Preferential Hydration (Molecular Biology)

Preferential hydration is the excess of water in the immediate domain of a protein relative to the water concentration in the bulk solvent (eg, in 3 M glycerol). It is related to the preferential binding of a ligand by a simple reciprocal relation (see Binding):

The term on the left-hand side is the excess of water molecules on the surface of the protein relative to the concentration of water in the bulk mixed solvent. As we see, this expression tells us that there is an excess of water on the protein surface if there is a deficiency of ligand, and vice versa. Understanding this and similar relations (see Binding) is of major importance in the stabilization and destabilization of protein structure by the addition of cosolvents, such as urea or sucrose. Preferential hydration must not be confused with total hydration.