Carboxylate anion binding in the cyclohexaamylose cavity: A steric and electronic evaluation

This investigation focuses on the steric and electronic requirements for the binding of carboxylate anions in the cyclohexaamylose cavity. The geometries and thermodynamic stabilities of the 3,5-dimethyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxycinnamic acid, and 3,5-dimethyl-4-hydroxyhydrocinnamic acid cyclohexaamylose complexes are evaluated at pH = 7.60 and 12.00. Results indicate that the carboxylate anions of 3,5-dimethyl-4-hydroxycinnamic acid and 3,5-dimethyl-4-hydroxyhydrocinnamic acid bind in the cyclohexaamylose cavity at both pH = 7.60 and 12.00. In addition, the dependence of the stability of the resulting complexes on pH is shown to be marginal. These findings suggest that if a carboxylate anion is to bind in the cyclohexaamylose cavity, it must be able to adopt a position in the cavity which allows for at least partial solvation of charge.