Electrochemical characterization and performance of phenothiazine derivatives as redox mediators

Two phenothiazine derivatives were synthesized as new redox mediators. Their electrochemical properties were compared with conventional redox mediators, such as thionine, ferricyanide(III), and hexaammineruthenium(III). Cyclic voltammetry experiments were performed under various conditions on glassy carbon and ultramicroelectrodes to investigate the proton-coupled electron transfer reaction mechanism, electrochemical reversibility, and chemical stability of the redox mediators. The number of intervening electrons and protons in the redox processes of redox mediators at each temperature was estimated accordingly. Furthermore, thermodynamic parameters (standard enthalpy change, standard entropy change, and standard Gibbs free energy) of redox mediators could be evaluated by analyzing their electrochemical behavior according to the reaction temperatures. The mediator performance was also analyzed for the oxidation of reduced nicotinamide adenine dinucleotide. These experimental and analytical results confirm that the performance of redox mediators is similar or superior to those of other mediators.