title: Gold single-crystal electrode surface modified with self-assembled monolayers for electron tunneling with bilirubin oxidase.
abstract: Using Au(111) and Au(100) single-crystal electrodes modified with self-assembled monolayers (SAMs), the direct electron transfer reaction of bilirubin oxidase (BOD) adsorbed onto their surfaces was investigated. The BOD adsorbed onto the Au(111), Au(100) and gold /mica electrodes, and the BOD adsorbed onto Au(111) electrodes modified with C(3)-SO(3)H and C(n)-COOH (n = 2, 5 and 7), showed the electrocatalytic currents of dioxygen reduction based on the direct electron transfer reaction. The BOD adsorbed onto Au(111) electrodes modified with C(6)-NH(2), C(6)-OH and C(5)-CH(3) did not show any electrocatalytic current. Negatively charged electrode surfaces can give a suitable molecular orientation for the direct electron transfer of BOD. The k degrees values evaluated by an analysis of the steady-state voltammogram with a simulated fitting method did not depend on the crystal structure of the gold electrode surface. Using a C(n)-COOH (n = 2, 5, 7) modified Au(111) electrode, the k degrees values decreased with an increasing alkyl chain length of C(n)-COOH. Based on the k degrees values obtained from the C(n)-COOH (n = 2, 5, 7) modified Au(111) electrodes, the electron tunneling distance was evaluated. The average distance between the type 1 Cu site of BOD and the outside of the BOD protein structure was evaluated to be 17 (+/-2) A.
authors.affiliation: Graduate School of Science and Technology, Kumamoto University, Kumamoto, 860-8555, Japan. masato@gpo.kumamoto-u.ac.jp
authors.forename: Masato
authors.initials: M
authors.lastname: Tominaga
authors.forename: Mai
authors.initials: M
authors.lastname: Ohtani
authors.forename: Isao
authors.initials: I
authors.lastname: Taniguchi
mesh_terms: D000327:Adsorption; D002384:Catalysis; D004566:Electrodes; D004583:Electrons; D006046:Gold; D018625:Microscopy, Atomic Force; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D006046:Gold; D044925:Oxidoreductases Acting on CH-CH Group Donors; C042401:bilirubin oxidase