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首页> 外文期刊>The Journal of Chemical Physics >Site-resolved multiple-quantum filtered correlations and distance measurements by magic-angle spinning NMR: Theory and applications to spins with weak to vanishing quadrupolar couplings
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Site-resolved multiple-quantum filtered correlations and distance measurements by magic-angle spinning NMR: Theory and applications to spins with weak to vanishing quadrupolar couplings

机译：通过魔角旋转NMR进行位点分辨的多量子滤波相关性和距离测量：四极偶极弱到消失的自旋的理论和应用

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摘要

We discuss and analyze four magic-angle spinning solid-state NMR methods that can be used to measure internuclear distances and to obtain correlation spectra between a spin I = 1/2 and a half-integer spin S > 1/2 having a small quadrupolar coupling constant. Three of the methods are based on the heteronuclear multiple-quantum and single-quantum correlation experiments, that is, high rank tensors that involve the half spin and the quadrupolar spin are generated. Here, both zero and single-quantum coherence of the half spins are allowed and various coherence orders of the quadrupolar spin are generated, and filtered, via active recoupling of the dipolar interaction. As a result of generating coherence orders larger than one, the spectral resolution for the quadrupolar nucleus increases linearly with the coherence order. Since the formation of high rank tensors is independent of the existence of a finite quadrupolar interaction, these experiments are also suitable to materials in which there is high symmetry around the quadrupolar spin. A fourth experiment is based on the initial quadrupolar-driven excitation of symmetric high order coherences (up to p = 2S, where S is the spin number) and subsequently generating by the heteronuclear dipolar interaction higher rank (l + 1 or higher) tensors that involve also the half spins. Due to the nature of this technique, it also provides information on the relative orientations of the quadrupolar and dipolar interaction tensors. For the ideal case in which the pulses are sufficiently strong with respect to other interactions, we derive analytical expressions for all experiments as well as for the transferred echo double resonance experiment involving a quadrupolar spin. We show by comparison of the fitting of simulations and the analytical expressions to experimental data that the analytical expressions are sufficiently accurate to provide experimental Li-7-C-13 distances in a complex of lithium, glycine, and water. Discussion of the regime for which such an approach is valid is given. (C) 2016 AIP Publishing LLC.
机译：我们讨论并分析了四种魔术角旋转固态NMR方法，这些方法可用于测量核间距离并获得自旋I = 1/2和半整数自旋S> 1/2（四极小）的相关光谱耦合常数。其中三种方法基于异核多量子和单量子相关性实验，即生成涉及半自旋和四极自旋的高阶张量。在此，允许半自旋的零和单量子相干，并且通过偶极相互作用的主动重耦合来生成并过滤四极自旋的各种相干阶。由于产生大于1的相干阶，四极核的光谱分辨率随相干阶线性增加。由于高阶张量的形成独立于有限的四极相互作用，因此这些实验也适用于四极自旋周围对称性高的材料。第四个实验基于对称性高阶相干的初始四极驱动激发（高达p = 2S，其中S为自旋数），随后通过异核偶极相互作用生成更高阶（l + 1或更高）的张量，该张量也涉及半旋转。由于该技术的性质，它还提供了有关四极和偶极相互作用张量的相对方向的信息。对于脉冲相对于其他相互作用足够强的理想情况，我们导出了所有实验以及涉及四极自旋的转移回波双共振实验的解析表达式。通过比较模拟和分析表达式与实验数据的拟合，我们表明，分析表达式足够准确，可以在锂，甘氨酸和水的复合物中提供实验性的Li-7-C-13距离。讨论了这种方法有效的机制。 （C）2016 AIP出版有限责任公司。

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