@article{lohmann_lehmkuhl_fleischer_rosen_chekmenev_theis_adams_appelt_2023, title={Exploring synchrony and chaos of parahydrogen-pumped two-compartment radio-frequency amplification by stimulated emission of radiation}, volume={108}, ISSN={["2469-9934"]}, url={https://doi.org/10.1103/PhysRevA.108.022806}, DOI={10.1103/PhysRevA.108.022806}, abstractNote={A nuclear-spin-based RASER (radio-frequency amplification by stimulated emission of radiation) is an ideal experimental system to explore nonlinear interaction phenomena of nuclear spins coupled via virtual photons to a resonator. This is due to the RASER being stable for several hours, allowing for extended observation of these phenomena. Nonlinear phenomena in multimode RASERs range from mode oscillations in synchrony, frequency shifts, frequency combs, period doublings, and even chaos. These phenomena are observed in a parahydrogen-pumped two-compartment proton RASER. In two independently pumped compartments, the separation in frequency space between the two RASER modes is precisely controlled with a magnetic field gradient. By controlling the mode separation, we can select the type of nonlinear phenomena observed. A key finding is that the ranges of mode separation where chaos and synchrony occur are very close together. The experimental results are supported by numerical simulations, based on two-mode RASER equations.}, number={2}, journal={PHYSICAL REVIEW A}, author={Lohmann, Lars and Lehmkuhl, Soeren and Fleischer, Simon and Rosen, Matthew S. and Chekmenev, Eduard Y. and Theis, Thomas and Adams, Alina and Appelt, Stephan}, year={2023}, month={Aug} }
 @article{macculloch_browning_tomhon_lehmkuhl_chekmenev_theis_2023, title={Parahydrogen in Reversible Exchange Induces Long-Lived 15N Hyperpolarization of Anticancer Drugs Anastrozole and Letrozole}, volume={5}, ISSN={["1520-6882"]}, url={https://doi.org/10.1021/acs.analchem.2c04817}, DOI={10.1021/acs.analchem.2c04817}, abstractNote={Hyperpolarization modalities overcome the sensitivity limitations of NMR and unlock new applications. Signal amplification by reversible exchange (SABRE) is a particularly cheap, quick, and robust hyperpolarization modality. Here, we employ SABRE for simultaneous chemical exchange of parahydrogen and nitrile-containing anticancer drugs (letrozole or anastrozole) to enhance 15N polarization. Distinct substrates require unique optimal parameter sets, including temperature, magnetic field, or a shaped magnetic field profile. The fine tuning of these parameters for individual substrates is demonstrated here to maximize 15N polarization. After optimization, including the usage of pulsed μT fields, the 15N nuclei on common anticancer drugs, letrozole and anastrozole, can be polarized within 1-2 min. The hyperpolarization can exceed 10%, corresponding to 15N signal enhancement of over 280,000-fold at a clinically relevant magnetic field of 1 T. This sensitivity gain enables polarization studies at naturally abundant 15N enrichment level (0.4%). Moreover, the nitrile 15N sites enable long-lasting polarization storage with [15N]T1 over 9 min, enabling signal detection from a single hyperpolarization cycle for over 30 min.}, number={20}, journal={ANALYTICAL CHEMISTRY}, author={MacCulloch, Keilian and Browning, Austin and TomHon, Patrick and Lehmkuhl, Soeren and Chekmenev, Eduard Y. and Theis, Thomas}, year={2023}, month={May} }
 @article{duchowny_denninger_lohmann_theis_lehmkuhl_adams_2023, title={SABRE Hyperpolarization with up to 200 bar Parahydrogen in Standard and Quickly Removable Solvents}, volume={24}, ISSN={["1422-0067"]}, url={https://doi.org/10.3390/ijms24032465}, DOI={10.3390/ijms24032465}, abstractNote={Parahydrogen (p-H2)-based techniques are known to drastically enhance NMR signals but are usually limited by p-H2 supply. This work reports p-H2-based SABRE hyperpolarization at p-H2 pressures of hundreds of bar, far beyond the typical ten bar currently reported in the literature. A recently designed high-pressure setup was utilized to compress p-H2 gas up to 200 bar. The measurements were conducted using a sapphire