Water and Membranes

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. In the DLVO theory intersurface water was considered to be a structureless dielectric continuum. The forces of interaction between membrane surfaces have been measured by using predominantly the vapor stress method and osmotic stress method. The general picture that emerges from the experiments is that up to ~3-nm-lipid bilayers in water repel each other with the monotonically decaying force. Experimental permeation rates of water molecules can be measured by means of osmotic, nuclear magnetic resonance, and radio tracer experiments, although the interpretation of the results is often difficult. It is clear that the ability of making hydrogen bonds with other water molecules increases toward the membrane.