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Direct Electron Transfer (direct + electron_transfer)

Distribution by Scientific Domains

Chemistry	66%

Selected Abstracts

Direct Electron Transfer and Electrocatalysis of Hemoglobin on Chitosan-TiO2 Nanorods-Glass Carbon Electrode

ELECTROANALYSIS, Issue 20 2008
Xiaoling Xiao
Abstract The direct electron transfer between hemoglobin (Hb) and the glassy carbon electrode (GC) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and TiO2 nanorods (TiO2 -NRs). TiO2 -NRs greatly promote the electron transfer between Hb and GC, which contribute to the higher redox peaks. UV-vis spectra result indicated the Hb entrapped in the composite film well keep its native structure. The immobilized Hb remains its bioelectrocatalytical activity to the reduction of H2O2 with a lower detection limit. A novel, sensitive, reproducible and stable electrochemical biosensing platform of H2O2 based on Hb-TiO2 -CHT electrode is explored. [source]

Conducting Polymer Enzyme Alloys: Electromaterials Exhibiting Direct Electron Transfer

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2010
Brianna C. Thompson
Abstract Glucose oxidase (GOx) is an important enzyme with great potential application for enzymatic sensing of glucose, in implantable biofuel cells for powering of medical devices in vivo and for large-scale biofuel cells for distributed energy generation. For these applications, immobilisation of GOx and direct transfer of electrons from the enzyme to an electrode material is required. This paper describes synthesis of conducting polymer (CP) structures in which GOx has been entrained such that direct electron transfer is possible between GOx and the CP. CP/enzyme composites prepared by other means show no evidence of such "wiring". These materials therefore show promise for mediator-less electronic connection of GOx into easily produced electrodes for biosensing or biofuel cell applications. [source]

Bioelectrocatalysis of Oxygen Reduction Reaction by Laccase on Gold Electrodes

ELECTROANALYSIS, Issue 13-14 2004
Gautam Gupta
Abstract Direct electron transfer (DET) reaction of oxygen electroreduction catalyzed by enzyme laccase on monolayer modified gold electrodes was studied. Three different monolayers were investigated, from which 4-aminothiophenol was found to be optimal for the direct electron transfer to take place. The electrocatalytic reduction of the oxygen at the electrode surface was found to depend significantly on the method of immobilization. Fungal laccase from Coriolus hirsitus modified with sodium-periodate demonstrated more anodic onset potential for oxygen reduction than the tree laccase from Rhus vernicifera. Physical immobilization of enzyme did not result in any manifestation of bioelectrocatalytic activity. A maximum anodic shift in reduction potential of 300,mV was observed for fungal laccase covalently coupled on the electrode surface. [source]

Bioelectrochemical Characterization of Horseradish and Soybean Peroxidases

ELECTROANALYSIS, Issue 21 2009
Marco Frasconi
Abstract Heme peroxidase are ubiquitous enzymes catalyzing the oxidation of a broad range of substrates by hydrogen peroxide. In this paper the bioelectrochemical characterization of horseradish peroxidase (HRP) and soybean peroxidase (SBP), belonging to class III of the plant peroxidase superfamily, was studied. The homogeneous reactions between peroxidases and some common redox mediators in the presence of hydrogen peroxide have been carried out by cyclic voltammetry. The electrochemical characterization of the reactions involving enzyme, substrate and mediators concentrations allowed us to calculate the kinetic parameters for the substrate,enzyme reaction (KMS) and for the redox mediator,enzyme reaction (KMM). A full characterization of the direct electron transfer kinetic parameters between the electrode and enzyme active site was also performed by opportunely modeling data obtained from cyclic voltammetry and square wave voltammetry experiments. The experimental data obtained with immobilized peroxidases show enhanced direct electron transfer and excellent electrocatalytical performance for H2O2. Despite the structural similarities and common catalytic cycle, HRP and SBP exhibit differences in their substrate affinity and catalytic efficiency. Basing on our results, it can be concluded that peroxidase from soybean represents an interesting alternative to the classical and largely employed one obtained from horseradish as biorecognition element of electrochemical mediated biosensors. [source]

Direct Electrochemistry of Hemoglobin Immobilized on Colloidal Gold-Hydroxyapatite Nanocomposite for Electrocatalytic Detection of Hydrogen Peroxide

