TY - CONF TI - Understanding trapping in photorefractive polymer composites for optical processing applications AU - Moerner, W.E. AU - Grunnet-Jepsen, A. AU - Wright, D. AU - Casperson, J. AU - Glazer, E. AU - DeClue, M. AU - Siegel, J.S. AU - Twieg, R.J. C2 - 1999/// C3 - IQEC, International Quantum Electronics Conference Proceedings DA - 1999/// SP - 186-187 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032645912&partnerID=MN8TOARS ER - TY - JOUR TI - Photorefractive properties of poly(N-vinyl carbazole)-based composites for high-speed applications AU - Díaz-García, M.A. AU - Wright, D. AU - Casperson, J.D. AU - Smith, B. AU - Glazer, E. AU - Moerner, W.E. AU - Sukhomlinova, L.I. AU - Twieg, R.J. T2 - Chemistry of Materials DA - 1999/// PY - 1999/// VL - 11 IS - 7 SP - 1784-1791 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0001188375&partnerID=MN8TOARS ER - TY - CONF TI - Chiral metal-containing polymers AU - Glazer, Edith C. AU - Tor, Yitzhak C2 - 1999/// C3 - American Chemical Society, Polymer Preprints, Division of Polymer Chemistry DA - 1999/// VL - 40 SP - 513-514 M1 - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033089595&partnerID=MN8TOARS ER - TY - CONF TI - Copper Zirconium Chloride Materials from Zero to Three Dimensions AU - Martin, J.D. T2 - 217th American Chemical Society National Meeting C2 - 1999/3/21/ CY - Anaheim, CA DA - 1999/3/21/ PY - 1999/3/21/ ER - TY - CONF TI - Putting Chemistry Back into Freshman Chemistry AU - Martin, J.D. T2 - Cottrell Scholars Conference C2 - 1999/// CY - Tucson, AZ DA - 1999/// PY - 1999/// ER - TY - CONF TI - From Crystal Structures to Liquid Crystals: Templated Extend Structure in Molten Metal Halides AU - Martin, James T2 - International Gordon Conference on Solid-State Chemistry C2 - 1999/9/19/ CY - Queens College, Oxford, United Kingdom DA - 1999/9/19/ PY - 1999/9/19/ ER - TY - RPRT TI - Halo-Zeotype Materials AU - Martin, J.D. AU - Greenwood, K.B. DA - 1999/3/23/ PY - 1999/3/23/ M1 - 5,885,542 M3 - U.S. Patent SN - 5,885,542 ER - TY - RPRT TI - Luminescent Copper Aluminum Halide Materials AU - Martin, James DA - 1999/3/3/ PY - 1999/3/3/ M1 - 5,876,637 M3 - U.S. Patent SN - 5,876,637 ER - TY - RPRT TI - On The Hydration And Dehydration Of Zinc Chloride AU - Euliss, L.E. AU - Martin, J.D. AU - Sullivan, R.M. AU - Goettler, S.J. AU - Hanson, J. A3 - Brookhaven National Laboratory DA - 1999/// PY - 1999/// PB - Brookhaven National Laboratory ER - TY - RPRT TI - Neutron Diffraction Studies Of The Structure Of Templated Zinc Chloride-Type Glasses And Melts AU - Martin, J.D. AU - Goettler, S.J. AU - Iton, L. AU - Badyal, Y. DA - 1999/// PY - 1999/// M3 - IPNS Progress Report, ER - TY - JOUR TI - Beyond the Textbook: A First Year Introduction to Research at a Research I University AU - Martin, James T2 - Crucible DA - 1999/// PY - 1999/// VL - 30 SP - 6–10 ER - TY - CONF TI - Use of Late Transition Metal Catalysts in Acetylene Polymerization AU - Gorman, C.B. AU - Vest, R.W. AU - Palovich, T.U. AU - Serron, S. C2 - 1999/// C3 - Polymeric materials : science and engineering, proceedings of the ACS Division of Polymeric Materials, Science and Engineering DA - 1999/// VL - 80 SP - 451 PB - American Chemical Society ER - TY - CONF TI - Contrasting Structural Features for Flexible and Rigid Electroactive Metallo-Dendrimers Experiment and Computation AU - Smith, J.C. AU - Gorman, C.B. C2 - 1999/// C3 - Polymeric materials : science and engineering, proceedings of the ACS Division of Polymeric Materials, Science and Engineering DA - 1999/// VL - 80 SP - 316 PB - American Chemical Society ER - TY - JOUR TI - Novel rearrangement of conformationally restrained [3.3]orthocyclophanes AU - Isobe, Shin-ichiro AU - Taniguchi, Masahiko AU - Sawada, Tsuyoshi AU - Thiemann, Thies AU - Yonemitsu, Tadashi AU - Mataka, Shuntaro T2 - Journal of the Chemical Society, Perkin Transactions 1 AB - Novel rearrangement of intermediate carbocations generated from rigid, layered [3.3]orthocyclophane-alcohols 4 are presented. The bicyclo[4.4.1]undecane framework of 4 rearranges to either bicyclo[5.4.0]- 5 and/or bicyclo[4.4.0]- 6 or tricyclo[5.4.0.02,11]- ring-system 11, depending upon the nature of the aryl substituent on the bridging tertiary carbon atom. X-Ray crystal structure analyses have been performed on the rearrangement products. DA - 1999/// PY - 1999/// DO - 10.1039/a903156a IS - 15 SP - 2101-2108 ER - TY - JOUR TI - Thieno[3.3]orthocyclophanes: preparations and structures AU - Thiemann, Thies AU - Ohira, Daisuke AU - Li, Yuanquiang AU - Sawada, Tsuyoshi AU - Taniguchi, Masahiko AU - Tashiro, Masashi AU - Mataka, Shuntaro T2 - New Journal of Chemistry AB - Rigid, layered hetareno/hetareno- and hetareno/areno-cyclophanes with closely held, non-distorted, interacting π-systems can be synthesized easily by using various building blocks. DA - 1999/// PY - 1999/// DO - 10.1039/a903746b VL - 23 IS - 7 SP - 675-678 ER - TY - JOUR TI - Synthesis of 8,16-dimethyl- and 8,16-dimethoxy-5,13-di-t-butyl[2.2]metacyclophane-1,2,9,10-tetraone AU - Tsukamoto, Ken-ichi AU - Sahade, Daniel A. AU - Taniguchi, Masahiko AU - Sawada, Tsuyoshi AU - Thiemann, Thies AU - Mataka, Shuntaro T2 - Tetrahedron Letters AB - Swern oxidation of 8,16-dimethoxy- and 8,16-dimethyl-5,13-di-t-butyl-1,2,9,10-tetrahydroxy[2.2]metacyclophane, 1 and 2, afforded 5,13-di-t-butyl-10-hydroxy-8,16-dimethoxy[2.2]metacyclophane-1,2,9-trione 3 and 4. By subsequent oxidation with DDQ, 8,16-dimethoxy- and 8,16-dimethyl-5,13-di-t-butyl[2.2]metacyclophane-1,2,9,10-tetraones, 5 and 6, were obtained. DA - 1999/6// PY - 1999/6// DO - 10.1016/s0040-4039(99)00845-x VL - 40 IS - 25 SP - 4691-4692 ER - TY - JOUR TI - Layered [3.3]Orthocyclophane Tricarbonylchromium Complexes AU - Taniguchi, Masahiko AU - Thiemann, Thies AU - Sawada, Tsuyoshi AU - Mataka, Shuntaro T2 - Zeitschrift für anorganische und allgemeine Chemie AB - The preparation of the layered [3.3]orthocyclophane tricarbonylchromium mono- and bis complexes, 4 and 5, are described. X-ray crystallographic analysis reveals the fact that the distances and the dihedral angle between the planes of the two benzo rings in mono complex 4 decrease as compared to those in 1. This is due to the decrease in π electron density in one benzo unit. DA - 1999/8// PY - 1999/8// DO - 10.1002/(sici)1521-3749(199908)625:8<1249::aid-zaac1249>3.0.co;2-o VL - 625 IS - 8 SP - 1249-1251 KW - cyclophanes KW - chromium KW - pi-interaction ER - TY - JOUR TI - Adsorption characteristics of Fe(CN)63−/4− on Au colloids as monolayer films on cysteamine-modified gold electrode AU - Hu, Xiao-Ya AU - Xiao, Yi AU - Chen, Hong-Yuan T2 - Journal of Electroanalytical Chemistry AB - Self-assembled monolayers (SAMs) of chemisorbed cysteamine on gold electrode surfaces have been used as base interfaces for the deposition of the Au colloid. Different Au colloids, ranging in particles of diameter 2.6, 16, 42 and 51 nm, can be deposited on self-assembled cysteamine monolayers on a gold electrode. Fe(CN)64− adsorbed on Au colloid surfaces yields a pair of symmetric adsorption peaks with half-peak width (W1/2) of 90.2 mV and peak-to-peak separation (ΔEp) of 3 mV in 1.0 M KNO3 solution containing 1.00×10−3 M K3Fe(CN)6. The dependence of peak current on scan rate (ν) is linear. ΔEp of the adsorption wave increases while the Au colloid size decreases. The apparent specific capacitances of a bare gold electrode, the cysteamine-modified electrode and the Au colloid modified electrode measured by cyclic voltammetry at 500 mV are 57.8, 32.0 and 81.1 μF cm−2, respectively. DA - 1999/5// PY - 1999/5// DO - 10.1016/s0022-0728(99)00113-8 VL - 466 IS - 1 SP - 26-30 J2 - Journal of Electroanalytical Chemistry LA - en OP - SN - 1572-6657 UR - http://dx.doi.org/10.1016/s0022-0728(99)00113-8 DB - Crossref KW - colloidal gold KW - self-assembled monolayers KW - gold electrode ER - TY - JOUR TI - Hydrogen peroxide sensor based on horseradish peroxidase-labeled Au colloids immobilized on gold electrode surface by cysteamine monolayer AU - Xiao, Yi AU - Ju, Huang-Xian AU - Chen, Hong-Yuan T2 - Analytica Chimica Acta AB - A novel strategy to construct a sensitive amperometric sensor of H2O2 was described. Horseradish peroxidase (HRP) was successfully immobilized on nanometer-sized Au colloids, which were supported by thiol-tailed groups of cysteamine monolayer. The thiol-tailed groups were formed through the covalent binding of glutaraldehyde on a cysteamine-modified gold electrode. With the aid of the catechol mediator in the solution, HRP-labeled Au colloids displayed excellent electrocatalytical response to the reduction of H2O2, which increased with decreasing size of Au colloids. The sensors responded to H2O2 in the concentration range of 0.39 μM–0.33 mM, and reached 95% of the steady-state current in less than 5 s with the detection limit of 0.15 μM. The response showed a Michaelis–Menten behavior at larger H2O2 concentrations. The KappM values for the sensors based on different sized HRP-labeled Au colloids (colloid A–D) were found to be 0.11, 0.094, 0.054 and 0.064 mM, respectively. The low KappM values demonstrated that HRP immobilized on Au colloids exhibited a high affinity to H2O2 with no loss of enzymatic activity. DA - 1999/5// PY - 1999/5// DO - 10.1016/s0003-2670(99)00196-8 VL - 391 IS - 1 SP - 73-82 J2 - Analytica Chimica Acta LA - en OP - SN - 0003-2670 UR - http://dx.doi.org/10.1016/s0003-2670(99)00196-8 DB - Crossref KW - self-assembled monolayers KW - HRP-labeled Au colloids KW - cysteamine KW - hydrogen peroxide KW - sensors KW - electrochemical sensors ER - TY - JOUR TI - A reagentless hydrogen peroxide sensor based on incorporation of horseradish peroxidase in poly(thionine) film on a monolayer modified electrode AU - Xiao, Y AU - Ju, H.-X AU - Chen, H.-Y T2 - Analytica Chimica Acta AB - A novel reagentless hydrogen peroxide sensor fabricated by the entrapment of horseradish peroxidase (HRP) into poly(thionine) film on a thionine self-assembled monolayer modified gold electrode is described. The direct electron transfer between the heme site of HRP and the electrode is mediated by thionine units incorporated in the polymer film. The sensor displays an excellent electrocatalytic response to the reduction of H2O2. The chronoamperometric current is proportional to the H2O2 concentration in the range of 6.2 μM to 9.4 mM with a correlation coefficient of 0.999. Moreover, such a modified electrode exhibits a good stability and reproducibility within the linear range of H2O2, the variation coefficients are 3.8% and 4.5% for 10 successive assays at a H2O2 concentration of 9.3 μM and 2.8 mM, respectively. DA - 1999/6// PY - 1999/6// DO - 10.1016/s0003-2670(99)00254-8 VL - 391 IS - 3 SP - 299-306 J2 - Analytica Chimica Acta LA - en OP - SN - 0003-2670 UR - http://dx.doi.org/10.1016/s0003-2670(99)00254-8 DB - Crossref KW - hydrogen peroxide sensor KW - poly(thionine) film KW - coimmobilization KW - horseradish peroxidase KW - thionine monolayer KW - gold electrode ER - TY - CHAP TI - Quantum Catalysis: The Modeling of Catalytic Transition States AU - Hall, Michael B. AU - Margl, Peter AU - Náray-Szabó, Gabor AU - Schramm, Vern L. AU - Truhlar, Donald G. AU - van Santen, Rutger A. AU - Warshel, Arieh AU - Whitten, Jerry L. T2 - Transition State Modeling for Catalysis : developed from a symposium sponsored by the Division of Computers in Chemistry at the 215th National Meeting of the American Chemical Society, Dallas, Texas, March 29-April 2, 1998 A2 - Truhlar, Donald G. A2 - Morokuma, Keiji T3 - ACS Symposium Series AB - We present an introduction to the computational modeling of transition states for catalytic reactions. We consider both homogeneous catalysis and heterogeneous catalysis, including organometallic catalysts, enzymes, zeolites and metal oxides, and metal surfaces. We summarize successes, promising approaches, and problems. We attempt to delineate the key issues and summarize the current status of our understanding of these issues. Topics covered include basis sets, classical trajectories, cluster calculations, combined quantum-mechanical/molecular-mechanical (QM/MM) methods, density functional theory, electrostatics, empirical valence bond theory, free energies of activation, frictional effects and nonequilibrium solvation, kinetic isotope effects, localized orbitals at surfaces, the reliability of correlated electronic structure calculations, the role of d orbitals in transition metals, transition state geometries, and tunneling. PY - 1999/4/8/ DO - 10.1021/bk-1999-0721.ch001 SP - 2–17 PB - American Chemical Society SN - 9780841236103 9780841217096 SV - 721 UR - http://dx.doi.org/10.1021/bk-1999-0721.ch001 ER - TY - JOUR TI - Quantification of singly charged biomolecules by electrospray ionization fourier transform ion cyclotron resonance mass spectrometry utilizing an internal standard AU - Gordon, Eric F. AU - Muddiman, David C. T2 - Rapid Communications in Mass Spectrometry AB - The quantification of Cyclosporin A (CsA) and related biological compounds by various mass spectrometric techniques is well established. It is precisely this fact that makes the use of CsA particularly appealing as a model system in evaluating the quantitative properties of electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). Utilizing the internal standard methodology, we have generated a linear calibration curve ranging from 5–250 ng/mL CsA described by the equation y = 0.00503x–0.00958, with a %RSDslope of 0.74% and a correlation coefficient (r0) equal to 0.9992 (N = 30). The internal standard (200 ng/mL Cyclosporin G) was found to be necessary to establish the reported dynamic range, two orders of magnitude based on an experimentally determined detection limit of 2.4 ng/mL CsA, and also significantly improved the overall precision of the method. The data represented in the standard curve were collected as 1.05 s single acquisitions (512 K data points at an ADC rate of 500 kHz) and unapodized prior to the Fourier transformation of the time-domain data. We report that full Hanning apodization has a statistically significant negative effect (F-test at 95% confidence level) on the regression statistics of the curve (i.e. increasing the %RSDslope to 1.33%). Finally, we report that acceptable quantitative properties of an FTICR-MS experiment can be realized as soon as the detection of a second isotopic beat for the targeted species is obtained. This should allow for the practical and effective coupling of on-line separation techniques for quantitative analysis using ESI-FTICR-MS. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/2/15/ PY - 1999/2/15/ DO - 10.1002/(sici)1097-0231(19990215)13:3<164::aid-rcm474>3.0.co;2-l VL - 13 IS - 3 SP - 164-171 J2 - Rapid Commun. Mass Spectrom. LA - en OP - SN - 0951-4198 1097-0231 UR - http://dx.doi.org/10.1002/(sici)1097-0231(19990215)13:3<164::aid-rcm474>3.0.co;2-l DB - Crossref ER - TY - JOUR TI - Hemoglobinase Activity of the Lysine Gingipain Protease (Kgp) of Porphyromonas gingivalis W83 AU - Lewis, Janina P. AU - Dawson, Janet A. AU - Hannis, James C. AU - Muddiman, David AU - Macrina, Francis L. T2 - Journal of Bacteriology AB - Porphyromonas gingivalis, an important periodontal disease pathogen, forms black-pigmented colonies on blood agar. Pigmentation is believed to result from accumulation of iron protoporphyrin IX (FePPIX) derived from erythrocytic hemoglobin. The Lys-X (Lys-gingipain) and Arg-X (Arg-gingipain) cysteine proteases of P. gingivalis bind and degrade erythrocytes. We have observed that mutations abolishing activity of the Lys-X-specific cysteine protease, Kgp, resulted in loss of black pigmentation of P. gingivalis W83. Because the hemagglutinating and hemolytic potentials of mutant strains were reduced but not eliminated, we hypothesized that this protease played a role in acquisition of FePPIX from hemoglobin. In contrast to Arg-gingipain, Lys-gingipain was not inhibited by hemin, suggesting that this protease played a role near the cell surface where high concentrations of hemin confer the black pigmentation. Human hemoglobin contains 11 Lys residues in the alpha chain and 10 Lys residues in the beta chain. In contrast, there are only three Arg residues in each of the alpha and beta chains. These observations are consistent with human hemoglobin being a preferred substrate for Lys-gingipain but not Arg-gingipain. The ability of the Lys-gingipain to cleave human hemoglobin at Lys residues was confirmed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry of hemoglobin fragments resulting from digestion with the purified protease. We were able to detect several of the predicted hemoglobin fragments rendered by digestion with purified Lys-gingipain. Thus, we postulate that the Lys-gingipain of P. gingivalis is a hemoglobinase which plays a role in heme and iron uptake by effecting the accumulation of FePPIX on the bacterial cell surface. DA - 1999/8/15/ PY - 1999/8/15/ DO - 10.1128/jb.181.16.4905-4913.1999 VL - 181 IS - 16 SP - 4905-4913 J2 - J. Bacteriol. LA - en OP - SN - 1098-5530 0021-9193 UR - http://dx.doi.org/10.1128/jb.181.16.4905-4913.1999 DB - Crossref ER - TY - JOUR TI - Consequences of Nucleic Acid Conformation on the Binding of a Trinuclear Platinum Drug† AU - Kloster, Miriam B. G. AU - Hannis, James C. AU - Muddiman, David C. AU - Farrell, Nicholas T2 - Biochemistry AB - BBR3464, a charged trinuclear platinum compound, is the first representative of a new class of anticancer drugs to enter phase I clinical trials. The structure of BBR3464 is characterized by two [trans-PtCl(NH3)2] units linked by a tetraamine [trans-Pt(NH3)2{H2N(CH2)6NH2}2] unit. The +4 charge of BBR3464 and the separation of the platinating units indicate that the mode of DNA binding will be distinctly different from those of classical mononuclear drugs such as cisplatin, cis-[PtCl2(NH3)2]. The reaction of BBR3464 with three different nucleic acid conformations was assessed by gel electrophoresis. Comparison of single-stranded DNA, RNA, and double-stranded DNA indicated that the reaction of BBR3464 with single-stranded DNA and RNA was faster than that with duplex DNA, and produced more drug−DNA and drug−RNA adducts. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to further characterize the binding modes of BBR3464 with the DNA substrates. BBR3464 binding to different nucleic acid conformations raises the possibility that the adducts of single-stranded DNA and RNA may play a role in the different antitumor efficacies of this novel drug as compared with cisplatin. DA - 1999/11// PY - 1999/11// DO - 10.1021/bi991202e VL - 38 IS - 45 SP - 14731-14737 J2 - Biochemistry LA - en OP - SN - 0006-2960 1520-4995 UR - http://dx.doi.org/10.1021/bi991202e DB - Crossref ER - TY - JOUR TI - Hydropathic influences on the quantification of equine heart cytochromec using relative ion abundance measurements by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry AU - Gordon, Eric F. AU - Mansoori, Bashir A. AU - Carroll, Charlotte F. AU - Muddiman, David C. T2 - Journal of Mass Spectrometry AB - The number of publications documenting the utility of electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for the analysis of biological molecules has increased in geometric proportion spanning diverse areas of research. Currently, we are investigating the capabilities of ESI-FTICR to quantify relative molecular ion abundances of biopolymers, an area which has not been explored rigorously. We present here the results of an investigation of a two-component system utilizing equine heart cytochrome c (EH) as the analyte and bovine heart cytochrome c (BH) as a constant concentration internal standard. As these compounds are relatively large (∼12 kDa), they will become multiply charged during the electrospray process. Using appropriate solution and instrument conditions, the 7+ and 8+ charge states were enhanced for both cytochrome c species. We report that using the average of the ion abundances for the two charge states observed for each species, the linear curve (intensity ratio vs concentration ratio) had a dynamic range of 0.045–2.348 µM (1.7 orders of magnitude). Linear least-squares regression analysis (LLSRA) of these averaged ion abundances (i.e. [(EH + 7H+)7+/(BH + 7H+)7+ + (EH + 8H+)8+/(BH + 8H+)8+]/2) yielded the equation y = 1.005x + 0.027. The slope of the line with its calculated precision, reported as one standard deviation, is 1.005 ± 0.0150, which is statistically ideal (i.e. equal to unity). However, LLSRA of the ion abundances of the two individual charge states were significantly different (i.e. the slope of the (EH + 7H+)7+/(BH + 7H+)7+ peak intensity ratio vs molar ratio data was 0.885 ± 0.0183 and the slope of the (EH + 8H+)8+/(BH + 8H+)8+ data was 1.125 ± 0.0308). We attribute this difference to the variation in primary amino acid sequence for the two cytochrome c species. Both have 104 amino acids, but there are three residue substitutions between EH and BH; one of the substitutions confers an additional basic site to EH. While this extra basic residue may imply an additional charging site, the low charge states observed under the solution conditions employed indicate that most (>66%) basic sites are not protonated. However, the extra basic site also renders EH slightly more hydrophilic. These results present significant considerations when choosing internal standards for the quantification of large proteins by ESI-FTICR-MS and demonstrate that relative molecular ion signals in FTICR can be used to quantify macromolecular species in the nanomolar regime. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/10// PY - 1999/10// DO - 10.1002/(sici)1096-9888(199910)34:10<1055::aid-jms864>3.0.co;2-e VL - 34 IS - 10 SP - 1055-1062 J2 - J. Mass Spectrom. LA - en OP - SN - 1076-5174 1096-9888 UR - http://dx.doi.org/10.1002/(sici)1096-9888(199910)34:10<1055::aid-jms864>3.0.co;2-e DB - Crossref KW - proteomics KW - quantification KW - hydropathy KW - electrospray ionization KW - Fourier transform ion cyclotron resonance mass spectrometry ER - TY - JOUR TI - Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry AU - Muddiman, David C. AU - Null, Allison P. AU - Hannis, James C. T2 - Rapid Communications in Mass Spectrometry AB - Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/µL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 ± 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3′-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/6/30/ PY - 1999/6/30/ DO - 10.1002/(sici)1097-0231(19990630)13:12<1201::aid-rcm643>3.0.co;2-x VL - 13 IS - 12 SP - 1201-1204 J2 - Rapid Commun. Mass Spectrom. LA - en OP - SN - 0951-4198 1097-0231 UR - http://dx.doi.org/10.1002/(sici)1097-0231(19990630)13:12<1201::aid-rcm643>3.0.co;2-x DB - Crossref ER - TY - JOUR TI - Accurate characterization of the tyrosine hydroxylase forensic allele 9.3 through development of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry AU - Hannis, James C. AU - Muddiman, David C. T2 - Rapid Communications in Mass Spectrometry AB - Accurate and precise determination of the number of repeats from a short tandem repeat (STR) sequence for a human gene locus is demonstrated for the first time by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). Specifically, the polymorphic human tyrosine hydroxylase (HUMTHO1) gene, a tetranucleotide STR forensic allele, was chosen as a model system to evaluate our approach for future characterization of both STRs and variable number of tandem repeats (VNTRs) by development of an ESI-FTICR-MS approach. The coding and noncoding strands from the HUMTHO1 9.3 allele are simultaneously resolved obtaining accurate (better than 70 ppm) average mass measurements of 25,783.23 and 24,754.55 Da for the coding and noncoding strands, respectively. The mass measurements are used to calculate the number of repeats for each strand, ‘n’, of 9.75169 and 9.75001 for the coding and noncoding strands, respectively. It will be shown how the value of ‘n’ can be used to directly determine the number of pure repeats and accurately determine the exact nature of the polymorphism within the repeat (if any). The single nucleotide deletion in the coding strand (adenine) and noncoding strand (thymine) were accurately identified using this approach. Interestingly, we observed the conversion of single-stranded to double-stranded DNA while the PCR product in the ESI buffer was being infused; the issues related to this observation will be presented. Previous results by other researchers investigating the HUMTHO1 9.3 allele using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) are directly compared with our results. Our results indicate that ESI-FTICR-MS is a powerful approach to rapidly and accurately characterize tandem repeating sequences which will ultimately lead towards the understanding of a complex class of diseases and in human identity determination. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/5/30/ PY - 1999/5/30/ DO - 10.1002/(sici)1097-0231(19990530)13:10<954::aid-rcm593>3.0.co;2-r VL - 13 IS - 10 SP - 954-962 J2 - Rapid Commun. Mass Spectrom. LA - en OP - SN - 0951-4198 1097-0231 UR - http://dx.doi.org/10.1002/(sici)1097-0231(19990530)13:10<954::aid-rcm593>3.0.co;2-r DB - Crossref ER - TY - JOUR TI - Characterization of a microdialysis approach to prepare polymerase chain reaction products for electrospray ionization mass spectrometry using on-line ultraviolet absorbance measurements and inductively coupled plasma-atomic emission spectroscopy AU - Hannis, James C. AU - Muddiman, David C. T2 - Rapid Communications in Mass Spectrometry AB - The desalting efficiencies for microdialysis have been quantitatively determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES) by analyzing samples which mimic polymerase chain reaction (PCR) conditions. Desalting efficiencies for the removal of Mg2+ from samples containing oligonucleotides were typically 99.94% for a single dialysis experiment and 99.98% for a tandem-dialysis experiment. The determination of the molecular weight selectivity of a microdialysis fiber with a 13,000 Da molecular weight cutoff (MWCO) employing a 10 mM NH4OAc countercurrent buffer was accomplished using on-line ultraviolet (UV) absorbance. Results revealed an insensitivity to molecular weight over a broad range represented by dNTPs (ca. 490 Da), PCR primers (ca. 5100 Da), and PCR products (extending to ca. 100 kDa) thus showing the inability of microdialysis to remove unincorporated deoxyribonucleotide 5′-triphosphates (dNTPs) and primers from PCRs. A comparison study conducted utilizing proteins ranging from ca. 1 to 29 kDa produced recoveries dictated by the MWCO of the microdialysis fiber. Recoveries were zero for the smallest proteins tested (ca. 1.3 and 2.9 kDa), but increased to 98% for the largest protein (ca. 29 kDa). The ability of microdialysis to convert double-stranded DNA to single-stranded DNA due to a rapid decrease in the ionic strength was examined along with the effects of buffer concentration, temperature, pH, tandem dialysis, and a denaturing additive, formamide. Melting temperature curves showed that microdialyzed samples remain double stranded while utilizing NH4OAc buffer concentrations of 0 (i.e. pure water) to 10 mM. Adjustment of the buffer up to pH 10.98, temperature increases to 51 °C, tandem dialysis, and the addition of formamide were also unable to produce the conversion of ds-DNA to ss-DNA in detectable amounts. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/3/15/ PY - 1999/3/15/ DO - 10.1002/(sici)1097-0231(19990315)13:5<323::aid-rcm485>3.0.co;2-b VL - 13 IS - 5 SP - 323-330 J2 - Rapid Commun. Mass Spectrom. LA - en OP - SN - 0951-4198 1097-0231 UR - http://dx.doi.org/10.1002/(sici)1097-0231(19990315)13:5<323::aid-rcm485>3.0.co;2-b DB - Crossref ER - TY - JOUR TI - Sc5Ni2Te2:  Synthesis, Structure, and Bonding of a Metal−Metal-Bonded Chain Phase, a Relative of Gd3MnI3 AU - Maggard, Paul A. AU - Corbett, John D. T2 - Inorganic Chemistry AB - Sc5Ni2Te2 has been prepared by high-temperature solid-state techniques and the structure determined at 23 °C by single crystal and powder X-ray diffraction methods to be orthorhombic, Pnma (No. 62) with Z = 4, a = 17.862(1) Å, b = 3.9533(3) Å, c = 10.6398(6) Å. The structure contains pairs of eclipsed zigzag chains of nickel atoms that are sheathed by scandium atoms and demarcated from other chains by tellurium atoms. The structure is isotypic with that of Hf5Co1+xP3-x, but shifted atomic positions and a different ordering of the main group and late transition elements give it a clearly 1D character. The differences in dimensionality, ordering, and bonding are discussed, and comparisons are made with Gd3MnI3 and rare-earth-metal cluster halides in general. DA - 1999/4// PY - 1999/4// DO - 10.1021/ic981073a VL - 38 IS - 8 SP - 1945-1950 J2 - Inorg. Chem. LA - en OP - SN - 0020-1669 1520-510X UR - http://dx.doi.org/10.1021/ic981073a DB - Crossref ER - TY - CONF TI - Understanding the photoluminescence of copper aluminum halide phosphors AU - Sullivan, R.M. AU - Martin, J.D. C2 - 1999/// C3 - Materials Research Society Symposium - Proceedings DA - 1999/// VL - 560 SP - 39-44 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033310103&partnerID=MN8TOARS ER - TY - CONF TI - Liquid Crystalline Zinc Chloride AU - Martin, James AU - Thornton, T.A. T2 - Materials Research Society National Meeting C2 - 1999/// C3 - Materials Research Society Symposium - Proceedings CY - San Francisco, CA DA - 1999/// PY - 1999/// VL - 559 SP - 243-248 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033322757&partnerID=MN8TOARS ER - TY - JOUR TI - α-K4R6I14Os (R = La, Pr): A novel iodine-rich structure with a layered network of electron-poor clusters. an incipient delocalized system with metal-like conductivity AU - Uma, S. AU - Martin, J.D. AU - Corbett, J.D. T2 - Inorganic Chemistry DA - 1999/// PY - 1999/// VL - 38 IS - 17 SP - 3825-3830 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0000241058&partnerID=MN8TOARS ER - TY - BOOK TI - Metal halide framework solids: Analogs of aluminosilicates and aluminophosphates AU - Martin, J.D. DA - 1999/// PY - 1999/// VL - 727 SE - 28-38 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0041911551&partnerID=MN8TOARS ER - TY - JOUR TI - Dioxygen Reactivity of Fully Reduced [LFeII···CuI]+Complexes Utilizing Tethered Tetraarylporphyrinates:  Active Site Models for Heme-Copper Oxidases AU - Ju, Telvin D. AU - Ghiladi, Reza A. AU - Lee, Dong-Heon AU - van Strijdonck, Gino P. F. AU - Woods, Amina S. AU - Cotter, Robert J. AU - Young, Victor G. AU - Karlin, Kenneth D. T2 - Inorganic Chemistry AB - For O2-reactivity studies aimed at modeling aspects of heme-copper oxidase enzyme function, use of heterobinucleating ligands (6-pyridyl (6L) or 5-pyridyl (5L) connection) gives rise to iron(II) (with “empty-tether”), 2a and 2b, and [LFeII···CuI]+ complexes, 3a and 3b, respectively. Reduced complexes 2 and 3 can exist in high-, intermediate-, or low-spin iron(II) configurations, depending on the solvent employed. Reaction of dioxygen with both 3a and 3b leads to a biomimetic reductive O−O bond cleavage forming μ-oxo species [(L)FeIII−O−CuII]+ (4a, 4b). The X-ray structure of 4a is reported. DA - 1999/5// PY - 1999/5// DO - 10.1021/ic9900511 VL - 38 IS - 10 SP - 2244-2245 J2 - Inorg. Chem. LA - en OP - SN - 0020-1669 1520-510X UR - http://dx.doi.org/10.1021/ic9900511 DB - Crossref ER - TY - JOUR TI - Advances in Fluorescence Spectroscopy: Multi-Photon Excitation, Engineered Proteins, Modulation Sensing and Microsecond Rhenium Metal-Ligand Complexes AU - Lakowicz, J.R. AU - Gryczynski, I. AU - Tolosa, L. AU - Dattelbaum, J.D. AU - Castellano, F.N. AU - Li, L. AU - Rao, G. T2 - Acta Physica Polonica A AB - The technology and applications of fluorescence spectroscopy are rapidly advancing. In this overview presentation we summarize some recent developments from this laboratory. Two and three-photon excitation have been observed for a wide variety of intrinsic and extrinsic fluorophores, including tryptophan, tyrosine, DNA stains, membrane probes, and even alkanes. It has been possible to observe multi-photon excitation of biopolymers without obvious photochemical or photo-thermal effects. Although not de-scribed in our lecture, another area of increasing interest is the use of engineered proteins for chemical and clinical sensing. We show results for the glucose-galactose binding protein from E. coli. The labeled protein shows