Dimethyl sulfoxide fosters larger micelles of docusate sodium in the mixed solutions with water

Abstract

Docusate sodium also referred to as sodium bis(2-ethylhexyl)sulfosuccinate and dioctyl sulfosuccinate sodium (AOT) represents a green salt with proven potential across pharmacy, biology, and medicine. Physicochemical understanding of its inherent structural patterns, transport properties, and phase behavior in solutions is a challenging but essential endeavor. We hereby report conductometry, surface tension, density, and dynamic light scattering measurements of AOT in the dimethyl sulfoxide (DMSO)-water mixtures. The ab initio simulations are used to shed light on the electron density distributions and non-covalent interactions in the systems of our interest. We determine critical micelle concentration (CMC) and thermodynamic parameters of micellization (Gibbs free energy, enthalpy, and entropy) using the conductometry data at 298.15, 303.15, 308.15, 313.15, and 318.15 K. The CMC of AOT increases as DMSO mole fraction in the DMSO-water mixture increases. Negative free energies of micellization are observed over the entire investigated temperature range. Furthermore, higher contents of DMSO foster micellization gradually.The high contents of DMSO (X > 0.3) in the DMSO-water mixtures lead to abrupt changes in CMC and thermodynamics of AOT micellization. We link such changes to the formation of the DMSO self-associates and the associated structural changes in the liquid phase. The dynamic light scattering measurements reveal that larger micellar agglomerates and multilamellar AOT vesicles emerge at high DMSO fractions. The reported data fosters the thoughtful design of practically important systems in medicine.