Simulations of zwitterionic and anionic phospholipid monolayers.

Results of atomistic molecular dynamics simulations of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol monolayers at the air/water interface are presented. Dipalmitoylphosphatidylcholine is zwitterionic and dipalmitoylphosphatidylglycerol is anionic at physiological pH. NaCl and CaCl2 water subphases are simulated. The simulations are carried out at different surface densities, and a simulation cell geometry is chosen that greatly facilitates the investigation of phospholipid monolayer properties. Ensemble average monolayer properties calculated from simulation are in agreement with experimental measurements. The dependence of the properties of the monolayers on the surface density, the type of the headgroup, and the ionic environment are explained in terms of atomistically detailed pair distribution functions and electron density profiles, demonstrating the strength of simulations in investigating complex, multicomponent systems of biological importance.