N-amination of peptides:: A theoretical study

A quantum mechanical study about the effects of replacing the amide link by the N-amino amide group in peptides is presented. More specifically, this work deals with (i) the isomerization process of the N-amino amide link and (ii) the conformational changes induced by N-amination on both the glycine- and proline-containing dipeptides. Molecular geometries were optimized at both HF/6-31G(d) and MP2/6-31G(d) levels of theory. High-level ab initio calculations were performed on the optimized geometries in order to investigate the effects of both the basis set and electron correlation on the relative energies. Furthermore, the reliability of the density functional approximation on the conformational studies of N-amino peptides was investigated by considering six different functionals. Calculations in solution (dielectric constants of is an element of = 2, 4, 8, 33, and 78.5) were performed using the polarizable continuum model in the framework of the ab initio HF/6-311++G(d,p) level.