Binary mixtures of novel sulfoxides and water: intermolecular structure, dynamic properties, thermodynamics, and...

Higher molecular weight dialkyl sulfoxides attract interest in the context of biomedical sciences due to their ability to penetrate phospholipid bilayers, dissolve drugs, and serve as cryoprotectants. Intermolecular interactions with water, a paramount component of the living cell, determine the performance of the sulfoxide-based artificial systems in their prospective applications. Herein, we simulated a wide composition range of 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 the entire range of compositions. Strong deviations from an ideal mixture of between 30-50 mol% (based on molar volume) of sulfoxide content lead to relatively high dynamic viscosities of the mixtures. The 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.