ELECTROANALYSIS, Issue 2 2009
Juan You
Abstract A novel nanocomposite of colloidal gold (GNPs) and hydroxyapatite nanotubes (Hap) was prepared for immobilization of a redox protein, hemoglobin (Hb), on glassy carbon electrode. The immobilized Hb showed fast direct electron transfer and excellent electrocatalytic behavior toward reduction of hydrogen peroxide. A synergic effect between GNPs and Hap for accelerating the surface electron transfer of Hb was observed, which led to a pair of redox peaks with a formal potential of (,340±2) mV at pH,7.0, and a new biosensor for hydrogen peroxide with a linear range from 0.5 to 25,,M and a limit of detection of 0.2,,M at 3,. Owing to the good biocompatibility of the nanocomposite, the biosensor exhibited good stability and acceptable reproducibility. The as-prepared nanocomposite film provided a good matrix for protein immobilization and biosensor preparation. [source]

Direct Electrochemistry and Electrocatalysis of Hemoglobin in Lipid Film Incorporated with Room-Temperature Ionic Liquid

ELECTROANALYSIS, Issue 20 2008
Gaiping Li
Abstract A facile phospholipid/room-temperature ionic liquid (RTIL) composite material based on dimyristoylphosphatidylcholine (DMPC) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) was exploited as a new matrix for immobilizing protein. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to characterize this composite film. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV-vis absorbance spectra showed that Hb still maintained its heme crevice integrity in this composite film. By virtue of the Hb/DMPC/[bmim]PF6 composite film-modified glassy carbon electrode (GCE), a pair of well-defined redox peaks of Hb was obtained through the direct electron transfer between protein and underlying GCE. Moreover, the reduction of O2 and H2O2 at the Hb/DMPC/[bmim]PF6 composite film-modified GCE was dramatically enhanced. [source]

Direct Electrochemistry and Electrocatalysis of Myoglobin Immobilized on Gold Nanoparticles/Carbon Nanotubes Nanohybrid Film

ELECTROANALYSIS, Issue 17 2008
Wei Cao
Abstract A novel nanohybrid material, constructed by gold nanoparticles (GNPs) and multiwalled carbon nanotubes (MWNTs), was designed for immobilization and biosensing of myoglobin (Mb). Morphology of the nanohybrid film was characterized by SEM. UV-vis spectroscopy demonstrated that Mb on the composite film could retain its native structure. Direct electrochemistry of Mb immobilized on the GNPs/MWNTs film was investigated. The immobilized Mb showed a couple of quasireversible and well-defined cyclic voltammetry peaks with a formal potential of about ,0.35,V (vs. Ag/AgCl) in pH,6.0 phosphate buffer solution (PBS) solution. Furthermore, the modified electrode also displayed good sensitivity, wide linear range and long-term stability to the detection of hydrogen peroxide. The experiment results demonstrated that the hybrid matrix provided a biocompatible microenvironment for protein and supplied a necessary pathway for its direct electron transfer. [source]

Direct Electrochemistry of Cytochrome c at Gold Electrode Modified with Fumed Silica

ELECTROANALYSIS, Issue 20 2005
Hongjun Chen
Abstract Direct electrochemistry of horse heart cytochrome c (cytc) has been obtained at a gold electrode constructed by self-assembling fumed silica particles (FSPs) onto a silane monolayer. A pair of well-defined and nearly symmetrical redox peaks of cytc is obtained at the FSPs film modified gold electrode. Cyclic voltammetry (CV) and tapping-mode atomic force microscopy (AFM) are used to characterize the FSPs film modified electrode, showing that the FSPs can provide a favorable microenvironment for cytc and facilitate the direct electron transfer between the cytc and the gold electrode, which may propose an approach to realize the direct electrochemistry of other proteins. [source]

Bioelectrocatalysis of Oxygen Reduction Reaction by Laccase on Gold Electrodes

Metagenome and mRNA expression analyses of anaerobic methanotrophic archaea of the ANME-1 group

ENVIRONMENTAL MICROBIOLOGY, Issue 2 2010
Anke Meyerdierks
Summary Microbial consortia mediating the anaerobic oxidation of methane with sulfate are composed of methanotrophic Archaea (ANME) and Bacteria related to sulfate-reducing Deltaproteobacteria. Cultured representatives are not available for any of the three ANME clades. Therefore, a metagenomic approach was applied to assess the genetic potential of ANME-1 archaea. In total, 3.4 Mbp sequence information was generated based on metagenomic fosmid libraries constructed directly from a methanotrophic microbial mat in the Black Sea. These sequence data represent, in 30 contigs, about 82,90% of a composite ANME-1 genome. The dataset supports the hypothesis of a reversal of the methanogenesis pathway. Indications for an assimilatory, but not for a dissimilatory sulfate reduction pathway in ANME-1, were found. Draft genome and expression analyses are consistent with acetate and formate as putative electron shuttles. Moreover, the dataset points towards downstream electron-accepting redox components different from the ones known from methanogenic archaea. Whereas catalytic subunits of [NiFe]-hydrogenases are lacking in the dataset, genes for an [FeFe]-hydrogenase homologue were identified, not yet described to be present in methanogenic archaea. Clustered genes annotated as secreted multiheme c -type cytochromes were identified, which have not yet been correlated with methanogenesis-related steps. The genes were shown to be expressed, suggesting direct electron transfer as an additional possible mode to shuttle electrons from ANME-1 to the bacterial sulfate-reducing partner. [source]

