An ab initio calculation of double zeta quality on glycyl-glycine at the crystal structure yielded nuclear quadrupole coupling constants at the peptide centres

An ab initio calculation of double zeta quality on glycyl-glycine at the crystal structure yielded nuclear quadrupole coupling constants at the peptide centres very close to experiment; yzz — 3.03, XyV + 2.14, /.v.v + 0.89 MHz. The first two couplings lie in the local jr-direction, and along the C-N bond, respectively. At the NHf centre the values were less satisfactory, but the (low) positive value of was obtained, and lies relatively close to the N-C bond. The results suggest that similar calculations may be successful for other H-bonded systems, provided that aromatic systems are not involved.