Comparisons in Voltammetry of Phenylenediamine Based Ureas on Platinum and Glassy Carbon Working Electrodes

Abstract

“Proton-coupled electron transfer” (PCET) reactions are essential to many of the fundamental chemical processes of biological systems. PCET has been studied for some time, but it is only recently that the role of H-bonding intermediates has been explored. One such H-bonding system under investigation consists of a phenylenediamine based urea that undergoes an apparent self-PCET reaction where one urea is oxidized by two electrons to the quinoidal cation, followed by the transfer of a proton and deactivation of the other half of the ureas. Reversibility of this process is due to the second electron transfer and proton transfer occurring through a H-bond complex between the oxidized urea and the dimethylamino group on an electroinactive urea. In this study it was sought to observe possible differences in voltammetry of the phenylenediamine based urea system using different working electrode surfaces, in this case: platinum and glassy carbon working electrodes. Differences in voltammetry were observed between platinum and glassy carbon in methylene chloride. These differences appear to be due to faster heterogeneous electron transfer on glassy carbon than on platinum. In order to further explore this faster rate of electron transfer that is observed on glassy carbon, the working electrode surface was methylated, intentionally disrupting the electrode surface. The resulting voltammetric behavior of the phenylenediamine based urea system using this compromised electrode was similar to that of platinum, suggesting that the rate of electron transfer on glassy carbon was slowed down. Further voltammetric experiments are being conducted in other solvents due to the solvent-dependence of the phenylenediamine based urea system. Possible differences in voltammetry between platinum and glassy carbon electrodes are currently being explored in dimethyl sulfoxide.