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

High-resolution solid-state 2H MAS NMR studies of the α and γ polymorphs of fully deuterated glycine (glycine-d 5) are reported. Analysis of spinning sideband patterns is used to determine the 2H quadrupole interaction parameters, and is shown to yield good agreement with the corresponding parameters determined from single-crystal 2H NMR measurements (the maximum deviation in quadrupole coupling constants determined from these two approaches is only 1%). From analysis of simulated 2H MAS NMR sideband patterns as a function of reorientational jump frequency (κ) for the −N+D3 group in glycine-d 5, the experimentally observed differences in the 2H MAS NMR spectrum for the −N+D3 deutrons in the α and γ polymorphs is attributed to differences in the rate of reorientation of the −N+D3 group. These simulations show severe broadening of the 2H MAS NMR signal in the intermediate motion regime, suggesting that deuterons undergoing reorientational motions at rates in the range κ ≈ 104–106 s–1 are likely to be undetectable in 2H MAS NMR measurements for materials with natural isotopic abundances. The 1H NMR chemical shifts for the α and γ polymorphs of glycine have been determined from the 2H MAS NMR results, taking into account the known second-order shift. Further quantum mechanical calculations of 2H quadrupole interaction parameters and 1H chemical shifts reveal the structural dependence of these parameters in the two polymorphs and suggest that the existence of two short intermolecular C–H···O contacts for one of the H atoms of the >CH2 group in the α polymorph have a significant influence on the 2H quadrupole coupling and 1H chemical shift for this site.