Influence of the solvation upon the reaction of α-cyclodextrin with carboxylic acids, their methyl esters, and their sodium salts in aqueous solution studied by calorimetric measurements

The complex formation of alpha-cyclodextrin with carboxylic acids, their methyl esters, and their sodium salts has been studied using calorimetric titrations. The stronger solvation of the carboxylic sodium salts compared with the free acid or their methyl esters lowers the values of the reaction enthalpy and entropy. Complex formation is influenced in the positive direction by the release of "high-energy water" from the cavity of alpha-cyclodextrin. The values of the reaction enthalpy and entropy increase for the complex formation of alpha-cyclodextrin with increasing chain length of the carboxylic acids and their derivatives, and reach an approximately constant upper limit in the case of five methylene groups.