Guest-host complex formed between ascorbic acid and β-cyclodextrin immobilized on the surface of an electrode.

This work deals with the formation of supramolecular complexes between ascorbic acid (AA), the guest, and beta-cyclodextrin (beta-CD), the host, that was first potentiodynamically immobilized on the surface of a carbon paste electrode (CPE) throughout the formation of a beta-CD-based conducting polymer (poly-beta-CD). With the bare CPE and the beta-CD-modified CPE, an electrochemical study was performed to understand the effect of such surface modification on the electrochemical response of the AA. From this study it was shown that on the modified-CPE, the AA was surface-immobilized through formation of an inclusion complex with beta-CD, which provoked the adsorption of AA in such a way that this stage became the limiting step for the electrochemical oxidation of AA. Moreover, from the analysis of the experimental voltammetric plots recorded during AA oxidation on the CPE/poly-beta-CD electrode surfaces, the Gibbs' standard free energy of the inclusion complex formed by the oxidation product of AA and beta-CD has been determined for the first time, Delta G(inclus)(0) = -36.4 kJ/mol.