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To extend the range of biofuel cell applications, we wish to increase their maximum operational temperatures. Using a thermostable alcohol dehydrogenase as a biocatalyst, we prepared an enzyme-immobilized bioanode that can operate at high temperatures. The catalytic current for ethanol oxidation was increased using this electrode at temperatures up to 80 °C. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical measurements were carried out by using thermophilic cytochrome P450 CYP119A2 (P450st) modified with poly(ethylene oxide) (PEO) in PEO200 as an electrochemical solvent. The PEO modified P450st gave clear reduction–oxidation peaks by cyclic voltammetry in oxygen-free PEO200 up to 120°C. The midpoint potential measured for the P450st was −120mV vs. [Fe(CN)6]4−/[Fe(CN)6]3− at 120°C. The peak separation, ΔE, was 16mV at 100mV/s. The estimated electron transfer rate of PEO-P450st at 120°C was 35.1s−1. The faster electron transfer reaction was achieved at higher temperatures. The electrochemical reduction of dioxygen was observed at 115°C with the PEO-modified P450st system. [Copyright &y& Elsevier]

β-Nicotinamide adenine dinucleotide (NADH) is a coenzyme for more than 300 dehydrogenases. The electrochemical oxidation of NADH has attracted considerable interest in terms of developing amperometric biodevices, such as biosensors and biofuel cells. However, the electrochemical oxidation of NADH on the conventional electrode results in large overpotential. A novel mediator for the oxidation of NADH, a polymeric film of [Fe(NH2-phen)3]2+/3+, is reported in this paper. An iron complex-modified electrode which exhibits the catalytic activity for the electrochemical oxidation of NADH was prepared by electropolymerization. Furthermore, the electrochemical oxidation of ethanol was observed using the alcohol dehydrogenase (ADH)-immobilized electrode. [ABSTRACT FROM AUTHOR]

A ruthenium complex containing phenanthroline quinone, [Ru(pdon)2(aphen)](ClO4)2 (pdon = 1,10-phenanthroline-5,6-dione, aphen = 5-amino-1,10-phenanthroline) (1), was prepared as an electrocatalytic adsorbate on a gold electrode. Immobilization of 1 on the gold electrode was confirmed by surface enhanced resonance Raman spectroscopy. The rate constant ks was calculated as 10s-1 at pH 7.0. The electrocatalytic oxidation of NADH using this modified electrode was investigated. [ABSTRACT FROM AUTHOR]

Abstract: The direct electron transfer reaction of fructose dehydrogenase (FDH) from Gluconobacter sp. on alkanethiol-modified silver nanoparticles (AgNPs) was examined using cyclic voltammetry and surface-enhanced resonance Raman scattering (SERRS). Using cyclic voltammetry, catalytic oxidation currents (based on the direct electron transfer reaction of FDH) were observed from a potential of approximately −100mV (vs. Ag/AgCl, 3MNaCl) in the presence of d-fructose, without a mediator. A comparison of the SERRS spectra and the resonance Raman spectra of FDH in solution indicated that the heme c site retained its six-coordinated low-spin heme after immobilization. Moreover, SERRS also demonstrated that the heme c of the adsorbed FDH was the electron transfer site within the enzyme. [Copyright &y& Elsevier]

A pyranose dehydrogenase from Coprinopsis cinerea ( Cc PDH) is an extracellular quinohemoeprotein, which consists a b -type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of Cc PDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c ) reacted via the cytochrome domain of intact Cc PDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of Cc PDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of l -fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of Cc PDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. [ABSTRACT FROM AUTHOR]

A bioanode has been developed based on the oxidation of ethanol by the recombinant pyrroloquinoline quinone (PQQ) dependent alcohol dehydrogenase from Pseudomonas putida KT2440 heterologously expressed in Pichia pastoris. The apo form of the recombinant protein (PpADH) was purified and displayed catalytic activity for binding PQQ in the presence of Ca2+. PpADH exhibited broad substrate specificity towards various alcohols and aldehydes. The K m values for the aldehydes of PpADH were increased compared to those for the alcohols, whereas the k cat values were unaltered. For instance, the K m values at T=298.15K (25°C) for ethanol and acetaldehyde were 0.21 (±0.02)mM and 5.8 (±0.60)mM, respectively. The k cat values for ethanol and acetaldehyde were 24.8 (±1.2)s−1 and 31.1 (±1.2)s−1, respectively. The aminoferrocene was used as an electron transfer mediator between PpADH and the electrode during electrochemical experiments. The catalytic currents for the oxidation of alcohol and acetaldehyde by PpADH were also observed in this system. The electric charge for the oxidation of ethanol (Q=2.09×10−3·C) was increased two-fold compared to that for the oxidation of acetaldehyde (Q=0.95×10−3·C), as determined by chronoamperometric measurements. Thus, we have electrochemically demonstrated the two-step oxidation of ethanol to acetate using only PpADH. [ABSTRACT FROM AUTHOR]

