Synthesis, electrochemical behavior and X-ray crystal and molecular structures of [Fe(diene)(CO)(2)PPh3] (diene = chalcone, sorbic acid)

The compounds [Fe(ch)(CO)(2)PP3] (1) (ch = chalcone) and [Fe(sba)(CO)(2)PPh3] (2) (sba = sorbic acid) were prepared by irradiating the tetracarbonyltriphenylphosphineiron(0) complex in benzene in the presence of ch or sba. The compounds were characterized by infrared and P-31 NMR spectroscopies. Their electrochemical behavior was investigated by cyclic voltammetry and the results suggest that their oxidations occur by more than one electrochemical step, producing free ch and sba, free PPh3 and solvated Fe(III). It was observed that sba ligand contributes more effectively to the stabilization of metal center in these complexes, the X-ray crystal and molecular structures of 1 and 2 were determined; it was shown that the Fe atom adopts a distorted octahedral coordinated geometry in which three of the sites are occupied by the ch or sba ligand. The [Fe(ch)(CO)(2)PPh3] complex is a monomer and the unit cell of complex 2 contains exist two identical and crystallographically independent molecules of [Fe(sba)(CO)(2)PPh3] which are linked by short hydrogen bonds O-H . . .O (C) 2001 Published by Elsevier B.V. Ltd.

The electrochemical behavior of pyrite-pyrrhotite mixtures

To assess the response of common sulfide minerals to oxidizing conditions, a methodology to immobilize mechanically solid particles on carbon surfaces (voltammetry of microparticles, VMP) was employed, to define the influence of the pyrrhotite content in pyrite-pyrrhotite mixtures. The influence of the galvanic interactions and local pH on the oxidation reaction of pyrite was also investigated. With this purpose, artificial two-mineral electrodes were constructed, ranging in weight from 20 to 80% pyrrhotite. The resulting cyclic voltammograms were analyzed and relative quantities of oxidation products were evaluated. The goal of this work was to define the boundary conditions, in terms of pyrrhotite content in the mixture, that determine the SO42-/S ratio obtained and to describe some parameters which influence this ratio: local pH and galvanic interactions. (C) 2003 Elsevier B.V. All rights reserved.

Electrochemical behavior of the N-nosyl-protected amino acids in N,N-dimethylformamide

The electrochemical reduction of serine, glycine, and leucine protected by the 4-nitrobenzenesulfonyl, group in N,N-dimethylformamide at mercury cathode occurs at two steps. The first one at -0.8 V vs. SCE, after a one-electron transfer, leads the anion radical formation that dimerizes and adsorbs at electrode. In the second step at -1.4 V, an instable dianion forms which then cleaves. The mechanism is discussed.

Gamma phases in Cu-Al alloys and the influence of a square shaped phase in the electrochemical behavior of a Cu-13.6wt% Al alloy

The electrochemical behavior of Cu-xAl alloys, with 11 wt%less than or equal to x less than or equal to 15wt%, in 0.5 M H2SO4 was studied by means of open-circuit potential decay measurements, quasi-stationary and fast cyclic voltammetry, and electrochemical impedance spectroscopy. Some of the alloys (x less than or equal to 14%), when quenched formed martensitic structures. Alloys with greater than or equal to 13% showed a little square-shaped phase when quenched from temperatures around 800 degrees C. It was observed that in sulfuric medium, these formations were dealuminized differently than the martensitic phase. The values of the rest potentials are more influenced by the heat treatment rather than by the alloy composition. An anodic Tafel slope of ca. 60 mV/decade was observed for all the alloys, independently of the heat treatment. This is explained in terms of a competition between two processes: copper oxidation and copper(I) deproportionation. In the cyclic voltammetric experiments it was observed an anodic current peak, related with copper oxidation with a possible formation of some interfacial species, and a cathodic current peak during the reverse potential scan, associated with the reduction of soluble species and/or of the film. The AC Impedance data were interpreted in terms of electric equivalent circuits.

