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首页> 外文期刊>The Journal of Chemical Physics >Handling the influence of chemical shift in amplitude-modulated heteronuclear dipolar recoupling solid-state NMR
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Handling the influence of chemical shift in amplitude-modulated heteronuclear dipolar recoupling solid-state NMR

机译：处理化学位移对调幅异核双极耦合固态NMR的影响

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摘要

We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear dipolar recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization (RESPIRATIONCP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer. In this description, it becomes transparent that the main attribute leading to non-ideal performance is a fictitious field along the rf field axis, which is generated from second-order cross terms arising mainly between chemical shift tensors and themselves. This insight is useful for the development of improved recoupling experiments. We discuss the validity of this approach and present quaternion calculations to determine the effective resonance conditions in a combined rf field and chemical shift offset interaction frame transformation. Based on this, we derive a broad-banded version of the RESPIRATIONCP experiment. The new sequence is experimentally verified using SNNFGAILSS amyloid fibrils where simultaneous N-15 -> (CO)-C-13 and N-15 -> Ca-13 coherence transfer is demonstrated on high-field NMR instrumentation, requiring great offset stability. Published by AIP Publishing.
机译：我们提出了对化学位移对固态NMR光谱中振幅调制的异核双极耦合实验的影响的理论分析。以转子回波短脉冲IRrAdiaTION介导的交叉极化（RESPIRATIONCP）实验为例进行了说明。通过进入脉冲序列rf交互框架并采用基于五元模式算子的Floquet方法，我们描述了化学位移偏移和各向异性化学位移如何影响异核极化转移的效率。在本说明书中，透明的是，导致非理想性能的主要属性是沿rf场轴的虚拟场，它是由主要在化学位移张量及其自身之间产生的二阶交叉项产生的。这种见解对于改进耦合实验的开发很有用。我们讨论了这种方法的有效性，并提出了四元数计算，以确定在组合的rf场和化学位移偏移相互作用框架变换中的有效共振条件。基于此，我们得出了RESPIRATIONCP实验的宽带版本。使用SNNFGAILSS淀粉样蛋白原纤维通过实验验证了新序列，其中在高场NMR仪器上证明了同时N-15->（CO）-C-13和N-15-> Ca-13相干转移，这需要很大的偏移稳定性。由AIP Publishing发布。

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