Local structural order and molecular associations in water-DMSO mixtures. Molecular dynamics study

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.…”

“…This strengthening of the water-water hydrogen bonds in the presence of DMSO was also concluded by Mancera et al from the temperature dependence of the properties of a dilute DMSO solution. 50 With increasing DMSO mole fraction even the water-DMSO g OO (r) function becomes more structured, its first peak gets higher and a second peak emerges around 5.5 Å, indicating, in accordance with earlier claims, 24,27,28 that even water-DMSO hydrogen bonding becomes stronger with increasing DMSO content. Finally, the comparison of the DMSO-DMSO oxygen-oxygen radial distribution function also becomes more structured as the DMSO mole fraction is increased.…”

“…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.…”

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

“…15,16 The existence of strongly hydrogen bonded one DMSO-2 water aggregates have also been proved through molecular dynamical simulations of these solvent mixtures. 9 In order to probe this associative character of DMSO and its influence on ion solvation, we have studied the solvation of the Na The PMF for the Na ϩ and Cl Ϫ ion pair in pure water has been reported by Berkowitz et al, 3 and by Karim and McCammon 4 using the umbrella sampling technique and also by Guardia, Rey, and Padro 5 using the constrained MD simulations. These two sets of results differ only slightly with respect to the location of the contact ion pair ͑CIP͒ minimum, the transition state ͑TS͒ maximum, the solvent separated ion pair ͑SSIP͒ minimum and also with respect to the magnitudes of dissociation and association barriers.…”

“…These studies cover many aspects of the NaCl solvation in the respective solvents including the evaluation of the potential of mean force ͑PMF͒, analysis of the solvation structure and dynamics, computation of solvent friction kernels, calculation of transmission coefficients across the PMF barriers and orientational distributions of the solvent molecules around the ions. The solvent mixtures like water-methanol, water-acetone and waterammonia have been simulated by Ferrario et al 8 Similarly, the water-DMSO mixture has been simulated by Vaisman and Berkowitz 9 and also by Luzar and Chandler. 10 Interestingly, the simulations of NaCl solutions in solvent mixtures are being reported only recently.…”