The interaction of α-cyclodextrin with aliphatic, aromatic and inorganic peracids, the corresponding parent acids and their respective anions

Potentiometric or combined potentiometric and spectrophotometric or kinetic techniques have been used to determine stability constants for complexes between α-cyclodextrin and 20 of the title compounds. Linear free energy relationships indicate that 4-substituted benzoic acids, perbenzoic acids and perbenzoates have predominantly the same orientation within the cyclodextrin cavity, with the carboxylic acid, percarboxylic acid and percarboxylate groups located at the narrow (primary hydroxy) end of the cavity. 4-Substituted benzoates orientate in the opposite way with the carboxylate group located at the wide end of the cavity. Alkyl carboxylic acids, percarboxylic acids and their anions show a linear dependence between log stability constant and the number of carbons. They are likely to bind with the functional group at the narrow end of the cavity, although the carboxylate groups will probably be located outside the cavity because of solvation requirements. 2:1 cyclodextrin-guest complexes are observed for several of the compounds studied.