Density Functional Theory Studies on Effects of Additive Hydration on Neutral and Zwitterionic Glycylalanine

Abstract

The density functional theory computations have been carried out to study the effect of stepwise hydration on the structures of various conformers of the Neutral Glycylalanine…(Water) n (NGA…(W) n ) (n=5-10) and Zwitterionic Glycylalanine...(Water) n (ZGA…(W)n) (n=5-9) clusters. This indicates that the most stable neural GA conformer is 50.2 kcal/mol lower in energy than its zwitterionic counterpart. The hydrogen bonding interaction energies with BSSE corrections have been analyzed. Starting from complexation with six water molecules, ZGA complexes turn out to be the most stable candidates than their neutral partners. Theories of Bader’s Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) are applied to examine the hydrogen bonds in the solvated complexes. In all hydrated complexes, the N-H (amino group)-Ow and O15-H16… Ow bonds are observed to be relatively short and possess comparatively higher values of (r) and (r). A good correlation between the structural parameters and the properties of charge density is found.