Showing papers on "Redox published in 1982"

One-electron redox potentials of phenols. Hydroxy- and aminophenols and related compounds of biological interest

Abstract: The rate constants for reversible electron transfer between a series of substituted phenolate ions and anilines and various substituted phenoxyl or anilino radicals in aqueous solution were measured by observing the formation or depletion of the radicals involved. Nonequilibrium concentrations of the radicals were produced in the presence of the corresponding phenols or anilines by using the pulse radiolysis technique. The relaxation of the system to equilibrium was monitored by optical detection methods. From the equilibrium constants for one-electron transfer, the one-electron redox potentials (E/sup 2/) for 38 phenolic or anilino type compounds were determined, many of which are natural products. The redox potentials are strongly influenced by electron-donating or -withdrawing substituents at the aromatic system. 3 figures, 5 tables.

Photo-oxidation of water sensitized by WO3 powder

Abstract: WO3 powder photosensitized the oxidation of water by Fe3+ ions with blue light (400–450 nm). The formal quantum efficiency for oxygen production at 405 nm was (3.1 ± 0.1)× 10–3 mol ein–1. Oxygen production was partially inhibited by Fe2+, oxygen and high concentrations of Fe3+(> 10–2 mol dm–3). Depositing RuO2 on to the semiconductor powder produced a moderate increase in the rate of oxygen production, while deposits of Pt, Rh and Ru lead to a decrease in the rate of oxygen formation. Unlike most of the artificial systems which have been described for the photo-oxidation of water with visible light, this system operates with an electron acceptor (Fe3+) which is part of a reversible redox couple (Fe3+/Fe2+).

Reversible electrochemical reduction and oxidation of cytochrome c at a bis(4-pyridyl) disulphide-modified gold electrode

Abstract: At a gold electrode on which bis(4-pyridyl) disulphide had been pre-adsorbed, horse heart ferricytochrome c exhibited a well developed quasi-reversible redox wave by cyclic voltammetry in the absence of any promoter in the solution.

Interactions of iron(II) and iron(III) with gallic acid and its homologues: a potentiometric and spectrophotometric study

Abstract: The reactions between iron(III) and the phenols gallic acid, catechol, protocatechuic acid and pyrogallol have been studied in aqueous solution at 25oC (I 0.10 M KCl). From spectrophotometric and pH titration data it was established that (i) complexes with 1 : 1, 1 : 2 and 1 : 3 (M : L) stoichiometry are formed in oxygenated solution, (ii) the redox reaction given at low pH by these ligands Fe3+ + ½phenol → Fe2+ + ½quinone + H+ is not reversed by complexing of Fe3+ at higher pH, and (iii) the percentage composition of iron(II) and iron(III) in solutions of these ligands is a function of ER (ligand), the pH and age of solutions and the partial pressure of dissolved oxygen.

Microspectrofluorometric approach to the study of free/bound nad(p)h ratio as metabolic indicator in various cell types

Abstract: Under excitation at 365 nm, the cell fluorescence is mainly due to bound and free NAD(P)H, plus a small contribution from flavins. Resolution is first attempted in the simplest case. i.e. the increase spectrum (δIf) due to microinjection of glucose-6-phosphate (G6P) into EL2 ascites cells. Above 510 nm, δIF is identical to the spectrum of free NADH. Below 510 nm. the presence of a second component is suggested, i.e. the intensity of the free NADH spectrum is lower than the measured δIF level. The difference between δIf and the free NADH spectrum (maximum at 475 nm) yields a spectrum suggestive of bound NADH with maximum at 450 nm. Thus, with free and bound NADH, the entire δIF can be reconstructed, with some assumptions as to the relative quantum yields of the two components. This seems to leave no place for a flavin component. The questions raised by the lack of such a component are answered using a new microspectrofluorometer, which aiiows correlated monitoring of NAD(P)H and flavins with excitations at 365 and 436 nm, respectively. As detected by excitation at 436 nm, injections of G6P, malate, ADP, and treatments with azide, cyanide or partial anaerobiosis, all indeed show a redox change of flavins, in the sense of decreased emission. It is understandable, however, that such a change which is not very large even using 436 nm excitation should remain undetected when flavins are excited at 365 nm, i.e. using the tail of their excitation spectrum. In contrast to the increased δIF spectrum recorded in response to injected substrate, the initial spectrum (If) of the cell prior to a metabolic perturbation reveals a third component, even with 365 nm excitation. The position and reactivity of this component shows flavin-like properties. The structural resolution attainable makes it possible to obtain the evaluation of free vs. bound NAD(P)H and flavin fluorochromes in the mitochondrial and cytosolic compartments of the intact cell.