spectral changes in response to micromolar concentrations of glucose. This protein was used with a novel sensing method based on the modulated emission of the labeled proteins and a long lifetime reference fluorophore. And finally, we describe a recently developed rhenium complex which displays a lifetime near 3 µs in oxygenated aqueous solution. Such long life-time probes allow detection of microsecond dynamic processes, bypassing the usual nanosecond timescale limit of fluorescence. The result of these developments in protein engineering, sensing methods, and metal-ligand probe chemistry will be the increased use of fluorescence in clinical chemistry and point-of-care analyses. DA - 1999/1// PY - 1999/1// DO - 10.12693/aphyspola.95.179 VL - 95 IS - 1 SP - 179-196 J2 - Acta Phys. Pol. A LA - en OP - SN - 0587-4246 1898-794X UR - http://dx.doi.org/10.12693/aphyspola.95.179 DB - Crossref ER - TY - JOUR TI - A comparison of observations and model simulations of NOx/NOyin the lower stratosphere AU - Gao, R. S. AU - Fahey, D. W. AU - Negro, L. A. Del AU - Donnelly, S. G. AU - Keim, E. R. AU - Neuman, J. A. AU - Teverovskaia, E. AU - Wennberg, P. O. AU - Hanisco, T. F. AU - Lanzendorf, E. J. AU - Proffitt, M. H. AU - Margitan, J. J. AU - Wilson, J. C. AU - Elkins, J. W. AU - Stimpfle, R. M. AU - Cohen, R. C. AU - McElroy, C. T. AU - Bui, T. P. AU - Salawitch, R. J. AU - Brown, S. S. AU - Ravishankara, A. R. AU - Portmann, R. W. AU - Ko, M. K. W. AU - Weisenstein, D. K. AU - Newman, P. A. T2 - Geophysical Research Letters AB - Extensive airborne measurements of the reactive nitrogen reservoir (NO y ) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model simulations that are constrained by observations of radical and long‐lived species and which include heterogeneous chemistry systematically underpredict the NO x (= NO + NO 2 ) to NO y ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO 2 and OH + HNO 3 reactions are used. When included in 2‐D models, the new rate coefficients significantly increase the calculated ozone loss due to NO x and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircraft are also altered. DA - 1999/4// PY - 1999/4// DO - 10.1029/1999gl900162 VL - 26 IS - 8 SP - 1153-1156 ER - TY - JOUR TI - The coupling of ClONO2, ClO, and NO2in the lower stratosphere from in situ observations using the NASA ER-2 aircraft AU - Stimpfle, R. M. AU - Cohen, R. C. AU - Bonne, G. P. AU - Voss, P. B. AU - Perkins, K. K. AU - Koch, L. C. AU - Anderson, J. G. AU - Salawitch, R. J. AU - Lloyd, S. A. AU - Gao, R. S. AU - Negro, L. A. Del AU - Keim, E. R. AU - Bui, T. P. T2 - Journal of Geophysical Research: Atmospheres AB - The first in situ measurements of ClONO 2 in the lower stratosphere, acquired using the NASA ER‐2 aircraft during the Polar Ozone Loss in the Arctic Region in Summer (POLARIS) mission, are combined with simultaneous measurements of ClO, NO 2 , temperature, pressure, and the calculated photolysis rate coefficient (J ClONO2 ) to examine the balance between production and loss of ClONO 2 . The observations demonstrate that the ClONO 2 photochemical steady state approximation, [ClONO 2 ] PSS = k × [ClO] × [NO 2 ] / J ClONO2 , is in good agreement with the direct measurement, [ClONO 2 ] MEAS . For the bulk of the data (80%), where T>220 K and latitudes >45°N, [ClONO 2 ] PSS = 1.15±0.36 (1σ) × [ClONO 2 ] MEAS , while for T<220 K and latitudes <45°N the result is somewhat less at 1.01±0.30. The cause of the temperature and/or latitude trend is unidentified. These results are independent of solar zenith angle and air density, thus there is no evidence in support of a pressure‐dependent quantum yield for photodissociation of ClONO 2 at wavelengths >300 nm. These measurements confirm the mechanism by which active nitrogen (NO x = NO + NO 2 ) controls the abundance of active chlorine (Cl x = ClO + Cl) in the stratosphere. DA - 1999/11/1/ PY - 1999/11/1/ DO - 10.1029/1999jd900288 VL - 104 IS - D21 SP - 26705-26714 ER - TY - JOUR TI - Comparison of modeled and observed values of NO2and JNO2during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission AU - Negro, L. A. Del AU - Fahey, D. W. AU - Gao, R. S. AU - Donnelly, S. G. AU - Keim, E. R. AU - Neuman, J. A. AU - Cohen, R. C. AU - Perkins, K. K. AU - Koch, L. C. AU - Salawitch, R. J. AU - Lloyd, S. A. AU - Proffitt, M. H. AU - Margitan, J. J. AU - Stimpfle, R. M. AU - Bonne, G. P. AU - Voss, P. B. AU - Wennberg, P. O. AU - McElroy, C. T. AU - Swartz, W. H. AU - Kusterer, T. L. AU - Anderson, D. E. AU - Lait, L. R. AU - Bui, T. P. T2 - Journal of Geophysical Research: Atmospheres AB - Stratospheric measurements of NO, NO 2 , O 3 , ClO, and HO 2 were made during spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO 2 and NO are in steady state through NO 2 photolysis and reactions involving O 3 , ClO, BrO, and HO 2 . By combining observations of O 3 , ClO, and HO 2 , observed and modeled values of the NO 2 photolysis rate coefficient (J NO 2 ), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO 2 and J NO 2 . An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (±50 to 70%). These results suggest that photochemistry controlling the NO 2 /NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + O 3 → NO 2 + O 2 would aid future analyses of these or similar atmospheric observations. DA - 1999/11/1/ PY - 1999/11/1/ DO - 10.1029/1999jd900246 VL - 104 IS - D21 SP - 26687-26703 ER - TY - JOUR TI - Comparison of MkIV balloon and ER-2 aircraft measurements of atmospheric trace gases AU - Toon, G. C. AU - Blavier, J.-F. AU - Sen, B. AU - Margitan, J. J. AU - Webster, C. R. AU - May, R. D. AU - Fahey, D. AU - Gao, R. AU - Negro, L. Del AU - Proffitt, M. AU - Elkins, J. AU - Romashkin, P. A. AU - Hurst, D. F. AU - Oltmans, S. AU - Atlas, E. AU - Schauffler, S. AU - Flocke, F. AU - Bui, T. P. AU - Stimpfle, R. M. AU - Bonne, G. P. AU - Voss, P. B. AU - Cohen, R. C. T2 - Journal of Geophysical Research: Atmospheres AB - On May 8, 1997, vertical profiles of over 30 different gases were measured remotely in solar occultation by the Jet Propulsion Laboratory MkIV Interferometer during a balloon flight launched from Fairbanks, Alaska. These gases included H 2 O, N 2 O, CH 4 , CO, NO x , NO y , HCl, ClNO 3 , CCl 2 F 2 , CCl 3 F, CCl 4 , CHClF 2 , CClF 2 CCl 2 F, SF 6 , CH 3 Cl, and C 2 H 6 , all of which were also measured in situ by instruments on board the NASA ER‐2 aircraft, which was making flights from Fairbanks during this same early May time period as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) experiment. A comparison of the gas volume mixing ratios in the upper troposphere and lower stratosphere reveals agreement better than 5% for most gases. The three significant exceptions to this are SF 6 and CCl 4 for which the remote measurements exceed the in situ observations by 15–20% at all altitudes, and H 2 O for which the remote measurements are up to 30% smaller than the in situ observations near the hygropause. DA - 1999/11/1/ PY - 1999/11/1/ DO - 10.1029/1999jd900379 VL - 104 IS - D21 SP - 26779-26790 ER - TY - JOUR TI - Formation and Characterization of a High-Spin Heme-Copper Dioxygen (Peroxo) Complex AU - Ghiladi, Reza A. AU - Ju, Telvin D. AU - Lee, Dong-Heon AU - Moënne-Loccoz, Pierre AU - Kaderli, Susan AU - Neuhold, Yorck-Michael AU - Zuberbühler, Andreas D. AU - Woods, Amina S. AU - Cotter, Robert J. AU - Karlin, Kenneth D. T2 - Journal of the American Chemical Society AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTFormation and Characterization of a High-Spin Heme-Copper Dioxygen (Peroxo) ComplexReza A. Ghiladi, Telvin D. Ju, Dong-Heon Lee, Pierre Moënne-Loccoz, Susan Kaderli, Yorck-Michael Neuhold, Andreas D. Zuberbühler, Amina S. Woods, Robert J. Cotter, and Kenneth D. KarlinView Author Information Department of Chemistry, The Johns Hopkins University Charles & 34th Streets, Baltimore, Maryland 21218 Department of Biochemistry and Molecular Biology Oregon Graduate Institute, Beaverton, Oregon 97006 Institute für Anorganische Chemie University of Basel, CH-4056 Basel, Switzerland Department of Pharmacology and Molecular Sciences The Johns Hopkins School of Medicine Baltimore, Maryland 21205 Cite this: J. Am. Chem. Soc. 1999, 121, 42, 9885–9886Publication Date (Web):October 8, 1999Publication History Received5 July 1999Published online8 October 1999Published inissue 1 October 1999https://doi.org/10.1021/ja992296iCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views709Altmetric-Citations66LEARN 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 Read OnlinePDF (83 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Adducts,Ligands,Pyrroles,Reactivity,Saturation Get e-Alerts DA - 1999/10// PY - 1999/10// DO - 10.1021/ja992296i VL - 121 IS - 42 SP - 9885-9886 J2 - J. Am. Chem. Soc. LA - en OP - SN - 0002-7863 1520-5126 UR - http://dx.doi.org/10.1021/ja992296i DB - Crossref ER - TY - JOUR TI - Dioxygen reactivity of fully reduced [LFeII⋯CuI]+ complexes utilizing tethered tetraarylporphyrinates: Active site models for heme-copper oxidases T2 - Inorganic Chemistry DA - 1999/// PY - 1999/// VL - 38 IS - 10 SP - 2244-2245 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0001509852&partnerID=MN8TOARS ER - TY - JOUR TI - Glucose sensor for low-cost lifetime-based sensing using a genetically engineered protein AU - Tolosa, L. AU - Gryczynski, I. AU - Eichhorn, L.R. AU - Dattelbaum, J.D. AU - Castellano, F.N. AU - Rao, G. AU - Lakowicz, J.R. T2 - Analytical Biochemistry AB - We describe a glucose sensor based on a mutant glucose/galactose binding protein (GGBP) and phase-modulation fluorometry. The GGBP from Escherichia coli was mutated to contain a single cysteine residue at position 26. When labeled with a sulfhydryl-reactive probe 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid, the labeled protein displayed a twofold decrease in intensity in response to glucose, with a dissociation constant near 1 microM glucose. The ANS-labeled protein displayed only a modest change in lifetime, precluding lifetime-based sensing of glucose. A modulation sensor was created by combining ANS26-GGBP with a long-lifetime ruthenium (Ru) metal-ligand complex on the surface of the cuvette. Binding of glucose changed the relative intensity of ANS26-GGBP and the Ru complex, resulting in a dramatic change in modulation at a low frequency of 2.1 MHz. Modulation measurements at 2.1 MHz were shown to accurately determine the glucose concentration. These results suggest an approach to glucose sensing with simple devices. DA - 1999/// PY - 1999/// DO - 10.1006/abio.1998.2974 VL - 267 IS - 1 SP - 114-120 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033081688&partnerID=MN8TOARS ER - TY - JOUR TI - Two-photon excitation of rhenium metal-ligand complexes AU - Lakowicz, J.R. AU - Castellano, F.N. AU - Gryczynski, I. AU - Gryczynski, Z. AU - Dattelbaum, J.D. T2 - Journal of Photochemistry and Photobiology A: Chemistry DA - 1999/// PY - 1999/// VL - 122 IS - 2 SP - 95-101 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0011578262&partnerID=MN8TOARS ER - TY - JOUR TI - Long-lifetime lipid rhenium metal-ligand complex for probing membrane dynamics on the microsecond timescale AU - Li, L. AU - Castellano, F.N. AU - Gryczynski, I. AU - Lakowicz, J.R. T2 - Chemistry and Physics of Lipids AB - We report the luminescence and spectral properties of a phospholipid analogue containing a long-lifetime luminescent rhenium metal–ligand complex (MLC) covalently linked to the amino group of phosphatidyl ethanolamine. When incorporated into synthetic membranes, this lipid probe displays intensity decay times near 3 μs. Importantly, the probe displays highly polarized emission with a maximal fundamental anisotropy of 0.33. This probe is expected to have numerous applications for studies of microsecond diffusion and dynamics of membranes. DA - 1999/// PY - 1999/// DO - 10.1016/S0009-3084(99)00002-X VL - 99 IS - 1 SP - 1-9 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032933714&partnerID=MN8TOARS KW - long-lifetime lipid KW - rhenium metal-ligand complex KW - membrane dynamics ER - TY - JOUR TI - Light-Harvesting Arrays with Coumarin Donors and MLCT Acceptors AU - Tyson, Daniel S. AU - Castellano, Felix N. T2 - Inorg. Chem. AB - We present a light-harvesting strategy that utilizes organic donor molecules to achieve sensitized metal-to-ligand charge transfer (MLCT) based emission. In this scheme, coumarin dye molecules are covalently linked to the periphery of diimine ligands in Ru(II) inorganic complexes that display MLCT excited states. Our findings suggest that the singlet−singlet energy transfer strategies traditionally employed in artificial light-harvesting arrays can be adapted to incorporate MLCT excited states. DA - 1999/10// PY - 1999/10// DO - 10.1021/ic9905300 VL - 38 IS - 20 SP - 4382-4383 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0001445634&partnerID=MN8TOARS ER - TY - JOUR TI - Intramolecular singlet and triplet energy transfer in a ruthenium(II) diimine complex containing multiple pyrenyl chromophores AU - Tyson, D.S. AU - Castellano, F.N. T2 - Journal of Physical Chemistry A DA - 1999/// PY - 1999/// VL - 103 IS - 50 SP - 10955-10960 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0001549018&partnerID=MN8TOARS ER - TY - JOUR TI - Synthesis and characterization of ReV, ReVI and ReVII complexes of the [α2-P2W17O61]10– isomer  AU - Venturelli, Anne AU - Nilges, Mark J. AU - Smirnov, Alex AU - Belford, R. L. AU - Francesconi, Lynn C. T2 - J. Chem. Soc., Dalton Trans. AB - 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. DA - 1999/// PY - 1999/// DO - 10.1039/a805286g IS - 3 SP - 301 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33846947615&partnerID=MN8TOARS ER - TY - JOUR TI - Magnetic resonance imaging in a hands‐on student experiment using an EPR spectrometer AU - Smirnov, Alex I. AU - Belford, R. L. T2 - Concepts Magn. Reson. AB - 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 DA - 1999/// PY - 1999/// DO - 10.1002/(sici)1099-0534(1999)11:5<277::aid-cmr1>3.3.co;2-y VL - 11 IS - 5 SP - 277-290 ER - TY - JOUR TI - Magnetic resonance imaging in a hands-on student experiment using an EPR spectrometer AU - Smirnov, A.I. AU - Belford, R.L. AU - Morse, R. T2 - Concepts Magn. Reson. AB - 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 DA - 1999/// PY - 1999/// DO - 10.1002/(sici)1099-0534(1999)11:5<277::aid-cmr1>3.0.co;2-6 VL - 11 IS - 5 SP - 277-290 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033435065&partnerID=MN8TOARS ER - TY - JOUR TI - Interaction of Gd(III) MRI contrast agents with membranes: A review of recent EPR studies AU - Smirnova, T.I. AU - Smirnov, A.I. AU - Belford, R.L. AU - Clarkson, R.B. T2 - Magnetic Resonance Materials in Physics, Biology and Medicine DA - 1999/// PY - 1999/// DO - 10.1016/S1352-8661(99)00031-9 VL - 8 IS - 3 SP - 214-229 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032850878&partnerID=MN8TOARS ER - TY - JOUR TI - A new water‐soluble and lipid‐insoluble spin probe: application to the study of aqueous sucrose solutions AU - Belton, Peter S. AU - Sutcliffe, Leslie H. AU - Gillies, Duncan G. AU - Wu, Xiaoping AU - Smirnov, Alex I. T2 - Magn. Reson. Chem. DA - 1999/1// PY - 1999/1// DO - 10.1002/(sici)1097-458x(199901)37:1<36::aid-mrc405>3.3.co;2-# VL - 37 IS - 1 SP - 36-42 ER - TY - JOUR TI - A new water-soluble and lipid-insoluble spin probe: application to the study of aqueous sucrose solutions AU - Belton, Peter S. AU - Sutcliffe, Leslie H. AU - Gillies, Duncan G. AU - Wu, Xiaoping AU - Smirnov, Alex I. T2 - Magn. Reson. Chem. AB - 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. DA - 1999/1// PY - 1999/1// DO - 10.1002/(sici)1097-458x(199901)37:1<36::aid-mrc405>3.0.co;2-8 VL - 37 IS - 1 SP - 36-42 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032590088&partnerID=MN8TOARS KW - ESR KW - spin probe KW - aqueous sucrose KW - rotational correlation times ER - TY - JOUR TI - Interaction of Gd(III) MRI contrast agents with membranes: a review of recent EPR studies AU - Smirnova, Tatyana I. AU - Smirnov, Alex I. AU - Belford, R. L. AU - Clarkson, R. B. T2 - MAGMA DA - 1999/8// PY - 1999/8// DO - 10.1007/bf02594601 VL - 8 IS - 3 SP - 214-229 ER - TY - JOUR TI - Bioreduction of Tempone and Spin-Labeled Gentamicin by Gram-Negative Bacteria: Kinetics and Effect of Ultrasound AU - Rapoport, Natalya AU - Smirnov, Alex I. AU - Pitt, William George AU - Timoshin, Alexander A. T2 - Archives of Biochemistry and Biophysics AB - 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, intoPseudomonas aeruginosaandEscherichia colicells. 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. DA - 1999/2// PY - 1999/2// DO - 10.1006/abbi.1998.1020 VL - 362 IS - 2 SP - 233-241 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033557094&partnerID=MN8TOARS KW - bioreduction KW - Pseudomonas aeruginosa KW - E-coli KW - EPR KW - tempone KW - gentamicin KW - cell membrane permeability ER - TY - JOUR TI - Solution Electron Affinity Perturbation Due to the Deuteration of [16]Annulene AU - Kurth, Todd L. AU - Brown, Eric C. AU - Smirnov, Alex I. AU - Reiter, Richard C. AU - Stevenson, Cheryl D. T2 - J. Phys. Chem. A AB - 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-. DA - 1999/10// PY - 1999/10// DO - 10.1021/jp992794d VL - 103 IS - 42 SP - 8566-8572 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0000987091&partnerID=MN8TOARS ER - TY - JOUR TI - A combined instantaneous normal mode and time correlation function description of the infrared vibrational spectrum of ambient water AU - Ahlborn, Heather AU - Ji, Xingdong AU - Space, Brian AU - Moore, Preston B. T2 - The Journal of Chemical Physics AB - A formal connection is made between the vibrational density of states (DOS) of a liquid and its approximation by way of instantaneous normal modes (INMs). This analysis leads to a quantum generalization of the INM method (QINM), and to the possibility of evaluating the classical DOS exactly. Further, INM approximations to spectroscopic quantities (e.g., infrared absorption and Raman scattering) follow in a consistent manner by evaluating the appropriate golden rule expressions for harmonic oscillators, using the INM or QINM DOS in place of the true DOS. INM and QINM methods are then applied along with traditional time correlation function (TCF) methods to analyze the entire infrared (IR) spectrum of ambient water. The INM and TCF approaches are found to offer complimentary information. TCF methods are shown to offer an unexpectedly accurate description of the O–H stretching line shape. Further, the 19-fold enhancement in liquid phase absorption compared to the gas phase is also reproduced. INM and QINM methods are used to analyze the molecular origin of the water spectrum, and prove especially effective in analyzing the broad O–H stretching absorption. Further, it is argued that a motional narrowing picture is qualitatively useful in analyzing INM approximations to spectroscopy. DA - 1999/12/15/ PY - 1999/12/15/ DO - 10.1063/1.480415 VL - 111 IS - 23 SP - 10622-10632 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.480415 DB - Crossref ER - TY - JOUR TI - Use of late transition metal catalysts in acetylene polymerization. AU - GORMAN, CB AU - VEST, RW AU - PALOVICH, TU AU - al., T2 - ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY DA - 1999/// PY - 1999/// VL - 217 SP - U432 ER - TY - JOUR TI - Preparation of poly(cyanoacetylene) using late-transition-metal catalysts AU - GORMAN, CB AU - VEST, RW AU - PALOVICH, TU AU - al., T2 - MACROMOLECULES DA - 1999/// PY - 1999/// VL - 32 IS - 13 SP - 4157-4165 ER - TY - JOUR TI - Molecular structure-property relationships for electron-transfer rate attenuation in redox-active core dendrimers AU - GORMAN, CB AU - SMITH, JC AU - HAGER, MW AU - al., T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY DA - 1999/// PY - 1999/// VL - 121 IS - 43 SP - 9958-9966 ER - TY - JOUR TI - Hybrid organic-inorganic, hexa-arm dendrimers based on an Mo6Cl8 core AU - GORMAN, CB AU - SU, WY AU - JIANG, HW AU - al., T2 - CHEMICAL COMMUNICATIONS DA - 1999/// PY - 1999/// IS - 10 SP - 877-878 ER - TY - JOUR TI - Contrasting structural features for flexible and rigid metallodendrimers - experiment and computation. AU - SMITH, JC AU - GORMAN, CB T2 - ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY DA - 1999/// PY - 1999/// VL - 217 SP - U398 ER - TY - PAT TI - Methods of etching articles via microcontact printing AU - Whitesides, G. M. AU - Xia, Y. AU - Wilbur, J. L. AU - Jackman, R. J. AU - Kim, E. AU - Prentiss, M. G. AU - Mrksich, M. AU - Kumar, A. AU - Gorman, C. B. AU - Biebuyck, H. AU - Berggren, K. K. C2 - 1999/// DA - 1999/// PY - 1999/// ER - TY - JOUR TI - Temperature effects on the kinetics of carbonate radical reactions in near-critical and supercritical water AU - Ferry, J. L. AU - Fox, M. A. T2 - Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment & General Theory DA - 1999/// PY - 1999/// VL - 103 IS - 18 SP - 3438-3441 ER - TY - JOUR TI - The Mukaiyama-Michael reaction of N-acyl-2,3-dihydro-4- pyridones: Regio- and stereoselective synthesis of cis-2,6- disubstituted 1,2,5,6-tetrahydropyridines AU - Kuethe, J. T. AU - Comins, D. L. T2 - Organic Letters AB - [formula: see text] A convenient regio- and stereoselective preparation of 1,2,5,6-tetrahydropyridines of the type 1 has been developed, starting from readily available N-acyl-2,3-dihydro-4-pyridones 2. DA - 1999/// PY - 1999/// DO - 10.1021/ol9908124 VL - 1 IS - 7 SP - 1031-1033 ER - TY - JOUR TI - Building fluorescent sensors by template polymerization: The preparation of a fluorescent sensor for D-Fructose AU - Wang, W AU - Gao, SH AU - Wang, BH T2 - ORGANIC LETTERS AB - [formula: see text] The application of molecular imprinting in making fluorescent sensors has been hampered by the lack of suitable fluorescent tags, which would respond to the binding event with significant fluorescence intensity changes. We have designed and synthesized a fluorescent monomer which allows for the preparation of fluorescent sensors of cis diols using molecular imprinting methods. This monomer was used for the preparation of sensitive fluorescent sensors for D-fructose. DA - 1999/10/21/ PY - 1999/10/21/ DO - 10.1021/ol9908732 VL - 1 IS - 8 SP - 1209-1212 SN - 1523-7060 ER - TY - JOUR TI - An efficient one-flask synthesis of N-confused tetraphenylporphyrin AU - Geier, GR AU - Haynes, DM AU - Lindsey, JS T2 - ORGANIC LETTERS AB - N-Confused meso-substituted porphyrin is a porphyrin isomer previously available from one-flask porphyrin syntheses as a low-yield byproduct (<7.5%). We have found that methanesulfonic acid catalyzed condensation of pyrrole and benzaldehyde followed by DDQ oxidation provides N-confused tetraphenylporphyrin (NC-TPP) in up to 39% yield in analytical scale experiments. Preparative synthesis provided an isolated yield of 35% (800 mg). This represents a >5-fold yield improvement and makes significant quantities of NC-TPP readily available. DA - 1999/11/4/ PY - 1999/11/4/ DO - 10.1021/ol9910114 VL - 1 IS - 9 SP - 1455-1458 SN - 1523-7060 ER - TY - JOUR TI - A novel optical sensor for metal ions based on ground-state intermolecular charge-transfer complexation AU - Gromov, SP AU - Ushakov, EN AU - Vedernikov, AI AU - Lobova, NA AU - Alfimov, MV AU - Strelenko, YA AU - Whitesell, JK AU - Fox, MA T2 - ORGANIC LETTERS AB - A derivative of dipyridylethylene 2 was synthesized in order to study intermolecular coordination between the 18-crown-6 ether units of bis-crown stilbene 1 and the NH3+ groups of 2. In acetonitrile solution, the formation of a supramolecular complex is evidenced by a considerable upfield shift of the 1H NMR signals from the aromatic and olefinic protons. Emission quenching and the appearance of a new absorption band in the visible spectral region indicate the formation of a charge-transfer complex. The addition of Ba2+ to a solution of the complex leads to significant fluorescence enhancement and to the disappearance of the charge-transfer absorption band. DA - 1999/12/2/ PY - 1999/12/2/ DO - 10.1021/ol990710d VL - 1 IS - 11 SP - 1697-1699 SN - 1523-7060 ER - TY - JOUR TI - Synthesis and characterization of a planarized, trimethylenemethane-type bis(semiquinone) biradical AU - Shultz, DA AU - Lee, HY AU - Fico, RM T2 - TETRAHEDRON AB - The synthesis and characterization of a biradical in which two semiquinone rings are held rigidly co-planar and are attached in a geminal fashion to a carbon-carbon double bond is described. The results of cyclic voltammetry and variable-temperature EPR studies are interpreted in terms of the interaction of the two semiquinones through the carbon-carbon double bond coupling unit. DA - 1999/10/8/ PY - 1999/10/8/ DO - 10.1016/s0040-4020(99)00714-0 VL - 55 IS - 41 SP - 12079-12086 SN - 0040-4020 KW - benzoquinone KW - conformation KW - electrochemistry KW - molecular design KW - radicals ER - TY - JOUR TI - Spectral and cyclic voltammetric characterization of self-assembled monolayers on gold of pyrene end-labeled oligonucleotide duplexes AU - Reese, RS AU - Fox, MA T2 - CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE AB - Self-assembled monolayers of sulfur-terminated oligonucleotide duplexes were formed on flat gold surfaces, either by exposure of a self-assembled monolayer bearing one oligonucleotide strand to the complementary strand or by preformation of a oligonucleotide duplex that was then deposited on a fresh gold surface. Virtually identical spectral behavior was observed whether the duplex was produced before deposition or by in situ complementary association. With a duplex bearing an appropriate pyrene end-label, the resulting thin film was photoresponsive. Surface emission measurements show no evidence for pyrene aggregation on the modified surfaces. The polarity of the photocurrent, reflecting photoinduced electron transfer initiated by photoexcitation of pyrene, is opposite that expected from the oligonucleotide-mediated reduction of the appended pyrene excited state.Key words: oligonucleotide, self-assembled monolayer, duplex formation, photoelectrochemistry, surface emission. DA - 1999/// PY - 1999/// DO - 10.1139/cjc-77-5-6-1077 VL - 77 IS - 5-6 SP - 1077-1084 SN - 0008-4042 KW - oligonucleotide KW - self-assembled monolayer KW - duplex formation KW - photoelectrochemistry KW - surface emission ER - TY - JOUR TI - Iron regulatory element and internal loop/bulge structure for ferritin mRNA studied by cobalt(III) hexammine binding, molecular modeling, and NMR spectroscopy (vol 37, pg 1505, 1998) AU - Gdaniec, Z AU - Sierzputowska-Gracz, H AU - Theil, EC T2 - BIOCHEMISTRY AB - ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionIron Regulatory Element and Internal Loop/Bulge Structure for Ferritin mRNA Studied by Cobalt(III) Hexammine Binding, Molecular Modeling, and NMR SpectroscopyZofia Gdaniec, Hanna Sierzputowska-Gracz, and Elizabeth C. TheilCite this: Biochemistry 1999, 38, 17, 5676Publication Date (Web):April 8, 1999Publication History Published online8 April 1999Published inissue 1 April 1999https://doi.org/10.1021/bi9950746Copyright © 1999 American Chemical SocietyRequest reuse permissions This publication is free to access through this site. Learn MoreArticle Views286Altmetric-Citations5LEARN 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 (5 KB) Get e-Alertsclose Get e-Alerts DA - 1999/4/27/ PY - 1999/4/27/ DO - 10.1021/bi9950746 VL - 38 IS - 17 SP - 5676-5676 SN - 0006-2960 ER - TY - JOUR TI - Importance of the indentation depth in tapping-mode atomic force microscopy study of compliant materials AU - Bar, G AU - Delineau, L AU - Brandsch, R AU - Bruch, M AU - Whangbo, MH T2 - APPLIED PHYSICS LETTERS AB - We studied the response of a cantilever tapping on polydimethylsiloxane (PDMS) samples of different crosslink density. It is shown experimentally that the tip deeply penetrates into the compliant PDMS samples. A more compliant material leads to a larger indentation such that at a given set-point ratio the indentation force is nearly constant on samples of different elastic moduli. This confirms the simulations by J. Tamayo and R. Garcia [Appl. Phys. Lett. 71, 2394 (1997)] that phase contrast acquired at constant set point does not depend on the sample’s modulus if other contrast relevant parameters remain identical. PDMS samples of different crosslink density are distinguished in terms of amplitude and phase versus distance measurements if the tip-sample interaction is made substantially large and indentation is taken into account. DA - 1999/12/27/ PY - 1999/12/27/ DO - 10.1063/1.125581 VL - 75 IS - 26 SP - 4198-4200 SN - 0003-6951 ER - TY - JOUR TI - Gold particles as templates for the synthesis of hollow polymer capsules. Control of capsule dimensions and guest encapsulation AU - Marinakos, SM AU - Novak, JP AU - Brousseau, LC AU - House, AB AU - Edeki, EM AU - Feldhaus, JC AU - Feldheim, DL T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - A method for synthesizing hollow nanoscopic polypyrrole and poly(N-methylpyrrole) capsules is described. The method employs gold nanoparticles as templates for polymer nucleation and growth. Etching the gold leaves a structurally intact hollow polymer capsule with a shell thickness governed by polymerization time (ca. 5 to >100 nm) and a hollow core diameter dictated by the diameter of the template particle (ca. 5−200 nm). Transport rates of gold etchant through the polymer shell to the gold core were found to depend on the oxidation state of the polymer, those rates being a factor of 3 greater for the reduced form of the polymer. We show for the first time that not only is the particle a useful template material but also that it can be employed to deliver guest molecules into the capsule core. For example, ligands attached to the gold surface prior to poly(N-methylpyrrole) formation remained trapped inside the hollow capsule following polymer formation and gold etching. DA - 1999/9/22/ PY - 1999/9/22/ DO - 10.1021/ja990945k VL - 121 IS - 37 SP - 8518-8522 SN - 0002-7863 ER - TY - CHAP TI - Conformational exchange modulation in trimethylenemethane-type biradicals AU - Shultz, D. A. T2 - Magnetic properties of organic materials CN - QD476 .M24 1999 PY - 1999/// SP - 103-126 PB - New York: Marcel Dekker ER - TY - JOUR TI - Both an oxidation/reduction sequence and deprotonation of a unique paramagnetic ligand lead to a mixed-valent complex AU - Shultz, DA AU - Bodnar, SH AU - Kumar, RK AU - Kampf, JW T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTBoth an Oxidation/Reduction Sequence and Deprotonation of a Unique Paramagnetic Ligand Lead to a Mixed-Valent ComplexDavid A. Shultz, Scot H. Bodnar, R. Krishna Kumar, and Jeff W. KampfView Author Information Department of Chemistry North Carolina State University Raleigh, North Carolina 27695-8204 Department of Chemistry, University of Michigan Ann Arbor, Michigan 48109-1055 Cite this: J. Am. Chem. Soc. 1999, 121, 45, 10664–10665Publication Date (Web):November 3, 1999Publication History Received2 September 1999Published online3 November 1999Published inissue 1 November 1999https://doi.org/10.1021/ja9931675Copyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views208Altmetric-Citations27LEARN 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 Read OnlinePDF (94 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Anions,Deprotonation,Ligands,Potassium,Redox reactions Get e-Alerts DA - 1999/11/17/ PY - 1999/11/17/ DO - 10.1021/ja9931675 VL - 121 IS - 45 SP - 10664-10665 SN - 0002-7863 ER - TY - JOUR TI - Atomistic simulations of structures and mechanical properties of polycrystalline diamond: Symmetrical < 001 > tilt grain boundaries AU - Shenderova, OA AU - Brenner, DW AU - Yang, LH T2 - PHYSICAL REVIEW B AB - Atomic structures and energies of symmetrical 〈001〉 tilt grain boundaries (GB's) in diamond have been calculated over a wide range of misorientation angle using a many-body analytic potential, and for some selected short-period grain boundaries with tight-binding and first-principles density-functional methods. The grain boundary energies from the tight-binding and first-principles methods are about 75% of those calculated with the analytic bond-order potential. The energy rankings of the GB's calculated with the empirical potential, however, are similar to that calculated from the tight-binding and the density functional approaches. Atomic-level energy and stress distributions calculated with the bond-order