Effect of functional groups at carbon nano-structured materials on electron transfer reaction of enzymes

Abstract

Bilirubin oxidase (BOD) contains multi active center copper sites (type 1, 2 and 3) and catalyzes the oxidation of bilirubin to biliverdin (at the type 1 site) with the concomitant four-electron reduction of dioxygen to water (at type 2-3 sites). BOD electron transfer reaction investigations at carbon electrodes are attractive studies, not only from the point of view for the basic understanding of multi-copper protein reactions, but also for the application of dioxygen biocathodes for biofuel cells operating near neutral pH solutions. Several studies on the mediated electrochemistry of BOD using monomeric and redox polymer mediators have been reported. Recently, the direct electron transfer reaction of BOD at carbon electrodes under anaerobic and aerobic conditions has been reported. In the present study, we investigated electrode reactions of BOD adsorbed on carbon black (CB). CB has an advantage for large surface area-to-volume ratios. Heterogeneous electron transfer rate constants (k°) between BOD and CB were evaluated by analyzing steady-state catalytic voltammograms under aerobic conditions. We found that k° values improved with the use of UV-ozone treated CB.