  Senior dialkyl sulfoxides constitute interest in the context of biomedical
sciences due to their abilities to penetrate phospholipid bilayers, dissolve
drugs, and serve as cryoprotectants. Intermolecular interactions with water, a
paramount component of the living cell, determine performance the
sulfoxide-based artificial systems in their prospective applications. Herein,
we simulated a wide composition range of the sulfoxide/water mixtures, up to 85
w/w% sulfoxide using classical molecular dynamics to determine structure,
dynamics, and thermodynamics as a function of the mixture composition. As
found, both diethyl sulfoxide (DESO) and ethyl methyl sulfoxide (EMSO) are
strongly miscible with water. DESO and EMSO based aqueous mixtures exhibit
similar structure and thermodynamic properties, however, quite different
dynamic properties over an entire range of compositions. Strong deviations from
an ideal mixture between 30 50 mol% of sulfoxide content leads to relatively
high shear viscosities of the mixtures. Free energy of mixing with water is
only slightly more favorable for EMSO than for DESO. The results, for the first
time, quantify high miscibilities of both sulfoxides with water and motivate
comprehensive in vivo investigation of the proposed mixtures.
