High-Resolution Solid-State 2H NMR Spectroscopy of Polymorphs of Glycine

High-resolution solid-state H-2 MAS NMR studies of the alpha and gamma polymorphs of fully deuterated glycine (glycine-d(5)) are reported. Analysis of spinning sideband patterns is used to determine the H-2 quadrupole interaction parameters, and is shown to yield good agreement with the corresponding parameters determined from single-crystal H-2 NMR measurements (the maximum deviation in quadrupole coupling constants determined from these two approaches is only 1%). From analysis of simulated H-2 MAS NMR sideband patterns as a function of reorientational jump frequency (kappa) for the -N+D3 group in glycine-d(5), the experimentally observed differences in the H-2 MAS NMR spectrum for the -N+D3 deutrons in the alpha and gamma polymorphs is attributed to differences in the rate of reorientation of the -N+D3 group. These simulations show severe broadening of the H-2 MAS NMR signal in the intermediate motion regime, suggesting that deuterons undergoing reorientational motions at rates in the range kappa approximate to 10(4)-10(6) s(-1) are likely to be undetectable in H-2 MAS NMR measurements for materials with natural isotopic abundances. The H-1 NMR chemical shifts for the alpha and gamma polymorphs of glycine have been determined from the H-2 MAS NMR results, taking into account the known second-order shift. Further quantum mechanical calculations of H-2 quadrupole interaction parameters and H-1 chemical shifts reveal the structural dependence of these parameters in the two polymorphs and suggest that the existence of two short intermolecular C-H center dot center dot center dot O contacts for one of the H atoms of the >CH2 group in the alpha polymorph have a significant influence on the H-2 quadrupole coupling and H-1 chemical shift for this site.