Anomalous diffusion of water molecules in hydrated lipid bilayers.

We present a molecular dynamics (MD) study of the water molecules in a hydrated lipid bilayer. Due to the interactions at the surface of a solvated lipid membrane, the dynamics of the water and lipid molecules are to some degree correlated. In spite of previous efforts reported in the literature, little is known about the time and length scales of these correlations. Here, by employing a 0.1 μs long equilibrium MD simulation of a dimyristoylphosphatidylcholine (DMPC) lipid bilayer, we show that the waters in a hydrated lipid bilayer can be classified into four dynamically connected water layers, and provide a detailed analysis of the water dynamics within these four regions. We also show that there exists a cooperative molecular motion between the hydration waters and the DMPC lipid molecules, and determine the corresponding characteristic time and length scales.