Effects Of Hydration On The Dynamics Of Water In Lipid Bilayer Systems: A Molecular Dynamics Study

Abstract

The properties of interlamellar water are critically important to the structure and function of biological membranes. Recent developments in femtosecond infrared spectroscopy on membrane systems at various hydration levels have opened the possibility of direct comparison between experiment and molecular dynamics simulations on the same time scales. The interpretation of experimental findings can benefit from a detailed computational study of water solvation structure and dynamics of inter-lamellar water at these hydration levels. In this presentation, we report molecular dynamics simulations of 1-palmitoyl-2-oleoyl-phosphatidylcholine POPC bilayers in the liquid-crystalline state and at three hydration levels. Simulations were performed in the canonical ensemble using the GROMACS software package. The extent to which water is influenced by the presence of membrane depends on the hydration level. We found the anisotropic diffusion constant of lipid water exhibits interesting crossover behavior as the water molecule moves from the head group region toward the bulk region. The anisotropic hydrodynamic diffusion of water is explained by structural perturbation of the water hydrogen bond network by the lipid. Radial distribution function, spatial distribution function, and power spectra of water are calculated to consolidate our interpretation. This work was partially supported by the National Science Foundation under Grant No. DGE-0221680.