Aqueous Media Effect on Molecular Recognition. II. Temperature Dependence of Chemical Selectivity in Alcohols and Water

Abstract

Oxidation of a pair of associating thiols (1 and 2), each having the binding site [–C(=O)NHC(=O)NH–] and the recognition site (R1 or R2), is examined at several temperatures in alcohols (MeOH, EtOH, n-PrOH, and i-PrOH) and water. The selectivity (r), a measure of molecular recognition of 1 by 2 (or of 2 by 1), in the oxidation is defined as the logarithmic ratio of the yield of an unsymmetrical disulfide (4) to twice that of a symmetrical one (3). It is found that the selectivity in the alcohols each decreases markedly with increasing temperature except for one case, whereas that in water increases with increasing temperature. Correlation of the observed selectivity with factors affecting the selectivity (e.g., intermolecular association, physicochemical properties of solvents, and hydrophobic interaction) is discussed.