Electrochemical measuring apparatus comprising enzyme electrode

Abstract: An immobilized enzyme electrode effective in measurement of the substrate concentration of the enzyme and in conversion from enzyme reaction energies into electric energies. The immobilized enzyme, of an oxidase system, such as glucose oxidase, amino acid oxidase, xanthine oxidase or the like and a metal oxide capable of constituting a redox system which is reduced through coupling with these enzyme reactions and is electrochemically oxidized (anodic oxidation) are combined with each other. The use of the enzyme electrode allows the determination quantity of the enzyme substrate as extremely low as approximately 10 -5 to 10 -6 mole/l in concentration.

Mechanism for Selective Perivenular Hepatotoxicity of Ethanol

Abstract: Chronic alcohol administration to baboons results in perivenular lesions in the liver. To study possible mechanisms, the effect of ethanol on splanchnic oxygen consumption was measured. Acute ethanol administration increased splanchnic oxygen consumption in the control baboons, but the consequences of this effect on oxygenation of the perivenular zones were offset by a concomitant rise in blood flow, resulting in unchanged hepatic venous oxygen tensions. In alcohol-fed baboons, splanchnic oxygen consumption was not increased, either in the withdrawal state or after ethanol infusion. To study the magnitude of the shift in redox state induced by ethanol in the perivenular zones, we compared the effects of ethanol on the lactate/pyruvate ratio in hepatic venous blood (an approximation of that in perivenular hepatocytes) with the ratio in total liver. Prior to ethanol infusion, the lactate and pyruvate were the same in liver and in hepatic venous blood. By contrast, in all baboons, ethanol produced a much greater rise in the lactate/pyruvate ratio and decreased pyruvate more in hepatic venous blood than in total liver. Moreover, in isolated rat hepatocytes, the ethanol-induced redox shift was markedly exaggerated by oxygen tensions similar to those found in centrolobular zones. This suggests that the normally low oxygen tensions existing in perivenular zones exaggerate the ethanol-induced redox shift, a change which may contribute to the exacerbation of the damage in the perivenular area of the hepatic lobule.

Transients generated upon photolysis of colloidal titanium dioxide in acetonitrile containing organic redox couples

Abstract: This report investigates the identity of transients formed upon irradiating colloidal TiO/sub 2/ particles in nonaqueous solvents in the presence of organic redox systems, a medium which simultaneously incorporates the heterogeneity of the powder-catalyzed reactions and the possibility for spectroscopic analysis of mechanistically relevant transients. Although semiconductor band theory predicts that photocatalyzed oxidations or reductions could occur with donors or acceptors whose redox potentials lie within the range between the valence and conduction bands of the metal oxide, little evidence for organic radical ion intermediates generated in this way from neutral precursors has yet been reported. This investigation describes transient spectra that affirm the occurrence of semiconductor-mediated electron transfer and demonstrate the involvement of radical ions, the first such data reported for organic redox couples in nonaqueous solvents.

Anodic dissolution of n-type and p-type chalcopyrite

Abstract: The anodic dissolution of n- and p-type chalcopyrite (CuFeS2) was studied in both acidic sulphate and acidic chloride media under conditions relevant to chemical leaching, i.e., at temperatures >70° C and over the potential region 0.2–0.6 V versus SCE. Double potential pulse chronoamperometry was used to probe the surface of the chalcopyrite anodes to determine the activation currents at various applied overpotentials. Analysis of the data obtained in both systems indicated the formation of a surface layer, a solid electrolyte interphase (SEI), which slows the rate of electron transfer. The electron transfer between various redox couples, including Cu2+/Cu2+, Fe2+/Fe2+ and I3−/I− on n- and p-type chalcopyrite and on Pt, was compared using cyclic voltammetry. In the potential region of interest, the Fe2+/Fe2+ couple is much less reversible on chalcopyrite than are the Cu2+/Cu2+ and I3−/I− redox couples. Chemical leaching of chalcopyrite in the presence of various oxidants was also carried out, and the results of the chemical experiments were discussed in terms of the electrochemical properties of the systems.

Separator membranes for redox-type electrochemical cells

Abstract: This disclosure is directed to improved redox type electrochemical cells, preferably those of the iron (+3)/iron (+2) or chromium (+3)/iron (+2) electrolyte variety, incorporating polymeric, ion-exchange separator membranes produced by radiation grafting techniques.