Molecular dynamics simulations of dimethyl sulfoxide and dimethyl sulfoxide-water mixture

Constant-pressure constant-temperature MD simulations at ambient conditions have been carried out to evaluate three different potential models for DMS O, both as pure liquid and in the (1:3) DMSO-H-2 O mixture, based on struct ural, thermodynamical, and dynamical properties. All the three models for D MSO: OPLS, P2, and NPS, the last one proposed by us, gave a good descriptio n of liquid DMSO. In combination with the SPC/E and TIP3P water models, the se three potential functions were applied to predict excess mixing function s, reorientational correlation times and diffusion coefficients of the (1:3 ) DMSO-water binary system. Results obtained with the P2 and NPS models in combination with the SPC/E model for water agreed better with experiment th an the OPLS model with either TIP3P or SPC/E water. The new NPS potential m odel was further used for an analysis of the spatial solvation structure ar ound DMSO in the 1:3 mixture of DMSO-water, based on pairwise spatial distr ibution functions of atomic number densities. To reveal key structural feat ures and molecular topologies beyond the first solvation shell, a new type of multiparticle spatial distribution function was introduced. Statistical analysis of the hydrogen-bond network, in the system with a large excess of accepters, revealed DMSO . 2H(2)O but not the previously suggested DMSO . 3H(2)O complexes. Also the widely accepted picture of the DMSO . 2H(2)O com plexes needs a revision since many of these water molecules were further bo und to nearby DMSO molecules. Moreover, another typical configuration, cons isting of two DMSO and three water molecules, of which one was bridged to t he two DMSO molecules, was found. In general, the heavy and slowly moving D MSO molecules are stronger competitors for available donated hydrogen bonds than water molecules.