Showing papers on "Redox published in 1970"

Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters

Abstract: Chemical Thermodynamics and Kinetics Acid-Base Dissolved Carbon Dioxide Atmosphere-Water Interactions Metal Ions in Aqueous Solution Aspects of Coordination Chemistry Precipitation and Dissolution Oxidation and Reduction Equilibria the Solid-Solution Interface Trace Metals: Cycling, Regulation and Biological Role Kinetics and Redox Processes Photochemical Processes Kinetics at the Solid-Water Interface Adsorption Dissolution of Minerals Nucleation and Crystal Growth Particle-Particle Interaction Colloids Coagulation and Filtration Regulation of the Chemical Composition of Natural Waters (Examples) Thermodynamic Data.

Electron transfer reactions of complex ions in solution

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ENERGY-COUPLING MECHANISMS IN MITOCHONDRIA: KINETIC, SPECTROSCOPIC, AND THERMODYNAMIC PROPERTIES OF AN ENERGY-TRANSDUCING FORM OF CYTOCHROME b

Abstract: The primary event of coupled electron transfer at phosphorylation site II is identified with a modification in one of the two chemically distinct forms of cytochrome b, designated as the energy-transducing cytochrome bT. This modification is expressed through a change in the redox midpoint potential and by an increase in its reaction half time with cytochrome c1. In pigeon heart mitochondria cytochrome bT exhibits an absorption maximum at 564 nm and on this basis, it can be distinguished from Keilin's cytochrome b which exhibits an absorption maximum at 560 nm and serves as an electron carrier on the substrate side of cytochrome bT. Kinetic capability of cytochrome bT is evidenced by its rapid electron transfer and energization time of less than 200 msec, its thermodynamic capability—by a 280 mV potential span suitable for providing one of the two electron transfer reactions required in ATP formation. Two secondary events of coupled electron flow may be identified with a charge separation across the lipid structure of the permeability barrier and a change in water structure; both events result in an increased 1-anilino-8-naphthalene-sulfonic acid (ANS) response to the altered environment.

Electron spin resonance studies. Part XXV. Reactions of the sulphate radical anion with organic compounds

Abstract: E.s.r. spectra are reported for the radicals obtained by the oxidation of a variety of organic compounds by the titanium(III)–persulphate redox system. Evidence is obtained that the sulphate radical anion is formed throughout the pH range employed (1–10·5) and that it can react with organic compounds in at least three ways: by abstracting a hydrogen atom from saturated carbon, by adding to unsaturated or aromatic carbon, and by removing one electron from carboxylate anions and from certain neutral molecules. It displays a marked degree of selectivity in its addition reactions and it behaves differently from the hydroxyl radical in several respects.

The Mechanism of Hydrogen Evolution by Chlamydomonas moewusii.

Abstract: Using manometric techniques, H(2) evolution in both darkness and light has been studied in the green alga, Chlamydomonas moewusii.Hydrogen evolution in the dark is accompanied by the release of only CO(2) in manometrically detectable amounts. It is depressed by dark starvation and inhibited both by monofluoroacetic acid and by uncouplers of phosphorylation. This evidence suggests that the reaction is dependent on oxidative carbon metabolism for reductant and phosphorylation for energy to raise the reductant to a redox potential capable of reducing H(+).Photoevolution of H(2) is also accompanied by the release of only CO(2). It is depressed by dark starvation and stimulated by acetate or a period of photosynthesis. Monofluoroacetic acid causes complete inhibition, while 3-(3,4-dichlorophenyl)-1,1-dimethylurea causes no or only slight inhibition. These results indicate that oxidative carbon metabolism is the source of reductant for the reaction. Photoevolution of H(2) does not show Emerson enhancement, and it has an action spectrum peaking at a longer wave length than that of photosynthesis. These characteristics, together with the slight effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea on the reaction, show that only system I of photosynthetic electron transport is involved in the reaction. Photoevolution of H(2) is stimulated by uncouplers; this indicates that the role of light is not to provide energy by phosphorylation. Rather, the results support an electron flow driven directly by light through system I from reductant produced in oxidative carbon metabolism to a redox potential capable of reducing H(+).

Factors influencing the inhibitory effect of carbon monoxide on cytochrome P-450-catalyzed mixed function oxidation reactions.

