Membrane Hydration: A Hint to a New Model for Biomembranes.

The classical view of a biological membrane is based on the Singer-Nicholson mosaic fluid model in which the lipid bilayer is the structural backbone. Under this paradigm, many studies of biological processes such as, permeability, active transport, enzyme activity and adhesion and fusion processes have been rationalized considering the lipid membrane as a low dielectric slab of hydrocarbon chains with polar head groups exposed to water at each side in which oil/water partition prevails. In spite of several analyses and evidence available in relation to membrane hydration, water is not taken into account as a functional component. For this purpose, new insights in the water organization in restricted environments and the thermodynamical and mechanical properties emerging from them are specifically analysed and correlated.This chapter summarizes the progress of the studies of water in membranes along the book in order to give a more realistic structural and dynamical picture accounting for the membrane functional properties.