potential reveal relations between local interface reconstruction and the extent and value of hydrostatic and shear stresses. From the calculated local volume strain and hydrostatic stress fields, the atomic bulk moduli are evaluated, and zones of different elastic behavior in the vicinity of the interface are defined. DA - 1999/9/1/ PY - 1999/9/1/ DO - 10.1103/physrevb.60.7043 VL - 60 IS - 10 SP - 7043-7052 SN - 1550-235X ER - TY - JOUR TI - Atomistic simulations of structures and mechanical properties of < 011 > tilt grain boundaries and their triple junctions in diamond AU - Shenderova, OA AU - Brenner, DW T2 - PHYSICAL REVIEW B AB - Atomic structures, energies, and stress distributions of symmetrical 〈011〉 tilt grain boundaries (GB's) and selected GB triple junctions (TJ's) in diamond as well as a multiply twinned diamond particle have been calculated using an analytic bond order potential function. In general, energies of 〈011〉 tilt GB's are about 1 ${\mathrm{J}/\mathrm{m}}^{2}$ lower than those for 〈001〉 tilt GB's calculated with the same analytic potential. Energy ordering for two models of the $\ensuremath{\Sigma}=3(21\mathbf{\ifmmode\bar\else\textasciimacron\fi{}}1)$ GB obtained with the present bond-order potential is consistent with results from a tight-binding model. Atomic structures of selected triple junctions of 〈011〉 grain boundaries are modeled and atomic reconstructions within TJ cores that eliminate dangling bonds are suggested. Despite a perfect geometrical matching of structural units within the triple junction cores, excess energies and stresses exist in the vicinity of these structures. Characteristics of atomic stress distributions in multiply twinned particles agree with predictions of continuum disclination theory. DA - 1999/9/1/ PY - 1999/9/1/ DO - 10.1103/physrevb.60.7053 VL - 60 IS - 10 SP - 7053-7061 SN - 1550-235X ER - TY - JOUR TI - An artificial photosynthetic antenna-reaction center complex AU - Kuciauskas, D AU - Liddell, PA AU - Lin, S AU - Johnson, TE AU - Weghorn, SJ AU - Lindsey, JS AU - Moore, AL AU - Moore, TA AU - Gust, D T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - A model photosynthetic antenna consisting of four covalently linked zinc tetraarylporphyrins, (PZP)3−PZC, has been joined to a free base porphyrin-fullerene artificial photosynthetic reaction center, P−C60, to form a (PZP)3−PZC−PC60 hexad. As revealed by time-resolved absorption and emission studies, excitation of any peripheral zinc porphyrin moiety (PZP) in 2-methyltetrahydrofuran solution is followed by singlet−singlet energy transfer to the central zinc porphyrin to give (PZP)3−1PZC−P−C60 with a time constant of ∼50 ps. The excitation is passed on to the free base porphyrin in 240 ps to produce (PZP)3−PZC−1P−C60, which decays by electron transfer to the fullerene with a time constant of 3 ps. The (PZP)3−PZC−P•+−C60•- charge-separated state thus formed has a lifetime of 1330 ps, and is generated with a quantum yield of 0.70 based on light absorbed by the zinc porphyrin antenna. The complex thus mimics the basic functions of natural photosynthetic antenna systems and reaction center complexes. DA - 1999/9/22/ PY - 1999/9/22/ DO - 10.1021/ja991255j VL - 121 IS - 37 SP - 8604-8614 SN - 1520-5126 ER - TY - JOUR TI - Theoretical studies of surface reactions on metals: I. Ethyl to ethylene conversion on platinum; II. Photodissociation of methane on platinum AU - Whitten, JL T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - An embedding method designed to provide a molecular level understanding of adsorbate energetics and surface reaction mechanisms is presented. Electronic structures, including relativistic effects, are described by an ab initio formalism that permits an accurate determination of energies and adsorbate structure. Applications to catalytic and photochemical reactions on transition metal surfaces are reported. (I) In the catalytic conversion of ethyl adsorbed on platinum surfaces to ethylene, the minimum energy pathway for the transfer of hydrogen to the metal surface is calculated. A detailed description of the transition state is presented. (II) In the photodissociation of methane physisorbed on platinum, results are reported for a methane molecule interacting with an embedded cluster model of Pt(111). Configuration interaction theory is used to sort out states resulting from electron attachment to methane from lower energy states that correspond to metal excitations. Energies of the ground and excited states of the Pt(111)CH4 complex are calculated as a function of geometrical distortions and the distance of methane from the surface. Key steps in the photodissociation process are described. DA - 1999/// PY - 1999/// DO - 10.1116/1.581878 VL - 17 IS - 4 SP - 1710-1716 SN - 0734-2101 ER - TY - JOUR TI - Direct analysis of the products of sequential cleavages of peptides and proteins affinity-bound to immobilized metal ion beads by matrix-assisted laser desorption/ionization mass spectrometry AU - Qian, XH AU - Zhou, W AU - Khaledi, MG AU - Tomer, KB T2 - ANALYTICAL BIOCHEMISTRY AB - Consecutive enzymatic reactions on analytes affinity-bound to immobilized metal ion beads with subsequent direct analysis of the products by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry have been used for detecting protein synthesis errors occuring at the N-terminus. The usefulness of this method was demonstrated by analyzing two commercially available recombinant HIV proteins with affinity tags at the N-terminus, and histatin-5, a peptide with multiple histidine residues. The high specificity, sensitivity, and speed of analysis make this method especially useful in obtaining N-terminal sequencing information of histidine-tagged recombinant proteins. DA - 1999/10/15/ PY - 1999/10/15/ DO - 10.1006/abio.1999.4268 VL - 274 IS - 2 SP - 174-180 SN - 1096-0309 KW - MALD/TOF/MS KW - immobilized metal ionaffinity chromatography KW - protein synthesis error ER - TY - JOUR TI - Correlation between frequency-sweep hysteresis and phase imaging instability in tapping mode atomic force microscopy AU - Bar, G AU - Brandsch, R AU - Whangbo, MH T2 - SURFACE SCIENCE AB - Abstract Frequency-sweep and phase imaging experiments of tapping mode atomic force microscopy were carried out for patterned self-assembled monolayers of S(CH 2 ) 15 CH 3 and S(CH 2 ) 12 OH groups on a polycrystalline Au substrate. The phase shift values of opposite signs associated with phase imaging instability are shown to be the same as the corresponding ones resulting from frequency-sweep hysteresis. DA - 1999/8/10/ PY - 1999/8/10/ DO - 10.1016/S0039-6028(99)00702-5 VL - 436 IS - 1-3 SP - L715-L723 SN - 1879-2758 KW - frequency-sweep hysteresis KW - phase imaging instability KW - surface analysis KW - tapping mode atomic force microscopy KW - (TMAFM) ER - TY - JOUR TI - Asymmetric synthesis and synthetic utility of 2,3-dihydro-4-pyridones AU - Comins, DL T2 - JOURNAL OF HETEROCYCLIC CHEMISTRY AB - Journal of Heterocyclic ChemistryVolume 36, Issue 6 p. 1491-1500 Article Asymmetric synthesis and synthetic utility of 2,3-dihydro-4-pyridones Daniel L. Comins, Daniel L. Comins Department of Chemistry, North Carolina State University, Raleigh, NC 27695–8204 USASearch for more papers by this author Daniel L. Comins, Daniel L. Comins Department of Chemistry, North Carolina State University, Raleigh, NC 27695–8204 USASearch for more papers by this author First published: 12 March 2009 https://doi.org/10.1002/jhet.5570360610Citations: 85AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume36, Issue6November/December 1999Pages 1491-1500 RelatedInformation DA - 1999/// PY - 1999/// DO - 10.1002/jhet.5570360610 VL - 36 IS - 6 SP - 1491-1500 SN - 1943-5193 ER - TY - JOUR TI - Analysis of the spin-spin interactions in layered oxides alpha '-NaV2O5, CaV2O5 and MgV2O5 and the spin-Peierls distortion in alpha '-NaV2O5 by molecular orbital, Madelung energy and bond valence sum calculations AU - Koo, HJ AU - Whangbo, MH T2 - SOLID STATE COMMUNICATIONS AB - The spin–spin exchange parameters of α′-NaV2O5, CaV2O5 and MgV2O5 were examined by calculating the spin–spin interaction energies of their spin dimers, and the probable pairing distortion leading to the (2a×2b×4c) superstructure of α′-NaV2O5 was investigated by performing Madelung energy and bond valence sum analyses. In the V2O5 layers of α′-NaV2O5, CaV2O5 and MgV2O5, ladder chains of vanadium atoms are arranged in a staggered manner. CaV2O5 and MgV2O5 have an unpaired spin at each vanadium site, while α′-NaV2O5 has one unpaired spin in each rung of the ladder chains. The latter makes α′-NaV2O5 behave as a spin 1/2 Heisenberg linear chain system. Madelung energy and bond valence sum calculations for α′-NaV2O5 show that the pairing distortion from the uniform spin lattice to the zigzag spin lattice proposed by Seo and Fukuyama is energetically favorable. In the zigzag spin lattice the paired spins do not reside in the ladder chains but in between the ladder chains, which makes α′-NaV2O5 different from a simple spin-Peierls system. DA - 1999/// PY - 1999/// DO - 10.1016/S0038-1098(99)00179-9 VL - 111 IS - 7 SP - 353-360 SN - 1879-2766 KW - magnetically ordered materials KW - semiconductors KW - electronic states (localized) KW - exchange and superexchange KW - phase transitions ER - TY - JOUR TI - Analysis of polarized optical excitations by electronic band structure calculations: organic superconductor beta ''-(BEDT-TTF)(2)SF5CH2CF2SO3 AU - Koo, HJ AU - Whangbo, MH AU - Dong, J AU - Olejniczak, I AU - Musfeldt, JL AU - Schlueter, JA AU - Geiser, U T2 - SOLID STATE COMMUNICATIONS AB - The room temperature polarized optical conductivity of the superconducting salt β″-(BEDT-TTF)2SF5CH2CF2SO3 was analyzed by calculating its electronic band structure using the extended Hückel tight binding method. The electronic band structure obtained with double-zeta orbitals is consistent with the observed optical properties. The optical transitions in the energy region of 0–0.75 eV are intraband transitions associated with the bands that result from the highest-occupied molecular orbitals of the BEDT-TTF molecules. The optical conductivity is much stronger along the interstack direction (b-axis direction) than along the direction perpendicular to it throughout the energy region of 0–0.75 eV. This anisotropy is readily accounted for by the band dispersion relations calculated for the wave vector directions parallel to the b∗ and a∗ directions. Polarized optical conductivity provides indirect information about the anisotropy of band dispersion relations. DA - 1999/// PY - 1999/// DO - 10.1016/S0038-1098(99)00379-8 VL - 112 IS - 7 SP - 403-407 SN - 0038-1098 KW - organic crystals KW - electronic band structure KW - optimal properties KW - light absorption and reflection ER - TY - JOUR TI - A novel resin linker for solid-phase peptide synthesis which call be cleaved using two sequential mild reactions AU - Zheng, AL AU - Shan, DX AU - Shi, XL AU - Wang, BH T2 - JOURNAL OF ORGANIC CHEMISTRY AB - The interest in developing new linkers for solid-phase peptide and organic synthesis has increased tremendously as a result of the rapid development of combinatorial chemistry. Herein, we report the development of a new redox-sensitive linker for solid-phase peptide synthesis. This linker can be readily cleaved under mild conditions by using two sequential mild reactions, a reduction followed by a base (Bu4N+F-)-catalyzed cyclic ether formation. By using this new linker, two short peptides, a tetrapeptide [Boc-Trp-Ala-Gly-Gly-OH] and a pentapeptide [Boc-Asn-Ala-Ser(OBn)-Gly-Glu(OBn)-OH)], were synthesized. Because the cleavage does not use acidic conditions, this resin linker provides an alternative when acidic conditions are not desirable. Furthermore, the cleavage conditions do not affect most of the side chain protecting group. Therefore, the peptides synthesized can be used for the segment synthesis of larger peptides without the need to reprotect the side chain functional groups. DA - 1999/10/1/ PY - 1999/10/1/ DO - 10.1021/jo990770x VL - 64 IS - 20 SP - 7459-7466 SN - 0022-3263 ER - TY - JOUR TI - The first systematic synthesis of heterobimetallic dithiolene-bridged complexes. Synthesis and characterization of metal complexes of 4-(1 ',2 '-ethylenedithiolate)-1,3-dithiole-2-one and dimeric metal complexes of 1,2,3,4-butadienetetrathiolate AU - Keefer, CE AU - Purrington, ST AU - Bereman, RD AU - Boyle, PD T2 - INORGANIC CHEMISTRY AB - The 1,2-dithiolene ligands 4-(1‘,2‘-ethylenedithiolate)-1,3-dithiole-2-one (eddo2-) and 1,2,3,4-butadienetetrathiolate (bdt4-) are synthesized by the controlled single or double 1,3-dithiole-2-one ring opening of 4,4‘-bis(1,3-dithiole-2-one) (bdo) (1). The synthesis and characterization of the novel transition metal complexes (COD)Pt(eddo) (2), (diphos)Ni(eddo) (3), [Bu4N][Ni(eddo)2] (4), (COD)Pt(bdt)Pt(COD) (5), and (diphos)Ni(bdt)Pt(COD) (6) (where COD = 1,5-cyclooctadiene, diphos = 1,2-bis(diphenylphosphino)ethane) are reported. Use of eddo2- and bdt4- results in the selective systematic synthesis of transition metal monomers and dimers. In addition, the synthesis of mixed metal dimeric complexes utilizing a “transition metal 1,2-dithiolene” ligand is demonstrated. The single-crystal X-ray structural analyses of the cocrystallized (COD)Pt(eddo)·1/2bdo, monoclinic, P21/n, a = 13.0388(4) Å, b = 9.2048(3) Å, c = 16.2384(5) Å, β = 97.289(5)°, Z = 4, and [Bu4N][Ni(eddo)2], monoclinic, P21/n, a = 8.3508(2) Å, b = 26.4703(7), c = 15.2778(3) Å, β = 99.8160(10)°, Z = 4, are reported. There is strong evidence of delocalization through the butadiene backbone of 1 which extends into the sulfur atoms. It also appears that there is some delocalization through the butadiene backbone of the eddo2- ligands in 2 and 4. DA - 1999/11/15/ PY - 1999/11/15/ DO - 10.1021/ic990841a VL - 38 IS - 23 SP - 5437-5442 SN - 0020-1669 ER - TY - JOUR TI - Template-directed synthesis, excited-state photodynamics, and electronic communication in a hexameric wheel of porphyrins AU - Li, JZ AU - Ambroise, A AU - Yang, SI AU - Diers, , JR AU - Seth, J AU - Wack, CR AU - Bocian, DF AU - Holten, D AU - Lindsey, JS T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - To investigate new architectures for molecular photonics applications, a shape-persistent cyclic hexameric architecture (cyclo-Zn3Fb3U-p/m) has been prepared that is comprised of three free base (Fb) porphyrins and three zinc porphyrins linked at the meso-positions via diphenylethyne units. The synthesis involves the Pd-mediated coupling of a p/p-substituted diethynyl Zn porphyrin and a m/m-substituted diiodo Fb porphyrin, forming p/m-substituted diphenylethyne linkages. The isolated yield of cyclo-Zn3Fb3U-p/m is 5.3% in the presence of a tripyridyl template. The array has C3v symmetry, 108 atoms in the shortest path, and a face-to-face distance of ∼35 Å across the cavity. The excited-state lifetime of the Zn porphyrin in cyclo-Zn3Fb3U-p/m is 17 ps, giving a rate of energy transfer to each adjacent Fb porphyrin of ktrans = (34 ps)-1 and a quantum efficiency of Φtrans = 99.2%. This rate is comparable to that in a dimer (ZnFbU-p/m) having an identical linker, but slower than that of a p/p-linked ZnFb dimer, which has ktrans = (24 ps)-1. At ambient temperatures, the hole/electron hopping rate in [cyclo-Zn6U-p/m]+ is comparable to or faster than the EPR time scale (∼4 MHz). The hole/electron hopping rate in [cyclo-Zn6U-p/m]+ appears to be more than 2-fold larger than for [Zn2U-p/m]+; [Zn2U-p/m]+ has a rate at least 10-fold slower than for the p/p-linked dimer [Zn2U]+. Both excited-state energy transfer and ground-state hole/electron hopping proceed via through-bond mechanisms mediated by the diphenylethyne linker. The origin of the slightly slower energy-transfer rate, and substantially slower ground-state hole/electron hopping rate, in the p/m-linked arrays versus the p/p-linked analogues, is attributed primarily to the larger electron density of the frontier molecular orbitals at the p- versus m-position of the phenyl ring in the diphenylethyne linker. Collectively, these results indicate that the site of attachment of the porphyrin to the linker could be used to direct energy and/or hole/electron flow in a controlled manner among porphyrins in diverse 3-dimensional (linear, cyclic, tubular) architectures. DA - 1999/9/29/ PY - 1999/9/29/ DO - 10.1021/ja991730d VL - 121 IS - 38 SP - 8927-8940 SN - 0002-7863 ER - TY - JOUR TI - Probing the molecular geometry of five-coordinate vanadyl complexes with pulsed ENDOR AU - Grant, CV AU - Geiser-Bush, KM AU - Cornman, CR AU - Britt, RD T2 - INORGANIC CHEMISTRY AB - The pulsed electron paramagnetic resonance (EPR) technique of (51)V electron spin echo-electron nuclear double resonance (ESE-ENDOR) has been used to measure the nuclear quadrupole coupling constants of a series of five-coordinate vanadyl complexes containing Schiff base ligands with geometries ranging from distorted square pyramidal to distorted trigonal bipyramidal. Vanadium nuclear quadrupole coupling constants are sensitive to the coordination geometry of the vanadyl ion, and thus sensitive to the structural distortions within this series of complexes. (51)V ESE-ENDOR has been shown to be a probe of the coordination geometry of vanadyl complexes. Such a spectroscopic probe should prove useful in the investigation of vanadyl of unknown coordination geometry, such as may be found in the interaction of the vanadyl ion with biomolecules. DA - 1999/12/27/ PY - 1999/12/27/ DO - 10.1021/ic9909173 VL - 38 IS - 26 SP - 6285-6288 SN - 0020-1669 ER - TY - JOUR TI - Photophysical quenching mediated by guanine groups in pyrenyl- N-alkylbutanoamide end-labeled oligonucleotides AU - Zahavy, E. AU - Fox, M. A. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 1999/// PY - 1999/// VL - 103 IS - 43 SP - 9321-9327 ER - TY - JOUR TI - Further development of a versatile microscale automated workstation for parallel adaptive experimentation AU - Cork, D. G. AU - Sugawara, T. AU - Lindsey, Jonathan AU - Corkan, L. A. AU - Du, H. T2 - Laboratory Robotics and Automation AB - We have further developed our microscale automated chemistry workstation for investigating the optimization of reaction conditions. The workstation includes a Cartesian robot for solvent delivery and reagent/sample handling, a 60-vessel reaction block, a UV–Vis absorption spectrometer, and vial racks for compound storage. This article describes the following hardware additions that increase the scope and versatility of the workstation: (a) an analytical high performance liquid chromatography (HPLC) instrument and accompanying hardware interface (slide rail, autosampler); (b) three reactor blocks of 20 vessels each, with independent temperature control of each reactor block between ca. 0 and 80°C; (c) a shaker rack for mixing, dilution, or extraction of samples; (d) a rotary valve on the dispense line for complete isolation of 4 independent solvent lines; (e) sample workup features using disposable cartridges or filters; (f) provisions for dispensing inert gas, for example, for flushing through reactors or for storing solvents and performing transfer/dispense operations under. Using the new features, we are able to obtain useful analytical data from a wider range of reaction mixtures, perform parallel reactions at different temperatures, and handle solvents and sensitive reagents. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 217–223, 1999 DA - 1999/// PY - 1999/// DO - 10.1002/(SICI)1098-2728(1999)11:4<217::AID-LRA6>3.3.CO;2-3 VL - 11 IS - 4 SP - 217–223 ER - TY - JOUR TI - Electronic interactions in verdazyl biradicals AU - Fico, RM AU - Hay, MF AU - Reese, S AU - Hammond, S AU - Lambert, E AU - Fox, MA T2 - JOURNAL OF ORGANIC CHEMISTRY AB - A series of bisverdazyl biradicals in which the atoms bearing the greatest spin density are separated by several different aromatic spacer groups has been prepared in order to compare their properties to those of the nonspaced 1,1‘,5,5‘-tetramethyl-6,6‘-dioxo-3,3‘-bisverdazyl (1). In addition, the 6,6‘-dithio derivative (1,1‘,5,5‘-tetramethyl-6,6‘-dithio-3,3‘-bisverdazyl (7)) was prepared. Cyclic voltammograms of 1,4-bis(1,5-dimethyl-6-oxo-3-verdazyl)benzene (5) and 2,5-bis(1,5-dimethyl-6-oxo-3-verdazyl)thiophene (6) both show a single two-electron oxidation near 700 mV. In contrast 1, 7, and 1,3-bis(1,5-dimethyl-6-oxo-3-verdazyl)benzene (4) display two one-electron oxidation waves, with the first oxidative wave appearing also near 700 mV. The absorption spectrum of each of these biradicals was red-shifted from the maximum observed for 1. Biradicals 4, 5, and 6 exhibited linear Curie plots, although a curved Curie plot was observed for 7 with J = 560 cm-1. DA - 1999/12/24/ PY - 1999/12/24/ DO - 10.1021/jo990962s VL - 64 IS - 26 SP - 9386-9392 SN - 0022-3263 ER - TY - JOUR TI - Charge transfer complexation of ruthenium tris-bipyridine by a stable carbene AU - Zhang, Y AU - Fox, MA T2 - ACTA CHEMICA SCANDINAVICA DA - 1999/10// PY - 1999/10// DO - 10.3891/acta.chem.scand.53-0857 VL - 53 IS - 10 SP - 857-860 SN - 0904-213X ER - TY - JOUR TI - Building fluorescent sensors by template polymerization: The preparation of a fluorescent sensor for L-tryptophan AU - Liao, Y AU - Wang, W AU - Wang, BH T2 - BIOORGANIC CHEMISTRY AB - The development of fluorescent sensors for organic molecules is of great practical importance in chemical, biological, and pharmaceutical sciences. Using l-tryptophan as an example, we have studied a new way of making polymeric fluorescent sensors using template polymerization or molecular imprinting techniques. The fluorescent polymers were prepared using functional monomers with a fluorescent probe attached to it. The fluorescence of this polymer could be quenched by 4-nitrobenzaldehyde. Addition of the template molecules, l-tryptophan, increased the fluorescence intensity of the imprinted polymer/quencher mixture in a concentration-dependent fashion, presumably through the displacement of the quencher from the binding sites by l-tryptophan. This fluorescence intensity change upon mixing with l-tryptophan allows the binding event to be detected easily. The sensor also exhibited enantioselectivity for the template molecules. For example, the effect of d-tryptophan on the fluorescence intensity of the polymer is about 70% that of its l-enantiomer. Furthermore, the effect of l-phenylalanine and l-alanine on the fluorescence intensity change is much smaller than that of l-tryptophan. Because the approach used does not require the de novo design of the complementary binding site and does not rely on any specific structural features of the template molecule or prior knowledge of its three-dimensional structure, the same principle could potentially be useful for the future construction of practical fluorescent sensors for many other compounds. DA - 1999/12// PY - 1999/12// DO - 10.1006/bioo.1999.1151 VL - 27 IS - 6 SP - 463-476 SN - 0045-2068 ER - TY - JOUR TI - Association of the A-204C polymorphism in the cholesterol 7 alpha-hydroxylase gene with variations in plasma low density lipoprotein cholesterol levels in the Framingham Offspring Study AU - Couture, P. AU - Otvos, J. D. AU - Cupples, L. A. AU - Wilson, P. W. F. AU - Schaefer, E. J. AU - Ordovas, J. M. T2 - Journal of Lipid Research DA - 1999/// PY - 1999/// VL - 40 IS - 10 SP - 1883-1889 ER - TY - JOUR TI - [H2NMe2]CuZrCl6: Hydrogen-bond induced distortions in a copper zirconium chloride analogue of a thiophosphate AU - Dattelbaum, AM AU - Martin, JD T2 - INORGANIC CHEMISTRY AB - The copper(I) zirconium(IV) halide, [H2NMe2]CuZrCl6 (1), has been synthesized, and its single-crystal X-ray structure was determined. The crystal undergoes a phase transition at −60 °C giving a room-temperature structure with a = 10.1105(6) Å, b = 9.9463(5) Å, c = 12.7254(8) Å, β = 110.287(5)° in the monoclinic space group C2/c, Z = 4, and a low-temperature structure (−116 °C) with a = 10.234(2) Å, b = 9.427(1) Å, c = 12.691(2) Å, β = 109.90(2)° in the monoclinic space group P21/c, Z = 4. [H2NMe2]CuZrCl6 is constructed from unique one-dimensional chains with zirconium and copper in alternating octahedral and tetrahedral coordination environments, respectively. The structural relationship between (CuCl4)3- and (PS4)3- is demonstrated by the analogy of this structure to that of KNiPS4. The phase transition, which occurs at approximately −60 °C, results in altered configurations of the dimethylammonium to metal−chloride hydrogen bonding. In addition, a remarkable distortion in the cuprous chloride tetrahedral unit is observed in the room-temperature structure, whereas the zirconium chloride octahedron is distorted in the low-temperature crystal structure. These distortions are discussed in terms of hydrogen-bond driven second-order Jahn−Teller-type distortions. DA - 1999/5/17/ PY - 1999/5/17/ DO - 10.1021/ic9811906 VL - 38 IS - 10 SP - 2369-2374 SN - 0020-1669 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0000236338&partnerID=MN8TOARS ER - TY - JOUR TI - Xe-129 NMR investigation of the free volume in dendritic and cross-linked polymers AU - Morgan, DR AU - Stejskal, EO AU - Andrady, AL T2 - MACROMOLECULES AB - 129Xe NMR spectroscopy was used to study the free-volume changes associated with cross-linking of linear polymers and extensive chain branching in dendritic tree molecules. Qualitative changes in the free volume in model networks of poly(oxypropylene) and in starburst dendrimers of poly(amidoamine) were studied as a function of the cross-link density and the generation, respectively. Consistent with the present understanding of these end-linked networks, the change in chemical shift of the xenon was found to correlate well with the reciprocal of the average molecular weight between cross-links of the end-linked networks. With dendrimers, the chemical shift of xenon varied linearly with the generation number. A modified form of the chain-end free volume theory applicable to dendritic molecules was used to interpret the data. DA - 1999/3/23/ PY - 1999/3/23/ DO - 10.1021/ma9813643 VL - 32 IS - 6 SP - 1897-1903 SN - 0024-9297 ER - TY - JOUR TI - Vanadium(V) complexes of 2,2 '-thiobis(4-methyl-6-tert-butylphenol) (H(2)mbp(2)S) and 2,2 '-sulfinylbis(4-methyl-6-tert-butylphenol) (H(2)mbp(2)SO) AU - Cornman, CR AU - Geiser-Bush, KM AU - Kampf, JW T2 - INORGANIC CHEMISTRY AB - The sulfide-containing ligand 2,2‘-thiobis(4-methyl-6-tert-butylphenol), H2mbp2S, coordinates facially to vanadium forming six-coordinate alkoxide- (1) or hydroxide-bridged (2) dimers that have been structurally characterized. 51V NMR indicates that structural isomers are present. Electrochemical studies indicate that the metal centers in 1 are strongly coupled (Kcom ≈ 105). The corresponding sulfoxide, H2mbp2SO, coordinates to vanadium(V) to form a six-coordinate complex with a 2:1 L:M stoichiometry. Under the conditions of this study, direct oxygenation of the coordinated sulfide in 1 and 2 has not been observed. Crystal data for 1 (C55H74O8S2V2): space group R-3, a = 35.6184(2) Å, b = 35.6184(2) Å, c = 13.52170(10) Å, α, β = 90°, γ = 120°, Z = 18. Crystal data for 2 (C26H35N2O4SV): space group P2(1)/n, a = 13.2894(2) Å, b = 12.9652(2) Å, c = 16.3639(2) Å, α,γ = 90°, β = 102.43°, Z = 4. Crystal data for 3 (C50H70O7S2V): space group P-1, a = 9.1567(5) Å, b = 13.9314(8) Å, c = 19.7196(11) Å, α = 79.1460(10)°, β = 86.5840(10)°, γ = 82.7570(10)°, Z = 2. DA - 1999/9/20/ PY - 1999/9/20/ DO - 10.1021/ic9900253 VL - 38 IS - 19 SP - 4303-4308 SN - 0020-1669 ER - TY - JOUR TI - Rational synthesis of trans-substituted porphyrin building blocks containing one sulfur or oxygen atom in place of nitrogen at a designated site AU - Cho, WS AU - Kim, HJ AU - Littler, BJ AU - Miller, MA AU - Lee, CH AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - The use of heteroatom-substituted porphyrins in bioorganic and materials chemistry requires the ability to position a variety of substituents in a controlled manner about the porphyrin periphery. We describe a rational route to trans-AB2C-type porphyrins bearing one oxygen atom (N3O) or one sulfur atom (N3S) in a designated location in the porphyrin core. The synthesis involved four stages: (1) Acid-catalyzed condensation of a furyl- or thienylcarbinol in excess pyrrole afforded the aryl-substituted furyl- or thienylpyrromethane in high yield. (2) Treatment of the furyl- or thienylpyrromethane with an acid chloride catalyzed by SnCl4 or AlCl3 afforded the corresponding diketo product. (3) Reduction with NaBH4 in alcoholic solvents gave the furyl- or thienylpyrromethanediols. (4) Reaction of a furylpyrromethanediol, thienylpyrromethanediol, or dipyrromethanediol with a dipyrromethane in a one-flask process of condensation followed by oxidation gave the corresponding porphyrin. Reaction conditions previously identified to minimize scrambling in a dipyrromethane−aldehyde condensation were found to be effective in this application. Thus, reaction with 10 mM reactants in acetonitrile at 0 °C containing BF3·Et2O and NH4Cl followed by oxidation with DDQ resulted in the desired porphyrin (10−20% yields) without acidolysis. In this manner, N3O-, N3S-, or N4-porphyrins bearing 5-(p-iodophenyl), 15-[4-(2-(trimethylsilyl)ethynyl)phenyl], and 10,20-di-p-tolyl groups have been made. This set of trans-substituted porphyrin building blocks is expected to be useful in the synthesis of biomimetic energy transduction systems. DA - 1999/10/15/ PY - 1999/10/15/ DO - 10.1021/jo9909305 VL - 64 IS - 21 SP - 7890-7901 SN - 0022-3263 ER - TY - JOUR TI - Polarized optical reflectance and electronic band structure of alpha '-NaV2O5 AU - Long, VC AU - Zhu, Z AU - Musfeldt, JL AU - Wei, X AU - Koo, HJ AU - Whangbo, MH AU - Jegoudez, J AU - Revcolevschi, A T2 - PHYSICAL REVIEW B AB - We report polarized optical reflectance studies of ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{-}{\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ between 0.5 and 6 eV as a function of temperature (T) and magnetic field $(H).$ The electronic excitations and their polarization dependence are interpreted according to our extended H\"uckel tight-binding polarized band structure calculations. Strong bands near 1 eV in both chain and rung directions are attributed to V $\stackrel{\ensuremath{\rightarrow}}{d}d$ transitions. Charge transfer excitations are estimated to begin near 3.3 eV and have significant strength at 4.4 eV and above. The reflectance ratios, $\ensuremath{\Delta}R(T)=R(T)/R(T=4 \mathrm{K}),$ measured at $H=0$ and 28 T, reveal broad polarization-dependent changes through the low temperature transition, ${T}_{c}.