Showing papers on "Redox published in 1973"
TL;DR: It is concluded, that also in the steady state the reduction and oxidation of the active Q-pool follow pseudo-first-order reactions, the rates of which are equal to the respiratory rate.
Abstract: The role of ubiquinone (Q) in the respiratory chain is quantitatively analyzed by correlating both the steady-state redox level of Q and the kinetics of oxidation and reduction with the flux of the overall electron transport in uncoupled submitochondrial particles. This is achieved by experimentally defining donor and acceptor activities for Q.
1
The degree of reduction of Q in the steady state is proportional to the respiratory activity with NADH and succinate, if the respiratory activity is varied by titrating the donor side for Q with rotenone and malonate, respectively. The proportionality constant (acceptor activity, Vox) is independent of the substrate used.
2
The degree of oxidation of Q in the steady state is proportional to the respiratory activity as varied by titration of the acceptor side for Q with antimycin. The proportionality constant (donor activity, Vred) is independent of the acceptor activity and depends on the dehydrogenase activity for NADH and succinate.
3
From these experimental relations, the redox state of Q in the steady state and the respiratory activity can be described as functions of the donor and the acceptor activity only. The equations are valid with both NADH and succinate as the substrates.
4
The kinetics of oxidation of Q on the addition of oxygen as measured by the quench-flow method are in agreement with that measured by direct absorption recording in a mixing chamber. The reaction is first order with a rate constant equal to the acceptor activity divided by the amount of redox-active Q (Vox/Qa). The final steady-state level (in the present case 15% reduction) is a result also of the reduction reaction with the first-order rate constant, VredQa.
5
The acceptor activity can also be measured as maximum respiratory activity with duro-hydroquinone. This activity is independent of the presence of Q but sensitive to antimycin. Thus, the acceptor activity for ubiquinone can be measured by three independent methods.
6
It is concluded, that also in the steady state the reduction and oxidation of the active Q-pool follow pseudo-first-order reactions, the rates of which are equal to the respiratory rate. The total amount of redox-active Q is kinetically and functionally homogeneous and is not divided into substrate-specific compartments.
312 citations
TL;DR: The role of ubiquinone (Q) in the respiratory chain is studied by analyzing the inhibition by antimycin of the electron transport in uncoupled submitochondrial particles and the observed nonlinearity is recognized to result from a hyperbolic relationship.
Abstract: The role of ubiquinone (Q) in the respiratory chain is studied by analyzing the inhibition by antimycin of the electron transport in uncoupled submitochondrial particles. As a result, the antimycin inhibition curve of substrate oxidation is quantitatively explained.
1
The participation of Q in the electron transport is required for the occurrence of nonlinear antimycin inhibition curves as demonstrated with external hydroquinones of different redox potentials as hydrogen donors. The respiration is non-linearly inhibited with a hydroquinone of sufficiently low redox potential to reduce the mitochondrial Q (menadiol) whereas a linear inhibition curve is found with hydroquinones of higher redox potentials (durohydroquinone, dimethoxy-dimethylbenzohydroquinone). If Q is extracted, the inhibition curve also with menadiol becomes linear. This demonstrates the relation of the nonlinearity of the inhibition curve to the function of Q as a distributor of hydrogen between parallel cytochrome chains.
2
The electron transport through the cytochrome segment is inhibited linearly with increasing amounts of antimycin as demonstrated by the linear titration of three different functions: (a) the oxidation rate of Qred on addition of oxygen to anaerobic submitochondrial particles, (b) the repiratory activity with added hydroquinones, (c) the acceptor activity as defined by the ratio of the respiration rate to the redox state of Q (Kroger, Klingenberg and Schweidler, 1973).
3
The ratio of donor to acceptor activity to Q (Vred/Vox) is the main parameter in controlling the shape of the antimycin titration curve. This curve becomes more nonlinear with decreasing this ratio. Also the redox state of Q is nonlinearly dependent on the amount of antimycin and controlled by the donor/acceptor activity ratio.
4
A theoretical hyperbolic relation of the rate of substrate oxidation to the amount of antimycin is derived, involving the ratio donor to acceptor activity and the linear inhibition by antimycin of the electron transport through the cytochrome segment. With independently measured donor/acceptor activity ratios, antimycin titration curves are calculated which give a good fit to the experimental titrations over the range from highly nonlinear to almost linear curves. The observed nonlinearity is thus recognized to result from a hyperbolic relationship. Also the calculated titration curves for the redox state of Q are in agreement with the experiments.
