Understanding how water hydrates cellular membranes is an important aspect of understanding how water-soluble compounds - such as drugs - can cross into a cell from the blood stream. This is especially important for the cells which make up the blood brain barrier (BBB) as these membranes are thought to be particularly well designed to exclude most highly water soluble compounds, though in reality many of these compounds do cross into the brain. The experiments here are designed to investigate how water interacts with the head groups of the lipid DOPE which is a component of BBB cellular membranes. We have previously investigated the hydration of the other two major components of this membrane - the PC head group and a sphingolipid - and this experiment will provide information that allows us to fully understand the hydration of these important merbranes.