Deuteron-proton isotope correlation spectroscopy of molecular solids

Abstract

A dissolution followed by recrystallization from a deuterated solvent allows the site-selective deuteration of labile protons in molecular solids. High yields of deuteration obtained by this approach facilitates the structure elucidation of powdered solids by solid-state NMR spectroscopy, for example, by acquiring 1D 2H and 2D 2H-1H correlation NMR spectra with short experimental times. Along these lines, we present a cross-polarization 2H-1H isotope correlation spectroscopy (CP-iCOSY) approach for the characterization of deuterated amino acids and pharmaceutical compounds. We show that the high field NMR (28.2 T) coupled with fast magic-angle spinning (MAS) overcomes the sensitivity and resolution barrier for acquiring 2H MAS spectra, enabling the rapid detection of 2H peaks in a few seconds to minutes. Specifically, two-dimensional 2H-1H CP-iCOSY experiment allows the local structures and through-space interactions in a partially deuterated compounds to be elucidated. Analysis of partially deuterated L-histidine·HCl·H2O and dopamine.HCl is presented, whereby the detection of 2D peaks corresponding to 2H-1H pairs separated by >4 Å demonstrates the sensitivity and resolution power of the presented approach for the characterization of solid-state packing interactions. 2D ssNMR results are corroborate by NMR crystallography analysis using Gauge Including Projector Augmented Wave (GIPAW) approach. Molecular-level analysis enabled by this study is of considerable interest for further investigation of labile sites in a variety of molecular solids, reactive surfaces and interfaces, and supramolecular assemblies.