Deuterium Quadrupole-Coupling and Chemical-Shielding Tensors in the Model Dipeptide Glycylglycine Monohydrochloride...

The electric field gradient (EFG) and chemical-shift (CS) tensors for the amide, carboxylic acid, and amino deuteron sites in glycylglycine monohydrochloride monohydrate were measured. For each site, the EFG tensors are found to lie nearly along the deuteron bond. The magnitudes of the quadrupole-coupling constants agree well with previous empirical relationships to hydrogen-bond lengths. A new relationship is presented which correlates hydrogen-bonding geometries and EFG asymmetry parameters for N-D··· (hydrogen-bond acceptor) systems that suggests the importance of intermolecular geometry in determining these parameters. The measured amino and amide CS tensors are found to agree well with the few examples in the literature and agree qualitatively with those determined from ab initio calculations. The carboxylic acid deuteron CS tensor agrees well with empirical relationships to hydrogen-bond distance.