DMSO Transport across Water/Hexane Interface by Molecular Dynamics Simulation

Configurational, energetic, and dynamical properties of dimethyl sulfoxide (DMSO) transport across the water/hexane interface are investigated by molecular dynamics simulations. It is shown that the interface accumulation caused by the interface activity of DMSO dominates the diffusion process. In this case the underlying transport process can be divided into two steps by different energy landscapes and kinetic motions of solute molecules. In addition, interface deformation caused by solutes also influences the process and its impact on solutes is different on each side. A transfer of DMSO from the hexane phase to the interface (step I) is facilitated by free energy gradient and the interface deformation does not hinder its motion toward the interface, whereas its escape from the interface to the water phase (step II) will be obstructed by high free energy gradient and the interface deformation also plays a negative role. Consequently, step II dictates the whole transport process. However, the solute concentration in the interface is much higher than that in the bulk, and it is deduced that a larger interface area can lead to higher capacity of DMSO with higher extractions. For such systems observed in our simulation studies, the distribution of dispersed phase can be a key factor for the efficient extraction process.