Measurement of Accurate Interfluorine Distances in Crystalline Organic Solids: A High-Frequency Magic Angle Spinning NMR Approach
Measurement of Accurate Interfluorine Distances in Crystalline Organic Solids: A High-Frequency Magic Angle Spinning NMR Approach
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DOI：
10.1021/acs.jpcb.9b08919
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发表时间：
2019-12-19
影响因子：
3.3
通讯作者：
Polenova, Tatyana
中科院分区：
文献类型：
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作者：
Fritz, Matthew;Kraus, Jodi;Polenova, Tatyana
长程原子间距离限制对于通过核磁共振光谱法确定溶液和固态分子结构至关重要。氟是一个强大的NMR探针在各种各样的情况下，由于其良好的磁性，易于纳入生物分子，并在设计用于各种应用的合成有机分子中无处不在的使用。由于100%天然丰富的F-19同位素的大旋磁比，在魔角旋转（MAS）偶极再耦合实验中，氟之间的距离可以达到20埃。在这里，我们提出了一种方法来确定准确的interfluorine的距离在多自旋系统，使用有限脉冲射频驱动的再耦合（fpRFDR）在高MAS频率为40-60 kHz。我们使用了一系列的晶体“分子统治者”的固体，二氟苯甲酸和7 F-L-色氨酸，其中的内部和分子间的interfluorine距离是已知的。我们描述了精确的距离测定的最佳实验条件，包括选择的相位周期，选择性反转一维与二维相关实验的相对优势，以及适当的数值模拟协议。提出了一种用于分析具有扩展自旋相互作用网络的有机固体中的RFDR交换曲线的最佳策略，即使在没有晶体结构的情况下，该策略也可以潜在地并入NMR结构测定中。
Long-range interatomic distance restraints are critical for the determination of molecular structures by NMR spectroscopy, both in solution and in the solid state. Fluorine is a powerful NMR probe in a wide variety of contexts, owing to its favorable magnetic properties, ease of incorporation into biological molecules, and ubiquitous use in synthetic organic molecules designed for diverse applications. Because of the large gyromagnetic ratio of the 100% naturally abundant F-19 isotope, interfluorine distances as long as 20 angstrom are accessible in magic-angle spinning (MAS) dipolar recoupling experiments. Herein, we present an approach for the determination of accurate interfluorine distances in multispin systems, using the finite pulse radio frequency driven recoupling (fpRFDR) at high MAS frequencies of 40-60 kHz. We use a series of crystalline "molecular ruler" solids, difluorobenzoic acids and 7F-L-tryptophan, for which the intra- and intermolecular interfluorine distances are known. We describe the optimal experimental conditions for accurate distance determinations, including the choice of a phase cycle, the relative advantages of selective inversion one-dimensional versus two-dimensional correlation experiments, and the appropriate numerical simulation protocols. An optimal strategy for the analysis of RFDR exchange curves in organic solids with extended spin interaction networks is presented, which, even in the absence of crystal structures, can be potentially incorporated into NMR structure determination.