Molecular dynamics and quantum chemical studies on incremental solvation of glycine

Abstract

The conformational analysis of Glycine (Gly) amino acid in the presence of explicit water molecules is done using Molecular Dynamics (MD) simulation for over 10 ns time scale with step of 2 fs. Based on the hydrogen bond interactions, the solvated states of Gly and their distribution functions have been analyzed to identify the number of water molecules which fall within the first and second solvation shells. The ab initio and density functional theory (DFT) methods have been used to study the incremental solvation effect on Gly in gas phase with one to nine water molecules by constructing a hydration shell around Gly. Molecular geometries and energetical parameters of Gly⋯(W) n n = 1–9 complexes were studied by MP2, B3LYP and B3PW91 methods using 6-311G (2d, 2p) basis set. The interaction energies with BSSE corrections and the strength of the hydrogen bonds have been analyzed. The chemical hardness at HF/6-311G (2d, 2p) level of theory has been calculated for all the optimized structures. The topological analysis has been carried out for the water interacting complexes using Bader’s atoms in molecule (AIM) theory. The charge transfer from the proton acceptor to the anti-bonding orbital of proton donor in Gly⋯(W) n n = 1–9 complexes has been analyzed through Natural bond orbital (NBO) analysis. NMR calculations have been carried out on the basis of Cheeseman coworkers method at B3LYP/6-311G (2d, 2p) level of theory to analyse the molecular environment as well as the delocalization activities of electron cloud.