Intermolecular hydrogen-bonding effect on carbon-13 NMR chemical shifts of glycine residue carbonyl carbons of peptides in the solid state

Abstract

Abstract: In order to investigate the effect of hydrogen bonding on I3C NMR chemical shifts carbonyl carbons in peptides in the solid state, C CP/MAS NMR spectra were measured for a series of oligopeptides containing glycine residues, of which the crystal structures were already determined by X-ray diffractions. It was found that the I3C chemical shifts of the carbonyl carbons in the >C=O-H-N C=O.-H--N++ type hydrogen bond form move upfield with a decrease in the hydrogen bond length. Further, the 13C chemical shift behavior of the carbonyl carbon of polyglycine with forms I and I1 was reasonably explained in terms of the difference in their hydrogen bond lengths. The quantum chemical calculation of the I3C shielding constant for the model compounds was done and reproduced reasonably the experimental results taking into account the hydrogen bond and conformational effects. Most recently, we have reported that the isotropic