Water activity coefficients in aqueous amino acid solutions by molecular dynamics simulation: 1. Force field development

Abstract

New force fields for molecular dynamics (MD) simulation of aqueous zwitterionic amino acid simulations were developed. These were especially designed to calculate activity coefficient of water in amino acid solutions with high accuracy. For example, aqueous solutions of the following amino acids were considered: glycine, alanine, α-aminobutyric acid, α-aminovalerianic acid, valine and leucine. The force fields were obtained by quantum chemical calculations using B3LYP/6-31G and MP2/6-311(d,p) model theories in combination with the Merz–Kollmann–Singh scheme. To further increase the accuracy of the force field, a polarised continuum was considered in all quantum chemical calculations. Water activity coefficients obtained from MD using different all-purpose literature force fields, namely, OPLS, AMBER ff03 and GROMOS 53A6 as well as experimental data are compared with the results utilising the new force field. The new force field is shown to give better results compared with experimental data than existing force fields.