$ Integrated intensities of $\ensuremath{\Delta}R$ features exhibit a second-order transition at 36 K in zero field and at $33\ifmmode\pm\else\textpm\fi{}1 \mathrm{K}$ in high field, consistent with a spin-Peierls aspect to the phase transition. DA - 1999/12/15/ PY - 1999/12/15/ DO - 10.1103/physrevb.60.15721 VL - 60 IS - 23 SP - 15721-15727 SN - 2469-9969 ER - TY - JOUR TI - Molecular structure-property relationships for electron-transfer rate attenuation in redox-active core dendrimers AU - Gorman, CB AU - Smith, JC AU - Hager, MW AU - Parkhurst, BL AU - Sierzputowska-Gracz, H AU - Haney, CA T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - Two series of redox-active, iron−sulfur core dendrimers of the general structure (nBu4N)2[Fe4S4(S-Dend)4] (Dend = dendrons of generations 1 through 4) were prepared. Heterogeneous electron-transfer rate constants indicated that the rigid series of dendrimers were more effective at attenuating the rate of electron transfer than were the flexible series of dendrimers. These results were rationalized using computationally derived models which indicated an offset and mobile iron−sulfur core in the flexible series of molecules and a more central and relatively immobile iron−sulfur core in the rigid series of molecules. Further consideration of these data indicated that, while the dendrimers containing rigid ligands had better encapsulated redox cores for a given molecular weight, these molecules had higher electron-transfer rates for a given molecular radius. DA - 1999/11/3/ PY - 1999/11/3/ DO - 10.1021/ja990875h VL - 121 IS - 43 SP - 9958-9966 SN - 1520-5126 ER - TY - JOUR TI - IMDA/retro-Mannich approach to cis-perhydroquinoline Lycopodium alkaloids: Asymmetric synthesis of (+)-luciduline AU - Comins, DL AU - Brooks, CA AU - Al-awar, RS AU - Goehring, RR T2 - ORGANIC LETTERS AB - [formula: see text] The first chiral auxiliary mediated asymmetric synthesis of the naturally occurring Lycopodium alkaloid (+)-luciduline has been accomplished. Key steps include an IMDA reaction of a chiral dihydropyridine, a subsequent retro-Mannich ring opening, and a novel cationic reductive cyclization reaction. DA - 1999/7/29/ PY - 1999/7/29/ DO - 10.1021/ol990028j VL - 1 IS - 2 SP - 229-231 SN - 1523-7060 ER - TY - PAT TI - Halo-zeo-type materials AU - Martin, J. D. AU - Greenwood, K. C2 - 1999/// DA - 1999/// PY - 1999/// ER - TY - JOUR TI - Enantiopure N-acyldihydropyridones as synthetic intermediates: Asymmetric synthesis of benzomorphans AU - Comins, DL AU - Zhang, YM AU - Joseph, SP T2 - ORGANIC LETTERS AB - [formula: see text] Concise asymmetric syntheses of several benzomorphan derivatives have been accomplished using enantiopure 2,3-dihydro-4-pyridones as chiral building blocks. DA - 1999/8/26/ PY - 1999/8/26/ DO - 10.1021/ol990738p VL - 1 IS - 4 SP - 657-659 SN - 1523-7060 ER - TY - JOUR TI - Electronic properties of bisporphyrin biradical dications AU - Shultz, DA AU - Lee, H AU - Gwaltney, KP AU - Sandberg, KA T2 - MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS AB - Abstract We describe the oxidations of bisporphyrins 1-Zn2 - 6-Zn2 , and present EPR spectra of chemically oxidized species that are consistent with exchange-coupled biradicals. DA - 1999/// PY - 1999/// DO - 10.1080/10587259908023342 VL - 334 IS - 1999 SP - 459-467 SN - 1058-725X ER - TY - JOUR TI - Distribution of the Se atoms in the layered compound Nb-3(Se1-xIx)I-7 studied by scanning tunneling microscopy and electronic structure calculations AU - Schmidt, PJ AU - Thiele, G AU - Cantow, HJ AU - Ren, JQ AU - Whangbo, MH T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The layered compound Nb3(Se1-xIx)I7 is obtained when the I atoms at the face-capping sites of Nb3I8 are substituted with Se atoms such that each Nb3(Se1-xIx)I7 layer is composed of Nb3I13 and Nb3SeI12 clusters. The amount and distribution of the Se atoms in Nb3(Se1-xIx)I7 were examined by carrying out scanning tunneling microscopy (STM) experiments for Nb3(Se1-xIx)I7. The reason the Nb3I13 and Nb3SeI12 clusters appear with different contrasts in the STM images Nb3(Se1-xIx)I7 was investigated by calculating partial density plots for ordered model layers [Nb3(Se1/3I2/3)I7]3 and (Nb3I8)3. In the STM images of Nb3(Se1-xIx)I7, the Nb3I13 and Nb3SeI12 clusters are distinguished because they undergo different extents of tip-force induced depression. Our analysis shows that the distribution of the Se atoms in Nb3Se1-xI7+x is random. DA - 1999/5/6/ PY - 1999/5/6/ DO - 10.1021/jp9843813 VL - 103 IS - 18 SP - 3626-3633 SN - 1089-5647 ER - TY - JOUR TI - Dislocation structure of low-angle grain boundaries in YBa2Cu3O7-delta/MgO films AU - Oktyabrsky, S AU - Kalyanaraman, R AU - Jagannadham, K AU - Narayan, J T2 - JOURNAL OF MATERIALS RESEARCH DA - 1999/7// PY - 1999/7// DO - 10.1557/JMR.1999.0369 VL - 14 IS - 7 SP - 2764-2772 SN - 0884-2914 ER - TY - JOUR TI - Determination of the Se atom distribution in the layered compound Nb-3(Se1-xIx)I-7 by scanning tunneling microscopy AU - Schmidt, P. J. AU - Thiele, G. AU - Whangbo, M. H. T2 - European Journal of Inorganic Chemistry AB - The layered compound Nb3(Se1–xIx)I7 is obtained when the I atoms at the face-capping sites of the layered compound Nb3I8 are replaced by Se atoms. The amount and distribution of the Se atoms in Nb3(Se1–xIx)I7 were examined by scanning tunneling microscopy. The analysis shows that the distribution of the Se atoms is completely random. DA - 1999/// PY - 1999/// DO - 10.1002/(sici)1099-0682(199905)1999:5<785::aid-ejic785>3.0.co;2-e IS - 5 SP - 785-787 ER - TY - JOUR TI - Chronoamperometry of strong acids without supporting electrolyte AU - Aoki, K AU - Baars, A AU - Jaworski, A AU - Osteryoung, J T2 - JOURNAL OF ELECTROANALYTICAL CHEMISTRY AB - The steady-state reduction current of the hydrogen ion in a 1:1 strong acid without adding supporting electrolyte at a microelectrode is known to be independent of the diffusion coefficient of the anion, although the anion diffuses to the electrode together with the hydrogen ion in order to maintain electroneutrality. This paper aims at resolving this inconsistency of the diffusion of the anion by investigating transient reduction currents of the hydrogen ion without supporting electrolyte. The time-dependent diffusion equation associated with migration was solved under the condition of the potential step toward the limiting current-domain at a hemi-spherical electrode. The theoretical transient current has a linear relation with the inverse square root of the time. The anion behaves as if it were electroactive. The slope of the line is expressed by an average of diffusion coefficients of the hydrogen ion and the interacted anion. Chronoamperometric measurements were made in hydrochloric acid including various concentrations of supporting electrolyte. DA - 1999/8/24/ PY - 1999/8/24/ DO - 10.1016/S0022-0728(99)00252-1 VL - 472 IS - 1 SP - 1-6 SN - 1873-2569 KW - strong acids KW - chronoamperometry KW - migration KW - ionic interaction KW - supporting electrolyte KW - Nernst-Planck equation ER - TY - JOUR TI - Adsorption energetics of NO and CO on Pt(111) AU - Yang, H AU - Sanz, JF AU - Wang, Y AU - Whitten, JL T2 - JOURNAL OF CLUSTER SCIENCE DA - 1999/12// PY - 1999/12// DO - 10.1023/A:1021965310593 VL - 10 IS - 4 SP - 581-590 SN - 1572-8862 KW - an initio quantum chemical embedded cluster calculations KW - NO and CO adsorption KW - platinum surfaces ER - TY - JOUR TI - Two new improved approaches to the synthesis of coumarin-based prodrugs AU - Zheng, AL AU - Wang, W AU - Zhang, HJ AU - Wang, B T2 - TETRAHEDRON AB - Abstract Our laboratory has recently reported the development of a coumarin-based, esterase-sensitive prodrug system for the preparation of prodrugs of amines, peptides, and peptidomimetics. Biological evaluations including animal studies have demonstrated the clinical potential of this prodrug system. However, the original synthetic method used required a long sequence of reactions with a relatively low overall yield. In this report, we describe two new approaches to the synthesis of these coumarin-based prodrugs. The first approach is a photochemical approach taking advantage of the photoisomerization of cinnamic acid and its derivatives. The second approach is through the catalytic hydrogenation of a triple bond for the generation of the cis double bond in the coumarinic acid moiety. Both approaches allow for the synthesis of these prodrugs in fewer steps with much improved overall yield. DA - 1999/4/2/ PY - 1999/4/2/ DO - 10.1016/S0040-4020(99)00121-0 VL - 55 IS - 14 SP - 4237-4254 SN - 0040-4020 KW - hydrogenation KW - photochemistry KW - coumarin KW - isomerization ER - TY - JOUR TI - Theoretical studies of surface reactions on metals. I. Ethyl to ethylene conversion on Ni(1 0 0). II. Photodissociation of methane on platinum AU - Whitten, JL AU - Yang, H T2 - CATALYSIS TODAY AB - The goal of this research is the development and application of theoretical techniques that will provide a molecular level understanding of surface processes, especially reaction mechanisms and energetics. Electronic structures are described by an ab initio embedding formalism that permits an accurate determination of energies and adsorbate structure. An overview of the theoretical method is presented and applications to catalytic and photochemical reactions on nickel and platinum surfaces are discussed. Preliminary studies of ethylene production from ethyl adsorbed on nickel are reported. A second study concerns the photodissociation of methane physisorbed on platinum. Results are reported for a methane molecule interacting with a Pt ring model of the surface. Configuration interaction theory is used to sort out states resulting from electron attachment to methane from lower energy states that correspond to metal excitations. A mechanism is proposed for the photodissociation process. DA - 1999/5/12/ PY - 1999/5/12/ DO - 10.1016/S0920-5861(98)00494-5 VL - 50 IS - 3-4 SP - 603-612 SN - 0920-5861 KW - photodissociation KW - ethylene KW - surfaces KW - catalysis ER - TY - JOUR TI - The T-1 rho C-13 spin-lattice relaxation time of helical polyguanidines AU - Lim, AR AU - Stewart, , JR AU - Novak, BM T2 - SOLID STATE COMMUNICATIONS AB - The solid state dynamics of three helical polyguanidines differing only in their stereochemistry was investigated by 13C CP/MAS NMR. From these studies, the structures of the polyguanidines were confirmed, and the 13C spin–lattice relaxation times in the rotating frame were measured. The relaxation times of all the polyguanidines indicated that they undergo fast motions, i.e. motions on the fast side of the T1ρ minimum. The main chain carbon of polyguanidine I-(R/S), with equal amounts of (R) and (S) chiral side chains, has higher activation energy, 10.7 kJ/mol, than the analogous polymers with enantiomerically pure side chains (I-(R) and I-(S)), 5.1 kJ/mol. DA - 1999/// PY - 1999/// DO - 10.1016/S0038-1098(99)00038-1 VL - 110 IS - 1 SP - 23-28 SN - 0038-1098 KW - insulators KW - polymers KW - elastomers and plastics KW - chemical synthesis KW - nuclear resonances ER - TY - JOUR TI - Synthesis, structure and EPR spectroscopy of a vanadium(IV)-amide metallacyclic complex AU - Cornman, CR AU - Zovinka, EP AU - Boyajian, YD AU - Olmstead, MM AU - Noll, BC T2 - INORGANICA CHIMICA ACTA AB - The crystal structures and EPR spectra for two dinuclear, metallacyclic VIV complexes are reported. The coordinating ligands include a rare example of vanadium(IV) coordinated to the carbonyl oxygen of an amide moiety. In the solid state, the cavity of these complexes encircles two molecules of methylene chloride which interact only weakly with the metallacycle. EPR spectra are typical of mononuclear VIV ion indicating that the spins are not interacting. Crystal data: for 1, C21H20Cl8N4O3V, M = 710.95, triclinic, space group P1, a = 10.543(2), b = 11.999(3), c = 13.654(2) Å, α = 64.170(14), β = 70.084(12), γ = 87.19(2)°, U = 1451.6(5) Å3, Z = 2, Dc = 1.627 g cm−3, T = 123(2) K, no. of unique reflections = 3797, no. of parameters = 355, R1 = 0.0882, wR2 = 0.1892 (all data). Crystal data for 2: C40.5H45Cl13N8O6V, M = 71302.63, triclinic, space group P1, a = 11.933(5), b = 12.020(3), c = 12.047(4) Å, α = 63.24(2), β = 65.46(3), γ = 80.06(3)°, U = 1403.4(9) Å3, Z = 2, Dc = 1.54 g cm−3, T = 130 K, no. of unique reflections = 3663, no. of parameters = 224, R1 = 0.1271, Rw = 0.1384 (F > 4.0σ(F)). DA - 1999/2/2/ PY - 1999/2/2/ DO - 10.1016/S0020-1693(98)00261-8 VL - 285 IS - 1 SP - 134-137 SN - 0020-1693 KW - crystal structures KW - vanadium complexes KW - amide complexes KW - metallocylic complexes ER - TY - JOUR TI - Non-aqueous capillary electrophoresis chiral separations with sulfated beta-cyclodextrin AU - Wang, F AU - Khaledi, MG T2 - JOURNAL OF CHROMATOGRAPHY B AB - This paper reports the application of an anionic cyclodextrin (CD), sulfated β-cyclodextrin with a degree of substitution of four (β-CD-(SO4−)4, in chiral separations of pharmaceutical enantiomers by non-aqueous capillary electrophoresis (NACE). Upon complexation with the anionic CD, electrophoretic mobilities of the basic enantiomers decreased, however, both separation selectivity and resolution were enhanced. The advantage of NACE chiral separations over the aqueous CE with the charged CD is that higher electric field strength and higher ionic strength could be applied due to the characteristics of the solvent formamide. The higher ionic strength leads to stacking of peaks and reduces the electrodispersion caused by the mobility mismatch between β-CD-(SO4−)4–analyte complexes and the co-ions in the running buffer. As a result, better peak shapes and higher separation efficiency were obtained. Comparing with NACE chiral separations with neutral CDs, lower concentration of β-CD-(SO4−)4 was needed due to the fact that the electrostatic attraction caused stronger binding between β-CD-(SO4−)4 and the enantiomers. The effects of the experimental parameters, such as concentration of the CD, apparent pH (pH*), degree of substitutions of the CDs, percentage of water in mixed solvent systems, and type of solvents were also studied. DA - 1999/8/20/ PY - 1999/8/20/ DO - 10.1016/S0378-4347(99)00217-0 VL - 731 IS - 2 SP - 187-197 SN - 0378-4347 KW - enantiomer separation KW - sulfated beta-cyclodextrin ER - TY - JOUR TI - N-confused tetraphenylporphyrin and tetraphenylsapphyrin formation in one-flask syntheses of tetraphenylporphyrin AU - Geier, GR AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - The yields of tetraphenylporphyrin (TPP), N-confused tetraphenylporphyrin (NC-TPP), and tetraphenylsapphyrin (TPS) were examined under diverse conditions in the one-flask room-temperature reaction of pyrrole and benzaldehyde. The conditions examined included TFA and BF3-etherate catalysis, acid concentrations, pyrrole and benzaldehyde concentrations, pyrrole:benzaldehyde ratios, the addition of salt, and reaction times. The quantities of TPP, NC-TPP, and TPS were determined by HPLC. The yield of NC-TPP mirrored that of TPP during systematic variation of reaction parameters but was consistently lower (≤7.5%). The rate of NC-TPP formation also resembled that of TPP. Excess pyrrole was not required to form NC-TPP. About 2-fold more NC-TPP was obtained with BF3-etherate compared with TFA catalysis. TPS was observed in only a few of the reactions examined. The yield of TPS peaked early and declined well before the maximum yields of TPP and NC-TPP were reached. The highest yield of TPS observed was 1.2%. TPS was produced in higher yields by TFA compared with BF3-etherate catalysis. Additional pigments with chromatographic properties spanning the range of TPP and NC-TPP were observed in very low yield but were not characterized. N-confused tetramesitylporphyrin was isolated from the reaction of mesitaldehyde and pyrrole under BF3-ethanol cocatalysis. Examination of the Adler reaction of benzaldehyde and pyrrole revealed the presence of NC-TPP and TPS in the filtrate but not in the crystalline TPP material. The substantial chromatographic differences between the porphyrins and N-confused porphyrins make for straightforward isolation of the purified porphyrin devoid of contaminating N-confused porphyrin. These studies indicate that the scope of conditions yielding NC-TPP is extremely broad. DA - 1999/3/5/ PY - 1999/3/5/ DO - 10.1021/jo982068r VL - 64 IS - 5 SP - 1596-1603 SN - 0022-3263 ER - TY - JOUR TI - Model of interfacial thermal resistance of diamond composites AU - Jagannadham, K T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - The effective thermal conductivity of diamond and aluminum nitride layered composites was analyzed for three different types of interfaces. A sharp interface with a stepwise discontinuity, a graded interface with a linear variation and a diffused interface with a minimum or a maximum in thermal conductivity across the interface were considered. The results of the modeling analysis were used to explain the experimental results described in the literature of improved heat spreader characteristics of diamond and aluminum nitride composites. DA - 1999/// PY - 1999/// DO - 10.1116/1.581597 VL - 17 IS - 2 SP - 373-379 SN - 1520-8559 ER - TY - JOUR TI - High field optical response of eta-Mo4O11 AU - Zhu, Z AU - Long, VC AU - Musfeldt, JL AU - Wei, X AU - Sarrao, J AU - Fisk, Z AU - Negishi, H AU - Inoue, M AU - Koo, HJ AU - Whangbo, MH T2 - JOURNAL DE PHYSIQUE IV DA - 1999/12// PY - 1999/12// DO - 10.1051/jp4:19991063 VL - 9 IS - P10 SP - 251-253 SN - 1155-4339 ER - TY - JOUR TI - Hepatic lipase activity influences high density lipoprotein subclass distribution in normotriglyceridemic men: genetic and pharmacological evidence AU - Grundy, S. M. AU - Vega, G. L. AU - Otvos, J. D. AU - Rainwater, D. L. AU - Cohen, J. C. T2 - Journal of Lipid Research DA - 1999/// PY - 1999/// VL - 40 IS - 2 SP - 229-234 ER - TY - JOUR TI - Fundamentals in the design of molecular electronic devices: Long-range charge carrier transport and electronic coupling AU - Fox, M. A. T2 - Accounts of Chemical Research DA - 1999/// PY - 1999/// VL - 32 IS - 3 SP - 201-207 ER - TY - JOUR TI - Expression and analysis of green fluorescent proteins in human embryonic kidney cells by capillary electrophoresis AU - Malek, A AU - Khaledi, MG T2 - ANALYTICAL BIOCHEMISTRY AB - The green fluorescent protein (GFP) has attracted much interest as a reporter for gene expression. In this paper, application of capillary electrophoresis with laser-induced fluorescent (CE-LIF) for quantitation of green fluorescence protein in cellular extracts and single cells is investigated. The S65T mutant form of GFP protein was successfully expressed in human embryonic kidney (HEK293) cells, and its production was confirmed by fluorescence microscopy and CE-LIF. The mass limit of detection for the mutant S65T was 5.3 x 10(-20) mol, which was better than that for the wild-type GFP by a factor of six. Detection of a small amount of GFP is difficult by conventional techniques such as fluorescent microscopy due to interference from cell autofluorescence at low GFP concentrations. The HEK293 cells were transfected with the GFP plasmid that produced S65T-GFP. Transient production of S65T protein was detected 2 h after the transfection and reached a maximum after 48 h. The protein concentration began to decrease significantly after 96 h. Single cell analysis of HEK293 cells after transfection with GFP plasmid indicate a nonuniform production of S65T-GFP protein among cells. DA - 1999/3/15/ PY - 1999/3/15/ DO - 10.1006/abio.1998.2975 VL - 268 IS - 2 SP - 262-269 SN - 0003-2697 ER - TY - JOUR TI - Electronic structure of the organic conductors kappa-ET2Cu(SCN)(2) and kappa-ET2Cu[N(CN)(2)]Br studied using soft X-ray absorption and soft X-ray emission AU - Stagarescu, CB AU - Duda, LC AU - Smith, KE AU - Seo, DK AU - Whangbo, MH AU - Jerome, D AU - Haddon, RC AU - Brooks, JS AU - Guo, JH AU - Nordgren, J T2 - JOURNAL OF SOLID STATE CHEMISTRY AB - The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using core-level photon spectroscopies. Specifically, the bulk C 2poccupied and unoccupied partial densities of states (PDOS) of the organic superconductorsκ-ET2Cu(SCN)2andκ-ET2Cu[N(CN)2]Br were measured using a combination of high-resolution soft X-ray absorption (SXA) and soft X-ray emission (SXE). The PDOS was also calculated using a tight binding model, and the measured spectra compared directly to that predicted by the calculations. The emission and absorption spectra from both materials were found to be quite similar, reflecting mostly contributions from the common conductive ET layers. The presence of two nonequivalent carbon sites of the ET molecule was identified in the SXA spectra. Contributions from theπandσstates were identified in the emission spectra. The occupied C 2pbandwidth was found to be approximately 17eV. An observed dependence of the SXE spectra on the excitation energy is partly accounted for by a simple model that considers the presence of the two nonequivalent ET carbon sites. We also find evidence in the SXE spectra for a high degree of localization in the lowest unoccupied states. DA - 1999/2/15/ PY - 1999/2/15/ DO - 10.1006/jssc.1998.8046 VL - 143 IS - 1 SP - 1-8 SN - 0022-4596 ER - TY - PCOMM TI - Effect of tip sharpness on the relative contributions of attractive and repulsive forces in the phase imaging of tapping mode atomic force microscopy AU - Bar, G AU - Brandsch, R AU - Whangbo, MH AB - The way in which the sharpness of a tip affects phase imaging in tapping mode atomic force microscopy was examined by performing experiments on polystyrene and Si surfaces with tips of different sharpness. The dominant tip–sample interaction controlling the cantilever vibration can be made repulsive with a sharp tip, and attractive with a dull tip. When the dominant interaction is either attractive or repulsive, the magnitude of the phase shift (Δφ) increases with decreasing set-point ratio rsp=Asp/A0, and the Δφ-vs.-rsp plots are nearly independent of the drive amplitude, A0. These observations indicate that the cantilever vibration is affected mainly by the amount of time the tip spends in going through the lower turning point of each oscillation and by the forces whose force derivatives change sharply during this period. DA - 1999/2/22/ PY - 1999/2/22/ DO - 10.1016/s0039-6028(98)00899-1 SP - L192-L199 KW - phase imaging KW - tip sharpness effect KW - trapping mode atomic force microscopy ER - TY - JOUR TI - Diastereoselective addition of prochiral metallo enolates to chiral 1-acylpyridinium salts AU - Comins, DL AU - Kuethe, JT AU - Hong, H AU - Lakner, FJ AU - Concolino, TE AU - Rheingold, AL T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY DA - 1999/3/24/ PY - 1999/3/24/ DO - 10.1021/ja990024+ VL - 121 IS - 11 SP - 2651-2652 SN - 0002-7863 ER - TY - JOUR TI - Cloning and expression of a novel juvenile hormone-metabolizing epoxide hydrolase during larval-pupal metamorphosis of the cabbage looper, Trichoplusia ni AU - Harris, SV AU - Thompson, DM AU - Linderman, RJ AU - Tomalski, MD AU - Roe, RM T2 - INSECT MOLECULAR BIOLOGY AB - A full-length cDNA encoding for a microsomal juvenile hormone (JH)-metabolizing epoxide hydrolase (TmEH-1) was isolated from a cDNA library constructed from fat body of last stadium (wandering) cabbage loopers, Trichoplusia ni, at the exact developmental time of maximum JH epoxide hydrolase activity. TmEH-1 was 1887 base pairs in length with a 1389 base pair open reading frame encoding 463 amino acids. Amino acid sequence analysis showed that TmEH-1 was most similar to and contained the exact catalytic triad (Asp-226, Glu-403 and His-430) found in microsomal epoxide hydrolases. TmEH-1-specific message was present along with JH III epoxide hydrolase activity in fat body in feeding (days 1 and 2) and wandering (day 3) larvae with the peak in message level preceding the peak in JH epoxide hydrolase activity by 1 day. When TmEH-1 was expressed in baculovirus-infected Spodoptera frugiperda cells, a 46,000 molecular weight protein appeared on SDS-PAGE which corresponded to the predicted size coded by the TmEH-1 message and which was positively correlated with increases in JH III epoxide hydrolase activity above that of wild-type controls. In subcellular distribution studies, 58% of the juvenile hormone III epoxide hydrolase activity was in the insoluble fractions. Baculovirus expressed TmEH-1 demonstrated a higher specific activity for JH III as compared to the general EH substrates, cis- and trans-stilbene oxide. Southern blot analyses suggested that multiple epoxide hydrolase genes are present in T. ni. DA - 1999/2// PY - 1999/2// DO - 10.1046/j.1365-2583.1999.810085.x VL - 8 IS - 1 SP - 85-96 SN - 1365-2583 KW - juvenile hormone KW - epoxide hydrolase KW - cabbage looper KW - Trichoplusia ni ER - TY - JOUR TI - Calculations and analysis of the electronic structures of transition-metal phosphosilicides Cu4SiP8, IrSi3P3, CoSi3P3, and FeSi4P4 AU - Lee, KS AU - Koo, HJ AU - Ren, J AU - Whangbo, MH T2 - JOURNAL OF SOLID STATE CHEMISTRY AB - Electronic structures of phosphosilicides Cu4SiP8, IrSi3P3, CoSi3P3, and FeSi4P4 were calculated using the extended Hückel tight-binding method and were analyzed in terms of a modified electron counting scheme. The d-block levels of these compounds appear well below the Fermi level, thereby indicating that the transition-metal atoms exist as d10 ions. Except for the case of IrSi3P3, the d-block energy levels of these compounds occur in a narrow energy window less than 1.5 eV wide. The Si 3p orbitals act as acceptor orbitals to the transition-metal d orbitals in IrSi3P3, CoSi3P3, and FeSi4P4. DA - 1999/10// PY - 1999/10// DO - 10.1006/jssc.1999.8142 VL - 147 IS - 1 SP - 11-18 SN - 0022-4596 ER - TY - JOUR TI - An indirect laser-induced temperature jump determination of the surface pK(a) of 11-mercaptoundecanoic acid monolayers self-assembled on gold AU - Smalley, JF AU - Chalfant, K AU - Feldberg, SW AU - Nahir, TM AU - Bowden, EF T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The indirect laser-induced temperature jump (ILIT) method is used to determine the acidity (pKa) of monolayers composed of 11-mercaptoundecanoic acid (MUA) self-assembled on vapor-deposited gold film electrodes in contact with either 0.10 or 1.0 M ionic strength NaClO4 electrolyte solutions. The ILIT technique may be used to measure the pKa of a surface-attached acid because the magnitude of the ILIT response is related to the potential gradient at the electrode/electrolyte interface which is, in turn, related to the extent of ionization of the acid. The relevant data are the potentials of zero ILIT response versus pH. A simple two-layer model of the acid-modified electrode/electrolyte interface and Gouy−Chapman double layer theory (modified for the onset of dielectric saturation effected by the large concentration of charge present at this interface when a substantial fraction of the carboxylic acid moieties are ionized) were employed to analyze these data. This analysis gives pKa = 5.7 ± 0.2 at 0.10 M ionic strength and pKa = 4.4 ± 0.2 at 1.0 M ionic strength while the total concentration of MUA comprising the self-assembled monolayer is determined to be essentially the same at both ionic strengths, averaging (5.4 ± 0.3) × 10-10 mol/cm2. Reasons for the observed variation of pKa with ionic strength are discussed. DA - 1999/3/11/ PY - 1999/3/11/ DO - 10.1021/jp983325z VL - 103 IS - 10 SP - 1676-1685 SN - 1089-5647 ER - TY - JOUR TI - An automated microscale chemistry workstation capable of parallel, adaptive experimentation AU - Du, H AU - Corkan, LA AU - Yang, KX AU - Kuo, PY AU - Lindsey, JS T2 - CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS AB - We have designed and constructed a 3rd-generation chemistry workstation and accompanying software for automated experimentation in relatively clean domains of chemistry. The workstation is designed for flexible, high-throughput, microscale chemistry and includes a reaction station with 60 reaction vessels. The experiment manager software includes a large number of features to facilitate experiment planning and implementation. The significant advances in software from the 2nd-generation system include the following: (1) Five experiment-planning modules have been incorporated to match different types of scientific experimentation, including open-loop and closed-loop experiments. The five modules enable plans to be composed for general-purpose (GP), decision-tree (DT), factorial design (FD), composite modified Simplex (CMS) and multidirectional search (MDS) experiments. (2) Parallel experimentation and adaptive experimentation have been blended so that some decision-making can be done using objective functions or early-termination functions while multiple experiments are in progress. Some planning modules (CMS, MDS and DT) can cause new experiments to be spawned based on the chemistry data obtained. (3) Decision-making can involve the local course of individual experiments and/or the global course of sets of experiments. (4) Resource management features provide the capability to look-ahead at experiments in queue, assess resource (chemicals, containers) availability and designate suitability for implementation. (5) Intelligent reagent-handling features support the autodilution of reagents, autoselection of appropriate stock solutions, autoassignment of containers and control over reaction volumes. (6) Opportunistic rescheduling features have been provided so that pending experiments can be advanced in queue whenever possible, leading to compressed experimental timeframes. (7) Templates composed for FD, CMS and MDS experiments can be stored and reused with modifications as required for specific experiments. (8) The scheduling module contains both a rigid scheduler and a flexible scheduler. (9) The software is modular and runs under Windows 95. This workstation is especially designed for fundamental investigations of chemical reactions and optimization of experimental reaction conditions. DA - 1999/8/2/ PY - 1999/8/2/ DO - 10.1016/S0169-7439(99)00019-2 VL - 48 IS - 2 SP - 181-203 SN - 0169-7439 KW - automated workstation KW - parallel experimentation KW - microscale chemistry ER - TY - JOUR TI - Synthesis and properties of star-shaped multiporphyrin-phthalocyanine light-harvesting arrays AU - Li, JZ AU - Diers, , JR AU - Seth, J AU - Yang, SI AU - Bocian, DF AU - Holten, D AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - Light-harvesting arrays containing four porphyrins covalently linked to a phthalocyanine in a star-shaped architecture have been synthesized. Cyclotetramerization of an ethyne-linked porphyrin−phthalonitrile in 1-pentanol in the presence of MgCl2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded the all-magnesium porphyrin−phthalocyanine pentad in 45% yield. Similar reaction using Zn(OAc)2·2H2O afforded the all-zinc porphyrin−phthalocyanine pentad in 15% yield. Arrays with different metals (free base, Mg, Zn) in the porphyrin and phthalocyanine macrocycles have been prepared by selective demetalation and metalation steps. This approach provides rapid and convergent access to multiporphyrin−phthalocyanine arrays in diverse metalation states. The arrays are reasonably soluble in organic solvents such as toluene, THF, and CH2Cl2. The arrays exhibit strong absorption in the blue and red regions. Time-resolved and static optical measurements indicate that intramolecular singlet-excited-state energy transfer from the porphyrin to the phthalocyanine moiety is extremely rapid (picoseconds) and efficient. Ground-state electronic communication among the porphyrins is indicated by rapid hole/electron hopping among the metalloporphyrins in the arrays as detected by EPR measurements on the singly oxidized pentads. These physical measurements indicate that the porphyrin−phthalocyanine pentads possess favorable characteristics for light harvesting and other photonics applications. DA - 1999/12/10/ PY - 1999/12/10/ DO - 10.1021/jo991001g VL - 64 IS - 25 SP - 9090-9100 SN - 0022-3263 ER - TY - JOUR TI - Semiempirical computational assessment of porphyrins as building blocks for molecule-based magnets: spin-spin coupling in radical-substituted metalloporphyrins AU - Shultz, DA AU - Sandberg, KA T2 - JOURNAL OF PHYSICAL ORGANIC CHEMISTRY DA - 1999/1// PY - 1999/1// DO - 10.1002/(SICI)1099-1395(199901)12:1<10::AID-POC85>3.3.CO;2-7 VL - 12 IS - 1 SP - 10-18 SN - 0894-3230 KW - porphyrins KW - radical-substituted metalloporphyrins KW - molecule-based magnets KW - spin-spin coupling ER - TY - JOUR TI - Photophysical characterization of dilute solutions and ordered thin films of alkyl-substituted polyfluorenes AU - Teetsov, J AU - Fox, MA T2 - JOURNAL OF MATERIALS CHEMISTRY AB - J. Teetsov and M. Anne Fox, J. Mater. Chem., 1999, 9, 2117 DOI: 10.1039/A902829C DA - 1999/9// PY - 1999/9// DO - 10.1039/a902829c VL - 9 IS - 9 SP - 2117-2122 SN - 0959-9428 ER - TY - JOUR TI - Migration and diffusion coupled with a fast preceding reaction. Voltammetry at a microelectrode AU - Jaworski, A AU - Donten, M AU - Stojek, Z AU - Osteryoung, JG T2 - ANALYTICAL CHEMISTRY AB - A mathematical model implemented by simulation is presented for voltammetry of a reversible couple that involves a fast preceding chemical reaction and mixed diffusional and migrational transport. The hydrogen couple, H+/H2, fulfills the above criteria. For strong acids there is no preceding reaction, whereas for weak acids the preceding reaction is HA = H+ + A-. The computed voltammograms are compared with experimental voltammograms for the reduction of strong and weak acids at Pt microelectrodes with excess of and without supporting electrolyte. The key assumption in the calculations is that the flux of hydrogen ion is independent of the anion. This assumption is supported by the experimental fact that the wave heights in the absence of supporting electrolyte of several strong acids of equal concentration and with anions of various size are identical. DA - 1999/1/1/ PY - 1999/1/1/ DO - 10.1021/ac980425s VL - 71 IS - 1 SP - 167-173 SN - 0003-2700 ER - TY - JOUR TI - Integrator contracts with many agents and bankruptcy AU - Tsoulouhas, T AU - Vukina, T T2 - AMERICAN JOURNAL OF AGRICULTURAL ECONOMICS AB - Abstract