Pub Date : 2025-08-05DOI: 10.1016/j.ssnmr.2025.102030
N. Vaisleib , M. Arbel-Haddad , A. Goldbourt
Geopolymers are aluminosilicate materials that exhibit effective immobilization properties for low-level radioactive nuclear waste, and more specifically for the immobilization of radioactive cesium. The identification of the cesium-binding sites and their distribution between the different phases making up the geopolymeric matrix can be obtained using solid-state NMR measurements of the quadrupolar spin 133Cs, which is a surrogate for the radioactive cesium species present in nuclear waste streams. For quadrupolar nuclei, acquiring two-dimensional multiple-quantum experiments allows the acquisition of more dispersed spectra when multiple sites overlap. However, 133Cs has a spin-7/2 and one of the smallest quadrupole moments, making multiple-quantum excitation highly challenging. In this work we present pulse schemes that enhance the excitation efficiency of 133Cs triple quantum coherences by a factor of ∼2 with respect to a two-pulse excitation scheme. The improved schemes were developed by using numerical simulation and verified experimentally by applying one and two-dimensional triple-quantum solid-state NMR experiments to a mixture of cesium-exchanged hydrated zeolites A and X, which possess dynamically averaged small quadrupolar coupling constants in the order of 10 kHz.
{"title":"Enhanced 133Cs triple-quantum excitation in solid-state NMR of Cs-bearing zeolites","authors":"N. Vaisleib , M. Arbel-Haddad , A. Goldbourt","doi":"10.1016/j.ssnmr.2025.102030","DOIUrl":"10.1016/j.ssnmr.2025.102030","url":null,"abstract":"<div><div>Geopolymers are aluminosilicate materials that exhibit effective immobilization properties for low-level radioactive nuclear waste, and more specifically for the immobilization of radioactive cesium. The identification of the cesium-binding sites and their distribution between the different phases making up the geopolymeric matrix can be obtained using solid-state NMR measurements of the quadrupolar spin <sup>133</sup>Cs, which is a surrogate for the radioactive cesium species present in nuclear waste streams. For quadrupolar nuclei, acquiring two-dimensional multiple-quantum experiments allows the acquisition of more dispersed spectra when multiple sites overlap. However, <sup>133</sup>Cs has a spin-7/2 and one of the smallest quadrupole moments, making multiple-quantum excitation highly challenging. In this work we present pulse schemes that enhance the excitation efficiency of <sup>133</sup>Cs triple quantum coherences by a factor of ∼2 with respect to a two-pulse excitation scheme. The improved schemes were developed by using numerical simulation and verified experimentally by applying one and two-dimensional triple-quantum solid-state NMR experiments to a mixture of cesium-exchanged hydrated zeolites A and X, which possess dynamically averaged small quadrupolar coupling constants in the order of 10 kHz.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"140 ","pages":"Article 102030"},"PeriodicalIF":2.4,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020586","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 : 2025-07-16DOI: 10.1016/j.ssnmr.2025.102028
Sara Andrés-Campos , Gustavo A. Titaux-Delgado , Fátima C. Escobedo-González, Miguel Mompeán
Solid-state NMR (SSNMR) of biomolecules typically requires several milligrams of sample to achieve sufficient sensitivity for multidimensional experiments, especially when relying on 13C detection. Recent developments in fast magic-angle spinning (MAS) and 1H-detected methods have enabled the use of submilligram samples in reduced-diameter rotors, but these approaches demand advanced hardware and often suffer from limited 1H chemical shift dispersion. Here, we demonstrate that a CPMAS CryoProbe enables the acquisition of high-quality 13C-detected 2D and 3D spectra from just ∼1.5 mg of uniformly labeled amyloid fibrils packed in a standard 3.2 mm rotor. As a proof of concept, we apply this approach to RIPK3, a key protein in immune signaling that forms functional amyloid assemblies. Using standard 3D experiments (NCACX and NCOCX), we obtain 13C and 15N backbone assignments and secondary structure information, despite the limited sample quantity and the use of only moderate magnetic fields. These findings highlight the potential of CPMAS CryoProbes to shift the paradigm in mass-limited SSNMR studies, from relying exclusively on 1H-detection and fast MAS to reembracing 13C-detected strategies.