(5,10,15,20-Tetra(4-pyridil)porphinato)manganes(III) acetate modified by four mu(3)-oxo-triruthenium acetate clusters: synthesis, characterization, electrochemical behavior and catalytic activity

A novel supermolecule constituted by four mu(3)-oxo-triruthenium acetate clusters coordinated to manganese(III)-meso -tetra(4-pyridil)porphyrin acetate ([MnTPyP]CH3COO) has been synthesized. Characterization has been performed by UV-Vis and H-1 NMR spectroscopy. The electrochemical behavior (cyclic voltammetry and spectroelectrochemistry) in N,N'-dimethylformamide has been analyzed in terms of five redox processes: three related to peripheral clusters (Ru-IV,Ru-III,Ru-III/Ru-III,Ru-III,Ru-III/Ru-III,Ru-II,Ru-II) and two centered on the Mn-porphyrin core ((MnP)-P-III/(MnP)-P-II/(MnP2-)-P-II). A direct comparison has been performed between MnTCP and MnTPyP as catalysts for the cyclooctene and cyclohexane oxidation reactions. The improved selectivity exhibited by the supramolecular catalyst for cyclohexane oxidation has been ascribed to electronic effects on the oxomanganese(V) porphyrin species induced by the four peripheral clusters, in the formal (RuRuRuIII)-Ru-IV-Ru-III oxidation state. (C) 2000 Elsevier B.V. S.A. All rights reserved.

Electrochemical behavior of cobalt oxide coatings on cold-rolled steel in alkaline sodium sulfate

The electrochemical behavior of a coating of cobalt oxide on cold-rolled steel in alkaline sodium sulfate was Studied using the electrochemical techniques of open-circuit potential measurements and electrochemical impedance spectroscopy. The coating was prepared at different annealing temperatures ranging from 350 to 750 degreesC and characterized by SEM, EDX and XRD. Below 550 degreesC the composition of the coating was basically of Co3O4. At 750 degreesC CoO was formed and big cracks appeared on the film exposing an inner layer of iron oxides. Analysis of the EIS data is very difficult because of the complexity of the interface structure. It can be inferred that the charge transfer resistance of the coatings prepared at 350 and 450 C were higher than those for the coatings prepared at temperatures above 550 degreesC. (C) 2002 Published by Elsevier B.V. Ltd.

Synthesis and electrochemical behavior of single-crystal magnetite nanoparticles

Water-dispersed magnetite nanoparticle synthesis from iron(II) chloride in dimethyl sulfoxide (DMSO)-water solution at different DMSO-water ratios in alkaline medium was reported. TEM and XRD results suggest a single-crystal formation with mean particle size in the range 4-27 nm. Magnetic nanoparticles are formed by the oxidative hydrolysis reaction from green rust species that leads to FeOOH formation, followed by autocatalysis of the adsorbed available Fe(II) on the FeOOH surfaces. The available hydroxyl groups seem to be dependent on the DMSO-water ratio due to strong molecular interactions presented by the solvent mixture. Goethite phase on the magnetite surface was observed by XRD data only for sample synthesized in the absence of DMSO. In addition, cyclic voltammetry with carbon paste electroactive electrode (CV-CPEE) results reveal two reduction peaks near 0 and +400 mV associated with the presence of iron(III) in different chemical environments related to the surface composition of magnetite nanoparticles. The peak near +400 mV is related to a passivate thin layer surface such as goethite on the magnetite nanoparticle, assigned to the intensive hydrolysis reaction due to strong interactions between DMSO-water molecules in the initial solvent mixture that result in a hydroxyl group excess in the medium. Pure magnetite phase was only observed in the samples prepared at 30% (30W) and 80% (80W) water in DMSO in agreement with the structured molecular solvent cluster formation. The goethite phase present on the, magnetite nanoparticle surface like a thin passivate layer only was detectable using CV-CPEE, which is a very efficient, cheap, and powerful tool for surface characterization, and it is able to determine the passivate oxyhydroxide or oxide thin layer presence on the nanoparticle surface.