Abstract: Liver microsomal reactions under conditions of high rates of electron flux were more CO sensitive, and the Warburg partition coefficient for CO and O/sub 2/ with cytochrome P-450 was increased.

Chapter IV Redox Potential

Abstract: Publisher Summary Redox potential may be determined as voltage (in volts or millivolts), when an inert noble metal electrode is connected to a reference electrode and both are placed in a solution containing a reversible redox system. This value gives information on the following: (1) the formation of redox potential in cultures of micro-organisms. (2) The order of redox substances in a redox chain (for example, arrangement of enzymes in the respiration chain). (3) The free enthalpy of redox substances, making it possible to describe chemical reactions. The potential difference between the aerated nutrient solution and the metabolically active bacterial culture can be used to perform work and obtain energy. The chapter discusses the measurement of redox potentials, including redox-potential determination with indicator dyes and electrometric redox-potential determinations. If the potential of a nutrient solution is measured and this solution then inoculated, a change of the redox potential to a more negative value indicates the start of growth. The chapter discusses Redox potential of different physiological types of bacteria, including aerobic bacteria, facultative anaerobes, and anaerobic bacteria. The buffering action of a redox substance is dependent on its concentration in the solution. The capacity term for redox potential is the “poising effect” that characterizes the capacity of a system to counteract a variation in potential. An example is the presence of methylene blue (MB) in a culture solution.

Methods for electrochemical analysis

Abstract: A MEASURING CELL FOR DETERMING THE CONCENTRATION OF A SELECTED COMPONENT (E.G. SO2,CO,NO2,O3,H2O2 OR ETHANOL) IN A MIXTURE. THE CELL INCLUDES AN ELECTRODE COVERED WITH A THIN LAYER OF ELECTROLYTE CONTAINING A REDOX SYSTEM (E.G. CU++FOR SO2 MEASUREMENT) WHICH REACTS WITH THE SELECTED COMPONENT TO FORM AN ELECTROACTIVE SPECIES. AT THE ELECTROACTIVE SPECIES THUS FORMED GAINS OR LOSES ELECTRONS, GIVING A CURRENT WHICH IS MEASURE OF THE CONCENTRATION OF THE SELECTED COMPONENT.

Process for oxidation of carbon monoxide

Abstract: AN IMPROVED PROCESS FOR THE SELECTIVE OXIDATION OF CARBON MONOXIDE CONTAINED IN FEED GASES FROM A STEAM REFORMER-CONVERTER WHEREIN THE FEED GASES IN ADMIXTURE WITH OXYGEN ARE CONTACTED WITH A PLATINUM GROUP METAL CATALYST AND THE ACTIVITY OF THE CATALYST FOR THE SELECTIVE OXIDATION REACTION IS MAINTAINED BY PERIODICALLY TREATING DEACTIVATED CATALYST WITH THE SELECTED OXIDATION REACTION EFFUENT GASES CONTAINING LESS THAN 50 P.P.M. CARBON MONOXIDE AT A TEMPERATURE OF 75* TO 200*C.

Studies of Auxin Protectors VIII. Evidence that Auxin Protectors Act as Cellular Poisers

Abstract: Auxin protectors completely inhibit the peroxidase-catalyzed oxidation of indoleacetic acid (IAA). Presumably only when the protector substance itself has been oxidized, does IAA oxidation begin. Reduced nicotinamide-adenine dinucleotide (NADH) mimics the native auxin protectors: In the presence of NADH, the peroxidase-catalyzed oxidation of IAA does not begin until almost all the NADH has been oxidized. Auxin protectors slow the oxidation of NADH in the presence of the peroxidase complex (enzyme plus manganese). However, in the absence of the peroxidase complex, protectors actually accelerate the spontaneous oxidation of NADH. Protectors can also accelerate the oxidation of the dye 2,6-dichlorophenol-indophenol, especially in the presence of manganese. Protector oxidized by boiling with traces of hydrogen peroxide will act as an electron acceptor in the peroxidase-catalyzed oxidation of NADH. The reversible redox role of auxin protectors implies that they can act as cellular poisers.

The respiratory chain of plant mitochondria. IV. Oxidation rates of the respiratory carriers of mung bean mitochondria in the presence of cyanide.

