Pub Date : 2025-10-10DOI: 10.1016/j.jmr.2025.107984
Yanan Li , Florin Teleanu , Alexej Jerschow
Intermolecular multiple quantum coherences (iMQCs) may arise in isotropic systems with high spin concentrations, of which ionic liquids are an important example. In examining the 1H, 19F, and 11B nuclei of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF]), we identified the existence of homonuclear iMQCs for all these nuclei. In addition, for the 11B quadrupolar nuclei, we investigated the possible excitation of intramolecular triple quantum coherences (TQCs) which could in principle arise from the slow tumbling in ionic liquids. These experiments showed that while iMQCs can be excited for 11B, (intramolecular) triple-quantum coherences were not detectable. These findings may help clarifying the ion dynamics and intermolecular interactions in ionic liquids.
{"title":"Identifying intermolecular multiple-quantum coherences in ionic liquids","authors":"Yanan Li , Florin Teleanu , Alexej Jerschow","doi":"10.1016/j.jmr.2025.107984","DOIUrl":"10.1016/j.jmr.2025.107984","url":null,"abstract":"<div><div>Intermolecular multiple quantum coherences (iMQCs) may arise in isotropic systems with high spin concentrations, of which ionic liquids are an important example. In examining the <sup>1</sup>H, <sup>19</sup>F, and <sup>11</sup>B nuclei of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>]), we identified the existence of homonuclear iMQCs for all these nuclei. In addition, for the <sup>11</sup>B quadrupolar nuclei, we investigated the possible excitation of intramolecular triple quantum coherences (TQCs) which could in principle arise from the slow tumbling in ionic liquids. These experiments showed that while iMQCs can be excited for <sup>11</sup>B, (intramolecular) triple-quantum coherences were not detectable. These findings may help clarifying the ion dynamics and intermolecular interactions in ionic liquids.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107984"},"PeriodicalIF":1.9,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145305109","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 : 2025-10-09DOI: 10.1016/j.jmr.2025.107973
Eloïse Mougel , Hélène Ratiney , Eric Van Reeth , Kevin Tse Ve Koon , Olivier Beuf , Denis Grenier
Contrast methods based on dipolar coupling are of great interest for imaging tissues containing large macromolecules, such as myelin. Most of these conventional methods deal with various “relaxation” phenomena influenced by dipolar coupling such as inhomogeneous magnetization transfer. In this work we propose to investigate the benefit of using another method, called magic sandwich echo (MSE), which allows direct modulation of the dipolar coupling (Hd) as described by the work of Matsui and the Redfield theory. To verify the potential of this method in biological tissue, we first proposed an experimental model for dipolar coupling modulation in an ex vivo tendon (as a highly anisotropic tissue) and used it to prove Hd modulation by varying the amplitude of the spin-lock radiofrequency pulse of this sequence. We then proposed a potential in vivo usable metric, directly related to the residual amount of Hd, which we called MaSteR for Magic sandwich echo to Stimulated echo ratio, as it is based on the ratio of the signal acquired with the MSE sequence and a stimulated echo sequence. First, we show that the higher Hd, the more effective the spin-lock radiofrequency amplitude. We measured with MaSteR that the change in radiofrequency amplitude allowed us to distinguish between different Hd intensities, with a greater MaSteR when Hd is higher.
