MOLECULAR-DYNAMICS SIMULATIONS OF A FLUID BILAYER OF DIPALMITOYLPHOSPHATIDYLCHOLINE AT FULL HYDRATION, CONSTANT-PRESSURE, AND CONSTANT-TEMPERATURE

Molecular dynamics simulations of 500 ps were performed on a system co nsisting of a bilayer of 64 molecules of the lipid dipalmitoylphosphat idylcholine and 23 water molecules per lipid at an isotropic pressure of 1 atm and 50 degrees C. Special attention was devoted to reproduce the correct density of the lipid, because this quantity is known exper imentally with a precision better than 1%. For this purpose, the Lenna rd-Jones parameters of the hydrocarbon chains were adjusted by simulat ing a system consisting of 128 pentadecane molecules and varying the L ennard-Jones parameters until the experimental density and heat of vap orization were obtained. With these parameters the lipid density resul ted in perfect agreement with the experimental density. The orientatio nal order parameter of the hydrocarbon chains agreed perfectly well wi th the experimental values, which, because of its correlation with the area per lipid, makes it possible to give a proper estimate of the ar ea per lipid of 0.61 +/- 0.01 nm(2).