Solid state nuclear magnetic resonance最新文献_第4页

Practical aspects of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet 使用可调电磁铁的塞曼摄动NQR光谱的实际方面

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-06-03 DOI: 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, C_Q, 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 C_Q(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.

四极摄动固体核磁共振波谱是研究四极核的一种行之有效的方法。该方法依赖于拉莫尔频率与四极频率的高比率，因此受限于适用于核磁共振的可用磁场强度（约为101 t），核四极共振（NQR）为研究强四极同位素提供了一种方法，但在测量高频跃迁、测量四极耦合常数CQ和不对称参数η、精度很高。我们在这里描述了使用可调节电磁铁的泽曼摄动NQR光谱的现代实现的技术和实践方面，克服了上述挑战。该方法将四极摄动固体核磁共振方法颠倒过来，使四极相互作用占主导地位，塞曼相互作用为摄动。在10−2 t量级的外加磁场下，记录了固体溴和碘苯粉末的79Br和127I泽曼摄动NQR光谱，讨论了各种实验考虑因素，包括最佳磁场，线圈角度的优化，频率步进，使用泽曼四极哈密顿量的精确对角化模拟光谱，以及如何确保得到的四极参数的高精度。例如，在室温下，在不到1小时的时间内测得对称-三碘三氟苯的CQ（127）值为2077.25±1.49 MHz （η = 0.114±0.008）。该方法有望在一系列材料中研究强四极性同位素，并在许多感兴趣的情况下消除对超高磁场的需要。

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引用次数: 0

Diverging errors: A comparison of DFT and machine-learning predictions of NMR shieldings 发散误差：核磁共振屏蔽的DFT和机器学习预测的比较

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-06-26 DOI: 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.

从第一性原理准确预测核磁共振参数对分子固体的结构表征至关重要。最近的研究表明，基于混合DFT计算的单分子校正方案可以显著提高核屏蔽周期DFT预测的准确性。在这里，我们不仅评估了这种校正方法在周期性DFT计算中的性能，还评估了ShiftML2（一种基于pbe计算的核磁共振数据训练的机器学习模型）的性能。对于13C原子核，将单分子PBE0校正应用于周期性PBE屏蔽，将均方根偏差（RMSD）从2.18 ppm降低到1.20 ppm，在1H内观察到的改善可以忽略不计。当应用于ShiftML2预测时，修正产生了13C RMSD的较小减少（从3.02到2.51 ppm）；同样，它们对1H预测的影响微乎其微。残差分析揭示了DFT和ML误差之间的弱相关性，这表明虽然系统偏差的一些来源可能是共享的，但其他来源可能是不同的。这些结果表明，dft特定的校正方案不能直接转化为机器学习模型，突出了对ml定制的后处理或再训练策略的需求。这些发现对于将机器学习集成到高通量NMR工作流程以及开发更准确的固态光谱预测工具具有重要意义。

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引用次数: 0

Editorial: Solid-state NMR and DNP of heterogeneous biomaterials and cellular systems 非均质生物材料和细胞系统的固态核磁共振和DNP

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-06-01 Epub Date: 2025-03-21 DOI: 10.1016/j.ssnmr.2025.102003

Patrick C.A. van der Wel , Tuo Wang

引用次数: 0

Solid-state NMR observation of chitin in whole cells by indirect 15N detection with NC, NCC, CNC and CNCC polarization transfers 用NC、NCC、CNC和CNCC极化转移间接15N检测全细胞甲壳素的固态核磁共振观察

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-06-01 Epub Date: 2025-03-14 DOI: 10.1016/j.ssnmr.2025.102002

Loic Delcourte , Mélanie Berbon , Marion Rodriguez , Laurence Delhaes , Birgit Habenstein , Antoine Loquet

