Conformations of the glycine tripeptide analog Ac-Gly-Gly-NHMe: a computational study including aqueous solvation...

A computational study of the conformational preferences of the glycine tripeptide analog, Ac-Gly-Gly-NHMe, has been carried out. The molecule is considered in isolation as well as with a continuum model of aqueous solvation. In the absence of solvent, several low-energy conformers are found that exhibit turnlike structures including type I and type II β turns. Upon consideration of aqueous solvation, two conformers, corresponding to the type I and II turn structures are found to be significantly lower in energy than all others. Results from ab initio molecular orbital theory calculations at MP2/aug-cc-pVTZ//MP2/6-311+G(d,p) are compared with those from density functional theory with B3LYP, ωB97X-D, B97-D, and M06-2X as well as several empirical force fields.