This article analyzes optimal livestock production contracts between an integrator company and many independent growers in three similar industries: broiler, turkey, and swine. The analysis provides an explanation for the simultaneous existence of distinct incentive schemes in these industries by examining the effects of bankruptcy. The key factors are shown to be the output price volatility and the firm size. With large companies dominating the broiler industry, a small price volatility facilitates the use of two‐part piece rate tournaments. By contrast, given the prevalence of smaller companies in the swine industry, a larger price volatility generates a bankruptcy risk which renders the use of tournaments infeasible. Given the combination of medium‐size companies in the turkey industry, an intermediate price volatility produces a mixed result where tournaments and fixed performance standards exist simultaneously. DA - 1999/2// PY - 1999/2// DO - 10.2307/1244450 VL - 81 IS - 1 SP - 61-74 SN - 0002-9092 KW - bankruptcy KW - contracts KW - moral hazard KW - multiple agents KW - tournaments ER - TY - JOUR TI - In-plane ESR microwave conductivity measurements and electronic band structure studies of the organic superconductor beta ''-(BEDT-TTF)(2)SF5CH2CF2SO3 AU - Wang, HH AU - VanZile, ML AU - Schlueter, JA AU - Geiser, U AU - Kini, AM AU - Sche, PP AU - Koo, HJ AU - Whangbo, MH AU - Nixon, PG AU - Winter, RW AU - Gard, GL T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The electronic structure of the organic superconductor β‘ ‘-(BEDT−TTF)2SF5CH2CF2SO3 (BEDT−TTF is bis(ethylenedithio)tetrathiafulvalene) was characterized with the use of electron spin resonance (ESR) spectroscopy and electronic band structure calculations. The room-temperature ESR line width is 24−27 G in the plane of a donor molecule layer (i.e., in the ab-plane) and ∼32 G along the normal to this plane (i.e., along the c*-direction). The ab-plane anisotropy of the microwave conductivity was extracted for the first time from the ESR Dysonian line shape analysis. The in-plane conductivity varies sinusoidally, is maximal along the interstack direction (b-axis), and is minimal along the donor stack direction (a-axis). The Fermi surfaces of the title compound consist of a 2D hole pocket and a pair of 1D wavy lines. The directions for the in-plane conductivity maximum and minimum are in excellent agreement with the electronic band structure calculated for β‘ ‘-(BEDT−TTF)2SF5CH2CF2SO3, and the origin of the in-plane conductivity anisotropy lies in the one-dimensional part of the Fermi surface. This is the first time that an organic conductor shows Dysonian ESR line shape due to its 2D and strongly metallic nature, yet the 1D character is revealed simultaneously through the in-plane conductivity anisotropy. DA - 1999/7/1/ PY - 1999/7/1/ DO - 10.1021/jp991268j VL - 103 IS - 26 SP - 5493-5499 SN - 1089-5647 ER - TY - JOUR TI - Implementation of the multidirectional search algorithm on an automated chemistry workstation. A parallel yet adaptive approach for reaction optimization AU - Du, H AU - Jindal, S AU - Lindsey, JS T2 - CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS AB - We have developed an experiment-planning module for applying a powerful new pattern search algorithm toward the problems of reaction investigation and optimization. The experiment planner works in conjunction with a closed-loop automated chemistry workstation equipped for parallel experimentation. The new algorithm, developed by Torczon for parallel computation of mathematical functions, achieves a focused yet parallel approach to finding regions of improved response. Like a full factorial design, the search space involves a regular grid of points. Like the Simplex algorithm, the multidirectional search (MDS) algorithm uses the movement of a simplex through a search space. However, with each movement all points except the single best are discarded, whereas the Simplex algorithm discards only the one worst point. Thus, in an n-dimensional space, the MDS algorithm projects n mandatory points at every cycle (beyond the initial). In addition, a larger number of exploratory points are identified by look-ahead projection of possible future simplices. Such exploratory points lie on multiple independent lines of search. The responses for the mandatory and exploratory points are acquired via parallel experimentation, with the latter points examined to the extent that the workstation has available capacity during the same schedule. The data from such exploratory points can be used in later cycles of experimentation, accelerating convergence on the region of optimal response. In the case of unlimited parallel experimentation capacity, all possible points in the space are projected, as in a full factorial design. The MDS algorithm thus adapts to the available parallel capacity of the workstation. The MDS planning module includes options for specifying initial points, stop criteria, and early-termination processes. Provisions are included for parallel scheduling of batches of experiments, convergence of the search, and movement at the boundaries of the search space. An MDS investigation can thus be implemented with global decision-making concerning movements through a search space, and local decision-making concerning termination of individual experiments. The MDS algorithm enables directed evolutionary searches in a parallel mode and is ideally suited for rapid optimization of chemical reactions using a microscale automated chemistry workstation. DA - 1999/8/2/ PY - 1999/8/2/ DO - 10.1016/S0169-7439(99)00022-2 VL - 48 IS - 2 SP - 235-256 SN - 0169-7439 KW - multidirectional search KW - simplex KW - automated chemistry workstation ER - TY - JOUR TI - Gold Nanoparticles as Templates for the Synthesis of Hollow Nanometer‐Sized Conductive Polymer Capsules AU - Marinakos, S.M. AU - Shultz, D.A. AU - Feldheim, D.L. T2 - Advanced Matter AB - Chemically directed assembly of nanoscale materials is often an attractive alternative to techniques such as chemical vapor deposition or lithography. In this paper the synthesis of one-dimensional (1D) assemblies of solid poly(pyrrole)—the Figure shows a transmission electron microscope image—and the use of metal nanoparticles as templates for hollow polymeric nanocapsules (see cover) are described. DA - 1999/1// PY - 1999/1// DO - 10.1002/(SICI)1521-4095(199901)11:1<34::AID-ADMA34>3.0.CO;2-I VL - 11 IS - 1 SP - 34–37 SN - 0935-9648 ER - TY - JOUR TI - Folding of pyrimidine-enriched RNA fragments from the vicinity of the internal ribosomal entry site of Hepatitis A virus AU - Hardin, CC AU - Sneeden, JL AU - Lemon, SM AU - Brown, BA AU - Guenther, RH AU - Sierzputowska-Gracz, H T2 - NUCLEIC ACIDS RESEARCH AB - Two RNA fragments from the region just upstream of the internal ribosome entry site of Hepatitis A virus (HAV) were studied, a 35mer (HAV-35), 5U4 C3 U3 C3 U4 C3 U3 C2 UAU2 C3 U33′, and a 23mer (HAV-23), 5′U4 C3 U3 C3 U4 C3 U33′. Secondary structural predictions and nuclease digestion patterns obtained with genomic RNAs suggested that they link two stable Watson-Crick (WC) hairpins in the genomic RNA and do not form conventional WC secondary structure, but do fold to form a condensed, stacked ‘domain’. To obtain more information, folding of HAV-23 and −35 RNA fragments was characterized using 1H nuclear magnetic resonance, in H2O as a function of pH and temperature, circular dichroism as a function of NaCl concentration, pH and temperature, and square-wave voltammetry as a function of pH. The results indicate that these oligonucleotides form intramolecular structures that contain transient U•U base pairs at pH 7 and moderate ionic strength (100 mM NaCl). This folded structure becomes destabilized and loses the U•U base pairs above and below neutral pH, especially at ionic strengths above 0.1. All of the cytidine protons exchange relatively rapidly with solvent protons (exchange lifetimes shorter than 1 ms), so the structure contains few if any C•CH+ base pairs at neutral pH, but can apparently form them at pH values below 6. We present a series of possible models in which chain folding draws the strand termini closer together, possibly serving to pull the attached WC hairpin domains together and providing a functional advantage by nucleating reversible formation of a more viable RNA substrate. DA - 1999/1/15/ PY - 1999/1/15/ DO - 10.1093/nar/27.2.665 VL - 27 IS - 2 SP - 665-673 SN - 1362-4962 ER - TY - JOUR TI - Flexibility of the MPS4- chains of the KMPS4 (M = Ni, Pd) compounds studied by molecular orbital calculations and atomic force microscopy measurements AU - Whangbo, MH AU - Bengel, H AU - Jobic, S AU - Brec, R T2 - JOURNAL OF SOLID STATE CHEMISTRY AB - The flexibility of the MPS−4 chains of KMPS4 (M=Ni, Pd) was examined by performing contact mode atomic force microscopy (AFM) measurements for the (001) surface of KNiPS4 and also by performing extended Hückel tight binding calculations for the [M(PS4)2]4− entities of KMPS4. The observed AFM images were analyzed by calculating the total electron density plots for an isolated [NiPS4]− slab of the (001) surface. Our calculations show that the PS3−4 ions are more strongly bound to the Pd2+ ions in KPdPS4 than to the Ni2+ ions in KNiPS4, and that the bonding between the PS3−4 anions and M2+ (M=Ni, Pd) cations is flexible with respect to the rotational motions of the PS3−4 anions. The AFM images recorded for the (001) surface of KNiPS4 indicate that the PS3−4 anions on the surface undergo a rotational relaxation when the scanning tip passes by. DA - 1999/10// PY - 1999/10// DO - 10.1006/jssc.1999.8245 VL - 147 IS - 1 SP - 235-239 SN - 0022-4596 ER - TY - JOUR TI - Evaluation of short term-high intensity thermal degradation of graphite fiber reinforced laminates via ultrasonic spectroscopy AU - Schueneman, GT AU - Lesser, AJ AU - Hobbs, TR AU - Novak, BM T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - In certain fire situations, a structural or load-bearing polymer matrix composite (PMC) may be exposed to excessive thermal loads that degrade the matrix. In this paper, we report the results of a study to assess the utility of ultrasonic spectroscopy as a means of assessing the residual physical and mechanical characteristics of PMCs exposed to excessive thermal loads. We show that the measured power spectra of ultrasonic energy correlates with performance of graphite fiber epoxy matrix composites exposed to thermal degradation. Unidirectional composites were exposed to short term–high intensity thermal loads at one end of the specimen. Thus, inducing a thermal gradient along the length of the specimen. Simultaneous thermogravimetric analysis–differential scanning calorimetry (TGA/DSC) and Fourier transform infrared spectroscopy (FTIR) analysis of the aged specimens revealed a gradient in thermal degradation. The thermal loads induced substantial degradation of the composite. However, the amplitude of the power spectra is observed to increase gradually then sharply prior to its complete attenuation due to delaminations. Mode I fracture toughness tests correlate with the observed changes in the ultrasonic spectra. FTIR, TGA/DSC, fracture toughness, and ultrasonic spectral analysis all indicate the same critical temperature at which thermally induced damage sharply increased. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2601–2610, 1999 DA - 1999/9/15/ PY - 1999/9/15/ DO - 10.1002/(SICI)1099-0488(19990915)37:18<2601::AID-POLB5>3.0.CO;2-Z VL - 37 IS - 18 SP - 2601-2610 SN - 1099-0488 KW - thermal degradation KW - polymer matrix composites KW - ultrasonic spectroscopy KW - fracture toughness ER - TY - JOUR TI - Dipolar Gay-Berne liquid crystals: A Monte Carlo study AU - Houssa, M. AU - Rull, L. F. AU - McGrother, S. C. T2 - International Journal of Modern Physics. C AB - The phase diagrams of several dipolar Gay–Berne systems are generated using Monte Carlo simulations. Particular emphasis is placed upon the location, order and nature of the liquid crystalline phases observed at high fluid densities. The accuracy of the reaction field method is re-affirmed. DA - 1999/// PY - 1999/// DO - 10.1142/S0129183199000292 VL - 10 IS - 2-3 SP - 391-401 ER - TY - JOUR TI - Cross-conjugated bis(porphryin)s: Synthesis, electrochemical behavior, mixed valency, and biradical dication formation AU - Shultz, DA AU - Lee, H AU - Kumar, RK AU - Gwaltney, KP T2 - JOURNAL OF ORGANIC CHEMISTRY AB - The synthesis and characterization of seven (ZnII)2bis(porphyrin) molecules are described. The molecular structures of two bis(porphyrin)s (6 and 7) were determined by X-ray diffraction methods. Four of the compounds have their porphyrin moieties attached in a meta-fashion to a substituted benzene ring (1−4), two have porphyrin rings attached in a gem-fashion to a carbon−carbon double bond (6 and 7), and one bis(porphyrin) (5) has a p-phenylene coupler. Bis(porphyrin)s 1, 4, and 5 contain tetraaryl-type porphyrins, while 2, 3, 6, and 7 contain triarylethynylporphyrins. Except for exciton coupling in the unoxidized species, interaction between porphyrins is greater in the triarylethynyl-type bis(porphyrin)s than in the tetraaryl-type bis(porphyrin)s regardless of the number of bonds through which the interaction propagates. The cyclic voltammetry of the bis(porphyrin)s was examined, and a varying degree of interaction between electrophores within the series was found. Redox splitting was observed for porphyrin ring oxidations of 3, 6, and 7, suggesting interaction between the oxidized porphyrin rings beyond simple electrostatic repulsions. No such redox splitting was observed for any of the tetraaryl-type bis(porphyrin)s (1, 4, and 5). We conclude that two porphyrin radical cations interact best when (1) the interaction pathway is short (ΔE1/2(6/7) > ΔE1/2(2/3)), (2) π-overlap between the electrophore and coupler is maximized (minimal bond torsions: ΔE1/2(6/7) > ΔE1/2(4/5)), and (3) the electron demand of the coupler matches that of the spin carrier (ΔE1/2(3) > ΔE1/2(2)). One-electron oxidized triarylethynyl-type bis(porphyrin)s exhibit spectral features characteristic of mixed-valent compounds. In two cases (6•+ and 7•+), near-IR bands near 8300 cm-1 were observed and are tentatively assigned to intervalence transitions. Singly oxidized tetraaryl-type bis(porphyrin)s exhibit no such near-IR transitions, and electronic absorption spectra recorded during electrochemical oxidations are marked by isosbestic points, suggesting negligible interaction between the two halves of the molecule, consistent with cyclic voltammetric results. Two-electron oxidation of 2−7 yields biradical dications whose frozen solution EPR spectra lack fine structure, but exhibit Δms = 2 transitions characteristic of exchange-coupled S = 1 states. Oxidation of 1 yields a biradical in which both exchange coupling and dipolar interaction between unpaired electrons are presumably very weak; consequently no Δms = 2 is observed. The results of variable-temperature EPR spectroscopy of 22•2+−72•2+ suggest either a triplet ground state or a singlet−triplet degeneracy. As a consequence of our results, we hypothesize that the exchange interaction, and therefore the singlet−triplet gap, in a biradical di-ion can be adjusted to favor the triplet state by simple substituent effects. DA - 1999/12/10/ PY - 1999/12/10/ DO - 10.1021/jo991046h VL - 64 IS - 25 SP - 9124-9136 SN - 0022-3263 ER - TY - JOUR TI - Coumarinic acid-based cyclic prodrugs of opioid peptides that exhibit metabolic stability to peptidases and excellent cellular permeability AU - Gudmundsson, OS AU - Pauletti, GM AU - Wang, W AU - Shan, DX AU - Zhang, HJ AU - Wang, BH AU - Borchardt, RT T2 - PHARMACEUTICAL RESEARCH DA - 1999/1// PY - 1999/1// DO - 10.1023/A:1018828207920 VL - 16 IS - 1 SP - 7-15 SN - 0724-8741 KW - esterase-sensitive prodrugs KW - peptide delivery KW - opioid peptides KW - Caco-2 cells KW - membrane permeability KW - chemical and enzymatic stability ER - TY - JOUR TI - Conditions of strict voltammetric reversibility of the H+/H-2 couple at platinum electrodes AU - Jaworski, A AU - Donten, M AU - Stojek, Z AU - Osteryoung, JG T2 - ANALYTICAL CHEMISTRY AB - Cyclic voltammetric curves obtained at Pt electrodes for the hydrogen couple, H+/H2, fit very well the Shuman theory, as corrected, for reversible electrode processes of other than 1:1 stoichiometry. Good agreement was obtained for acid concentrations in the millimolar range and for normal scan rates, which minimize the effect of the adsorption peaks. An error in Shuman's equation for potential is corrected. Voltammograms obtained at Pt microelectrodes fit well the theoretical simulated data. DA - 1999/1/1/ PY - 1999/1/1/ DO - 10.1021/ac9804240 VL - 71 IS - 1 SP - 243-246 SN - 1520-6882 ER - TY - JOUR TI - A planning module for performing grid search, factorial design, and related combinatorial studies on an automated chemistry workstation AU - Kuo, PY AU - Du, H AU - Corkan, LA AU - Yang, KX AU - Lindsey, JS T2 - CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS AB - The investigation of combinations of factors in a defined search space has broad application in chemistry experimentation. The factors can involve continuous variables such as concentration and temperature, or discrete variables such as chemical reactants or reagents. The number of data points rapidly becomes quite large in such factorial experimentation, which can be adequately handled through the use of an automated chemistry workstation. The automated chemistry workstation utilizes experiment templates for implementation of factorial designs. Experimental templates represent generic plans that are used repetitively with slight variation of designated parameters for the chemical system under investigation. A linkage is established between the dimensions of the search space and the variables in the experimental template. Various patterns of points can be selected, enabling the composition of full factorial or partial factorial designs. The search space points are inscribed in the experimental template, giving rise to one experimental plan per point in the search space. The experimental plans are assessed for resource availability and those for which resources are sufficient are then scheduled for parallel implementation on a microscale automated chemistry workstation. An adaptive feature allows unproductive experiments to be terminated early, de-allocating resources for use in other experiments. Experimental plans can be readily composed and implemented for fundamental studies of chemical reactions, generating response surfaces, performing parallel screening procedures, and creating indexed combinatorial chemical libraries. DA - 1999/8/2/ PY - 1999/8/2/ DO - 10.1016/S0169-7439(99)00021-0 VL - 48 IS - 2 SP - 219-234 SN - 0169-7439 KW - grid search KW - factorial design KW - automated chemistry workstation ER - TY - JOUR TI - Three-dimensional solution structure of mouse [Cd-7]-metallothionein-1 by homonuclear and heteronuclear NMR spectroscopy AU - Zangger, K AU - Oz, G AU - Otvos, JD AU - Armitage, IM T2 - PROTEIN SCIENCE AB - Sequential 1H-NMR assignments of mouse [Cd7]-metallothionein-1 (MT1) have been carried out by standard homonuclear NMR methods and the use of an accordion-heteronuclear multiple quantum correlation (HMQC) experiment for establishing the metal, 113Cd2+, to cysteine connectivities. The three-dimensional structure was then calculated using the distance constraints from two-dimensional nuclear Overhauser effect (NOE) spectroscopy spectra and the Cys-Cd connectivities as input for a distance geometry-dynamical simulated annealing protocol in X-PLOR 3.851. Similar to the mammalian MT2 isoforms, the homologous primary structure of MT1 suggested two separate domains, each containing one metal cluster. Because there were no interdomain constraints, the structure calculation for the N-terminal beta- and the C-terminal alpha-domain were carried out separately. The structures are based on 409 NMR constraints, consisting of 381 NOEs and 28 cysteine-metal connectivities. The only elements of regular secondary structure found were two short stretches of 3(10) helices along with some half-turns in the alpha-domain. Structural comparison with rat liver MT2 showed high similarity, with the beta-domain structure in mouse MT1 showing evidence of increased flexibility compared to the same domain in MT2. The latter was reflected by the presence of fewer interresidue NOEs, no slowly exchanging backbone amide protons, and enhanced cadmium-cadmium exchange rates found in the beta-domain of MT1. DA - 1999/12// PY - 1999/12// DO - 10.1110/ps.8.12.2630 VL - 8 IS - 12 SP - 2630-2638 SN - 1469-896X KW - Cd-113 KW - 2D NMR KW - accordion-HMQC KW - mouse metallothionein-1 KW - nuclear magnetic resonance KW - structure ER - TY - CHAP TI - Theoretical Studies of Ethyl to Ethylene Conversion on Nickel and Platinum AU - Whitten, J. L. AU - Yang, H. T2 - ACS Symposium Series AB - Ethylene production from ethyl adsorbed on nickel and platinum surfaces is investigated using first-principles theory. Calculations are based on an embedded cluster formalism that permits an accurate determination of energies and adsorbate structure. The key issue is the nature of the activation barrier associated with the transfer of a beta hydrogen to the metal surface. The minimum energy pathway is found to require an initial repulsive interaction with the surface in which the adsorbed ethyl fragment is tilted until there is a slight penetration of the electron density of the metal surface by the ethyl beta hydrogen. The H atom can then be transferred from this more energetic configuration with an overall activation energy of 17 kcal/mol for Ni(100) and 14 kcal/mol for Pt(100). Differences between nickel and platinum are discussed. CN - QD505 .T735 1999 PY - 1999/4/8/ DO - 10.1021/bk-1999-0721.ch021 SP - 274-285 OP - PB - American Chemical Society SN - 9780841236103 9780841217096 UR - http://dx.doi.org/10.1021/bk-1999-0721.ch021 DB - Crossref ER - TY - JOUR TI - The strength of acids in alcohols as determined by steady-state voltammetry AU - Jaworski, A AU - Osteryoung, JG AU - Donten, M AU - Stojek, Z T2 - ANALYTICAL CHEMISTRY AB - Steady-state voltammograms for reduction of acids of various strengths in alcohols with excess supporting electrolyte and without any supporting electrolyte can be used to infer charge type and strength of the acid on the basis of the phenomenon of migration. For strong and moderately weak acids (K(a)/[Formula: see text] > 10(-)(3)) in alcohols, the ratio of steady-state transport-limited current to diffusion-limited current, corrected appropriately for ion-ion interactions, the presence of ionic impurities, and changes in viscosity, for hydrogen ion reduction without supporting electrolyte and with excess supporting electrolyte equals 2. For acetic acid, which is very weak (K(a)/[Formula: see text] < 10(-)(6)), the value of the steady-state transport-limited current is, under the experimental conditions applied here, independent of supporting electrolyte concentration. In the case of a homogeneous acid-base equilibrium, a novel analytical procedure yields diffusion coefficients of both hydrogen ion and undissociated weak acid molecules from the diffusional and migrational currents. Limiting currents obtained in alcohols with excess supporting electrolyte and without supporting electrolyte are compared by means of an extended formula that incorporates the ionic strength dependence of diffusion coefficients. DA - 1999/9/1/ PY - 1999/9/1/ DO - 10.1021/ac9814593 VL - 71 IS - 17 SP - 3853-3861 SN - 0003-2700 ER - TY - JOUR TI - The effect of conformation on the membrane permeation of coumarinic acid- and phenylpropionic acid-based cyclic prodrugs of opioid peptides AU - Gudmundsson, OS AU - Jois, SDS AU - Vander Velde, DG AU - Siahaan, TJ AU - Wang, B AU - Borchardt, RT T2 - JOURNAL OF PEPTIDE RESEARCH AB - Abstract: In an earlier study using Caco‐2 cells, an in vitro cell culture model of the intestinal mucosa, we have shown that the coumarinic‐based ( 3 and 4 ) and the phenylpropionic acid‐based ( 5 and 6 ) cyclic prodrugs were more able to permeate the cell monolayers than were the corresponding opioid peptides, [Leu 5 ]‐enkephalin ( 1 , H‐Tyr‐Gly‐Gly‐Phe‐Leu‐OH) and DADLE ( 2 , H‐Tyr‐D‐Ala‐Gly‐Phe‐D‐Leu‐OH). In an attempt to explain the increased permeation of the cyclic prodrugs, we have determined the possible conformations of these cyclic prodrugs in solution, using spectroscopic techniques (2D‐NMR, CD) and molecular dynamics simulations. Spectroscopic as well as molecular dynamic studies indicate that cyclic prodrug 4 exhibits two major conformers ( A and B ) in solution. Conformer A exhibited a type I β‐turn at Tyr1‐D‐Ala2‐Gly3‐Phe4. The presence of a turn was supported by ROE cross‐peaks between the NH of D‐Ala2 and the NH of Gly3 and between the NH of Gly3 and the NH of Phe4. Conformer B of cyclic prodrug 4 consisted of type II β‐turns at the same positions. The type II turn was stabilized by hydrogen bonding, thus forming a more compact structure, whereas the type I turn did not exhibit similar intramolecular hydrogen bonding. Spectroscopic data for compounds 3, 5 and 6 are consistent with the conclusion that these cyclic prodrugs have solution structures similar to those observed with cyclic prodrug 4 . The increased lipophilicity and well‐defined secondary structures in cyclic prodrugs 3 – 6 , but not in the linear peptides 1 and 2, could both contribute to the enhanced ability of these prodrugs to permeate membranes. DA - 1999/4// PY - 1999/4// DO - 10.1034/j.1399-3011.1999.00076.x VL - 53 IS - 4 SP - 383-392 SN - 1397-002X KW - membrane permeability KW - nuclear magnetic resonance spectroscopy KW - opioid peptide delivery KW - solution conformation ER - TY - JOUR TI - The C-13 spin-lattice relaxation time for poly (di-N-hexyl) AU - Lim, A. R. AU - Novak, B. M. T2 - Solid State Communications DA - 1999/// PY - 1999/// VL - 109 IS - 1 SP - 29-34 ER - TY - JOUR TI - Synthesis of beta-substituted porphyrin building blocks and conversion to diphenylethyne-linked porphyrin dimers AU - Balasubramanian, T AU - Lindsey, JS T2 - TETRAHEDRON AB - A recent hypothesis concerning effects of orbital ordering on electronic communication (excited-state energy transfer, ground-state hole-hopping) in covalently linked porphyrin arrays prompted the development and application of methodology for the synthesis of β-linked porphyrin dimers. Reaction of a β-substituted pyrrole with 2-hydroxymethylpyrrole led to the dipyrromethane bearing a single β-substituent and no meso- nor α-substituents. Condensation of the β-substituted dipyrromethane with an aldehyde and a meso-substituted dipyrromethane gave the desired β-substituted porphyrin building block, albeit in low yield. Four building blocks were prepared with a p-iodophenyl or p-ethynylphenyl group at one β-position, no substituent at the flanking meso-position, and mesityl or pentafluorophenyl groups at the three non-flanking meso-positions. The porphyrin building blocks were coupled via Pd-mediated reactions, affording diphenylethyne-linked dimers with the linker attached at β-positions. This approach provided access to zinc-free base porphyrin dimers and bis-zinc dimers bearing mesityl or pentafluorophenyl groups at the three non-linking meso-positions. The availability of these dimers and monomeric benchmarks enabled a critical test of the orbital ordering hypothesis. This methodology for preparing porphyrin building blocks bearing a lone, non-hindered β-substituent complements existing methods for preparing meso-substituted porphyrin building blocks. The ability to position the linker at the meso- or β-positions provides a desirable level of versatility for incorporating porphyrinic molecules with an a2u or a1u HOMO in various molecular devices. DA - 1999/5/28/ PY - 1999/5/28/ DO - 10.1016/S0040-4020(99)00339-7 VL - 55 IS - 22 SP - 6771-6784 SN - 0040-4020 KW - alkynes KW - orbital effects KW - porphyrins KW - pyrroles ER - TY - JOUR TI - Synthesis and evaluation of the physicochemical properties of esterase-sensitive cyclic prodrugs of opioid peptides using coumarinic acid and phenylpropionic acid linkers AU - Wang, B AU - Nimkar, K AU - Wang, W AU - Zhang, H AU - Shan, D AU - Gudmundsson, O AU - Gangwar, S AU - Siahaan, T AU - Borchardt, RT T2 - JOURNAL OF PEPTIDE RESEARCH AB - In an attempt to improve the membrane permeabilities of opioid peptides, we have synthesized cyclic prodrugs of [Leu5]-enkephalin and DADLE using a coumarinic acid or a phenylpropionic acid linker. The synthesis of the coumarinic acid- and phenylpropionic acid-based cyclic prodrugs followed similar strategies. Key intermediates were the compounds with the C-terminal amino acids of opioid peptides (L-Leu, [Leu5]-enkephalin; D-Leu, DADLE) attached to the phenol hydroxyl group and the remaining amino acids of the peptide linked via the N-terminal amino acid (L-Tyr) attached to the carboxylic acid groups of the prodrug moieties (coumarinic acid or propionic acid). Cyclization of these linear precursors gave the cyclic prodrugs in 30-50% yields. These cyclic prodrugs exhibited excellent transcellular permeation characteristics across Caco-2 cell monolayers, an in vitro model of the intestinal mucosa. To correlate the cellular permeabilities of these cyclic prodrugs with their physicochemical properties, we calculated their Stokes-Einstein molecular radii from their diffusion coefficients which were determined by NMR and we determined their membrane interaction potentials using immobilized artificial membrane (IAM) column chromatography. The cyclic prodrugs exhibited molecular radii similar to those of the parent compounds, [Leu5]-enkephalin and DADLE. However, these cyclic prodrugs were shown to have much higher membrane interaction potentials than their corresponding opioid peptides. Therefore, the enhanced cellular permeation of the cyclic prodrugs is apparently due to the alteration of their lipophilicity and hydrogen bonding potential, but not their molecular sizes. DA - 1999/4// PY - 1999/4// DO - 10.1034/j.1399-3011.1999.00071.x VL - 53 IS - 4 SP - 370-382 SN - 1397-002X KW - membrane transport KW - opioid peptide KW - physicochemical properties KW - prodrugs ER - TY - JOUR TI - Synthesis and evaluation of novel coumarin-based esterase- sensitive cyclic prodrugs of peptidomimetic RGD analogs with improved membrane permeability AU - Wang, B. H. AU - Wang, W. AU - Camenisch, G. P. AU - Elmo, J. AU - Zhang, H. J. AU - Borchardt, R. T. T2 - Chemical & Pharmaceutical Bulletin DA - 1999/// PY - 1999/// VL - 47 IS - 1 SP - 90-95 ER - TY - JOUR TI - Suppression of boron transport out of p(+) polycrystalline silicon at polycrystalline silicon dielectric interfaces AU - Wu, Y. AU - Niimi, H. AU - Yang, H. AU - Lucovsky, G. AU - Fair, R. B. T2 - Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures DA - 1999/// PY - 1999/// VL - 17 IS - 4 SP - 1813-1822 ER - TY - JOUR TI - Steroid analysis in single cells by capillary electrophoresis with collinear laser-induced fluorescence detection AU - Malek, A AU - Khaledi, MG T2 - ANALYTICAL BIOCHEMISTRY AB - Capillary electrophoresis with collinear laser-induced fluorescence detection was used for the analysis of steroids in single R2C cells. Progesterone secretion was monitored from cultured cells and subsequently detected in single cells. Mass detection limit of 10−18mol for dansylated steroids was achieved with the 325-nm line of a helium–cadmium laser. Dansylhydrazine proved to be an effective fluorescent tag for derivatization of steroids outside and inside the biological cell. Fluorescence microscopy indicates that a dimethyl sulfoxide-containing physiological buffer was sufficient to incorporate the tag inside the cell for subsequent steroid derivatization. DA - 1999/5/15/ PY - 1999/5/15/ DO - 10.1006/abio.1999.3096 VL - 270 IS - 1 SP - 50-58 SN - 1096-0309 ER - TY - JOUR TI - Spin-spin interactions in the oxides A(3)M ' MO6 (M = Rh, Ir; A = Ca, Sr; M ' = alkaline earth, Zn, Cd, Na) of the K4CdCl6 structure type examined by electronic structure calculations AU - Lee, KS AU - Koo, HJ AU - Whangbo, MH T2 - INORGANIC CHEMISTRY AB - The oxides A(3)M'MO(6) (M = Rh, Ir; A = Ca, Sr; M' = alkaline earth, Zn, Cd) of the K(4)CdCl(6) structure type consist of isolated (MO(6))(8)(-) octahedral anions and exhibit an antiferromagnetic ordering at low temperatures. The