A mechanism for ion transport across the water/dichloromethane interface: A molecular dynamics study using polarizable potential models

In this work, we used molecular dynamics techniques and potential of mean f orce approaches to compute the ion transfer free energy for the water/dichl oromethane liquid-liquid interface. We used polarizable potential models to describe the interactions among the species. Both foward and reverse direc tions simulations were carried out to evaluate the differences in the free energy profiles. On the basis of the results of our calculations, we have p roposed a mechanism that describes the transport of a chloride inn across t he interface. The computed ion transfer free energy is 14 +/- 2 kcal/mol, w hich is in qualitative agreement with the experimentally reported value of 10 +/- 1 kcal/mol. A smooth transition from the aqueous phase to the nonaqu eous phase on the free energy profile clearly indicates that the ion transf er mechanism is a nonactivated process. The computed hydration number for t he chloride ion indicates that some water molecules are associated with the ion inside the nonaqueous phase. This result is in excellent agreement wit h the experimental interpretation of the ion transfer mechanism reported re cently by Osakai et al.