Fast Magic-Angle Spinning Three-Dimensional NMR Experiment for Simultaneously Probing H—H and N—H Proximities in Solids

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• 作者：G. N. Manjunatha Reddy ; Michal Malon ; Andrew Marsh ; Yusuke Nishiyama ; Steven P. Brown
• 刊名：Analytical Chemistry
• 出版年：2016
• 出版时间：December 6, 2016
• 年：2016
• 卷：88
• 期：23
• 页码：11412-11419
• 全文大小：583K
• ISSN：1520-6882

文摘

A fast magic-angle spinning (MAS, 70 kHz) solid-state NMR experiment is presented that combines ¹H Double-Quantum (DQ) and ¹⁴N—¹H HMQC (Heteronuclear Multiple-Quantum Coherence) pulse-sequence elements, so as to simultaneously probe H—H and N—H proximities in molecular solids. The proposed experiment can be employed in both two-dimensional (2D) and three-dimensional (3D) versions: first, a 2D ¹⁴N HMQC-filtered ¹H-DQ experiment provides specific DQ-SQ correlation peaks for proton pairs that are in close proximities to the nitrogen sites, thereby achieving spectral filtration. Second, a proton-detected three-dimensional (3D) ¹H(DQ)-¹⁴N(SQ)-¹H(SQ) experiment correlates ¹H(DQ)-¹H(SQ) chemical shifts with ¹⁴N shifts such that longer range N···H—H correlations are observed between protons and nitrogen atoms with internuclear NH distances exceeding 3 Å. Both 2D and 3D versions of the proposed experiment are demonstrated for an amino acid hydrochloride salt, l-histidine·HCl·H₂O, and a DNA nucleoside, guanosine·2H₂O. In the latter case, the achieved spectral filtration ensures that DQ cross peaks are only observed for guanine NH and CH8 ¹H resonances and not ribose and water ¹H resonances, thus providing insight into the changes in the solid-state structure of this hydrate that occur over time; significant changes are observed in the NH and NH₂ ¹H chemical shifts as compared to the freshly recrystallized sample previously studied by Reddy et al., Cryst. Growth Des. 2015, 15, 5945.