{"title":"Effect of the spin-locking B1 radiofrequency field strength on the signal enhancement with Magic Sandwich Echo sequence","authors":"Eloïse Mougel , Hélène Ratiney , Eric Van Reeth , Kevin Tse Ve Koon , Olivier Beuf , Denis Grenier","doi":"10.1016/j.jmr.2025.107973","DOIUrl":"10.1016/j.jmr.2025.107973","url":null,"abstract":"<div><div>Contrast methods based on dipolar coupling are of great interest for imaging tissues containing large macromolecules, such as myelin. Most of these conventional methods deal with various “relaxation” phenomena influenced by dipolar coupling such as inhomogeneous magnetization transfer. In this work we propose to investigate the benefit of using another method, called magic sandwich echo (MSE), which allows direct modulation of the dipolar coupling (<em>H</em><sub><em>d</em></sub>) as described by the work of Matsui and the Redfield theory. To verify the potential of this method in biological tissue, we first proposed an experimental model for dipolar coupling modulation in an <em>ex vivo</em> tendon (as a highly anisotropic tissue) and used it to prove <em>H</em><sub><em>d</em></sub> modulation by varying the amplitude of the spin-lock radiofrequency pulse of this sequence. We then proposed a potential <em>in vivo</em> usable metric, directly related to the residual amount of <em>H</em><sub><em>d</em></sub>, which we called MaSteR for Magic sandwich echo to Stimulated echo ratio, as it is based on the ratio of the signal acquired with the MSE sequence and a stimulated echo sequence. First, we show that the higher <em>H</em><sub><em>d</em></sub>, the more effective the spin-lock radiofrequency amplitude. We measured with MaSteR that the change in radiofrequency amplitude allowed us to distinguish between different <em>H</em><sub><em>d</em></sub> intensities, with a greater MaSteR when <em>H</em><sub><em>d</em></sub> is higher.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107973"},"PeriodicalIF":1.9,"publicationDate":"2025-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145350838","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 : 2025-10-08DOI: 10.1016/j.jmr.2025.107985
Eugeny Kryukov , Alexander Karabanov , Denis Langlais , Dinu Iuga , Shashwata Moitra , Jeremy Good
We show that the magnetic field in cryogen-free magnets is stable enough for high-resolution solid-state and liquid-state NMR. The same magnet can be used at different magnetic fields, which can be changed every day without compromising the spectral resolution. The magnet performance was demonstrated on a series of solid-state and liquid-state NMR experiments. Hardware and software correction can additionally be applied to improve the quality of 1D and 2D NMR spectra.
{"title":"An experimental demonstration of the use of a cryogen-free system for high-resolution 1D and 2D solid and liquid state NMR","authors":"Eugeny Kryukov , Alexander Karabanov , Denis Langlais , Dinu Iuga , Shashwata Moitra , Jeremy Good","doi":"10.1016/j.jmr.2025.107985","DOIUrl":"10.1016/j.jmr.2025.107985","url":null,"abstract":"<div><div>We show that the magnetic field in cryogen-free magnets is stable enough for high-resolution solid-state and liquid-state NMR. The same magnet can be used at different magnetic fields, which can be changed every day without compromising the spectral resolution. The magnet performance was demonstrated on a series of solid-state and liquid-state NMR experiments. Hardware and software correction can additionally be applied to improve the quality of 1D and 2D NMR spectra.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107985"},"PeriodicalIF":1.9,"publicationDate":"2025-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145268537","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 : 2025-10-06DOI: 10.1016/j.jmr.2025.107980
Mark Tseytlin , Oxana Tseytlin
Four-dimensional spectral–spatial imaging (4D SSI) enables noninvasive mapping of spin probes and their microenvironments. Despite its demonstrated utility, 4D SSI remains constrained by substantial computational demands, including large data volumes, the iterative nature of reconstruction algorithms, and significant requirements for memory and computational resources. These resource demands scale cubically with the size of the imaged object. To address these limitations, a set of computational strategies has been developed to improve reconstruction efficiency without compromising image fidelity. These include the use of filtered back projection (FBP) to generate an initial spin concentration map, which serves both as an initial guess for further iterations and as a mask to exclude non-signal voxels. Eliminating these empty voxels significantly reduces the problem size, thereby lowering memory usage and computation time. Additional acceleration is achieved by transforming the 4D reconstruction into a reduced 2D problem, minimizing redundant computation through precomputed values, and employing a compact look-up table for spectral fitting. The resulting workflow, implemented in MATLAB with performance-critical routines compiled as C-based MEX functions, achieves iteration times as low as one minute. Numerical phantom simulations and experimental data from physical phantoms confirm that convergence is substantially improved by excluding non-signal voxels. Among all evaluated approaches, the FBP-based masking of non-signal voxels and the use of a lookup table proved most effective in accelerating algorithm convergence. These improvements enable scalable and computationally efficient 4D SSI suitable for high-resolution, larger-animal preclinical studies and future clinical imaging applications.
