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Redox Mediator (redox + mediator)

Distribution by Scientific Domains

Chemistry	70%
Life Sciences	30%

Selected Abstracts

Poly(neutral red): Electrosynthesis, Characterization, and Application as a Redox Mediator

ELECTROANALYSIS, Issue 12 2008
Rasa Pauliukaite
Abstract The synthesis by electropolymerization, the characterization, and applications of poly(neutral red) (PNR), including as a redox mediator, are reviewed. PNR's high electrical conductivity and its redox characteristics have led to special applications of the polymer, and it has been used for the development of electrochemical and optical sensors. Moreover, the attractive properties of PNR allow it to be applied in the development of electrochemical biosensors. Future perspectives are indicated. [source]

Catalytic and Surface-Electrocatalytic Water Oxidation by Redox Mediator,Catalyst Assemblies,

ANGEWANDTE CHEMIE, Issue 50 2009
Javier
Alles in einem bieten die Assoziate aus ,Single-Site"-Wasseroxidationskatalysatoren (rot und blau) und Redoxvermittlern (grün und blau), die , sowohl in Lösung als auch über Phosphonatlinker an Metalloxidoberflächen gebunden , als stabile, robuste Katalysatoren für die Wasseroxidation wirken. Mehr als 28,000 Umsätze wurden mit einer Ladungseffizienz >95,% für die Sauerstoffproduktion ohne Abnahme der katalytischen Aktivität erreicht. [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]

Synthesis and Characterization of MWNTs/Au NPs/HS(CH2)6Fc Nanocomposite: Application to Electrochemical Determination of Ascorbic Acid

ELECTROANALYSIS, Issue 16 2008
Jian-Ding Qiu
Abstract In this article, a detailed electrochemical study of a novel 6-ferrocenylhexanethiol (HS(CH2)6Fc) self-assembled multiwalled carbon nanotubes-Au nanoparticles (MWNTs/Au NPs) composite film was demonstrated. MWNTs/Au NPs were prepared by one-step in situ synthesis using linear polyethyleneimine (PEI) as bifunctionalizing agent. HS(CH2)6Fc, which acted as the redox mediator, was self-assembled to MWNTs/Au NPs via Au-S bond. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transformed infrared absorption spectroscopy (FT-IR), UV-visible absorption spectroscopy, and cyclic voltammetry were used to characterize the properties of the MWNTs/Au NPs/HS(CH2)6Fc nanocomposite. The preparation of the nanocomposite was very simple and effectively prevented the leakage of the HS(CH2)6Fc mediator during measurements. The electrooxidation of AA could be catalyzed by Fc/Fc+ couple as a mediator and had a higher electrochemical response due to the unique performance of MWNTs/Au NPs. The nanocomposite modified electrode exhibited excellent catalytic efficiency, high sensitivity, good stability, fast response (within 3,s) and low detection limit toward the oxidation of AA at a lower potential. [source]

Poly(neutral red): Electrosynthesis, Characterization, and Application as a Redox Mediator

Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol-Gel Thin Film Electrode Derived from 3-Aminopropyl Trimethoxy Silane

ELECTROANALYSIS, Issue 22 2007
K. Thenmozhi
Abstract An organically modified sol-gel electrode using 3-aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2,V to ,0.6,V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ,0.265,V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ,0.34,V. A good linear working range from 2.94×10,6,M to 2.11×10,3,M with a detection limit of 1.76×10,6,M and quantification limit of 5.87×10,6,M was obtained for nitrite determination. The stable and quick response (4,s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol-gel matrix. [source]

Spatial Imaging of Cu2+ -Ion Release by Combining Alternating Current and Underpotential Stripping Mode Scanning Electrochemical Microscopy

ELECTROANALYSIS, Issue 2-3 2007
Dirk Ruhlig
Abstract Anodic underpotential stripping voltammetry was integrated into SECM in order to characterize local corrosion of metallic copper deposits on metal surfaces as a model for copper containing alloys. Primarily, the alternating current mode of SECM was applied in an electrolyte of low ionic strength for localizing possible corrosion sites without any perturbation of the corroding surface, e.g., by the presence of any redox mediator. Sequentially, the release of Cu2+ -ions was confirmed and locally visualized at the previously detected electrochemically active sites by means of spatially resolved anodic underpotential stripping voltammetry performed during SECM scanning. Underpotential stripping voltammetry of Cu2+ -ions was performed at a specifically developed 15,,m gold-coated Pt microelectrode used as SECM tip with a detection limit of 0.15,nM Cu2+ (N=4, RSD=6%) for an accumulation of 45,s at ,0.4,V. SECM images of model samples such as copper coated microelectrodes and lacquered metallic copper workpieces demonstrated the feasibility and applicability of combining AC- and underpotential stripping mode of SECM for local visualization of Cu2+ -ion release from corroding surfaces. [source]

Development of Novel Glucose and Pyruvate Biosensors at Poly(Neutral Red) Modified Carbon Film Electrodes.

