Understanding the Effects of Crystal Packing on NMR Chemical Shift Tensors


Martin Babinský, Kateřina Bouzková, Lucie Novosadová, Matej Pipíška, and Radek Marek

Abstract

Solid-state NMR spectroscopy is one of the most powerful techniques used for the characterization
of solid samples. This method is nowadays routinely used for the study of the structure and
dynamics of pharmaceutical compounds, biomolecules, polymers and nanomaterials. However, the
relationship between the NMR observables and the supramolecular structure of any system is not
straightforward. In this work we examine the influence of the crystal packing for three purine
derivatives (hypoxanthine, theobromine, and 6-(2-methoxy)benzylaminopurine) on the principal
components of the NMR chemical shift tensors (CSTs). We employ density functional calculations to
obtain various molecular properties (the ground-state electron density, the magnitudes and
orientations of the components of NMR chemical shift tensor, and the spatial distribution of the
isotropic magnetic shielding) for the isolated molecules and for the molecules embedded in
supramolecular clusters modeling the crystal environment and evaluate their differences. The
concept has enabled us to rationalize the effect of the crystal packing on the NMR CSTs in terms of
the redistribution of the ground-state electron density induced by intermolecular interactions in
the solid state.