov, Alex I.}, year={2010}, month={Jan}, pages={87a} }
 @article{banerjee_perez-castillejos_hahn_smirnov_grebel_2010, title={Micro-fluidic channels on nanopatterned substrates: Monitoring protein binding to lipid bilayers with surface-enhanced Raman spectroscopy}, volume={489}, ISSN={["1873-4448"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77949487267&partnerID=MN8TOARS}, DOI={10.1016/j.cplett.2010.02.053}, abstractNote={We used Surface Enhanced Raman Spectroscopy (SERS) to detect binding events between streptavidin and biotinylated lipid bilayers. The binding events took place at the surface between microfluidic channels and anodized aluminum oxide (AAO) with the latter serving as substrates. The bilayers were incorporated in the substrate pores. It was revealed that non-bound molecules were easily washed away and that large suspended cells (Salmonella enterica) are less likely to interfere with the monitoring process: when focusing to the lower surface of the channel, one may resolve mostly the bound molecules.}, number={1-3}, journal={CHEMICAL PHYSICS LETTERS}, publisher={Elsevier BV}, author={Banerjee, Amrita and Perez-Castillejos, R. and Hahn, D. and Smirnov, Alex I. and Grebel, H.}, year={2010}, month={Apr}, pages={121–126} }
 @article{wei_nori_jin_narayan_narayan_ponarin_smirnov_2010, title={Mott transition in Ga-doped MgxZn1-xO: A direct observation}, volume={171}, ISSN={["1873-4944"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77953133966&partnerID=MN8TOARS}, DOI={10.1016/j.mseb.2010.03.078}, abstractNote={This paper reports the direct evidence for Mott transition in Ga-doped MgxZn1−xO thin films. Highly transparent Ga-doped MgxZn1−xO thin films were grown on c-plane sapphire substrates using pulsed laser deposition. 0.1 at.%, 0.5 at.% and 1 at.% Ga-doped Mg0.1Zn0.9O films were selected for resistivity measurements in the temperature range from 250 K to 40 mK. The 0.1 at.% Ga-doped Mg0.1Zn0.9O thin film showed typical insulator-like behavior and the 1 at.% Ga-doped Mg0.1Zn0.9O thin film showed typical metal-like behavior. The 0.5 at.% Ga-doped Mg0.1Zn0.9O film showed increasing resistivity with decreasing temperature; resistivity was saturated with a value of 1.15 × 10−2 Ω cm at 40 mK, which is characteristic of the metal–insulator transition region. Temperature-dependent conductivity σ(T) in the low temperature range revealed that the electron-electron scattering is the dominant dephasing mechanism. The inelastic scattering time is found to vary as T−3/2.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS}, publisher={Elsevier BV}, author={Wei, Wei and Nori, Sudhakar and Jin, Chunming and Narayan, Jagdish and Narayan, Roger J. and Ponarin, Dmtri and Smirnov, Alex}, year={2010}, month={Jul}, pages={90–92} }
 @article{mal_nori_jin_narayan_nellutla_smirnov_prater_2010, title={Reversible room temperature ferromagnetism in undoped zinc oxide: Correlation between defects and physical properties}, volume={108}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3491037}, DOI={10.1063/1.3491037}, abstractNote={We report a systematic study of the structural, chemical, electrical, optical, and magnetic properties of undoped ZnO thin films grown under different conditions as well as the films that were annealed in various environments. Oxygen-annealed films displayed a sequential transition from ferromagnetism to diamagnetism as a function of the annealing temperature. An increase in the green band intensity has been observed in oxygen-annealed ZnO films. Reversible switching of room-temperature ferromagnetism and n-type conductivity have been demonstrated by oxygen and vacuum annealing. Electron paramagnetic resonance data were found to be in agreement with the results of magnetization and conductivity measurements. Possibility of external ferromagnetic impurity as the origin of the unconventional room temperature ferromagnetism in these films has been ruled out by secondary ion mass spectrometer and electron energy loss spectroscopy studies. Correlation between structural, electrical, optical, and magnetic properties has been established in terms of defects and defect complexes. Taken together, our data indicate that the ferromagnetic order in ZnO matrix might be defect-mediated.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mal, Siddhartha and Nori, Sudhakar and Jin, Chunming and Narayan, J. and Nellutla, S. and Smirnov, A. I. and Prater, J. T.}, year={2010}, month={Oct}, pages={073510} }
 @article{marek_voinov_smirnov_2010, title={Surface Electrostatics and Lipid-Substrate Interactions of Nanopore-Confined Lipid Bilayers}, volume={98}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2009.12.2165}, DOI={10.1016/j.bpj.2009.12.2165}, abstractNote={Substrate-supported lipid bilayers serve many purposes: from acting as versatile models of cellular membranes to biotechnological applications including substrate functionalization and stabilizing membrane proteins in functional conformations. While adsorption and subsequent reorganization of phospholipid vesicles on solid substrates were studied in the past, the exact nature of physicochemical interactions between the lipids and substrate surfaces remain largely unknown. Here we employed recently synthesized pH-sensitive spin-labeled phospholipids - derivatives of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (PTE) with pH-reporting nitroxides that are covalently attached to the lipid's headgroup - to investigate surface electrostatics of nanotubular lipid bilayers confined in cylindrical nanopores. The lipid nanotubes were formed by self-assembling phospholipids inside ordered nanochannels of anodic aluminum oxide with pore diameters from 60 to 170 nm and diameter-to-pore length ratio of up to 1:1000. 31P NMR confirmed formation of macroscopically aligned lipid nanotubes with just 1-2° mosaic spread from zwitterionic DMPC, anionic DMPG, and their mixtures. Interfacial potentials were measured by carrying out titration experiments and observing the protonation state of the nitroxide tag by EPR. For nanopore-confined DMPC:DMPG (1:1) bilayers the protonation equilibrium was shifted to more acidic values: when the single lipid bilayer was deposited per nanopore the pKa of the nitroxide probe was shifted by (−0.91±0.05) pH units but only by (−0.34±0.05) when three bilayers per nanopore were present. Notably, the nitrogen hyperfine coupling constant for non-protonated nitroxides remained the same in all the samples indicating essentially the same interfacial dielectric environment. Thus, these shifts in pKa must come from changes in the lipid bialyer surface potential that was estimated to increase by 52±3 mV. EPR data on the lipid-substrate interface were combined with differential scanning calorimetry to elucidate effects of pore curvature, surface modification, and binding of antibacterial peptides on lipid-substrate interactions. Supported by DE-FG02-02ER15354.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Marek, Antonin and Voinov, Maxim A. and Smirnov, Alex I.}, year={2010}, month={Jan}, pages={402a} }
 @article{nazaretski_pelekhov_martin_zalalutdinov_ponarin_smirnov_hammel_movshovich_2009, title={Detection of localized ferromagnetic resonance in a continuous thin film via magnetic resonance force microscopy}, volume={79}, ISSN={["1098-0121"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-65149101952&partnerID=MN8TOARS}, DOI={10.1103/physrevb.79.132401}, abstractNote={We present magnetic resonance force microscopy (MRFM) measurements of ferromagnetic resonance in a 50 nm thick permalloy film tilted with respect to the direction of the external magnetic field. At small probe-sample distances the MRFM spectrum breaks up into multiple modes, which we identify as local ferromagnetic resonances confined by the magnetic field of the MRFM tip. Micromagnetic simulations support this identification of the modes and show they are stabilized in the region where the dipolar tip field has a component antiparallel to the applied field.}, number={13}, journal={PHYSICAL REVIEW B}, author={Nazaretski, E. and Pelekhov, D. V. and Martin, I. and Zalalutdinov, M. and Ponarin, D. and Smirnov, A. and Hammel, P. C. and Movshovich, R.}, year={2009}, month={Apr} }
 @inproceedings{smirnov_sosin_glazkov_petrenko_balakrishnan_zhitomirsky_2009, title={Low-frequency spin dynamics of the frustrated pyrochlore magnet Gd <inf>2</inf>Ti<inf>2</inf>O<inf>7</inf>}, volume={150}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77952472894&partnerID=MN8TOARS}, DOI={10.1088/1742-6596/150/4/042188}, abstractNote={The adiabatic T(H) curves measured in a Heisenberg pyrochlore Gd2Ti2O7 prove the existence of a macroscopic number of local soft modes in this compound. A spin gap of 25 GHz, developing in Gd2Ti2O7 on cooling down to 1.3 K (in the collective paramagneti phase), was observed by ESR spectroscopy. ESR of diamagnetically diluted crystals revealed the single-ion anisotropy energy to be about a quarter of Curie-Weiss temperature. This might be responsible for the observed energy gap. Below 1 K, in the magneticaly ordered phase, the pin excitations have a threebranch spectum with two enegy gaps}, number={4}, booktitle={Journal of Physics: Conference Series}, author={Smirnov, A.I. and Sosin, S.S. and Glazkov, V.N. and Petrenko, O.A. and Balakrishnan, G. and Zhitomirsky, M.E.}, year={2009} }
 @misc{smirnov_2009, title={Nanotube structures having a surfactant bilayer inner wall coating}, volume={7,521,225}, number={2009 Apr. 21}, author={Smirnov, A. I.}, year={2009} }
 @article{smirnova_voinov_smirnov_2009, title={Spin Probes and Spin Labels}, DOI={10.1002/9780470027318.a9049}, abstractNote={Electron paramagnetic resonance (EPR) spectroscopy is a versatile and exceptionally sensitive technique for detecting and studying molecular systems possessing unpaired electronic spins. It finds substantial use in characterizing paramagnetic metal ions and organic free radicals. The scope of EPR applications in analytical chemistry can be expanded significantly by means of spin labels and spin probes — exogenous EPR-active species that are introduced solely for the purpose of gaining information on the system under study. These labels and probes are persistent free radicals or paramagnetic metal ions designed to be partitioned or attached to specific molecular sites. To be suitable for analytical applications, spin labels and probes should readily report on properties of interest, exhibit distinguishable from background EPR signals, and leave the system only minimally perturbed by their presence. In this article, we describe a series of spin labels and probes as well as the associated EPR methods that are tailored to specific analytical applications of EPR spectroscopy — from assessing local oxygen and proton concentration to profiling electrostatic properties of biopolymers and lipid bilayers. The primary focus is bioanalytical applications of spin label/probe methods, with an emphasis on the synergy between the rational design of spin-bearing molecules using the tools of organic chemistry and desired analytical capabilities.}, journal={Encyclopedia of Analytical Chemistry}, author={Smirnova, Tatyana I. and Voinov, Maxim A. and Smirnov, Alex I.}, year={2009} }
 @article{voinov_kirilyuk_smirnov_2009, title={Spin-Labeled pH-Sensitive Phospholipids for Interfacial pKa Determination: Synthesis and Characterization in Aqueous and Micellar Solutions}, volume={113}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/jp810993s}, DOI={10.1021/jp810993s}, abstractNote={The synthesis and characterization of spin-labeled phospholipids (SLP)--derivatives of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (PTE)--with pH-reporting nitroxides that are covalently attached to the lipid's polar headgroup are being reported. Two lipids were synthesized by reactions of PTE with thiol-specific, pH-sensitive methanethiosulfonate spin labels methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL) and S-4-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-1-oxyl-2,5-dihydro-1H-imidazol-2-yl)benzyl methanethiosulfonate (IKMTSL). The pKa values of the IMTSL-PTE lipid measured by EPR titration in aqueous buffer/isopropyl alcohol solutions of various compositions were found to be essentially the same (pKa approximately 2.35), indicating that in mixed aqueous/organic solvents, the amphiphilic lipid molecules could be shielded from changing bulk conditions by a local shell of solvent molecules. To overcome this problem, the spin-labeled lipids were modeled by synthesizing IMTSL- and IKMTSL-2-mercaptoethanol adducts. These model compounds yielded the intrinsic pKa0's for IMTSL-PTE and IKMTSL-PTE in aqueous buffers as 3.33 +/- 0.03 and 5.98 +/- 0.03, respectively. A series of EPR titrations of IMTSL-PTE in mixed water/isopropyl alcohol solution allowed for calibrating the polarity-induced pKa shifts, deltapKapol, vs bulk solvent dielectric permittivity. These calibration data allowed for estimating the local dielectric constant, epsilon(eff), experienced by the reporter nitroxide of the IMTSL-PTE lipid incorporated into the nonionic Triton X-100 micelles as 60 +/- 5 and 57 +/- 5 at 23 and 48 degrees C, respectively. For micelles formed from an anionic surfactant sodium dodecyl sulfate (SDS) the electrostatic-induced pKa shift, deltapKael = 2.06 +/- 0.04 units of pH, was obtained by subtracting the polarity-induced contribution. This shift yields psi = -121 mV electric potential of the SDS micelle surface.}, number={11}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Kirilyuk, Igor A. and Smirnov, Alex I.}, year={2009}, month={Mar}, pages={3453–3460} }
 @article{marek_smirnov_2009, title={Two-dimensional Calorimetry: Imaging Thermodynamics and Kinetics of Phase Transitions of Biological Membranes}, volume={96}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2008.12.2973}, DOI={10.1016/j.bpj.2008.12.2973}, abstractNote={Differential scanning calorimetry (DSC) is a relatively rapid and informative biophysical method for studying thermotropic phase behavior of biological membranes. More recently a pressure perturbation calorimetry has been introduced. The latter method is capable of characterizing membrane thermal volume expansion coefficient and kinetics associated with the phase transition. Notably, pressure perturbation calorimetry requires both pressure jump accessory and, most importantly, fast and sophisticated temperature control system to ensure constant sample temperature upon the pressure jump. Here we describe a calorimetry procedure and associated method of data analysis to characterize sample thermal properties as a two-dimensional (2D) object (temperature-time thermal image) whereas data obtained by conventional calorimetry are essentially one-dimensional. In brief, the method utilizes mathematical formalism of the Radon transform (back-projecting algorithm) to separate temperature and time dimensions from a series of thermal flux measurements obtained by a conventional DSC calorimeter at different scanning rates. By this manner static and time-dependent (i.e., relaxation) thermodynamic parameters of an object become resolved and displayed as a single 2D temperature-time thermal image. There are two main advantages of our 2D-calorimetry method: 1) 2D temperature-time thermal image separates and characterizes equilibrium and non-equilibrium thermal properties of a sample; 2) the method improves signal-to-noise ratio for conventional DSC measurements of equilibrium heat capacity as a function of temperature. We demonstrate these advantages of the 2D calorimetry method on examples of imaging thermodynamics and heat relaxation properties of lipid bilayers composed from single and mixed phospholipids with and without cholesterol. We also show that confining lipid bilayers inside nanopores of ca. 175 nm in diameter results in heterogeneous heat transfer kinetics while conventional equilibrium calorimetry curves remain unperturbed. Supported by the DOE Contract DE-FG02-02ER15354.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Marek, Antonin and Smirnov, Alex I.}, year={2009}, month={Feb}, pages={549a} }
 @article{smirnova_smirnov_chadwick_walker_2008, title={Characterization of magnetic and electronic properties of trimetallic nitride endohedral fullerenes by SQUID magnetometry and electron paramagnetic resonance}, volume={453}, ISSN={["1873-4448"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-44549085132&partnerID=MN8TOARS}, DOI={10.1016/j.cplett.2008.01.036}, abstractNote={Magnetic and electronic properties of high-purity trimetallic nitride endohedral fullerenes Er3[email protected]80, Lu3[email protected]80, Sc3[email protected]80 diluted in a diamagnetic host were characterized by SQUID DC magnetometry and electron paramagnetic resonance (EPR) at multiple frequencies. The Er3[email protected]80 sample followed the Curie–Weiss law with negligible Weiss temperature of 0.16 K. Based on temperature dependence and isothermal saturation magnetization the effective magnetic moment of Er3[email protected]80 was estimated as 10.2 μB. The magnetic behavior of these fullerenes is ascribed to quenching of the orbital moment of the metal ions due to interactions between the metal centers with the nitrogen and the fullerene cage.}, number={4-6}, journal={CHEMICAL PHYSICS LETTERS}, publisher={Elsevier BV}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Chadwick, Thomas G. and Walker, Kenneth L.}, year={2008}, month={Mar}, pages={233–237} }
 @article{narayan_nori_pandya_avasthi_smirnov_2008, title={Defect dependent ferromagnetism in MgO doped with Ni and Co}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2977614}, DOI={10.1063/1.2977614}, abstractNote={We have investigated magnetic properties of MgO single crystals doped with Ni and Co impurities, and studied changes in magnetic properties after heavy ion irradiation. These results are compared with doped single-crystal thin films that contain a higher concentration of trapped defects. The as-grown bulk single crystals, which contain a small equilibrium concentration of vacancies, exhibit a perfect paramagnetic behavior throughout the temperature range and magnetic field. By introducing defects either by ion irradiation or by thin film deposition, which have trapped defects, we are able to achieve defect-mediated ferromagnetic ordering.}, number={8}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Narayan, J. and Nori, Sudhakar and Pandya, D. K. and Avasthi, D. K. and Smirnov, A. I.}, year={2008}, month={Aug}, pages={082507} }
