Molecular dynamics simulation of dilute aqueous DMSO solutions. A temperature-dependence study of the hydrophobic and hydrophilic behaviour around DMSO

We have studied the temperature dependence of the hydrophobic and hydrophilic hydration properties of dimethyl sulfoxide (DMSO) in water by performing a series of molecular dynamics simulations of such aqueous solutions at a concentration of 0.055 mole fraction at 298, 318 and 338 K. Our results corroborate the existence of an enhancement in the structure of water. There is a well-defined hydration structure around the oxygen atom of DMSO, which establishes strong linear hydrogen-bonds with water molecules. Such interactions increase the lifetime of water-water hydrogen bonds in the vicinity of the OS group. Hydrophobic hydration around the Me groups of DMSO is observed, shown by the formation of an ordered hydration shell around these groups, with strong water-water hydrogen bonds that have longer lifetimes than in the bulk of the solution. We could find no evidence for a temperature-dependent hydrophobic interaction between these groups. All these combined effects reveal that the hydrophilic hydration of DMSO dominates over any hydrophobic effects as the temperature is increased.