This work presents the PyEPRI package, an open-source Python package for Electron Paramagnetic Resonance Imaging. The PyEPRI package implements low-level operators, like projection and backprojection, involved in Electron Paramagnetic Resonance (EPR) and also high-level advanced algorithms, like total variation based EPR image reconstruction, for end-users. The package is fully implemented in Python and provides both CPU and GPU computation capabilities, through the libraries Numpy, PyTorch and Cupy. This package comes with a detailed documentation, including precise mathematical definitions and many reproducible demonstration examples and tutorials, making it easy for users with no particular expertise on coding image processing algorithms to get started. This package is also highly modular and only relies on standard data types, as such, it can also be easily used by advanced users to develop new algorithms while benefiting from an optimized computing environment and some rigorously tested operators.
{"title":"PyEPRI: A CPU & GPU compatible python package for electron paramagnetic resonance imaging","authors":"Rémy Abergel , Sylvain Durand , Yves-Michel Frapart","doi":"10.1016/j.jmr.2025.107891","DOIUrl":"10.1016/j.jmr.2025.107891","url":null,"abstract":"<div><div>This work presents the PyEPRI package, an open-source Python package for Electron Paramagnetic Resonance Imaging. The PyEPRI package implements low-level operators, like projection and backprojection, involved in Electron Paramagnetic Resonance (EPR) and also high-level advanced algorithms, like total variation based EPR image reconstruction, for end-users. The package is fully implemented in Python and provides both CPU and GPU computation capabilities, through the libraries Numpy, PyTorch and Cupy. This package comes with a detailed documentation, including precise mathematical definitions and many reproducible demonstration examples and tutorials, making it easy for users with no particular expertise on coding image processing algorithms to get started. This package is also highly modular and only relies on standard data types, as such, it can also be easily used by advanced users to develop new algorithms while benefiting from an optimized computing environment and some rigorously tested operators.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"376 ","pages":"Article 107891"},"PeriodicalIF":2.0,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144116455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-05-16DOI: 10.1016/j.jmr.2025.107887
Mengjuan Gao , Sihui Luo , Lin Zhu , Lizhi Xiao , Huabing Liu , Guangzhi Liao , Xinman Lv , Hao Chen , Yi Wang
Halbach magnets have been widely employed to NMR instruments due to their low weight, low cost, and minimal leakage of magnetic field. However, field inhomogeneity remains challenge due to discrete magnet rings and manufacturing deviations of the magnetic elements. This paper aims to address this limitation through an effective passive shimming approach, which is considered the first step toward constructing high-homogeneity magnets because of its non-powered and inherently stable characteristics. We focus on the transverse dipole field generated by Halbach magnets and develop an easily implementable linear programming-genetic algorithm (LP-GA) hybrid optimization approach for passive shimming. Our methodology first employs an equivalent magnetic dipole model to calculate the sensitivity matrix of the shim pieces in the Region of Interest (ROI). Then, the LP-GA hybrid optimization algorithm determines the optimal position, number, and thickness of the shim pieces. By combining shim pieces of three different thicknesses (1 mm, 1.5 mm, and 2 mm), we significantly reduce the field inhomogeneity of a 48 mT Halbach magnet system. The effectiveness of our approach is validated through NMR measurements using water samples with copper sulfate at different concentrations, demonstrating an improvement in field homogeneity from approximately 1229 ppm to 320 ppm. The experimental results confirm that the proposed approach effectively enhances magnetic field homogeneity of low-field Halbach magnet systems and could be applied to shimming various Halbach-like magnet arrays.