{"title":"Computationally efficient 4D spectral-spatial EPR imaging","authors":"Mark Tseytlin , Oxana Tseytlin","doi":"10.1016/j.jmr.2025.107980","DOIUrl":"10.1016/j.jmr.2025.107980","url":null,"abstract":"<div><div>Four-dimensional spectral–spatial imaging (4D SSI) enables noninvasive mapping of spin probes and their microenvironments. Despite its demonstrated utility, 4D SSI remains constrained by substantial computational demands, including large data volumes, the iterative nature of reconstruction algorithms, and significant requirements for memory and computational resources. These resource demands scale cubically with the size of the imaged object. To address these limitations, a set of computational strategies has been developed to improve reconstruction efficiency without compromising image fidelity. These include the use of filtered back projection (FBP) to generate an initial spin concentration map, which serves both as an initial guess for further iterations and as a mask to exclude non-signal voxels. Eliminating these empty voxels significantly reduces the problem size, thereby lowering memory usage and computation time. Additional acceleration is achieved by transforming the 4D reconstruction into a reduced 2D problem, minimizing redundant computation through precomputed values, and employing a compact look-up table for spectral fitting. The resulting workflow, implemented in MATLAB with performance-critical routines compiled as C-based MEX functions, achieves iteration times as low as one minute. Numerical phantom simulations and experimental data from physical phantoms confirm that convergence is substantially improved by excluding non-signal voxels. Among all evaluated approaches, the FBP-based masking of non-signal voxels and the use of a lookup table proved most effective in accelerating algorithm convergence. These improvements enable scalable and computationally efficient 4D SSI suitable for high-resolution, larger-animal preclinical studies and future clinical imaging applications.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107980"},"PeriodicalIF":1.9,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145314455","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 : 2025-10-06DOI: 10.1016/j.jmr.2025.107981
George Mitrikas , Rania Giourtsidou
Dynamical decoupling methods like the Carr-Purcell-Meiboom-Gill (CPMG) or XY4- and XY8-based sequences play a key role in the measurement of reliable electron spin coherence times as they help to disentangle different sources of decoherence. Although these methods are mainly evaluated for their robustness and ability to mitigate pulse imperfections, to date little attention has been paid to the selectivity of the microwave pulses (mw), which is a factor that affects the determination of in two ways: first, unwanted stimulated echoes, which decay with , overlap with desired refocused echoes, resulting in overestimated values of . Second, under selective mw excitation, the amplitude of the different refocused echoes shows an additional time decay even in the absence of relaxation processes. Here, we investigate the characteristics of CPMG, XY4 and XY8-based sequences by performing numerical simulations for a two-level spin system. Using the Liouville space representation of the spin state, we introduce relaxation effects in the simulations. We show that our numerical calculations reproduce well all the features of the experimental echoes and allow for the accurate determination of times without the need to perform tedious phase-cycle protocols to eliminate unwanted signals.
