Electrochemical Stability of Catechols with a Pyrene Side Chain Strongly Adsorbed on Graphite Electrodes for Catalytic Oxidation of Dihydronicotinamide Adenine Dinucleotide

Article abstract of DOI:10.1021/ja00345a021

The electrochemical stability and reactivity of 4-<2-(1-pyrenyl)vinyl>catechol (PSCH2) and 4-<2-(1-pyrenyl)ethano>catechol (PECH2) strongly adsorbed on graphite electrodes were investigated as a function of the applied potential at pH 7.0.The surface coverage of these compounds ranged from 0.1 x 10^-9 to 2.7 x 10^-9 mol/cm².The ''modified'' electrodes exhibited deactivation which could be explained by second-order reactions between the catechols and the electrochemically produced quinones coupled with a second-order reaction between the quinones.The ethano compound showed a much larger decay rate, probably because of free rotation around the saturated bond connecting the pyrene part and the catechol group.The deactivation was apparently not associated with decomposition of the compounds.The catechols in the oxidized form could catalytically oxidize NADH.The overpotential for NADH oxidation was thus decreased from 410 to 150 mV vs.SCE at pH 7.0.However, the catalytic current was found to decrease exponentially with increasing number of scans.The rate of this deactivation of the catalytic electrode was found to be inversely proportional to the coverage of immobilized mediator.The deactivation could be explained by a chemical coupling reaction between the mediator and NADH, forming a complex which gradually blocked off the surface of the electrode.The probable nature of the complex makes it unlikely that ''capping'' of active sites, e.g., the 2, 5, and 6 positions, on the catechol ring would effectively prevent the blocking and, hence, deactivation of the catalytic electrodes.