{"title":"Easy-to-implement passive shimming approach of Halbach magnet for low-field NMR measurement","authors":"Mengjuan Gao , Sihui Luo , Lin Zhu , Lizhi Xiao , Huabing Liu , Guangzhi Liao , Xinman Lv , Hao Chen , Yi Wang","doi":"10.1016/j.jmr.2025.107887","DOIUrl":"10.1016/j.jmr.2025.107887","url":null,"abstract":"<div><div>Halbach magnets have been widely employed to NMR instruments due to their low weight, low cost, and minimal leakage of magnetic field. However, field inhomogeneity remains challenge due to discrete magnet rings and manufacturing deviations of the magnetic elements. This paper aims to address this limitation through an effective passive shimming approach, which is considered the first step toward constructing high-homogeneity magnets because of its non-powered and inherently stable characteristics. We focus on the transverse dipole field generated by Halbach magnets and develop an easily implementable linear programming-genetic algorithm (LP-GA) hybrid optimization approach for passive shimming. Our methodology first employs an equivalent magnetic dipole model to calculate the sensitivity matrix of the shim pieces in the Region of Interest (ROI). Then, the LP-GA hybrid optimization algorithm determines the optimal position, number, and thickness of the shim pieces. By combining shim pieces of three different thicknesses (1 mm, 1.5 mm, and 2 mm), we significantly reduce the field inhomogeneity of a 48 mT Halbach magnet system. The effectiveness of our approach is validated through NMR measurements using water samples with copper sulfate at different concentrations, demonstrating an improvement in field homogeneity from approximately 1229 ppm to 320 ppm. The experimental results confirm that the proposed approach effectively enhances magnetic field homogeneity of low-field Halbach magnet systems and could be applied to shimming various Halbach-like magnet arrays.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"376 ","pages":"Article 107887"},"PeriodicalIF":2.0,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144069153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-05-15DOI: 10.1016/j.jmr.2025.107898
Yihui Huang , Zi Wang , Xinlin Zhang , Jian Cao , Zhangren Tu , Meijin Lin , Lv Li , Xianwang Jiang , Di Guo , Xiaobo Qu
Undersampling accelerates signal acquisition at the expense of introducing artifacts. Removing these artifacts is a fundamental problem in signal processing and this task is also called signal reconstruction. Through modeling signals as the superimposed exponential functions, deep learning has achieved fast and high-fidelity signal reconstruction by training a mapping from the undersampled exponentials to the fully sampled ones. However, the mismatch, such as undersampling rates (25 % vs. 50 %), anatomical region (knee vs. brain), and contrast configurations (PDw vs. T2w), between the training and target data will heavily compromise the reconstruction. To overcome this limitation, we propose Alternating Deep Low-Rank (ADLR), which combines deep learning solvers and classic optimization solvers. Experimental validation on the reconstruction of synthetic and real-world biomedical magnetic resonance signals demonstrates that ADLR can effectively alleviate the mismatch issue and achieve lower reconstruction errors than state-of-the-art methods.
欠采样以引入伪影为代价加速信号采集。去除这些伪影是信号处理中的一个基本问题，这项任务也被称为信号重建。通过将信号建模为叠加的指数函数，深度学习通过训练从欠采样指数到全采样指数的映射，实现了快速高保真的信号重建。然而，训练数据和目标数据之间的不匹配，如采样不足率（25% vs 50%）、解剖区域（膝盖vs大脑）和对比配置（PDw vs T2w），将严重影响重建。为了克服这一限制，我们提出了交替深度低秩（ADLR），它结合了深度学习求解器和经典优化求解器。对合成和真实生物医学磁共振信号的重建实验验证表明，ADLR可以有效地缓解不匹配问题，实现比现有方法更低的重建误差。
{"title":"Improve robustness to mismatched sampling rate: An alternating deep low-rank approach for exponential function reconstruction and its biomedical magnetic resonance applications","authors":"Yihui Huang , Zi Wang , Xinlin Zhang , Jian Cao , Zhangren Tu , Meijin Lin , Lv Li , Xianwang Jiang , Di Guo , Xiaobo Qu","doi":"10.1016/j.jmr.2025.107898","DOIUrl":"10.1016/j.jmr.2025.107898","url":null,"abstract":"<div><div>Undersampling accelerates signal acquisition at the expense of introducing artifacts. Removing these artifacts is a fundamental problem in signal processing and this task is also called signal reconstruction. Through modeling signals as the superimposed exponential functions, deep learning has achieved fast and high-fidelity signal reconstruction by training a mapping from the undersampled exponentials to the fully sampled ones. However, the mismatch, such as undersampling rates (25 % vs. 50 %), anatomical region (knee vs. brain), and contrast configurations (PDw vs. T<sub>2</sub>w), between the training and target data will heavily compromise the reconstruction. To overcome this limitation, we propose Alternating Deep Low-Rank (ADLR), which combines deep learning solvers and classic optimization solvers. Experimental validation on the reconstruction of synthetic and real-world biomedical magnetic resonance signals demonstrates that ADLR can effectively alleviate the mismatch issue and achieve lower reconstruction errors than state-of-the-art methods.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"376 ","pages":"Article 107898"},"PeriodicalIF":2.0,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144099376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-05-08DOI: 10.1016/j.jmr.2025.107888