 @article{khlestkin_polienko_voinov_smirnov_chechik_2008, title={Interfacial Surface Properties of Thiol-Protected Gold Nanoparticles:  A Molecular Probe EPR Approach}, volume={24}, ISSN={0743-7463 1520-5827}, url={http://dx.doi.org/10.1021/la702823n}, DOI={10.1021/la702823n}, abstractNote={We present a molecular probe technique for accessing interfacial surface electrostatics of ligand-protected gold nanoparticles. A series of ligands with variable length of the hydrocarbon bridge between the anchoring sulfur and the reporting pH-sensitive nitroxide is described. The protonation state of this probe is directly observed by EPR spectroscopy. For tiopronin-protected Au nanoparticles, we observed an increase in pKa of up to ca. 1.1 pH units that was affected by the position of the reporter moiety with respect to the monolayer interface.}, number={3}, journal={Langmuir}, publisher={American Chemical Society (ACS)}, author={Khlestkin, Vadim K. and Polienko, Julya F. and Voinov, Maxim A. and Smirnov, Alex I. and Chechik, Victor}, year={2008}, month={Feb}, pages={609–612} }
 @article{voinov_ruuge_reznikov_grigor’ev_smirnov_2008, title={Mapping Local Protein Electrostatics by EPR of pH-Sensitive Thiol-Specific Nitroxide}, volume={47}, ISSN={0006-2960 1520-4995}, url={http://dx.doi.org/10.1021/bi800272f}, DOI={10.1021/bi800272f}, abstractNote={A first thiol-specific pH-sensitive nitroxide spin-label of the imidazolidine series, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL), has been synthesized and characterized. X-Band (9 GHz) and W-band (94 GHz) EPR spectral parameters of the new spin-label in its free form and covalently attached to an amino acid cysteine and a tripeptide glutathione were studied as a function of pH and solvent polarity. The pKa value of the protonatable tertiary amino group of the spin-label was found to be unaffected by other ionizable groups present in side chains of unstructured small peptides. The W-band EPR spectra were shown to allow for pKa determination from precise g-factor measurements. Is has been demonstrated that the high accuracy of pKa determination for pH-sensitive nitroxides could be achieved regardless of the frequency of measurements or the regime of spin exchange: fast at X-band and slow at W-band. IMTSL was found to react specifically with a model protein, iso-1-cytochrome c from the yeast Saccharomyces cerevisiae, giving EPR spectra very similar to those of the most commonly employed cysteine-specific label MTSL. CD data indicated no perturbations to the overall protein structure upon IMTSL labeling. It was found that for IMTSL, giso correlates linearly with Aiso, but the slopes are different for the neutral and charged forms of the nitroxide. This finding was attributed to the solvent effects on the spin density at the oxygen atom of the NO group and on the excitation energy of the oxygen lone-pair orbital.}, number={20}, journal={Biochemistry}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Ruuge, Andres and Reznikov, Vladimir A. and Grigor’ev, Igor A. and Smirnov, Alex I.}, year={2008}, month={May}, pages={5626–5637} }
 @book{likhtenshtein_yamauchi_nakatsuji_smirnov_tamura_2008, title={Nitroxides}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-62949108328&partnerID=MN8TOARS}, DOI={10.1002/9783527621743}, journal={Nitroxides: Applications in Chemistry, Biomedicine, and Materials Science}, publisher={Wiley-Blackwell}, author={Likhtenshtein, Gertz I. and Yamauchi, Jun and Nakatsuji, Shin'ichi and Smirnov, Alex I. and Tamura, Rui}, year={2008}, month={Feb}, pages={1–419} }
 @book{nitroxides : applications in chemistry, biomedicine, and materials science_2008, ISBN={9783527318896}, publisher={Weinheim: Wiley-VCH}, year={2008} }
 @article{turro_chen_2008, title={Nitroxides. Applications in Chemistry, Biomedicine, and Materials Science. Von Gertz L. Likhtenshtein, Jun Yamauchi, Shin'ichi Nakatsuji, Alex I. Smirnov und Rui Tamura.}, volume={120}, DOI={10.1002/ange.200885605}, number={50}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Turro, Nicholas J. and Chen, Judy Y.-C.}, year={2008}, pages={9739–9740} }
 @article{li_marek_smirnov_grebel_2008, title={Polarization-dependent fluorescence of proteins bound to nanopore-confined lipid bilayers}, volume={129}, ISSN={0021-9606}, url={http://dx.doi.org/10.1063/1.2972143}, DOI={10.1063/1.2972143}, abstractNote={Lipid bilayers are essential structural component of biological membranes of all the living species: from viruses and bacteria to plants and humans. Biophysical and biochemical properties of such membranes are important for understanding physical mechanisms responsible for drug targeting. Binding events between proteins and the membrane may be ascertained by introducing fluorescence markers (chromophores) to the proteins. Here we describe a novel biosensing platform designed to enhance signals of these fluorescence markers. Nanoporous aluminum oxide membranes with and without gold (Au) surface coating have been employed for optical detection of bound conjugated streptavidin to biotinylated lipid bilayers-a model system that mimics protein docking to the membrane surface. Unexpectedly, it was found that fluorescence signals from such structures vary when pumped with E-polarized and H-polarized incident optical beams. The origin of the observed polarization-dependent effects and the implications for enhanced fluorescence detection in a biochip format are being discussed.}, number={9}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Li, R.-Q. and Marek, A. and Smirnov, Alex I. and Grebel, H.}, year={2008}, pages={095102} }
 @article{smirnov_2008, title={Post-processing of IEPR spectra by convolution filtering: Calculation of a harmonics' series and automatic separation of fast-motion components from spin-label EPR spectra}, volume={190}, ISSN={["1090-7807"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36849012041&partnerID=MN8TOARS}, DOI={10.1016/j.jmr.2007.10.006}, abstractNote={This communication reports on post-processing of continuous wave EPR spectra by a digital convolution with filter functions that are subjected to differentiation or the Kramers-Krönig transform analytically. In case of differentiation, such a procedure improves spectral resolution in the higher harmonics enhancing the relative amplitude of sharp spectral features over the broad lines. At the same time high-frequency noise is suppressed through filtering. These features are illustrated on an example of a Lorentzian filter function that has a principal advantage of adding a known magnitude of homogeneous broadening to the spectral shapes. Such spectral distortion could be easily and accurately accounted for in the consequent least-squares data modeling. Application examples include calculation of higher harmonics from pure absorption echo-detected EPR spectra and resolving small hyperfine coupling that are unnoticeable in conventional first derivative EPR spectra. Another example involves speedy and automatic separation of fast and broad slow-motion components from spin-label EPR spectra without explicit simulation of the slow motion spectrum. The method is illustrated on examples of X-band EPR spectra of partially aggregated membrane peptides.}, number={1}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Smirnov, Alex I.}, year={2008}, month={Jan}, pages={154–159} }
 @book{smirnov_2008, title={Recent Advances in ESR Techniques and Methods Employed in Nitroxide Experiments}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84889425865&partnerID=MN8TOARS}, DOI={10.1002/9783527621743.ch4}, journal={Nitroxides: Applications in Chemistry, Biomedicine, and Materials Science}, author={Smirnov, A.I.}, year={2008}, pages={121–159} }
 @article{smirnov_glazkov_kashiwagi_kimura_hagiwara_kindo_shapiro_demianets_2008, title={Triplet spin resonance of the Haldane magnet Pb Ni2 V2 O8 with interchain coupling}, volume={77}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41449105978&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.77.100401}, abstractNote={Spin resonance absorption of the triplet excitations is studied experimentally in the Haldane magnet PbNi2V2O8. The spectrum has features of spin S=1 resonance in a crystal field, with all three components, corresponding to transitions between spin sublevels, being observable. The resonance field is temperature dependent, indicating the renormalization of excitation spectrum in interaction between the triplets. Magnetic resonance frequencies and critical fields of the magnetization curve are consistent with a boson version of the macroscopic field theory [Affleck 1992, Farutin & Marchenko 2007], implying the field induced ordering at the critical field, while contradict the previously used approach of noninteracting spin chains.}, number={10}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Smirnov, A.I. and Glazkov, V.N. and Kashiwagi, T. and Kimura, S. and Hagiwara, M. and Kindo, K. and Shapiro, A.Ya. and Demianets, L.N.}, year={2008} }
 @article{smirnova_smirnov_paschenko_poluektov_2007, title={Geometry of hydrogen bonds formed by lipid bilayer nitroxide probes: A high-frequency pulsed ENDOR/EPR study}, volume={129}, ISSN={["1520-5126"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33947673323&partnerID=MN8TOARS}, DOI={10.1021/ja068395v}, abstractNote={Solvent effects on magnetic parameters of nitroxide spin labels in combination with side-directed spin-labeling EPR methods provide very useful means for elucidating polarity profiles in lipid bilayers and mapping local electrostatic effects in complex biomolecular systems. One major contributor to these solvent effects is the hydrogen bonds that could be formed between the nitroxide moiety and water and/or the available hydroxyl groups. Here, formation of hydrogen bonds between a lipid bilayer spin probe5-doxyl stearic acid, 5DSAand hydrogen-bond donors has been studied using high-frequency (HF) pulsed ENDOR and EPR. A hydrogen-bonded deuteron was directly detected in HF ENDOR (130 GHz) spectra of 5DSA dissolved in several deuterated alcohols, while the characteristic signal was absent in nonpolar toluene-d8. The length of the hydrogen bond, 1.74 ± 0.06 Å, and its geometry were found to be essentially the same for all four alcohols studied, indicating that nearly identical hydrogen bonds have been formed regardless of the solvent dielectric constant. This strengthens a hypothesis that HF EPR spectra are exclusively sensitive to formation of hydrogen bonds and could be used for probing the hydrogen-bond network in complex biomolecular assemblies and lipid bilayers with site-directed spin-labeling methods.}, number={12}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Paschenko, Serguei V. and Poluektov, Oleg G.}, year={2007}, month={Mar}, pages={3476-+} }
 @article{smirnov_glazkov_2007, title={Mesoscopic spin clusters, phase separation, and induced order in spin-gap magnets: A review}, volume={105}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36448985299&partnerID=MN8TOARS}, DOI={10.1134/S1063776107100214}, number={4}, journal={Journal of Experimental and Theoretical Physics}, author={Smirnov, A.I. and Glazkov, V.N.}, year={2007}, pages={861–879} }
 @article{jagannadham_reed_lance_watkins_verghese_butler_smirnov_2007, title={Neutron transmutation of B-10 doped diamond}, volume={16}, ISSN={["1879-0062"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33751334357&partnerID=MN8TOARS}, DOI={10.1016/j.diamond.2006.03.019}, abstractNote={Free standing {sup 10}B isotope doped diamond films deposited by chemical vapor deposition in a microwave chamber were irradiated to thermal neutron fluence values of 0.32 x 10{sup 19}, 0.65 x 10{sup 19}, 1.3 x 10{sup 19}, and 2.6 x 10{sup 19} n/cm{sup 2}. Cooling of the diamond films was maintained during irradiation. In a separate experiment, neutron irradiation to a total fluence of 2.4 x 10{sup 20} n/cm{sup 2} with equal fast and thermal neutrons was also performed on a diamond epilayer without cooling during irradiation. The formation of defects in the diamond films was characterized using Raman, FTIR, photoluminescence, electron paramagnetic resonance spectroscopy, and X-ray diffraction. It was found that defect configurations in diamond responsible for an increase in continuum background in the one-phonon region of Raman spectrum were absent in the films that have been cooled. The FTIR peak at 1530 cm{sup -1} annealed in the sample irradiated to a fluence of 2.6 x 10{sup 19} n/cm{sup 2} indicating that the sample reached a temperature of 300 C during irradiation. Absence of characteristic infrared absorption peaks that were observed only upon annealing neutron irradiated diamond is used to conclude that the temperature of the sample during neutronmore » irradiation to a fluence of 2.6 x 10{sup 19} n/cm{sup 2} was well below 650 C needed for mobility of defects and accumulation of stable unrecoverable damage. On the other hand, results from diamond epilayer subjected to equal thermal and fast neutron fluence of 2.4 x 10{sup 20} n/cm{sup 2} and without cooling showed that defects formed from displaced carbon atoms became mobile and formed complex configurations of irrecoverable damage. Electrical conductance of the unirradiated and irradiated diamond samples was measured as a function of temperature to determine the compensation of the p-type by the n-type charge carriers.« less}, number={1}, journal={DIAMOND AND RELATED MATERIALS}, author={Jagannadham, K. and Reed, M. L. and Lance, M. J. and Watkins, T. R. and Verghese, K. and Butler, J. E. and Smirnov, A.}, year={2007}, month={Jan}, pages={50–62} }
 @article{zhang_smirnov_hahn_grebel_2007, title={Surface enhanced Raman scattering of biospecies on anodized aluminum oxide films}, volume={440}, ISSN={["1873-4448"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34248645144&partnerID=MN8TOARS}, DOI={10.1016/j.cplett.2007.04.041}, abstractNote={Abstract Traditionally, aluminum and anodized aluminum oxide films (AAO) are not the platforms of choice for surface-enhanced raman scattering (SERS) experiments despite of the aluminum’s large negative permittivity value. Here we examine the usefulness of aluminum and nanoporous alumina platforms for detecting soft biospecies ranging from bacterial spores to protein markers. We used these flat platforms to examine SERS of a model protein (cytochrome c from bovine heart tissue) and bacterial cells (spores of Bacillus subtilis ATCC13933 used as Anthrax simulant) and demonstrated clear Raman amplification.}, number={4-6}, journal={CHEMICAL PHYSICS LETTERS}, author={Zhang, C. and Smirnov, A. I. and Hahn, D. and Grebel, H.}, year={2007}, month={Jun}, pages={239–243} }
 @article{smirnov_yashiro_kimura_hagiwara_narumi_kindo_kikkawa_katsumata_shapiro_demianets_2007, title={Triangular lattice antiferromagnet RbFe (Mo O4) 2 in high magnetic fields}, volume={75}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34247157757&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.75.134412}, abstractNote={The saturation of magnetization was studied in pulsed magnetic fields $(H)$ for the triangular lattice antiferromagnet $\mathrm{Rb}\mathrm{Fe}{(\mathrm{Mo}{\mathrm{O}}_{4})}_{2}$ at temperatures $(T)$ below the magnetic ordering point ${T}_{N}$. The field-driven transition from the antiferromagnetic to the paramagnetic phase was studied by specific-heat measurements in a steady magnetic field. The specific heat shows a sharp peak at a value of the magnetic field below which a singularity in the magnetization curve occurs, indicating a splitting of the field-induced transition to the paramagnetic phase. This splitting vanishes at low temperatures. A complete $T\text{\ensuremath{-}}H$ phase diagram is derived experimentally both for the magnetic field lying in the spin plane and perpendicular to the plane. A spin-flip magnetic-resonance mode with the softening of the spin-wave spectrum at the saturation field has been observed. The gap of the spin-wave spectrum was found to be reduced by zero-point fluctuations by a factor of $0.82\ifmmode\pm\else\textpm\fi{}0.08$ with respect to the prediction of the molecular-field theory.}, number={13}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Smirnov, A.I. and Yashiro, H. and Kimura, S. and Hagiwara, M. and Narumi, Y. and Kindo, K. and Kikkawa, A. and Katsumata, K. and Shapiro, A.Ya. and Demianets, L.N.}, year={2007} }
 @article{smirnov_smirnova_macarthur_good_hall_2006, title={Cryogen-free superconducting magnet system for multifrequency electron paramagnetic resonance up to 12.1T}, volume={77}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.2182571}, DOI={10.1063/1.2182571}, abstractNote={Multifrequency and high field/high frequency (HF) electron paramagnetic resonance (EPR) is a powerful spectroscopy for studying paramagnetic spin systems ranging from organic-free radicals to catalytic paramagnetic metal ion centers in metalloproteins. Typically, HF EPR experiments are carried out at resonant frequencies ν=95–300GHz and this requires magnetic fields of 3.4–10.7T for electronic spins with g≈2.0. Such fields could be easily achieved with superconducting magnets, but, unlike NMR, these magnets cannot operate in a persistent mode in order to satisfy a wide range of resonant fields required by the experiment. Operating and maintaining conventional passively cooled superconducting magnets in EPR laboratories require frequent transfer of cryogens by trained personnel. Here we describe and characterize a versatile cryogen-free magnet system for HF EPR at magnetic fields up to 12.1T that is suitable for ramping the magnetic field over the entire range, precision scans around the target field, and/or holding the field at the target value. We also demonstrate that in a nonpersistent mode of operation the magnetic field can be stabilized to better than 0.3ppm∕h over 15h period by employing a transducer-controlled power supply. Such stability is sufficient for many HF EPR experiments. An important feature of the system is that it is virtually maintenance-free because it is based on a cryogen-free technology and therefore does not require any liquid cryogens (liquid helium or nitrogen) for operation. We believe that actively cooled superconducting magnets are ideally suited for a wide range of HF EPR experiments including studies of spin-labeled nucleic acids and proteins, single-molecule magnets, and metalloproteins.}, number={3}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Smirnov, Alex I. and Smirnova, Tatyana I. and MacArthur, Ryan L. and Good, Jeremy A. and Hall, Renny}, year={2006}, month={Mar}, pages={035108} }
