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Abstract

Single-crystal samples of the peptide N-acetyl-D,L-valine (NAV) with the exchangeable amide and carboxyl hydrogens replaced by deuterons were investigated by deuterium NMR spectroscopy. The electric field gradient (EFG) and chemical shift (CS) tensors for the amide and the carboxyl hydrogens, both of which are involved in intermolecular hydrogen bonds, were determined. The relationship of these tensors to the structure of NAV is discussed. The orientations of the EFG and the CS tensors of the amide hydrogen in a protein can provide information about the polypeptide backbone structure. For NAV the eigenvector of the largest eigenvalue of the EFG tensor coincides with the NH bond direction, as found by X-ray crystallography, within 2°, and the eigenvector of the intermediate eigenvalue with the normal (n peptide) to the peptide plane within 1°. The directions of largest and smallest shielding are similarly aligned with NH and n peptide respectively. However, the deviations are considerably larger, namely 9° and 11°, respectively. The anisotropy of the CS tensor is determined to be 13.4 +− 2.7 ppm, confirming that the amide hydrogen is involved in a weak hydrogen bond.