Computational Study of Room-Temperature Ionic Liquids Interacting with a POPC Phospholipid Bilayer

Molecular dynamics simulations based on an empirical force field have been carried out to investigate the properties of a zwitter-ionic phospholipid (POPC) bilayer in contact with a water solution of [bmim][Cl], [bmim][PF6] and [bmim][Tf2N] at concentration c = 0.5 M. The results reveal important and specific interactions of cations and anions with the bilayer. The [bmim](+) cation, in particular, shows a clear tendency to be incorporated tail-first into the bilayer. [Cl](-) remains in solution, [PF6](-) forms a thin layer on the lipid surface, and [bmim][Tf2N] precipitates out of the solution, giving rise to an ionic droplet deposited on the lipid surface. The simulation results provide a microscopic basis to interpret the available experimental observations.