Competitive preferential solvation theory of weak molecular interactions

Abstract

The use of linear Benesi–Hildebrand, Scott or Scatchard equations to characterize molecular interactions leads frequently to anomalous results which cannot be interpreted easily in terms of traditional concepts. The situation is more serious for weak interactions, whose study requires the use of high concentrations of interacting partners. In the present paper a simple theory is proposed (Competitive Preferential Solvation theory or COPS theory) which can reasonably account for the observed anomalies without employing ad hoc arguments for individual problems. The theory is applied to a series of eighteen molecular interactions involving some degree of charge-transfer. These interactions have been studied by high resolution nuclear magnetic resonance spectroscopy. It is shown that the theory can be applied successfully to various physico-chemical techniques such as u.v. spectroscopy, kinetics and molecular relaxation processes. The new theory is compared with current ones.