high-pressure NMR tube and a 43 MHz benchtop NMR spectrometer. In standard methanol solutions, it could be shown that the signal intensities increased with pressure until they eventually reached a plateau. A polarization of about 2%, equal to a molar polarization of 1.2 mmol L−1, could be achieved for the sample with the highest substrate concentration. While the signal plateaued, the H2 solubility increased linearly with pressure from 1 to 200 bar, indicating that p-H2 availability is not the limiting factor in signal enhancement beyond a certain pressure, depending on sample composition. Furthermore, the possibility of using liquefied ethane and compressed CO2 as removable solvents for hyperpolarization was demonstrated. The use of high pressures together with quickly removable organic/non-organic solvents represents an important breakthrough in the field of hyperpolarization, advancing SABRE as a promising tool for materials science, biophysics, and molecular imaging.}, number={3}, journal={INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES}, author={Duchowny, Anton and Denninger, Johannes and Lohmann, Lars and Theis, Thomas and Lehmkuhl, Soeren and Adams, Alina}, year={2023}, month={Feb} }
 @article{browning_macculloch_tomhon_mandzhieva_chekmenev_goodson_lehmkuhl_theis_2023, title={Spin dynamics of [1,2-C-13(2)]pyruvate hyperpolarization by parahydrogen in reversible exchange at micro Tesla fields}, volume={25}, ISSN={["1463-9084"]}, url={https://doi.org/10.1039/D3CP00843F}, DOI={10.1039/d3cp00843f}, abstractNote={The spin dynamics during SABRE of [1,2-13C2]pyruvate are detailed. An analytical model and numerical simulations are used to understand the selective formation of hyperpolarized magnetization or singlet order on the 13C2-spin pair.}, number={24}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Browning, Austin and Macculloch, Keilian and TomHon, Patrick and Mandzhieva, Iuliia and Chekmenev, Eduard Y. and Goodson, Boyd M. and Lehmkuhl, Soeren and Theis, Thomas}, year={2023}, month={Jun}, pages={16446–16458} }
 @article{nelson_schmidt_adelabu_nantogma_kiselev_abdurraheem_maissin_lehmkuhl_appelt_theis_et al._2022, title={Parahydrogen-Induced Carbon-13 Radiofrequency Amplification by Stimulated Emission of Radiation}, volume={12}, ISSN={["1521-3773"]}, url={https://doi.org/10.1002/anie.202215678}, DOI={10.1002/anie.202215678}, abstractNote={Abstract}, number={5}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Nelson, Christopher and Schmidt, Andreas B. and Adelabu, Isaiah and Nantogma, Shiraz and Kiselev, Valerij G. and Abdurraheem, Abubakar and Maissin, Henri and Lehmkuhl, Soeren and Appelt, Stephan and Theis, Thomas and et al.}, year={2022}, month={Dec} }
 @article{lehmkuhl_fleischer_lohmann_rosen_chekmenev_ada_theis_appelt_2022, title={RASER MRI: Magnetic resonance images formed spontaneously exploiting cooperative nonlinear interaction}, volume={8}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.abp8483}, DOI={10.1126/sciadv.abp8483}, abstractNote={
            The spatial resolution of magnetic resonance imaging (MRI) is limited by the width of Lorentzian point spread functions associated with the transverse relaxation rate 1/
            T
            2
            *
            . Here, we show a different contrast mechanism in MRI by establishing RASER (radio-frequency amplification by stimulated emission of radiation) in imaged media. RASER imaging bursts emerge out of noise and without applying radio-frequency pulses when placing spins with sufficient population inversion in a weak magnetic field gradient. Small local differences in initial population inversion density can create stronger image contrast than conventional MRI. This different contrast mechanism is based on the cooperative nonlinear interaction between all slices. On the other hand, the cooperative nonlinear interaction gives rise to imaging artifacts, such as amplitude distortions and side lobes outside of the imaging domain. Contrast mechanism and artifacts are explored experimentally and predicted by simulations on the basis of a proposed RASER MRI theory.
