Probing O–H Bonding through Proton Detected 1H–17O Double Resonance Solid-State NMR Spectroscopy

• Published in: Journal of the American Chemical Society 2019-01, Vol.141 (1), p.441-450
• Main Authors: Carnahan, Scott L, Lampkin, Bryan J, Naik, Pranjali, Hanrahan, Michael P, Slowing, Igor I, VanVeller, Brett, Wu, Gang, Rossini, Aaron J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b10878

The ubiquity of oxygen in organic, inorganic, and biological systems has stimulated the application and development of 17O solid-state NMR spectroscopy as a probe of molecular structure and dynamics. Unfortunately, 17O solid-state NMR experiments are often hindered by a combination of broad NMR signals and low sensitivity. Here, it is demonstrated that fast MAS and proton detection with the D-RINEPT pulse sequence can be generally applied to enhance the sensitivity and resolution of 17O solid-state NMR experiments. Complete 2D 17O → 1H D-RINEPT correlation NMR spectra were typically obtained in less than 10 h from less than 10 mg of material, with low to moderate 17O enrichment (less than 20%). Two-dimensional 1H–17O correlation solid-state NMR spectra allow overlapping oxygen sites to be resolved on the basis of proton chemical shifts or by varying the mixing time used for 1H–17O magnetization transfer. In addition, J-resolved or separated local field (SLF) blocks can be incorporated into the D-RINEPT pulse sequence to allow the direct measurement of one-bond 1H–17O scalar coupling constants (1 J OH) or 1H–17O dipolar couplings (D OH), respectively, the latter of which can be used to infer 1H–17O bond lengths. 1 J OH and D OH calculated from plane-wave density functional theory (DFT) show very good agreement with experimental values. Therefore, the 2D 1H–17O correlation experiments, 1H–17O scalar and dipolar couplings, and plane-wave DFT calculations provide a method to precisely determine proton positions relative to oxygen atoms. This capability opens new opportunities to probe interactions between oxygen and hydrogen in a variety of chemical systems.