Chitin is the most important nitrogen-containing polysaccharide found on Earth. This polysaccharide is a polymer of an N-acetylglucosamine and it is a crucial structural component of fungal cell walls and crustaceans. Magic-angle spinning solid-state NMR is emerging as a powerful analytical approach to study polysaccharides in the context of intact cell walls and whole cells. The presence of an acetamido group in chitin is attractive for ¹⁵N solid-state NMR. Here we investigate the use of various multi-step polarization transfer experiments incorporating indirect ¹⁵N detection at moderate spinning frequency, adapted from pulse sequences commonly employed for residue resonance assignment in biosolid proteins. The ¹³C,¹⁵N chitin spin topology slightly differs from amino acids, and we discussed the use of frequency-selective ¹⁵N-¹³C cross-polarization transfers followed by broadband or frequency-selective homonuclear ¹³C–¹³C transfers to detect chitin resonances. Demonstrated here for chitin found in the cell wall of the fungus Aspergillus fumigatus, the use of indirect ¹⁵N detection through multi-step polarization transfers could be advantageous to investigate more complex nitrogen-containing polysaccharides found in whole cells and peptidoglycan samples.

几丁质是地球上发现的最重要的含氮多糖。这种多糖是一种n -乙酰氨基葡萄糖的聚合物，是真菌细胞壁和甲壳类动物的重要结构成分。魔角旋转固体核磁共振正在成为一种强大的分析方法，在完整细胞壁和整个细胞的背景下研究多糖。甲壳素中乙酰氨基的存在对15N固态核磁共振是有吸引力的。在这里，我们研究了不同的多步极化转移实验，包括在中等旋转频率下间接检测15N，适应于生物固体蛋白质中常用的残基共振分配的脉冲序列。13C，15N几丁质自旋拓扑结构与氨基酸略有不同，我们讨论了使用频率选择性的15N-13C交叉极化转移，然后是宽带或频率选择性的同核13C -13C转移来检测几丁质共振。对于烟曲霉细胞壁中发现的几丁质，通过多步极化转移的间接15N检测可能有利于研究在全细胞和肽聚糖样品中发现的更复杂的含氮多糖。

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引用次数: 0

Low-power 14N decoupling at fast MAS of 70 kHz 在70 kHz的快速MAS下低功率14N去耦

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-06-01 Epub Date: 2025-05-13 DOI: 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.

固体中较高的各向同性分辨率对于精确分配多位点化学和生物系统中的化学位移至关重要；因此，在固体样品中追求类似溶液的分辨率仍然是一个持续的挑战。MAS将各向异性相互作用有效地平均到一阶，而高阶相互作用（如残余偶极分裂（RDS））和各向同性相互作用（如J耦合）仍然存在。随着更快的MAS的出现，RDS和J耦合成为14N键合各向同性1H峰分辨率和灵敏度的重要制约因素。然而，占主导地位的四极耦合阻碍了1H-14N的去耦，因为可实现的14N rf场强度远小于四极耦合的大小。因此，14N编辑光谱通常在没有14N去耦的情况下进行，导致更宽的1H线宽和降低的灵敏度。在此背景下，我们提出了14N-1H自旋对在70 kHz的快速MAS下在1H检测下的连续波（CW） 14N去耦。实验表明，在快速MAS下的非共振低功率14N连续波辐照产生更窄的线宽。利用四极振动框架描述，对最佳解耦效果进行了定性分析。

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引用次数: 0

Dynamic nuclear polarization of TEMPO radical cross conjugated with a thioanisole scaffold 硫代苯甲醚支架交联TEMPO自由基的动态核极化

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-06-01 Epub Date: 2025-04-25 DOI: 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.

核磁共振波谱是测定分子结构的重要技术，但其灵敏度低是其固有的局限性。近年来，动态核极化（DNP）技术的出现克服了核磁共振波谱固有的低灵敏度，通过在微波照射下将未对电子自旋的极化转移到核自旋上，使探测1H的理论灵敏度提高了658倍。在这项研究中，我们报道了一系列TEMPO（2,2,6,6-四甲基哌啶-1-氧基）基自由基的合成和表征，这些自由基被硫代苯甲醚支架功能化，旨在促进金表面的自组装单层。采用电子顺磁共振（EPR）和DNP核磁共振光谱对自由基进行了研究。这些自由基表现出与标准TEMPO一致的特性，同时保持稳定性和功能性。在10 mM浓度的TCE（1,1,2,2-四氯乙烷）中，radical -亚胺-1对1H原子核的DNP增强因子为3.2，而标准TEMPO在14.1 t时的DNP增强因子约为2.8。弛豫测量显示，纵向弛豫时间（T1）随着自由基浓度的增加而减少，而横向弛豫时间（T2）基本不受影响，表明顺磁淬火的扰动最小。甲基巯基的结构稳定性和表面结合潜力使这些衍生物适合于基于表面的DNP应用。