 @article{chekmenev_gor’kov_cross_alaouie_smirnov_2006, title={Flow-Through Lipid Nanotube Arrays for Structure-Function Studies of Membrane Proteins by Solid-State NMR Spectroscopy}, volume={91}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33749506571&partnerID=MN8TOARS}, DOI={10.1529/biophysj.106.085191}, abstractNote={A novel method for studying membrane proteins in a native lipid bilayer environment by solid-state NMR spectroscopy is described and tested. Anodic aluminum oxide (AAO) substrates with flow-through 175 nm wide and 60-mum-long nanopores were employed to form macroscopically aligned peptide-containing lipid bilayers that are fluid and highly hydrated. We demonstrate that the surfaces of both leaflets of such bilayers are fully accessible to aqueous solutes. Thus, high hydration levels as well as pH and desirable ion and/or drug concentrations could be easily maintained and modified as desired in a series of experiments with the same sample. The method allows for membrane protein NMR experiments in a broad pH range that could be extended to as low as 1 and as high as 12 units for a period of up to a few hours and temperatures as high as 70 degrees C without losing the lipid alignment or bilayers from the nanopores. We demonstrate the utility of this method by a solid-state 19.6 T (17)O NMR study of reversible binding effects of mono- and divalent ions on the chemical shift properties of the Leu(10) carbonyl oxygen of transmembrane pore-forming peptide gramicidin A (gA). We further compare the (17)O shifts induced by binding metal ions to the binding of protons in the pH range from 1 to 12 and find a significant difference. This unexpected result points to a difference in mechanisms for ion and proton conduction by the gA pore. We believe that a large number of solid-state NMR-based studies, including structure-function, drug screening, proton exchange, pH, and other titration experiments, will benefit significantly from the method described here.}, number={8}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Chekmenev, Eduard Y. and Gor’kov, Peter L. and Cross, Timothy A. and Alaouie, Ali M. and Smirnov, Alex I.}, year={2006}, month={Oct}, pages={3076–3084} }
 @article{alaouie_smirnov_2006, title={Formation of a ripple phase in nanotubular dimyristoylphosphatidylcholine Bilayers confined inside nanoporous aluminum oxide substrates observed by DSC}, volume={22}, ISSN={["0743-7463"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33745760734&partnerID=MN8TOARS}, DOI={10.1021/la060448z}, abstractNote={Phase properties of substrate-supported nanotubular dimyristoylphosphatidylcholine (DMPC) bilayers confined within nanoporous channels of anodic aluminum oxide were characterized by DSC and compared with unsupported vesicles. In addition to the main phase transition, all samples exhibited a pretransition with a characteristic midpoint hysteresis between heating and cooling scans. The pretransition indicates that nanotubular bilayers could exist in a ripple phase, whereas hysteresis points to a similarity in the phase transition mechanisms. Observance of the ripple phase in lipid nanotubes is an indication of fully hydrated and only slightly perturbed bilayer surface.}, number={13}, journal={LANGMUIR}, publisher={American Chemical Society (ACS)}, author={Alaouie, Ali M. and Smirnov, Alex I.}, year={2006}, month={Jun}, pages={5563–5565} }
 @article{svistov_smirnov_prozorova_petrenko_micheler_büttgen_shapiro_demianets_2006, title={Magnetic phase diagram, critical behavior, and two-dimensional to three-dimensional crossover in the triangular lattice antiferromagnet RbFe (Mo O4) 2}, volume={74}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33746050896&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.74.024412}, abstractNote={We have studied the magnetic and thermodynamic properties as well as the NMR spectra of the quasi-two-dimensional (quasi-2D) Heisenberg antiferromagnet $\mathrm{Rb}\mathrm{Fe}{(\mathrm{Mo}{\mathrm{O}}_{4})}_{2}$. The observed temperature dependence of the order parameter, the critical indices, and the overall magnetic $H\text{\ensuremath{-}}T$ phase diagram are all in a good agreement with the theoretical predictions for a 2D $XY$ model. The temperature dependence of the specific heat at low temperature demonstrates a crossover from a ${T\phantom{\rule{0.2em}{0ex}}}^{2}$ law characteristic of a two-dimensional antiferromagnet to a three-dimensional ${T\phantom{\rule{0.2em}{0ex}}}^{3}$ law.}, number={2}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Svistov, L.E. and Smirnov, A.I. and Prozorova, L.A. and Petrenko, O.A. and Micheler, A. and Büttgen, N. and Shapiro, A.Ya. and Demianets, L.N.}, year={2006} }
 @article{smirnov_2006, title={Magnetic resonance modes in spin-gap magnets}, volume={49}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33750416689&partnerID=MN8TOARS}, DOI={10.1070/PU2006v049n06ABEH006077}, number={6}, journal={Physics-Uspekhi}, author={Smirnov, A.I.}, year={2006}, pages={649–652} }
 @article{smirnov_glazkov_2006, title={Magnetic resonance of collective states in spin-gap magnets}, volume={300}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33644696100&partnerID=MN8TOARS}, DOI={10.1016/j.jmmm.2005.10.066}, abstractNote={Various types of magnetic resonance signals observed in quantum-disordered magnets of the Haldane and dimer types are reported. The collective states of correlated spins near the breaks of the S=1 spin chains in the Haldane magnet PbNi2V2O8 demonstrate magnetic response of an effective spin S=1/2, while the excited states of long chains reveal the ESR spectrum of an effective spin S=1 in a crystal field. A magnetic resonance spectrum of the latter type is also observed for the collective excited states in the system of coupled S=12 dimers in crystals of TlCuCl3. Further, the interaction of triplet excitations and defects in PbNi2V2O8 is shown to result in a hybrid spin resonance mode.}, number={1}, journal={Journal of Magnetism and Magnetic Materials}, author={Smirnov, A.I. and Glazkov, V.N.}, year={2006}, pages={216–220} }
 @article{alaouie_smirnov_2006, title={Ultra-stable temperature control in EPR experiments: Thermodynamics of gel-to-liquid phase transition in spin-labeled phospholipid bilayers and bilayer perturbations by spin labels}, volume={182}, ISSN={["1090-7807"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33749070613&partnerID=MN8TOARS}, DOI={10.1016/j.jmr.2006.07.002}, abstractNote={An ultra-stable variable temperature accessory for EPR experiments with biological samples has been designed and tested. The accessory is comprised from a digitally controlled circulator bath that pumps fluid through high-efficiency aluminum radiators attached to an EPR resonator of a commercial X-band EPR spectrometer. Temperature stability of this new accessory after a 15 min re-equilibration is at least +/-0.007 K. For a standard 1-cm-long capillary sample arranged inside an EPR tube filled with silicon oil, the temperature variations do not exceed +/-0.033 K over the sample temperature range from 283 to 333 K. This new accessory has been tested by carrying out a comparative spin-labeling EPR and differential scanning calorimetry (DSC) study of the gel-to-liquid phase transition in multilamellar vesicles (MLV) composed of a synthetic phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). We demonstrate that the gel-to-liquid phase transition temperatures of MLV DMPC measured by EPR and DSC agree within +/-0.02 K experimental error even though the sample for EPR study was labeled with 1 mol% of 5PC (1-palmitoyl-2-stearoyl-(5-doxyl)-sn-glycero-3 phosphocholine). Cooperative unit number measured by EPR, N=676+/-36, was almost 50% higher than that obtained from DSC (N=458+/-18). These high values of N indicate that (i) the lipid domains should include at least several spin-labeled lipid molecules and (ii) the spin-probe 5PC molecules are not excluded into domains that are different from the bulk lipid phase as was speculated earlier. Overall, our data provide DSC and EPR evidence that in studies of the gel-to-liquid phase transition, the effect of bilayer perturbation by spin-labeled lipids is negligible and therefore thermodynamic parameters of the phase transition can be accurately measured by spin-labeling EPR. This might serve as an indication when spin-labeled molecules with structures similar to those of lipids are introduced at low concentrations, they are easily accommodated by fluid phospholipid bilayers without significant losses of the lipid cooperativity.}, number={2}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Alaouie, Ali M. and Smirnov, Alex I.}, year={2006}, month={Oct}, pages={229–238} }
 @article{sosin_prozorova_smirnov_golov_berkutov_petrenko_balakrishnan_zhitomirsky_2005, title={Adiabatic demagnetization of a pyrochlore antiferromagnet Gd<inf>2</inf>Ti<inf>2</inf>O<inf>7</inf>}, volume={290-291 PART 1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-14944365553&partnerID=MN8TOARS}, DOI={10.1016/j.jmmm.2004.11.344}, abstractNote={Abstract An adiabatic demagnetization process is studied in the pyrochlore antiferromagnet Gd 2 Ti 2 O 7 . A strong cooling of the sample is observed by decreasing magnetic field in the range 120–60 kOe corresponding to a crossover between saturated and spin–liquid phases. This phenomenon indicates that a considerable part of the magnetic entropy associated with a macroscopic number of local soft modes survives in the strongly correlated paramagnetic state. Monte Carlo simulations demonstrate good agreement with the experiment. The cooling power of the process is experimentally estimated with a view to possible technical applications. The results on Gd 2 Ti 2 O 7 are compared to those for Gd 3 Ga 5 O 12 , a related material for low-temperature magnetic cooling.}, journal={Journal of Magnetism and Magnetic Materials}, author={Sosin, S.S. and Prozorova, L.A. and Smirnov, A.I. and Golov, A.I. and Berkutov, I.B. and Petrenko, O.A. and Balakrishnan, G. and Zhitomirsky, M.E.}, year={2005}, pages={709–711} }
 @article{kocherginsky_kostetski_smirnov_2005, title={Antioxidant pool in beer and kinetics of EPR spin-trapping}, volume={53}, ISSN={["1520-5118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-24344504386&partnerID=MN8TOARS}, DOI={10.1021/jf051045s}, abstractNote={The kinetics of spin-trap adduct formation in beer oxidation exhibits an induction period if the reaction is carried out at elevated temperatures and in the presence of air. This lag period lasts until the endogenous antioxidants are almost completely depleted, and its duration is used as an indicator of the flavor stability and shelf life of beer. This paper demonstrates that the total kinetics of the process can be characterized by three parametersthe lag period, the rate of spin-trap adduct formation, and, finally, the steady-state spin-adduct concentration. A steady-state chain reaction mechanism is described, and quantitative estimates of the main kinetic parameters such as the initiation rate, antioxidant pool, effective content of organic molecules participating in the chain reactions, and the rate constant of the 1-hydroxyethyl radical EtOH• spin-adduct disappearance are given. An additional new dimensionless parameter is suggested to characterize the antioxidant poolthe product of the lag time and the rate of spin-trap radical formation immediately after the lag time, normalized by the steady-state concentration of the adducts. The results of spin-tapping EPR experiments are compared with the nitroxide reduction kinetics measured in the same beer samples. It is shown that although the kinetics of nitroxide reduction in beer can be used to evaluate the reducing power of beer, the latter parameter does not correlate with the antioxidant pool. The relationship of free radical processes, antioxidant pool, reducing power, and beer staling is discussed. Keywords: Beer; EPR; nitroxides; reducing power; spin traps; lag period; antioxidant pool}, number={17}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Kocherginsky, NM and Kostetski, YY and Smirnov, AI}, year={2005}, month={Aug}, pages={6870–6876} }
 @article{alaouie_smirnov_2005, title={Cooperativity and kinetics of phase transitions in nanopore-confined bilayers studied by differential scanning calorimetry}, volume={88}, ISSN={["1542-0086"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-21244463058&partnerID=MN8TOARS}, DOI={10.1529/biophysj.104.056523}, abstractNote={The first-order nature of the gel-to-liquid crystal phase transition of phospholipid bilayers requires very slow temperature rates in differential scanning calorimetry (DSC) experiments to minimize any rate-dependent distortions. Proportionality of the DSC signal to the rate poses a problem for studies of substrate-supported bilayers that contain very small volumes of the lipid phase. Recently, we described lipid bilayers self-assembled inside nanoporous substrates. The high density of the nanochannels in these structures provides at least a 500-fold increase in the bilayer surface area for the same size of the planar substrate chips. The increased surface area enables the DSC studies. The rate-dependent DSC curves were modeled as a convolution of a conventional van't Hoff shape and a first-order decay curve of the lipid rearrangement. This analysis shows that although confinement of bilayers to the nanopores of approximately 177 nm in diameter results in a more than threefold longer characteristic time of the lipid rearrangement and a decrease in the cooperative unit number, the phase transition temperature is unaffected.}, number={2}, journal={BIOPHYSICAL JOURNAL}, publisher={Elsevier BV}, author={Alaouie, AM and Smirnov, AI}, year={2005}, month={Feb}, pages={L11–L13} }
 @article{glazkov_smirnov_von nidda_loidl_uchinokura_masuda_2005, title={Field-controlled phase separation at the impurity-induced magnetic ordering in the spin-peierls magnet CuGeO<inf>3</inf>}, volume={94}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-18144422770&partnerID=MN8TOARS}, DOI={10.1103/PhysRevLett.94.057205}, abstractNote={The paramagnetic fraction surviving at the impurity-induced antiferromagnetic phase transition in the spin-Peierls magnet CuGeO3 is found to increase with an external magnetic field. This effect is explained by the competition of the Zeeman interaction and of the exchange interaction of local antiferromagnetic clusters formed on the spin-gap background near impurities.}, number={5}, journal={Physical Review Letters}, author={Glazkov, V.N. and Smirnov, A.I. and Von Nidda, H.-A.K. and Loidl, A. and Uchinokura, K. and Masuda, T.}, year={2005} }
 @article{sosin_prozorova_smirnov_golov_berkutov_petrenko_balakrishnan_zhitomirsky_2005, title={Magnetocaloric effect in pyrochlore antiferromagnet Gd<inf>2</inf>Ti<inf>2</inf>O<inf>7</inf>}, volume={71}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-20344370707&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.71.094413}, abstractNote={An adiabatic demagnetization process is studied in Gd2Ti2O7, a geometrically frustrated antiferromagnet on a pyrochlore lattice. In contrast to conventional paramagnetic salts, this compound can exhibit a temperature decrease by a factor of ten in the temperature range below the Curie-Weiss constant. The most efficient cooling is observed in the field interval between 120 and 60 kOe corresponding to a crossover between saturated and spin-liquid phases. This phenomenon indicates that a considerable part of the magnetic entropy survives in the strongly correlated state. According to the theoretical model, this entropy is associated with a macroscopic number of local modes remaining gapless till the saturation field. Monte Carlo simulations on a classical spin model demonstrate good agreement with the experiment. The cooling power of the process is experimentally estimated with a view to possible technical applications. The results for Gd2Ti2O7 are compared to those for Gd3Ga5O12, a well-known material for low temperature magnetic refrigeration.}, number={9}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Sosin, S.S. and Prozorova, L.A. and Smirnov, A.I. and Golov, A.I. and Berkutov, I.B. and Petrenko, O.A. and Balakrishnan, G. and Zhitomirsky, M.E.}, year={2005} }
 @article{chekmenev_hu_gor'kov_brey_cross_ruuge_smirnov_2005, title={N-15 and P-31 solid-state NMR study of transmembrane domain alignment of M2 protein of influenza A virus in hydrated cylindrical lipid bilayers confined to anodic aluminum oxide nanopores}, volume={173}, ISSN={["1096-0856"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-14844354285&partnerID=MN8TOARS}, DOI={10.1016/j.jmr.2004.12.006}, abstractNote={This communication reports the first example of a high resolution solid-state 15N 2D PISEMA NMR spectrum of a transmembrane peptide aligned using hydrated cylindrical lipid bilayers formed inside nanoporous anodic aluminum oxide (AAO) substrates. The transmembrane domain SSDPLVVA(A-15N)SIIGILHLILWILDRL of M2 protein from influenza A virus was reconstituted in hydrated 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine bilayers that were macroscopically aligned by a conventional micro slide glass support or by the AAO nanoporous substrate. 15N and 31P NMR spectra demonstrate that both the phospholipids and the protein transmembrane domain are uniformly aligned in the nanopores. Importantly, nanoporous AAO substrates may offer several advantages for membrane protein alignment in solid-state NMR studies compared to conventional methods. Specifically, higher thermal conductivity of aluminum oxide is expected to suppress thermal gradients associated with inhomogeneous radio frequency heating. Another important advantage of the nanoporous AAO substrate is its excellent accessibility to the bilayer surface for exposure to solute molecules. Such high accessibility achieved through the substrate nanochannel network could facilitate a wide range of structure–function studies of membrane proteins by solid-state NMR.}, number={2}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Chekmenev, EY and Hu, J and Gor'kov, PL and Brey, WW and Cross, TA and Ruuge, A and Smirnov, AI}, year={2005}, month={Apr}, pages={322–327} }
