The performance of non-polarizable and polarizable force-field parameter sets for ethylene glycol in molecular dynamics simulations of the pure liquid and its aqueous mixtures

Abstract

Non-polarizable and polarizable force-field parameter sets for liquid ethylene glycol (EG) were developed for use in biomolecular simulation. In the polarizable models, electronic polarization effects were explicitly taken into account using the charge-on-spring method. The quality of the new force fields and two non-polarizable EG models taken from the literature was investigated by calculating relevant properties of the pure liquid and its aqueous mixtures, and comparing simulation results with experimental data. The performance of the EG models as a co-solvent in aqueous mixtures was additionally evaluated in a hydrophobic hydration study. The question was whether the experimentally known maximum in the solvation free enthalpy of argon at intermediate mixture compositions could be reproduced in the simulations. Values for the dielectric properties and excess free energy were found to be more off from experiment for the polarizable models than for the non-polarizable ones. However, a Kirkwood–Buff analysis of the aqueous mixtures and the hydrophobic hydration results exemplified that electronic polarization plays an important role in correctly describing attractive interactions between the EG and water co-solvent molecules. The trans/gauche ratio for ethylene glycol's O–C–C–O torsional angle was not found to systematically affect the properties of the pure liquid and aqueous mixtures.

Acknowledgement

The authors want to thank Merijn Schenk for the effort put into the polarizable GROMOS96 code and Nico F. A. van der Vegt for pointing out to us the experimental data on argon solubility in aqueous EG mixtures. Financial support from the National Centre of Competence in Research (NCCR) in Structural Biology and from grant number 200021–109227 of the Swiss National Science Foundation is gratefully acknowledged.