Tobias Splith , Andreas Chwala , Thomas Hiller , Aaron C. Davis , Raphael Dlugosch , Ronny Stolz , Mike Müller-Petke
We present pre-polarization surface nuclear magnetic resonance (PP-SNMR) measurements performed with a Superconducting QUantum Interference Device (SQUID) magnetometer on water-filled pallet boxes. The SQUID directly detects the three components of the magnetic field (B-field) NMR response, while conventional SNMR experiments would detect its time derivative and most of the time only a single component. Each of the three vector components of the magnetic field NMR response consists of a component oscillating at Larmor frequency and of a non-oscillating component. We extend the general SNMR theory to model the measured signals. For the non-oscillating signal, another magnetic decay with a large amplitude is superimposed on the signal originating from the water-filled boxes, and we were unable to extract the desired signal. For the oscillating signal component, however, we report good agreement between the measured signal and the forward model in amplitude and phase. Measuring all three components of the B-field introduces a sensitivity to lateral inhomogeneities, which we demonstrate by repeating the experiment with one and two emptied boxes.
{"title":"PP-SNMR measurements using SQUIDs as compact three-component B-field sensors for spatial imaging","authors":"Tobias Splith , Andreas Chwala , Thomas Hiller , Aaron C. Davis , Raphael Dlugosch , Ronny Stolz , Mike Müller-Petke","doi":"10.1016/j.jmr.2025.107888","DOIUrl":"10.1016/j.jmr.2025.107888","url":null,"abstract":"<div><div>We present pre-polarization surface nuclear magnetic resonance (PP-SNMR) measurements performed with a Superconducting QUantum Interference Device (SQUID) magnetometer on water-filled pallet boxes. The SQUID directly detects the three components of the magnetic field (B-field) NMR response, while conventional SNMR experiments would detect its time derivative and most of the time only a single component. Each of the three vector components of the magnetic field NMR response consists of a component oscillating at Larmor frequency and of a non-oscillating component. We extend the general SNMR theory to model the measured signals. For the non-oscillating signal, another magnetic decay with a large amplitude is superimposed on the signal originating from the water-filled boxes, and we were unable to extract the desired signal. For the oscillating signal component, however, we report good agreement between the measured signal and the forward model in amplitude and phase. Measuring all three components of the B-field introduces a sensitivity to lateral inhomogeneities, which we demonstrate by repeating the experiment with one and two emptied boxes.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"376 ","pages":"Article 107888"},"PeriodicalIF":2.0,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143916808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-30DOI: 10.1016/j.jmr.2025.107890
Tianzhi Wang , Daniel Arcos , F. David Doty , B. Montgomery Pettitt , Junji Iwahara
NMR-based diffusion measurements of potassium (K+), magnesium (Mg2+), chloride (Cl−), and sulfate (SO42−) ions have been challenging even though these ions are biologically important. For these ions, the gyromagnetic ratios of the NMR-active nuclei, 39K, 25Mg, 35Cl, and 33S, are less than 1/10 of the 1H gyromagnetic ratio, causing a low sensitivity in NMR detection and a low efficiency in NMR dephasing needed for diffusion measurements. These nuclei also undergo rapid longitudinal and transverse NMR relaxation via the quadrupolar mechanism, severely limiting the effectiveness of NMR-based diffusion measurements. Interactions with biomolecules promote the NMR relaxation of these ions, hindering measurements of the ion diffusion. We demonstrate that, despite these challenges, diffusion of K+, Mg2+, Cl−, and SO42− ions in biomolecular solutions can be measured accurately and precisely through use of appropriately designed high-field NMR probe hardware that can generate strong field gradients >1000 G/cm. The NMR-based diffusion coefficients measured at 17.6 T for these ions in the absence of biomolecules agreed well with conductivity-based values in the literature. This consistency supports that ion diffusion along the magnetic field is unaffected by the Lorentz force acting on the ions, as previously predicted. Our data on ion diffusion in solutions of proteins and DNA illuminate the effect of electrostatic interactions on the apparent diffusion coefficients of ions. Thus, high-field NMR probe hardware that can generate strong field gradients opens a new avenue to characterize the dynamic behavior of various ions around biomolecules and their effect on biomolecular electrostatics.