 @article{grinberg_smirnov_grinberg_grinberg_ja o'hara_swartz_2005, title={Practical conditions and limitations for high-spatial-resolution multisite EPR oximetry}, volume={28}, ISSN={["1613-7507"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-19044398296&partnerID=MN8TOARS}, DOI={10.1007/BF03166994}, number={1-2}, journal={APPLIED MAGNETIC RESONANCE}, author={Grinberg, VO and Smirnov, AI and Grinberg, OY and Grinberg, SA and JA O'Hara and Swartz, HM}, year={2005}, pages={69–78} }
 @article{tennant_claridge_mccammon_smirnov_beck_2005, title={Structural studies of New Zealand pounamu using Mossbauer spectroscopy and electron paramagnetic resonance}, volume={35}, ISSN={["0303-6758"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-30444441777&partnerID=MN8TOARS}, DOI={10.1080/03014223.2005.9517790}, abstractNote={Abstract We report Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy (EPR) studies of a number of New Zealand minerals that can be classified under the non‐specific names “pounamu” or “greenstone”. Mössbauer measurements allowed the distribution of iron in its +2 and +3 oxidation states to be assigned to the M1 to M4 sites of the constituent minerals, tremolite‐actinolite in the case of nephrite jades. EPR at two frequencies, 9.4 GHz (X‐band) and 94.1 GHz (W‐band), allowed the determination of the distribution of Mn2+ in these sites. The results are apparently contrary to the usual assignments made for the parent minerals tremolite and actinolite. In two cases, one a nephrite jade and the other a serpentine, significant quantities of magnetically ordered minerals chalcopyrite and magnetite were identified by Mössbauer spectroscopy. These minerals could not be found in the X‐ray diffraction patterns of the same minerals leading to the conclusion that they are very finely divided in the samples studied.}, number={4}, journal={JOURNAL OF THE ROYAL SOCIETY OF NEW ZEALAND}, publisher={Informa UK Limited}, author={Tennant, WC and Claridge, RFC and McCammon, CA and Smirnov, AT and Beck, RJ}, year={2005}, month={Dec}, pages={385–398} }
 @article{voinov_polienko_schanding_bobko_khramtsov_gatilov_rybalova_smirnov_grigor'ev_2005, title={Synthesis, Structure, and X-Band (9.5 GHz) EPR Characterization of the New Series of pH-Sensitive Spin Probes: N,N-Disubstituted 4-Amino-2,2,5,5-tetramethyl-3-imidazoline 1-Oxyls}, volume={70}, ISSN={0022-3263 1520-6904}, url={http://dx.doi.org/10.1021/jo0510890}, DOI={10.1021/jo0510890}, abstractNote={An approach to the synthesis of new imidazoline nitroxides bearing an N‘,N‘-disubstituted amidine group is reported. The approach is based on the alkylation of diamagnetic 4-R-amino-1,2,2,5,5-pentamethyl-3-imidazolines with bromoacetic acid ethyl ester; the products of alkylation are further oxidized to the corresponding nitroxides. The approach allows a variety of functional groups to be introduced into the nitroxide molecule structure. Alkylation with bromoacetic acid ethyl ester was found to proceed with high regioselectivity and afford the products of exo-alkylation. The regiochemical assignment is made on the basis of 13C NMR spectra and confirmed by X-ray diffraction study. All of the nitroxides synthesized here were shown to have pH-dependent EPR spectra with pKa ranging from 3.5 to 6.2. For nitroxides 13 bearing the carboxylic group remote to the nitroxide moiety, the changes in isotropic magnetic parameters of EPR spectra due to reversible deprotonation of the carboxylic group were found to be small. For these nitroxides, we demonstrate an alternative approach for pKa determination that is based on measuring the peak-to-peak line width of the EPR spectrum in the presence of the paramagnetic broadening agent potassium ferricyanide. The partition coefficients of nitroxides in octanol/H2O and octanol/phosphate buffer solution mixtures were measured to reveal a range of their lipophilicities.}, number={24}, journal={The Journal of Organic Chemistry}, publisher={American Chemical Society (ACS)}, author={Voinov, Maxim A. and Polienko, Julya F. and Schanding, Thomas and Bobko, Andrey A. and Khramtsov, Valery V. and Gatilov, Yury V. and Rybalova, Tatyana V. and Smirnov, Alex I. and Grigor'ev, Igor A.}, year={2005}, month={Nov}, pages={9702–9711} }
 @article{smirnov_2005, title={The method of possible states and its application to the chemical thermodynamic analysis of nonequilibrium processes in a multicomponent mixture of reacting gases under isobaric adiabatic conditions}, volume={39}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-21444448255&partnerID=MN8TOARS}, DOI={10.1007/s11236-005-0072-x}, number={3}, journal={Theoretical Foundations of Chemical Engineering}, author={Smirnov, A.I.}, year={2005}, pages={250–258} }
 @article{kocherginsky_kostetski_smirnov_2005, title={Use of nitroxide spin probes and electron paramagnetic resonance for assessing reducing power of beer. Role of SH groups}, volume={53}, ISSN={["1520-5118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-13944249843&partnerID=MN8TOARS}, DOI={10.1021/jf034787z}, abstractNote={Intensity of EPR spectra of stable organic free radicals, nitroxides, is decreasing with time if the radicals are dissolved in beer. The process is determined by a chemical reaction of nitroxide reduction by components naturally present in beer. Kinetics can be described as a simple irreversible first order with respect to both nitroxide and one reducing agent. Effective concentration of the reducing agent and the corresponding reaction rate constant has been determined. It is demonstrated that the nitroxide reduction is sensitive to the presence of solvent-accessible SH groups of proteins present in beer. It is proposed that quantitative analysis of reduction kinetics of small water-soluble nitroxide radicals such as TEMPO and TEMPOL can be used to assess the reducing power of beer. The effect of accelerated aging of beer achieved at elevated temperatures on nitroxide reduction kinetics is demonstrated.}, number={4}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Kocherginsky, NM and Kostetski, YY and Smirnov, AI}, year={2005}, month={Feb}, pages={1052–1057} }
 @article{smirnov_smirnova_2004, title={Convolution-Based Algorithm: from Analysis of Rotational Dynamics to EPR Oximetry and Protein Distance Measurements}, DOI={10.1007/978-1-4419-8951-2_6}, abstractNote={Spectral simulations and optimization of simulation parameters to fit experimental data are very powerful tools for data analysis in EPR spectroscopy. Data modeling serves two purposes, namely, (i) an aid to the interpretation of raw spectra, and (ii) reducuction of the data file, which usually contains from a few hundred to thousands of data points, to a much smaller set of meaningful physical parameters. It has been shown (e.g., Halpern et al., 1993) that the use of the whole EPR spectrum instead of a few characteristic data points can significantly, sometimes by an order of magnitude, increase the accuracy of the extracted spectral parameters. If the theoretical model is suitable for the experiment, and the experimental noise has a Gaussian or similar distribution, then the least square’s criterion (χ2) can be chosen for parameter optimization. Since the EPR spectrum usually depends on several (≥3) parameters, a multi-dimensional minimization algorithm is required to optimize parameters based on the value of χ2.}, journal={EPR: Instrumental Methods}, publisher={Springer Science \mathplus Business Media}, author={Smirnov, Alex I. and Smirnova, Tatyana I.}, year={2004}, pages={277–348} }
 @article{earle_smirnov_2004, title={High Field ESR: Applications to Protein Structure and Dynamics}, DOI={10.1007/978-1-4757-4379-1_4}, abstractNote={Electron Spin Resonance at high magnetic fields (HF ESR) is rapidly developing into a powerful biophysical tool which is uniquely positioned to address complex aspects of structure and dynamics of proteins, membranes, and macromolecular assemblies at molecular level. The source of the contemporary resurgence of interest in ESR as a biophysical tool is that there are, broadly speaking, three large groups of problems, which can be approached with ESR methods but cannot easily be studied by traditional structural techniques: (1) structure and dynamics of large molecular weight proteins in solution; (2) membrane and membrane-associated proteins: structure, location with respect to the membrane, side-chain dynamics, and interactions with other membrane components or DNA’s and RNA’s; (3) fast conformational transitions of proteins and RNA’s in solution, protein folding and re-folding. The focus of this review is mainly on HF ESR spin-labeling techniques, primarily via nitroxide spin labels, as this method is the most flexible and is even applicable to proteins which are otherwise ESR-silent. We start with physical aspects of ESR of nitroxide spin labels at high magnetic fields in order to categorize the characteristic information that can be gained from such experiments. Then we describe practical applications of spin-labeling HF ESR to study structure and dynamics of complex biophysical systems. We also discuss several details of the ESR motional theory based on the stochastic Liouville equation (SLE) that are relevant to nitroxide line shape analysis in order to appreciate both the information available from and the limitations of the method. Particular emphasis is given to multifrequency HF ESR methods in studies of spin-labeled membranes and biopolymers. Finally, we review the use of HF ESR in applications to molecular structure including distance measurements, determination of molecular orientations from ESR of ordered samples, and structural studies based on g-factor measurements.}, journal={Very High Frequency (VHF) ESR/EPR}, publisher={Springer Science \mathplus Business Media}, author={Earle, Keith A. and Smirnov, Alex I.}, year={2004}, pages={95–143} }
 @article{smirnov_krug von nidda_loidl_demianets_shapiro_2004, title={Interaction of triplet excitations with spin chain ends in the Haldane magnet PbNi<inf>2</inf>V<inf>2</inf>O<inf>8</inf>}, volume={272-276}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-2642515798&partnerID=MN8TOARS}, DOI={10.1016/j.jmmm.2003.12.1144}, abstractNote={ESR signals of two kinds were detected in the doped Haldane magnet Pb(Ni 1− x Mg x ) 2 V 2 O 8 . The low-temperature ESR with the value of g -factor 2.2 corresponds to effective spins S= 1 2 at the ends of the spin chains. The signal of the second type is thermally activated, has a spectrum with the zero-field frequency 86 GHz and is described by an effective spin S =1 in an axial crystal field . The last signal is due to the splitting of the spin sublevels of the triplet excitations in a magnetic and crystal fields. An exchange coupled ESR mode of triplets and spin-chain ends is found at intermediate temperatures.}, journal={Journal of Magnetism and Magnetic Materials}, author={Smirnov, A.I. and Krug Von Nidda, H.-A. and Loidl, A. and Demianets, L.N. and Shapiro, A.Ya.}, year={2004}, pages={880–881} }
 @article{ammar_menetrier_villesuzanne_matar_chevalier_etourneau_villeneuve_rodriguez-carvajal_koo_smirnov_et al._2004, title={Investigation of the electronic and structural properties of potassium hexaboride, KB6, by transport, magnetic susceptibility, EPR, and NMR measurements, temperature-dependent crystal structure determination, and electronic band structure calculations}, volume={43}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-3843112209&partnerID=MN8TOARS}, DOI={10.1021/ic049444c}, abstractNote={The electronic and structural properties of potassium hexaboride, KB6, were examined by transport, magnetic susceptibility, EPR, and NMR measurements, temperature-dependent crystal structure determination, and electronic band structure calculations. The valence bands of KB6 are partially empty, but the electrical resistivity of KB6 reveals that it is not a normal metal. The magnetic susceptibility as well as EPR and NMR measurements show the presence of localized electrons in KB6. The EPR spectra of KB6 have two peaks, a broad (∼320 G) and a narrow (less than ∼27 G) line width, and the temperature-dependence of the magnetic susceptibility of KB6 exhibits a strong hysteresis below 70 K. The temperature-dependent crystal structure determination of KB6 shows the occurrence of an unusual variation in the unit cell parameter hence supporting that the hysteresis of the magnetic susceptibility is a bulk phenomenon. The line width ΔHpp of the broad EPR signal is independent of temperature and EPR frequency. This finding indicates that the line broadening results from the dipole−dipole interaction, and the spins responsible for the broad EPR peak has the average distance of ∼1.0 nm. To explain these apparently puzzling properties, we examined a probable mechanism of electron localization in KB6 and its implications.}, number={16}, journal={INORGANIC CHEMISTRY}, author={Ammar, A and Menetrier, M and Villesuzanne, A and Matar, S and Chevalier, B and Etourneau, J and Villeneuve, G and Rodriguez-Carvajal, J and Koo, HJ and Smirnov, AI and et al.}, year={2004}, month={Aug}, pages={4974–4987} }
 @article{smirnov_ruuge_reznikov_voinov_grigor'ev_2004, title={Site-Directed Electrostatic Measurements with a Thiol-Specific pH-Sensitive Nitroxide:  Differentiating Local pK and Polarity Effects by High-Field EPR}, volume={126}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja048801f}, DOI={10.1021/ja048801f}, abstractNote={This communication describes the use of a methanethiosulfonate derivative of an imidazolidine nitroxide, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethyl-imidazolidin-4-ylmethyl) ester, IMTSL, for site-directed pKa determination of peptides by electron paramagnetic resonance. This spin label is covalently attached to the thiol group of unique cysteines incorporated into peptide structures. The tertiary amine nitrogen N3 of the label readily participates in proton exchange reactions, which are monitored through changes in EPR spectra of nitroxide moiety. Using EPR at 95 GHz (W-band) isotropic magnetic parameters of this nitroxide, both Aiso and giso, were calibrated in solvents of different polarity and pH. Two different linear correlations between Aiso and giso for acidic and basic forms of IMTSL were observed, making it possible to differentiate effects of local polarity from N3 protonation on nitroxide EPR spectra. Titration of a synthetic P11 peptide fragment of the laminin B1 chain illustrates the utility of this method.}, number={29}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Smirnov, Alex I. and Ruuge, Andres and Reznikov, Vladimir A. and Voinov, Maxim A. and Grigor'ev, Igor A.}, year={2004}, month={Jul}, pages={8872–8873} }
 @article{smirnova_smirnov_2003, title={Dynamic molecular oxygen accessibility to a buried Mn2+ protein site: A high-field EPR experiment}, volume={107}, ISSN={["1520-6106"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0042203966&partnerID=MN8TOARS}, DOI={10.1021/jp0349637}, abstractNote={A high-field (W-band, 3.35 T, 95 GHz) electron paramagnetic resonance (EPR) experiment to measure dynamic molecular oxygen accessibility to manganese(II) ions in liquids is described. The method is based on the direct observation of magnetic interactions between molecular oxygen and the manganese(II) ion in solution. The effect is observed as a Lorentzian broadening of the EPR line. The observation of this effect is facilitated by narrowing the manganese(II) EPR signal at high magnetic field and utilizing elevated oxygen pressures of up to 3 atm. The magnitude of the broadening effect is dependent on both the oxygen permeability of the solvent and the coordination of the manganese(II) ion and is independent of the frequency of the EPR experiment. The latter indicates that Heisenberg spin exchange between the electronic spins of oxygen and manganese(II) during bimolecular collisions is the likely broadening mechanism. The method can be also used to study dynamic molecular oxygen accessibility to manganese(II) sites in biological macromolecules, as demonstrated by an example of a buried site in Concanavalin A lectin. It was found that the oxygen accessibility of this site is significantly smaller (by a factor of 4) than that of an aqua ion and is recovered upon denaturing of the protein.}, number={29}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, publisher={American Chemical Society (ACS)}, author={Smirnova, TI and Smirnov, AI}, year={2003}, month={Jul}, pages={7212–7215} }
 @article{smirnov_glazkov_masuda_uchinokura_demianets_shapiro_2003, title={Microscopic magnetic phase separation at the impurity stimulated antiferromagnetic ordering of two spin-gap magnets}, volume={329-333}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-23044446245&partnerID=MN8TOARS}, DOI={10.1016/S0921-4526(02)02011-2}, abstractNote={Abstract The ESR spectra of spin-Peierls crystal CuGeO3 and Haldane magnet PbNi2V2O8 doped with Mg revealed the coexistence of paramagnetic and antiferromagnetic spin resonance modes below the points of the impurity induced ordering. The ordering is known to be due to the restoring of the AFM staggered magnetization near impurities. The surprising paramagnetic component observed at low doping indicates a nonuniform structure of the ordered phase with a portion of clusters of staggered magnetization which are isolated from the merged clusters by slightly disturbed spin-gap matrix. Isolated clusters provide paramagnetic signals due to their net spin.}, number={II}, journal={Physica B: Condensed Matter}, author={Smirnov, A.I. and Glazkov, V.N. and Masuda, T. and Uchinokura, K. and Demianets, L.N. and Shapiro, A.Ya.}, year={2003}, pages={699–700} }
 @article{smirnov_2003, title={Spin-Labeling in High-Field EPR}, volume={34}, DOI={10.1002/chin.200333299}, abstractNote={For Abstract see ChemInform Abstract in Full Text.}, number={33}, journal={ChemInform}, publisher={Wiley-Blackwell}, author={Smirnov, Alex I.}, year={2003}, month={Aug} }
