Dynamical properties of phospholipid bilayers from computer simulation

We present the results of a 10-ns molecular dynamics simulation of a dipalmitoylphosphatidylcholine/water system. The main emphasis of the present study is on the investigation of the stability over a long time and the dynamic properties of the water/membrane system. The motion of the lipid molecules is characterized by the center of mass movement and the displacement of individual atom groups. Because of the slow movement of the headgroup atoms, their contributions to the dipole potential vary slowly and with a large amplitude. Nevertheless, the water molecules compensate the strong fluctuations and maintain an almost constant total dipole potential. From the lateral displacement of the center of masses, we calculate the lateral diffusion coefficient to be D-lat = (3 +/- 0.6) x 10(-7) cm(2)/s, in agreement with neutron scattering results. The rotational motion is also investigated in our simulations. The calculated value for the rotational diffusion coefficient parallel to the molecular long axis, D-parallel to = (1.6 +/- 0.1) x 10(8) s(-1), is in good agreement with the experiment.