{"title":"High-quality 13C-detected structural analysis of mass-limited amyloid samples using a CPMAS CryoProbe and moderate magnetic fields","authors":"Sara Andrés-Campos , Gustavo A. Titaux-Delgado , Fátima C. Escobedo-González, Miguel Mompeán","doi":"10.1016/j.ssnmr.2025.102028","DOIUrl":"10.1016/j.ssnmr.2025.102028","url":null,"abstract":"<div><div>Solid-state NMR (SSNMR) of biomolecules typically requires several milligrams of sample to achieve sufficient sensitivity for multidimensional experiments, especially when relying on <sup>13</sup>C detection. Recent developments in fast magic-angle spinning (MAS) and <sup>1</sup>H-detected methods have enabled the use of submilligram samples in reduced-diameter rotors, but these approaches demand advanced hardware and often suffer from limited <sup>1</sup>H chemical shift dispersion. Here, we demonstrate that a CPMAS CryoProbe enables the acquisition of high-quality <sup>13</sup>C-detected 2D and 3D spectra from just ∼1.5 mg of uniformly labeled amyloid fibrils packed in a standard 3.2 mm rotor. As a proof of concept, we apply this approach to RIPK3, a key protein in immune signaling that forms functional amyloid assemblies. Using standard 3D experiments (NCACX and NCOCX), we obtain <sup>13</sup>C and <sup>15</sup>N backbone assignments and secondary structure information, despite the limited sample quantity and the use of only moderate magnetic fields. These findings highlight the potential of CPMAS CryoProbes to shift the paradigm in mass-limited SSNMR studies, from relying exclusively on <sup>1</sup>H-detection and fast MAS to reembracing <sup>13</sup>C-detected strategies.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"139 ","pages":"Article 102028"},"PeriodicalIF":1.8,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144656609","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 : 2025-07-11DOI: 10.1016/j.ssnmr.2025.102020
Austin Peach , Nicolas Fabregue , David Gajan , Frédéric Mentink-Vigier , Faith Scott , Christel Gervais , Danielle Laurencin
The importance of (bi)carbonate salts cannot be understated. They are vital to the Earth's geology and ecosystems and are used as precursors by chemists for the synthesis of functional materials. Naturally, solid-state NMR (ssNMR) appears as the spectroscopic tool of choice to probe the atomic-level structure and dynamics of (bi)carbonate salts. Of the possible nuclei available as spectroscopic probes in carbonate and bicarbonate ions (i.e., 1H, 13C, and 17O), oxygen-17 is highly attractive. Yet, it is seldom employed, largely due to its low natural abundance (0.04 %) and lack of practical enrichment protocols. Recently, we reported an effective 17O-labeling strategy involving mechanochemistry of Na2CO3·H2O, Na2CO3, NaHCO3, K2CO3·1.5H2O, and KHCO3, and recorded their 17O NMR spectral fingerprints near room temperature. In this work, ultra-low temperature (i.e., 100 K) 17O ssNMR spectra of these phases are acquired at two magnetic fields, 14.1 and 18.8 T, to extract the 17O NMR parameters δiso, CQ, and ηQ for the different oxygen sites, and to further study the influence of dynamics on the spectra. We compare the experimental 17O NMR parameters to those computed with GIPAW-DFT calculations both on static models, and after averaging by molecular dynamics (MD) simulations. This approach was taken to aid in analyzing the structure-spectra relationships and shed light on the dynamics. Lastly, we report the static GIPAW-DFT calculations of 17O NMR parameters for a series of other carbonate salts of interest, further expanding upon current experimental 17O ssNMR results.