Hydrogenase- and outer membrane c -type cytochrome-facilitated reduction of technetium(VII) by Shewanella oneidensis MR-1

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2008
Matthew J. Marshall
Summary Pertechnetate, 99Tc(VII)O4,, is a highly mobile radionuclide contaminant at US Department of Energy sites that can be enzymatically reduced by a range of anaerobic and facultatively anaerobic microorganisms, including Shewanella oneidensis MR-1, to poorly soluble Tc(IV)O2(s). In other microorganisms, Tc(VII)O4, reduction is generally considered to be catalysed by hydrogenase. Here, we provide evidence that although the NiFe hydrogenase of MR-1 was involved in the H2 -driven reduction of Tc(VII)O4,[presumably through a direct coupling of H2 oxidation and Tc(VII) reduction], the deletion of both hydrogenase genes did not completely eliminate the ability of MR-1 to reduce Tc(VII). With lactate as the electron donor, mutants lacking the outer membrane c -type cytochromes MtrC and OmcA or the proteins required for the maturation of c -type cytochromes were defective in reducing Tc(VII) to nanoparticulate TcO2·nH2O(s) relative to MR-1 or a NiFe hydrogenase mutant. In addition, reduced MtrC and OmcA were oxidized by Tc(VII)O4,, confirming the capacity for direct electron transfer from these OMCs to TcO4,. c -Type cytochrome-catalysed Tc(VII) reduction could be a potentially important mechanism in environments where organic electron donor concentrations are sufficient to allow this reaction to dominate. [source]

Exocellular electron transfer in anaerobic microbial communities

ENVIRONMENTAL MICROBIOLOGY, Issue 3 2006
Alfons J. M. Stams
Summary Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory syntrophic consortia of proton-reducing acetogenic bacteria and hydrogen-consuming methanogenic archaea. Anaerobic microorganisms that use insoluble electron acceptors for growth, such as iron- and manganese-oxide as well as inert graphite electrodes in microbial fuel cells, also transfer electrons exocellularly. Soluble compounds, like humic substances, quinones, phenazines and riboflavin, can function as exocellular electron mediators enhancing this type of anaerobic respiration. However, direct electron transfer by cell,cell contact is important as well. This review addresses the mechanisms of exocellular electron transfer in anaerobic microbial communities. There are fundamental differences but also similarities between electron transfer to another microorganism or to an insoluble electron acceptor. The physical separation of the electron donor and electron acceptor metabolism allows energy conservation in compounds as methane and hydrogen or as electricity. Furthermore, this separation is essential in the donation or acceptance of electrons in some environmental technological processes, e.g. soil remediation, wastewater purification and corrosion. [source]

Conducting Polymer Enzyme Alloys: Electromaterials Exhibiting Direct Electron Transfer

Direct Electrochemistry of Cytochrome,c at Modified Si(100) Electrodes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2010
Simone Ciampi
Abstract This paper demonstrates the direct electron transfer between the heme moiety of horse hearth cytochrome,c and a pyridinyl group on self-assembled-monolayer-modified Si(100) electrodes. Self-assembled monolayers (SAMs) containing the putative receptor ligand were prepared by a step-wise procedure using "click" reactions of acetylene-terminated alkyl monolayers and isonicotinic acid azide derivatives. Unoxidized Si(100) electrodes, possessing either isonicotinate or isonicotinamide receptor ligands, were characterized using X-ray photoelectron spectroscopy, contact-angle goniometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The ability of isonicotinic acid terminated layers to coordinatively bind the redox center of cytochrome,c was found to be restricted to pyridinyl assemblies with a para -ester linkage present. The protocol detailed here offers an experimentally simple modular approach to producing chemically well-defined SAMs on silicon surfaces for direct electrochemistry of a well-studied model redox protein. [source]

Carbon Dioxide Activation by Surface Excess Electrons: An EPR Study of the CO2, Radical Ion Adsorbed on the Surface of MgO

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007
Mario Chiesa Dr.
Abstract The CO2, radical anion has been generated at the surface of MgO by direct electron transfer from surface trapped excess electrons and characterized by electron paramagnetic resonance spectroscopy. Both 13C and 17O hyperfine structures have been resolved for the first time, leading to a detailed mapping of the unpaired electron spin density distribution over the entire radical anion. The magnetic equivalence of the two O nuclei has been ascertained allowing a side-on adsorption structure at low-coordinate Mg2+ ions to be proposed for the surface stabilized radical. [source]