ELECTROANALYSIS, Issue 8 2006
Application to Natural Samples
Abstract Amperometric biosensors based on the corresponding oxidase enzyme with poly(neutral red) redox mediator have been developed for the determination of glucose and pyruvate. The enzymes have been immobilized on top of poly(neutral red) modified carbon film electrodes with glutaraldehyde as the cross-linking agent. The biosensors were characterized by cyclic voltammetry and by electrochemical impedance spectroscopy. The glucose biosensor exhibited a linear response in the range 90,,M to 1.8,mM with a detection limit of 22,,M and the pyruvate biosensor in the range 90 to 600,,M with a detection limit of 34,,M. The relative standard deviations were found to be 2.1% (n=3) and 2.8% (n=4) respectively. The interference effects of various compounds were also studied. The glucose content of several types of wine and the amount of pyruvate in onion and garlic were determined and the results were compared with those obtained by standard spectrophotometric methods. [source]

Gold Nanoparticle-Based Mediatorless Biosensor Prepared on Microporous Electrode

ELECTROANALYSIS, Issue 3 2006
Fenghua Zhang
Abstract A mediatorless biosensor was fabricated with a double-sided microporous gold electrode by successively immobilizing a mixed self-assembled monolayer (SAM) comprising carboxylic-acid- and thiol-terminated thiolate (dl -thiorphan and 1,8-octanedithiol), glucose oxidase (GOx) and finally gold nanoparticle (Au NP) on one working side. The double-sided microporous gold electrodes were formed by plasma sputtering of gold on a porous nylon substrate, yielding a face-to-face type two-electrode electrochemical cell. While the straight chain molecule 1,8-octanedithiol forms a dense insulating monolayer, the side armed dl -thiorphan forms a low density layer for the diffusion of redox couples to the electrode surface. The mixed SAM not only provided the linking functional groups for both enzyme and Au NP but also resulted in the appropriately spaced monolayer for direct electron tansfer (ET) process from the center of the redox enzyme to the electrode surface. After covalently immobilizing GOx onto the carboxylic-acid-terminated monolayer, Au NP was easily immobilized to both enzyme and nearby thiols by simple dispensing of the colloidal gold solution. It was observed that the resulting amperometric biosensor exhibited quantitatively the same response to glucose in the presence and in the absence of dissolved oxygen, which evidence that the Au NPs immobilized on and around the GOx promote direct ET from the enzymes to the electrode, assuming the role of a common redox mediator. [source]

Characterization of a nif-regulated flavoprotein (FprA) from Rhodobacter capsulatus

FEBS JOURNAL, Issue 3 2000
2S] ferredoxin, Redox properties, molecular interaction with a [2Fe
A flavoprotein from Rhodobacter capsulatus was purified as a recombinant (His)6 -tag fusion from an Escherichia coli clone over-expressing the fprA structural gene. The FprA protein is a homodimer containing one molecule of FMN per 48-kDa monomer. Reduction of the flavoprotein by dithionite showed biphasic kinetics, starting with a fast step of semiquinone (SQ) formation, and followed by a slow reduction of the SQ. This SQ was in the anionic form as shown by EPR and optical spectroscopies. Spectrophotometric titration gave a midpoint redox potential for the oxidized/SQ couple of Em1 = +20 mV (pH 8.0), whereas the SQ/hydroquinone couple could not be titrated due to the thermodynamic instability of SQ associated with its slow reduction process. The inability to detect the intermediate form, SQ, upon oxidative titration confirmed this instability and led to an estimate of Em2 , Em1 of > 80 mV. The reduction of SQ by dithionite was significantly accelerated when the [2Fe,2S] ferredoxin FdIV was used as redox mediator. The midpoint redox potential of this ferredoxin was determined to be ,275 ± 2 mV at pH 7.5, consistent with FdIV serving as electron donor to FprA in vivo. FdIV and FprA were found to cross-react when incubated together with the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, giving a covalent complex with an Mr of , 60 000. Formation of this complex was unaffected by the redox states of the two proteins. Other [2Fe,2S] ferredoxins, including FdV and FdVI from R. capsulatus, were ineffective as electron carriers to FprA, and cross-reacted poorly with the flavoprotein. The possible function of FprA with regard to nitrogen fixation was investigated using an fprA -deleted mutant. Although nitrogenase activity was significantly reduced in the mutant compared with the wild-type strain, nitrogen fixation was apparently unaffected by the fprA deletion even under iron limitation or microaerobic conditions. [source]

Redox-Active Catalyst Based on Poly(Anilinesulfonic Acid)- Supported Gold Nanoparticles for Aerobic Alcohol Oxidation in Water