          }, number={28}, journal={SCIENCE ADVANCES}, author={Lehmkuhl, Soeren and Fleischer, Simon and Lohmann, Lars and Rosen, Matthew S. and Chekmenev, Eduard Y. and Ada, Alina and Theis, Thomas and Appelt, Stephan}, year={2022}, month={Jul} }
 @article{tomhon_han_lehmkuhl_appelt_chekmenev_abolhasani_theis_2021, title={A Versatile Compact Parahydrogen Membrane Reactor}, volume={10}, ISSN={["1439-7641"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118185085&partnerID=MN8TOARS}, DOI={10.1002/cphc.202100667}, abstractNote={Abstract}, number={24}, journal={CHEMPHYSCHEM}, author={TomHon, Patrick M. and Han, Suyong and Lehmkuhl, Soren and Appelt, Stephan and Chekmenev, Eduard Y. and Abolhasani, Milad and Theis, Thomas}, year={2021}, month={Oct} }
 @article{lin_tomhon_lehmkuhl_laasner_theis_blum_2021, title={Density Functional Theory Study of Reaction Equilibria in Signal Amplification by Reversible Exchange}, volume={9}, ISSN={["1439-7641"]}, url={https://doi.org/10.1002/cphc.202100204}, DOI={10.1002/cphc.202100204}, abstractNote={Abstract}, number={19}, journal={CHEMPHYSCHEM}, publisher={Wiley}, author={Lin, Kailai and TomHon, Patrick and Lehmkuhl, Soren and Laasner, Raul and Theis, Thomas and Blum, Volker}, year={2021}, month={Sep} }
 @article{arunkumar_bucher_turner_tomhon_glenn_lehmkuhl_lukin_park_rosen_theis_et al._2021, title={Micron-Scale NV-NMR Spectroscopy with Signal Amplification by Reversible Exchange}, volume={2}, ISSN={2691-3399}, url={http://dx.doi.org/10.1103/prxquantum.2.010305}, DOI={10.1103/PRXQuantum.2.010305}, abstractNote={High-resolution sensing of weak signals is implemented by means of an integrated diamond---nuclear-magnetic-resonance technique}, number={1}, journal={PRX Quantum}, publisher={American Physical Society (APS)}, author={Arunkumar, Nithya and Bucher, Dominik B. and Turner, Matthew J. and TomHon, Patrick and Glenn, David and Lehmkuhl, Sören and Lukin, Mikhail D. and Park, Hongkun and Rosen, Matthew S. and Theis, Thomas and et al.}, year={2021}, month={Jan}, pages={010305} }
 @article{appelt_lehmkuhl_fleischer_joalland_ariyasingha_chekmenev_theis_2021, title={SABRE and PHIP pumped RASER and the route to chaos}, volume={322}, ISSN={1090-7807}, url={http://dx.doi.org/10.1016/j.jmr.2020.106815}, DOI={10.1016/j.jmr.2020.106815}, abstractNote={In a RASER (Radio-frequency Amplification by Stimulated Emission of Radiation), the fast relaxing electromagnetic modes of an LC resonator are enslaved by the slow nuclear spin motion, whose coherence decays with the transverse relaxation rate γm=1/T2∗. Such a system obeys the slaving principle, mathematically identical with the adiabatic elimination procedure, leading to multi-mode RASER equations. If the pumping rate of nuclear spin polarization Γ>>γm, a second adiabatic elimination process applies and the spectral properties of the RASER can be predicted. The resulting model is similar to the model of two non-linear coupled oscillators and predicts the observed RASER phenomena, including frequency combs and mode collapse. If the second adiabatic elimination is not applicable, mode collapse is completely absent and successive period doubling processes and chaos occur at very high population inversions. We compare these theoretical predictions with experimental results from a PHIP (Para-Hydrogen Induced Polarization) pumped 1H RASER. Moreover, in SABRE (Signal Amplification By Reversible Exchange) pumped 1H experiments, RASER revivals are observed long after the parahydrogen pumping source has been switched off. All these findings shed light onto the links between NMR spectroscopy, RASER physics, synergetics and chaos theory. Several new applications are envisioned in the fields of quantum sensor technology, structure investigation or magnetic resonance imaging (MRI).}, journal={Journal of Magnetic Resonance}, publisher={Elsevier BV}, author={Appelt, Stephan and Lehmkuhl, Sören and Fleischer, Simon and Joalland, Baptiste and Ariyasingha, Nuwandi M. and Chekmenev, Eduard Y. and Theis, Thomas}, year={2021}, month={Jan}, pages={106815} }
