Molecular dynamics simulations of sodium chloride solutions in water–dimethyl sulphoxide mixtures: Potentials of mean force and solvation structures

Five solutions of sodium chloride in mixtures of water and dimethyl sulphoxide ͑DMSO͒ have been simulated using the conventional molecular dynamics technique. The potentials of mean force ͑PMFs͒ of the sodium chloride ion pair in the presence of the five water–DMSO mixtures with DMSO mole fractions (x DMSO) of 0.10, 0.21, 0.35, 0.48 and 0.91 have been computed. The derived PMFs have been confirmed by the long time dynamical ion-pair trajectories. The solvation structures of the ions in the presence of these mixtures have been analyzed using the ion-solvent radial distribution functions and the corresponding integration numbers. It has been found that the Na ϩ ion is always preferentially solvated by the water molecules in all the water–DMSO solvent mixtures. The Cl Ϫ ion is slightly preferred by the DMSO molecules in these mixed solvents.