Abstract: We have examined a direct electron transfer reaction of bilirubin oxidase (BOD) at a gold nanoparticle (AuNP) electrode in the mixtures of ionic liquid (IL) and water. No catalytic current induced by BOD was observed when neat ILs were used as an electrolyte solution. However, BOD-induced catalytic currents were observed when small quantities of water were added to hydrophobic ILs. The BOD-modified AuNP electrode provided a current density as high as 218μAcm−2 in 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide ([C2OHmim][Tf2N]) containing 7.4wt% H2O. To investigate the effect of the added water to ILs on the enzymatic activity we compared the physicochemical properties of the IL/H2O mixtures. There was a certain relation between the water activity (a W) of the IL/H2O mixtures and the current density of BOD. The BOD was confirmed to catalyze the four-electron reduction of O2 to H2O in the [C2OHmim][Tf2N]/H2O mixture by the data with cyclic voltammetry measurements using a rotating ring-disk electrode. [Copyright &y& Elsevier]

Abstract: In this communication, we describe a novel and facile method for the immobilization of NAD+/NADH on an electrode surface using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]). By taking advantage of the insolubility of NAD+/NADH in hydrophobic ionic liquids, it is expected that NAD+/NADH can be retained on the electrode''s surface. Alcohol dehydrogenase (ADH) and NAD+/NADH were immobilized with a gelatin hydrogel on an electrode that was modified with an electropolymerized ruthenium complex containing 5-amino-1,10-phenanthroline (pAPRu) as a mediator for NADH oxidation. The (ADH, NAD+)/pAPRu-immobilized electrode exhibited the electrocatalytic oxidation of ethanol in [C4mim][Tf2N]. The obtained catalytic current in [C4mim][Tf2N] was comparable to that in buffer solution containing NAD+. It was confirmed by UV–vis spectroscopy that NAD+ did not dissolve in the [C4mim][Tf2N] and was retained on the electrode''s surface. Furthermore, we succeeded in constructing an ethanol/O2 biofuel cell comprised of an (ADH, NAD+)/pAPRu anode and a bilirubin oxidase cathode using [C4mim][Tf2N] as an electrolyte. [Copyright &y& Elsevier]

Abstract: The direct electron transfer reaction of fructose dehydrogenase (FDH) from Gluconobacter sp. on alkanethiol-modified gold nanoparticles (AuNPs) was examined. AuNP-modified electrodes were simply fabricated by depositing citrate-reduced gold nanoparticles onto a gold electrode and carbon fiber paper and then covering the surface with a self-assembled monolayer of alkanethiols. The immobilization of AuNPs provided a large effective surface area for the adsorption of FDH. Catalytic oxidation currents based on the direct electron transfer reaction of FDH were observed from a potential about −100mV (vs. Ag/AgCl, 3M NaCl) in the presence of d-fructose without a mediator. The current density reached as high as 14.3±0.93mA/cm2 (at +500mV), which was achieved in the presence of 200mM d-fructose by immobilization of FDH on 2-mercaptoethanol-modified AuNP/carbon fiber paper electrodes. [Copyright &y& Elsevier]

• The electron transfer reaction of Cc PDH is summarized. • A biosensor of l -fucose, a cancer marker, was prepared using Cc PDH. • Cc PDH is also useful as an anode catalyst for DET-type biofuel cells. Pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase is one of the extensively studied sugar-oxidizing enzymes used as a biocatalyst for biosensors and biofuel cells. A novel pyranose dehydrogenase (Cc PDH) derived from the basidiomycete Coprinopsis cinerea is the first discovered eukaryotic PQQ-dependent enzyme. This enzyme carries a b -type cytochrome domain that is homologous to the cytochrome domain of cellobiose dehydrogenase (CDH); thus, Cc PDH is a quinohemoprotein. Cc PDH catalyzes the oxidation of various aldose sugars and shows significant activity toward the reverse-chair conformation of pyranoses. Interdomain electron transfer occurs in Cc PDH similar to CDH, from the PQQ cofactor in the catalytic domain to the heme b in the cytochrome domain. This enzyme is able to direct electrical communication with electrodes, without artificial electron mediators, thus allowing direct electron transfer (DET)-type bioelectrocatalysis. In this review, we briefly describe recent progress in research on the biochemical discovery of Cc PDH and the development of (bio)electrochemical applications (an amperometric biosensor) based on DET reactions. [ABSTRACT FROM AUTHOR]