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. NaCI and CaCI2 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.
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YNK wishes to thank Pfizer Global Research and Development, Ann Arbor Laboratories for funding of his postdoctoral fellowship. We thank Scott Feller for useful suggestions on the simulations, and we thank Ka Yee Lee and Ajaykumar Gopal for invaluable insight into the experimental behavior of lipid monolayers. We also gratefully acknowledge support by the National Computational Science Alliance under grant MCB000007N at the NCSA Origin2000.