LOCAL STRUCTURAL ORDER AND MOLECULAR ASSOCIATIONS IN WATER DMSO MIXTURES - MOLECULAR-DYNAMICS STUDY

Pure dimethyl sulfoxide (DMSO) and water-DMSO mixtures at three concentrations (x(DMSO) = 0.005, 0.04, and 0.2) are studied using molecular dynamics simulations. Structural properties of water in different regions of DMSO hydration are investigated by using radial distribution functions (RDF), hydrogen-bonded network parameters, and the statistical geometry approach. Reliability of RDF as indicators of structure changes at different concentrations is discussed. Enhancement of the water structure at the lowest DMSO concentration and its breakdown at x(DMSO) = 0.04 and 0.2 is observed. Structural effects in water-DMSO mixtures are attributed to the prevailing influence of the DMSO polar group on the water structure. It is found that the complex consisting of 1 DMSO and 2 water molecules hydrogen bonded to the DMSO oxygen exists at all studied concentrations. Local order in pure DMSO is determined by dipolar forces as well as molecular association. Both components in water-DMSO mixture are tending to preserve their structural order upon dilution. All simulation results are compared with numerous experimental data. A good agreement is found in most cases.