THEORETICAL-STUDY OF N-METHYLACETAMIDE IN VACUUM AND AQUEOUS-SOLUTION - IMPLICATIONS FOR THE PEPTIDE-BOND ISOMERIZATION

A theoretical study on the changes in energy and charge distribution upon rotation of the amide bond of N-methylacetamide is presented. Both gas-phase and aqueous environments have been simulated in semiempirical (AM1) and ab initio (STO-3G, 6-31G and 6-31G*) calculations with inclusion of electron correlation effects at the Moller-Plesset level. Relevant changes in the charge distribution are found during rotation of the peptide bond. The inclusion of water largely affects not only the energetics and the pathway of the amide twisting but also the charge distribution of the different conformers. Results are in good agreement with available experimental data and with results derived from high-level theoretical calculations. The chemical and biochemical importance of the results is discussed.