Masato Tominaga

Gold single-crystal electrode surface modified with self-assembled monolayers for electron tunneling with bilirubin oxidase

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.

Laccase bioelectrocatalyst at a steroid-type biosurfactant-modified carbon nanotube interface.

Achieving oxygen reduction at high positive potentials with fast heterogeneous electron transfer is desirable for the biocathode of fuel cells based on enzymes. Here, we present an effective interface for obtaining direct electron transfer from a laccase (Lac)-based cathode for O2 reduction, starting from a potential very close to the redox equilibrium potential of the oxygen/water couple. The interface between Lac and single-walled carbon nanotubes was improved by modification with the steroid biosurfactant sodium cholate. The heterogeneous electron-transfer rate between the type-1 Cu site of Lac and the modified electrode was determined to be 3000 s(-1). The electron-transfer rate was sensitive to the side chain of the steroid biosurfactant, and the rate decreased more than 10-fold when sodium deoxycholate was used as the side chain.

Polypeptide-modified indium oxide electrodes for direct electron tranfer of ferredoxin

Indium oxide, surface modified with a polypeptide, e.g. polylysine or polyornithine, is an effective promoter-modified electrode for direct quasi-reversible electron transfer of ferredoxin.

Determination of the Diameter-Dependent Onset Potential for the Oxygenation of SWCNTs†

The evaluation of the diameter-dependent onset potential for the oxygenation of a SWCNT (single-walled carbon nanotube) is an important issue because its chemical and physical properties, such as chemical reactivity, electronic conductance, and optical characteristics, would be changed. We investigated the diameter-dependent onset potential for the oxygenation of SWCNTs in neutral aqueous solution by using in situ Raman spectroelectrochemical measurements, which was explained quantitatively in terms of the strain energy per carbon atom. These results will be useful for the fabrication of materials in which CNTs are used as a platform for applications such as fuel cells, capacitors, and Li-ion batteries.

Direct electrochemistry of iron(III)- and copper(II)-transferrins embedded in a bilayer membrane film composed of artificial cationic-type lipid

Abstract Fe(III)- and Cu(II)-transferrins were embedded into a cast film composed of artificial cationic-type lipid, 2C 16 N + Br − . However, for the lipid films composed of 2C 16 N + PSS − , 2C 12 SucSO 3 − Na + and 2C 12 gluco, the incorporation of Fe(III)- and Cu(II)-transferrins into the lipid films was spectrochemically and electrochemically undetectable even at temperatures above the phase transition temperature of the lipids. The incorporation of transferrin into the 2C 16 N + Br − film was completely inhibited under high electrolyte concentrations. These results indicate that the incorporation of transferrin into the cationic-type lipid film, 2C 16 N + Br − , can be attributed to ion exchange between the bromide anion of the lipid and the negatively charged transferrin. The Fe(III)- and Cu(II)-transferrins embedded into the 2C 16 N + Br − film on a graphite electrode showed well-defined redox waves. The evaluated redox potentials of Fe(III)- and Cu(II)-transferrin were approximately 0.017 and 0.237 V (vs. NHE), respectively, in a phosphate buffer (pH 7, μ =0.1) solution containing 0.1 mmol dm −3 K 2 C 2 O 4 at 30 °C. The results obtained in the present study indicate that an electrode modified with a cast film of this cationic-type of lipid is useful as an electrochemical interface for not only Fe(III)-transferrin but also metal reconstituted transferrins such as Cu(II)-transferrin.

Catalytic Current Based on Direct Electron Transfer Reactions of Enzymes Immobilized onto Carbon Nanotubes

Multi-walled and single-walled carbon nanotubes were synthesized on platinum plate (MWCNTs/pt) and gold wire (SWCNTs/Au) electrodes, respectively, using a chemical vapor deposition (CVD) method. These carbon nanotube-modified electrodes were immersed into solutions of glucose oxidase (GOX) and D-fructose dehydrogenase (FDH) to immobilize these enzymes onto the electrode surfaces. After GOX was immobilized onto the MWCNT/Pt electrode, the well-defined catalytic oxidation current was increased from ca. -0.45 V (vs. Ag/AgCl/saturated KCl), which was close to the redox potential of flavin adenine dinucleotide as a prosthetic group of GOX under physiological pH values. Furthermore, catalytic oxidation currents of fructose based on direct heterogeneous electron transfer reactions between FDH and the SWCNT/Pt electrode were observed.

Sensitivity to electrical stimulation of human immunodeficiency virus type 1 and MAGIC-5 cells

To determine the sensitivities to low electrical potential of human immunodeficiency virus type 1 (HIV-1) and its target cells, HIV-1 and MAGIC-5 cells were directly stimulated with a constant direct current potential of 1.0 V (vs. Ag/AgCl). HIV-1 was incubated for 3 h at 37°C on a poly-L-lysine-coated indium-tin oxide electrode, and then stimulated by an electrical potential. MAGIC-5 cells were seeded onto the electrically stimulated HIV-1 and cultured for 3 days at 37°C. HIV-1-infected cells were measured by multinuclear activation via a galactosidase indicator assay. MAGIC-5 cells were also stimulated by an electrical potential of 1.0 V; cell damage, proliferation and apoptosis were evaluated by trypan blue staining, cell counting and in situ apoptosis detection, respectively. HIV-1 was found to be damaged to a greater extent by electrical stimulation than the cells. In particular, after application of a 1.0-V potential for 3 min, HIV-1LAI and HIV-1KMT infection were inhibited by about 90%, but changes in cell damage, proliferation and apoptosis were virtually undetectable. These results suggested that HIV-1 is significantly more susceptible to low electrical potential than cells. This finding could form the basis of a novel therapeutic strategy against HIV-1 infection.

Spectroelectrochemical Study of some μ3-Oxo-μ-acetato Trinuclear Rhodium(III) and Iridium(III) Complexes

New trinuclear rhodium(III) complexes, [Rh3(μ3-O)(μ-CH3COO)6(L)3]+ (L = imidazole (Him), 1-methylimidazole (Meim), and 4-methylpyridine (Mepy)) have been prepared. The Him, Meim, and Mepy complexes show reversible one-electron oxidation waves at E1/2 = +1.12, +1.12, and +1.28 V vs Ag/AgCl, respectively, in acetonitrile. Electronic absorption spectra of the one electron oxidized species of these complexes and [Rh3(μ3-O)(μ-CH3COO)6(py)3]+ (py = pyridine) (E1/2 = +1.32 V ) were obtained by spectroelectrochemical techniques. While the Rh3(III,III,III) states show no strong visible absorption, the Rh3(III,III,IV ) species give a band at ca. 700 nm (ε = 3390-5540 mol dm-3 cm-1). [Ir3(μ3-O)(μ-CH3COO)6(py)3]+ with no strong absorption in the visible region, shows two reversible one-electron oxidation waves at +0.68 and +1.86 V in acetonitrile. The electronic absorption spectrum of the one-electron oxidized species (Ir3(III,III,IV )) also shows some absorption bands (688 nm (ε, 5119), 1093 (2325) and 1400 (ca. 1800)). It is suggested that the oxidation removes an electron from the fully occupied anti-bonding orbital based on metal-dπ-μ3-O-pπ interactions, the absorption bands of the (III,III,IV ) species being assigned to transitions to the anti-bonding orbital.