When we plotted the forward and backward components of the total current (Figure SI 2.1A) we observed that the forward component of the current showed the peak at the same potential as the total current, while on the backward component, no cathodic peak occurred, which confirmed the irreversibility of first oxidation process on CV. The CV recorded for the solution at pH 5.0 and 6.0 (v = 100 mV/s) showed two oxidation peaks (Figure ). The same behaviour was observed in Figure . At the beginning, we assumed that it could be related to the pKa of the tested molecule.