Water and Membranes

I. INTRODUCTION Water is unquestionably playing a very important part in the functioning of biomolecular assemblies. Depending on the character of the functional groups of biomolecules, the interactions of these groups with water and with themselves while solvated in water, are called hydrophobic or hydrophilic. These interactions are responsible for protein folding, the subject of a very intense study in the recent past and at the present time.1 The same interactions are also responsible for the creation of membrane structures in biology.2,3 The subject of water and its influence on the biomembrane properties is very broad, so we decided to concentrate here on the discussion of water properties in the region between lipid membranes and permeability of water across membranes. It is believed that water between membrane surfaces strongly influences the interactions between the surfaces. These interactions are determining the process of primary significance in biology: membrane and vesicle fusion.4 Understanding the basic mechanistic steps in the fusion process can result in the ability to mimic fusion for pharmacological applications, such as liposomal drug delivery. The interaction between membranes across water will be discussed in the part of our review dealing with the hydration force.