The Correlated States Theory of Hydrophobic Effect: The Physicochemical Analogue

It was found that within the framework of the correlated states theory of the hydrophobic effect (CST-theory), the hydrophobic hydration (HH) may be interpreted in terms of a Langmuir adsorption of water molecules on the surface of a nonpolar solute, leading to the formation of correlated solute-water pairs (sw-pairs) and formation of a water surface at the solute-water interface (referred to as the physicochemical analogue of the CST-theory). Such an approach has led to a general formulation of the partition function for HH, the definition of the correlated and noncorrelated states of the sw-pairs, and derivation of the equations for thermodynamic functions. It has been proved that the thermodynamic parameters of HH may be presented as a sum of two principal terms: the first one is related to the sw-pair formation, and the second one is related to the water molecules located on the surface of the solute-containing cavity. It has also been concluded that the entropy change on HH may be viewed as a sum of three fundamental terms, viz., the averaged sum of entropies of individual correlated sw-pairs, the configurational entropy characterizing the equilibrium distribution of correlated/uncorrelated sw-pairs, and the negative entropy of water molecules on the surface of the cavity. Some well-known experimental manifestations of HH have been discussed within the framework of the developed physicochemical analogue of the CST theory.