5
The deviation of the experiment from the calculated curves near equimolarity between the amount of antimycin and inhibition sites can be accounted for by the dissociation of antimycin from the site of inhibition.
220 citations
TL;DR: In this paper, the potentiodynamic sweep technique was applied to detect surface oxides on carbon black (Vulcan XC-72) which was subjected to heat treatment, electrochemical and chemical oxidation and gas phase oxidation.
218 citations
TL;DR: The standard redox potential at I= 0.01, 25°C and pH 7.0 has been determined for the following species of cytochrome c: horse heart, baker's yeast isoenzyme-1, Candida species yeast, tuna heart and turkey heart, and the thermodynamic parameters of the redox reaction were evaluated.
Abstract: The standard redox potential at I= 0.01, 25°C and pH 7.0 has been determined for the following species of cytochrome c: horse heart, baker's yeast isoenzyme-1, Candida species yeast, tuna heart and turkey heart. The thermodynamic parameters of the redox reaction were evaluated and found to be identical, within experimental error, in the five species investigated. The effect of pH on the standard redox potential of horse heart cytochrome c was studied in the pH range 7.0–11.2. A single heme-linked ionization of the oxidized protein was observed in this pH range, with a dissociation constant of 3 × 10−9 at I= 0 and 25°C. The effects of the electrostatic media on the standard redox potential of horse heart cytochrome c depend on the nature of the anions employed. For non-binding medium at 25°C, the observed potential dependence on the ionic strength is given by the equation: E0obs= 0.274–0.336 √I/(1 + 6√I). In binding medium, specific binding of ions to the protein takes place.
195 citations
TL;DR: In the two clostridia all catabolic oxidations-reductions are specific for NAD(H) and that the usual NADPH-producing processes such as the glucose 6-phosphate dehydrogenase or malate enzyme reactions are absent.
188 citations
TL;DR: The decay half time, which after five flashes is in the region of 500 ms without addition, can be reduced to c is used to demonstrate that the course of carotenoid band shift decay has no obligate relationship to the redox state or electron transfer events of the electron carriers.
170 citations
TL;DR: It is shown that a simple molecular mechanism embodying coupled proton-electron transfer can explain many key experimental observations and the reasons for the use of Mo are discussed and other metals that may replace Mo are considered.
Abstract: The reactions catalyzed by Mo enzymes each find the product differing from the substrate by two electrons and two protons (or some multiple thereof). The coordination chemistry of Mo suggests that there is a distinct relationship between acid-base and redox properties of Mo complexes, and that a coupled electron-proton transfer (to or from substrate) may be mediated by Mo in enzymes. Each of the Mo enzymes (nitrogenase, nitrate reductase, xanthine oxidase, aldehyde oxidase, and sulfite oxidase) is discussed; it is shown that a simple molecular mechanism embodying coupled proton-electron transfer can explain many key experimental observations. In view of this mechanism, the reasons for the use of Mo (from an evolutionary and chemical point of view) are discussed and other metals that may replace Mo are considered.
106 citations
TL;DR: The combination of redox potentiometry with low temperature electron spin resonance (ESR) spectroscopy has led to further characterization of electron transfer components of Chromatium D, including the readily buffer-soluble cytochromes c 553 and c ′ and the high-potential iron-sulfur protein in the isolated state and associated with the chromatophore membrane.
95 citations
TL;DR: In this article, the authors investigated the anodic oxygen evolution at platinum electrodes in 1N H 2 SO 4 in dependence on the oxide layer thickness d and the electrode potential e. The thickness d (1·5−10 A) was obtained from cathodic charging curves.
86 citations
TL;DR: It was found that hydroquinone can quantitatively reduce •O 2− to H2O2, k(•O2− + QH2 → QH• + HO2−) = 1.6 ± 0.1 × 107 M−1 sec−1 at pH 7.0 and 22°C.
77 citations
TL;DR: In this paper, the effect of small amounts of manganese species on the capacity of carbon-air electrode in alkaline electrolyte was investigated and a new redox potential for the system Mn(III)/Mn(II, both species being strongly and irreversibly adsorbed at the carbon surface was found.
Abstract: To increase the overload capacity of the carbon-air electrode in alkaline electrolyte, without seriously changing the electrode potential during short-time overload periods, small amounts of MnO2 were added to carbon and the effects investigated. The potentiodynamic investigations revealed the existence of two reducible manganese species with reduction potentials of about −280 mV and −400 mV. The second potential corresponds to the known reduction process Mn(III) → Mn(II) whilst the first one corresponds to a reversible process (the product is easily reoxidized by air or anodically), not reported in literature as yet. It was explained in terms of a new redox potential for the system Mn(III)/Mn(II), both species being strongly and irreversibly adsorbed at the carbon surface. The galvanostatic discharge curves in the absence of air indicate that a sufficient overload capacity of about 40 C cm−2 is available if 22% (wt) MnO2 is added. Steady-state polarization curves in the presence of air indicate the catalytic effect of small amounts of MnO2 for the oxygen reduction reaction.
