Probing crystal packing of uniformly C-13-enriched powder samples using homonuclear dipolar coupling measurements

Abstract : The relationship between the crystal packing of powder samples and long-range C-13-C-13 homonuclear dipolar couplings is presented and illustrated for the case of uniformly C-13-enriched L-alanine and r histidine HCI center dot H2O. Dipolar coupling measurement is based on the partial reintroduction of dipolar interactions by spinning the sample slightly off-magic-angle, while the coupling of interest for a given spin pair is isolated with a frequency-selective pulse. A cost function is used to correlate the so-derived dipolar couplings to trial crystal structures of the samples under study. This procedure allowed for the investigation of the L-alanine space group and r histidine HCl center dot H2O space group and unit-cell parameters. (C) 2014 Elsevier Inc. All rights reserved.