 @article{klimin_popova_mavrin_loosdrecht_svistov_smirnov_prozorova_nidda_seidov_loidl_et al._2003, title={Structural phase transition in the two-dimensional triangular lattice antiferromagnet RbFe(MoO<inf>4</inf>)<inf>2</inf>}, volume={68}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0346880240&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.68.174408}, abstractNote={We report temperature-dependent x-ray powder diffraction patterns and single-crystal electron spin resonance (ESR) and Raman spectra of the two-dimensional triangular-lattice antiferromagnet $\mathrm{RbFe}({\mathrm{MoO}}_{4}{)}_{2}.$ A structural phase transition is found to occur in this compound at ${T}_{c}\ensuremath{\simeq}190\mathrm{K}.$ By analyzing our data and the literature data on similar compounds, we conclude that the 190 K transition comprises rotations of ${\mathrm{MoO}}_{4}$ tetrahedra and is, most likely, a transformation from a highly symmetric $P3\ifmmode\bar\else\textasciimacron\fi{}m1$ room-temperature structure into a very similar but less symmetric $P3\ifmmode\bar\else\textasciimacron\fi{}c1$ low-temperature one. The shift of the ESR frequency and the ESR linewidth were found to be determined by the crystal field influence and are described well considering the single-ion anisotropy with the constant ${D/k}_{B}=0.25\mathrm{K}.$ The change of the crystal field at the iron site below the phase-transition point ${T}_{c}$ is estimated.}, number={17}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Klimin, S.A. and Popova, M.N. and Mavrin, B.N. and Loosdrecht, P.H.M.M. and Svistov, L.E. and Smirnov, A.I. and Prozorova, L.A. and Nidda, H.-K. and Seidov, Z. and Loidl, A. and et al.}, year={2003} }
 @article{smirnov_poluektov_2003, title={Substrate-supported lipid nanotube arrays}, volume={125}, ISSN={["1520-5126"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0038713934&partnerID=MN8TOARS}, DOI={10.1021/ja0349406}, abstractNote={This Communication describes the self-assembly of phospholipids into lipid nanotubes inside nanoporous anodic aluminum oxide substrate. Orientations of the lipid molecules in such lipid nanoscale structures were verified by high-resolution spin labeling EPR at 95 GHz. The static order parameter of lipids in such nanotube arrays was determined from low-temperature EPR spectra and was found to be exceptionally high, Sstatic approximately 0.9. We propose that substrate-supported lipid nanotube arrays have potential for building robust biochips and biosensors in which rigid nanoporous substrates protect the bilayer surface from contamination. The total bilayer surface in the lipid nanotube arrays is much greater than that in the planar substrate-supported membranes. The lipid nanotube arrays seem to be suitable for developing patterned lipid deposition and could be potentially used for patterning of membrane-associated molecules.}, number={28}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Smirnov, AI and Poluektov, OG}, year={2003}, month={Jul}, pages={8434–8435} }
 @article{prozorova_svistov_smirnov_petrenko_demianets_shapiro_2003, title={Triangular lattice antiferromagnet RbFe(MoO<inf>4</inf>)<inf>2</inf>in an applied magnetic field}, volume={258-259}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-18544403461&partnerID=MN8TOARS}, DOI={10.1016/S0304-8853(02)01125-3}, abstractNote={Abstract RbFe(MoO4)2 is a rare example of a nearly two-dimensional Heisenberg antiferromagnet on a triangular lattice. We have studied its low-temperature magnetic properties by means of single crystal ESR spectroscopy and magnetization measurements. On the basis of the obtained results an H–T phase diagram, containing at least five different magnetic phases is constructed. In zero field, RbFe(MoO4)2 undergoes a phase transition at TN=3.8 K into a noncollinear spin structure with all the spins confined in the hexagonal plane. The application of an external magnetic field in the plane induces a collinear spin state (Hc1=47 kOe, Hc2=71 kOe) and produces magnetization plateaux at one-third of the saturation moment. Both the ESR and magnetization measurements also clearly indicate an additional first-order phase transition in a field of 35 kOe. The exact nature of this phase transition is unclear.}, journal={Journal of Magnetism and Magnetic Materials}, author={Prozorova, L.A. and Svistov, L.E. and Smirnov, A.I. and Petrenko, O.A. and Demianets, L.N. and Shapiro, A.Ya.}, year={2003}, pages={394–397} }
 @article{smirnov_glazkov_nidda_loidl_demianets_shapiro_2002, title={Paramagnetic and antiferromagnetic resonances in the diamagnetically diluted Haldane magnet PbNi<inf>2</inf>V<inf>2</inf>O<inf>8</inf>}, volume={65}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036573703&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.65.174422}, abstractNote={The impurity-induced antiferromagnetic ordering of the doped Haldane magnet Pb(Ni{1-x}Mg{x})2V2O8 (0 < x <0.06) was studied by electron spin resonance (ESR) on ceramic samples in the frequency range 9-110 GHz. Below the N\'{e}el temperature a transformation of the ESR spectrum was found, indicating an antiferromagnetic resonance mode of spin precession. The excitation gap of the spin-wave spectrum increases with increasing Mg-concentration $x$ in the same manner as the N\'{e}el temperature, reaching its maximum value of 80 GHz at x > 0.04. At small concentrations x < 0.02 the signals of antiferromagnetic resonance were found to coexist with the signal of the paramagnetic resonance indicating a microscopic separation of the magnetic phases.}, number={17}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Smirnov, A.I. and Glazkov, V.N. and Nidda, H.-A. and Loidl, A. and Demianets, L.N. and Shapiro, A.Y.}, year={2002}, pages={1744221–1744228} }
 @article{glazkov_smirnov_uchinokura_masuda_2002, title={Separation of the magnetic phases at the Néel point in the diluted spin-Peierls magnet (formula presented)}, volume={65}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85038316995&partnerID=MN8TOARS}, DOI={10.1103/PhysRevB.65.144427}, abstractNote={The impurity-induced antiferromagnetic ordering of the doped spin-Peierls magnet ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{GeO}}_{3}$ was studied by the electron-spin-resonance (ESR) technique. Crystals with $x<4%$ demonstrate the coexistence of paramagnetic and antiferromagnetic ESR modes. This coexistence indicates the separation of a macroscopically uniform sample in the paramagnetic and antiferromagnetic phases. In the presence of long-range spin-Peierls order (at $x=1.71%)$ the volume of the antiferromagnetic phase immediately below the N\'eel point ${T}_{N}$ is smaller than the volume of the paramagnetic phase. In the presence of the short-range spin-Peierls order $(x=2.88$ and 3.2%) there are comparable volumes of two phases at ${T=T}_{N}.$ The fraction of the antiferromagnetic phase increases with lowering temperature. In the absence of the spin-Peierls dimerization (at $x=4.57%)$ the whole sample exhibits a transition into an antiferromagnetic state, and there is no phase separation. These results are explained by a consideration of clusters of staggered magnetization appearing near impurities within the singlet spin-Peierls matrix. Overlapping clusters form the antiferromagnetic phase, and isolated clusters contribute to the paramagnetic resonance signal.}, number={14}, journal={Physical Review B - Condensed Matter and Materials Physics}, author={Glazkov, V.N. and Smirnov, A.I. and Uchinokura, K. and Masuda, T.}, year={2002}, pages={1–7} }
 @article{smirnov_sen_2001, title={High field electron paramagnetic resonance of Gd3+-doped glasses: Line shapes and average ion distances in silicates}, volume={115}, ISSN={["1089-7690"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035935353&partnerID=MN8TOARS}, DOI={10.1063/1.1403436}, abstractNote={The average distances between Gd3+ ions in multicomponent silicate glasses doped with 0.058 to up to 4.64 wt % Gd2O3 are characterized by electron paramagnetic resonance (EPR) line broadening effects at high-field (95 GHz, W band). Increase in the EPR resonant field/frequency above that of the conventional X band (9.5 GHz) simplifies the Gd3+ EPR spectra and increases the sensitivity of the EPR linewidth to concentration induced broadening effects. Least squares line shape simulations show that the broadening can be described by a Lorentzian function with a width proportional to the average Gd3+ concentration which is in good agreement with the existing theories. Analyses of the concentration dependence of Lorentzian line broadening indicate an onset of clustering of Gd3+ ions at > 1wt % doping levels.}, number={16}, journal={JOURNAL OF CHEMICAL PHYSICS}, publisher={AIP Publishing}, author={Smirnov, AI and Sen, S}, year={2001}, month={Oct}, pages={7650–7656} }
 @article{grinberg_smirnov_swartz_2001, title={High spatial resolution multi-site EPR oximetry - The use of a convolution-based fitting method}, volume={152}, ISSN={["1096-0856"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035743038&partnerID=MN8TOARS}, DOI={10.1006/jmre.2001.2408}, abstractNote={We describe a new method to enhance the spatial resolution of multi-site electron paramagnetic resonance (EPR) oximetry. The method is suitable for any shape (density distribution function) of a solid paramagnetic material implanted in tissue. It corrects distortions of lineshapes caused by the gradient and thus overcomes limitations of previous multi-site EPR oximetry methods that restricted the ratio of the particle size to the distance between sites. The new method is based on consecutive applications of magnetic field gradients with the same direction but with a different magnitude and uses a convolution-based fitting algorithm to derive Lorentzian EPR linewidths of each individual peak of the EPR spectrum. The method is applicable for any particulate EPR oxygen sensitive materials whose EPR spectra can be approximated by a Lorentzian function or a superposition of Lorentzian functions. By incorporating this model of the lineshape in the data processing, we are able to decrease significantly the number of parameters needed for the calculations and to recover the oxygen concentration, even from quite noisy spectra. We (i) describe our method and the data-processing algorithm, (ii) demonstrate our approach in model and in vivo experiments, and (iii) discuss the limitations.}, number={2}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Grinberg, OY and Smirnov, AI and Swartz, HM}, year={2001}, month={Oct}, pages={247–258} }
 @article{mangels_harper_smirnov_howard_lorigan_2001, title={Investigating magnetically aligned phospholipid bilayers with EPR spectroscopy at 94 GHz}, volume={151}, ISSN={["1096-0856"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035743313&partnerID=MN8TOARS}, DOI={10.1006/jmre.2001.2368}, abstractNote={In this paper, we report our initial results on studying magnetically aligned phospholipid bilayers (bicelles) at high magnetic fields (approximately 3.4 T) with electron paramagnetic resonance (EPR) spectroscopy at 95 GHz (W-band). In order to characterize this system for W-band EPR studies, we have utilized the nitroxide spin probe 3beta-doxyl-5alpha-cholestane to demonstrate the effects of macroscopic bilayer alignment. At W-band due to the increase in magnetic field strength (when compared to X-band studies at 9.5 GHz) (S. M. Garber et al., J. Am. Chem. Soc. 121, 3240-3241 (1999)), we were able to examine magnetically aligned phospholipid bilayers at two orientations with the bilayer normal oriented either perpendicular or parallel (upon addition of YbCl3) with respect to the direction of the static magnetic field. Additionally, at a magnetic field of 3.4 T (g=2 resonance at W-band), we were able to study the parallel alignment with a lower concentration of Yb3+, thereby eliminating the possible unwanted effects associated with lanthanide-protein interactions and paramagnetic shifts and/or line broadening induced by the lanthanide ions. The development of this new spin label alignment technique will open up a whole new area of investigation for phospholipid bilayer systems and membrane protein EPR studies at high magnetic fields.}, number={2}, journal={JOURNAL OF MAGNETIC RESONANCE}, publisher={Elsevier BV}, author={Mangels, ML and Harper, AC and Smirnov, AI and Howard, KP and Lorigan, GA}, year={2001}, month={Aug}, pages={253–259} }
 @article{eaton_eaton_stoner_quine_rinard_smirnov_weber_krzystek_hassan_brunel_et al._2001, title={Multifrequency electron paramagnetic resonance of ultramarine blue}, volume={21}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035528071&partnerID=MN8TOARS}, DOI={10.1007/BF03162429}, number={3-4}, journal={Applied Magnetic Resonance}, author={Eaton, G.R. and Eaton, S.S. and Stoner, J.W. and Quine, R.W. and Rinard, G.A. and Smirnov, A.I. and Weber, R.T. and Krzystek, J. and Hassan, A.K. and Brunel, L.-C. and et al.}, year={2001}, pages={563–570} }
 @article{breitzer_smirnov_szczepura_wilson_rauchfuss_2001, title={Redox Properties of C 6 S 8  n   - and C 3 S 5  n   - ( n = 0, 1, 2):  Stable Radicals and Unusual Structural Properties for C−S−S−C Bonds}, volume={40}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035952488&partnerID=MN8TOARS}, DOI={10.1021/ic000999r}, abstractNote={The new anionic carbon sulfides C6S10(2-) and C12S16(2-) are described and crystallographically characterized. The C12S16(2-) anion consists of two C6S8 units connected by an exceptionally long (2.157(12) A) S-S bond. In solution, C12S16(2-) exists in equilibrium with the radical C6S8(-*). The equilibrium constant for radical formation (293 K, THF) is 1.2 x 10(-4) M, as determined by optical spectroscopy at varying concentrations. Radical formation occurs through scission of the S-S bond. On the basis of variable temperature EPR spectra, the thermodynamic parameters of this process are DeltaH = +51.5 +/- 0.5 kJ x mol(-1) and DeltaS = +110 +/- 3 J x mol(-1) x K(-1). C6S10(2-) is an oxidation product of C3S5(2-) and consists of two C3S5 units connected by an S-S bond. The S-S bond length (2.135(4) A) is long, and the CS-SC torsion angle is unusually acute (52.1 degrees ), which is attributed to an attractive interaction between C3S2 rings. The oxidation of (Me4N)2C3S5 occurs at -0.90 V vs Fc+/Fc in MeCN, being further oxidized at -0.22 V. The similarity of the cyclic voltammogram of (Me4N)2C6S10 to that of (Me4N)2C3S5 indicates that C6S10(2-) is the initial oxidation product of C3S5(2-).}, number={7}, journal={Inorg. Chem.}, publisher={American Chemical Society (ACS)}, author={Breitzer, Jonathan G. and Smirnov, Alex I. and Szczepura, Lisa F. and Wilson, Scott R. and Rauchfuss, Thomas B.}, year={2001}, month={Mar}, pages={1421–1429} }
 @article{smirnov_smirnova_2001, title={Resolving domains of interdigitated phospholipid membranes with 95 GHz spin labeling EPR}, volume={21}, ISSN={["1613-7507"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035528064&partnerID=MN8TOARS}, DOI={10.1007/BF03162420}, number={3-4}, journal={APPLIED MAGNETIC RESONANCE}, author={Smirnov, AI and Smirnova, TI}, year={2001}, pages={453–467} }
 @article{bakker_granger_smirnov_2001, title={Studies of Cetylpyridinium Chloride and Cetylpyridinium Salicylate in Solution and Adsorbed on Silica Surfaces Using X- and W-Band Electron Paramagnetic Resonance Spectroscopy}, volume={17}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035901799&partnerID=MN8TOARS}, DOI={10.1021/la001517r}, abstractNote={The electron paramagnetic resonance (EPR) spin probe 4-[N,N-dimethyl-N-(n-hexadecyl)ammonium]-2,2,6,6-tetramethylpiperindinyl-N‘-oxyl (HTAB*) has been used to study the adsorption and aggregation of cetylpyridinium chloride (CPC) and cetylpyridinium salicylate (CPSa) on silica particles. In CPC micelles, the local viscosity, as determined from the rotational correlation times of HTAB*, was found to be approximately constant, as was the local polarity determined from Aiso, giso, and HTAB* equilibrium constants. In CPSa micelles at concentrations above the sphere-to-rod transition, significant decreases in polarity and local viscosity were observed. The affinity of CPC for the strong binding site on the silica surface was found to be higher than the affinities of CPSa and HTAB. The polarities and local viscosities of the surfactant aggregates and the corresponding micelles were found to be similar. From analysis of the line widths of the EPR spectra, it was concluded that CPSa on silica surfaces forms two c...}, number={8}, journal={Langmuir}, publisher={American Chemical Society (ACS)}, author={Bakker, Martin G. and Granger, Edward L. and Smirnov, Alex I.}, year={2001}, month={Apr}, pages={2346–2356} }
 @article{smirnov_glazkov_leonyuk_vetkin_2000, title={ESR study of the residual magnetism in the spin-Peierls phase}, volume={284-288}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033689888&partnerID=MN8TOARS}, DOI={10.1016/S0921-4526(99)02793-3}, abstractNote={Abstract Weak ESR signals of pure CuGeO 3 crystals found at low temperature indicate three types of defects in spin–Peierls state: single spins, pairs of spins, spin clusters. These defects in high-quality crystals are ascribed to boundaries between domains arising due to breaks of the coherence of lattice dimerization.}, number={PART II}, journal={Physica B: Condensed Matter}, author={Smirnov, A.I. and Glazkov, V.N. and Leonyuk, L.I. and Vetkin, A.G.}, year={2000}, pages={1649–1650} }
 @article{bottle_gillies_hughes_micallef_smirnov_sutcliffe_2000, title={Synthesis, single crystal X-ray structure and W-band (95 GHz) EPR spectroscopy of a new anionic isoindoline aminoxyl: synthesis and characterisation of some derivatives}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034236760&partnerID=MN8TOARS}, DOI={10.1039/b002497j}, abstractNote={Here we describe the improved synthesis and full characterisation, including W-band EPR analysis and X-ray crystallography, of an anionic isoindoline aminoxyl, 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl 6 (CTMIO), which is more water soluble than the parent 1,1,3,3-tetramethylisoindolin-2-yloxyl 1 (TMIO). We also report the synthesis and characterisation of three novel CTMIO derivatives: the n-hexyl ester 9, anhydride 10, and N-hydroxysuccinimide ester 11.
 Selective AlCl3-catalysed bromination of 2-benzyl-1,1,3,3-tetramethylisoindoline 2 produces the aminoxyl precursor, 5-bromo-1,1,3,3-tetramethylisoindoline 3 in high yield. Lithiation and subsequent carboxylation of this species generates 5-carboxy-1,1,3,3-tetramethylisoindoline 5, which undergoes tungstate–H2O2 oxidation to give the target aminoxyl, CTMIO 6. The analogous synthesis of 5-formyl-1,1,3,3-tetramethylisoindolin-2-yloxyl 8 is also described.