{"title":"Measuring reliable electron spin coherence times with dynamical decoupling sequences that use selective mw pulses","authors":"George Mitrikas , Rania Giourtsidou","doi":"10.1016/j.jmr.2025.107981","DOIUrl":"10.1016/j.jmr.2025.107981","url":null,"abstract":"<div><div>Dynamical decoupling methods like the Carr-Purcell-Meiboom-Gill (CPMG) or XY4- and XY8-based sequences play a key role in the measurement of reliable electron spin coherence times as they help to disentangle different sources of decoherence. Although these methods are mainly evaluated for their robustness and ability to mitigate pulse imperfections, to date little attention has been paid to the selectivity of the microwave pulses (mw), which is a factor that affects the determination of <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> in two ways: first, unwanted stimulated echoes, which decay with <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>, overlap with desired refocused echoes, resulting in overestimated values of <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>. Second, under selective mw excitation, the amplitude of the different refocused echoes shows an additional time decay even in the absence of relaxation processes. Here, we investigate the characteristics of CPMG, XY4 and XY8-based sequences by performing numerical simulations for a two-level spin system. Using the Liouville space representation of the spin state, we introduce relaxation effects in the simulations. We show that our numerical calculations reproduce well all the features of the experimental echoes and allow for the accurate determination of <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> times without the need to perform tedious phase-cycle protocols to eliminate unwanted signals.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107981"},"PeriodicalIF":1.9,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145260335","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 : 2025-10-04DOI: 10.1016/j.jmr.2025.107972
Marco Schiavina , David Joseph , Christian Griesinger , Isabella C. Felli , Roberta Pierattelli
Carbon-13 detected Nuclear Magnetic Resonance (NMR) experiments have become a well-established and powerful tool for investigating a wide variety of biomolecular systems, offering unique insights into structure and dynamics. High field NMR spectrometers offer unprecedented resolution, particularly when working at 1.2 GHz, which is crucial in general and particularly important for samples with crowded NMR spectra. However, operating at such high fields introduces new challenges, including the need for efficient spin manipulations across broad frequency ranges while adhering to the power limitations of modern probes. Optimal control (OC) theory offers a powerful framework for designing Radio-Frequency (RF) pulses that achieve desired spin manipulations with high efficiency, even under strict experimental constraints. In this work, we focus on the implementation of OC-designed 15N pulses to enhance the performance of 13C-detected experiments at 1.2 GHz. Specifically, we demonstrate how these pulses improve both excitation bandwidth and signal sensitivity. The approach is validated using a small, well-folded protein and a more challenging intrinsically disordered protein (IDP) dissolved in a high-salt buffer as commonly required for IDPs' stability. Our results show that 15N OC pulses provide clear benefits across sample types and conditions, confirming their utility as a robust solution for bandwidth-limited NMR experiments at the highest available magnetic fields.
{"title":"15N optimal control pulses: an efficient approach to enhance heteronuclear-detected NMR experiments at high magnetic fields","authors":"Marco Schiavina , David Joseph , Christian Griesinger , Isabella C. Felli , Roberta Pierattelli","doi":"10.1016/j.jmr.2025.107972","DOIUrl":"10.1016/j.jmr.2025.107972","url":null,"abstract":"<div><div>Carbon-13 detected Nuclear Magnetic Resonance (NMR) experiments have become a well-established and powerful tool for investigating a wide variety of biomolecular systems, offering unique insights into structure and dynamics. High field NMR spectrometers offer unprecedented resolution, particularly when working at 1.2 GHz, which is crucial in general and particularly important for samples with crowded NMR spectra. However, operating at such high fields introduces new challenges, including the need for efficient spin manipulations across broad frequency ranges while adhering to the power limitations of modern probes. Optimal control (OC) theory offers a powerful framework for designing Radio-Frequency (RF) pulses that achieve desired spin manipulations with high efficiency, even under strict experimental constraints. In this work, we focus on the implementation of OC-designed <sup>15</sup>N pulses to enhance the performance of <sup>13</sup>C-detected experiments at 1.2 GHz. Specifically, we demonstrate how these pulses improve both excitation bandwidth and signal sensitivity. The approach is validated using a small, well-folded protein and a more challenging intrinsically disordered protein (IDP) dissolved in a high-salt buffer as commonly required for IDPs' stability. Our results show that <sup>15</sup>N OC pulses provide clear benefits across sample types and conditions, confirming their utility as a robust solution for bandwidth-limited NMR experiments at the highest available magnetic fields.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107972"},"PeriodicalIF":1.9,"publicationDate":"2025-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145260354","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 : 2025-09-27DOI: 10.1016/j.jmr.2025.107969
