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 force approaches to compute the ion transfer free energy for the water/dichloromethane liquid-liquid interface. We used polarizable potential models to describe the interactions among the species. Both foward and reverse directions simulations were carried out to evaluate the differences in the free energy profiles. On the basis of the results of our calculations, we have proposed a mechanism that describes the transport of a chloride inn across the interface. The computed ion transfer free energy is 14 +/- 2 kcal/mol, which is in qualitative agreement with the experimentally reported value of 10 +/- 1 kcal/mol. A smooth transition from the aqueous phase to the nonaqueous phase on the free energy profile clearly indicates that the ion transfer mechanism is a nonactivated process. The computed hydration number for the chloride ion indicates that some water molecules are associated with the ion inside the nonaqueous phase. This result is in excellent agreement with the experimental interpretation of the ion transfer mechanism reported recently by Osakai et al.