Showing papers on "Redox published in 1977"

The redox mechanism of the chelate-catalysed oxygen cathode

Abstract: The electro-reduction of oxygen is effectively catalysed by metal chelates of the N4-type. The mechanism of this process has been found to be a modified ‘redox catalysis’. O2 molecules and the products of their reaction, at least up to H2O2, remain strongly co-ordinated to the central metal ion of the chelates XMeII. The potential-determining step, which regenerates the reduced form, is the following: (XMeIII...O2H)++H++ 2e→XMeII+H2O2.

A simple preparation of phenols from diazonium ions via the generation and oxidation of aryl radicals by copper salts

Abstract: The standard method of preparation of phenols from diazonium salts consists of heating the latter in highly acidic aqueous solution; the high temperature and acidity often cause a variety of unwanted side reactions. We advocate an entirely different procedure which can be performed in a few minutes in neutral solution at room temperature, or below. The method is based on our previous observation that aryl radicals can be oxidized to phenols by cupric ion and it consists of adding cuprous oxide to a dilute solution of the diazonium salt dissolved in a solution containing a large excess of cupric nitrate. In one case the presence of siIver(1) appeared to accelerate the radical oxidation. Not only is the redox procedure simpler than the thermal method, but in all cases studied to date, the yields are equivalent or superior to those obtained by the thermal procedure. In four cases in which the latter is unsatisfactory, the redox method is quite successful and it is considered the method of choice for new cases.

Biochemical fuel cell utilizing immobilized cells of clostridium butyricum

Abstract: A bacteria utilizing biochemical fuel cell has been investigated. Previously, the authors applied the hydrogenase system of a microbial cell to the anodic reaction of a biochemical fuel cell. In the anodic reaction of the biochemical fuel cell, hydrogenase from Escherichia coli was involved and methylene blue was used as an organic redox compound. One of the first biochemical fuel cell systems designed to use hydrogen was developed by Rohrback et al. They reported on the production of hydrogen from glucose by Clostridium butyricum. The production of the hydrogen from the fermentation of glucose by C. butyricum and the utilization of hydrogen as a reactant at the anode in a hydrogen oxygen (air) fuel cell were mentioned by DelDuca et al. However, the hydrogen producing system, especially hydrogenase, was very unstable. Therefore, continuous hydrogen production by intact cells was difficult. Recently, hydrogen was produced continuously by immobilized whole cells. The anode reaction of a biochemical fuel cell which utilizes immobilized bacteria is described.

The oxygen electrode. Part 8.—Oxygen evolution at ruthenium dioxide anodes

Abstract: The electrocatalytic behaviour of Ti-supported RuO2, prepared by thermal decomposition of RuCl3, as substrate for oxygen evolution was investigated by a variety of techniques. B.E.T. adsorption experiments showed that the RuO2 layers are highly porous with large surface area values which, however, decrease rapidly as the annealing temperature increases above ∼ 300°C. Both the charge involved in the cyclic voltammograms and the oxygen evolution rates are dependent on the true (rather than apparent) area of these electrode surfaces, and also on the pH of the solution. The results for oxygen evolution are discussed in terms of electrochemically generated unstable surface oxides whose decomposition is catalysed by protons in acid, and hydroxide ions in base. The lower reactivity of the oxide at intermediate pH value is attributed on the one hand to loss of protons by OH groups, resulting in oxygen bridging, and on the other to lack of enhanced coordination of surface ruthenium species by OH– ions, which in this pH region are present only at low activity. The charge associated with voltammetric sweeps is accounted for in terms of surface redox processes rather than bulk penetration of protons into the oxide. The need for surface area measurements as a guide to the interpretation of the electrochemical data in the case of these oxide systems is stressed.

Solar energy storage, production of hydrogen by 546-nm irradiation of a dinuclear rhodium(I) complex in acidic aqueous solution

Abstract: A logical avenue for exploratory research on (Rh/sub 2/(bridge)/sub 4/)/sup 2 +/ (bridge = 1,3-diisocyanopropane) involves its excited-state reactivity behavior, as a directly coupled dinuclear redox center might be able to channel charge-transfer excitation energy into redox-substrate chemical bond formation at rates that are competitive with back electron transfer. This goal has been achieved in one important case, namely, in the reduction of protons 40 hydrogen through 546-nm irradiation of (Rh/sub 2/(bridge)/sub 4/)/sup 2 +/ in aqueous HCl solution.

