ELECTROCHEMICAL-BEHAVIOR OF CALIX[4]ARENEDIQUINONES AND THEIR CATION-BINDING PROPERTIES

The redox and cation-binding properties of three quinone-functionalized calix[4]arenes have been studied in acetonitrile. Cation-bound calix[4]arenediquinone produces a new set of redox peaks at positively shifted potentials. Thus, the association constant between cation and calix[4]arenediquinone is found to be enhanced by the electrochemical reduction of the receptor molecule. The enhancement is dependent on the charge and size of cations. The magnitude of the potential shift can be explained on the basis of stabilization due to the transition of binding characteristics from ion-dipole to ion-ion interaction by an electron transfer reaction. Substituents in the lower rim exert considerable influence on the redox behavior of the complex. NH4+ produces extraordinary voltammetric behavior due to the fact that only NH4+ can form hydrogen bondings with calix[4]arenes, in contrast to other metal ions.