spin-spin interactions in these oxides, Ca(3)NaMO(6) (M = Ir, Ru), and Sr(3)NaRuO(6) were examined by calculating how strongly the t(2g)-block levels of adjacent (MO(6))((6+)(n)()())(-) (n = 1, 2) anions interact in the presence and absence of the intervening cations A(2+) and M' (n)()(+) (n = 1, 2). Our calculations show that the spin-spin interactions in these oxides are three-dimensional, and the superexchange interactions occur mainly through the short intrachain and interchain M-O.O-M linkages. When the M(n)()(+) cation is very small compared with the A(2+) cation, the intrachain interaction is substantially stronger than the interchain interaction. The opposite is found when the sizes of the M(n)()(+) and A(2+) cations become similar. DA - 1999/5/3/ PY - 1999/5/3/ DO - 10.1021/ic9813819 VL - 38 IS - 9 SP - 2199-2203 SN - 0020-1669 ER - TY - JOUR TI - Reaction and adsorption energetics of CN+O -> OCN on nickel AU - Yang, H. AU - Whitten, Jerry T2 - Journal of Molecular Structure [including Theochem] AB - The reaction energetics of O+CN→OCN on Ni(100) are studied using an ab initio embedding theory. The Ni(100) surface is modeled as a three-layer, 30-atom cluster with the Ni atoms fixed at bulk lattice sites. Adsorption geometries of CN and OCN, both N-bonded and O-bonded in an end-on geometry with the molecular axis perpendicular to the surface and in a side-on geometry, are considered in the present study. Our calculations show that the molecular axis of OCN is normal to the surface and that the most stable adsorption site is the fourfold one with adsorption energies of 103 kcal mol−1 for the N-bonded OCN and 87 kcal mol−1 for the O-bonded OCN, respectively. The bridge and atop sites are about 3 and 10 kcal mol−1 less stable. The adsorption energy for the side-on bonded OCN with the molecular axis parallel to the surface is 84 kcal mol−1. The present calculations also show that CN is able to bind to the surface either via the carbon, or the nitrogen, or in a side-on geometry with very small differences in total energy, ≤2 kcal mol−1. It was found that CN is nearly free to rotate to other geometries over very small energy barriers, ≤2 kcal mol−1. With O coadsorbed at a fourfold site, the adsorption of CN at the next nearest bridge or on-top sites is energetically more favorable than adsorption at the adjacent fourfold site, and the C–N bond is perpendicular to the surface. The reaction of O+CN→OCN on Ni(100) has an energy barrier via the Langmuir–Hinshelwood mechanism, but no energy barrier via the Eley–Rideal process. The formation of surface OCN is due to the formation of a C–O bond by the interaction between the adsorbed O and the C atom of cyanide. DA - 1999/// PY - 1999/// DO - 10.1016/s0166-1280(98)00356-x VL - 458 IS - 1-2 SP - 131–142 ER - TY - JOUR TI - Preparation of poly(cyanoacetylene) using late-transition-metal catalysts AU - Gorman, CB AU - Vest, RW AU - Palovich, TU AU - Serron, S T2 - MACROMOLECULES AB - Poly(cyanoacetylene) has been prepared by polymerization of cyanoacetylene using a variety of late-transition-metal (Pd- and Ni-based) catalysts. The effect of reaction conditions on molecular weight and polymer yield was explored. Significant catalyst residues remain in the polymer samples. However, spectra are consistent with the proposed poly(cyanoacetylene) structure. Notable differences in molecular weight, effective conjugation length, and ability to undergo thermal cyclization to a supposed aromatic ladder polymer were observed between these polymers and those prepared using conventional anionic or radical initiators. DA - 1999/6/29/ PY - 1999/6/29/ DO - 10.1021/ma981773z VL - 32 IS - 13 SP - 4157-4165 SN - 0024-9297 ER - TY - JOUR TI - Predictions of enhanced chemical reactivity at regions of local conformational strain on carbon nanotubes: Kinky chemistry AU - Srivastava, D AU - Brenner, DW AU - Schall, JD AU - Ausman, KD AU - Yu, MF AU - Ruoff, RS T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Simulations that model the effects of conformational strain on the chemical reactivity of single-walled carbon nanotubes suggest a method for significantly enhancing their reactivity locally by controlled deformations. The chemisorption of hydrogen atoms is predicted to be enhanced by as much as 1.6 eV at regions of high conformational deformation, suggesting that local reactivity will be significantly enhanced. Analysis of the local electronic density of states suggests the introduction of radical p orbital character to the sites that are locally deformed, consistent with the heightened reactivity and large pyramidalization angles at these sites. Preliminary experimental data consistent with this predicted heightened reactivity is also presented. DA - 1999/5/27/ PY - 1999/5/27/ DO - 10.1021/jp990882s VL - 103 IS - 21 SP - 4330-4337 SN - 1520-5207 ER - TY - JOUR TI - Measurement of triglyceride-rich lipoproteins by nuclear magnetic resonance spectroscopy AU - Otvos, J. T2 - Clinical Cardiology (Los Altos, Calif.) AB - Nuclear magnetic resonance (NMR) spectroscopy is being used to determine the concentrations of very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) subclasses of different size. These subclasses have unequal associations with coronary heart disease. Nuclear magnetic resonance distinguishes among the subclasses on the basis of slight differences in the spectral properties of the lipids carried within the particles, which vary according to the diameter of the phospholipid shell. Studies using NMR spectroscopy have shown that individuals with elevated triglycerides are likely to have higher-risk lipoprotein subclass profiles. Triglyceride-rich lipoproteins drive the metabolic reactions that produce LDL of abnormal size and cholesterol content. The quantities of these abnormal LDL particles and the associated risk of coronary heart disease are underestimated by conventional cholesterol measurements. Nuclear magnetic resonance spectroscopy measures lipoprotein subclasses directly and efficiently, and produces information that may improve the assessment and management of cardiovascular disease risk. DA - 1999/// PY - 1999/// DO - 10.1002/clc.4960221405 VL - 22 IS - 6 Suppl. SP - II 21-27 ER - TY - JOUR TI - Investigation and refinement of palladium-coupling conditions for the synthesis of diarylethyne-linked multiporphyrin arrays AU - Wagner, RW AU - Ciringh, Y AU - Clausen, C AU - Lindsey, JS T2 - CHEMISTRY OF MATERIALS AB - The synthesis of diarylethyne-linked multiporphyrin arrays requires Pd-mediated coupling conditions that are performed in dilute solution in the absence of copper and that give reaction mixtures that are easily purified. We previously developed copper-free Pd-mediated coupling conditions (Pd2(dba)3 and AsPh3 in toluene/triethylamine (5:1) at 35 °C) but extensive chromatography was required to remove unidentified porphyrinic byproducts. We have used laser-desorption mass spectrometry (LD-MS) and analytical size-exclusion chromatography (SEC) to assay the products from the coupling reaction of a zinc(II) iodophenylporphyrin (ZnI) and a zinc(II) ethynylphenylporphyrin (ZnU‘). Analysis of the crude reaction mixture revealed the diphenylethyne-linked dimer (Zn2U) as the major product, byproducts plausibly derived from phenyl−aryl exchange processes (a phenylated derivative of ZnU‘, a Ph2As-substituted derivative of ZnI), byproducts believed to originate from direct phenylation processes (a phenylated derivative of ZnI, the phenylated dimer Ph-Zn2U), and higher molecular weight material (HMWM) comprised of undefined porphyrin oligomers. The HMWM is readily removed but the phenylated dimer causes severe purification problems. Our observations concerning the phenylation processes are as follows: (1) The phenylated dimer was observed in significant quantity (∼7:1 ratio of Zn2U/Ph-Zn2U by LD-MS). (2) Control experiments showed that direct phenylation of free base (Fb) porphyrins or zinc porphyrins occurred with Pd2(dba)3 and AsPh3 in the absence of iodo- or ethynylporphyrins. (3) Phenylation occurred at the earliest stage of the reaction (3 min time point). (4) The inclusion of CuI (with Pd2(dba)3 and PPh3) accelerated formation of Zn2U but did not reduce the amount of phenylation. (5) The use of P(o-tol)3 in conjunction with Pd2(dba)3 caused slower reaction, a slight increase in HMWM, and significantly diminished arylation (Zn2U/Ar-Zn2U ratio ∼65:1). (6) Replacement of Pd2(dba)3 with Pd(OAc)2 gave the same arylation ratio (65:1) but slightly lower yield. Application of the refined conditions (Pd2(dba)3 and P(o-tol)3 in toluene/triethylamine (5:1) at 35 °C) to the stepwise synthesis of porphyrin trimers having metalation states of Zn and Fb (ZnZnFbU) or Mg, Zn, and Fb (MgZnFbU) afforded coupling efficiencies of 45−55% and a substantially simpler chromatographic purification process. DA - 1999/10// PY - 1999/10// DO - 10.1021/cm9903529 VL - 11 IS - 10 SP - 2974-2983 SN - 0897-4756 ER - TY - JOUR TI - Interplay of orbital tuning and linker location in controlling electronic communication in porphyrin arrays AU - Yang, SI AU - Seth, J AU - Balasubramanian, T AU - Kim, D AU - Lindsey, JS AU - Holten, D AU - Bocian, DF T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - The β-diphenylethyne-linked porphyrin dimers ZnFbU-β (nonlinking meso-mesityl substituents) and F30ZnFbU-β (nonlinking meso-pentafluorophenyl substituents) and their bis-Zn analogues have been examined by static spectroscopic (absorption, fluorescence, electron paramagnetic resonance), time-resolved spectroscopic (absorption, fluorescence), and electrochemical (cyclic and square-wave voltammetry, coulometry) methods. The β-linked dimers were examined to test the hypothesis that the nature of the porphyrin HOMO (a1u versus a2u) in concert with the position of the linker (β-pyrrole or meso carbon) mediates electronic communication (excited-state energy transfer, ground-state hole-hopping). The major findings are as follows: (1) The rate of energy transfer is (56 ps)-1 for ZnFbU-β and (24 ps)-1 for F30ZnFbU-β. (2) The rate of hole/electron hopping in the monooxidized bis-Zn complex [F30Zn2U-β]+ is in the fast-exchange limit and is at least comparable to that for [Zn2U-β]+. These findings indicate that the presence of pentafluorophenyl groups causes enhancement of electronic communication in the β-linked dimers but attenuation in the meso-linked dimers. These opposite effects in the β- versus meso-linked dimers are explained by the fact that both pentafluorophenyl-substituted dimers have a1u HOMOs, which exhibit significant β-pyrrole electron density, whereas both mesityl-substituted dimers have a2u HOMOs, which exhibit large meso-carbon density. Thus, the combination of an a1u HOMO with a β-linker or an a2u HOMO with a meso linker results in optimal electronic communication. Collectively, these results demonstrate that the nature of the frontier orbitals and position of connection of a covalent linker (in addition to distance, orientation, and energetics) must be considered in the design architecture of molecular photonic devices. DA - 1999/4/28/ PY - 1999/4/28/ DO - 10.1021/ja9842060 VL - 121 IS - 16 SP - 4008-4018 SN - 0002-7863 ER - TY - JOUR TI - In situ monitoring of diffuse double layer structure changes of electrochemically addressable self-assembled monolayers with an atomic force microscope AU - Hu, K AU - Chai, Z AU - Whitesell, JK AU - Bard, AJ T2 - LANGMUIR AB - An alkyl disulfide containing two sulfonate-substituted ferrocenes, 7,8-dithiatetradecane-1,14-di(aminocarbonyl)-bis(1‘-ferrocene-1-sulfonic acid), was synthesized and used to form electroactive self-assembled monolayers on gold electrodes. Atomic force microscope (AFM) force curves were employed to measure in situ the change in surface charge as the ferrocene groups were oxidized to compensate for the negative charges on the sulfonate groups. The electrode surface charge density was calculated from the surface coverage measured by electrochemical oxidation of the ferrocene groups, while the diffuse double layer charges were obtained from theoretical fits of the force data to solutions of the complete nonlinear Poisson−Boltzmann (PB) equation with knowledge of the silica probe surface potential. A significant difference between the AFM measured (i.e., effective) surface charge and the surface charge calculated from electrochemical measurements was found. This difference is attributed to a layer of counterions near the surface that screens a large fraction of the surface charge (variously described as “ion condensation” or failure of the nonlinear PB theory). The experimental results also showed that the extent of this ion screening (∼97%) was relatively constant and independent of the total electrode surface charge. DA - 1999/4/27/ PY - 1999/4/27/ DO - 10.1021/la9813937 VL - 15 IS - 9 SP - 3343-3347 SN - 0743-7463 ER - TY - JOUR TI - IUPAC-NIST solubility data series 68. Halogenated aliphatic hydrocarbon compounds C-3-C-14 with water AU - Horvath, AL AU - Getzen, FW T2 - JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA AB - This volume covers the solubilities of halogenated aliphatic C3–C14 compounds with water, heavy water, and electrolyte solutions. All data were critically examined for their reliability and best value estimates were selected on the basis of such evaluations. Referenced works are presented in the standard IUPAC-NIST Solubility Data Series format. Reported and best value data are presented in tabular form and, where justified, data correlation equations and graphical illustrations are provided. Throughout the volume, SI conventions have been employed as the customary units. The importance of these data arises from the fact that halogenated aliphatics have considerable commercial uses in a variety of applications such as industrial chemicals, process raw materials, solvents, and the like. In such applications they are often in contact with water and are routinely exposed to the atmosphere. Sometimes such contact and exposure results from spillage, leakage, or mishandling. Reliable data are essential for concentration estimates for the halogenated aliphatics in drinking and ground water, foodstuffs, human tissue, marine organisms, and the atmosphere. The halogenated aliphatics are of particular interest to health scientists, engineers, environmentalists, and atmospheric chemists in that they represent a class of chemical materials which has many significant industrial applications. However, at the same time, some of this class of substances have been shown to be carcinogenic and also to be especially harmful for the earth’s atmospheric and natural water composition. Indeed, the chemical reactivity of some halogenated aliphatics has resulted in atmospheric ozone depletion. The high ozone depletion potentials of such chemical substances emphasizes the importance of having available complete, accurate, and reliable data for mutual solubilities with water. The availability of such data is essential for estimates of halogenated aliphatic hydrocarbon levels in both natural water and aqueous industrial liquids which result from industrial fabrication, industrial liquids which result from industrial fabrication, industrial waste removal processes, and the like. The data also provide significant solubility values for studies concerning the health of humans and other biological systems. DA - 1999/// PY - 1999/// DO - 10.1063/1.556051 VL - 28 IS - 3 SP - 649-778 SN - 0047-2689 KW - aqueous solutions KW - halogenated hydrocarbons KW - solubility ER - TY - JOUR TI - Hybrid organic-inorganic, hexa-arm dendrimers based on an Mo6Cl8 core AU - Gorman, CB AU - Su, WY AU - Jiang, HW AU - Watson, CM AU - Boyle, P T2 - CHEMICAL COMMUNICATIONS AB - Dendrons with focal phenoxide groups were shown to substitute for triflate or methoxide ligands around an Mo6Cl8 core to form molecules of the form Mo6(µ3-Cl)8(OR)6 where R = dendrons with zero to two hyperbranches, respectively; these molecules represent a new type of metal cluster core dendrimer with six arms and high symmetry. DA - 1999/5/21/ PY - 1999/5/21/ DO - 10.1039/a901590f IS - 10 SP - 877-878 SN - 1359-7345 ER - TY - JOUR TI - Effects of metalation state (Free base, Mg, Zn, Cd) on excited-state energy transfer in diarylethyne-linked porphyrin dimers AU - Hascoat, P AU - Yang, SI AU - Lammi, RK AU - Alley, J AU - Bocian, DF AU - Lindsey, JS AU - Holten, D T2 - INORGANIC CHEMISTRY AB - The ground- and excited-state properties of two new porphyrin dimers have been examined using static and time-resolved optical techniques. One dimer consists of a zinc porphyrin and a magnesium porphyrin (ZnMgU), and the other dimer consists of a cadmium porphyrin and a free base (Fb) porphyrin (CdFbU). In both arrays, the porphyrins are joined by a diarylethyne linker at one meso position with mesityl groups at the nonlinking meso positions. The rates of photoinduced energy transfer are faster for ZnMgU ((9 ps)(-)(1)) and CdFbU ((15 ps)(-)(1)) than found previously for ZnFbU ((24 ps)(-)(1)) and MgFbU ((31 ps)(-)(1)). Only for CdFbU does the yield of excited-state energy transfer (87%) drop below the near-quantitative (>/=99%) level, and this effect derives solely from competition with a very short inherent lifetime ( approximately 100 ps) of the photoexcited Cd porphyrin. The results further illustrate (1) the efficacy of this dimeric architecture for ultrafast excited-state energy transfer, (2) how molecular/electronic properties can be manipulated to tune photoinduced energy flow in multiporphyrin arrays, and (3) key factors impacting effective inter-porphyrin electronic communication, including porphyrin orbital tuning. DA - 1999/10/18/ PY - 1999/10/18/ DO - 10.1021/ic990469z VL - 38 IS - 21 SP - 4849-4853 SN - 0020-1669 ER - TY - JOUR TI - Effects of feeding program and crude protein intake during rearing on fertility of broiler breeder females AU - Walsh, TJ AU - Brake, J T2 - POULTRY SCIENCE AB - Arbor Acres broiler breeder pullets were grown from hatch to 24 wk on one of four feeding programs that achieved similar cumulative intakes of ME and CP at 24 wk, but not 20 wk (photostimulation), in Experiment 1. Graphing the four programs in terms of feed per bird per day by week of age gave the general shapes of linear, convex, concave, and deeply concave with respect to 0 and 24 wk reference points. The linear program, which achieved 1,192 g CP at 20 wk (photostimulation), as compared to < 1,150 g CP for the two concave programs, exhibited the best fertility. Although the pullets reared on the convex program consumed 1,255 g CP, fertility was poor, probably due to the reduced rate of increase in feed allocation late in rearing that delayed oviduct development. In Experiment 2, pullets were fed to the same cumulative ME intake at 20 wk using either a concave or convex feeding program with respect to 0 and 20 wk reference points with two levels of dietary protein. The higher level of CP intake (1,363 vs 1,212 g) produced higher fertility. A significant feeding program by dietary protein interaction was found. Level of CP intake at photostimulation had no effect on fertility with the concave feeding program but the convex program decreased fertility at the lower CP intake as in Experiment 1. DA - 1999/6// PY - 1999/6// DO - 10.1093/ps/78.6.827 VL - 78 IS - 6 SP - 827-832 SN - 0032-5791 KW - broiler breeders KW - fertility KW - crude protein KW - feeding programs ER - TY - JOUR TI - Distortional isomers of a mixed-valence binuclear Cu complex AU - Miskowski, VM AU - Franzen, S AU - Shreve, AP AU - Ondrias, MR AU - Wallace-Williams, SE AU - Barr, ME AU - Woodruff, WH T2 - INORGANIC CHEMISTRY AB - The resonance Raman spectra of a mixed-valence copper dimer [Cu2(L)]3+ encapsulated by the ligand L = N(CH2CH2N(H)CH2CH2N(H)CH2CH2)3N are reported. Copper isotope data (63/65Cu) of solution spectra of [Cu2(L)]3+ allow identification of vibrational bands at 289 and 172 cm-1 as predominately Cu−Cu stretching and Cu−Cu−Neq bending modes. The results indicate that the Cu−Cu bond is sufficiently weak that ligand conformations, influenced by hydrogen bonding, can give rise to distortional isomers of the Cu−Cu bond. DA - 1999/5/31/ PY - 1999/5/31/ DO - 10.1021/ic981415c VL - 38 IS - 11 SP - 2546-2547 SN - 0020-1669 ER - TY - JOUR TI - Decision-tree programs for an adaptive automated chemistry workstation. Application to catalyst screening experiments AU - Du, H AU - Shen, W AU - Kuo, PY AU - Lindsey, JS T2 - CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS AB - Abstract Automated chemistry workstations with the capability of altering the course of experimentation based on acquired data are essential for performing strategic searches. Such adaptive experimentation requires the ability to compose experimental plans for initiating, monitoring, evaluating, and making decisions about experiments. We have developed a decision-tree (DT) experiment-planning module that includes a complete command set for adaptive operation of the workstation. Functions for dialog prompts are included, enabling generic programs to be tailored for specific applications by various users. The DT experiment-planning module is one component of an experiment planner for an automated microscale chemistry workstation. The DT functions are also used to compose early-termination programs and describe objective functions for use in the companion factorial design, composite-modified simplex, and multidirectional search experiment-planning modules. The features of the DT experiment-planning module are illustrated with a program that screens a list of candidate compounds for catalytic activity. A set of dialog boxes at the beginning of the program prompts the user for information. Based on this information, the candidates are examined automatically (in a serial process) in exhaustive or hill-climbing searching strategies. A yield vs. time pattern-matching procedure is performed dynamically in order to assess whether monitoring should be continued. Decisions also are made concerning examination of the candidate at higher or lower concentrations. Higher concentrations are achieved by addition of aliquots of the candidate to the ongoing reaction, while lower concentrations are achieved by spawning a new reaction. When a user-defined yield threshold is reached or the entire user-specified concentration range has been spanned, catalysts and their effective concentration ranges are identified. This experiment-planning module enables composition of flexible programs for adaptive experimentation that can be used as stand-alone programs or as decision-making components of other searching programs. DA - 1999/8/2/ PY - 1999/8/2/ DO - 10.1016/S0169-7439(99)00020-9 VL - 48 IS - 2 SP - 205-217 SN - 0169-7439 KW - decision-tree programs KW - automated chemistry workstations KW - screening compounds ER - TY - JOUR TI - Cu(II) potentiation of Alzheimer A beta neurotoxicity - Correlation with cell-free hydrogen peroxide production and metal reduction AU - Huang, XD AU - Cuajungco, MP AU - Atwood, CS AU - Hartshorn, MA AU - Tyndall, JDA AU - Hanson, GR AU - Stokes, KC AU - Leopold, M AU - Multhaup, G AU - Goldstein, LE AU - Scarpa, RC AU - Saunders, AJ AU - Lim, J AU - Moir, RD AU - Glabe, C AU - Bowden, EF AU - Masters, CL AU - Fairlie, DP AU - Tanzi, RE AU - Bush, AI T2 - JOURNAL OF BIOLOGICAL CHEMISTRY AB - Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Abeta amyloid deposits in Alzheimer's disease. The neurotoxicity of Abeta in cell culture has been linked to H(2)O(2) generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Abeta in cell culture. The potentiation of toxicity is greatest for Abeta1-42 > Abeta1-40 >> mouse/rat Abeta1-40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H(2)O(2) in cell-free assays and to exhibit amyloid pathology. The copper complex of Abeta1-42 has a highly positive formal reduction potential ( approximately +500-550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Abeta-mediated oxidative damage in Alzheimer's disease. DA - 1999/12/24/ PY - 1999/12/24/ DO - 10.1074/jbc.274.52.37111 VL - 274 IS - 52 SP - 37111-37116 SN - 0021-9258 ER - TY - JOUR TI - Comparison of the core size distribution in iron dextran complexes using Mossbauer spectroscopy and X-ray diffraction AU - Knight, B AU - Bowen, LH AU - Bereman, RD AU - Huang, SY AU - De Grave, E T2 - JOURNAL OF INORGANIC BIOCHEMISTRY AB - Mössbauer spectra of a series of iron dextran complexes in the intermediate temperature range where both sextet and doublet coexist may be used to obtain a qualitative description of the distribution of core sizes in these samples. Eight samples from five suppliers have been examined at 100 and 77 K. These differ markedly in the relative doublet contribution to the total spectral area and also in the hyperfine fields characterizing the sextets. The results indicate three distinct types of distribution. One sample from each type has also been examined at 4 K, where the doublet component has vanished and the hyperfine field distribution has become narrow and symmetric. These data are compared with estimates of average core diameters from X-ray line broadening. DA - 1999/4/15/ PY - 1999/4/15/ DO - 10.1016/S0162-0134(99)00020-3 VL - 73 IS - 4 SP - 227-233 SN - 0162-0134 KW - Mossbauer spectroscopy KW - iron dextran KW - akaganeite KW - core size KW - nanophase KW - hyperfine-field distribution KW - line broadening ER - TY - JOUR TI - Characterization of the RuS2(100) surface by scanning tunneling microscopy, atomic force microscopy, and near-edge X-ray absorption fine structure measurements and electronic band structure calculations AU - Kelty, SP AU - Li, J AU - Chen, JG AU - Chianelli, RR AU - Ren, J AU - Whangbo, MH T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The (100) surface of single-crystal RuS2 was characterized using atomic force microscopy (AFM), scanning tunneling microscopy (STM), near-ddge X-ray absorption fine structure (NEXAFS), and electronic band structure calculations. High-resolution STM and AFM images show that the as-cleaved RuS2(100) surface has a square lattice with the same cell parameters as does bulk RuS2, but the unit cell features are distinctly differently from those expected for the unreconstructed surface. Tunneling spectra reveal that significant surface states are present within the band gap of bulk RuS2. Comparison of the electron and fluorescence yield NEXAFS analysis of the RuS2(100) surface indicates that the surface Ru atoms are bonded only to S atoms and exist in a bulklike valence state. Some of the surface S atoms are passivated with bound oxygen atoms. On the basis of electronic band structure calculations, we propose a model for the reconstructed RuS2(100) surface consistent with the experimental observations. DA - 1999/6/3/ PY - 1999/6/3/ DO - 10.1021/jp9842594 VL - 103 IS - 22 SP - 4649-4655 SN - 1089-5647 ER - TY - JOUR TI - C-13 NMR study on helix inversion barrier in polyguanidines AU - Lim, AR AU - Novak, BM T2 - SOLID STATE COMMUNICATIONS AB - The activation energy of the main-chain carbons for copolymerization of both enantiomers in polyguanidines has been studied using measurements of 13C T1ρ relaxation times. The activation energies of main-chain carbons depend on the ratios for copolymerization of both enantiomers. The activation energies of the carbons in three polyguanidines are distinctly different from those in pure [R] and [S] polyguanidines previously reported. It is worth noting that the carbon of 24.6% EE has a larger activation energy than 48.8 and 81.7%EE polymers. This large activation energy means that the backbone mobility is hindered; we think that this prevents a smooth precession of the chain around the helix axis. DA - 1999/// PY - 1999/// DO - 10.1016/s0038-1098(99)00324-5 VL - 112 IS - 8 SP - 459-464 SN - 0038-1098 KW - insulators KW - polymers KW - chemical synthesis KW - nuclear resonances, elastomers, and plastics ER - TY - JOUR TI - Asymmetric synthesis of dienomycin C AU - Comins, DL AU - Green, GM T2 - TETRAHEDRON LETTERS AB - The first asymmetric synthesis of dienomycin C was accomplished in seven steps and 46% overall yield. DA - 1999/1/8/ PY - 1999/1/8/ DO - 10.1016/S0040-4039(98)02273-4 VL - 40 IS - 2 SP - 217-218 SN - 0040-4039 ER - TY - JOUR TI - Assembly of phenylacetylene-bridged gold nanocluster dimers and trimers AU - Brousseau, LC AU - Novak, JP AU - Marinakos, SM AU - Feldheim, DL T2 - ADVANCED MATERIALS AB - 2- and 3-Dimensional crystalline arrangements of metal nanoparticles are of interest because of their unique optical and electronic behavior. Discrete assemblies of nanoclusters (e.g. dimers, trimers) studied in this paper allow the effects of local symmetry on collective particle properties to be studied. The distance and the medium between clusters is known to influence the optical absorption and electron transport. The use of phenylacetylene oligomers as ‘molecular wire’ linkers between the nanoparticles is demonstrated to allow well-defined, rigid arrays with a variety of geometries to be produced. DA - 1999/4/16/ PY - 1999/4/16/ DO - 10.1002/(SICI)1521-4095(199904)11:6<447::AID-ADMA447>3.0.CO;2-I VL - 11 IS - 6 SP - 447-+ SN - 0935-9648 ER - TY - JOUR TI - Analysis of bonding and d-electron count in the transition-metal carbides and transition-metal-silicide carbides with discrete linear M-C-M units (M = Cr, Fe, Re) by electronic structure calculations AU - Koo, HJ AU - Whangbo, MH T2 - INORGANIC CHEMISTRY AB - Electronic structures of the silicide carbides Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and ThFe(2)SiC and the carbide Ho(2)Cr(2)C(3) were calculated, using the extended Hückel tight binding method, to probe the d-electron counts of their transition metal atoms M (Cr, Fe, Re) the bonding of their linear M-C-M (M = Cr, Fe, Re) units. The nature of the short interlayer X.X (X = C, Si) bonds in Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and Ho(2)Cr(2)C(3) was also examined. Our study shows that the M-C bonds of the M-C-M units exist as double bonds. There is significant bonding in the interlayer Si.Si contacts of the silicide carbides R(2)M(2)Si(2)C (M = Fe, Re). The transition-metal atoms exist as d(10) ions in Tm(2)Fe(2)Si(2)C and Th(2)Re(2)Si(2)C. The d-electron count is slightly lower than d(10) in ThFe(2)SiC and close to d(5) in Ho(2)Cr(2)C(3). DA - 1999/5/3/ PY - 1999/5/3/ DO - 10.1021/ic981309a VL - 38 IS - 9 SP - 2204-2210 SN - 0020-1669 ER - TY - JOUR TI - A redox-sensitive resin linker for the solid phase synthesis of C-terminal modified peptides AU - Zheng, A AU - Shan, D AU - Wang, B T2 - JOURNAL OF ORGANIC CHEMISTRY AB - With the rapid development of combinatorial chemistry using solid phase synthesis, there is a great deal of interest in developing new solid phase linkers, which are stable during the solid phase synthesis process and yet readily cleavable under mild conditions. By taking advantage of a "trimethyl lock"-facilitated lactonization reaction, we have developed a redox-sensitive resin linker for the synthesis of C-terminal-modified peptides. The cleavage only requires mild reducing agents such as sodium hydrosulfite, which is not expected to cause any problem with the commonly seen organic functional groups. Using this new linker, three short peptides were synthesized with high isolated yields (70-90%). Such a linker could potentially be used for the synthesis of modified peptide libraries, which allows for the ready cleavage of the linker under mild conditions. DA - 1999/1/8/ PY - 1999/1/8/ DO - 10.1021/jo981528d VL - 64 IS - 1 SP - 156-161 SN - 0022-3263 ER - TY - JOUR TI - Structure-property relationships in trimethylenemethane-type biradicals. 