{"title":"Experimental and computational 17O solid-state NMR investigation of Na- and K-(bi)carbonate salts","authors":"Austin Peach , Nicolas Fabregue , David Gajan , Frédéric Mentink-Vigier , Faith Scott , Christel Gervais , Danielle Laurencin","doi":"10.1016/j.ssnmr.2025.102020","DOIUrl":"10.1016/j.ssnmr.2025.102020","url":null,"abstract":"<div><div>The importance of (bi)carbonate salts cannot be understated. They are vital to the Earth's geology and ecosystems and are used as precursors by chemists for the synthesis of functional materials. Naturally, solid-state NMR (ssNMR) appears as the spectroscopic tool of choice to probe the atomic-level structure and dynamics of (bi)carbonate salts. Of the possible nuclei available as spectroscopic probes in carbonate and bicarbonate ions (<em>i.e.</em>, <sup>1</sup>H, <sup>13</sup>C, and <sup>17</sup>O), oxygen-17 is highly attractive. Yet, it is seldom employed, largely due to its low natural abundance (0.04 %) and lack of practical enrichment protocols. Recently, we reported an effective <sup>17</sup>O-labeling strategy involving mechanochemistry of Na<sub>2</sub>CO<sub>3</sub>·H<sub>2</sub>O, Na<sub>2</sub>CO<sub>3</sub>, NaHCO<sub>3</sub>, K<sub>2</sub>CO<sub>3</sub>·1.5H<sub>2</sub>O, and KHCO<sub>3</sub>, and recorded their <sup>17</sup>O NMR spectral fingerprints near room temperature. In this work, ultra-low temperature (<em>i.e.</em>, 100 K) <sup>17</sup>O ssNMR spectra of these phases are acquired at two magnetic fields, 14.1 and 18.8 T, to extract the <sup>17</sup>O NMR parameters <em>δ</em><sub>iso</sub>, <em>C</em><sub>Q</sub>, and η<sub>Q</sub> for the different oxygen sites, and to further study the influence of dynamics on the spectra. We compare the experimental <sup>17</sup>O NMR parameters to those computed with GIPAW-DFT calculations both on static models, and after averaging by molecular dynamics (MD) simulations. This approach was taken to aid in analyzing the structure-spectra relationships and shed light on the dynamics. Lastly, we report the static GIPAW-DFT calculations of <sup>17</sup>O NMR parameters for a series of other carbonate salts of interest, further expanding upon current experimental <sup>17</sup>O ssNMR results.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"139 ","pages":"Article 102020"},"PeriodicalIF":2.4,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621830","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 : 2025-06-26DOI: 10.1016/j.ssnmr.2025.102019
Ema Chaloupecká , Ondřej Socha , Martin Dračínský
Accurate prediction of NMR parameters from first principles is essential for the structural characterization of molecular solids. Recent studies have shown that single-molecule correction schemes—based on hybrid DFT calculations—can significantly improve the accuracy of periodic DFT predictions of nuclear shieldings. Here, we evaluate the performance of this correction approach not only for periodic DFT calculations but also for ShiftML2, a machine-learning model trained on PBE-calculated NMR data. For 13C nuclei, the application of single-molecule PBE0 corrections to periodic PBE shieldings has reduced the root-mean-square deviation (RMSD) from 2.18 to 1.20 ppm, with negligible improvement observed for 1H. When applied to ShiftML2 predictions, the corrections have yielded a smaller reduction in 13C RMSD (from 3.02 to 2.51 ppm); again, they have had minimal impact on 1H predictions. Residual analysis has revealed weak correlation between DFT and ML errors, suggesting that while some sources of systematic deviation may be shared, others are likely distinct. These results demonstrate that DFT-specific correction schemes do not straightforwardly translate to machine-learning models, highlighting the need for ML-tailored post-processing or retraining strategies. The findings have important implications for the integration of machine learning into high-throughput NMR workflows and the development of more accurate predictive tools for solid-state spectroscopy.
