Enhanced direct electron transfer-type bioelectrocatalysis of bilirubin oxidase on negatively charged aromatic compound-modified carbon electrode

•Negatively charged aromatic character on electrodes increases DET-type bioelectrocatalytic current of BOD.•Electrostatic interaction between enzyme and electrode induces an orientation suitable for bioelectrocatalysis of BOD.•The modification causes an increase in the electron transfer rate constant and a decrease in randomness of orientation.•The basic idea is applicable to copper efflux oxidase in an opposed sign.

Effects of chemical modification of mesoporous Ketjen Black (KB) electrodes on direct electron transfer (DET)-type bioelectrocatalytic reduction of dioxygen by bilirubin oxidase (BOD) were investigated under air-saturated neutral conditions. Several amines were electrochemically oxidized at KB-modified electrode to generate nitrogen–carbon bond. The modification with negatively charged aromatic amines such as 4-aminobenzoic acid (4-ABA) drastically increased the catalytic current density compared with that by positively charged and non-charged aromatic compounds and negatively charged non-aromatic compound. Considering the basic amino acid residues around the type I site of BOD, it can be concluded that weakly negative charge on electrode surface induces a favorable orientation of BOD for the DET-type catalysis via the electrostatic interaction, while the π–π interaction is also essential for effective orientation of BOD on the electrode surface. The 4-ABA-modification leads to an increase in the heterogeneous electron transfer rate constant and a decrease in the randomness of the orientation as well as a slight increase in the surface concentration of BOD.

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