Home About us Contact
|
Home About us Contact | ||
|
|
||
Formal Potential (formal + potential)
Selected AbstractsRuthenium ,6 -Hexamethylbenzene Complexes Containing Dichalcogenoimidodiphosphinate LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2009Wai-Man Cheung Abstract Treatment of [Ru(,6 -C6Me6)Cl2]2 with AgOTf (OTf, = triflato) followed by K[N(R2PQ)2] gave the 16-electron complexes [Ru(,6 -C6Me6){,2 -N(R2PQ)2}][OTf] [Q = S, R = Ph (1) or iPr (2); Q = Se, R = Ph (3) or iPr (4)] which were isolated as air-stable blue or dark green crystals. For complex 1, when the crude product was recrystallised from CH2Cl2/hexane in air, orange crystals of [Ru(,6 -C6Me6){,3 -N(Ph2PS)2}][OTf] (1a) were isolated as a minor product. The reaction of compound 1 with ammonia, hydrazine hydrate and 4,4,-bipyridyl(4,4,-bpy) gave the 18-electron adducts [Ru(,6 -C6Me6){,2 -N(Ph2PS)2}L][OTf] [L = NH3 (5), N2H4 (6)] and dinuclear[{Ru(,6 -C6Me6)[,2 -N(Ph2PS)2]}2(,-4,4,-bpy)][OTf]2 (7), respectively. Treatment of compound 2 with Li[BEt3H] and NaBH4 afforded the ethyl [Ru(,6 -C6Me6){N(iPr2PS)2}Et] (8) andhydride [Ru(,6 -C6Me6){,2 -N(iPr2PS)2}H] (9) compounds, respectively. Formal potentials for Ru[N(R2PQ)2] complexes have been determined. The structures for complexes 1, 1a, 5, 6, 8 and 9 have been established by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Direct Electrochemistry of Hemoglobin Immobilized on Colloidal Gold-Hydroxyapatite Nanocomposite for Electrocatalytic Detection of Hydrogen PeroxideELECTROANALYSIS, Issue 2 2009Juan 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 Myoglobin Immobilized on Gold Nanoparticles/Carbon Nanotubes Nanohybrid FilmELECTROANALYSIS, Issue 17 2008Wei 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] Electrochemistry of Cytochrome P450 2B6 on Electrodes Modified with Zirconium Dioxide Nanoparticles and Platin ComponentsELECTROANALYSIS, Issue 7 2008Lei Peng Abstract The direct electrochemical and electrocatalytic behavior of the immobilized cytochrome P450 2B6 (CYP2B6) on zirconium dioxide nanoparticles (ZrO2) was investigated. The film of nano-structured ZrO2 that incorporated cytochrome P450 2B6 (CYP2B6) with colloidal paltin, which was stabilized by poly-lysine (Pt-PLL), was prepared on glassy carbon electrodes. In anaerobic solutions, the immobilized CYP2B6 exhibited a reversible electron transfer between the heme electroactive center of CYP2B6 and electrodes with a formal potential of ,(0.449±0.004) V at pH,7.4. In air-saturated solutions, an increased bioelectrocatalytic reduction current could be obtained with the CYP2B6-modified electrode with the addition of anticancer drugs, such as lidocaine. This leads to the construction of disposable biosensors for drugs by utilizing the electrochemical activity and catalytic reactions of the immobilized CYP2B6. [source] Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol-Gel Thin Film Electrode Derived from 3-Aminopropyl Trimethoxy SilaneELECTROANALYSIS, Issue 22 2007K. 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] Electrochemical Preparation of Poly(acriflavine) Film-Modified Electrode and Its Electrolcatalytic Properties Towards NADH, Nitrite and Sulfur OxoanionsELECTROANALYSIS, Issue 9 2007Shen-Ming Chen Abstract Electrochemical polymerization of acriflavine (AF) was carried out onto glassy carbon electrodes (GCE) from the aqueous buffer solution containing 1.5×10,3,M AF monomer (pH,3.5) which produced a thin electrochemically active film. This is noted as poly(AF) film modified electrodes (PAF/GCE). This modified electrode was shown a stable reversible redox couple centered at +0.22,V in pH,3.5 buffer solutions. PAF/GCE was found to be more stable in acidic solutions and its formal potential was found to be pH dependent with a slope close to ,60,mV/pH. The electrochemical deposition kinetics of poly(AF) onto gold coated quartz crystal was studied by using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). PAF/GCE was found be good mediator for electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) in pH,5 buffer solutions. The electrocatalytic oxidation of SO and electrocatalytic reduction of NO, SO and S2O were carried out at PAF/GCE electrode in acidic aqueous solutions. The electrocatalytic oxidation of NADH was also investigated by using amperometric method. [source] Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube-Modified ElectrodesELECTROANALYSIS, Issue 11 2006Xiliang Luo Abstract The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)-modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH,7.4 phosphate buffer solutions (PBS) with the formal potential of about ,455,mV (vs. Ag/AgCl) and shows a surface-controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0,mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD. [source] The Solid State Electrochemistry of Dysprosium(III) Hexacyanoferrate(II)ELECTROANALYSIS, Issue 17 2005Ping Wu Abstract A new electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, dysprosium hexacyanoferrate (DyHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV-vis spectrometry and X-ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of DyHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 217,mV (vs. SCE) at a scan rate of 100,mV/s in 0.2,M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates. [source] Fabrication and Characterization of DNA/QPVP-Os Redox-Active Multilayer FilmELECTROANALYSIS, Issue 23 2004Jianyun Liu Abstract Calf thymus DNA was immobilized on functionalized glassy carbon, gold and quartz substrates, respectively, by the layer-by-layer (LBL) assembly method with a polycation QPVP-Os, a quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2,-bipyridine) as counterions. UV-visible absorption and surface plasmon resonance spectroscopy (SPR) showed that the resulting film was uniform with the average thickness 3.4,nm for one bilayer. Cyclic voltammetry (CV) showed that the total surface coverage of the polycations increases as each QPVP-Os/DNA bilayer added to the electrode surface, but the surface formal potential of Os-centered redox reaction shifts negatively, which is mainly attributed to the intercalation of redox-active complex to DNA chain. The electron transfer kinetics of electroactive QPVP-Os in the multilayer film was investigated by electrochemical impedance experiment for the first time. The permeability of Fe(CN) in the solution into the multilayer film depends on the number of bilayers in the film. It is worth noting that when the multilayer film is up to 4 bilayers, the CV curves of the multilayer films display the typical characteristic of a microelectrode array. The nanoporous structure of the multilayer film was further confirmed by the surface morphology analysis using atomic force microscopy (AFM). [source] Immobilized Cytochrome c Sensor in Organic/Aqueous Media for the Characterization of Hydrophilic and Hydrophobic AntioxidantsELECTROANALYSIS, Issue 18 2003Moritz Beissenhirtz Abstract A method for the characterization of antioxidants is introduced, which allows the measurement of pure hydrophilic and hydrophobic substances as well as complex cosmetic creams. The sensor is based on cytochrome c covalently immobilized on a gold wire electrode working in mixtures of phosphate buffer and organic solvents. It is combined with a superoxide generating enzyme system. The decrease of the superoxide concentration in the test solution by the added antioxidants is detected and used for the quantification of their antioxidative efficiency. Electrochemical properties of immobilized cytochrome c, such as formal potential and heterogeneous electron transfer rate constant, have been investigated in mixtures of aqueous buffer and DMSO, methanol, butanediol, and THF. The maximum organic solvent content for quasi-reversible electrode behavior was correlated to spectroscopic measurements. The activity of the radical producing enzyme in such media was determined and the radical generation characterized. The antioxidative properties of pure substance such as ascorbic acid and Biochanin A as well as of five anti-ageing cosmetic creams were studied. This showed also the influence of matrix composition on the efficiency of antioxidative supplements. [source] Catalytic Voltammetric Determination of Cladribine in Biological SamplesELECTROANALYSIS, Issue 5-6 2003Noemí de-los-Santos-Álvarez Abstract An electrochemical method for the citotoxic prodrug cladribine determination is proposed. Graphite electrodes modified with cladribine showed a redox process with a formal potential of 0.173,V at pH 6, after the oxidation of the adenine moiety of the drug, whose current can be employed as analytical signal with a detection limit of 75,nM by square-wave voltammetry. As these oxidation products exhibit great electrocatalytic activity toward the electro-oxidation of NADH at low potentials, the analytical response can further be amplified. As a result, the detection limit was improved up to 1,nM using differential pulse voltammetry. The method was applied to the determination of cladribine in serum and urine samples after solid-phase extraction. No electroactive interferences were found in both fluids. The method allows the selective detection of the drug in the presence of the main metabolite, 2-chloroadenosine, which is not able to electrocatalize the NADH oxidation. [source] Topological and Electron-Transfer Properties of Yeast Cytochrome c Adsorbed on Bare Gold ElectrodesCHEMPHYSCHEM, Issue 11 2003Beatrice Bonanni Dr. Abstract The redox metalloprotein yeast cytochrome c was directly self-chemisorbed on "bare" gold electrodes through the free sulfur-containing group Cys102. Topological, spectroscopic, and electron transfer properties of the immobilised molecules were investigated by in situ scanning probe microscopy and cyclic voltammetry. Atomic force and scanning tunnelling microscopy revealed individual protein molecules adsorbed on the gold substrate, with no evidence of aggregates. The adsorbed proteins appear to be firmly bound to gold and display dimensions in good agreement with crystallographic data. Cyclic voltammetric analysis showed that up to 84,% of the electrode surface is functionalised with electroactive proteins whose measured redox midpoint potential is in good agreement with the formal potential. Our results clearly indicate that this variant of cytochrome c is adsorbed on bare gold electrodes with preservation of morphological properties and redox functionality. [source] Electrochemical Preparation and Characterization of Lanthanum Hexacyanoferrate Modified ElectrodeCHINESE JOURNAL OF CHEMISTRY, Issue 2 2005Wu Ping Abstract An electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, lanthanum hexacyanoferrate (LaHCF), was prepared by electrochemical deposition on the surface of a glassy carbon electrode with a potential cycling procedure. The cyclic voltammogram of LaHCF exhibits a pair of well-defined redox peaks with the formal potential of 208 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increase linearly with the square root of the scan rate up to 1000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of LaHCF were studied by voltammetry. LaHCF was also characterizated by scanning electron microscope (SEM), FTIR and XPS techniques. [source] | ||||||||||