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.