TL;DR: In this article, a linear dependence of log i o on Φ, the work function of the metal, first indicated by Bockris and his group for noble metals, is confirmed in this work also for low-Φ metals which usually form anodic oxide films.
TL;DR: In this paper, pyridine and β-picoline-containing oxo-centred complex ions [M3IIIO(CO2Me)6L3]+, M = Cr, Mn, Fe, Co, Rh, and Ir, L = py and βpic, were synthesized and their redox behaviour studied electrochemically.
Abstract: New pyridine- and β-picoline-containing oxo-centred complex ions [M3IIIO(CO2Me)6L3]+, M = Cr, Mn, Fe, Co, Rh, and Ir, L = py and β-pic, were synthesised and their redox behaviour studied electrochemically. There is evidence for reduced species in which the oxo-centred triangular structure is maintained in the case of the Mn, Fe, and Co complexes but these could not be isolated. For iridium, complexes [Ir3III,III,IVO(CO2Me)6L3]+2 in which the metal atom is in the mean oxidation state 3⅓ have also been characterised and shown to undergo reduction to the IrIII species. Attempts to prepare oxo-centred complexes of Cu, Ag, Ni, Pd, Pt, and Mo were unsuccessful. The cobalt complex ion [Co3O(CO2Me)6L3]+ appears to be different from the other oxo-centred ions and a structure with both bridging and chelate acetato-groups is proposed.
TL;DR: In this article, a heterogeneous catalyst system was developed for the vapor-phase oxidation of ethylene to acetaldehyde, which consists of palladium-doped vanadium pentoxide and, usually, a third component such as Ti, Ru, Pt, or Ir.
TL;DR: In this paper, it was shown that direct electron transfer from filled redox levels to empty levels in the valence band is highly improbable, so that the observed hole capture by Fe(CN)64− from the UV-illuminated ZnO anode presumably occurs by a more complicated mechanism, e.g. involving surface states.
TL;DR: The kinetics of these reactions indicate stability of the reduced protein toward oxygen and facilitation of reoxidation by anion binding and the results support the same type of mechanism.
TL;DR: The redox potentials of aerated seawaters do not appear to be governed by the oxygen/water couple which would yield for a pH of 8.0 at 25°C an equilibrium Eh of 0.75 V (pE=12.5).
Abstract: The redox potentials of aerated seawaters do not appear to be governed by the oxygen/water couple which would yield for a pH of 8.0 at 25° C an equilibrium Eh of 0.75 V (pE=12.5). Garrels and Christ1 prefer a value closer to 0.22 V (pE=3.7) from measurements with platinum electrodes on systems exposed to air. Breck2 suggests that the Eh is controlled by an oxygen/peroxide couple as a result of measurements he made with a novel cell in which small amounts of various redox pairs are equilibrated with seawater and the resultant potential measured. His results indicate an Eh of about 0.5 V, as compared with values of 0.4 V he obtained with platinum electrodes.
TL;DR: For all the complexes examined, the relative ordering of the redox potentials with the dithiocarbamate substituents is remarkably consistent for both oxidation and reduction processes as mentioned in this paper.
Abstract: The one-electron oxidation and reduction processes for some 80 dithiocarbamates of Cr, Mn, Fe, Co, Ni, and Cu reveal a marked dependence of redox potential on the metal 3dn electron configuration. For all the complexes examined, the relative ordering of the redox potentials with the dithiocarbamate substituents is remarkably consistent for both oxidation and reduction processes.
TL;DR: The redox normal potential (Eo) of the peat water system has been determined through an indirect, experimental method as discussed by the authors, and it has been established that peatwater system can be regarded as a regarded as reversible redox one.
Abstract: The redox normal potential (Eo) of the peat-water system has been determined through an indirect, experimental method. It has been established that the peat-water system can be regarded as a regarded as a reversible redox one. Consequently, it can exert a reducing or oxidizing effect on metal ions. The reducing property plays a role in the geochemical enrichment of metals that migrate in anionic form under natural conditions and, as a result of reduction, turn into cations. Therefore, metal enrichment in humic acids can be interpreted as a cation-exchange process.
