Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 115, Issue 44, Pages 12201-12211Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp207592u
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Funding
- EPSRC
- BBSRC
- University of Warwick
- Advantage West Midlands (AWM)
- European Regional Development Fund (ERDF)
- Engineering and Physical Sciences Research Council [EP/F017901/1] Funding Source: researchfish
- EPSRC [EP/F017901/1] Funding Source: UKRI
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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.
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