NMR Spectroelectrochemistry in Studies of Dopamine Oxidation

In this paper, the electrochemical oxidation of dopamine was studied by using gold nanoparticles modified nano-polyaniline film as the catalyst. Electrochemistry and nuclear magnetic resonance spectroscopy (EC–NMR) was used to investigate electro-catalytic mechanism and evaluate the electro-catalytic capacity. The influence of varied pH values and voltages in the electrocatalytic process was studied. The oxidation mechanism of dopamine can be proposed: (1) at pH 1 and 600 mV, the main oxidation product is dopamine quinone (DQ). Only a small amount of DQ occurs cyclization reaction to form quinone aminochrome (AC); (2) at pH 1 and 800 mV, the oxidation products are DQ and 5,6-dihydroxyindole (DHI). (3) With the pH value increases, the oxidation of dopamine steps over DQ and AC, and directly produces DHI. DHI is aggregated to form melanin sediment. Our results indicate that the gold nanoparticles modified electrode displays high catalytic performance toward dopamine electrochemical oxidation.