{"title":"Strong field gradients enable NMR-based diffusion measurements for K+, Mg2+, Cl−, and SO42− ions in biomolecular solutions","authors":"Tianzhi Wang , Daniel Arcos , F. David Doty , B. Montgomery Pettitt , Junji Iwahara","doi":"10.1016/j.jmr.2025.107890","DOIUrl":"10.1016/j.jmr.2025.107890","url":null,"abstract":"<div><div>NMR-based diffusion measurements of potassium (K<sup>+</sup>), magnesium (Mg<sup>2+</sup>), chloride (Cl<sup>−</sup>), and sulfate (SO<sub>4</sub><sup>2−</sup>) ions have been challenging even though these ions are biologically important. For these ions, the gyromagnetic ratios of the NMR-active nuclei, <sup>39</sup>K, <sup>25</sup>Mg, <sup>35</sup>Cl, and <sup>33</sup>S, are less than 1/10 of the <sup>1</sup>H gyromagnetic ratio, causing a low sensitivity in NMR detection and a low efficiency in NMR dephasing needed for diffusion measurements. These nuclei also undergo rapid longitudinal and transverse NMR relaxation via the quadrupolar mechanism, severely limiting the effectiveness of NMR-based diffusion measurements. Interactions with biomolecules promote the NMR relaxation of these ions, hindering measurements of the ion diffusion. We demonstrate that, despite these challenges, diffusion of K<sup>+</sup>, Mg<sup>2+</sup>, Cl<sup>−</sup>, and SO<sub>4</sub><sup>2−</sup> ions in biomolecular solutions can be measured accurately and precisely through use of appropriately designed high-field NMR probe hardware that can generate strong field gradients >1000 G/cm. The NMR-based diffusion coefficients measured at 17.6 T for these ions in the absence of biomolecules agreed well with conductivity-based values in the literature. This consistency supports that ion diffusion along the magnetic field is unaffected by the Lorentz force acting on the ions, as previously predicted. Our data on ion diffusion in solutions of proteins and DNA illuminate the effect of electrostatic interactions on the apparent diffusion coefficients of ions. Thus, high-field NMR probe hardware that can generate strong field gradients opens a new avenue to characterize the dynamic behavior of various ions around biomolecules and their effect on biomolecular electrostatics.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"376 ","pages":"Article 107890"},"PeriodicalIF":2.0,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143916807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-26DOI: 10.1016/j.jmr.2025.107876
Xiaoqing Li , Jacob R. Lindale , Loren L. Smith , Warren S. Warren
Signal Amplification By Reversible Exchange (SABRE) is a parahydrogen-based hyperpolarization technique that can generate orders-of-magnitude larger signals than thermal spin polarization within a minute. However, this method is limited by the availability of parahydrogen to the solution. Previous work demonstrated SABRE-derived 1H hyperpolarization at pressures up to 200 bar and using liquid carbon dioxide as a solvent. Here, we extend this work to demonstrate heteronuclear (15N) SABRE hyperpolarization using conventional solvents with hydrogen pressures up to 400 bar as well as the possibility of using supercritical CO2 as the solvent. We demonstrate that in both modes, 15N hyperpolarization comparable to SABRE-SHEATH may be achieved, providing a route for future optimization efforts as well as scale-up. We also present first steps towards exploring SABRE hyperpolarization of 129Xe.
