Guaicolic spices curcumin and capsaicin electrochemical oxidation behaviour at a glassy carbon electrode

The electrochemical behaviour of the spice biomarkers, curcumin and capsaicin, two polyphenolic compound with a large spectrum of medical application, has been studied by cyclic, differential pulse and square wave voltammetry at a glassy carbon electrode. The oxidation of curcumin is an irreversible process that in acidic and mild alkaline supporting electrolytes proceeds in two steps. The first irreversible oxidation step leads to the formation of a catechol moiety, and the second reversible step occurs for a higher potential. The oxidation mechanism of ferulic acid, capsaicin and dihydrocapsaicin, curcumin chemical analogues was also investigated. The oxidation of ferulic acid is similar to curcumin whereas the oxidation of capsaicin and dihydrocapsaicin led to the formation of only one oxidation product. A redox mechanism for curcumin oxidation has been proposed.