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.
{"title":"Using the amide 15N CEST NMR experiment to study slow exchange between ‘visible’ protein states","authors":"Nihar Pradeep Khandave , Ved Prakash Tiwari , Pramodh Vallurupalli","doi":"10.1016/j.jmr.2025.107883","DOIUrl":"10.1016/j.jmr.2025.107883","url":null,"abstract":"<div><div>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 <sup>15</sup>N CEST experiment as an alternative to the <sup>1</sup>H<sup>N</sup>–<sup>15</sup>N ZZ exchange experiment to study exchange between ‘visible’ protein states. In the case of two-state exchange, the <sup>1</sup>H<sup>N</sup>–<sup>15</sup>N correlation map contains two correlations for each exchanging site, one arising from each state. Thus, two <sup>15</sup>N CEST profiles can be recorded for each of these sites using a single <sup>15</sup>N CEST experiment. We find that site-specific exchange parameters can then be obtained by simultaneously analysing both these <sup>15</sup>N CEST profiles recorded at a single ‘high’ <em>B</em><sub><em>1</em></sub> 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 <sup>15</sup>N 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<sup>−1</sup>) at 40 °C.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107883"},"PeriodicalIF":2.0,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143887739","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 : 2025-03-30DOI: 10.1016/j.jmr.2025.107873
Ivan Argatov, Vitaly Kocherbitov
A two-site magnetic exchange model comprising a set of two linear first-order differential Bloch–McConnell equations is considered. The relaxation and exchange behavior is described using a symmetrical form of the general solution derived in the case of longitudinal magnetization for the zero initial conditions. The inverse problem with limited magnetization information has been solved exactly in an analytical explicit form under mild a priori knowledge about the exchange and relaxation parameters.
{"title":"Exact solution of the parameter identification inverse problem for the Bloch–McConnell equations. Longitudinal magnetization","authors":"Ivan Argatov, Vitaly Kocherbitov","doi":"10.1016/j.jmr.2025.107873","DOIUrl":"10.1016/j.jmr.2025.107873","url":null,"abstract":"<div><div>A two-site magnetic exchange model comprising a set of two linear first-order differential Bloch–McConnell equations is considered. The relaxation and exchange behavior is described using a symmetrical form of the general solution derived in the case of longitudinal magnetization for the zero initial conditions. The inverse problem with limited magnetization information has been solved exactly in an analytical explicit form under mild <em>a priori</em> knowledge about the exchange and relaxation parameters.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107873"},"PeriodicalIF":2.0,"publicationDate":"2025-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143760667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-28DOI: 10.1016/j.jmr.2025.107875
Ke Xu, Jörn Schmedt auf der Günne
Nuclear magnetic resonance (NMR) is a routine method to study chemical exchange in reactions and molecular rearrangements in solution. However, when it comes to exchange of molecular species in liquid-liquid, two phase systems like in phase-transfer catalysis, the rate becomes a function of the surface area between two phases, which means that only persistent emulsions could be studied with standard equipment. Unstable emulsions, which rapidly demix, require a continuous application of shear forces by stirring. Here, a setup is described with which unstable emulsions can be produced and studied in-situ by solution NMR spectroscopy. The setup provides sufficient torque and spinning frequency for generating an unstable two-phase water/oil mixture by rapid stirring. The pneumatically driven stirrer in the probe head was designed using ideas borrowed from magic angle sample spinning and a prototype was produced by 3D printing. As proof of concept, the dynamics in an aniline water emulsion over the phase boundary are studied by regular exchange spectroscopy NMR experiments.
{"title":"Chemical exchange in unstable emulsions","authors":"Ke Xu, Jörn Schmedt auf der Günne","doi":"10.1016/j.jmr.2025.107875","DOIUrl":"10.1016/j.jmr.2025.107875","url":null,"abstract":"<div><div>Nuclear magnetic resonance (NMR) is a routine method to study chemical exchange in reactions and molecular rearrangements in solution. However, when it comes to exchange of molecular species in liquid-liquid, two phase systems like in phase-transfer catalysis, the rate becomes a function of the surface area between two phases, which means that only persistent emulsions could be studied with standard equipment. Unstable emulsions, which rapidly demix, require a continuous application of shear forces by stirring. Here, a setup is described with which unstable emulsions can be produced and studied in-situ by solution NMR spectroscopy. The setup provides sufficient torque and spinning frequency for generating an unstable two-phase water/oil mixture by rapid stirring. The pneumatically driven stirrer in the probe head was designed using ideas borrowed from magic angle sample spinning and a prototype was produced by 3D printing. As proof of concept, the dynamics in an aniline water emulsion over the phase boundary are studied by regular exchange spectroscopy NMR experiments.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107875"},"PeriodicalIF":2.0,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143746888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-28DOI: 10.1016/j.jmr.2025.107874
Noella D'Souza , Kieren A. Harkins , Cooper Selco , Ushoshi Basumallick , Samantha Breuer , Zhuorui Zhang , Paul Reshetikhin , Marcus Ho , Aniruddha Nayak , Maxwell McAllister , Emanuel Druga , David Marchiori , Ashok Ajoy
Optical dynamic nuclear polarization (DNP) offers an attractive approach to enhancing the sensitivity of nuclear magnetic resonance (NMR) spectroscopy. Efficient, optically-generated electron polarization can be leveraged to operate across a broad range of temperatures and magnetic fields, making it particularly appealing for applications requiring high DNP efficiency or spatial resolution. While a large class of systems hold promise for optical DNP, many candidates display both variable electron polarizability and electron and nuclear T1 relaxation times as functions of magnetic field and temperature. This necessitates tools capable of studying DNP under diverse experimental conditions. To address this, we introduce a cryogenic field cycling instrument that facilitates optical DNP studies across a wide range of magnetic fields (10 mT–9.4 T) and temperatures (∼10 K–300 K) for wide-bore magnets. Continuous cryogen replenishment enables sustained, long-term operation. Additionally, the system supports the ability to manipulate and probe rapidly hyperpolarized (∼60 s) nuclear spins via pulse sequences involving millions of RF pulses. We describe innovations in the device design and demonstrate its operation on a model system of 13C nuclear spins in diamond polarized through optically pumped nitrogen vacancy (NV) centers. We anticipate the use of the instrument for a broad range of optical DNP systems and studies.
光学动态核极化（DNP）是提高核磁共振（NMR）光谱灵敏度的一种有吸引力的方法。利用高效的光学产生的电子极化可以在广泛的温度和磁场范围内工作，这使得它对需要高DNP效率或空间分辨率的应用特别有吸引力。虽然一大类系统有望实现光学DNP，但许多候选系统显示出可变的电子极化率以及电子和核T1弛豫时间作为磁场和温度的函数。这就需要能够在不同实验条件下研究DNP的工具。为了解决这个问题，我们引入了一种低温场循环仪器，该仪器有助于在宽口径磁体的大范围磁场（10 mT-9.4 T）和温度（~ 10 K - 300 K）下进行光学DNP研究。持续的冷冻剂补充可以保证持续、长期的运行。此外，该系统支持通过涉及数百万RF脉冲的脉冲序列操纵和探测快速超极化（~ 60秒）核自旋的能力。我们描述了器件设计上的创新，并在一个通过光泵浦氮空位中心偏振的金刚石13C核自旋模型系统上演示了其操作。我们期望将该仪器用于广泛的光学DNP系统和研究。
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