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  • Fast Acquisition of Proton‐...
    Wijesekara, Anuradha V.; Venkatesh, Amrit; Lampkin, Bryan J.; VanVeller, Brett; Lubach, Joseph W.; Nagapudi, Karthik; Hung, Ivan; Gor'kov, Peter L.; Gan, Zhehong; Rossini, Aaron J.

    Chemistry : a European journal, June 23, 2020, Volume: 26, Issue: 35
    Journal Article

    Fast magic‐angle spinning (MAS), frequency selective (FS) heteronuclear multiple quantum coherence (HMQC) experiments which function in an analogous manner to solution SOFAST HMQC NMR experiments, are demonstrated. Fast MAS enables efficient FS excitation of 1H solid‐state NMR signals. Selective excitation and observation preserves 1H magnetization, leading to a significant shortening of the optimal inter‐scan delay. Dipolar and scalar 1H{14N} FS HMQC solid‐state NMR experiments routinely provide 4‐ to 9‐fold reductions in experiment times as compared to conventional 1H{14N} HMQC solid‐state NMR experiments. 1H{14N} FS resonance‐echo saturation‐pulse double‐resonance (RESPDOR) allowed dipolar dephasing curves to be obtained in minutes, enabling the rapid determination of NH dipolar coupling constants and internuclear distances. 1H{14N} FS RESPDOR was used to assign multicomponent active pharmaceutical ingredients (APIs) as salts or cocrystals. FS HMQC also provided enhanced sensitivity for 1H{17O} and 1H{35Cl} HMQC experiments on 17O‐labeled Fmoc‐alanine and histidine hydrochloride monohydrate, respectively. FS HMQC and FS RESPDOR experiments will provide access to valuable structural constraints from materials that are challenging to study due to unfavorable relaxation times or dilution of the nuclei of interest. Frequency selective (FS) 1H{14N} HMQC and RESPDOR solid‐state NMR experiments provide four‐ to ninefold reductions in experiment times, permitting the fast acquisition of 2D 1H{14N} HMQC spectra and rapid measurements of NH bond lengths in organic materials (see figure).