Dynamical properties of a hydrated lipid bilayer from a multinanosecond molecular dynamics simulation

A fully hydrated dimiristoylphosphatidylcholine (DMPC) bilayer has been stu died by a molecular dynamics simulation. The system, which consisted of 64 DMPC molecules and 1792 water molecules, was run in the NVE ensemble at a t emperature of 333 K for a total of 10 ns. The resulting trajectory was used to analyze structural and dynamical quantities. The electron density, bila yer spacing, and order parameters (S,,,), based on the AMBER forcefield and SPCE water model are in good agreement with previous calculations and expe rimental data. The simulation reveals evidence for two types of lateral dif fusive behavior: cage hopping and that of a two-dimensional liquid. The lat eral diffusion coefficient is 8 X 10(-8) cm(2)/s. We characterize the rotat ional motion, and find that the lipid tail rotation (D-rot_tall = -0.04 rad (2)/ns) is slower then the head group rotation (D-rot_hg = 2.2 rad(2)/ns), which is slower than the overall in plane (D-rot = 3.2 rad(2)/ns) for the l ipid molecule.