Since the times employed were so short, the left-hand planar diffusion term dominates and no steady state signal from the voltammetry was observed. Instead, an anodic peak corresponding to Cu(II) oxidation was observed. In such conditions the limiting factor for the observation of a cathodic peak on the return scan is the subsequent quenching of Cu(III) by the tyrosine. By scanning at faster rates, the Cu(III) could be reduced before the quenching could take place, resulting in the observation of a cathodic peak.