New Interaction Parameters for Oxygen Compounds in the GROMOS Force Field: Improved Pure-Liquid and Solvation Properties for Alcohols, Ethers, Aldehydes, Ketones, Carboxylic Acids, and Esters.

A new parameter set (53A6OXY) is developed for the GROMOS force field, that combines reoptimized parameters for the oxygen-containing chemical functions (alcohols, ethers, aldehydes, ketones, carboxylic acids, and esters) with the current biomolecular force field version (53A6) for all other functions. In the context of oxygen-containing functions, the 53A6OXY parameter set is obtained by optimization of simulated pure-liquid properties, namely the density ρliq and enthalpy of vaporization ΔHvap, as well as solvation properties, namely the free energies of solvation in water ΔGwat and in cyclohexane ΔGche, against experimental data for 10 selected organic compounds, and further tested for 25 other compounds. The simultaneous refinement of atomic charges and Lennard-Jones interaction parameters against the four mentioned types of properties provides a single parameter set for the simulation of both liquid and biomolecular systems. Small changes in the covalent parameters controlling the geometry of the oxygen-containing chemical functions are also undertaken. The new 53A6OXY force-field parameters reproduce the mentioned experimental data within root-mean-square deviations of 22.4 kg m(-3) (ρliq), 3.1 kJ mol(-1) (ΔHvap), 3.0 kJ mol(-1) (ΔGwat), and 1.7 kJ mol(-1) (ΔGche) for the 35 compounds considered.