 W-band (95 GHz) EPR studies of toluene solutions of CTMIO, both liquid and frozen, indicate that aggregates are formed: the liquid state was used to measure the equilibrium dimer formation constant (30 ± 40 M−1 at 298 K); the solid state was used to estimate the distance (19.3 A) between the two aminoxyl groups in the dimer. A single crystal X-ray examination reveals that there is short-range intermolecular hydrogen bonding between aminoxyl and carboxylic groups, and that the aminoxyl groups are separated by 10.2 A. However, it is concluded from the EPR spectral evidence that, in toluene solution, the dimers are formed by hydrogen bonding between pairs of carboxylic groups. Using the molecular dimensions determined by X-ray analysis, the distance between the aminoxyl groups in the dimer in frozen solution was estimated to be 17 A.}, number={7}, journal={J. Chem. Soc., Perkin Trans. 2}, publisher={Royal Society of Chemistry (RSC)}, author={Bottle, Steven E. and Gillies, Duncan G. and Hughes, David L. and Micallef, Aaron S. and Smirnov, Alex I. and Sutcliffe, Leslie H.}, year={2000}, pages={1285–1291} }
 @article{belton_sutcliffe_gillies_wu_smirnov_1999, title={A new water-soluble and lipid-insoluble spin probe: application to the study of aqueous sucrose solutions}, volume={37}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032590088&partnerID=MN8TOARS}, DOI={10.1002/(sici)1097-458x(199901)37:1<36::aid-mrc405>3.0.co;2-8}, abstractNote={A new ESR spin probe, sodium 1,1,3,3-tetrakis(trideuteromethyl)isoindolin-2- yloxyl-4-sulphonate, which is related to the extensively studied generic free radical 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO), was synthesized. The latter has greater chemical and biochemical stability than any other nitroxyl radical and in low-viscosity media it exhibits near isotropic tumbling motion. It is therefore a very useful spin probe for ESR investigations of (i) microviscosity, (ii) measurements of oxygen concentrations and rates of oxygen diffusion and (iii) ESR imaging experiments. Substituents can be introduced into the basic TMIO radical: here the synthesis of the sulphonated form is described; it has a very high solubility in water, which is important for in vivo biological applications where a low-volume, high-concentration spin probe may need to be injected. In this paper, its use is demonstrated in a study of the microviscosities of aqueous sucrose solutions at concentrations up to 65% and over a range of temperatures. General assumptions were tested concerning the effect of inhomogeneous broadening from unresolved proton hyperfine coupling constants on the calculations of rotational correlation times. For this purpose, the well known spin probes Fremy' salt (peroxylamine disulphonate) and di-tert-butyl nitroxide were used. The ESR results are compared with those from previous NMR relaxation studies of aqueous sucrose solutions. © 1999 John Wiley & Sons, Ltd.}, number={1}, journal={Magn. Reson. Chem.}, publisher={Wiley-Blackwell}, author={Belton, Peter S. and Sutcliffe, Leslie H. and Gillies, Duncan G. and Wu, Xiaoping and Smirnov, Alex I.}, year={1999}, month={Jan}, pages={36–42} }
 @article{belton_sutcliffe_gillies_wu_smirnov_1999, title={A new water‐soluble and lipid‐insoluble spin probe: application to the study of aqueous sucrose solutions}, volume={37}, DOI={10.1002/(sici)1097-458x(199901)37:1<36::aid-mrc405>3.3.co;2-#}, number={1}, journal={Magn. Reson. Chem.}, publisher={Wiley-Blackwell}, author={Belton, Peter S. and Sutcliffe, Leslie H. and Gillies, Duncan G. and Wu, Xiaoping and Smirnov, Alex I.}, year={1999}, month={Jan}, pages={36–42} }
 @article{rapoport_smirnov_pitt_timoshin_1999, title={Bioreduction of Tempone and Spin-Labeled Gentamicin by Gram-Negative Bacteria: Kinetics and Effect of Ultrasound}, volume={362}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033557094&partnerID=MN8TOARS}, DOI={10.1006/abbi.1998.1020}, abstractNote={The primary objective of this study is the investigation of bioreduction kinetics of hydrophilic spin probes, 2,2,6,6, -tetramethyl-4-oxo-piperidinyl-1-oxyl (Tempone), and spin-labeled antibiotic gentamicin by gram-negative bacteria maintained at various oxygen tensions, with emphasis on the effect of probe penetration rate. This information was used to evaluate the effect of ultrasound on the penetration of hydrophilic compounds, including antibiotics, into Pseudomonas aeruginosa and Escherichia coli cells. Penetration of spin-labeled compounds into the cells was assessed by the reduction rate of the nitroxyl moiety measured by EPR. In cell suspensions, both Tempone and spin-labeled gentamicin were localized predominantly in the aqueous phase surrounding the cells. However, a gradual reduction of the probes in contact with the cells indicated that the probes penetrated through the outer membrane and periplasmic space into the cytoplasmic membrane, where the electron transport chains and other metabolic activities of gram-negative bacteria are localized. The kinetics of probe reduction depended on oxygen tension and presence of electron transport chain blockers. It was found that probe penetration rate through the outer cell membrane affected the rate of probe reduction; damaging the permeability barrier by cell incubation with EDTA or by powerful insonation above the cavitation threshold increased the rate of probe reduction. In contrast, insonation below the cavitation threshold did not affect the rate of probe reduction. These findings imply that the recently observed synergistic effect between hydrophilic antibiotics and low frequency ultrasound in killing gram-negative bacteria did not result from the enhanced antibiotic penetration through bacterial cell walls.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Rapoport, Natalya and Smirnov, Alex I. and Pitt, William George and Timoshin, Alexander A.}, year={1999}, month={Feb}, pages={233–241} }
 @article{smirnova_smirnov_belford_clarkson_1999, title={Interaction of Gd(III) MRI contrast agents with membranes: A review of recent EPR studies}, volume={8}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032850878&partnerID=MN8TOARS}, DOI={10.1016/S1352-8661(99)00031-9}, number={3}, journal={Magnetic Resonance Materials in Physics, Biology and Medicine}, author={Smirnova, T.I. and Smirnov, A.I. and Belford, R.L. and Clarkson, R.B.}, year={1999}, pages={214–229} }
 @article{smirnova_smirnov_belford_clarkson_1999, title={Interaction of Gd(III) MRI contrast agents with membranes: a review of recent EPR studies}, volume={8}, DOI={10.1007/bf02594601}, number={3}, journal={MAGMA}, publisher={Springer Science \mathplus Business Media}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Belford, R. L. and Clarkson, R. B.}, year={1999}, month={Aug}, pages={214–229} }
 @article{smirnov_belford_morse_1999, title={Magnetic resonance imaging in a hands-on student experiment using an EPR spectrometer}, volume={11}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033435065&partnerID=MN8TOARS}, DOI={10.1002/(sici)1099-0534(1999)11:5<277::aid-cmr1>3.0.co;2-6}, abstractNote={Many modern medical diagnostic techniques, including magnetic resonance imaging (MRI) and computed tomography, are based on image reconstruction from projections. Unfortunately, the high cost of acquiring, maintaining, and operating MRI equipment makes it unavailable for hands-on undergraduate student laboratory experiments. Here, we describe a laboratory module for teaching the principles of MRI. It is based on a minor modification of an ordinary continuous wave electron paramagnetic resonance spectrometer. By applying magnetic field gradients, students learn the basic principles of MRI and practice with samples made from stable free radicals and a roasted coffee bean. The value of this laboratory experiment is to connect magnetic resonance spectroscopy with its application in imaging and to provide students with hands-on experience in the basics of computer-assisted tomography. ©1999 John Wiley & Sons, Inc. Concepts Magn Reson 11: 277–290, 1999}, number={5}, journal={Concepts Magn. Reson.}, publisher={Wiley-Blackwell}, author={Smirnov, A.I. and Belford, R.L. and Morse, R.}, year={1999}, pages={277–290} }
 @article{smirnov_belford_1999, title={Magnetic resonance imaging in a hands‐on student experiment using an EPR spectrometer}, volume={11}, DOI={10.1002/(sici)1099-0534(1999)11:5<277::aid-cmr1>3.3.co;2-y}, abstractNote={Many modern medical diagnostic techniques, including magnetic resonance imaging (MRI) and computed tomography, are based on image reconstruction from projections. Unfortunately, the high cost of acquiring, maintaining, and operating MRI equipment makes it unavailable for hands-on undergraduate student laboratory experiments. Here, we describe a laboratory module for teaching the principles of MRI. It is based on a minor modification of an ordinary continuous wave electron paramagnetic resonance spectrometer. By applying magnetic field gradients, students learn the basic principles of MRI and practice with samples made from stable free radicals and a roasted coffee bean. The value of this laboratory experiment is to connect magnetic resonance spectroscopy with its application in imaging and to provide students with hands-on experience in the basics of computer-assisted tomography. ©1999 John Wiley & Sons, Inc. Concepts Magn Reson 11: 277–290, 1999}, number={5}, journal={Concepts Magn. Reson.}, publisher={Wiley-Blackwell}, author={Smirnov, Alex I. and Belford, R. L.}, year={1999}, pages={277–290} }
 @article{kurth_brown_smirnov_reiter_stevenson_1999, title={Solution Electron Affinity Perturbation Due to the Deuteration of [16]Annulene}, volume={103}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000987091&partnerID=MN8TOARS}, DOI={10.1021/jp992794d}, abstractNote={X-Band (9.8 GHz) EPR measurements show that the free energy change controlling the electron transfer from the anion radical of perdeuterated [16]annulene to neutral [16]annulene (C16D16•- + C16H16 ⇋ C16H16•- + C16D16) is ΔG° = −0.65 kcal/mol. When supplied with vibrational frequencies from B3LYP/6-31+G* calculations, the QUIVER program determines a ΔG° value of −0.142 kcal/mol. Thus, the experimental and theoretical values are in qualitative agreement. This result is the opposite of that obtained for the [8]annulene system, where the solution electron affinity of C8D8 proved to be slightly greater that that for C8H8. 1H NMR (400 MHz) experiments reveal that the barrier to ring flattening is greater in the C16D16 system than in the C16H16 system. Coupled with the DFT prediction that the C16D16•- is nearly planar, this accounts for the equilibrium isotope effect observed in the electron transfer. The W-Band (94 GHz) EPR spectra, showing that the isotropic g-factor of the [16]annulene anion radical is not altered via perdeuteration, further support a nearly planar C16D16•-. The DFT calculations also predict that the dianion of [16]annulene is completely planar. However, deuteration of all but one of the hydrogens in C16H162- results in an upfield chemical shift of 0.086 ppm for the internal proton resonance at 153 K. This increase in ring current (π-delocalization) is accounted for in terms of a CCC bond angle (σ-framework) relaxation, as shorter CD bonds attenuate the internal steric interactions in C16D15H2-.}, number={42}, journal={J. Phys. Chem. A}, publisher={American Chemical Society (ACS)}, author={Kurth, Todd L. and Brown, Eric C. and Smirnov, Alex I. and Reiter, Richard C. and Stevenson, Cheryl D.}, year={1999}, month={Oct}, pages={8566–8572} }
 @article{venturelli_nilges_smirnov_belford_francesconi_1999, title={Synthesis and characterization of ReV, ReVI and ReVII complexes of the [α2-P2W17O61]10– isomer }, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33846947615&partnerID=MN8TOARS}, DOI={10.1039/a805286g}, abstractNote={Rhenium-(V), -(VI) and -(VII) complexes of the [α2-P2W17O61]10– isomer, a mono-lacunary derivative of the [α-P2W18O62]6– (Wells–Dawson) ion have been prepared and characterized by multinuclear NMR spectroscopy, electrospray mass spectrometry and electron paramagnetic resonance spectroscopy, among other techniques. The molecules have the formulation [α2-ReOP2W17O61]n–, where n = 7,6,5 for ReV, ReVI and ReVII, respectively. 183W NMR spectroscopy for the ReV and ReVII analogs shows that the molecules have Cs symmetry, as expected for substitution in the α2 site. Simulations of the X-band and Q-band EPR spectra of the ReVI analog, using Cs symmetry, allow determination of the g, hyperfine and quadrupole coupling tensors. X-Band, Q-band and W-band EPR spectroscopy show extreme variations in linewidths due to random strains or distortions of the complex.}, number={3}, journal={J. Chem. Soc., Dalton Trans.}, publisher={Royal Society of Chemistry (RSC)}, author={Venturelli, Anne and Nilges, Mark J. and Smirnov, Alex and Belford, R. L. and Francesconi, Lynn C.}, year={1999}, pages={301} }
 @book{smirnov_nilges_belford_clarkson_1998, title={Coal and Coal Constituent Studies by Advanced EMR Techniques}, DOI={10.2172/2106}, abstractNote={Advanced electronic magnetic resonance (EMR) methods are used to examine properties of coals, chars, and molecular species related to constituents of coal. We have achieved substantial progress on upgrading the high field (HF) EMR (W-band, 95 GHz) spectrometers that are especially advantageous for such studies. Particularly, we have built a new second W-band instrument (Mark II) in addition to our Mark I. Briefly, Mark II features: (i) an Oxford custom-built 7 T superconducting magnet which is scannable from 0 to 7 T at up to 0.5 T/min; (ii) water-cooled coaxial solenoid with up to ±550 G scan under digital (15 bits resolution) computer control; (iii) custom-engineered precision feed-back circuit, which is used to drive this solenoid, is based on an Ultrastab 860R sensor that has linearity better than 5 ppm and resolution of 0.05 ppm; (iv) an Oxford CF 1200 cryostat for variable temperature studies from 1.8 to 340 K. During this grant period we have completed several key upgrades of both Mark I and II, particularly microwave bridge, W-band probehead, and computer interfaces. We utilize these improved instruments for HF EMR studies of spin-spin interaction and existence of different paramagnetic species in carbonaceous solids.}, institution={Office of Scientific and Technical Information (OSTI)}, author={Smirnov, Alex I. and Nilges, Mark J. and Belford, R. Linn and Clarkson, Robert B.}, year={1998}, month={Mar} }
 @article{nilges_smirnov_clarkson_belford_1998, title={Electron paramagnetic resonance W-band spectrometer with a low-noise amplifier}, volume={16}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032252841&partnerID=MN8TOARS}, number={2}, journal={Applied Magnetic Resonance}, author={Nilges, M.J. and Smirnov, A.I. and Clarkson, R.B. and Belford, R.L.}, year={1998}, pages={167–183} }
 @article{smirnova_smirnov_belford_clarkson_1998, title={Lipid Magnetic Resonance Imaging Contrast Agent Interactions:  A Spin-Labeling and a Multifrequency EPR Study}, volume={120}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032572062&partnerID=MN8TOARS}, DOI={10.1021/ja973427n}, abstractNote={The interactions of two lipophilic magnetic resonance imaging paramagnetic contrast agents, gadolinium complexes of 1,4,7,10-tetraazacyclododecane-N-(n-pentyl)-N‘,N‘‘,N‘‘‘-triacetic acid (Gd-DOTAP) and 3,6,9-triaza-3,6,9-tris(carboxymethyl)-4-(4-ethoxybenzyl)undecandicarboxylic acid (Gd-EOB-DTPA), with model multilamellar liposomes prepared from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were assessed in three sets of EPR experiments. The first two experiments were carried out with phospholipids selectively labeled with a series of spin-labeled doxyl stearic acids. By means of counting the collisions of molecular oxygen with a spin-labeled site, local oxygen permeability across the bilayer was measured with the contrast agents present and compared with control experiments in which contrast agents were absent. The maximum increase of 6.5 ± 0.3% for oxygen permeability at 20 mM Gd-DOTAP concentration was observed at 30.8 °C for the label located at the twelfth carbon position of the acyl chain. This result implied that Gd-DOTAP partitions within the DMPC bilayer, its preferred location being close to the bilayer center, and that the overall effect of Gd-DOTAP on the structural organization of the membrane is rather small. In contrast, no significant changes in local oxygen permeability were observed for Gd-EOB-DTPA. In the second set of spin-labeling experiments, the broadening of the spin-label spectra in the presence of Gd-DOTAP was measured as a function of position of the label across the bilayer. Again, maximum broadening was observed for the center of the bilayer, confirming the preferred location of this contrast agent. The third set of experiments utilized EPR spectroscopy of solutions of Gd3+ complexes at multiple high magnetic fields (corresponding microwave frequencies from 35 to 249 GHz). At these fields, Gd3+ serves as a useful probe to report on the microenvironment. Partitioning of Gd-DOTAP in DMPC liposomes resulted in partially resolved EPR spectra at 35 and 94.3 GHz. EPR experiments at multiple high fields (35, 94.3, and 249 GHz) show that the variation in spectral resolution observed across this frequency range arises from, first, line narrowing due to a decreased relative contribution of the zero field splitting (ZFS) in the spin Hamiltonian and, second, the shift of the resonance signal due to remaining ZFS effects. The frequency dependence of the apparent g-factor at multiple high magnetic fields as analyzed with third-order perturbation theory demonstrates a relationship between the observed shifts and the ZFS parameter. The analysis shows that Δ, the square root of the trace of the squared ZFS matrix, increases to 8.1 rad GHz when Gd-DOTAP partitions in the lipid phase of DMPC liposomes, up from 5.65 rad GHz for the aqueous phase. The high-field EPR method provides a direct measure of the populations of Gd complexes in various environments as well as an estimate of ZFS parameters in solutions.}, number={20}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Belford, R. L. and Clarkson, R. B.}, year={1998}, month={May}, pages={5060–5072} }
 @article{clarkson_smirnov_smirnova_kang_belford_earle_freed_1998, title={Multi-frequency EPR determination of zero field splitting of high spin species in liquids: Gd(III) chelates in water}, volume={95}, ISSN={0026-8976 1362-3028}, url={http://dx.doi.org/10.1080/00268979809483262}, DOI={10.1080/00268979809483262}, abstractNote={Multi-frequency EPR spectroscopy at 9.5, 35, 94, and 249 GHz has been employed to investigate the zero field splitting (ZFS) of high spin ions in liquids. In particular, experiments are reported on aqueous solutions of DTPA and DOTA chelates of Gd(III), and on the uncomplexed ion, which are relevant to the effectiveness of paramagnetic contrast agents for magnetic resonance imaging (MRI). The field dependence of the centroid of the resonance line, characterized by an effective g factor, geff, has been analysed in order to determine δ1, the trace of the square of the ZFS matrix. Analysis of the variation in transverse electron spin relaxation (T 2e) with experimental frequency provides yet another route to measure δ2 from EPR data. This analysis also gives δv, a correlation time describing the time-dependent ZFS effect. The ZFS parameters so obtained agree well with results obtained by the analysis of proton nuclear magnetic relaxation dispersion. At 94 GHz, partially resolved spectra from chelated and unchelated Gd(III) were observed. The shifts in resonance field for Gd(III) in these two compounds are due primarily to differences in the magnitude of ZFS. The spectral resolution as a function of frequency exhibits a maximum in the range of our experiments; the resolution disappeared at either higher or lower resonance frequency. Study of ZFS by EPR at multiple high fields offers a new and sensitive route to probe water interactions and chelate dynamics in biologically relevant systems having high spin ions.}, number={6}, journal={Molecular Physics}, publisher={Informa UK Limited}, author={Clarkson, R. B. and Smirnov, Alex I. and Smirnova, T. I. and Kang, H. and Belford, R. L. and Earle, K. and Freed, Jack H.}, year={1998}, month={Dec}, pages={1325–1332} }
