Molecular Mechanism of Ion Binding to the Liquid/Vapor Interface of Water

Abstract

We have carried out extensive molecular dynamics simulations to study the electrostatic surface potentials and molecular mechanism of iodide binding to the liquid/vapor interface of water using both nonpolarizable and polarizable potential models. Both simulated electrostatic surface potentials are negative with a value of about −0.50 ± 0.01 V. The simulated results are compared to the experimental estimates of the surface potentials ranging from −1.1 V to 0.4 V. This paper contributes to a better understanding of the molecular mechanisms of ion binding to the liquid/vapor interface of water. A free energy minimum was observed near the Gibbs dividing surface for simulations that employed polarizable models. In contrast, simulations that used nonpolarizable models provided no surface state as the iodide crossed the liquid/vapor interface of water. Corroborating observations were recently reported by Finlayson-Pitts and co-workers (Knipping, E. M.; Lakin, M. J.; Foster, K. L.; Jungwirth, P.; Tobias, D. J.; Gerber, R. B.; Daddub, D.; Finlayson-Pitts Science 2000, 301, 288) using different approaches.