{"title":"Diverging errors: A comparison of DFT and machine-learning predictions of NMR shieldings","authors":"Ema Chaloupecká , Ondřej Socha , Martin Dračínský","doi":"10.1016/j.ssnmr.2025.102019","DOIUrl":"10.1016/j.ssnmr.2025.102019","url":null,"abstract":"<div><div>Accurate prediction of NMR parameters from first principles is essential for the structural characterization of molecular solids. Recent studies have shown that single-molecule correction schemes—based on hybrid DFT calculations—can significantly improve the accuracy of periodic DFT predictions of nuclear shieldings. Here, we evaluate the performance of this correction approach not only for periodic DFT calculations but also for ShiftML2, a machine-learning model trained on PBE-calculated NMR data. For <sup>13</sup>C nuclei, the application of single-molecule PBE0 corrections to periodic PBE shieldings has reduced the root-mean-square deviation (RMSD) from 2.18 to 1.20 ppm, with negligible improvement observed for <sup>1</sup>H. When applied to ShiftML2 predictions, the corrections have yielded a smaller reduction in <sup>13</sup>C RMSD (from 3.02 to 2.51 ppm); again, they have had minimal impact on <sup>1</sup>H predictions. Residual analysis has revealed weak correlation between DFT and ML errors, suggesting that while some sources of systematic deviation may be shared, others are likely distinct. These results demonstrate that DFT-specific correction schemes do not straightforwardly translate to machine-learning models, highlighting the need for ML-tailored post-processing or retraining strategies. The findings have important implications for the integration of machine learning into high-throughput NMR workflows and the development of more accurate predictive tools for solid-state spectroscopy.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"138 ","pages":"Article 102019"},"PeriodicalIF":1.8,"publicationDate":"2025-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144514240","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 : 2025-06-20DOI: 10.1016/j.ssnmr.2025.102018
Riley Nickles , Emily C. Heider , James K. Harper
A necessary step in characterizing solid-phase organic materials is the accurate assignment of the ionization state at acidic and basic sites. Solution phase pKa's are not always reliable reference points because local environments can significantly change pKa values in solids. Herein, an approach for distinguishing R–NH2 and R–NH3+ is described based on experimental 15N chemical shift tensors principal values for a given site (i.e. δ11, δ22 and δ33) from 18 model compounds. Those 15N sites that are present as R–NH3+ have anisotropies between 5 and 15 ppm. In contrast, all R–NH2 sites have anisotropies between 14 and 115 ppm. These R–NH2 moieties can be further categorized into three subgroups. The differences observed are postulated to arise from differences in the symmetry of the intermolecular hydrogen bonding environment, or the direct attachment of the NH2 to an aromatic ring.
{"title":"A solid-state NMR approach for distinguishing between RNH2 and RNH3+ sites","authors":"Riley Nickles , Emily C. Heider , James K. Harper","doi":"10.1016/j.ssnmr.2025.102018","DOIUrl":"10.1016/j.ssnmr.2025.102018","url":null,"abstract":"<div><div>A necessary step in characterizing solid-phase organic materials is the accurate assignment of the ionization state at acidic and basic sites. Solution phase pK<sub>a</sub>'s are not always reliable reference points because local environments can significantly change pK<sub>a</sub> values in solids. Herein, an approach for distinguishing R–NH<sub>2</sub> and R–NH<sub>3</sub><sup>+</sup> is described based on experimental <sup>15</sup>N chemical shift tensors principal values for a given site (i.e. <em>δ</em><sub>11</sub>, <em>δ</em><sub>22</sub> and <em>δ</em><sub>33</sub>) from 18 model compounds. Those <sup>15</sup>N sites that are present as R–NH<sub>3</sub><sup>+</sup> have anisotropies between 5 and 15 ppm. In contrast, all R–NH<sub>2</sub> sites have anisotropies between 14 and 115 ppm. These R–NH<sub>2</sub> moieties can be further categorized into three subgroups. The differences observed are postulated to arise from differences in the symmetry of the intermolecular hydrogen bonding environment, or the direct attachment of the NH<sub>2</sub> to an aromatic ring.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"138 ","pages":"Article 102018"},"PeriodicalIF":1.8,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335597","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 : 2025-06-04DOI: 10.1016/j.ssnmr.2025.102017
Jérôme Hirschinger
A simple method proposed in an insightful paper by A. J. Vega [J. Magn. Reson. 65 (1985) 252–267] is applied for calculating the effects of chemical exchange on magic-angle spinning (MAS) NMR spectra in the case of a two-site rotational jump motion. This approach which only requires two basic expressions of for the limiting cases of fast and slow exchange is compared with exact numerical calculations for arbitrary rates of motion and spinning frequencies. This comparison justifies the application of relaxation theory (RT) to calculate fast-exchange lineshapes but the slow-exchange time constant originally derived by A. Schmidt and S. Vega [J. Chem. Phys. 87 (1987) 6895–6907] using Floquet-perturbation theory (FPT) fails to account for the differences in the spinning sideband linewidths. In this paper, the complete FPT (cFPT) expression of the MAS spectrum is shown to account for all details of differential sideband broadening observed in the slow-exchange regime. Moreover, the RT and cFPT solutions give insight into the effects of molecular dynamics on the MAS spectra and decrease dramatically the computation time. The calculation procedure using the RT and cFPT formulas yield lineshape simulations that are in very good agreement with exact numerical results except in the intermediate-exchange regime when the sideband linewidths become comparable with or larger than the MAS rate. This is a minor drawback in practice as fast relaxation then makes quantitative measurements difficult.