Jinhao Liu , Miutian Wang , Wenchen Wang , Yaohui Wang , Wenhui Yang , Weimin Wang , Feng Liu
This study proposes a simple and computationally efficient method to optimize the structural design parameters of passive shimming slots, aiming to improve magnetic field homogeneity in cryogen-free 3 T/200 mm superconducting magnets used across diverse application environments. The proposed method combines Latin Hypercube Sampling (LHS), utilizing over 300 sampled configurations, with a linear programming (LP)-based optimization framework to explore high-dimensional design spaces while adhering to structural constraints. The method was applied to four distinct magnets, each characterized by unique field inhomogeneity patterns resulting from manufacturing and assembly variations. Through harmonic decomposition, system-specific sensitivities were identified and effectively mitigated using customized passive shimming strategies tailored to each magnet. The optimization process achieved substantial improvements in magnetic field homogeneity, with peak-to-peak (PP) values enhanced to 12.16, 10.04, 27.28, and 54.59 parts per million (ppm) for Magnets 1 to 4, respectively. Correspondingly, the root-mean-square error (RMSE) homogeneity improved to 2.28, 1.98, 5.07, and 9.68 ppm. Furthermore, the magnitudes of all harmonic terms were reduced by 1-2 orders of magnitude, with suppression levels exceeding 90%, while minimizing the use of ferromagnetic materials. The practical feasibility of the proposed strategy was validated on-site: Magnet 1 successfully delivered high-quality animal MRI imaging with excellent signal-to-noise ratios (SNRs), and the remaining magnets are currently undergoing final calibration and delivery. This work presents a robust and scalable optimization framework for precise and resource-efficient passive shimming, offering valuable guidance for future magnet design, customization, and deployment in biomedical and industrial applications.
{"title":"Passive shimming performance in 3 T MRI systems: Influence of shim parameters under varying magnet field distributions","authors":"Jinhao Liu , Miutian Wang , Wenchen Wang , Yaohui Wang , Wenhui Yang , Weimin Wang , Feng Liu","doi":"10.1016/j.jmr.2025.107969","DOIUrl":"10.1016/j.jmr.2025.107969","url":null,"abstract":"<div><div>This study proposes a simple and computationally efficient method to optimize the structural design parameters of passive shimming slots, aiming to improve magnetic field homogeneity in cryogen-free 3 T/200 mm superconducting magnets used across diverse application environments. The proposed method combines Latin Hypercube Sampling (LHS), utilizing over 300 sampled configurations, with a linear programming (LP)-based optimization framework to explore high-dimensional design spaces while adhering to structural constraints. The method was applied to four distinct magnets, each characterized by unique field inhomogeneity patterns resulting from manufacturing and assembly variations. Through harmonic decomposition, system-specific sensitivities were identified and effectively mitigated using customized passive shimming strategies tailored to each magnet. The optimization process achieved substantial improvements in magnetic field homogeneity, with peak-to-peak (PP) values enhanced to 12.16, 10.04, 27.28, and 54.59 parts per million (ppm) for Magnets 1 to 4, respectively. Correspondingly, the root-mean-square error (RMSE) homogeneity improved to 2.28, 1.98, 5.07, and 9.68 ppm. Furthermore, the magnitudes of all harmonic terms were reduced by 1-2 orders of magnitude, with suppression levels exceeding 90%, while minimizing the use of ferromagnetic materials. The practical feasibility of the proposed strategy was validated on-site: Magnet 1 successfully delivered high-quality animal MRI imaging with excellent signal-to-noise ratios (SNRs), and the remaining magnets are currently undergoing final calibration and delivery. This work presents a robust and scalable optimization framework for precise and resource-efficient passive shimming, offering valuable guidance for future magnet design, customization, and deployment in biomedical and industrial applications.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107969"},"PeriodicalIF":1.9,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145202542","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 : 2025-09-24DOI: 10.1016/j.jmr.2025.107968
Janez Stepišnik , Aleš Mohorič
Nuclear magnetic resonance is a powerful technique for examining chemical exchange in liquids by observing how molecular structures evolve. The Carr-Purcell-Meiboom-Gill technique, one of key NMR methods, enables the detection of molecular conformation fluctuations and their influence on observed chemical shifts. This study proposes how NMR measurements of chemical exchange processes can be interpreted using a molecular conformation fluctuation spectrum framework together with chemical Langevin equations. Experimental results obtained for sucrose solutions support the proposed approach, revealing insights into chemical exchange dynamics and spectral line behavior.