2. Synthesis and EPR spectral characterization of dinitroxide biradicals AU - Shultz, DA AU - Boal, AK AU - Lee, H AU - Farmer, GT T2 - JOURNAL OF ORGANIC CHEMISTRY AB - Several trimethylenemethane-type (TMM-type) dinitroxide biradicals have been prepared that differ in tert-butylaminoxylphenyl ring torsion angles by virtue of different steric demands of their “spin-protecting groups”. In addition, the synthesis of a TMM-type dinitroxide having a planar π-system is reported. The synthetic route employed for the planar TMM-type biradical is general and should therefore expand the utility of TMM-type biradicals that are susceptible to bond torsions that attenuate exchange coupling. The compounds presented are designed to be effective to map out J-coupling/conformation space in TMM-type biradicals. EPR spectroscopic parameters (hfcc and D-values) were compared to determine if their values reflected differences in conformation in the series of biradicals. Interestingly, neither N- nor H-hfcc varied within our series of biradicals/monoradicals in a regular fashion, indicating that there is no apparent relationship between N- or H-hfcc and conformation (as judged by molecular mechanics calculations). However, D-values, estimated from relative intensities of Δms = 1 and Δms = 2 transitions, are consistent with a varied degree of delocalization in the dinitroxides: smaller D-values for biradicals having smaller aryl torsions (and greater delocalization), and larger D-values for dinitroxides having greater aryl torsions (and less delocalization). All the biradicals studied, except 5••, exhibited linear Curie plots. The linear Curie plots are consistent with both triplet ground-states and singlet−triplet degeneracies. Interestingly, dinitroxide 6•• exhibited a linear Curie plot, despite the lack of a π-coupling fragment. Biradical 5••, however, is a ground-state singlet species with the triplet lying about 140 cal/mol above the singlet. DA - 1999/6/11/ PY - 1999/6/11/ DO - 10.1021/jo990061j VL - 64 IS - 12 SP - 4386-4396 SN - 0022-3263 ER - TY - JOUR TI - Solid state NMR of SiO2 nanotube coated ammonium tartrate crystal AU - Lim, AR AU - Schueneman, GT AU - Novak, BM T2 - SOLID STATE COMMUNICATIONS AB - Ammonium tartrate crystal and SiO2 nanotube coated ammonium tartrate crystal were studied by 13C CP/MAS NMR, and the structure of two samples were verified using the 13C NMR spectrum. The spin–lattice relaxation times for the carbons in the rotating frame, T1ρ, have been measured as a function of temperature. All relaxation times of the carbons in the two materials undergo slow motions, i.e. motions on the slow side of the T1ρ minimum. From these relaxation times, we determine the activation energy for the ammonium tartrate crystal and SiO2 nanotube coated ammonium tartrate crystal, respectively. The activation energies for the SiO2 nanotube coated ammonium tartrate crystal were found to be generally higher than those of ammonium tartrate crystal. We think that the higher activation energy for the hydrocarbon in the SiO2 nanotube coated ammonium tartrate crystal is because of the bonding between the oxygen in the SiO2 nanotube and the hydroxyl group of the ammonium tartrate crystal. DA - 1999/// PY - 1999/// DO - 10.1016/S0038-1098(99)00046-0 VL - 110 IS - 6 SP - 333-338 SN - 0038-1098 KW - nanostructures KW - polymers KW - chemical synthesis KW - nuclear resonances ER - TY - JOUR TI - Rigidity of the backbone for poly(bis(4-butoxycarbonylphenyl))carbodiimide and poly(bis(4-butylphenyl))carbodiimide studied by solid state C-13 T-1p measurements AU - Lim, AR AU - Kim, JH AU - Novak, BM T2 - CHEMICAL PHYSICS AB - Abstract The structure and rigidity of the backbone of two polycarbodiimides as a function of the side chains were studied by 13 C CP/MAS NMR. From these results, the structures of the polycarbodiimides were determined, and the 13 C spin–lattice relaxation times in the rotating frame were measured. Based on our findings, we discuss the mobility for the backbone of the two polycarbodiimides with and without ester linkage between the aromatic and aliphatic side chains. The backbone carbon of polycarbodiimide I with ester linkage has a lower activation energy, 18.63 kJ/mol, than the polycarbodiimide II without ester linkage, 23.20 kJ/mol. Also, the activation energies of the aliphatic side chains show gradually increasing values. We think that this increase results from the greater mobility of the alkyl chain toward its free end. DA - 1999/7/15/ PY - 1999/7/15/ DO - 10.1016/S0301-0104(99)00126-3 VL - 246 IS - 1-3 SP - 373-380 SN - 0301-0104 ER - TY - JOUR TI - On the growth of polycrystalline diamond on transition metals by microwave-plasma-assisted chemical vapour deposition AU - Mallika, K AU - Ramamohan, TR AU - Jagannadham, K AU - Komanduri, R T2 - PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES AB - Abstract The role of transition-metal substrates on the deposition of polycrystalline diamond was investigated using a microwave—plasma-assisted chemical vapour deposition process. Diamond deposition was carried out on the transition elements of the first series (3d block) and on the elements belonging to groups VB and VIB. It was found that the chemical nature of the transition metals plays an important role in the formation of diamond. Similarity in morphological features was observed on the diamond films grown on the substrates belonging to the same group. Micro-Raman (μ-Raman) spectroscopy indicated that diamond films on substrates belonging to groups VB and VIB have lower internal stresses than those deposited on group VIII. An attempt was made to relate the trends observed from the μ-Raman spectroscopy to the chemical properties of the transition elements. The mechanism of diamond growth seem to vary across the period. Elements belonging to the first half of the transition series, namely Ti, V. Nb, Ta, Mo and W, form stable carbides. These elements appear to form diamond by a gas—solid-phase reaction, while transition metals, such as Ni and Co appear to nucleate diamond by precipitation from the molten liquid. It may be noted that Ni and Co do not form stable carbides. This tendency appears to be related to the 3d shell structure of these elements. A mechanism based on the electronic structure of the substrate atoms, particularly on their 3d shell structure, is proposed to account for the above behaviour. DA - 1999/4// PY - 1999/4// DO - 10.1080/13642819908205738 VL - 79 IS - 4 SP - 593-624 SN - 0141-8637 ER - TY - JOUR TI - Molecular components of the bulk electronic structure of organic conductors: A soft X-ray absorption and soft X-ray emission spectroscopy approach AU - Stagarescu, CB AU - Duda, LC AU - Smith, KE AU - Seo, DK AU - Whangbo, MH AU - Jerome, D AU - Haddon, RC AU - Brooks, JS AU - Guo, JH AU - Nordgren, J T2 - JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA AB - Abstract The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using soft X-ray absorption (SXA) and soft X-ray emission (SXE) spectroscopy. These techniques are powerful probes of the site and angular-momentum resolved partial density of states (PDOS) for both occupied and unoccupied states. Therefore these spectroscopies are particularly suited for an analysis of the density of states of multi-atomic, complex materials as the ET-based organic conductors, allowing site-specific electronic structure to be measured. We present a preliminary picture of the electronic structure of κ-ET 2 Cu(SCN) 2 and κ-ET 2 Cu[N(CN) 2 ]Br as measured by SXE and SXA performed at the C1s and N1s core levels. DA - 1999/6// PY - 1999/6// DO - 10.1016/S0368-2048(98)00346-6 VL - 101 SP - 539-544 SN - 0368-2048 KW - soft X-ray emission spectroscopy KW - organic conductors KW - density of states ER - TY - JOUR TI - Grafted polymer tail loop mixtures differing in chain length AU - Driscoll, DC AU - Gulati, HS AU - Spontak, RJ AU - Hall, CK T2 - POLYMER AB - Abstract Studies examining the structure of monolayers formed by polymer chains grafted to a surface typically focus on chains attached at one end (tails). Bond fluctuation simulations are performed here to probe monolayers composed of equimolar mixtures of tails and double-grafted loops in which the looped chain length (Nloop) is varied at constant surface density and tail length (Ntail). Loops force the tails to adopt an extended trajectory normal to the surface, resulting in monolayer stratification. As Nloop increases, the height of the tail sublayer increases to a maximum, and then decreases to converge with the loop sublayer as Nloop→2Ntail. These results are compared to predictions from a self-consistent field theory for bidisperse mixtures of grafted tails. DA - 1999/8// PY - 1999/8// DO - 10.1016/S0032-3861(98)00804-0 VL - 40 IS - 18 SP - 5207-5211 SN - 1873-2291 KW - grafted polymer chains KW - brushes KW - polymer thin films ER - TY - JOUR TI - Characterization of chemical selectivity in micellar electrokinetic chromatography. 4. Effect of surfactant headgroup AU - Trone, MD AU - Khaledi, MG T2 - ANALYTICAL CHEMISTRY AB - The influence of surfactant headgroups on migration behavior in micellar electrokinetic chromatography is examined. Using linear solvation energy relationships (LSER) and functional group selectivity studies, the effect of six anionic headgroups on chemical selectivity is characterized. The sodium dodecyl surfactants of the sulfate [SO4-], sulfonate [SO3-], carboxylate [CO2-], carbonyl valine [OC(O)NHCH(CH(CH3)2)CO2-], and sulfoacetate [OC(O)CH2SO3-] anions are investigated. Solute size and the hydrogen-bond-donating ability of the micellar phase play the most significant roles in solute retention in all of the surfactants studied. While solute-micelle hydrogen bonding plays a dominant role in the observed selectivity, the dipolarity and polarizability of the micellar phase also have a small influence. The results also suggest that the hydrogen-bond-accepting ability for surfactants is inversely proportional to the proton acidity (pKa) of its headgroup. The observed hydrogen-bond-donating ability and dipolarity of surfactant systems are believed to be a result of the water that resides near the micelle surface. DA - 1999/4/1/ PY - 1999/4/1/ DO - 10.1021/ac9809736 VL - 71 IS - 7 SP - 1270-1277 SN - 1520-6882 ER - TY - JOUR TI - CaCl2 and MgCl2 as buffering agents for room-temperature chloroaluminate ionic liquids AU - Koronaios, P AU - Osteryoung, RA T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - We have found that it is possible to buffer acidic 1‐ethyl‐3‐methylimidazolium chloride melts to neutrality using as a buffering agent, while will partially buffer acidic melts. The buffering reaction is DA - 1999/8// PY - 1999/8// DO - 10.1149/1.1392041 VL - 146 IS - 8 SP - 2995-2999 SN - 1945-7111 ER - TY - JOUR TI - Acute changes in serum lipids and lipoprotein subclasses in triathletes as assessed by proton nuclear magnetic resonance spectroscopy AU - Yu, HH AU - Ginsburg, GS AU - ML O'Toole, AU - Otvos, JD AU - Douglas, PS AU - Rifai, N T2 - ARTERIOSCLEROSIS THROMBOSIS AND VASCULAR BIOLOGY AB - Exercise is associated with changes in lipids that may protect against coronary heart disease (CHD). In this study of 28 triathletes, we analyzed acute changes in serum lipid and lipoprotein concentrations after completion of the 1995 World Championship Hawaii Ironman Triathlon. With standard laboratory assays, we demonstrate significant decreases in total cholesterol, VLDL cholesterol, ApoB100, and Lp(a). Total HDL cholesterol increased significantly immediately after the race. With a novel proton NMR spectroscopy assay, we demonstrate that smaller diameter LDL particles, corresponding to small, dense LDL, declined by 62%. Moreover, larger HDL subclasses, whose levels are inversely associated with CHD, increased significantly by 11%. Smaller HDL subclasses, which have been directly associated with CHD in some studies, acutely decreased by 16%. Therefore, exercise not only acutely induces changes in lipoprotein concentrations among the standard species in a manner that favorably affects CHD risk, but also induces favorable changes in specific lipoprotein subclass size distribution that also may alter CHD risk independently of the total lipoprotein serum concentration. DA - 1999/8// PY - 1999/8// DO - 10.1161/01.ATV.19.8.1945 VL - 19 IS - 8 SP - 1945-1949 SN - 1524-4636 KW - cholesterol KW - exercise KW - NMR KW - subclass ER - TY - JOUR TI - A convenient trimethylsilylthioxy-dehalogenation reaction for the preparation of functionalized thiols AU - Hu, J AU - Fox, MA T2 - JOURNAL OF ORGANIC CHEMISTRY AB - ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTA Convenient Trimethylsilylthioxy-Dehalogenation Reaction for the Preparation of Functionalized ThiolsJun Hu and Marye Anne FoxView Author Information Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, and Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695 Cite this: J. Org. Chem. 1999, 64, 13, 4959–4961Publication Date (Web):June 2, 1999Publication History Received15 January 1999Published online2 June 1999Published inissue 1 June 1999https://doi.org/10.1021/jo990076hCopyright © 1999 American Chemical SocietyRequest reuse permissions Your access to this publication has been provided by Learn MoreArticle Views2845Altmetric-Citations57LEARN 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 (80 KB) open URLGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Alkyls,Anions,Halogens,Mixtures,Thiols Get e-Alerts DA - 1999/6/25/ PY - 1999/6/25/ DO - 10.1021/jo990076h VL - 64 IS - 13 SP - 4959-4961 SN - 0022-3263 ER - TY - JOUR TI - Periodic table live! 2nd edition AU - Banks, A. J. AU - Holmes, J. L. AU - Jacobsen, J. J. AU - Moore, J. W. AU - Schatz, P. F. AU - Tweedale, J. AU - Kotz, J. C. AU - Young, S. T2 - Journal of Chemical Education DA - 1999/// PY - 1999/// VL - 76 IS - 3 SP - 447-448 ER - TY - JOUR TI - Paramagnetic zinc(II) complexes of a bis(catechol): Dependence of product spin state on tantomerization of the bis(catechol) ligand AU - Shultz, DA AU - Bodnar, SH T2 - INORGANIC CHEMISTRY AB - We report the preparation and characterization of zinc(II) hydrotris(3-cumenyl-5-methylpyrazolyl)borate (LZn) complexes, (LZn)(2)()1'-H and (LZn)(2)()1, of a bis(catechol) ligand. The formation of (LZn)(2)()1'-H, an S = (1)/(2) complex, rather than (LZn)(2)()1, an S = 1 complex, is observed due to tautomerization of a reaction intermediate. The biradical complex, (LZn)(2)()1, can be prepared from (LZn)(2)()1'-H by oxidation, a conversion that is accompanied by a blue-green to red-purple color change and an increase in spin from (1)/(2) to 1. The frozen solution EPR spectrum of the biradical complex (LZn)(2)()1 exhibits zero-field splitting and a Deltam(s)() = 2 transition characteristic of a triplet state. The temperature dependence of the EPR signal intensity is consistent with high-spin coupling of the unpaired electrons of the ligand. DA - 1999/2/8/ PY - 1999/2/8/ DO - 10.1021/ic981092k VL - 38 IS - 3 SP - 591-594 SN - 1520-510X ER - TY - JOUR TI - Investigation of conditions giving minimal scrambling in the synthesis of trans-porphyrins from dipyrromethanes and aldehydes AU - Littler, BJ AU - Ciringh, Y AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - A diverse range of reaction conditions for the MacDonald-type 2 + 2 condensation of a 5-substituted dipyrromethane and an aldehyde has been studied with the goal of eliminating acid-catalyzed polypyrrolic rearrangement reactions in the synthesis of trans-porphyrins. A rapid screening method based on laser desorption mass spectrometry has enabled the degree of rearrangement to be examined as a function of the acid catalyst, reagent concentration, reagent stoichiometry, solvent, salts, and temperature. For condensations involving 5-mesityldipyrromethane, we identified reaction at 10 mM concentration in CH(2)Cl(2) with 17.8 mM TFA as optimal conditions for suppression of the rearrangement reaction. A synthetic procedure based on these conditions allowed the expedient synthesis of multigram batches of eight trans-porphyrins in 48-14% yield from 5-mesityldipyrromethane, with minimal chromatography. The same conditions were also effective for the synthesis of two trans-porphyrins derived from 5-(2,6-dichlorophenyl)dipyrromethane. Application of the same conditions to condensations involving 5-phenyldipyrromethane showed extensive rearrangement. Examination of a wide range of conditions showed that slow reactions are associated with less rearrangement. Two sets of conditions were identified that gave little or no scrambling: (1) condensation at 10 mM in MeCN at 0 degrees C with BF(3).Et(2)O catalysis in the presence of NH(4)Cl followed by DDQ oxidation and (2) condensation at 0.1 M in DMSO at 100 degrees C in the presence of NH(4)Cl (with no added acid catalyst) with air oxidation. Although yields are typically less than 10%, the elimination of the need to perform tedious chromatography improves the methodology available for the preparation of trans-porphyrins, derived from sterically unhindered dipyrromethanes. DA - 1999/4/16/ PY - 1999/4/16/ DO - 10.1021/jo982452o VL - 64 IS - 8 SP - 2864-2872 SN - 0022-3263 ER - TY - JOUR TI - Fused ring aromatic solvency in destabilizing water-in-asphaltene-heptane-toluene emulsions AU - Singh, S AU - McLean, JD AU - Kilpatrick, PK T2 - JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY AB - Abstract The role of asphaltenes in stabilizing water-in-crude oil emulsions is extremely well established. The mechanism appears to be one in which planar, disk-like asphaltene molecules aggregate through lateral intermolecular forces to form primary aggregates or micelles which are interfacially active. These aggregates — upon adsorbing at the oil-water interface — crosslink through physical interactions to form a viscoelastic network, which has been characterized by some as a “skin” or a “plastic film”. The strength of this film, as gauged by shear and elastic moduli, seems to correlate well with water-in-oil emulsion stability. What is still relatively unknown is the role of chemistry in governing the strength of these lateral inter-asphaltene interactions. The candidate interactions include π-bonding between the delocalized electrons in the fused aromatic ring core, H-bonding between proton donors and acceptors imbedded in the asphaltenic cores, and metal-electron interactions between, for example, heavy metal ions such as vanadium or nickel and electron pairs in pyrrolic or porphyrin functional groups. We have probed these interactions indirectly by studying the destabilization of water-in-oil emulsions by a variety of aromatic solvents. In this paper, we review our previous results on both water-in-crude oil systems, as well as water-in-model oil (heptane-toluene-asphaltene mixtures) systems, in which the emulsions were progressively destabilized by addition of aromatic solvents. We also present new results with fused ring aromatic solvents, specifically methyl-naphthalene, phenanthrene, and phenanthridine. Our results suggest that fused ring aromatic solvents are considerably more effective at destabilizing asphaltene emulsions and proton-accepting fused ring aromatic solvents are most effective. These results indicate that both π-bonding and H-bonding play significant roles in mediating the aggregation of asphaltenes in oil-water interfacial films. DA - 1999/// PY - 1999/// DO - 10.1080/01932699908943792 VL - 20 IS - 1-2 SP - 279-293 SN - 1532-2351 ER - TY - JOUR TI - Combinatorial peptide on-resin analysis: optimization of static nanoelectrospray ionization technique for sequence determination AU - Biederman, KJ AU - Lee, H AU - Haney, CA AU - Kaczmarek, M AU - Buettner, JA T2 - JOURNAL OF PEPTIDE RESEARCH AB - The optimizations of static nanoelectrospray parameters to determine peptide or mimetic sequences released from resin were explored. Several different manufacturers of probe tips were utilized and a method was developed for the direct analysis of bead‐bound peptides by nanoelectrospray. The method involved minimum sample handling to assure maximum recovery from individual beads. Parameters that were explored included an inside and outside wash of the probe tip, the distance from the probe housing to the probe tip, source temperature, drying gas flow, individual tips and presence of beads. The same soluble synthetic peptide was used in all comparisons, which had a molecular weight of 717 amu. The discovery of the sequence of a bead‐bound peptide was achieved. The parameters that were found to effect signal were outside wash, presence of bead and distance. There was the need for pneumatic assist to initiate electrospray on some occasions, although this generally resulted in unsatisfactory performance. DA - 1999/3// PY - 1999/3// DO - 10.1034/j.1399-3011.1999.00047.x VL - 53 IS - 3 SP - 234-243 SN - 1397-002X KW - bead-bound peptide KW - electrospray mass spectrometry KW - nanoflow electrospray KW - peptide combinatorial library ER - TY - JOUR TI - Capillary electrophoresis chiral separation of basic pharmaceutical enantiomers with different charges using sulfated beta-cyclodextrin AU - Wang, F AU - Khaledi, MG T2 - JOURNAL OF MICROCOLUMN SEPARATIONS AB - Journal of Microcolumn SeparationsVolume 11, Issue 1 p. 11-21 Research Article Capillary electrophoresis chiral separation of basic pharmaceutical enantiomers with different charges using sulfated β-cyclodextrin Fang Wang, Fang Wang Department of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USASearch for more papers by this authorMorteza G. Khaledi, Corresponding Author Morteza G. Khaledi Department of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USADepartment of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USASearch for more papers by this author Fang Wang, Fang Wang Department of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USASearch for more papers by this authorMorteza G. Khaledi, Corresponding Author Morteza G. Khaledi Department of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USADepartment of Chemistry, Box 8204, North Carolina State University, Raleigh, NC 27695-8204, USASearch for more papers by this author First published: 07 January 1999 https://doi.org/10.1002/(SICI)1520-667X(1999)11:1<11::AID-MCS2>3.0.CO;2-PCitations: 28AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract A negatively charged cyclodextrin, sulfated β-cyclodextrin [β-CD-(SO4−)4], was used as a chiral selector for capillary electrophoresis separations of basic pharmaceutical enantiomers. The charges of the basic enantiomers were controlled by adjusting the buffer pH. At pH 2.5, basic compounds are positively charged and interact stronger with the negatively charged CD than with neutral CDs, owing to the extra electrostatic interaction. This additional interaction is very useful for chiral separations of the enantiomers that interact weakly with the neutral CDs. For example, chiral separations of acebutolol, metanephrine, normetanephrine, nafronyl, labetalol, and nadolol were achieved at this pH. For labetalol and nadolol that have two chiral centers, three of the four isomers were separated. The capillary surface was dynamically coated with poly(vinyl alcohol) (PVA) to reduce the possible interactions between solutes and the capillary wall, to improve efficiency and reduce the electroosmotic flow (EOF) for enhancing resolution. PVA reduced the interactions between the analytes and the chiral selector; nevertheless, peak tailing was observed owing to the electrodispersion for the compounds that interact too strongly with the anionic CD. At pH 11.6, most of the basic test compounds (except those having phenol groups) are neutral and have weaker interactions with the negatively charged CD. The separation efficiency increased dramatically for all analytes at higher pH owing to the absence of electrodispersion. The existence of the neutral PVA polymer in the buffer solution increased the solubility of the neutral hydrophobic amines and reduced the solute–CD complexation. Chiral separations of a large number of compounds were achieved at a single concentration of the charged cyclodextrin. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 11–21, 1999 Citing Literature Volume11, Issue11999Pages 11-21 RelatedInformation DA - 1999/// PY - 1999/// DO - 10.1002/(SICI)1520-667X(1999)11:1<11::AID-MCS2>3.0.CO;2-P VL - 11 IS - 1 SP - 11-21 SN - 1040-7685 KW - capillary electrophoresis KW - chiral separations KW - charged cyclodextrin KW - basic pharmaceutical enantiomers ER - TY - PCOMM TI - Asymmetric synthesis of the Lycopodium alkaloid, N-a-acetyl-N-b-methylphlegmarine AU - Comins, DL AU - Libby, AH AU - Al-awar, RS AU - Foti, CJ AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTAsymmetric Synthesis of the Lycopodium Alkaloid, Na-Acetyl-Nb-methylphlegmarineDaniel L. Comins, Adam H. Libby, Rima S. Al-awar, and Christopher J. FotiView Author Information Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204 Cite this: J. Org. Chem. 1999, 64, 7, 2184–2185Publication Date (Web):March 6, 1999Publication History Received2 February 1999Published online6 March 1999Published inissue 1 April 1999https://doi.org/10.1021/jo990192kCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1204Altmetric-Citations59LEARN 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 Read OnlinePDF (151 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Enantioselective synthesis,Hydrocarbons,Organic compounds,Redox reactions,Stereochemistry Get e-Alerts DA - 1999/4/2/ PY - 1999/4/2/ DO - 10.1021/jo990192k SP - 2184-2185 ER - TY - JOUR TI - The T-l rho C-13 spin-lattice relaxation time of interpenetrating networks by solid state NMR AU - Lim, AR AU - Schueneman, GT AU - Novak, BM T2 - SOLID STATE COMMUNICATIONS AB - Poly (2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate) interpenetrated with 5% SiO2 (PHEMA-IPN) were studied by 13C CP/MAS NMR. From these results, the structure of two polymers were verified by 13C NMR. Spin-lattice relaxation times for the polymer carbons in the rotating frame, T1ρ, have been measured as a function of temperature. The T1ρ spin-lattice relaxation times of the α-quarternary and carbonyl in the PHEMA and PHEMA-IPN undergo slow motions, i.e., motions on the slow side of the T1ρ minimum, while those of the 1-,2-, β-methylene, and 3-methyl undergo fast motions, i.e., motions on the fast side of the T1ρ minimum. From these T1ρ spin-lattice relaxation times, we discuss the mobility, the correlation time, and activation energy for the PHEMA and PHEMA-IPN, respectively. The activation energies for the PHEMA-IPN were found to be generally higher than those of PHEMA. The higher activation energy for the side-chain 2-methylene in the PHEMA-IPN is attributed to bonding between the SiO2 and the hydroxyl group of the PHEMA. DA - 1999/// PY - 1999/// DO - 10.1016/S0038-1098(98)00576-6 VL - 109 IS - 7 SP - 465-470 SN - 0038-1098 KW - polymers KW - nanostructures KW - nano fabrications KW - chemical synthesis KW - nuclear resonance ER - TY - JOUR TI - Separation and characterization of peanut phospholipid molecular species using high-performance liquid chromatography and fast atom bombardment mass spectrometry AU - Singleton, JA AU - Ruan, M AU - Sanford, JH AU - Haney, CA AU - Stikeleather, LF T2 - JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY AB - Abstract Total lipid extracts from peanut seed were separated on a silica column into a triacylglycerol fraction and a polar lipid fraction by high‐performance liquid chromatography (HPLC). The polar fraction containing the phospholipids was retained on the precolumn, and the triacylglycerol fraction was eluted to a waste flask by a special valve arrangement. Phospholipids were eluted from the precolumn and separated into various classes on a silica analytical column. Each phospholipid class was manually collected and subsequently subjected to reversed‐phase HPLC in tandem with a fast atom bombardment mass spectrometer. Phosphatidylethanolamine was separated into five molecular species. Phosphatidylinositol and phosphatidylcholine were each separated into six molecular species. DA - 1999/1// PY - 1999/1// DO - 10.1007/s11746-999-0046-y VL - 76 IS - 1 SP - 49-56 SN - 0003-021X KW - fast atom bombardment mass spectrometry KW - HPLC KW - lipids KW - molecular species KW - peanuts KW - phospholipids KW - reversed-phase HPLC ER - TY - JOUR TI - Mechanical properties of nanotubule fibers and composites determined from theoretical calculations and simulations (vol 36, pg 1, 1998) AU - Sinnott, S. B. AU - Shenderova, O. A. AU - White, C. T. AU - Brenner, D. W. T2 - Carbon DA - 1999/// PY - 1999/// VL - 37 IS - 2 SP - 347 ER - TY - JOUR TI - Investigation of cocatalysis conditions using an automated microscale multireactor workstation: Synthesis of meso-tetramesitylporphypin AU - Wagner, RW AU - Li, FR AU - Du, H AU - Lindsey, JS T2 - ORGANIC PROCESS RESEARCH & DEVELOPMENT AB - Prior manual work has shown that the condensation of mesitaldehyde and pyrrole leading to tetramesitylporphyrin depends sensitively on concentration and requires cocatalysis involving BF3·O(Et)2 and ethanol or other protic species. We have applied an automated microscale chemistry workstation capable of parallel or adaptive experimentation to systematically investigate these cocatalysis conditions. Examination of experimental grids spanning a 1000-fold range of the concentrations of BF3·O(Et)2 and ethanol identified the best cocatalysis conditions for various mesitaldehyde and pyrrole concentrations. As the reaction concentration increased from 10 to 200 mM, the optimal yields were achieved with a parallel increase in BF3·O(Et)2 concentration (from 3.3 to 56 mM), but the amount of ethanol remained relatively constant. Catalysis conditions were identified that afforded ∼30% yields for reactants in the range of 10−73 mM, thereby enabling the reaction to be performed at increased concentration without loss in yield. Application of a catalyst searching protocol identified ethylene glycol, 2-methoxyethanol, and methanol as effective cocatalysts from a set of 12 candidates. Collectively, these results show the utility of an automated chemistry workstation in acquiring a comprehensive set of data concerning the scope of cocatalysis in the reaction of mesitaldehyde and pyrrole. DA - 1999/// PY - 1999/// DO - 10.1021/op9800459 VL - 3 IS - 1 SP - 28-37 SN - 1083-6160 ER - TY - JOUR TI - Electron counting scheme relevant for late transition metal compounds with weakly electronegative ligands. Electronic band structure study of phosphosilicides PtSi3P2 and NiSi2P3 AU - Lee, KS AU - Koo, HJ AU - Dai, D AU - Ren, J AU - Whangbo, MH T2 - INORGANIC CHEMISTRY AB - The conventional electron counting scheme often leads to erroneous predictions for late transition metal compounds with weakly electronegative main group ligand atoms. The cause for this deficiency was analyzed, and a modified electron counting scheme was proposed for predicting the frontier orbitals of such compounds. The modified scheme predicts that the transition metal atoms of such compounds have a d10 electron count, and their frontier orbitals are represented by the highest-lying lone pair levels of the main group ligand atoms. These predictions were tested by carrying out electronic band structure calculations for phosphosilicides PtSi3P2 and NiSi2P3. The relevance of nonstoichiometric compositions of these phases was also discussed. DA - 1999/1/25/ PY - 1999/1/25/ DO - 10.1021/ic980761r VL - 38 IS - 2 SP - 340-345 SN - 0020-1669 ER - TY - JOUR TI - Substituted coumarins as esterase-sensitive prodrug moieties with improved release rates AU - Liao, Y. AU - Wang, B. H. T2 - Bioorganic & Medicinal Chemistry Letters DA - 1999/// PY - 1999/// VL - 9 IS - 13 SP - 1795-1800 ER - TY - JOUR TI - Refined synthesis of 5-substituted dipyrromethanes AU - Littler, BJ AU - Miller, MA AU - Hung, CH AU - Wagner, RW AU - DF O'Shea, AU - Boyle, PD AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTRefined Synthesis of 5-Substituted DipyrromethanesBenjamin J. Littler, Mark A. Miller, Chen-Hsiung Hung, Richard W. Wagner, Donal F. O'Shea, Paul D. Boyle, and Jonathan S. LindseyView Author Information Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204 Cite this: J. Org. Chem. 1999, 64, 4, 1391–1396Publication Date (Web):January 27, 1999Publication History Received6 October 1998Published online27 January 1999Published inissue 1 February 1999https://doi.org/10.1021/jo982015+Copyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views14111Altmetric-Citations364LEARN 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 Read OnlinePDF (85 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Chromatography,Condensation,Distillation,Purification,Pyrroles Get e-Alerts DA - 1999/2/19/ PY - 1999/2/19/ DO - 10.1021/jo982015+ VL - 64 IS - 4 SP - 1391-1396 SN - 0022-3263 ER - TY - JOUR TI - Prodrug approaches to the improved delivery of peptide drugs AU - Wang, W. AU - Jiang, J. AU - Ballard, C. E. AU - Wang, B. T2 - Current Pharmaceutical Design DA - 1999/// PY - 1999/// VL - 5 IS - 4 SP - 265-287 ER - TY - JOUR TI - Lack of polymerization of fluorinated acrylates AU - McElroy, K. T. AU - Purrington, S. T. AU - Bumgardner, C. L. AU - Burgess, J. P. T2 - Journal of Fluorine Chemistry AB - trans-Ethyl 3-fluoroacrylate and ethyl 2-methyl-3,3-difluoroacrylate do not undergo radical initiated polymerization. They form 1:1 adducts with α-alkoxy radicals in high yield. DA - 1999/// PY - 1999/// DO - 10.1016/S0022-1139(99)00019-6 VL - 95 IS - 1-2 SP - 117-120 ER - TY - JOUR TI - Investigation of MALDI-TOF mass spectrometry of diverse synthetic metalloporphyrins, phthalocyanines and multiporphyrin arrays AU - Srinivasan, N AU - Haney, CA AU - Lindsey, JS AU - Zhang, WZ AU - Chait, BT T2 - JOURNAL OF PORPHYRINS AND PHTHALOCYANINES AB - We investigated the utility of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for analyzing porphyrinic compounds using a variety of different synthetic porphyrins, azaporphyrins, phthalocyanines and multiporphyrin arrays. Comparisons of spectra obtained from these analytes deposited either as neat samples or codeposited with neutral or acidic matrices have been made with the goal of identifying conditions that yield minimal demetalation, transmetalation, adduct formation and fragmentation. It was found that the molecular masses of many porphyrins can be successfully measured from neat sample preparations and do not require a matrix to facilitate desorption and ionization, although the measurement of large multiporphyrin arrays was facilitated by the use of matrices. Demetalation of magnesium porphyrins occurred in the presence of acidic matrices, but not with neutral matrices such as 1,4-benzoquinone. Positive ion spectra were obtained for each compound and negative ion spectra were also collected for the azaporphyrins and phthalocyanines. Examination of selected samples (prepared neat, with 1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone or α-cyano-4-hydroxycinnamic acid) showed that the dominant process of ionization involved oxidation yielding the radical cation M +· rather than the protonated molecule [M+H] + . MALDI-TOF-MS is shown to be a powerful analytical tool for the characterization of diverse synthetic porphyrinic compounds. DA - 1999/4// PY - 1999/4// DO - 10.1002/(SICI)1099-1409(199904)3:4<283::AID-JPP132>3.0.CO;2-F VL - 3 IS - 4 SP - 283-291 SN - 1088-4246 KW - mass spectrometry KW - LDI KW - MALDI KW - radical cations KW - metalloporphyrins KW - porphyrin arrays KW - phthalocyanines ER - TY - JOUR TI - Ground and excited state electronic properties of halogenated tetraarylporphyrins. Tuning the building blocks for porphyrin- based photonic devices AU - Yang, S. I. AU - Seth, J. AU - Strachan, J. P. AU - Gentemann, S. AU - Kim, D. AU - Holten, D. AU - Lindsey, Jonathan AU - Bocian, D. F. T2 - Journal of Porphyrins and Phthalocyanines AB - The rational design of molecular photonic devices relies on the ability to select components with predictable electronic structure, excited state lifetimes and redox chemistry. Electronic communication in multiporphyrin arrays depends critically on the relative energies and electron density distributions of the frontier molecular orbitals, especially the energetically close highest occupied molecular orbitals (a 2u and a 1u ). To explore how these ground and excited state properties can be modulated, we have synthesized and characterized 40 free base ( Fb ), magnesium and zinc tetraarylporphyrins. The porphyrins bear meso-substituents with the following substitution patterns: (1) four identical substituents (phenyl, o-chlorophenyl, p-chlorophenyl, o,o'-difluorophenyl, pentafluorophenyl, mesityl); (2) one, two, three or four o,o'-dichlorophenyl substituents; (3) one p-ethynylphenyl group and three mesityl or pentafluorophenyl groups; (4) one p-ethynyl-o,o″-dichlorophenyl or p-ethynyl-o,o″-dimethylphenyl and three phenyl groups. For each neutral complex the ground state electronic properties were investigated using electrochemical methods and optical absorption spectroscopy. Similarly the absorption, emission, and relaxation properties of the lowest singlet excited state were probed by time-resolved absorption and fluorescence methods. Each oxidized complex was investigated by static absorption and liquid and frozen solution EPR spectroscopy. The collective results of these investigations have provided insights into the direct (orbital overlap) and indirect (inductive/conjugative) mechanisms by which halogenated phenyl rings influence the static and dynamic electronic properties of neutral and oxidized porphyrinic chromophores. Three key findings are as follows. (1) The effective electron-withdrawing strength of halogenated phenyl rings required to reverse the ordering of the a 2u and a 1u HOMOs in Mg versus Zn tetraarylporphyrins has been elucidated. (2) Appropriate halogenation can significantly increase the excited state lifetime of a Zn porphyrin relative to the unsubstituted complex. (3) Halogenation can be used to modulate redox potentials in a manner that complements the enhancement of other electronic properties. The insights gained from study of this library of porphyrins provide a foundation for tuning the electronic properties of monomeric porphyrins as building blocks for multichromophoric assemblies in optoelectronics and other applications. DA - 1999/// PY - 1999/// DO - 10.1002/(SICI)1099-1409(199902)3:2<117::AID-JPP110>3.0.CO;2-X VL - 3 IS - 2 SP - 117–147 ER - TY - JOUR TI - Friedel-Crafts reactions of fluorinated allylic compounds AU - Gyenes, F AU - Purrington, ST AU - Liu, YS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTFriedel−Crafts Reactions of Fluorinated Allylic CompoundsFerenc Gyenes, Suzanne T. Purrington, and Yan-Song LiuView Author Information Department of Chemistry, North Carolina State University Raleigh, North Carolina 27695-8204 Cite this: J. Org. Chem. 1999, 64, 4, 1366–1368Publication Date (Web):January 16, 1999Publication History Received17 August 1998Published online16 January 1999Published inissue 1 February 1999https://doi.org/10.1021/jo981670eCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views447Altmetric-Citations8LEARN 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 Read OnlinePDF (69 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Anions,Aromatic compounds,Distillation,Fluorine,Substitution reactions Get e-Alerts DA - 1999/2/19/ PY - 1999/2/19/ DO - 10.1021/jo981670e VL - 64 IS - 4 SP - 1366-1368 SN - 0022-3263 ER - TY - JOUR TI - Eutrophication of Lake Wingra: A chemistry-based environmental science module AU - Howe, AC AU - Cizmas, L AU - Bereman, R T2 - JOURNAL OF CHEMICAL EDUCATION AB - The paper describes the development and field test of a curriculum module for introductory chemistry by an interinstitutional, interdisciplinary team representing the disciplines of chemistry, biology, political science, environmental management and computer visualization. The module was designed to show that a serious and common worldwide environmental problem, the eutrophication of freshwater lakes, is directly related to the chemical reactions of phosphates. The module, which includes a student manual, an instructor's manual, and a computer visualization component, is based on a case study of Lake Wingra in Madison, Wisconsin. The module was field tested at two sites, after which 80% of students gave it a high overall rating. Attitude questionnaires administered before and after the unit was taught showed that students increased their interest in environmental problems, increased their understanding of the complexity of the problems, and had a higher level of personal commitment to address environmental problems. With changes in emphasis the module is suitable for use in other courses, including economics, biological science, and environmental science. DA - 1999/7// PY - 1999/7// DO - 10.1021/ed076p924 VL - 76 IS - 7 SP - 924-926 SN - 0021-9584 ER - TY - JOUR TI - Enhanced diastereoselectivity in the asymmetric Ugi reaction using a new "convertible" isonitrile AU - Linderman, RJ AU - Binet, S AU - Petrich, , SR T2 - JOURNAL OF ORGANIC CHEMISTRY AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTADDITION / CORRECTIONThis article has been corrected. View the notice.Enhanced Diastereoselectivity in the Asymmetric Ugi Reaction Using a New “Convertible” IsonitrileRussell J. Linderman, Sophie Binet, and Samantha R. PetrichView Author Information Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204 Cite this: J. Org. Chem. 1999, 64, 2, 336–337Publication Date (Web):December 31, 1998Publication History Received2 November 1998Published online31 December 1998Published inissue 1 January 1999https://doi.org/10.1021/jo982186eCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1787Altmetric-Citations82LEARN 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 Read OnlinePDF (37 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Amides,Peptides and proteins,Reaction products,Stereoselectivity,Ugi reaction Get e-Alerts DA - 1999/1/22/ PY - 1999/1/22/ DO - 10.1021/jo982186e VL - 64 IS - 2 SP - 336-337 SN - 0022-3263 ER - TY - JOUR TI - Liquid catalyst interactions in slurry reactors: methanol synthesis over zinc chromite AU - Roberts, GW AU - Marquez, MA AU - Haney, CA T2 - APPLIED CATALYSIS A-GENERAL AB - The performance of a `zinc chromite' catalyst was studied in a continuous slurry reactor using three different liquids: decahydronaphthalene, tetrahydronaphthalene, and tetrahydroquinoline. The reactor feed was a mixture of hydrogen and carbon monoxide with a H2/CO ratio of either 0.5 or 2. The reactor was operated over a temperature range of 598–698 K and at a total pressure of about 14 MPa. The characteristics of the slurry liquid had a major influence on both the overall reaction rate and the product distribution. The rate of methanol synthesis was much higher when tetrahydroquinoline was used than with the other two liquids. The product distribution was shifted away from oxygenates and towards hydrocarbons when tetrahydronaphthalene was used. The slurry liquid was analyzed by GC/MS (gas chromatography/mass spectrometry) during and after the reaction. There was no evidence of significant cracking or hydrocracking of any of the liquids. However, tetrahydroquinoline was alkylated during the reaction, and tetrahydronaphthalene was dehydrogenated to some extent. Tetrahydroquinoline, and perhaps tetrahydronaphthalene, may have participated in the catalytic cycle. DA - 1999/7/19/ PY - 1999/7/19/ DO - 10.1016/S0926-860X(99)00076-9 VL - 183 IS - 2 SP - 395-410 SN - 0926-860X KW - methanol KW - slurry reactor KW - zinc chromite KW - decahydronaphthalene KW - tetrahydronaphthalene KW - tetrahydroquinoline ER - TY - JOUR TI - Hydrodynamics of gas-lift reactors with a fast, liquid-phase reaction AU - Marquez, MA AU - Amend, RJ AU - Carbonell, RG AU - Saez, AE AU - Roberts, GW T2 - CHEMICAL ENGINEERING SCIENCE AB - The reactive absorption of CO2 into concentrated KOH solutions was studied in an external-loop, gas-lift reactor. Three different inlet gas compositions were used: air, 50–50 vol% air–CO2, and pure CO2. The downcomer liquid velocity and the axial profile of the cross-sectionally averaged gas holdup in the riser were measured. The reaction is so fast that the CO2 is consumed appreciably along the riser, and this causes a significant reduction in the liquid circulation relative to a system with no reaction. A one-dimensional, pseudo-steady-state model has been developed to describe the interactions of hydrodynamics, mass transfer, and chemical reaction for the bubbly flow regime in the riser. The model considers mass transfer from the gas to the liquid phase and its enhancement due to the chemical reaction, and is based on the spatially averaged equations of continuity, momentum, and macroscopic mechanical energy. The rate of liquid circulation, and the axial variation of gas holdup, gas composition, pressure, and gas and liquid velocity, are predicted. The gas/liquid mass transfer coefficient and the bubble radius at the sparger, neither of which was known a priori, were used to minimize the error of the data with respect to the model. DA - 1999/7// PY - 1999/7// DO - 10.1016/S0009-2509(98)00351-0 VL - 54 IS - 13-14 SP - 2263-2271 SN - 0009-2509 KW - carbon dioxide KW - gas-lift reactor KW - hydrodynamics KW - mass transfer KW - modeling KW - potassium hydroxide ER - TY - JOUR TI - Continuous culture as a tool for investigating the growth physiology of heterotrophic hyperthermophiles and extreme thermoacidophiles AU - Rinker, K. D. AU - Han, C. J. AU - Kelly, R. M. T2 - Journal of Applied Microbiology DA - 1999/// PY - 1999/// VL - 85 IS - 1999 SP - 118S-127 ER - TY - JOUR TI - Computer simulation of the competition between protein folding and aggregation AU - Gupta, P AU - Hall, CK AU - Voegler, A T2 - FLUID PHASE EQUILIBRIA AB - In an attempt to gain insights that might eventually lead to the development of new ways to avoid or minimize losses due to protein aggregation, we have performed dynamic Monte Carlo simulations on very simple lattice models of systems containing both isolated and multiple protein chains. Protein folding pathways, intermediate populations, refolding yields and aggregation were monitored as a function of both denaturant and protein concentrations. We find that there exists optimum levels of denaturant and protein concentration at which the refolding yield is highest, in agreement with some experimental observations. DA - 1999/6// PY - 1999/6// DO - 10.1016/s0378-3812(99)00119-3 VL - 158 SP - 87-93 SN - 1879-0224 KW - protein folding KW - protein aggregation KW - folding pathways KW - folding intermediates KW - computer simulation ER - TY - JOUR TI - 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrinato-palladium(II) as a differentiation probe for sensing binding modes with B-DNA duplexes: Electronic MCD and CD spectra AU - Barnes, NR AU - Stroud, PD AU - Robinson, KE AU - Horton, C AU - Schreiner, AF T2 - BIOSPECTROSCOPY AB - We report our detailed electronic MCD, CD, and optical spectroscopic measurements and analysis of the porphyrin Soret (B(o)) region of four-coordinate 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrinatopalladium( II), PdP(4), and its bound states with B-DNA duplexes poly(A-T)2, poly(G-C)2, and calf thymus DNA (CT DNA). For system PdP(4)/poly(A-T)2 it was possible to conclude that the porphyrin is bound edge-on in the major groove, specifically at the 5'AT3' site. For this orientation the porphyrin's electric dipole transition moments (edtm), mu(x) (most perturbed direction) and mu(y) (least perturbed direction), have tilt angles alpha approximately 90 degrees and approximately 45 degrees , respectively, relative to the helix axis. It was further concluded from the small shifts of B(o) optical and MCD band intensities and wavelengths and from the net MCD (+) A-term sign retention upon binding that the porphyrin's frontier ppi MOs (1a(1u) 3a(2u) 4eg) are only weakly perturbed by the heterocyclic bases of poly(A-T)2, and therefore that the LUMO (4eg) splitting is less than the |1a(1u)-3a(2u| energy separation, deltaHOMO, that is, deltaLUMO < deltaHOMO for the bound state in PdP(4)/poly(A-T)2. For intercalation systems PdP(4)/ poly(G-C)2 and /CT DNA, with PdP(4) centered in the intercalation "pocket" and having two of its 4-N-methylpyridyls extending into each of the major and minor grooves, the edtms mu(x) and mu(y) were determined to be oriented perpendicular (gamma approximately 0 degrees) and parallel (gamma approximately 90 degrees) to the hydrogen bonds of the base pairs, respectively. Intercalation is characterized by a much stronger binding interaction, viz., the B(o) optical band and net MCD extrema wavelength shifts are relatively large, and the net MCD (+) A-term of PdP(4) is substantially quenched as it becomes the (-) pseudo-A-term of intercalated PdP(4)/poly(G-C)2. This A-term sign reversal informs that the porphyrin MOs are so strongly perturbed by the GC base pairs that deltaLUMO > deltaHOMO, which gives rise to a (-) pseudo-A-term. Also, the findings demonstrate (1) the potential of PdP(4) as a sensitive, discriminating analytical probe of DNA sequences and (2) the diagnostic capability of the composite of five spectra [net MCD, CD, and optical of free and bound PdP(4)] in differentiating the site and sequence selectivity and preferred binding mode of this porphyrin. DA - 1999/// PY - 1999/// DO - 10.1002/(SICI)1520-6343(1999)5:3<179::AID-BSPY7>3.0.CO;2-U VL - 5 IS - 3 SP - 179-188 SN - 1075-4261 KW - metalloporphyrin KW - nucleic acid KW - outside binding KW - intercalation KW - CD KW - MCD ER - TY - JOUR TI - Enantiopure N-acyldihydropyridones as synthetic intermediates: Asymmetric synthesis of (-)-slaframine AU - Comins, DL AU - Fulp, AB T2 - ORGANIC LETTERS AB - [formula: see text] An asymmetric synthesis of (-)-slaframine and N-acetylslaframine has been accomplished starting from an enantiopure dihydropyridone building block. The oxygen-carbon bond at C-1 was incorporated with complete stereoselectivity by using an efficient phenylselenocyclocarbamation reaction. DA - 1999/12/16/ PY - 1999/12/16/ DO - 10.1021/ol991083v VL - 1 IS - 12 SP - 1941-1943 SN - 1523-7060 ER - TY - JOUR TI - Efficient synthesis of light-harvesting arrays composed of eight porphyrins and one phthalocyanine AU - Li, JZ AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - Effective light-harvesting arrays require multiple photoactive energy donors that funnel energy to an energy acceptor. Porphyrins and phthalocyanines are attractive components for light-harvesting arrays due to their strong absorption in the blue and red regions, respectively, and because energy transfer can occur from porphyrin to phthalocyanine regardless of their respective metalation states. Star-shaped light-harvesting arrays comprised of eight peripheral porphyrins and one core phthalocyanine have been prepared by a streamlined synthesis involving minimal reliance on protecting groups, a high degree of convergence, and facile chromatographic purification. The synthesis involves three distinct stages of complementary chemistries (porphyrin formation, Pd-mediated porphyrin dimer formation, phthalocyanine formation). Statistical reaction of p-iodobenzaldehyde, a phthalonitrile-linked benzaldehyde, and 5-mesityldipyrromethane afforded the desired trans-iodo/phthalonitrile-substituted porphyrin, which underwent Pd-mediated coupling with a monoethynyl porphyrin to give the porphyrin dimer bearing a phthalonitrile unit. Reaction of the dimer in 1-pentanol in the presence of MgCl2 and DBU for 48 h at 145 °C afforded the all-magnesium (porphyrin)8−phthalocyanine nonamer (MgP)8MgPc in 5.0% yield. The same reaction with lithium pentoxide in 1-pentanol for 2 h at 145 °C gave the all-free base nonamer (H2P)8H2Pc in 34% yield. The all-zinc nonamer (ZnP)8ZnPc was prepared by addition of zinc acetate at the end of the reaction. Similar treatment of a monomeric porphyrin−phthalonitrile afforded the pentameric (ZnP)4ZnPc in 58% yield. The (MgP)8MgPc was also obtained by magnesium insertion of (H2P)8H2Pc. The three nonamers were readily purified and are soluble in solvents such as toluene, THF, and CH2Cl2. Each nonamer absorbs strongly across the solar spectrum and exhibits efficient energy transfer from the porphyrins to the phthalocyanine. DA - 1999/12/10/ PY - 1999/12/10/ DO - 10.1021/jo991102e VL - 64 IS - 25 SP - 9101-9108 SN - 1520-6904 ER - TY - JOUR TI - Efficiency studies in nonaqueous capillary electrophoresis AU - Ward, VL AU - Khaledi, MG T2 - JOURNAL OF CHROMATOGRAPHY A AB - Nonaqueous capillary electrophoresis (NACE) is a relatively new area with several advantages that include enhanced efficiency and improved detection sensitivity. The goal of this study was to investigate the influence of NACE compared to aqueous CE on the separation efficiency of oligosaccharides. The applied voltage and buffer concentration were optimized for the aqueous and nonaqueous buffer media to minimize the band broadening effects of Joule heating and electrophoretic dispersion. At the optimized conditions a 1.5-fold enhancement in efficiency was obtained with the nonaqueous buffer medium. DA - 1999/10/29/ PY - 1999/10/29/ DO - 10.1016/S0021-9673(99)00839-0 VL - 859 IS - 2 SP - 203-219 SN - 0021-9673 KW - nonaqueous capillary electrophoresis KW - efficiency KW - buffer composition KW - oligosaccharides ER - TY - JOUR TI - Computer simulations of dipolar liquid crystal phases AU - Houssa, M. AU - McGrother, S. C. AU - Rull, L. F. T2 - Computer Physics Communications DA - 1999/// PY - 1999/// VL - 122 IS - 1999 Sept./Oct. SP - 259-261 ER - TY - JOUR TI - Benzene-copper(I) coordination in a bimetallic chain complex AU - Dattelbaum, AM AU - Martin, JD T2 - INORGANIC CHEMISTRY AB - The solvothermal reaction of CuCl and ZrCl(4) in benzene yields ((bz)CuCl(3))(2)Zr (1) (bz = eta(2)-benzene), which has been characterized by single-crystal X-ray diffraction with a = 6.1206(4) Å, b = 11.1242(4) Å, c = 13.6222(6) Å, beta = 93.675(3) degrees in the monoclinic space group P2(1)/m, Z = 2. 1 adopts a one-dimensional chain structure constructed from zirconium chloride octahedra and [(bz)CuCl(3)](2)(-) tetrahedra. The [(bz)CuCl(3)](2)(-) units are shown to be metal halide analogues of the phosphonate unit [RPO(3)](2)(-). Interchain interactions link chains of 1 along the crystallographic c direction via an edge-to-face pi-stacking of the coordinated benzene molecules. The crystal packing forces influence dramatic second-order Jahn-Teller distortions, making each of the two ((bz)CuCl(3))(2)(-) units distinct. These interactions further result in ligand-to-metal and metal-to-ligand charge transfers that cause an activation of the benzene ligands. DA - 1999/12/27/ PY - 1999/12/27/ DO - 10.1021/ic991064h VL - 38 IS - 26 SP - 6200-6205 SN - 1520-510X UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0000387767&partnerID=MN8TOARS ER - TY - JOUR TI - Thiol-derivatized porphyrins for attachment to electroactive surfaces AU - Gryko, DT AU - Clausen, C AU - Lindsey, JS T2 - JOURNAL OF ORGANIC CHEMISTRY AB - The attachment of porphyrin monomers and multiporphyrin arrays in controlled architectures on electroactive surfaces opens many opportunities for electrochemical studies. Toward this goal, we have developed routes for the preparation of thiol-derivatized porphyrin monomers and porphyrin building blocks that require minimal or no handling of free thiols. Routes to S-protected p-thiobenzaldehydes and m-(thiomethyl)benzaldehydes have been developed. Two sets of meso-substituted porphyrins with variation in electrochemical potentials have been prepared for vertical or horizontal orientation with respect to the electroactive surface. In one set, each porphyrin bears one S-protected p-thiophenyl unit and substituents at the three remaining meso-positions. In the other set each porphyrin possesses four S-protected m-(thiomethyl)phenyl units. Tuning the electrochemical potential in the former set has been achieved by variation of the meso substituents (mesityl, 2,4,6-trimethoxyphenyl, n-pentyl, pentafluorophenyl) and in the latter set by variation of the central metal (Zn, Cu, Co, Ag). Six thiol protecting groups [S-cyano, S-(N-ethylcarbamoyl), S-acetyl, S-(9-anthrylmethyl), S-(2,4-dinitrophenyl), S-pivaloyl] have been found to be compatible with porphyrin formation and metalation with zinc. The S-cyano, S-(N-ethylcarbamoyl), and S-acetyl groups undergo in situ cleavage and/or binding on a gold surface. Of these three, only the S-acetyl protecting group is compatible with the Pd-mediated iodo-ethyne coupling conditions for the preparation of multiporphyrin arrays. Three trans-substituted porphyrin building blocks have been prepared for the synthesis of multiporphyrin arrays that can be attached to an electroactive surface. One porphyrin has two mesityl, one p-iodophenyl, and one p-(S-acetylthio)phenyl substituent for vertical positioning, and two porphyrins each have two m-iodophenyl and two S-protected m-(thiomethyl)phenyl substituents for horizontal positioning. Altogether, 16 free base and 16 metalloporphyrins have been prepared. This work establishes the foundation for preparing diverse thiol-derivatized porphyrin monomers and building blocks. DA - 1999/11/12/ PY - 1999/11/12/ DO - 10.1021/jo9911084 VL - 64 IS - 23 SP - 8635-8647 SN - 1520-6904 ER - TY - JOUR TI - The Pt-195 NMR of L2Pt(1,2-dithiolene) complexes AU - Keefer, CE AU - Bereman, RD AU - Purrington, ST AU - Knight, BW AU - Boyle, PD T2 - INORGANIC CHEMISTRY AB - The syntheses and characterizations of the novel platinum(II) mono-1,2-dithiolenes (COD)Pt(dddt) (1), (Ph3P)2Pt(dddt) (2), (COD)Pt(edt) (3), (Ph3P)2Pt(edt) (4), (bipy)Pt(edt) (5), and (Ph3P)(CO)Pt(dddt) (6) (COD = 1,5-cyclooctadiene; dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate; edt = ethylene-1,2-dithiolate, bipy = 2,2‘-bipyridyl) are reported. 195Pt NMR spectral analysis was performed on the above-mentioned compounds along with the previously reported compounds (COD)Pt(dmid) (7), (Ph3P)2Pt(dmid) (8), (Ph3P)2Pt(dmit) (9), (COD)Pt(mnt) (10), (Ph3P)2Pt(mnt) (11), (COD)Pt(dt) (12), and (Ph3P)2Pt(dt) (13) (dmid = 1,3-dithiole-2-oxo-4,5-dithiolate; dmit = 1,3-dithiole-2-thione-4,5-dithiolate; mnt = maleonitrile-1,2-dithiolate; dt = ethane-1,2-dithiolate). 195Pt NMR results show that, depending on the nature of L2 in L2Pt(1,2-dithiolene) complexes, the 1,2-dithiolene ligands behave as either π donors or acceptors toward the Pt metal center. 195Pt NMR is also sensitive to the relative electron-withdrawing ability of the substituents on the 1,2-dithiolene backbone which results in an ordering of chemical shifts into a series independent of L2. Support is also provided by electrochemistry, UV−vis spectroscopy, and 13C NMR. X-ray structural analysis results are given for 1, monoclinic, P21/a, a = 10.2420(10) Å, b = 10.7510(10) Å, c = 13.2890(20) Å, β = 102.870(10), Z = 4, and for 5, monoclinic, I2/a, a = 7.2294(2) Å, b = 11.4574(4) Å, c = 14.9103(6) Å, β = 89.380(15), Z = 4. DA - 1999/5/17/ PY - 1999/5/17/ DO - 10.1021/ic980369d VL - 38 IS - 10 SP - 2294-2302 SN - 0020-1669 ER - TY - JOUR TI - An illuminating framework: Understanding the photoluminescence of alpha-CuAlCl4 AU - Sullivan, RM AU - Martin, JD T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - CuAlCl4 exemplifies a new class of phosphors based on metal halide analogues of aluminophosphates. The α- and β-CuAlCl4 phases show brilliant blue to blue-green luminescence. The electronic structure of the CuAlCl4 corner sharing tetrahedral frameworks has been explored by fluorimetric and diffuse reflectance measurements on the isomorphous series α-CuAlBrxCl4-x (x = 0−4). The photoluminescence is demonstrated to be a bulk property of the electronically isolated CuCl4/2 tetrahedra within the framework matrix. Remarkably, the structural framework is flexible such that at least 1 mol of small molecule gases per CuAlCl4 formula unit can be reversibly sorbed. The sorption/desorption of small molecule gases further results in the reversible quenching of the photoluminescence. DA - 1999/11/3/ PY - 1999/11/3/ DO - 10.1021/ja9925204 VL - 121 IS - 43 SP - 10092-10097 SN - 1520-5126 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033520680&partnerID=MN8TOARS ER - TY - PAT TI - Luminescent copper aluminum halide materials AU - Martin, J. D. C2 - 1999/// DA - 1999/// PY - 1999/// ER - TY - JOUR TI - In vitro metabolism of alachlor by human liver microsomes and human cytochrome P450 isoforms AU - Coleman, S AU - Liu, SM AU - Linderman, R AU - Hodgson, E AU - Rose, RL T2 - CHEMICO-BIOLOGICAL INTERACTIONS AB - Alachlor (2-chloro-N-methoxymethyl-N-(2,6-diethylphenyl)acetamide) is a widely used pre-emergent chloroacetanilide herbicide which has been classified by the USEPA as a probable human carcinogen. The putative carcinogenic metabolite, 2,6-diethylbenzoquinone imine (DEBQI), is formed through a complex series of oxidative and non-oxidative steps which have been characterized in rats, mice, and monkeys but not in humans. A key metabolite leading to the formation of DEBQI is 2-chloro-N-(2,6-diethylphenyl)acetamide (CDEPA). This study demonstrates that male human liver microsomes are able to metabolize alachlor to CDEPA. The rate of CDEPA formation for human liver microsomes (0.0031±0.0007 nmol/min per mg) is significantly less than the rates of CDEPA formation for rat liver microsomes (0.0353±0.0036 nmol/min per mg) or mouse liver microsomes (0.0106±0.0007). Further, we have screened human cytochrome P450 isoforms 1A1, 1A2, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, and 3A4 and determined that human CYP 3A4 is responsible for metabolism of alachlor to CDEPA. Further work is necessary to determine the extent to which humans are able to metabolize CDEPA through subsequent metabolic steps leading to the formation of DEBQI. DA - 1999/8/30/ PY - 1999/8/30/ DO - 10.1016/S0009-2797(99)00107-6 VL - 122 IS - 1 SP - 27-39 SN - 0009-2797 KW - alachlor KW - CDEPA KW - human CYP KW - herbicides ER - TY - JOUR TI - IUPAC-NIST solubility data series - 67. Halogenated ethanes and ethenes with water AU - Horvath, AL AU - Getzen, FW AU - Maczynska, Z T2 - JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA AB - This volume covers the solubilities of halogenated ethanes and ethenes with water, heavy water, seawater, and aqueous electrolyte solutions. All data were critically examined for their reliability and best value estimates were selected on the basis of such evaluations. Referenced works are presented in the standard IUPAC-NIST Solubility Data Series format. Reported and best value data are presented in tabular form and, where justified, data correlation equations and graphical illustrations are provided. Throughout the volume, SI conventions have been employed as the customary units. The importance of these data arises from the fact that halogenated ethanes and ethenes have commercial uses as industrial chemicals, propellants, solvents, and the like. In such applications, often from spillage, leakage, or mishandling, they contact water and are exposed to the atmosphere. The data are essential for concentration estimates for the halogenated ethanes and ethenes in drinking and ground water, foodstuffs, human tissue, marine organisms, and the atmosphere. The halogenated aliphatics are of particular interest to health scientists, engineers, environmentalists, and atmospheric chemists in that they represent a class of chemical materials which has many significant industrial applications. However, at the same time, these substances have been shown, in some cases, to be carcinogenic and also to be especially damaging to the earth’s atmospheric composition through their chemical reactivity which results in atmospheric ozone depletion. The high ozone depletion potentials of this class of chemical substances emphasizes the importance of having available complete, accurate, and reliable data for mutual solubilities with water. The availability of such data is essential for estimates of halogenated hydrocarbon levels in both natural waters and aqueous industrial liquids which result from industrial fabrication, industrial waste removal processes, and the like. The data also provide significant solubility values for studies concerning the health of human and other biological systems. DA - 1999/// PY - 1999/// DO - 10.1063/1.556039 VL - 28 IS - 2 SP - 395-627 SN - 0047-2689 KW - aqueous solutions KW - halogenated ethanes KW - halogenated ethenes KW - solubility ER - TY - JOUR TI - Counterion diffusion reveals coil-to-helix transition in a polyelectrolyte AU - Ciszkowska, M AU - Osteryoung, JG T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTCounterion Diffusion Reveals Coil-to-Helix Transition in a PolyelectrolyteMalgorzata Ciszkowska and Janet G. OsteryoungView Author Information Departments of Chemistry Brooklyn College, The City University of New York Brooklyn, New York 11210-2889 North Carolina State University Raleigh, North Carolina 27695-8204 Cite this: J. Am. Chem. Soc. 1999, 121, 7, 1617–1618Publication Date (Web):February 4, 1999Publication History Received14 October 1998Published online4 February 1999Published inissue 1 February 1999https://doi.org/10.1021/ja983607cCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views126Altmetric-Citations11LEARN 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 Read OnlinePDF (39 KB) Get e-AlertsSUBJECTS:Counterions,Diffusion,Electrolytes,Ions,Transport properties Get e-Alerts DA - 1999/2/24/ PY - 1999/2/24/ DO - 10.1021/ja983607c VL - 121 IS - 7 SP - 1617-1618 SN - 1520-5126 ER -