A. J. Vega在一篇颇有见地的论文中提出了一种简单的方法[J]。粉剂。在两个位置旋转跳跃运动的情况下，应用reason . 65(1985) 252-267]计算化学交换对魔角旋转（MAS）核磁共振谱的影响。对于快慢交换的极限情况，这种方法只需要T2的两个基本表达式，并与任意运动速率和旋转频率的精确数值计算进行了比较。这一比较证明了弛豫理论（RT）在计算快速交换线形时的应用，而最初由A. Schmidt和S. Vega导出的慢交换T2时间常数的应用是正确的。化学。物理学报87(1987)6895-6907]使用的floquet -摄动理论（FPT）不能解释旋转边带线宽的差异。在本文中，完整的FPT （cFPT）表达的MAS频谱被证明可以解释在慢交换制度中观察到的微分边带展宽的所有细节。此外，RT和cFPT解决方案可以深入了解分子动力学对MAS光谱的影响，并显着减少了计算时间。使用RT和cFPT公式的计算过程产生的线形模拟与精确的数值结果非常吻合，除非在中间交换制度中，边带线宽与MAS速率相当或大于MAS速率。这在实践中是一个小缺点，因为快速松弛会使定量测量变得困难。
{"title":"A simple formulation of dynamic magic-angle spinning NMR derived from relaxation and Floquet theories","authors":"Jérôme Hirschinger","doi":"10.1016/j.ssnmr.2025.102017","DOIUrl":"10.1016/j.ssnmr.2025.102017","url":null,"abstract":"<div><div>A simple method proposed in an insightful paper by A. J. Vega [J. Magn. Reson. 65 (1985) 252–267] is applied for calculating the effects of chemical exchange on magic-angle spinning (MAS) NMR spectra in the case of a two-site rotational jump motion. This approach which only requires two basic expressions of <span><math><mrow><msub><mi>T</mi><mn>2</mn></msub></mrow></math></span> for the limiting cases of fast and slow exchange is compared with exact numerical calculations for arbitrary rates of motion and spinning frequencies. This comparison justifies the application of relaxation theory (RT) to calculate fast-exchange lineshapes but the slow-exchange <span><math><mrow><msub><mi>T</mi><mn>2</mn></msub></mrow></math></span> time constant originally derived by A. Schmidt and S. Vega [J. Chem. Phys. 87 (1987) 6895–6907] using Floquet-perturbation theory (FPT) fails to account for the differences in the spinning sideband linewidths. In this paper, the complete FPT (cFPT) expression of the MAS spectrum is shown to account for all details of differential sideband broadening observed in the slow-exchange regime. Moreover, the RT and cFPT solutions give insight into the effects of molecular dynamics on the MAS spectra and decrease dramatically the computation time. The calculation procedure using the RT and cFPT formulas yield lineshape simulations that are in very good agreement with exact numerical results except in the intermediate-exchange regime when the sideband linewidths become comparable with or larger than the MAS rate. This is a minor drawback in practice as fast relaxation then makes quantitative measurements difficult.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"138 ","pages":"Article 102017"},"PeriodicalIF":1.8,"publicationDate":"2025-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144307767","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 : 2025-06-03DOI: 10.1016/j.ssnmr.2025.102014
Alireza Nari, Patrick M.J. Szell, David L. Bryce
Quadrupolar-perturbed solid-state NMR spectroscopy is a highly useful and well-established method for studying quadrupolar nuclei. This method relies on a high ratio of the Larmor frequency to the quadrupolar frequency and is limited, therefore, by the available magnetic field strengths suitable for NMR, which are on the order of 101 T. Nuclear quadrupole resonance (NQR) provides an approach to studying strongly quadrupolar isotopes, but there are technical challenges associated with measuring high-frequency transitions, and with measuring both the quadrupolar coupling constant, CQ, and asymmetry parameter, η, with good precision. We describe here the technical and practical aspects of a modern implementation of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet, which overcomes the aforementioned challenges. This approach flips the quadrupolar-perturbed solid-state NMR method upside down, so that the quadrupolar interaction is dominant and the Zeeman interaction is the perturbation. 79Br and 127I Zeeman-perturbed NQR spectra are recorded for some solid bromo- and iodobenzene powders using applied magnetic fields on the order of 10−2 T. Various experimental considerations are discussed, including the optimal magnetic field to be used, the optimization of the coil angle, frequency stepping, the simulation of spectra using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian, and how to ensure high precision in the resulting quadrupolar parameters. As an example, a CQ(127) value of 2077.25 ± 1.49 MHz (with η = 0.114 ± 0.008) is measured for sym-triiodotrifluorobenzene in less than an hour at room temperature. The approach holds promise for studying strongly quadrupolar isotopes in a range of materials and obviates the need for ultrahigh magnetic fields in many situations of interest.
