Structure and dynamics of the dilauroylphosphatidylethanolamine lipid bilayer.

A 200-ps molecular dynamics (MD) simulation trajectory of a model dilauroylphosphatidylethanolamine (DLPE) bilayer in water at 315 K has been generated. Segmental order parameters, electron density profiles, and water pair distribution functions have been calculated. Comparison to experiment is made where possible. The dynamics of the system has been studied by analyzing the velocity autocorrelation functions (VAF) of both water and lipid atoms. Furthermore, the diffusive properties of water have been analyzed by computing the mean square displacement (MSD) and orientational correlation function (OCF) of water in two regions around the bilayer. The calculated order parameters show a behavior similar to the liquid crystalline phase of other bilayers, but the region around C1-C3 does not show the expected behavior. The electron density profile shows features that are characteristic of the liquid crystalline phase. The radial distribution functions suggest ordering of water near the charged head groups, which results in about 15 water molecules solvating each lipid molecule. We find from the VAF, MSD, and OCF calculation that the water molecules near the head groups of the lipid bilayer move more slowly than those further away. The VAF of the hydrocarbon chains have features of low-frequency motions that are probably cooperative nature in addition to the high-frequency motions associated with bond angle and torsional motions.