TL;DR: For energy conservation, coupled to electon flow in Photosystem I, it seems necessary that the lipophilic redox compound in the reduced form can carry hydrogens through the chloroplast membrane.
TL;DR: The effects of o-phenanthroline may have more than one site of action, as suggested by assuming that it chelates the reduced form of the primary electron acceptor of a metal chelated by o- and batho-phenAnthroline.
TL;DR: Simultaneous measurements of the redox state of cytochrome a+a3 with the dual wavelength spectrophotometer, or of the fluorescence of flavin and NADH with an additional fluorescence device, showed that the oxidation of mitochondria was achieved at oxygen pressures below the range which can be measured with the polarographic method.
Abstract: Polarographic measurements were performed in respiring suspensions of mitochondria with membrane-covered platinum electrodes, using an optical cuvette which was provided with a Teflon window located parallel to the light path. When gases containing different amounts of oxygen were passing before the Teflon window, then in stirred probes the oxygen which had been consumed by respiration, could be replaced and steady-state conditions could be established with respect to oxygen pressure. Simultaneous measurements of the redox state of cytochrome a+a3 with the dual wavelength spectrophotometer, or of the fluorescence of flavin and NADH with an additional fluorescence device, showed that the oxidation of mitochondria was achieved at oxygen pressures below the range (0.05 Torr oxygen pressure) which can be measured with the polarographic method.
TL;DR: Evidence is presented indicating that catechols and ferricytochrome c can react directly with the reduced flavin-oxygen compound by a pathway which is not susceptible to inhibition by superoxide dismutase.
TL;DR: A study of the effects of inhibitors, uncoupling agents and ion-transporting antibiotics on the chromatophores from photosynthetic bacteria has led to the suggestion that hydrogen-ions bind at two distinct sites in the electron transport chain.
Abstract: The light-driven hydrogen-ion pump of chromatophores from photosynthetic bacteria is related to the processes of electron transport and the phosphorylation of ADP.1, 2, 3 Using pH indicator techniques4, 5, 6 a rapid component of H+-binding, whose kinetic parameters lie within the time range of the chromatophore electron transport reactions7 has been detected. A study of the effects of inhibitors, uncoupling agents and ion-transporting antibiotics on this phenomenon has led to the suggestion that hydrogen-ions bind at two distinct sites in the electron transport chain.6 Two models have been proposed to explain rapid H+-binding.
TL;DR: In this article, a nuclear technique has been used to study the oxidation of Fe-Cr alloys having Cr contents of 16, 19, 28, 38, 50 and 100 wt.
Abstract: A nuclear technique has been used to study the oxidation of Fe-Cr alloys having Cr contents of 16, 19, 28, 38, 50 and 100 wt.%. The yield of the lgO(p, α)l5N reaction was used to determine the 180 distribution in the oxide scale. Specimens were oxidized at 850°C and 950°C first in natural oxygen and then in 18O and vice versa. Any diffusion of oxygen would have shown as a mixing of the oxygen isotopes in the scale. The evidence indicates that bulk oxygen diffusion plays a negligible role in the oxidation reaction. Evidence for penetration of oxygen through the existing scale is found for the alloys of high Cr content (≥ 38%) oxidized at 950°C and it seems that this is due to cracking of the scale giving short-circuit gas diffusion paths.
TL;DR: In this paper, the adsorptive properties of platinum electrodes were studied using linear sweep voltammetry, and the activity for the anodic oxidation of methanol was determined using a multi-pulse potential program.
Abstract: Platinum electrodes were pretreated in various ways with the aim of producing surfaces of different structure. The adsorptive properties were studied using linear sweep voltammetry, and the activity for the anodic oxidation of methanol was determined using a multi-pulse potential program. Although chemical etching and different kinds of heat treatment altered the hydrogen adsorptive properties of platinum, the specific activity for methanol oxidation was not significantly affected. A relationship between the shapes of anodic voltammograms in the hydrogen region and at the start of the oxide region was noted and used in deducing the nature of the adsorbed oxygen-containing species and its involvement in the methanol oxidation reaction. Electro- chemical activation of cold-worked electrodes was attributed to the removal, by anodic dissolution, of a structurally disturbed layer of surface platinum atoms of lower activity than a crystalline surface. The activity of platinum for methanol oxidation was concluded to be a property of a well-ordered crystalline surface, independent of orientation.
TL;DR: In the presence of air, the carbonyl group becomes important at temperatures above 80 °C and that via the decomposition of the carbonate groups above 200 °C.