Peptide models XI. Substitution effects on peptide chains. The magnitude of side-chain–backbone interactions in oligopeptides HCO-(NHCHRCO)n-NH2 for R=CH3. An ab initio study

The stabilization effect of the Me group with respect to H has been determined for peptides of the type HCO-(NH-CHR-CO)n-NH2 for 1 ≤ n ≤ 3. It was found that for the Me group the stabilization energy was in the vicinity of 5.4 kcal/mol. The site of substitution had no appreciable effect on the stabilization energy. The stabilization energy for monomethyl substitution (R=CH3) ranged from 5.21 to 5.60 kcal/mol. For dimethyl substitution the values were between 10.53 and 10.81 kcal/mol, and for trimethyl substitution it was 15.99 kcal/mol. Keywords: stabilization effects of substituents, oligopeptide conformations, ab initio study on HCO-(NHCHRCO)n-NH2.