NADH oxidation using carbonaceous electrodes modified with dibenzo-dithia-diazapentacene

The electrochemical and the electrocatalytic behavior for NADH oxidation of a newly synthesized phenothiazine derivative, 16H,18H-dibenzo[c,1]-7,9-dithia-16,18-diazapentacene (DDDP), adsorbed on solid spectrographic graphite and on graphite powder or on zirconium phosphate (ZP), both entrapped in carbon paste, were compared. Experiments using cyclic voltammetry and a rotating disk electrode, performed in different experimental conditions (various pH values and NADH concentrations), showed that i) in the pH range between 4 and 8, the E°' value for DDDP adsorbed on ZP becomes pH independent; ii) in contrast to other redox mediators, adsorption of DDDP on ZP induced a significant negative shift of the E°' value; iii) the reaction rate for electrocatalytic oxidation of NADH is markedly increased by adsorbing the mediator on ZP, being further improved by the presence of Ca2+ ions in the solution.