 @article{tomhon_akeroyd_lehmkuhl_chekmenev_theis_2020, title={Automated pneumatic shuttle for magnetic field cycling and parahydrogen hyperpolarized multidimensional NMR}, volume={312}, ISSN={1090-7807}, url={http://dx.doi.org/10.1016/j.jmr.2020.106700}, DOI={10.1016/j.jmr.2020.106700}, abstractNote={We present a simple-to-implement pneumatic sample shuttle for automation of magnetic field cycling and multidimensional NMR. The shuttle system is robust allowing automation of hyperpolarized and non-hyperpolarized measurements, including variable field lifetime measurements, SABRE polarization optimization, and SABRE multidimensional experiments. Relaxation-protected singlet states are evaluated by variable-field T1 and TS measurements. Automated shuttling facilitates characterization of hyperpolarization dynamics, field dependence and polarization buildup rates. Furthermore, reproducible hyperpolarization levels at every shuttling event enables automated 2D hyperpolarized NMR, including the first inverse 15N/1H HSQC. We uncover binding mechanisms of the catalytic species through cross peaks that are not accessible in standard one-dimensional hyperpolarized experiments. The simple design of the shuttling setup interfaced with standard TTL signals allows easy adaptation to any standard NMR magnet.}, journal={Journal of Magnetic Resonance}, publisher={Elsevier BV}, author={TomHon, Patrick and Akeroyd, Evan and Lehmkuhl, Sören and Chekmenev, Eduard Y. and Theis, Thomas}, year={2020}, month={Mar}, pages={106700} }
 @article{joalland_ariyasingha_lehmkuhl_theis_appelt_chekmenev_2020, title={Parahydrogen‐Induced Radio Amplification by Stimulated Emission of Radiation}, volume={59}, ISSN={1433-7851 1521-3773}, url={http://dx.doi.org/10.1002/anie.201916597}, DOI={10.1002/anie.201916597}, abstractNote={Abstract}, number={22}, journal={Angewandte Chemie International Edition}, publisher={Wiley}, author={Joalland, Baptiste and Ariyasingha, Nuwandi M. and Lehmkuhl, Sören and Theis, Thomas and Appelt, Stephan and Chekmenev, Eduard Y.}, year={2020}, month={Mar}, pages={8654–8660} }
 @article{lehmkuhl_suefke_kentner_yen_blümich_rosen_appelt_theis_2020, title={SABRE polarized low field rare-spin spectroscopy}, volume={152}, ISSN={0021-9606 1089-7690}, url={http://dx.doi.org/10.1063/5.0002412}, DOI={10.1063/5.0002412}, abstractNote={High-field nuclear magnetic resonance (NMR) spectroscopy is an indispensable technique for identification and characterization of chemicals and biomolecular structures. In the vast majority of NMR experiments, nuclear spin polarization arises from thermalization in multi-Tesla magnetic fields produced by superconducting magnets. In contrast, NMR instruments operating at low magnetic fields are emerging as a compact, inexpensive, and highly accessible alternative but suffer from low thermal polarization at a low field strength and consequently a low signal. However, certain hyperpolarization techniques create high polarization levels on target molecules independent of magnetic fields, giving low-field NMR a significant sensitivity boost. In this study, SABRE (Signal Amplification By Reversible Exchange) was combined with high homogeneity electromagnets operating at mT fields, enabling high resolution 1H, 13C, 15N, and 19F spectra to be detected with a single scan at magnetic fields between 1 mT and 10 mT. Chemical specificity is attained at mT magnetic fields with complex, highly resolved spectra. Most spectra are in the strong coupling regime where J-couplings are on the order of chemical shift differences. The spectra and the hyperpolarization spin dynamics are simulated with SPINACH. The simulations start from the parahydrogen singlet in the bound complex and include both chemical exchange and spin evolution at these mT fields. The simulations qualitatively match the experimental spectra and are used to identify the spin order terms formed during mT SABRE. The combination of low field NMR instruments with SABRE polarization results in sensitive measurements, even for rare spins with low gyromagnetic ratios at low magnetic fields.}, number={18}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Lehmkuhl, Sören and Suefke, Martin and Kentner, Arne and Yen, Yi-Fen and Blümich, Bernhard and Rosen, Matthew S. and Appelt, Stephan and Theis, Thomas}, year={2020}, month={May}, pages={184202} }