 @article{rapoport_smirnov_timoshin_pratt_pitt_1997, title={Factors Affecting the Permeability ofPseudomonas aeruginosaCell Walls toward Lipophilic Compounds: Effects of Ultrasound and Cell Age}, volume={344}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031215007&partnerID=MN8TOARS}, DOI={10.1006/abbi.1997.0176}, abstractNote={The objective of this research was to elucidate the factors effecting the permeability of cell membranes of gram-negative bacteria toward hydrophobic compounds. Ultrasound treatment, cell age, and the phase state of phospholipid membranes were considered. Spin-labeling EPR method was used to quantify the penetration and distribution of a lipophilic spin probe, 16-doxylstearic acid (16-DS), in Pseudomonas aeruginosa cell membranes. This bacterium was chosen because of its reported resistance to the action of hydrophobic antibiotics caused by the low permeability of the outer cell membrane for hydrophobic compounds. EPR spectra were collected from cell pellets and cell lysates. The overall spin probe uptake was measured in 10% SDS-cell lysates. Lysis with 0.6% SDS revealed the fraction of the probe located in membrane sites readily accessible to the surfactant. The results indicated a structural heterogeneity of P. aeruginosa membranes, with the presence of structurally "stronger" and "weaker" sites characterized by different susceptibility to the SDS treatment. The intracellular concentration of 16-DS was higher in insonated cells and increased linearly with the sonication power. EPR spectra indicated that ultrasound enhanced the penetration of the probe into the structurally stronger sites of the inner and outer cell membranes. The effect of ultrasound on the cell membranes was transient in that the initial membrane permeability was restored upon termination of the ultrasound treatment. These results suggest that the resistance of gram-negative bacteria to the action of hydrophobic antibiotics was caused by a low permeability of the outer cell membranes. This resistance may be reduced by the simultaneous application of antibiotic and ultrasound. This hypothesis was confirmed in our experiments with P. aeruginosa exposed to erythromycin.}, number={1}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Rapoport, Natalya and Smirnov, Alex I. and Timoshin, Alexander and Pratt, Andrea M. and Pitt, William George}, year={1997}, month={Aug}, pages={114–124} }
 @article{smirnova_smirnov_clarkson_belford_kotake_janzen_1997, title={High-Frequency (95 GHz) EPR Spectroscopy To Characterize Spin Adducts}, volume={101}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001390213&partnerID=MN8TOARS}, DOI={10.1021/jp963066i}, abstractNote={EPR spin-trapping experiments are usually carried out at X-band (9.5 GHz) because of the good concentration sensitivity and ready availability of this method. The radical precursors are then characterized from an analysis of isotropic hyperfine coupling and comparison of these coupling factors with those for the reference spin adducts. These experiments encounter two major challenges:  (i) spin adducts from many carbon-centered free radicals have g factors that are nearly the same (resulting in strongly overlapping spectra at 9.5 GHz), and (ii) measurable hyperfine couplings correspond to interactions of the electron spin with just the nearest nuclei. Therefore, very little or no information is obtained on the overall structure of the spin adduct molecule. Some of these difficulties can be overcome by carrying out spin-trapping experiments at 10-fold higher frequency, 95 GHz (W-band). Examples of two spin adducts with nearly the same isotropic g factors (Δgiso = 1.2 × 10-4) are the benzene solutions of ph...}, number={19}, journal={J. Phys. Chem. B}, publisher={American Chemical Society (ACS)}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Clarkson, R. B. and Belford, R. L. and Kotake, Y. and Janzen, E. G.}, year={1997}, month={May}, pages={3877–3885} }
 @article{smirnova_smirnov_belford_clarkson_jeevarajan_jeevarajan_hand_roos_vallance_wood_1997, title={Interaction of MRI Gadolinium Contrast Agents with Phospholipid Bilayers as Studied by 95 GHz EPR.}, volume={51}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031137466&partnerID=MN8TOARS}, DOI={10.3891/acta.chem.scand.51-0562}, abstractNote={Interactions of two MRI gadolinium contrast agents, gadolinium ethoxybenzyl-diethylenetriaminepentaacetate (Gd-EOB-DTPA) and gadolinium N-pentyl-1,4,7,10-tetraazacyclododecane-N',N",N'"- triacetic acid (Gd-DOTA-P), with multibilayer phospholipid dispersions prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) have been investigated with high resolution EPR spectroscopy at 95 GHz. At a resonance field of 3.3 T, EPR spectra of a small nitroxide probe, 2,2,6,6-tetramethyl-1-piperidinyloxyl (Tempo), partitioned between aqueous and membrane phases are clearly resolved, making measurements of dynamics parameters of the probe accurate and unambiguous. Results show that although the presence of the more lipophilic contrast agent, Gd-DOTA-P, can be detected within the bilayer, the structural organization of the membrane remains unaffected even at physiologically high (5 mM) concentrations. The temperature of the main phase transition of the bilayer was also unaffected to within the 0.4 degree C accuracy of its determination.}, number={5}, journal={Acta Chem. Scand.}, publisher={Danish Chemical Society}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Belford, R. L. and Clarkson, R. B. and Jeevarajan, A. S. and Jeevarajan, J. A. and Hand, E. and Roos, Björn O. and Vallance, Claire and Wood, Bryan R.}, year={1997}, pages={562–566} }
 @article{britton_fawthrop_gillies_sutcliffe_wu_smirnov_1997, title={Matched spin probes for the study of the overall motion of model lubricants}, volume={35}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000449627&partnerID=MN8TOARS}, DOI={10.1002/(SICI)1097-458X(199708)35:8<493::AID-OMR121>3.0.CO;2-I}, abstractNote={For ESR studies of molecular rotation in liquids, it is desirable to match the spin probe as closely as possible to the solvent molecules. In this work the solvents were model lubricants whose overall motion has been characterized from carbon-13 NMR relaxation measurements. Two compounds were studied, the approximately cylindrical mol-ecule 5-(n-octyl)naphthalene (ON) (a model low-traction fluid) and the approximately spherical molecule dicyclohexy-3,4-furan dicarboxylate (DCFDC) (a model high-traction fluid). For these two compounds the matched spin probes 5-(n-octyl)-1,1,13,3-tetrakis(trideuteriomethyl)isoindolin-2-yloxyl (OTMIOD) and 4,5-bis(cyclohexyloxycarbonyl)-1,3,2-dithiazol-2-yl (BCCD), respectively, were prepared. ESR measurements were made on OTMIOD in ON and in toluene at two frequencies, namely 9 GHz (X band) and 94 GHz (W band), and the importance of making the high-frequency measurements was demonstrated for evaluation of the anisotropy parameters. The results are different for the two solvents, thus proving the necessity for matching the spin probe to the solvent. BCCD was shown to be tumbling isotropically in DCFDC. Activation energies were derived for the overall motions from the ESR and NMR measurements. These activation energies were compared with those for the viscosities of the solvents. The viscosities of both ON and DCFDC were measured over a wide temperature range using an ESR method. © 1997 John Wiley & Sons, Ltd.}, number={8}, journal={Magnetic Resonance in Chemistry}, author={Britton, M.M. and Fawthrop, S.A. and Gillies, D.G. and Sutcliffe, L.H. and Wu, X. and Smirnov, A.I.}, year={1997}, pages={493–501} }
 @article{hustedt_smirnov_laub_cobb_beth_1997, title={Molecular distances from dipolar coupled spin-labels: The global analysis of multifrequency continuous wave electron paramagnetic resonance data}, volume={72}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0030950516&partnerID=MN8TOARS}, DOI={10.1016/S0006-3495(97)78832-5}, abstractNote={For immobilized nitroxide spin-labels with a well-defined interprobe geometry, resolved dipolar splittings can be observed in continuous wave electron paramagnetic resonance (CW-EPR) spectra for interelectron distances as large as 30 A using perdeuterated probes. In this work, algorithms are developed for calculating CW-EPR spectra of immobilized, dipolar coupled nitroxides, and then used to define the limits of sensitivity to the interelectron distance as a function of geometry and microwave frequency. Secondly, the CW-EPR spectra of N epsilon-spin-labeled coenzyme NAD+ bound to microcrystalline, tetrameric glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been collected at 9.8, 34, and 94 GHz. These data have been analyzed, using a combination of simulated annealing and global analysis, to obtain a unique fit to the data. The values of the intermitroxide distance and the five angles defining the relative orientation of the two nitroxides are in reasonable agreement with a molecular model built from the known crystal structure. Finally, the effect of rigid body isotropic rotational diffusion on the CW-EPR spectra of dipolar coupled nitroxides has been investigated using an algorithm based on Brownian dynamics trajectories. These calculations demonstrate the sensitivity of CW-EPR spectra to dipolar coupling in the presence of rigid body rotational diffusion.}, number={4}, journal={Biophysical Journal}, author={Hustedt, E.J. and Smirnov, A.I. and Laub, C.F. and Cobb, C.E. and Beth, A.H.}, year={1997}, pages={1861–1877} }
 @article{dalal_smirnov_belford_1997, title={Quantification of coal-diesel particulate mixtures by W-band (94-GHz) electron spin resonance spectroscopy}, volume={51}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031221244&partnerID=MN8TOARS}, DOI={10.1366/0003702971942178}, number={9}, journal={Applied Spectroscopy}, author={Dalal, N.S. and Smirnov, A.I. and Belford, R.L.}, year={1997}, pages={1429–1431} }
 @article{dalal_smirnov_smirnova_belford_katritzky_belyakov_1997, title={Single-Crystal Multifrequency EPR Evidence for a Quasi-Low-Dimensional Spin Exchange in 3- n -Butyl-2,4,6-Triphenylverdazyl}, volume={101}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031365794&partnerID=MN8TOARS}, DOI={10.1021/jp973023h}, abstractNote={Verdazyls, 1,2,3,4-tetrahydro-s-tetrazin-1-(2H-yls), are a series of stable organic free radicals some of which in solid form exhibit ferromagnetism and spin-Peierls transitions. Molecular mechanisms responsible for these properties remain somewhat unclear. This study reports on the growth of single crystals of several substituted verdazyls and multifrequency (1.4−94.3 GHz) EPR measurements on single crystals of 3-n-butyl-2,4,6-triphenylverdazyl, a model compound in the series. The angular, temperature, and magnetic field dependence of the EPR line width and the temperature dependence of the g-factor anisotropy provide direct evidence of a pseudo-low-dimensional spin diffusion in the crystal lattice. Analysis of the EPR line width for the crystal, oriented with the c-axis at the magic angle, θ ≈ 54.7° with respect to the external magnetic field, indicates a weak logarithmic dependence upon the frequency of the EPR experiment typical for a quasi-two-dimensional spin system.}, number={51}, journal={J. Phys. Chem. B}, publisher={American Chemical Society (ACS)}, author={Dalal, N. S. and Smirnov, Alex I. and Smirnova, Tatyana I. and Belford, R. L. and Katritzky, A. R. and Belyakov, S. A.}, year={1997}, pages={11249–11253} }
 @article{smirnov_clarkson_belford_1996, title={EPR Linewidth (T2) Method to Measure Oxygen Permeability of Phospholipid Bilayers and Its Use to Study the Effect of Low Ethanol Concentrations}, volume={111}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0030139747&partnerID=MN8TOARS}, DOI={10.1006/jmrb.1996.0073}, abstractNote={It is well known that continuous-wave EPR spectra of nitroxide probes (labels) introduced into phospholipid bilayers are sensitive to molecular oxygen. However, accurate determination of oxygen broadening from these experiments is complicated by the complex shapes of EPR spectra, which are strongly influenced by anisotropic restricted motion of the probe molecules. An accurate method is presented to extract the oxygen broadening from the spectra measured with and without oxygen and at the same temperature. The method is based on a fast convolution algorithm with Levenberg–Marquardt optimization. This method was previously applied to EPR oximetry with nitroxides exhibiting rotational motion in the fast limit. It is shown that for several membrane spin probes, the oxygen broadening can be described as homogeneous; thus, a one-linewidth-parameter fitting model is appropriate. The method is applied to measure permeability profiles of model membranes composed from 1,2-dimyristoyl-sn-glycero-3-phosphocholine above and below the main phase transition. For both membrane phases, the broadening of doxyl- and sterol-type labels is found to be homogeneous, a finding consistent with the model of Heisenberg exchange between molecular oxygen and spin probes. As an example, the method is applied to study the ethanol effect on local oxygen permeability of a phospholipid bilayer. It is shown that ethanol concentrations as low as 1% (v/v) increase oxygen permeability of the bilayer. The effect is larger at the surface of the membrane than at its center, indicating that ethanol molecules interact primarily within the polar head region of the bilayer.}, number={2}, journal={Journal of Magnetic Resonance, Series B}, publisher={Elsevier BV}, author={Smirnov, Alex I. and Clarkson, R.B. and Belford, R.L.}, year={1996}, month={May}, pages={149–157} }
 @article{smirnova_smirnov_clarkson_belford_1995, title={Accuracy of Oxygen Measurements inT2 (Line Width) EPR Oximetry}, volume={33}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0029034106&partnerID=MN8TOARS}, DOI={10.1002/mrm.1910330610}, abstractNote={EPR oximetry is used for in vivo and in vitro measurements of oxygen in biological systems, including experimental animals. The accuracy of oxygen measurements in T2 (line width) EPR oximetry is significantly improved if least-squares simulation is used to extract the line width parameters. The oxygen effect on the EPR spectra of nitroxide solutions and aqueous suspensions of fusinite can be described as an additional homogeneous broadening that modifies the EPR spectrum of the oxygen-free probe. This allows one to use a one-parameter line width model in most cases. The simulations were carried out with the use of a fast-convolution algorithm followed by Levenberg-Marquardt optimization. The validity of error estimates provided by this method was tested on sets of experimental spectra taken under common conditions. It is shown that the accuracy of oxygen measurements in line width (T2) oximetry is determined not only by the probe sensitivity (rate of line width change versus oxygen concentration), but also by the signal-to-noise ratio, inhomogeneous contribution to the line shape (e.g., unresolved proton superhyperfine structure), and the spectral window. The accuracy of oxygen measurements is compared for aqueous solutions of two nitroxide radicals with different superhyperfine structure and for aqueous suspensions of fusinite.}, number={6}, journal={Magn. Reson. Med.}, publisher={Wiley-Blackwell}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Clarkson, Robert B. and Belford, R. Linn}, year={1995}, month={Jun}, pages={801–810} }
 @article{clarkson_norby_smirnov_boyer_vahidi_nims_wink_1995, title={Direct measurement of the accumulation and mitochondrial conversion of nitric oxide within Chinese hamster ovary cells using an intracellular electron paramagnetic resonance technique}, volume={1243}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0028938258&partnerID=MN8TOARS}, DOI={10.1016/0304-4165(94)00181-V}, abstractNote={We have developed an electron paramagnetic resonance (EPR) method for the nondestructive detection and quantification of intracellular NO in real time. Based upon this technique, we have obtained evidence for the metabolism of this bioregulatory molecule by mitochondria. Line-broadening of the EPR signal of a coal derivative, fusinite, was calibrated as a function of NO concentration in aqueous solution. The methodology was validated using two compounds which release NO in a controlled and predictable manner with first-order rate constants k1 = 5.0 x 0.10(-3) s-1 and k'1 = 3.4 x 10(-4) s-1 (35 degrees C). Fusinite was internalized in Chinese hamster ovary cells (CHO) by phagocytosis, after which the cells were allowed to consume the available O2, producing an hypoxic environment. The NO released from one of the NO donors, added to the culture fluid at an initial concentration of 50 microM, was directly measured in the intracellular environment as line-broadening of the fusinite EPR signal. The linewidth diminished with time, indicating that NO was being converted to a non-paramagnetic species by the cells with an apparent zero-order rate constant of 5 x 10(8) NO molecules cell-1 min-1 (20 degrees C). Addition of cyanide to the culture medium (5 mM final concentration) inhibited this disappearance of NO. NO also was converted in the presence of isolated mitochondria in the absence of oxygen. These observations suggest that under hypoxic conditions, there exists in CHO cells a metabolic pathway for the conversion of NO to diamagnetic species, which involves interactions with mitochondria.}, number={3}, journal={BBA - General Subjects}, author={Clarkson, R.B. and Norby, S.W. and Smirnov, A. and Boyer, S. and Vahidi, N. and Nims, R.W. and Wink, D.A.}, year={1995}, pages={496–502} }
 @article{smirnov_belford_1995, title={Rapid Quantitation from Inhomogeneously Broadened EPR Spectra by a Fast Convolution Algorithm}, volume={113}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-58149212601&partnerID=MN8TOARS}, DOI={10.1006/jmra.1995.1057}, abstractNote={An inhomogeneous lineshape model based on a convolution of Gaussian and Lorentzian functions is very common in EPR spectroscopy. For convenience, the convolution integral often is approximated by a sum of Gaussian and Lorentzian functions. A more accurate and general approach to linewidth simulation and fitting by use of a fast convolution algorithm is described. A Levenberg-Marquardt method is applied in the multidimensional optimization of simulation parameters. The partial-derivative matrix required for the Levenberg-Marquardt procedure is calculated without digital differentiation. To account for a microwave shift observed in 94 and 1.1 GHz EPR experiments, a dispersion parameter is included in the fitting function. All fitting parameters, including Lorentzian and Gaussian components to the linewidth, microwave phase shift, resonance position, and intensity, are extracted from experimental spectra directly. A fixed and/or variable superhyperfine pattern (or envelope function) may be included in the fitting procedure without a significant increase in computational time. Three examples of this technique are shown: extraction of Lorentzian broadening for a nitroxide EPR spectrum at various oxygen concentrations, penetration of a 1.1 GHz microwave field into a lossy dielectric sample, and processing of a mixed absorption-dispersion nitroxide 94 GHz EPR spectrum in the fast-motion limit.}, number={1}, journal={Journal of Magnetic Resonance, Series A}, author={Smirnov, A.I. and Belford, R.L.}, year={1995}, pages={65–73} }
 @article{morse_smirnov_1995, title={Simultaneous ESR measurements of the kinetics of oxygen consumption and spin label reduction by mammalian cells}, volume={33}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0039963555&partnerID=MN8TOARS}, DOI={10.1002/mrc.1260331309}, abstractNote={Nitroxide spin labels and probes were applied to measurements of cell redox activities and oxygen concentration by ESR. Current experimental methods often require large numbers of cells and monitoring of only the amplitude of the ESR signal. This can result in experimental artifacts and data misinterpretation. An improved method is described for accurate measurement of nitroxide intensity and linewidth, which in turn provides information about cell redox activities and oxygen concentration. The method is based on fitting of ESR spectra using a fast convolution least-squares algorithm suitable for inhomogeneously broadened ESR lines. All fitting parameters, including the Lorentzian component of the linewidth and the double integrated intensity, are extracted from the experimental spectra directly. The experiments were carried out at cell concentrations of 5 × 106 cell ml−1 or less to prevent cell crowding and at initial nitroxide concentration of 1 mM or 100 μM to ensure that nitroxide metabolism by the cells was not diffusion limited. Examples include experiments with cultured baby hamster kidney and adenovirus transformed hamster cells using the nitroxide radicals TEMPOL (2,2,6,6-tetramethylpiperidine-N-oxyl-4-ol) and 15N-labeled perdeuteriated TEMPONE (15NPDT) (2,2,6,6-tetramethylpiperidine-N-oxyl-4-one). Under these experimental conditions, the rates of nitroxide metabolism derived from changes in nitroxide intensity are independent of oxygen concentration.}, number={13}, journal={Magn. Reson. Chem.}, publisher={Wiley-Blackwell}, author={Morse, Philip D. and Smirnov, Alex I.}, year={1995}, pages={S46–S52} }
