Role of water in the hydration force acting between lipid bilayers

To understand the nature of the hydration forces acting between biomembranes, we perform computer simulations on liquid crystalline dilauroylphosphatidylethanolamine (DLPE)/water and compare the results with previously reported dipalmitoylphosphatidylcholine (DPPC)/water systems. From our simulations of both systems we find that the influence of the surface on water properties is detectable only over a short range and that the membrane surfaces are rough on a molecular scale. We find that the hydration force is due to (a) the removal of only one or two layers of solvating water from the membrane surface and (b) steric interactions. The detailed structure of the solvating water is responsible for the difference in the hydration force acting between DLPE membranes compared to DPPC membranes.