The Hydrophobic Interaction

Abstract

The peculiar features exhibited by aqueous solutions of some very simple molecules have been studied for some 30 years and various attempts have been made to account for the nature of such solutions in terms of conceptual models which take particular account of the observed solution behavior. The solutes in question include the rare gases, alkanes, and alkyl and aromatic compounds with only one, or at most two, polar functional groups. However, since we are dealing with a special type of interaction between water and apolar residues, a whole range of polymers must be included in the discussion, and indeed it is the influence of these particular interactions on polymer conformation and aggregation behavior which provides the most interesting manifestation of the phenomenon under discussion. The role of apolar group interactions (hydrophobic bonding) in maintaining the tertiary (native) structures of proteins was reviewed by Kauzmann,⁽⁷⁵⁹⁾ who suggested that comparatives studies of aqueous and nonaqueous solutions of simple analogs of apolar amino acid side chains, ideally alkanes, might provide a valuable insight into the peculiarities of water as a solvent. His suggestion was taken up by many physical chemists and biochemists, and thanks to their efforts, the properties of simple and, more usually, not so simple molecules in aqueous solution are well documented. Although hydrophobic hydration and solute association are now accepted phenomena, it must be emphasized that, as yet, we have no knowledge of the origin of such behavior.