 @article{ahn_smirnov_smirnova_belford_1995, title={Superconducting Quantum Interference Device Magnetic Susceptibility Measurements: Determination of Free-Radical Concentrations in PMR-15 Polyimide Resin}, volume={28}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0039317043&partnerID=MN8TOARS}, DOI={10.1021/ma00124a047}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSuperconducting Quantum Interference Device Magnetic Susceptibility Measurements: Determination of Free-Radical Concentrations in PMR-15 Polyimide ResinMyong K. Ahn, Alex I. Smirnov, Tatyana I. Smirnova, and R. Linn BelfordCite this: Macromolecules 1995, 28, 20, 7026–7028Publication Date (Print):September 1, 1995Publication History Published online1 May 2002Published inissue 1 September 1995https://doi.org/10.1021/ma00124a047RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (360 KB) Get e-Alerts Get e-Alerts}, number={20}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Ahn, Myong K. and Smirnov, Alex I. and Smirnova, Tatyana I. and Belford, R. Linn}, year={1995}, month={Sep}, pages={7026–7028} }
 @article{smirnov_smirnova_morse_1995, title={Very high frequency electron paramagnetic resonance of 2,2,6,6-tetramethyl-1-piperidinyloxy in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine liposomes: partitioning and molecular dynamics}, volume={68}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0029054719&partnerID=MN8TOARS}, DOI={10.1016/S0006-3495(95)80417-0}, abstractNote={Partitioning and molecular dynamics of 2,2,6,6,-tetramethylpiperedine-1-oxyl (TEMPO) nitroxide radicals in large unilamellar liposomes (LUV) composed from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine were investigated by using very high frequency electron paramagnetic resonance (EPR) spectroscopy. Experiments carried out at a microwave frequency of 94.3 GHz completely resolved the TEMPO EPR spectrum in the aqueous and hydrocarbon phases. An accurate computer simulation method combined with Levenberg-Marquardt optimization was used to analyze the TEMPO EPR spectra in both phases. Spectral parameters extracted from the simulations gave the actual partitioning of the TEMPO probe between the LUV hydrocarbon and aqueous phases and allowed analysis of picosecond rotational dynamics of the probe in the LUV hydrocarbon phase. In very high frequency EPR experiments, phase transitions in the LUV-TEMPO system were observed as sharp changes in both partitioning and rotational correlation times of the TEMPO probe. The phase transition temperatures (40.5 +/- 0.2 and 32.7 +/- 0.5 degrees C) are in agreement with previously reported differential scanning microcalorimetry data. Spectral line widths were analyzed by using existing theoretical expressions for motionally narrowed nitroxide spectra. It was found that the motion of the small, nearly spherical, TEMPO probe can be well described by anisotropic Brownian diffusion in isotropic media and is not restricted by the much larger hydrocarbon chains existing in ripple structure (P beta') or fluid bilayer structure (L alpha) phases.}, number={6}, journal={Biophysical Journal}, author={Smirnov, A.I. and Smirnova, T.I. and Morse, P.D.}, year={1995}, pages={2350–2360} }
 @article{smirnova_smirnov_clarkson_belford_1995, title={W-Band (95 GHz) EPR Spectroscopy of Nitroxide Radicals with Complex Proton Hyperfine Structure: Fast Motion}, volume={99}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000726737&partnerID=MN8TOARS}, DOI={10.1021/j100022a011}, number={22}, journal={J. Phys. Chem.}, publisher={American Chemical Society (ACS)}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Clarkson, R. B. and Belford, R. Linn}, year={1995}, month={Jun}, pages={9008–9016} }
 @article{auteri_belford_boyer_motsegood_smirnov_smirnova_vahidi_clarkson_1994, title={Carbon-based standards for electron paramagnetic resonance spectroscopy}, volume={6}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-21344494866&partnerID=MN8TOARS}, DOI={10.1007/BF03162495}, number={1-2}, journal={Applied Magnetic Resonance}, author={Auteri, F.P. and Belford, R.L. and Boyer, S. and Motsegood, K. and Smirnov, A. and Smirnova, T. and Vahidi, N. and Clarkson, R.B.}, year={1994}, pages={287–308} }
 @article{smirnova_smirnov_clarkson_belford_1994, title={Half-field EPR transitions in synthetic carbohydrate chars}, volume={91}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0028464737&partnerID=MN8TOARS}, DOI={10.1016/0038-1098(94)90309-3}, abstractNote={Abstract Half-field EPR transitions (g = 4.00) were observed in some synthetic carbohydrate chars prepared by heat treatment at temperatures less than 620°C. The half-field line has a lineshape similar to that of the main resonance and about the same intensity at transverse and longitudinal microwave excitation. Its relative intensity decreases with increasing char heat-treatment temperature. In contrast, no g = 4 transitions were detected for chars synthesized at temperatures greater than 620°C. The ratio of intensity of the half-field transition to that of the main resonance is about 10−6 and does not change from 4.5–55K. At 4.5K, the g = 4.00 line has about half of the linewidth of the main resonance. The observed half-field resonance can be explained by the existence of isolated aromatic radical clusters or by a low-dimensional spin-exchange network within the solid.}, number={4}, journal={Solid State Communications}, publisher={Elsevier BV}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Clarkson, R.B. and Belford, R.L.}, year={1994}, month={Jul}, pages={319–323} }
 @article{smirnova_smirnov_clarkson_belford_1994, title={Magnetic Susceptibility and Spin Exchange in Fusinite and Carbohydrate Chars}, volume={98}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000920317&partnerID=MN8TOARS}, DOI={10.1021/j100060a039}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMagnetic Susceptibility and Spin Exchange in Fusinite and Carbohydrate CharsTatyana I. Smirnova, Alex I. Smirnov, R. B. Clarkson, and R. Linn BelfordCite this: J. Phys. Chem. 1994, 98, 9, 2464–2468Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://doi.org/10.1021/j100060a039RIGHTS & PERMISSIONSArticle Views162Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (604 KB) Get e-Alerts}, number={9}, journal={J. Phys. Chem.}, publisher={American Chemical Society (ACS)}, author={Smirnova, Tatyana I. and Smirnov, Alex I. and Clarkson, R. B. and Belford, R. Linn}, year={1994}, month={Mar}, pages={2464–2468} }
 @article{li_weissman_lin_gaspar_cowley_smirnov_1994, title={Observation of a Triplet Phosphinidene by ESR Spectroscopy}, volume={116}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0006169819&partnerID=MN8TOARS}, DOI={10.1021/ja00096a058}, number={17}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Li, Xinhua and Weissman, S. I. and Lin, Tien-Sung and Gaspar, Peter P. and Cowley, Alan H. and Smirnov, Alex I.}, year={1994}, month={Aug}, pages={7899–7900} }
 @article{smirnov_norby_walczak_liu_swartz_1994, title={Physical and Instrumental Considerations in the Use of Lithium Phthalocyanine for Measurements of the Concentration of the Oxygen}, volume={103}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0028373460&partnerID=MN8TOARS}, DOI={10.1006/jmrb.1994.1016}, abstractNote={The use of crystals of lithium phthalocyanine (LiPc) to measure the concentration of oxygen in vivo and in vitro by electron paramagnetic resonance leads to experimental constraints due to the very narrow EPR lines that may occur (as narrow as 11-13 mG in the absence of O2), distortions induced by the automatic frequency control system, anisotropy in the spectra (orientation-dependent linewidth is 11-17 mG in the absence of O2), microwave power saturation, and the effect of physiological motion. These constraints can be overcome if recognized. This article highlights the experimental and theoretical basis of these properties of the EPR signal of LiPc and suggests some technical solutions. It is most important to recognize that paramagnetic species such as LiPc present problems that are not commonly encountered in EPR spectroscopy.}, number={2}, journal={Journal of Magnetic Resonance, Series B}, author={Smirnov, A.I. and Norby, S.-W. and Walczak, T. and Liu, K.J. and Swartz, H.M.}, year={1994}, pages={95–102} }
 @article{smirnov_norby_weyhenmeyer_clarkson_1994, title={The effect of temperature on the respiration of cultured neural cells as studied by a novel electron paramagnetic resonance technique}, volume={1200}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0028358508&partnerID=MN8TOARS}, DOI={10.1016/0304-4165(94)90137-6}, abstractNote={A new technique to study cellular respiration under steady-state conditions is described. For detection of oxygen concentration the technique utilizes lithium phthalocyanine crystals whose, electron paramagnetic resonance (EPR) spectra are highly sensitive to oxygen. A gas permeable poly(tetrafluoroethylene) (TFE) capillary (i.d. = 0.81 mm; o.d. = 0.86 mm) is used to control the oxygen flux to the sample of cultured neural cells (N1E-115) of 50 microliters volume. The measured oxygen permeability of the TFE capillary exhibits Arrhenius law behavior (Ep = 21.2 kJ/mole) in the temperature range 15-43 degrees C. The observed increase in the respiratory rate of the N1E-115 cells with temperature can be described with an apparent activation energy of Ea = 110 +/- 20 kJ/mol. Cellular depolarization with 35 mM KCl increases the respiratory rate of the cells but gives the same activation energy. The results confirm a hypothesis that respiratory depolarizers affect only the total enzyme concentration and do not change the apparent Ea of the substrate-enzyme decomposition reaction. The theoretical treatment of oxygen diffusion in the system provides guidelines for designing steady-state cellular respiration experiments.}, number={2}, journal={Biochimica et Biophysica Acta (BBA) - General Subjects}, publisher={Elsevier BV}, author={Smirnov, Alex I. and Norby, Shong-Wan and Weyhenmeyer, James A. and Clarkson, R.B.}, year={1994}, month={Jul}, pages={205–214} }
 @article{smirnov_norby_clarkson_walczak_swartz_1993, title={Simultaneous multi-site EPR spectroscopyin vivo}, volume={30}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0027312643&partnerID=MN8TOARS}, DOI={10.1002/mrm.1910300210}, abstractNote={A gradient technique to measure electron paramagnetic resonance spectra simultaneously at several different locations is described. The technique is based on the use of point probes containing paramagnetic centers. The value of the magnetic field gradient is chosen to be sufficient to separate the EPR signals from the different paramagnetic probes yet at the same time small enough to change only minimally the shape of individual signals. The conditions to apply this technique are considered in detail. When experimental data have a high signal-to-noise ratio, the lineshape distortion induced by the gradient can be corrected with the aid of a known distribution function of paramagnetic centers within the probe. The maximum entropy deconvolution algorithm is successfully applied for the correction of significantly distorted lines. The technique is experimentally tested and applied to measure the concentration of oxygen in hypertrophied rat myocardium and normal rat kidney in vivo by low frequency EPR (L-band, 1.2 GHz). No types of EPR oxygen-sensitive probes-lithium phthalocyanine crystals and synthetic carbohydrate chars-were used.}, number={2}, journal={Magn. Reson. Med.}, publisher={Wiley-Blackwell}, author={Smirnov, Alex I. and Norby, Shong-Wan and Clarkson, R. B. and Walczak, Ted and Swartz, Harold M.}, year={1993}, month={Aug}, pages={213–220} }
 @article{smirnov_poluectov_lebedev_1992, title={High-field EPR imaging}, volume={97}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0011431422&partnerID=MN8TOARS}, DOI={10.1016/0022-2364(92)90233-w}, abstractNote={Abstract High-field EPR imaging at 5 T (140 GHz) is experimentally demonstrated. The measurements employed a spectrometer equipped with a TE 011 cylindrical resonator and a superconducting magnet system. Two shapes of ferromagnetic structures—discs and wedges—were applied for the generation of ultrahigh magnetic-field gradients up to 78 T/m. This gives an opportunity to explore microimaging techniques with spatial resolution up to 1 μm. Reconstruction of a one-dimensional image in the case of nonlinear magnetic-field dependence is demonstrated. As an example of applications, linear dimensions of heterogeneous structure components are estimated for frozen solutions of stable radicals.}, number={1}, journal={Journal of Magnetic Resonance (1969)}, publisher={Elsevier BV}, author={Smirnov, Alex I and Poluectov, Oleg G and Lebedev, Yakob S}, year={1992}, month={Mar}, pages={1–12} }
 @article{smirnov_golovina_yakimchenko_aksyonov_lebedev_1992, title={In vivo Seed Investigation by Electron Paramagnetic Resonance Spin Probe Technique}, volume={140}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000379935&partnerID=MN8TOARS}, DOI={10.1016/s0176-1617(11)80823-0}, abstractNote={Summary The methodology of the electron paramagnetic resonance nitroxide spin probe technique to study seeds at low moisture content has been developed. A wheat embryo was imbibed in 10 m m 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl aqueous solution together with potassium ferricyanide as a broadening agent. The detected resonance signals have been related to nitroxides within the aqueous phase of the cytoplasm of intact cells, the lipid bodies, and the lipid bilayer of the membranes. The experimental data indicate that some of the cellular membranes of embryos from seeds with 13 % and higher moisture content are essentially impermeable to ferricyanide ions and semipermeable to nitroxide molecules from the beginning of soaking. This property of cellular membranes is lost when seeds were artificially aged, and it is absent from cells within the central part of the endosperm tissue. The kinetics of observed signals during of soaking has been presented.}, number={4}, journal={Journal of Plant Physiology}, publisher={Elsevier BV}, author={Smirnov, Alex I. and Golovina, Helen A. and Yakimchenko, Olga E. and Aksyonov, Sergej I. and Lebedev, Yakob S.}, year={1992}, month={Sep}, pages={447–452} }
 @article{swartz_boyer_brown_chang_gast_glockner_hu_liu_moussavi_nilges_et al._1992, title={The use of EPR for the measurement of the concentration of oxygen in vivo in tissues under physiologically pertinent conditions and concentrations}, volume={317}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0027056754&partnerID=MN8TOARS}, journal={Advances in Experimental Medicine and Biology}, author={Swartz, H.M. and Boyer, S. and Brown, D. and Chang, K. and Gast, P. and Glockner, J.F. and Hu, H. and Liu, K.J. and Moussavi, M. and Nilges, M. and et al.}, year={1992}, pages={221–228} }
 @article{smirnov_yakimchenko_golovina_bekova_lebedev_1991, title={EPR imaging with natural spin probes}, volume={91}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0009579211&partnerID=MN8TOARS}, DOI={10.1016/0022-2364(91)90201-4}, abstractNote={Electron paramagnetic resonance imaging (EPRI) is a rapidly developing method for establishing spatial distribution of paramagnetic centers in a sample under study. This method has a wide field of potential applications, including biology and plant physiology. However, the concentration of native paramagnetic centers in such samples as a rule is insufficient for imaging experiments. The simple solution to this problem is to introduce into the object under study the necessary quantity of stable radicals as imaging substances. The most wide-spread type of such substance seems to be stable nitroxide radicals which have been applied recently to the study of spatial nonhomogeneity and diffusion in systems of chemical and biological interest (1-3). Nitroxide free radicals are very convenient imaging substances because the shapes of their EPR spectra are very sensitive to intermolecular conditions and can provide information about some important biological parameters, oxygen concentration, for example. In Ref. (4) the EPRI technique with nitroxide spin probes was used to investigate oxygen diffusion in models of biological systems. Nitroxide radicals were also used to study spatial characteristics of water penetration into wheat seeds during imbibition (5). In the latter work it was shown that nitroxide radicals may cause membrane destruction, thereby suppressing functions of cells. Much more attractive is the possibility of using some natural spin probes which demonstrate biological activity themselves and are compatible with biological tissues. In the present study we suggest the use, as natural probes, of the water-soluble fraction of soil humic substances (HS). These contain paramagnetic centers up to 10 ‘* spin/g, exhibiting at X band a single EPR signal with a linewidth about six gauss. The investigation of HS penetration into the seeds and their distribution is an important subject because of their biological effects on the seeds. It is well known that seeds are influenced by HS. It was reported that HS, which accelerated water uptake into the seeds (6)) could affect the rate of germination and initial seedling growth ( 7). Some observations indicate that humic substances act at the membrane level, but do not reveal the mode of action of these substances.}, number={2}, journal={Journal of Magnetic Resonance (1969)}, publisher={Elsevier BV}, author={Smirnov, Alex I and Yakimchenko, Olga E and Golovina, Helen A and Bekova, Shakhrazada Kh and Lebedev, Yakob S}, year={1991}, month={Feb}, pages={386–391} }
 @article{vinnik_smirnov_1991, title={Kinetics and mechanism of the hydrolysis of 2,4,6-trimethylbenzosulfonic acid in concentrated hydrochloric and sulfuric acid solution}, volume={32}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0026259936&partnerID=MN8TOARS}, number={3 pt 1}, journal={Kinetics and Catalysis}, author={Vinnik, M.I. and Smirnov, A.I.}, year={1991}, pages={534–540} }
 @article{yakimchenko_degtyarev_smirnov_borisov_bobolev_1990, title={EPR tomography of the diffusion kinetic process of the formation of Ag2+ in heterogeneous catalysts}, volume={31}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0025498797&partnerID=MN8TOARS}, number={2 pt 2}, journal={Kinetics and Catalysis}, author={Yakimchenko, O.E. and Degtyarev, E.N. and Smirnov, A.I. and Borisov, Yu.V. and Bobolev, A.V.}, year={1990}, pages={433–435} }
 @article{smirnov_erhart_senning_waldner_1990, title={Parametric spin wave testing by observation of transition processes}, volume={92}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0025519602&partnerID=MN8TOARS}, DOI={10.1016/0304-8853(90)90687-L}, abstractNote={Relaxation rates and coupling coefficients of spin waves have been determined in the layered ferromagnet (CH3NH3)2CuCl4. The parameters could be measured by observing the transient response of the parallel pumped microwave absorption to rapid magnetic field changes.}, number={1}, journal={Journal of Magnetism and Magnetic Materials}, author={Smirnov, A.I. and Erhart, P. and Senning, B. and Waldner, F.}, year={1990}, pages={116–124} }
 @article{smirnov_degtyarev_yakimchenko_lebedev_1988, title={EPR tomography with rotation of magnetic-field gradient}, volume={31}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0024070669&partnerID=MN8TOARS}, number={2 pt 1}, journal={Instruments and experimental techniques New York}, author={Smirnov, A.I. and Degtyarev, E.N. and Yakimchenko, O.E. and Lebedev, Ya.S.}, year={1988}, pages={374–377} }
 @article{prosorova_smirnov_1980, title={Variation of the spin wave spectrum in interaction between magnons}, volume={15-18}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-49149143575&partnerID=MN8TOARS}, DOI={10.1016/0304-8853(80)91099-9}, abstractNote={Abstract The change in the spin wave spectrum was observed under parametric excitation of 10 16 magnons cm −3 in a specimen of antiferromagnetic CsMnF 3 at a temperature of T = 1.6 K. The relative change in the characteristic frequency of magnons is 10 −5 and is negative. The frequency of investigated magnons was 10.5 and 17.8 GHz.}, number={PART 1}, journal={Journal of Magnetism and Magnetic Materials}, author={Prosorova, L.A. and Smirnov, A.I.}, year={1980}, pages={385–386} }
 @article{smirnov_belford_clarkson, title={Comparative Spin Label Spectra at X-Band and W-band}, DOI={10.1007/0-306-47072-1_3}, journal={Biological Magnetic Resonance}, publisher={Springer Science \mathplus Business Media}, author={Smirnov, Alex I. and Belford, R. L. and Clarkson, R. B.}, pages={83–107} }
 @article{smirnova_smirnov, title={High-Field ESR Spectroscopy in Membrane and Protein Biophysics}, DOI={10.1007/978-0-387-49367-1_6}, journal={ESR Spectroscopy in Membrane Biophysics}, publisher={Springer Science \mathplus Business Media}, author={Smirnova, Tatyana I. and Smirnov, Alex I.}, pages={165–251} }
 @article{smirnov, title={Spin-labeling in high-field EPR}, DOI={10.1039/9781847553553-00109}, journal={Electron Paramagnetic Resonance}, publisher={Royal Society of Chemistry (RSC)}, author={Smirnov, Alex I.}, pages={109–136} }