Showing papers on "Redox published in 1975"
TL;DR: H2O2 was determined by two methods that are applicable to conditions existing during microsomal mixed function oxidation reactions, provided that contaminating catalase activity is inhibited by azide and that interference by other mixedfunction oxidation reactions can be excluded.
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TL;DR: The types of sulfur bonding that occur in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two-electron donors as discussed by the authors.
Abstract: The types of sulfur bonding—as sulfane or sulfide—encountered in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two-electron donors by bridging two metal atoms, as four-electron donors by bridging three or four metal atoms, or as six-electron donors by incorporation between four metal atoms. In such complexes, the metal-metal bond can be modified over a wide range by chemical or electrochemical variation of the number of electrons present. The readiness with which polynuclear complexes containing metals and sulfur undergo redox reactions is also utilized by Nature in the active sites of some redox proteins.
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TL;DR: In this paper, it was shown that the non-stoichiometry of the oxide film is a function of the temperature of preparation and also of the atmosphere of annealing.
Abstract: RuO2 films on Ta and Pt as supports have been prepared by thermal decomposition of RuCl3 at different temperatures in various atmospheres. Bulk and surface electronic properties of these films have been deduced from their behaviour as electrodes with respect to reactions involving or not involving the adsorption of reactants and/or products, (for example Fe2+/Fe3+, I−/I2, H2/H+ and some simple organic reactions). Results indicate that the non-stoichiometry of the oxide film is a function of the temperature of preparation and also of the atmosphere of annealing. In particular, smaller fractions of Ru3+are obtained as the temperature of preparation is increased and/or the atmosphere of annealing is made more oxygenated. Kinetics of electrode reactions suggest an essentially metallic nature for RuO2 films. They behave very well with redox systems but exhibit poor electrocatalytic features in that rates of reactions involving adsorption steps are usually lower on RuO2 films than on noble metals. Possible reasons for this are discussed in detail.
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TL;DR: Strong evidence is obtained that in photosynthetic bacteria a component with an EPR signal at g = 1.82 has been identified as the primary electron acceptor of the photochemical system and it is possible that a similar component might be involved in chloroplast photochemical reactions.
Abstract: PHOTOSYSTEM I (PSI) is the photochemical reaction complex involved in the generation of a low potential reductant in oxygen-evolving photosynthetic organisms The primary photochemical reaction in PSI has been identified as the photo-oxidation of a reaction centre chlorophyll complex P700 (ref 1) This photo-oxidation occurs both at room temperature and in the frozen state at temperatures as low as 42 K At cryogenic temperatures this photo-oxidation has generally been found to be irreversible2 Malkin and Bearden3 showed that the electron acceptor for this photo-oxidation reaction is a bound ferredoxin This ferredoxin has two iron–sulphur centres with very low redox potentials (Em10 = −550 and −590 mV)4–6 It has been proposed that these centres are the primary electron acceptor of PSI3,4 More recent evidence suggests it may not be7–11, and we have shown11 that when the bound ferredoxin is chemically reduced, illumination at low temperature results in the photo-oxidation of P700 without any change in the bound ferredoxin, this oxidation is reversible In photosynthetic bacteria a component with an EPR signal at g = 182 has been identified as the primary electron acceptor of the photochemical system12,13 and it is possible that a similar component might be involved in chloroplast photochemical reactions McIntosh et al14 obtained kinetic evidence for the presence in PSI particles of a component with an EPR signal at g = 206 and g = 176 which showed a reversible redox change on illumination of the particles at low temperature parallel to that of P700 The changes observed were small and it was not possible to obtain a spectrum of the component Using a more highly purified PSI preparation we have now obtained strong evidence that this component is the primary electron acceptor of PSI
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TL;DR: A pH- dependent induction period observed during the nitrosation of morpholine in the presence of ascorbate and excess nitrite was accounted for by the kinetics of the reactions.