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010
Daisuke Saio
Abstract The hybrid consisting of gold nanoparticles and poly(2-methoxyaniline-5-sulfonic acid), which works as a redox mediator for transferring protons and electrons, catalyzed the oxidation reaction of various alcohols in water under molecular oxygen. [source]

Kinetic modeling of a bi-enzymatic system for efficient conversion of lactose to lactobionic acid

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009
Wouter Van Hecke
Abstract A model has been developed to describe the interaction between two enzymes and an intermediary redox mediator. In this bi-enzymatic process, the enzyme cellobiose dehydrogenase oxidizes lactose at the C-1 position of the reducing sugar moiety to lactobionolactone, which spontaneously hydrolyzes to lactobionic acid. 2,2,-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt is used as electron acceptor and is continuously regenerated by laccase. Oxygen is the terminal electron acceptor and is fully reduced to water by laccase, a copper-containing oxidase. Oxygen is added to the system by means of bubble-free oxygenation. Using the model, the productivity of the process is investigated by simultaneous solution of the rate equations for varying enzyme quantities and redox mediator concentrations, solved with the aid of a numerical solution. The isocharts developed in this work provide an easy-to-use graphical tool to determine optimal process conditions. The model allows the optimization of the employed activities of the two enzymes and the redox mediator concentration for a given overall oxygen mass transfer coefficient by using the isocharts. Model predictions are well in agreement with the experimental data. Biotechnol. Bioeng. 2009;102: 1475,1482. © 2008 Wiley Periodicals, Inc. [source]

Bubble-free oxygenation of a bi-enzymatic system: effect on biocatalyst stability

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009
Wouter Van Hecke
Abstract The effect of bubble-free oxygenation on the stability of a bi-enzymatic system with redox mediator regeneration for the conversion of lactose to lactobionic acid was investigated in a miniaturized reactor with bubbleless oxygenation. Earlier investigations of this biocatalytic oxidation have shown that the dispersive addition of oxygen can cause significant enzyme inactivation. In the process studied, the enzyme cellobiose dehydrogenase (CDH) oxidizes lactose at the C-1 position of the reducing sugar moiety to lactobionolactone, which spontaneously hydrolyzes to lactobionic acid. 2,2,-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt was used as electron acceptor for CDH and was continuously regenerated (reoxidized) by laccase, a blue multi-copper oxidase. Oxygen served as the terminal electron acceptor of the reaction and was fully reduced to water by laccase. The overall mass transfer coefficient of the miniaturized reactor was determined at 30 and 45°C; conversions were conducted both in the reaction-limited and diffusion-limited regime to study catalyst inactivation. The bubbleless oxygenation was successful in avoiding gas/liquid interface inactivation. It was also shown that the oxidized redox mediator plays a key role in the inactivation mechanism of the biocatalysts unobserved during previous studies. Biotechnol. Bioeng. 2009;102: 122,131. © 2008 Wiley Periodicals, Inc. [source]

Pyrroloquinoline quinone-dependent carbohydrate dehydrogenase: Activity enhancement and the role of artificial electron acceptors

BIOTECHNOLOGY JOURNAL, Issue 8 2010
Juozas Kulys Professor
Abstract Pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (PQQ-GDH) offers a variety of opportunities for applications, e.g. in highly sensitive biosensors and electrosynthetic reactions. Here we report on the acceleration (up to 4.9 x 104 -fold) of enzymatic ferricyanide reduction by artificial redox mediators (enhancers). The reaction mechanism includes reduction of the PQQ-GDH by glucose followed by oxidation of the reduced PQQ cofactor with either ferricyanide or a redox mediator. A synergistic effect occurs through the oxidation of a reduced mediator by ferricyanide. Using kinetic description of the coupled reaction, the second order rate constant for the reaction of an oxidized mediator with the reduced enzyme cofactor (kox) can be calculated. For different mediators this value is 2.2 x 106,1.6 x 108 M -1s -1 at pH 7.2 and 25°C. However, no correlation of the rate constant with the midpoint redox potential of the mediator could be established. For low-potential mediators the synergistic effect is proportional to the ratio of kox(med)/kox(ferricyanide), whereas for the high-potential mediators the effect depends on both this ratio and the concentration of the oxidized mediator, which can be calculated from the Nernst equation. The described effect can be applied in various ways, e.g. for substrate reactivity determination, electrosynthetic PQQ cofactor regeneration or building of new highly sensitive biosensors. [source]

Imaging Local Proton Fluxes through a Polycarbonate Membrane by Using Scanning Electrochemical Microscopy and Functionalized Alkanethiols

