Dopamine oxidation at gold electrodes: mechanism and kinetics near neutral pH

The two-electron electrochemical oxidation of dopamine is studied voltammetrically at gold macroelectrodes around neutral pH with simulations used to give kinetic and mechanistic data. In particular, the system shows "potential inversion" in which the thermodynamic oxidation potential of dopamine to form the corresponding semi-quinone formation occurs at a more positive potential than that of the oxidation of the semi-quinone to the quinone form. The use of Tafel slopes measured from the voltammograms as a function of the voltage scan rate is show to be a particularly sensitive indicator of mechanism showing the effect of the follow-up chemistry in which the two-electron oxidation product undergoes an irreversible cyclization reaction.