量化旋转固体中自旋 1/2 核的 NMR 谱中的四极效应,Physical Chemistry Chemical Physics

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量化旋转固体中自旋 1/2 核的 NMR 谱中的四极效应
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2023-06-29 , DOI: 10.1039/d3cp02094k
Nisha Bamola ₁ , Mohit Bansal ₁ , Ramesh Ramachandran ₁

Affiliation

在固态魔角自旋 (MAS) NMR 实验中，量化与四极自旋耦合的自旋I = 1/2 核（自旋量子数S > 1/2 的核）的 NMR 谱仍然是一项艰巨的任务。特别是，在 MAS 实验中，从与四极自旋 ( S = 1) 耦合的自旋I = 1/2 核的线形中提取化学位移各向异性 (CSA) 张量仍然具有挑战性，因为同时存在异核偶极相互作用和四极相互作用。与仅涉及自旋 1/2 核的实验不同，四极自旋上更快的自旋频率和更强的解耦场强对于平均/最小化异核偶极相互作用的贡献至关重要。为此，提出了一种基于“有效场”概念的定量理论，以推导涉及异核偶极相互作用同时重耦合和解耦合的实验中的最佳条件。通过解析表达式，对实验中观察到的光谱频率和强度进行量化和严格验证。由于 NMR 实验中分子约束的提取涉及实验数据的迭代拟合，因此我们相信导出的分析表达式将加速并有利于量化此类实验。

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Quantifying quadrupole effects in the NMR spectra of spin-1/2 nuclei in rotating solids

Quantifying the NMR spectra of spin I = 1/2 nuclei coupled to quadrupolar spins (nuclei with spin quantum number, S > 1/2) has remained an arduous task in solid-state magic angle spinning (MAS) NMR experiments. In particular, extraction of chemical shift anisotropy (CSA) tensors from line-shapes of spin I = 1/2 nuclei coupled to quadrupolar spin (S = 1) in MAS experiments has remained challenging owing to the simultaneous presence of both heteronuclear dipolar interactions and quadrupolar interactions. Unlike experiments that involve only spin-1/2 nuclei, both faster spinning frequencies and stronger decoupling field strengths on the quadrupolar spins are essential to average/minimize the contributions from heteronuclear dipolar interactions. To this end, a quantitative theory based on the concept of “effective fields” is proposed to deduce optimal conditions in experiments that involve simultaneous recoupling and decoupling of heteronuclear dipolar interactions. Through analytic expressions, the spectral frequencies and intensities observed in experiments are quantified and rigorously verified. Since extraction of molecular constraints in NMR experiments involves iterative fitting of experimental data, we believe that the analytic expressions derived would speed up and be beneficial in quantifying such experiments.

更新日期：2023-06-29

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