Voltammetric behavior of 1,2-dihydroxyanthraquinones attached to glassy carbon electrodes and their surface complexation with copper

The adsorption behavior of 1,2-dihydroxyanthraquinones on electrochemically treated GC electrodes has been analyzed on the basis of the Frumkin adsorption isotherm allowing for long-range interactions between adsorbed species. Their slow-scan voltammetric response corresponded with a voltammetric theory for reversible surface reactions accompanied by intermolecular interactions. The negative interaction parameter obtained indicated a repulsive interaction between the surface-confined species, which bound Cu2+ firmly at weakly acidic pHs. Although 1,2-dihydroxyanthraquinones behave normally as a bidentate ligand, the surface-immobilized species formed only a 1:1 complex with Cu(II), probably because of motional restraints imposed on them. The 1,2-dihydroxy groups of the ligand chelated a partially hydrolyzed copper(II) species, their oxidation thus being depressed. Surface-bound copper underwent a two-electron redox reaction repetitively without being released from the surface.