{"title":"Practical aspects of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet","authors":"Alireza Nari, Patrick M.J. Szell, David L. Bryce","doi":"10.1016/j.ssnmr.2025.102014","DOIUrl":"10.1016/j.ssnmr.2025.102014","url":null,"abstract":"<div><div>Quadrupolar-perturbed solid-state NMR spectroscopy is a highly useful and well-established method for studying quadrupolar nuclei. This method relies on a high ratio of the Larmor frequency to the quadrupolar frequency and is limited, therefore, by the available magnetic field strengths suitable for NMR, which are on the order of 10<sup>1</sup> T. Nuclear quadrupole resonance (NQR) provides an approach to studying strongly quadrupolar isotopes, but there are technical challenges associated with measuring high-frequency transitions, and with measuring both the quadrupolar coupling constant, <em>C</em><sub>Q</sub>, and asymmetry parameter, <em>η</em>, with good precision. We describe here the technical and practical aspects of a modern implementation of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet, which overcomes the aforementioned challenges. This approach flips the quadrupolar-perturbed solid-state NMR method upside down, so that the quadrupolar interaction is dominant and the Zeeman interaction is the perturbation. <sup>79</sup>Br and <sup>127</sup>I Zeeman-perturbed NQR spectra are recorded for some solid bromo- and iodobenzene powders using applied magnetic fields on the order of 10<sup>−2</sup> T. Various experimental considerations are discussed, including the optimal magnetic field to be used, the optimization of the coil angle, frequency stepping, the simulation of spectra using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian, and how to ensure high precision in the resulting quadrupolar parameters. As an example, a <em>C</em><sub>Q</sub>(<sup>127</sup>) value of 2077.25 ± 1.49 MHz (with <em>η</em> = 0.114 ± 0.008) is measured for <em>sym</em>-triiodotrifluorobenzene in less than an hour at room temperature. The approach holds promise for studying strongly quadrupolar isotopes in a range of materials and obviates the need for ultrahigh magnetic fields in many situations of interest.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"138 ","pages":"Article 102014"},"PeriodicalIF":1.8,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144279234","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 : 2025-05-13DOI: 10.1016/j.ssnmr.2025.102006
Ekta Nehra , Vipin Agarwal , Yusuke Nishiyama
Higher isotropic resolution in solids is essential for accurate assignment of the chemical shifts in multisite chemical and biological systems; consequently, the pursuit of solution-like resolution in solid samples remains an ongoing challenge. MAS provides the effective averaging of the anisotropic interactions to the first-order while the higher order interactions, such as residual dipolar splitting (RDS), and isotropic interactions like J coupling remain. With the emergence of faster MAS, RDS and J couplings become significant constraints in the resolution and sensitivity of isotropic 1H peaks bonded to 14N. However, the dominant quadrupolar coupling hampers the decoupling of 1H-14N, since the achievable 14N RF-field strength is much smaller than the size of the quadrupolar coupling. Therefore, 14N edited spectroscopy is typically performed in the absence of 14N decoupling, leading to broader 1H linewidth and reduced sensitivity. In this context, we propose the continuous-wave (CW) 14N decoupling of 14N-1H spin pair under 1H detection at a fast MAS of 70 kHz. We experimentally show that the on-resonance low-power 14N CW irradiation at fast MAS yields the narrower linewidth. Utilizing the quadrupolar jolting frame description, a qualitative analysis of the optimum decoupling effect is provided.