{"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 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.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"137 ","pages":"Article 102005"},"PeriodicalIF":1.8,"publicationDate":"2025-06-01","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}

引用次数: 0

Extending 17O transverse relaxation measurement to satellite transitions as a direct probe of molecular dynamics in solids 将 17O 横向弛豫测量扩展到卫星跃迁，作为固体分子动力学的直接探针

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-06-01 Epub Date: 2025-04-15 DOI: 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。

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引用次数: 0

Deuteron-proton isotope correlation spectroscopy at high magnetic fields 强磁场下氘核-质子同位素相关光谱

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-04-01 Epub Date: 2025-02-04 DOI: 10.1016/j.ssnmr.2025.101993

Neethu Thomas , Claire Welton , Tomasz Pawlak , Parth Raval , Julien Trébosc , Sheetal K. Jain , G.N. Manjunatha Reddy

A cross-polarization ²H–¹H isotope correlation spectroscopy (CP-iCOSY) approach is presented for characterizing a deuterated amino acid, pharmaceutical compound and a solid formulation. This can be achieved by isotopic enrichment in conjunction with high magnetic field (28.2 T) and fast magic-angle spinning (MAS), enabling the rapid detection of ²H NMR spectra in a few seconds to minutes. Specifically, two-dimensional (2D) ²H–¹H CP-iCOSY experiment allows the local structures and through-space interactions in a partially deuterated compounds to be elucidated. In doing so, we compare conventional spin-lock and rotor-echo-short-pulse-irradiation ^RESPIRATIONCP sequences for acquiring 2D ¹H–²H correlation spectra. The ^RESPIRATIONCP sequence allows the detection of 2D peaks at lower CP contact times (0.1–1 ms) than the conventional CP (0.2–4 ms) sequence. Analysis of partially deuterated L-histidine·HCl·H₂O and dopamine.HCl is presented, in which the detection of 2D peaks corresponding to ²H–¹H pairs separated by greater than 4 Å distance demonstrates the potential of the presented approach for the characterization of packing interactions. These results are corroborated by NMR crystallography analysis using the Gauge-Including Projector Augmented-Wave (GIPAW) approach.

提出了一种交叉极化2H-1H同位素相关光谱（CP-iCOSY）方法，用于表征氘化氨基酸、药物化合物和固体制剂。这可以通过与高磁场（28.2 T）和快速魔角旋转（MAS）相结合的同位素富集来实现，从而在几秒到几分钟内快速检测2H核磁共振光谱。具体来说，二维（2D） 2H-1H CP-iCOSY实验可以阐明部分氘化化合物的局部结构和通过空间的相互作用。在此过程中，我们比较了传统的自旋锁定和转子回波短脉冲辐照呼吸器cp序列，以获得二维1H-2H相关光谱。与传统的CP （0.2-4 ms）序列相比，呼吸器CP序列可以在较低的CP接触时间（0.1-1 ms）下检测2D峰。部分氘化l -组氨酸·HCl·H2O和多巴胺的分析。提出了HCl，其中检测到的2D峰对应于间隔大于4 Å距离的2H-1H对，表明了所提出的方法表征包装相互作用的潜力。这些结果证实了核磁共振晶体学分析使用仪表-包括投影仪增强波（GIPAW）方法。

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引用次数: 0

Spin-dynamics and efficiency of single 14N-1H cross-polarization at fast magic angle spinning in solids 固体中快速魔角自旋下单14N-1H交叉极化的自旋动力学和效率

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-04-01 Epub Date: 2025-01-28 DOI: 10.1016/j.ssnmr.2025.101992

