Molecular association between water and dimethyl sulfoxide in solution: A molecular dynamics simulation study

Abstract

A molecular dynamics simulation study of the local structures and H-bond distribution for water–dimethyl sulfoxide (DMSO) mixtures over the entire composition range is presented. Analysis of several site-site pair distribution functions reveals that two well-defined kinds of aggregates characterize the molecular association between water and DMSO in solution. One of them, already identified through recent neutron diffraction experiments and computer simulations, consists of two water molecules H-bonded to the oxygen atom of a DMSO molecule, such that the angle between the two H-bonds is nearly tetrahedral. The other complex features a central water molecule and two DMSO, making H-bonds to water hydrogens. According to the simulation data, these molecular aggregates coexist with each other in the mixture, but their proportions change with composition. 1DMSO-2water complexes predominate over 2DMSO-1water aggregates for water-rich mixtures (water mole fractions >50%), whereas the opposite is true for DMSO-rich mixtures. The present simulations also seem to indicate that an association between a pair of DMSO molecules through their oxygen atoms is made possible by the formation of the 2DMSO-1water complexes. Implications of the existence of these aggregates to the mobility and other dynamic properties of these mixtures are briefly discussed.

The local environment of the molecules in water–DMSO mixtures, as seen from computer simulations and Voronoi polyhedra analysis

“…It should also be noted that the aforementioned molecular scale mixing of water and DMSO is in a full accordance with a number of previous experimental 13,17 and computer simulation studies, [24][25][26][27]31 and it is also compatible with the assumption 7,13,[24][25][26][27]54,55 This view is also consistent with the fact that, unlike in the case of the first and fourth peak, corresponding to always very similar local environments, the positions of the second and third peaks show non-negligible composition dependence (see Fig. 4), reflecting the above change of the mixed local environment with the composition of the system.…”

“…In fact, there is a convergence in the literature that in the DMSO mole percentage range of 30-40 % the water-DMSO interactions due to hydrogen bonds are at maximum. 18 Indeed, DMSO:water complexes of the stoichiometry of 2:1 at high DMSO mole fraction, 24,26,30,32 as well as of 1:2, 6,8,24,[26][27][28] 2:3, 27 and 1:3 33 at low DMSO content were proposed in the literature, although the existence of the latter has also been questioned. 27 However, such complexes were rather scarcely observed directly, e.g., through a detailed multiparticle spatial distribution analysis, 27 instead, their existence was merely hypothesized in explaining anomalous dynamical and thermodynamic properties of the mixture and other experimental data, or concluded on the basis of indirect evidences, such as radial distribution functions.…”

A hybrid neutron diffraction and computer simulation study on the solvation of N-methylformamide in dimethylsulfoxide

“…45,55,[62][63][64][65][66][67][68][69] Thus, it is likely that in DMSO-water medium of moderate composition, the H-bond competition of DMSO with water and NMF favors the OD-water H-bond. As a consequence, the delocation of the water molecules H-bonded to the NMF would be lower in that case, in a good parallelism with previous results.…”

Rotational Dynamics of Nonpolar and Dipolar Molecules in Polar and Binary Solvent Mixtures

“…The largest deviations from the ideal mixing occur around 33% mole of DMSO, thus suggesting the existence of stoichiometrically well defined 1DMSO:2water complexes. Recently, a number of MD simulations (Vaisman and Berkowitz, 1992;Soper and Luzar, 1992;Luzar and Chandler, 1993;Borin and Skaf, 1998; and neutron diffraction experiments have indeed identified the structure of the 1DMSO:2water complex and linked many of the structural and dynamical features of DMSO water mixtures to the presence of such aggregates. Of late, Borin and Skaf (Borin and Skaf, 1998; have found from MD simulations, another distinct type of aggregate consisting of two DMSO molecules linked by a central water molecule through H-bonding, which is expected to be the predominant form of molecular association between DMSO and water in DMSO-rich mixtures.…”