Water Behavior Near the Lipid Bilayer

In this chapter, we focus on the dynamics of water molecules situated in the vicinity of a phospholipid bilayer. Using a molecular dynamics simulation method, we studied interactions between water and the bilayer and tracked trajectories of the water molecules. Based on the hypothesis that molecules trapped inside the bilayer make different motions than the ones which are either attached to the surface or move freely in the water bulk, we divided the water molecules into three groups – the ones that exhibited subdiffusion (confined) motion, the ones that move diffusionally in the bulk and the ones that move superdiffusively due to interactions with the moving bilayer. In detail, the water behavior near the bilayer has been analyzed by mean squared displacement and entropy computed separately for the above mentioned three groups of molecules. To explain the subdiffusion motion of the water molecules, the number and the duration of hydrogen bonds created between water molecules and the bilayer have been investigated. In addition, we examined the mechanism of water molecule self-diffusion, by means of statistical tests. Our studies aim to present insight into the understanding of the lipid’s role in water self-diffusion, which can be responsible for triggering different tribological responses of the system.