{"title":"Investigation of 15N-SABRE hyperpolarization at high pressures and in supercritical fluids","authors":"Xiaoqing Li , Jacob R. Lindale , Loren L. Smith , Warren S. Warren","doi":"10.1016/j.jmr.2025.107876","DOIUrl":"10.1016/j.jmr.2025.107876","url":null,"abstract":"<div><div>Signal Amplification By Reversible Exchange (SABRE) is a parahydrogen-based hyperpolarization technique that can generate orders-of-magnitude larger signals than thermal spin polarization within a minute. However, this method is limited by the availability of parahydrogen to the solution. Previous work demonstrated SABRE-derived <sup>1</sup>H hyperpolarization at pressures up to 200 bar and using liquid carbon dioxide as a solvent. Here, we extend this work to demonstrate heteronuclear (<sup>15</sup>N) SABRE hyperpolarization using conventional solvents with hydrogen pressures up to 400 bar as well as the possibility of using supercritical CO<sub>2</sub> as the solvent. We demonstrate that in both modes, <sup>15</sup>N hyperpolarization comparable to SABRE-SHEATH may be achieved, providing a route for future optimization efforts as well as scale-up. We also present first steps towards exploring SABRE hyperpolarization of <sup>129</sup>Xe.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107876"},"PeriodicalIF":2.0,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-24DOI: 10.1016/j.jmr.2025.107886
Matthias Bretschneider, Burkhard Endeward, Jörn Plackmeyer, Thomas F. Prisner
We investigated the accuracy and limitation of using the modulation depth of pulsed electron-electron double resonance experiments to count the number of coupled spins. For this purpose, synthesized multi-nitroxide molecules with 2–6 spins were used. We could show that the main limitation on accurately counting larger number of coupled spins at Q-band frequencies is determined by the reproducibility of adjusting and calibrating the pump pulse excitation efficiency. Using broadband sech/tanh or short 10 ns rectangular pump pulses modulation depth suppression effects arising from non-ideal coverage of the dipolar-split signals can be avoided for molecules with intra-molecular spin distances larger than 2 nm. The transverse relaxation times for our model compounds with one to six spins did not depend on the spin number and were all the same. Nevertheless, the signal intensity of the primary Hahn echo signal in a 4-pulse PELDOR sequence decreased strongly with the number of coupled spins. This is due to the dipolar defocusing if more than one spin is excited by the first two pulses at the detection frequency, resulting in a loss of refocused echo intensity of the PELDOR experiments. This effect further reduces the accuracy of using the PELDOR modulation depth for spin counting. Altogether, our results demonstrate that this method is potentially applicable up to hexameric complexes with nitroxides.