{"title":"NMR of chemical exchange: Revisited","authors":"Janez Stepišnik , Aleš Mohorič","doi":"10.1016/j.jmr.2025.107968","DOIUrl":"10.1016/j.jmr.2025.107968","url":null,"abstract":"<div><div>Nuclear magnetic resonance is a powerful technique for examining chemical exchange in liquids by observing how molecular structures evolve. The Carr-Purcell-Meiboom-Gill technique, one of key NMR methods, enables the detection of molecular conformation fluctuations and their influence on observed chemical shifts. This study proposes how NMR measurements of chemical exchange processes can be interpreted using a molecular conformation fluctuation spectrum framework together with chemical Langevin equations. Experimental results obtained for sucrose solutions support the proposed approach, revealing insights into chemical exchange dynamics and spectral line behavior.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107968"},"PeriodicalIF":1.9,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156202","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 : 2025-09-22DOI: 10.1016/j.jmr.2025.107956
A. Guinness , Alec A. Beaton , John M. Franck
When developing or deploying a Nuclear Magnetic Resonance (NMR) spectrometer, especially for Overhauser Dynamic Nuclear Polarization (ODNP) or other experiments that require low-volume low-field measurements, the ability to mitigate noise and to quantitatively predict signal amplitude prove crucial. A quantitative treatment allows separate analysis of signal and noise and independent optimization of each. In particular, the results here emphasize that clarity and insight come from (1) characterizing the spectral distribution of the noise, and (2) integrating elements of theory and notation originally developed for Electron Spin Resonance (ESR) spectroscopy. Specifically, the spectral noise density “fingerprint spectrum” identifies sources of electromagnetic interference (EMI) and definitively confirms which actions do and do not mitigate the EMI, while the quantitative ratio () of to the square root of the power on the transmission line provides a useful focal point that simplifies the prediction of signal intensity and that decomposes into a few simple but exact factors. Thus, this article provides a relatively comprehensive overview of signal and noise in low-field NMR instruments. The protocol/toolkit introduced here should apply to a wide range of instruments, and give most spectroscopists the freedom to systematically design sensitive NMR hardware even in cases where it must be integrated with multiple other hardware modules (e.g., an existing ESR system), or where other requirements constrain the design of the NMR hardware. It enables a systematic approach to instrument design and optimization. For the specific X-band ODNP design demonstrated here (and utilized in other laboratories), it facilitates a reduction of the noise power by more than an order of magnitude, and accurately predicts the signal amplitude from measurements of the nutation frequency. Finally, it introduces reasoning to exactly determine the field distribution factor (, essentially, a more specific definition of the filling factor) experimentally from and thus identifies the inefficient distribution of fields in the hairpin loop probe as the main remaining bottleneck for the improvement of low-field, low-volume ODNP signal-to-noise ratio (SNR).