CHEMPHYSCHEM, Issue 1 2009
Norman Baltes Dr.
Abstract A new application of scanning electrochemical microscopy (SECM) to probe the transport of protons through membranes is described. Herein, a probe ultramicroelectrode (UME) is modified with a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid to qualitatively image areas within different pH regions above a track-etched membrane. The current response of the modified electrode in the presence of potassium hexacyanoferrate as electroactive component is different in acidic and alkaline solutions. Depending on the pH value of the solution, the SAM-covered electrode exposes either a neutral or a negatively charged insulating monolayer at pH 3 or 7, respectively, which leads to an increase/decrease in the faradaic current due to electrostatic interactions between the neutral/charged surface and the charged redox mediator. Therefore, local pH changes in the close vicinity of a membrane-like substrate lead to different current responses recorded at the tip electrode when scanning above the surface. [source]

Bioelectrochemical Characterization of Horseradish and Soybean Peroxidases

Carbon Nanotubes Paste Electrodes.

ELECTROANALYSIS, Issue 7-8 2007
A New Alternative for the Development of Electrochemical Sensors
Abstract In this work we summarize the recent activities of our group regarding the analytical performance of a new composite material, the so-called carbon nanotubes paste electrode (CNTPE) obtained by dispersion of multiwall carbon nanotubes in mineral oil. The electrocatalytic properties towards different redox systems, especially those involved in important enzymatic reactions are discussed. Significant shifting in the overpotentials for the oxidation and/or reduction of hydrogen peroxide, NADH, phenol, catechol, dopamine, ascorbic acid, uric acid and hydroquinone are obtained at CNTPE in comparison with the analogous graphite paste electrode (CPE). The usefulness of the electrode as a matrix for immobilizing enzymes is also demonstrated. Highly sensitive and selective glucose quantification is accomplished even without using permselective films or redox mediators. Enzymatic biosensors obtained by incorporation of lactate oxidase, polyphenol oxidase and alcohol dehydrogenase/NAD+ within the composite material have allowed the successful quantification of lactate, phenol, dopamine, catechin and ethanol. The sensitive quantification of traces of oligonucleotides and double stranded calf thymus DNA by adsorptive stripping is reported. The confined DNA layer demonstrated to be stable either in air, acetate or phosphate buffer. The advantages of incorporating copper particles for the quantification of amino acids and albumin is also discussed. [source]

Decolorization of simulated textile dye baths by crude laccases from Trametes hirsuta and Cerrena unicolor

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 3 2010
Ulla Moilanen
Abstract In this study crude laccases from the white-rot fungi Cerrena unicolor and Trametes hirsuta were tested for their ability to decolorize simulated textile dye baths. The dyes used were Remazol Brilliant Blue R (RBBR) (100,mg/L), Congo Red (12.5,mg/L), Lanaset Grey (75,mg/L) and Poly R-478 (50,mg/L). The effect of redox mediators on dye decolorization by laccases was also assessed. C. unicolor laccase was able to decolorize all the dyes tested. It was especially effective towards Congo Red and RBBR with 91 and 80% of color removal in 19.5,h despite the fact that simulated textile dye baths were used. Also Poly R-478 and Lanaset Grey were partially decolorized (69 and 48%, respectively). C. unicolor laccase did not need any mediators for removing the dyes. However, T. hirsuta laccase was only able to decolorize simulated Congo Red and RBBR dye baths (91 and 45%, respectively) in 19.5,h without mediators. When using mediators the decolorization capability was enhanced substantially, e.g. Poly R-478 was decolorized by 78% in 25.5,h. On the whole, both laccases showed potential to be used in industrial applications. [source]

Impedance spectroscopy as a tool for non-intrusive detection of extracellular mediators in microbial fuel cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009
Ramaraja P. Ramasamy
Abstract Endogenously produced, diffusible redox mediators can act as electron shuttles for bacterial respiration. Accordingly, the mediators also serve a critical role in microbial fuel cells (MFCs), as they assist extracellular electron transfer from the bacteria to the anode serving as the intermediate electron sink. Electrochemical impedance spectroscopy (EIS) may be a valuable tool for evaluating the role of mediators in an operating MFC. EIS offers distinct advantages over some conventional analytical methods for the investigation of MFC systems because EIS can elucidate the electrochemical properties of various charge transfer processes in the bio-energetic pathway. Preliminary investigations of Shewanella oneidensis DSP10-based MFCs revealved that even low quantities of extracellular mediators significantly influence the impedance behavior of MFCs. EIS results also suggested that for the model MFC studied, electron transfer from the mediator to the anode may be up to 15 times faster than the electron transfer from bacteria to the mediator. When a simple carbonate membrane separated the anode and cathode chambers, the extracellular mediators were also detected at the cathode, indicating diffusion from the anode under open circuit conditions. The findings demonstrated that EIS can be used as a tool to indicate presence of extracellular redox mediators produced by microorganisms and their participation in extracellular electron shuttling. Biotechnol. Bioeng. 2009; 104: 882,891. © 2009 Wiley Periodicals, Inc. [source]