Electrochemical Behavior of Cu-9% Al-5% Ni-2% Mn Alloy in Chloride Media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Study of the Electrochemical Behavior of Histamine Using a Nafion (R)-Copper(II) Hexacyanoferrate Film-Modified Electrode.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical behavior of a nitrobenzenesulfonyl derivative of aniline in aqueous solution

The electrochemical behavior of aniline protected by a nitrobenzene sulphonyl group in aqueous solution at a mercury electrode is reported. At pH < 10 the compound was reduced in a single well-defined step. Reduction of the nitro group involving a preceding protonation step was postulated. Two reduction steps are present at higher pH (pH > 11). Controlled potential electrolysis confirms that the reduction of the nitro group in a four-electron step to N-phenyl-4-hydroxylamine sulphonamide is always the preponderant process. ©1997 Soc. Bras. Química.

Microstructural characteristics and electrochemical behavior of Co3O4 sintered electrodes

Co3O4 can be used as electrocatalyst for oxygen evolution reaction. The macro and microstructure of the oxide, obtained by compacting and sintering lithium-doped Co3O4 powder in atmosphere of dry air and in conditions of controlled temperature and time was analyzed by metallographic techniques. The porous material was characterized by XRD, SEM and EDS combined techniques. For working temperatures up to 1200°C, the pellet was consituted of particles with varying sizes over a wide range of particle size and, at higher temperatures CoO is formed and polymorphic transformation was observed. The materials were also characterized electrochemically in alkaline media by open circuit potential and potentiodynamic I/E measurements. The results were compared to those previously prepared by others by thermal deposition.

Study of the electrochemical behavior of histamine using a Nafion®-copper (II) hexacyanoferrate film-modified electrode

A study on the electrochemical behavior of histamine species in aqueous medium is described. A glassy carbon electrode chemically modified with copper (II) hexacyanoferrate (CuHCFe) film and covered with Nafion® film was employed. The interaction between the analyte and the CuHCFe film can be demonstrated by a decrease in both the cathodic and anodic peak currents at 0.68V (vs. Ag/AgCl), attributed to the film and the appearance of new peak current at 0.47V. Cyclic voltammetric parameters obtained for histamine indicate the formation of stable complex between histamine adsorbed at the electrode surface. The dependence of peak currents on the concentration of the analyte is not linear in the employed work range, indicating the presence of a coupled chemical reaction in the electrodic process. © 2010 by ESG.

Electrochemical behavior and voltammetric determination of pyrazinamide using a poly-histidine modified electrode

Pyrazinamide (Pyrazinecarboxamide-PZA) is a drug that is used to treatment tuberculosis. In the present work, the voltammetric behavior of PZA was studied using a screen-printed modified electrode (SPCE). The modified electrode was constructed using poly-histidine films, and it showed an electrocatalytic effect, thus promoting a decrease in PZA reduction potential and improving the voltammetric response. Cyclic voltammetry and electrochemical impedance spectroscopy techniques have been employed in order to elucidate of the electrodic reaction. The results allowed the proposal that in the PZA reduction, a further chemical reaction occurs that corresponds to a second-order process which is subsequent to the electrode reaction. In addition, a sensitive voltammetric method was developed, and it was successfully applied for PZA determination in human urine samples. The best response was found using SPCE modified with poly-histidine prepared by histidine monomer electropolymerization (SPCE/EPH). The electroanalytical performance of the SPCE/EPH was investigated by linear sweep (LSV), differential pulse (DPV), and square wave voltammetry (SWV). A linear relationship between peak current and PZA concentrations was obtained from 9.0 × 10-7 to 1.0 × 10-4 mol L-1 by using DPV. The limit of detection at 5.7 × 10 -7 mol L-1 was estimated, and a relative standard deviation of the 5.0 × 10-6 mol L-1 of PZA of 10 measurement was 3.7%. © 2012 Elsevier B.V. All rights reserved.

Electrochemical behavior of ruthenium-hexacyanoferrate modified glassy carbon electrode and catalytic activity towards ethanol electrooxidation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)