An MO study of nuclear quadrupolar coupling constant and nuclear shielding of the carbonyl oxygen in solid peptides with hydrogen bonds Original Research Article

The theoretical calculations of the electric field gradients of hydrogen-bonded carbonyl oxygens in glycine containing peptides were successfully carried out by the MNDO-PM3 method. From these calculated results, it was found that the calculated e2qQ/h value decreases with a decrease in the hydrogen bond length, and the chemical shielding values increase with a decrease in the hydrogen bond length. These calculations reasonably explain the experimental findings previously reported by us. Further, the direction of the principal axes of the electric field gradient and chemical shielding tensor of the carbonyl oxygen were reasonably obtained by the FPT-MNDO-PM3 method.