Abstract: In this study of the nitrosation of morpholine in the presence of ascorbic acid, the amount of ascorbate required to inhibit completely the formation of nitrosomorpholine depended on whether oxygen was present in the system. The nitric oxide (produced during the oxidation of ascorbate by nitrous acid) might have reacted with oxygen to yield additional oxidizing equivalents, or oxygen might have directly oxidized the ascorbate semiquinone intermediate produced in the initial step of oxidation reaction. A pH- dependent induction period observed during the nitrosation of morpholine in the presence of ascorbate and excess nitrite was accounted for by the kinetics of the reactions.
TL;DR: Univalent oxidation-reduction reactions coupled with the oxygen-superoxide system were investigated in the reactions shown in eq 3 and 8, where Q and Q.- stand for p-benzoquinone and p-Benzosemiquinone, respectively.
Abstract: Univalent oxidation-reduction reactions coupled with the oxygen-superoxide system were investigated in the reactions shown in eq 3 and 8, where Q and Q.- stand for p-benzoquinone and p-benzosemiquinone, respectively. From kinetic experiments the following rate constants were obtained at pH 7.0:k3 = 4.5 x 10(4) M-1 sec-1 and k8 = 3 x 10(-2) M-1 sec-1. With known values of k-3 and k-8, and of E0' for the systems Q-Q.- (0.10 V) and Cyt c3+ - Cyt c2+ (0.255 V), the calculated values of E0(O2-O2.-) were found to lie in the range between -0.27 and -0.33 V.
TL;DR: Results support the previous conclusion that Kr represents a proton dissociation constant of a distal amino acid residue and that there is a strong hydrogen bonding between its base and the water oxygen atom as a sixth ligand in the ferric state of peroxidases.
TL;DR: The primary intermediate in the oxidase reaction with oxygen is concluded to be a bridged a 3 2+ - O 2 - Cu 1+ complex and the oxidation-reduction properties of the CO compound are utilized to determine the midpoint potential of the “invisible” copper.
TL;DR: In this article, anodic niobium oxide in a n-type semiconductor due to an oxygen deficit was determined from measurements of space-charge capacitances as a function of electrode potential.
TL;DR: In this article, the capacity of carotenes to accept or donate electrons reversibly was revealed, and the kinetics of the reactions with the participation of these particles were studied.
TL;DR: In this paper, the authors make use of the previously observed fact that oxygen is reduced, in aqueous solutions at surfactant-covered mercury electrodes, to the superoxide stage only, the redox system O2/O2− as well as the spontaneous decay of O2− have been studied.
TL;DR: From the chemical shift obtained, it is concluded that the glutathione peroxidase shuttles between a selenol or Se 3d derivative in its reduced form and aseleninyl or selenonyl compound in its oxidized form.
TL;DR: In this paper, a linear diffusion model of oxygen ions in the crystal, which was theoretically derived, was used to calculate the diffusion constants at 25°C and 60°C, respectively.
Abstract: The compounds , which show high electrical conductivity, are electrochemically reduced in an aqueous alkaline solution to give rise to the oxygen deficient state . The electrochemical redox reactions are reversible in the range . The electrode potentials of in a solution have been measured as a function of δ. From these data and the measurements of potential change in the cathodic processes under constant current density, the oxygen ion diffusion constants have been calculated on the basis of a linear diffusion model of oxygen ions in the crystal, which was theoretically derived. The calculated diffusion constants at 25°C are for and, respectively. These values are very large as compared with ordinary oxides.
TL;DR: It is postulated that, in the absence of NH3, states S2 and S3 are stabilized by manganese-coordinated, bound water.
TL;DR: In this article, a polycrystalline palladium foil initially exposed to relatively large amounts of oxygen at high temperatures, was dosed alternately with oxygen and carbon monoxide and transient carbon dioxide production was monitored mass spectrometrically.
TL;DR: This comprehensive study into the irreversible oxidation and reduction properties of the triplet state of zinc uroporphyrin (ZnUP) found the similarities in the redox and spectral properties between ZnUP and chlorophyll excited states rendered this study relevant.