The reactions of lignins with oxygen and hydrogen peroxide in alkaline media

Abstract: The reactions of lignins upon treatment with oxygen and hydrogen peroxide in alkaline media are summarized on the basis of the results from studies with appropriate model compounds. Two types of initial oxidation reactions may be distinguished: (1) Electrophilic attack on carbanions by molecular oxygen (oxygenations) (2) Nucleophilic addition of hydroperoxide anions to carbonyl and conjugated carbonyl structures. These two oxidants attack in phenolic and enolic lignin structures centres having alternately high (oxygen) and low (hydrogen peroxide) electron density. Both the reactions with oxygen and those with hydrogen peroxide result in the formation of intermediates of the hydroperoxide type. Subsequently, the intermediates undergo rearrangements, resulting in the cleavage of carbon-carbon bonds or in the formation of epoxide intermediates, or alternatively are converted into ortho-or para-quinoid structures. The products of the cleavage of carbon-carbon bonds and the quinoid and epoxide intermediates undergo alkaline-oxidative degradation ultimately yielding simple acids and hydrophilic polymerization products. The two types of initial oxidation (1 and 2) may take place simultaneously or sequentially, both during treatment with oxygen in alkali (oxygen pulping and bleaching). In the former process, hydrogen peroxide is generated by the autoxidation of enediol structures while, in the latter process, oxygen is originally present in the atmosphere and/or is formed by the decomposition of hydrogen peroxide. Although intimately connected with each other during both processes, these two types of oxidation reactions should be considered separately. By doing so, known observations from technical treatments of wood, pulps and lignins with oxygen or hydrogen peroxide can be interpreted in chemical terms.

Modified Viologens with Improved Electrochemical Properties for Display Applications

Abstract: The redox reaction of 1,1'‐diheptyl‐4,4'‐dipyridinium dibromide in water was investigated by means of linear potential sweep voltammetry. It was found that aging of the radical salt film or the occurrence of the second reduction step results in an additional oxidation peak. This additional oxidation peak is accompanied by a decrease of charge efficiency, leading to display failure. It was demonstrated that these problems can be largely avoided by use of modified viologens in combination with tin dioxide electrodes. The influence of the electrode material was also investigated.

Redox properties of microsomal reduced nicotinamide adenine dinucleotide-cytochrome b5 reductase and cytochrome b5.

Abstract: Hepatic NADH-cytochrome b5 reductase was reduced by 1 mol of dithionite or NADH per mol of enzyme-bound FAD, without forming a stable semiquinone or intermediate during the titrations. However, the addition of NAD+ to the partially reduced enzyme or illumination in the presence of both NAD+ and EDTA yielded a new intermediate. The intermediate had an absorption band at 375 nm and the optical spectrum resembled anionic semiquinones seen on reduction of other flavin enzymes. Electron paramagnetic resonance measurements confirmed the free-radical nature of the species. To explain the results, a disproportionation reaction between the oxidized and reduced NAD+ complexes (E-FAD-NAD+ + E-FADH2-NAD+ in equilibrium 2E-FADH.-NAD+) is assumed. Potentiometric titration of NADH-cytochrome b5 reductase at pH 7.0 with dithionite gave a midpoint potential of -258 mV; titration with NADH gave -160 mV. This difference may be due to a difference in the relative affinity of NAD+ for the reduced and oxidized forms of the enzyme. The effects of pH on the midpoint potential of the NAD+-free enzyme were very similar to those which have been measured with free FAD. At pH 7.0, midpoint potentials of trypsin-solubilized and detergent-solubilized cytochrome b5 were 13 and 0 mV, respectively.

1-Methoxy-5-Methylphenazinium Methyl Sulfate

Abstract: This paper describes the properties and application of 1-methoxy-5-methylphenazinium methyl sulfate (1-methoxyPMS), which is a photochemically stable, versatile electron carrier. Like 5-methylphenazinium methyl sulfate (PMS), it mediates electron transfer between NADH and various electron acceptors such as tetrazolium dyes or the electrode of an enzymic electric cell, and yet it does not deteriorate upon storage under scattered light in normal laboratories. The rate of reduction of 1-methoxyPMS coupled to the reoxidation of NADH produced by the lactate dehydrogenase reaction, was even faster than that of PMS. It was also successfully employed as an electron mediator in the enzymic electric cell method for the assay of NAD-linked dehydrogenases. 1-MethoxyPMS solution is rosy pink, and its standard redox potential (E0') is approximately +0.063 V. The use of 1-methoxyPMS will be beneficial in biochemistry as well as medical technology, where PMS has been used as an electron mediator in various electron transfer systems.

