Large Slowdown of Water Dynamics at Stacked Phospholipid Membranes for Increasing Hydration Level: All-Atoms Molecular Dynamics

Abstract: Water hydrating phospholipid membranes determine their stability and function, as well as their interaction with other molecules. In this article we study, using all-atom molecular dynamics simulations, the rotational and translational dynamical properties of water molecules confined in stacked phospholipid membranes at different levels of hydration, from poorly hydrated to a completely hydrated membrane. We find that both the translational and the reorientation dynamics of water are dramatically slowed down as the hydration is reduced. Analyzing in details the structure and dynamics of the hydrogen bond at the interface, we show that both those among water molecules and those between water and lipids slow down by decreasing the hydration, however the latter are always slower than the former. By increasing hydration, water saturates all the possible hydrogen bonds with the lipids and, by further increase of hydration, the hydrogen bonds among waters becomes the majority. However, the dynamics of the water-lipids hydrogen bonds becomes up to one order of magnitude slower than that of the water-water hydrogen bonds, inducing a large slowing down of the dynamics of the entire system even at large hydration level.