A molecular dynamics study of the effects of fast molecular motions on solid-state NMR parameters

Abstract

The influence of fast molecular motions on NMR parameters in molecular organic solids is explored on a set of amino acids and nucleic acid bases. A combination of DFT molecular dynamics and calculations of shielding and electric field gradient (EFG) tensors reveals the impact of vibrational motions on isotropic chemical shifts, chemical shift anisotropies (CSAs) and quadrupolar interactions. We demonstrate that molecular motion has a significant effect on average molecular structures, and that neglecting the effects of motion on crystal structures derived by diffraction methods may lead to significant errors of calculated isotropic chemical shifts. Re-orientation of the NMR tensors by molecular motion reduces the magnitudes of the NMR anisotropies, and inclusion of molecular dynamics can significantly improve the agreement between calculated quadrupolar couplings and experimental values.