{"title":"Using PELDOR to count spins on multi-nitroxides","authors":"Matthias Bretschneider, Burkhard Endeward, Jörn Plackmeyer, Thomas F. Prisner","doi":"10.1016/j.jmr.2025.107886","DOIUrl":"10.1016/j.jmr.2025.107886","url":null,"abstract":"<div><div>We investigated the accuracy and limitation of using the modulation depth of pulsed electron-electron double resonance experiments to count the number of coupled spins. For this purpose, synthesized multi-nitroxide molecules with 2–6 spins were used. We could show that the main limitation on accurately counting larger number of coupled spins at Q-band frequencies is determined by the reproducibility of adjusting and calibrating the pump pulse excitation efficiency. Using broadband sech/tanh or short 10 ns rectangular pump pulses modulation depth suppression effects arising from non-ideal coverage of the dipolar-split signals can be avoided for molecules with intra-molecular spin distances larger than 2 nm. The transverse relaxation times for our model compounds with one to six spins did not depend on the spin number and were all the same. Nevertheless, the signal intensity of the primary Hahn echo signal in a 4-pulse PELDOR sequence decreased strongly with the number of coupled spins. This is due to the dipolar defocusing if more than one spin is excited by the first two pulses at the detection frequency, resulting in a loss of refocused echo intensity of the PELDOR experiments. This effect further reduces the accuracy of using the PELDOR modulation depth for spin counting. Altogether, our results demonstrate that this method is potentially applicable up to hexameric complexes with nitroxides.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107886"},"PeriodicalIF":2.0,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143887737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-21DOI: 10.1016/j.jmr.2025.107885
Tomas Orlando , Huyen Bui , Jhersie Cabigting , Natalie Ibbetson , Johan van Tol , Thierry Dubroca , Xiaoling Wang , Frederic Mentink-Vigier
Dynamic nuclear polarization (DNP) in liquids can enhance NMR signals by up to two orders of magnitude at magnetic fields greater than 9.4 T. The DNP experiment relies on driving electron spin transitions through microwave irradiation of the sample, which requires the solvent/sample to be transparent to microwaves. The physical models describing spin polarization transfer neglect the role of the solvent, despite recent experimental results suggesting that its impact on DNP efficiency can be as much as a factor of three. In this study, we aim to clarify how and why the solvent may affect DNP experiments at high magnetic fields. We examined known systems (13C-CCl4/TEMPO and PPh3/BDPA) dispersed in CCl4, heptane, and benzene. By measuring their EPR properties, simulating microwave propagation patterns, and quantitatively assessing the DNP enhancements at 14.1 T, we determined that the choice of non-polar solvent is not critical to the outcome of a DNP experiment. Furthermore, our experimental results and electromagnetic simulations enable us to assess the state-of-the-art capabilities of DNP instruments at high magnetic fields and propose directions for possible future improvements.
{"title":"Impact of non-polar solvents in dynamic nuclear polarization at high magnetic fields","authors":"Tomas Orlando , Huyen Bui , Jhersie Cabigting , Natalie Ibbetson , Johan van Tol , Thierry Dubroca , Xiaoling Wang , Frederic Mentink-Vigier","doi":"10.1016/j.jmr.2025.107885","DOIUrl":"10.1016/j.jmr.2025.107885","url":null,"abstract":"<div><div>Dynamic nuclear polarization (DNP) in liquids can enhance NMR signals by up to two orders of magnitude at magnetic fields greater than 9.4 T. The DNP experiment relies on driving electron spin transitions through microwave irradiation of the sample, which requires the solvent/sample to be transparent to microwaves. The physical models describing spin polarization transfer neglect the role of the solvent, despite recent experimental results suggesting that its impact on DNP efficiency can be as much as a factor of three. In this study, we aim to clarify how and why the solvent may affect DNP experiments at high magnetic fields. We examined known systems (<sup>13</sup>C-CCl<sub>4</sub>/TEMPO and PPh<sub>3</sub>/BDPA) dispersed in CCl<sub>4</sub>, heptane, and benzene. By measuring their EPR properties, simulating microwave propagation patterns, and quantitatively assessing the DNP enhancements at 14.1 T, we determined that the choice of non-polar solvent is not critical to the outcome of a DNP experiment. Furthermore, our experimental results and electromagnetic simulations enable us to assess the state-of-the-art capabilities of DNP instruments at high magnetic fields and propose directions for possible future improvements.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107885"},"PeriodicalIF":2.0,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143887738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-17DOI: 10.1016/j.jmr.2025.107884
Zachary G. Mayes, Yugandhara A.M. Eriyagama, Lingyu Chi, Thomas P. Schuman, Klaus Woelk
Split-Inversion-Pulse and Recovery (SIP-R) is a recently introduced NMR methodology for acquiring spin-lattice relaxation data with a robust decay-to-zero intensity profile as a function of recovery time. This decay-to-zero behavior is particularly advantageous for extracting multiple relaxation times and coefficients using inverse Laplace transformation (ILT) algorithms. In this study, two frequency-selective adaptations of SIP-R are introduced, incorporating either one or two frequency-selective pulses in the SIP-R dual-scan experiment to excite only specific spectral regions. In a test using a non-viscous, small-molecule solution of ethanol in D₂O, both single- and double-selective SIP-R sequences reproduced reasonably well the relaxation times obtained with the non-selective SIP-R method. However, the double-selective SIP-R experiment introduced additional, shorter relaxation times, which were interpreted as artifacts due to the extended duration of the second frequency-selective pulse. Applying the non-selective SIP-R method to a polymer hydrogel enabled the quantitative differentiation of freely moving water molecules (95 %) and water tightly bound to the polymer chains (5 %). The frequency-selective SIP-R variants revealed strong NOE effects between water and polymeric amide resonances, similar to previous findings that suggest strong interactions between water molecules and amine groups in a different type of polymer hydrogel.
