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

A fully hydrated dimiristoylphosphatidylcholine (DMPC) bilayer has been studied 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 temperature of 333 K for a total of 10 ns. The resulting trajectory was used to analyze structural and dynamical quantities. The electron density, bilayer spacing, and order parameters (S,,,), based on the AMBER forcefield and SPCE water model are in good agreement with previous calculations and experimental data. The simulation reveals evidence for two types of lateral diffusive behavior: cage hopping and that of a two-dimensional liquid. The lateral diffusion coefficient is 8 X 10(-8) cm(2)/s. We characterize the rotational 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 lipid molecule.