Abstract: The necessity of unraveling the complex reactions of photosynthesis inspired this comprehensive study into the irreversible oxidation and reduction properties of the triplet state of zinc uroporphyrin (ZnUP). The similarities in the redox and spectral properties between ZnUP and chlorophyll excited states rendered this study relevant. In addition, the eight ionized acetic and propionic acid groups on the periphery of the uroporphyrin molecule permitted the determination of a distance of electron transfer from the triplet state t o various acceptors. The importance of these findings t o porphyrin photochemistry and photosynthesis will be presented in this report. The absorption spectra and decay kinetics of some free base and metalloporphyrin triplet states have been That the ground state of metalloporphyrins undergo successive one-electron aromatic ring oxidations6-'0 and reductions1 '-' is well documented. Similarly, one-electron electrochemical oxidations of tetraphenylporphin,' and successive one-electron electrochemical reductions of various free-base porphyrins have been reported.' 6 i 1 Photochemical reductions of uroporphyrin' 8 -2 and zinc porphin2 have been demonstrated, although the reactive state was not conclusively identified. The one-electron reduction of ground state zinc etioporphyrinZ3 and the one-electron oxidations of the triplet state of zinc t e t r a p h e n y l p ~ r p h y r i n ~ ~ by chemical means have also been reported. PhotoreductionSv2 5 , 2 6 and p h o t o ~ x i d a t i o n ~ > ~ 6 9 2 7 of chlorophyll and chlorophyll-related2 8 30 compounds have also been studied, and reaction from the triplet state was demonstrated in several cases.26-28g30 A quantitative mechanistic study, however, has not been reported and will be presented for triplet state ZnUP in this report.
TL;DR: In this paper, a particular choice of experimental conditions permits study of the electrochemical behavior of hydrogen on the surface of palladium, and two adsorbed states are distinguished by two different features of the electron screening of the proton by the conduction electrons of the metal.
TL;DR: Active transport of amino acids in whole cells and membrane vesicles from the facultative photo-synthetic bacterium Rhodopseduomonas spheroides is coupled to electron flow in the respiratory chain and in the cyclic electron transfer system.
Abstract: Active transport of amino acids in whole cells and membrane vesicles from the facultative photo-synthetic bacterium Rhodopseduomonas spheroides is coupled to electron flow in the respiratory chain and in the cyclic electron transfer system. In vesicles made from cells grown aerobically in the dark transport of amino acids is most effectively energized by the oxidation of NADH and to a lesser extent by ascorbate or succinate in the presence of N,N,N',N'-tetramethyl-1, 4-phenyldiamine dihydrochloride or by ascorbate + phenazine methosulphate via the respiratory chain with oxygen as terminal electron acceptor. In membrane vesicles from cells grown anaerobically in the light the energy for active transport of amino acids is supplied upon illumination by photo-oxidation of bacteriochlorophyll and subsequent electron flow through the cyclic electron transfer system. The initial rate of transport increases with the light intensity upto saturation levels. In both vesicle preparations, inhibitors of electron transfer flow inhibit amino acid uptake. In order to obtain light-driven amino acid transport the isolation of membrane vesicles needs to be performed in a medium with a redox potential between 0 and 100 mV. Illumination of vesicles made from cells grown anaerobically in the light results in the generation of a membrane potential as is indicated by the uptake of the lipophylic cation triphenyl-methylphosphonium.
TL;DR: A method of investigation of the enzyme-mediated charge transfer across a water-lipid interface is reported, consisting in the measurement of the Volta potential difference between an octane and water solution, containing the enzyme system studied.
TL;DR: The chemical reactions involved in the antioxidant behavior of the thiodipropionate esters have been investigated and three distinct mechanisms have been identified as discussed by the authors, namely, a radical trapping process involving the sulphenic acid formed by breakdown of the sulphinyldipropianate ester which is an oxidation product of thiodiopionate.
TL;DR: In this article, the rate constants for tris(2,2'-bipyridine) complexes of iron, ruthenium, osmium, chromium, titanium, vanadium and molybdenum in low and high oxidation states are measured in N,N-dimethylformamide with a dropping mercury electrode and a platinum electrode by the galvanostatic double-pulse method.