Vipin Agarwal , Sreejith Raran-Kurussi , Yusuke Nishiyama

The naturally abundant ¹⁴N isotope (>99 %) is sparingly employed for characterization in solid-state nuclear magnetic resonance (NMR) despite the importance of nitrogen atoms in shaping molecular structures and properties. This inhibition can be attributed to large quadrupolar couplings (∼several MHz), resulting in more involved spin methodologies for ¹⁴N nuclei. Experimentally, spin-½ nuclei are utilized for excitation and detection through two-way (¹H→¹⁴N→¹H) polarization transfer between spin-½ nuclei and ¹⁴N. Herein, we show direct ¹⁴N spin excitation followed by ¹⁴N→¹H cross-polarization (CP) is an efficient method for polarization transfer even for ¹⁴N spins with a large quadrupolar coupling constant (3–4 MHz). This contrasts previous studies, which indicate that ¹H-¹⁴N spectra can only be observed with a pair of at least a rotor period-long symmetric ¹⁴N pulses (J. Chem. Phys. 151 (2019) 154202). The ¹⁴N→¹H CP spin dynamics have been experimentally established and can be explained in analogy to spin-½ Hartmann-Hahn CP if visualized in the quadrupolar jolting frame. The ¹⁴N→¹H CP is ∼1.9–2.7 times more efficient in polarization transfer than other ¹⁴N edited experiments. Considering shorter ¹⁴N T₁ relaxation times compared to protons, ¹⁴N edited spectra were recorded using ¹⁴N→¹H CP, resulting in enhanced sensitivity per unit of time.

天然丰富的14N同位素（> 99%）很少用于固态核磁共振（NMR）表征，尽管氮原子在塑造分子结构和性质方面很重要。这种抑制可以归因于大的四极耦合（~几MHz），导致14N核的自旋方法更复杂。实验中，利用自旋1 / 2原子核与14N之间的双向（1H→14N→1H）极化转移，利用自旋1 / 2原子核进行激发和探测。本研究表明，直接14N自旋激发后进行14N→1H交叉极化（CP）是一种有效的极化转移方法，即使对于具有较大四极耦合常数（3-4 MHz）的14N自旋也是如此。这与先前的研究形成了对比，这些研究表明，只有用一对至少一个转子周期长的对称14N脉冲才能观察到1H-14N光谱(J. Chem。物理学报，151(2019):154202)。在实验中建立了14N→1H CP的自旋动力学，如果在四极振动框架中可视化，可以用自旋- 1 / 2 Hartmann-Hahn CP的类比来解释。14N→1H CP的极化转移效率是其他14N编辑实验的1.9 ~ 2.7倍。考虑到与质子相比，14N T1弛豫时间更短，使用14N→1H CP记录14N编辑光谱，从而提高了单位时间的灵敏度。

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引用次数: 0

Highly sensitive measurements of methylene dynamics with a frequency-selective double-quantum sideband method 用频率选择性双量子边带方法高灵敏度测量亚甲基动力学

IF 1.8 3区化学 Q4 CHEMISTRY, PHYSICAL

Solid state nuclear magnetic resonance

Pub Date : 2025-04-01 Epub Date: 2025-02-21 DOI: 10.1016/j.ssnmr.2025.101994

Jacob Mayer , Frédéric A. Perras

Probing the fast dynamics of surface sites using NMR spectroscopy is highly challenging owing to the sites' high dilution and the difficulties often associated with isotopic enrichment. Intra-CH₂ ¹H–¹H dipolar couplings are ideal probes of motions given that they only involve ¹H's and the tensor has a well-defined size and orientation. We introduce a frequency-selective variant of the double-quantum sideband method to measure like-spin ¹H–¹H dipolar coupling constants. The experiment dramatically reduces the instrument time required to measure dynamically-averaged intra-CH₂ dipolar couplings. We demonstrate the performance of the sequence using silica-supported silanes as model highly-mobile surface species.

利用核磁共振光谱探测表面位点的快速动力学是极具挑战性的，因为这些位点的高度稀释和往往与同位素富集相关的困难。ch2内1H - 1H偶极耦合是运动的理想探针，因为它们只涉及1H，而且张量具有明确的大小和方向。我们引入了双量子边带方法的频率选择变体来测量类自旋1H-1H偶极耦合常数。该实验极大地减少了测量动态平均ch2内偶极耦合所需的仪器时间。我们用二氧化硅支撑的硅烷作为模型高流动性表面物种来证明该序列的性能。

引用次数: 0