Electrochemical oxidation of a hexasulfonated calix[6]arene

The water-soluble calixarene p-hexasulfonato-calix[6]arene 1 was subjected to voltammetric studies of its oxidation. At glassy carbon or platinum electrodes in aqueous electrolyte solutions, oxidation was observed at E>0.7 V versus SCE in pH 2 solution. On glassy carbon, a stable derivatisation of the electrode surface was inferred from the perturbation in the electrochemistry of the anionic probe species Fe(CN)63−/4− while the electrochemistry of the cationic probe Ru(NH3)63+/2+ was unchanged. Investigation of the electrochemistry of 1 as a function of pH (2<pH<10) showed the expected dependence on the acid–base chemistry of 1 for the derivatisation of the electrode surface. On platinum electrodes, the electrochemical derivatisation was less stable and less obvious than on carbon, indicating a weakly adsorbed modifying layer.