{"title":"Low-power 14N decoupling at fast MAS of 70 kHz","authors":"Ekta Nehra , Vipin Agarwal , Yusuke Nishiyama","doi":"10.1016/j.ssnmr.2025.102006","DOIUrl":"10.1016/j.ssnmr.2025.102006","url":null,"abstract":"<div><div>Higher isotropic resolution in solids is essential for accurate assignment of the chemical shifts in multisite chemical and biological systems; consequently, the pursuit of solution-like resolution in solid samples remains an ongoing challenge. MAS provides the effective averaging of the anisotropic interactions to the first-order while the higher order interactions, such as residual dipolar splitting (RDS), and isotropic interactions like J coupling remain. With the emergence of faster MAS, RDS and J couplings become significant constraints in the resolution and sensitivity of isotropic <sup>1</sup>H peaks bonded to <sup>14</sup>N. However, the dominant quadrupolar coupling hampers the decoupling of <sup>1</sup>H-<sup>14</sup>N, since the achievable <sup>14</sup>N RF-field strength is much smaller than the size of the quadrupolar coupling. Therefore, <sup>14</sup>N edited spectroscopy is typically performed in the absence of <sup>14</sup>N decoupling, leading to broader <sup>1</sup>H linewidth and reduced sensitivity. In this context, we propose the continuous-wave (CW) <sup>14</sup>N decoupling of <sup>14</sup>N-<sup>1</sup>H spin pair under <sup>1</sup>H detection at a fast MAS of 70 kHz. We experimentally show that the on-resonance low-power <sup>14</sup>N CW irradiation at fast MAS yields the narrower linewidth. Utilizing the quadrupolar jolting frame description, a qualitative analysis of the optimum decoupling effect is provided.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"137 ","pages":"Article 102006"},"PeriodicalIF":1.8,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144089173","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 : 2025-04-25DOI: 10.1016/j.ssnmr.2025.102005
Renny Mathew , Jagriti Gupta , M.D. Devadarsan , Sagar Mavi , Mohammed Jasil , Jerry A. Fereiro , Benesh Joseph , Keshaba N. Parida , Brijith Thomas
Nuclear magnetic resonance (NMR) spectroscopy is an important technique for molecular structure determination but is inherently limited by its low sensitivity. Recently, the Dynamic nuclear polarization (DNP) technique has emerged as a solution to overcome the intrinsic low sensitivity of NMR spectroscopy by transferring polarization from the unpaired electron spins to nuclear spins under microwave irradiation, achieving a theoretical sensitivity enhancement of up to 658-fold for the detection of 1H. In this study, we report the synthesis and characterization of a series of TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl)-based radicals functionalized with a thioanisole scaffold, designed to facilitate self-assembled monolayers on gold surfaces. The radicals were investigated using electron paramagnetic resonance (EPR) and DNP NMR spectroscopy. These radicals demonstrated properties consistent with the standard TEMPO while maintaining stability and functionality. At 10 mM concentration in TCE (1,1,2,2-tetrachloroethane), Radical-Imine-1 yielded a DNP enhancement factor of 3.2 for 1H nuclei and that of standard TEMPO is around 2.8 at 14.1 T. Relaxation measurements revealed that longitudinal relaxation times (T1) decreased with radical concentration, while transverse relaxation times (T2) remain largely unaffected, indicating minimal perturbation from paramagnetic quenching. The structural stability and surface-binding potential of the methyl thiol group make these derivatives suitable for surface-based DNP applications.
{"title":"Dynamic nuclear polarization of TEMPO radical cross conjugated with a thioanisole scaffold","authors":"Renny Mathew , Jagriti Gupta , M.D. Devadarsan , Sagar Mavi , Mohammed Jasil , Jerry A. Fereiro , Benesh Joseph , Keshaba N. Parida , Brijith Thomas","doi":"10.1016/j.ssnmr.2025.102005","DOIUrl":"10.1016/j.ssnmr.2025.102005","url":null,"abstract":"<div><div>Nuclear magnetic resonance (NMR) spectroscopy is an important technique for molecular structure determination but is inherently limited by its low sensitivity. Recently, the Dynamic nuclear polarization (DNP) technique has emerged as a solution to overcome the intrinsic low sensitivity of NMR spectroscopy by transferring polarization from the unpaired electron spins to nuclear spins under microwave irradiation, achieving a theoretical sensitivity enhancement of up to 658-fold for the detection of <sup>1</sup>H. In this study, we report the synthesis and characterization of a series of TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl)-based radicals functionalized with a thioanisole scaffold, designed to facilitate self-assembled monolayers on gold surfaces. The radicals were investigated using electron paramagnetic resonance (EPR) and DNP NMR spectroscopy. These radicals demonstrated properties consistent with the standard TEMPO while maintaining stability and functionality. At 10 mM concentration in TCE (1,1,2,2-tetrachloroethane), Radical-Imine-1 yielded a DNP enhancement factor of 3.2 for <sup>1</sup>H nuclei and that of standard TEMPO is around 2.8 at 14.1 T. Relaxation measurements revealed that longitudinal relaxation times (T<sub>1</sub>) decreased with radical concentration, while transverse relaxation times (T<sub>2</sub>) remain largely unaffected, indicating minimal perturbation from paramagnetic quenching. The structural stability and surface-binding potential of the methyl thiol group make these derivatives suitable for surface-based DNP applications.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"137 ","pages":"Article 102005"},"PeriodicalIF":1.8,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143894297","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 : 2025-04-15DOI: 10.1016/j.ssnmr.2025.102004
Yizhe Dai , Ivan Hung , Zhehong Gan , Gang Wu
We report utilization of transverse relaxation rate (R2) of 17O (I = 5/2) satellite transitions (STs) as a probe of molecular dynamics in solids. A simple theoretical model using spectral density functions is proposed to describe the general R2 behaviors of half-integer quadrupolar nuclei in solids in the presence of molecular motion (or chemical exchange). Experimental 17O R2 data recorded for both CT and ST from 17O-labeled NaNO2 over a large temperature range are used to verify the theoretical predictions. Our theoretical model is shown to be fully consistent with a full quantum mechanical treatment of the chemical exchange problem involving half-integer quadrupolar nuclei in solids by numerically solving the Liouville-von Neumann equation. The new 17O ST R2 method was also applied to study the carboxylate flipping motion in two [17O]carboxylic acid-pyridine adducts in the solid state. The advantages of the ST R2 approach are discussed. This ST R2 approach adds a new dimension to the currently available CT-based solid-state NMR techniques for probing molecular motion in solids.
我们报道了利用17O （I = 5/2）卫星跃迁（STs）的横向弛豫率（R2）作为固体分子动力学的探针。提出了一种简单的理论模型，利用谱密度函数来描述固体中存在分子运动（或化学交换）的半整数四极核的一般R2行为。实验用17O标记的NaNO2在大温度范围内记录的CT和ST的17O R2数据用于验证理论预测。通过数值求解Liouville-von Neumann方程，我们的理论模型与固体中涉及半整数四极核的化学交换问题的全量子力学处理完全一致。采用新的17O ST R2方法研究了两种[17O]羧酸-吡啶加合物在固体状态下的羧酸翻转运动。讨论了str2方法的优点。这种str2方法为目前可用的基于ct的固态核磁共振技术增加了一个新的维度，用于探测固体中的分子运动。
{"title":"Extending 17O transverse relaxation measurement to satellite transitions as a direct probe of molecular dynamics in solids","authors":"Yizhe Dai , Ivan Hung , Zhehong Gan , Gang Wu","doi":"10.1016/j.ssnmr.2025.102004","DOIUrl":"10.1016/j.ssnmr.2025.102004","url":null,"abstract":"<div><div>We report utilization of transverse relaxation rate (<em>R</em><sub>2</sub>) of <sup>17</sup>O (<em>I</em> = 5/2) satellite transitions (STs) as a probe of molecular dynamics in solids. A simple theoretical model using spectral density functions is proposed to describe the general <em>R</em><sub>2</sub> behaviors of half-integer quadrupolar nuclei in solids in the presence of molecular motion (or chemical exchange). Experimental <sup>17</sup>O <em>R</em><sub>2</sub> data recorded for both CT and ST from <sup>17</sup>O-labeled NaNO<sub>2</sub> over a large temperature range are used to verify the theoretical predictions. Our theoretical model is shown to be fully consistent with a full quantum mechanical treatment of the chemical exchange problem involving half-integer quadrupolar nuclei in solids by numerically solving the Liouville-von Neumann equation. The new <sup>17</sup>O ST <em>R</em><sub>2</sub> method was also applied to study the carboxylate flipping motion in two [<sup>17</sup>O]carboxylic acid-pyridine adducts in the solid state. The advantages of the ST <em>R</em><sub>2</sub> approach are discussed. This ST <em>R</em><sub>2</sub> approach adds a new dimension to the currently available CT-based solid-state NMR techniques for probing molecular motion in solids.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"137 ","pages":"Article 102004"},"PeriodicalIF":1.8,"publicationDate":"2025-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143847453","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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