{"title":"Separate and detailed characterization of signal and noise at low resonance frequencies","authors":"A. Guinness , Alec A. Beaton , John M. Franck","doi":"10.1016/j.jmr.2025.107956","DOIUrl":"10.1016/j.jmr.2025.107956","url":null,"abstract":"<div><div>When developing or deploying a Nuclear Magnetic Resonance (NMR) spectrometer, especially for Overhauser Dynamic Nuclear Polarization (ODNP) or other experiments that require low-volume low-field measurements, the ability to mitigate noise and to quantitatively predict signal amplitude prove crucial. A quantitative treatment allows separate analysis of signal and noise and independent optimization of each. In particular, the results here emphasize that clarity and insight come from (1) characterizing the spectral distribution of the noise, and (2) integrating elements of theory and notation originally developed for Electron Spin Resonance (ESR) spectroscopy. Specifically, the spectral noise density “fingerprint spectrum” identifies sources of electromagnetic interference (EMI) and definitively confirms which actions do and do not mitigate the EMI, while the quantitative ratio (<span><math><mi>Λ</mi></math></span>) of <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> to the square root of the power on the transmission line provides a useful focal point that simplifies the prediction of signal intensity and that decomposes into a few simple but exact factors. Thus, this article provides a relatively comprehensive overview of signal and noise in low-field NMR instruments. The protocol/toolkit introduced here should apply to a wide range of instruments, and give most spectroscopists the freedom to systematically design sensitive NMR hardware even in cases where it must be integrated with multiple other hardware modules (<em>e.g.</em>, an existing ESR system), or where other requirements constrain the design of the NMR hardware. It enables a systematic approach to instrument design and optimization. For the specific X-band ODNP design demonstrated here (and utilized in other laboratories), it facilitates a reduction of the noise power by more than an order of magnitude, and accurately predicts the signal amplitude from measurements of the nutation frequency. Finally, it introduces reasoning to exactly determine the field distribution factor (<span><math><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>, essentially, a more specific definition of the filling factor) experimentally from <span><math><mi>Λ</mi></math></span> and thus identifies the inefficient distribution of fields in the hairpin loop probe as the main remaining bottleneck for the improvement of low-field, low-volume ODNP signal-to-noise ratio (SNR).</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107956"},"PeriodicalIF":1.9,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120051","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 : 2025-09-13DOI: 10.1016/j.jmr.2025.107967
Shengyu Zhang , Jhinuk Saha , Yuchen Li , Xinhua Peng , Ryan P. McGlinchey , Ayyalusamy Ramamoorthy , Riqiang Fu
Previous experimental strategies aimed at completely suppressing diagonal peaks in NMR homonuclear correlation spectra often resulted in reduced sensitivity for cross peaks. In this work, we report a spectral shearing approach that transforms diagonal peaks along the diagonal axis of a homonuclear correlation spectrum into a zero-frequency line in the indirect dimension. This allows for effective extraction and substantial suppression of diagonal peaks using a recently proposed data processing algorithm based on quadrature-detected spin-echo diagonal peak suppression. Since the shearing process only rearranges the positions of cross peaks without affecting their intensities, the sensitivity of cross peaks is fully preserved while diagonal peaks are significantly reduced. The effectiveness of this method is demonstrated using uniformly 13C,15N labeled α-synuclein amyloid fibrils and aquaporin Z membrane protein samples.
{"title":"A simple algorithm to suppress diagonal peaks in high-resolution homonuclear chemical shift correlation NMR spectra","authors":"Shengyu Zhang , Jhinuk Saha , Yuchen Li , Xinhua Peng , Ryan P. McGlinchey , Ayyalusamy Ramamoorthy , Riqiang Fu","doi":"10.1016/j.jmr.2025.107967","DOIUrl":"10.1016/j.jmr.2025.107967","url":null,"abstract":"<div><div>Previous experimental strategies aimed at completely suppressing diagonal peaks in NMR homonuclear correlation spectra often resulted in reduced sensitivity for cross peaks. In this work, we report a spectral shearing approach that transforms diagonal peaks along the diagonal axis of a homonuclear correlation spectrum into a zero-frequency line in the indirect dimension. This allows for effective extraction and substantial suppression of diagonal peaks using a recently proposed data processing algorithm based on quadrature-detected spin-echo diagonal peak suppression. Since the shearing process only rearranges the positions of cross peaks without affecting their intensities, the sensitivity of cross peaks is fully preserved while diagonal peaks are significantly reduced. The effectiveness of this method is demonstrated using uniformly <sup>13</sup>C,<sup>15</sup>N labeled α-synuclein amyloid fibrils and aquaporin Z membrane protein samples.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107967"},"PeriodicalIF":1.9,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145093324","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}
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