Oxidation of cerebral cytochrome aa3 by oxygen plus carbon dioxide at hyperbaric pressures

Abstract: The reduction-oxidation level of cytochrome aa3 in the intact cerebral cortex of cerveau isole or pentobarbital-anesthetized cats was monitored by means of dual-beam reflectance spectrophotometry. Respiratory gases containing varying fractions of carbon dioxide and oxygen were administered at increased pressures, allowing titration of the cytochrome redox state from maximum reduction during nitrogen ventilation to the completely oxidized state. We show that the fully oxidized state could be reached with about 5% CO2-95% O2 inspired at 4 ATA. Maximum oxidation was achieved only through the relaxation of oxygen-induced vasoconstriction of the cerebral vessels, as our data indicated that large blood volume responses accompanied the increases in inspired carbon dioxide. With out technique, we have established that under resting air-breathing conditions cytochrome aa3 is about 85% reduced in the cat cerebral cortex, and that the absorption peak for cytochrome aa3 in situ is located near 602 nm. A free energy change of an additional 8 kcal is calculated to occur with donation of an electron pair from 85% reduced cytochrome aa3 to oxygen as compared to a 1% reduction level.

Metal-ion oxidations in solution. Part XIX. Redox pathways in the oxidation of penicillamine and glutathione by chromium(VI)

Abstract: Three moles of penicillamine or glutathione are required to reduce chromium(VI) to chromium(III). The kinetics and mechanism of the redox reaction have been studied using the stopped-flow method. The reaction proceeds via the formation of a transient intermediate (K1) which decomposes either in a proton-catalyzed pathway or by reaction with a second mole of thiol. The rate lawwhere n = 1 for penicillamine and 2 for glutathione has been shown to hold over a range of thiol and hydrogen-ion concentrations. At 25 °C k2 = 14.3 ± 1.0 M−1 s−1 for penicillamine (ΔH≠ = 9 ± 2 kcal mol−1, ΔS≠ = −33 ± 6 cal K−1 mol−1) and 12.1 ± 0.4 M−1 s−1 for glutathione (ΔH≠ = 7 ± 2 kcal mol−1, ΔS≠ = −40 ± 5 cal K−1 mol−1). Several chromium(III) products have been identified by ion-exchange methods. The significance of the second-order pathways in these reactions is discussed.

Redox behaviour of transition metal ions in zeolites. Part 6.—Reversibility of the reduction reaction in silver zeolites

Abstract: In this paper is shown that hydrogen is formed by oxidative thermal desorption from Y-zeolite or mordenite containing highly dispersed silver metal in the cages. Upon thermal degassing above 573 K, hydrogen is desorbed from previously reduced Ag zeolites. At the same time, silver metal is reoxidized and located as Ag+ ions in lattice positions and lattice hydroxyl groups disappear.The following methods are used to characterize the system; isothermal and temperature programmed consumption or desorption of hydrogen in a volumetric system; i.r. spectroscopy of the hydroxyl region; i.r. spectroscopy of adsorbed carbon monoxide and pyridine; X-ray diffraction of Ag0 crystallites.

Process for the wet oxidation of organic substances

Abstract: of the Disclosure A process has been developed for the oxidation of organic substances, dissolved or dispersed in an aqueous system, with a gas containing molecular oxygen at elevated temperature and under elevated pressure chiefly to carbon dioxide and water, with subsequent phase separation of the reaction mixture into a gaseous phase substantially containing inert gas, carbon dioxide, steam and organic constituents and a liquid phase substantially containing water, characterized in that the pressure is adjusted, at the given temperature, so that by evaporation of water from the aqueous system, more steam than the exotherm-icity of the oxidation reaction gives rise to,goes into the gaseous phase, which is fed to a heat exchanger in which the amount of heat required to maintain the oxidation temperature is completely or partially transferred to a mixture of water and a gas containing molecular oxygen, which mixture flows in on the other side of the heat exchanger and is subsequently fed to the reactor. A particular advantage of the process of the invention is that, in addition to the oxidation of organic substances, it is possible to fed inorganic constituents, after the oxidative degradation of the organic substances, to a re-use or recovery process.