{"title":"Single and double-selective split-inversion pulse and recovery (SIP-R) sequences for targeted T1 relaxation measurements","authors":"Zachary G. Mayes, Yugandhara A.M. Eriyagama, Lingyu Chi, Thomas P. Schuman, Klaus Woelk","doi":"10.1016/j.jmr.2025.107884","DOIUrl":"10.1016/j.jmr.2025.107884","url":null,"abstract":"<div><div>Split-Inversion-Pulse and Recovery (SIP-R) is a recently introduced NMR methodology for acquiring spin-lattice relaxation data with a robust decay-to-zero intensity profile as a function of recovery time. This decay-to-zero behavior is particularly advantageous for extracting multiple relaxation times and coefficients using inverse Laplace transformation (ILT) algorithms. In this study, two frequency-selective adaptations of SIP-R are introduced, incorporating either one or two frequency-selective pulses in the SIP-R dual-scan experiment to excite only specific spectral regions. In a test using a non-viscous, small-molecule solution of ethanol in D₂O, both single- and double-selective SIP-R sequences reproduced reasonably well the relaxation times obtained with the non-selective SIP-R method. However, the double-selective SIP-R experiment introduced additional, shorter relaxation times, which were interpreted as artifacts due to the extended duration of the second frequency-selective pulse. Applying the non-selective SIP-R method to a polymer hydrogel enabled the quantitative differentiation of freely moving water molecules (95 %) and water tightly bound to the polymer chains (5 %). The frequency-selective SIP-R variants revealed strong NOE effects between water and polymeric amide resonances, similar to previous findings that suggest strong interactions between water molecules and amine groups in a different type of polymer hydrogel.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107884"},"PeriodicalIF":2.0,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143847904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-12DOI: 10.1016/j.jmr.2025.107883
Nihar Pradeep Khandave , Ved Prakash Tiwari , Pramodh Vallurupalli
Slow exchange between ‘visible’ protein states is often studied using the two-dimensional ZZ exchange class of magnetisation transfer experiments. However, the cross-peaks that arise due to magnetisation transfer between different states can lead to additional overlap in the two-dimensional ZZ exchange NMR spectrum. To overcome this overlap problem, here we have explored the utility of the 15N CEST experiment as an alternative to the 1HN–15N ZZ exchange experiment to study exchange between ‘visible’ protein states. In the case of two-state exchange, the 1HN–15N correlation map contains two correlations for each exchanging site, one arising from each state. Thus, two 15N CEST profiles can be recorded for each of these sites using a single 15N CEST experiment. We find that site-specific exchange parameters can then be obtained by simultaneously analysing both these 15N CEST profiles recorded at a single ‘high’ B1 field supplemented with experimentally derived information regarding the initial magnetisation or as in the case of the ZZ exchange experiment, the minor state population. The utility of the 15N CEST based approach to characterise exchange between visible protein states is demonstrated by studying the interconversion of the ∼18 kDa T34A mutant of T4 lysozyme between its native state and a minor state populated to ∼21 % (exchange rate ∼5 s−1) at 40 °C.
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