Probing O-H Bonding through Proton Detected H-O Double Resonance Solid-State NMR Spectroscopy.

The ubiquity of oxygen in organic, inorganic, and biological systems has stimulated the application and development of O solid-state NMR spectroscopy as a probe of molecular structure and dynamics. Unfortunately, O 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 O solid-state NMR experiments. Complete 2D O → H D-RINEPT correlation NMR spectra were typically obtained in less than 10 h from less than 10 mg of material, with low to moderate O enrichment (less than 20%). Two-dimensional H-O 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 H-O 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 H-O scalar coupling constants ( J) or H-O dipolar couplings ( D), respectively, the latter of which can be used to infer H-O bond lengths. J and D calculated from plane-wave density functional theory (DFT) show very good agreement with experimental values. Therefore, the 2D H-O correlation experiments, H-O 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.