Study of water diffusion on single-supported bilayer lipid membranes by quasielastic neutron scattering

High-energy-resolution quasielastic neutron scattering has been used to elucidate the diffusion of water molecules in proximity to single bilayer lipid membranes supported on a silicon substrate. By varying sample temperature, level of hydration, and deuteration, we identify three different types of diffusive water motion: bulk-like, confined, and bound. The motion of bulk-like and confined water molecules is fast compared to those bound to the lipid head groups (7-10 H ₂O molecules per lipid), which move on the same nanosecond time scale as H atoms within the lipid molecules.