Abstract: The half-time for oxidation of cytochrome b557 in mitochondria from etiolated mung bean (Phaseolus aureus) hypocotyls is 5.8 milliseconds at 24 Celsius in the absence or presence of 0.3 mm KCN, when the oxidation is carried out by injecting a small amount of oxygenated medium into a suspension of mitochondria made anaerobic in the presence of succinate plus malonate. Since oxygen is consumed by the alternate, cyanide-insensitive respiratory pathway of these mitochondria, cycles of oxidation and reduction can be obtained with the oxygen pulses when cyanide is present. Reduced cytochromes (a + a3) also become oxidized at nearly the uninhibited rate under these conditions, a3 completely and a partially. The half-time for oxidation of c547 is also unaffected by 0.3 mm KCN, but c549 has a half-time equal to that of c547 in the presence of KCN, compared to the shorter one observed in the absence of inhibitor. The maximum extent of oxidation of the cytochromes c is about 70% in the presence of 0.3 mm KCN; this oxidation is rapidly followed by an extensive reduction which is synchronous with the reduction of cytochrome a observed under the same conditions. In the presence of cyanide, it appears likely that the cytochromes c and b557 are oxidized by cytochrome oxidase in oxygen pulse experiments, rather than by the alternate oxidase. The oxidation of cytochrome b553 is partially inhibited by KCN, but complete oxidation is attained in the aerobic steady state with excess oxygen. If the oxygen pulse experiment is carried out in the presence of sufficient malonate so that entry of reducing equivalents into the respiratory chain occurs at a rate negligible compared to inter-carrier electron transport, the half-time for flavoprotein oxidation is unaffected by 0.3 mm KCN while that for ubiquinone oxidation is but 2-fold larger. The observed net oxidation rate of these two carriers in mung bean mitochondria is more sensitive to the entry rate of reducing equivalents, as set by succinate concentration and malonate to succinate ratio, then it is in skunk cabbage (Symplocarpus foetidus) mitochondria. These observations are interpreted in terms of a respiratory carrier Y, placed between flavoprotein plus ubiquinone and the cytochromes, which is the fork in the split respiratory pathway to the two terminal oxidases and which has lower electron transport capacity in mung bean mitochondria than in skunk cabbage mitochondria.

Homogeneous and heterogeneous electron exchange in the reduction of aromatic hydrocarbons

Abstract: Homogeneous electron exchange rates, determined by a modified e.s.r. method in both the slow and fast exchange limits, are compared with published heterogeneous rates at mercury for aromatic hydrocarbon reduction in dimethylformamide; the ratio is approximately constant. This constant can be derived from theories of Marcus and Hush on a model in which image forces are negligible in the electrode process and homogeneous exchange occurs only on contact. Potential-step methods are used to study the source of electrons transferred to radicals formed by protonation of the hydrocarbon radical anions (e.c.e. mechanism) : electron transfer occurs from other radical anions for anthracene and from the electrode for naphthalene. This result is interpreted in terms of relative rates of cross-exchange reactions as predicted by Marcus theory from the “isotopic” exchange rates and redox potentials of the systems. General considerations imply that cross-exchange reactions will predominate in many aromatic systems. Proton addition from phenol to the radical anions appears to involve direct contact of acid and base rather than the free (solvated) proton.

The oxidation of reduced nicotinamide nucleotides by hydrogen peroxide in the presence of lactoperoxidase and thiocyanate, iodide or bromide

Abstract: Lactoperoxidase (EC 1.11.1.7) catalysed the oxidation of NADH by hydrogen peroxide in the presence of either thiocyanate, iodide or bromide. In the presence of thiocyanate, net oxidation of thiocyanate occurred simultaneously with the oxidation of NADH, but in the presence of iodide or bromide, only the oxidation of NADH occurred to a significant extent. In the presence of thiocyanate or bromide, NADH was oxidized to NAD+ but in the presence of iodide, an oxidation product with spectral and chemical properties distinct from NAD+ was formed. Thiocyanate, iodide and bromide appeared to function in the oxidation of NADH by themselves being oxidized to products which in turn oxidized NADH, rather than by activating the enzyme. Iodine, which oxidized NADH non-enzymically, appeared to be an intermediate in the oxidation of NADH in the presence of iodide. NADPH was oxidized similarly under the same conditions. An assessment was made of the rates of these oxidation reactions, together with the rates of other lactoperoxidase-catalysed reactions, at physiological concentrations of thiocyanate, iodide and bromide. The results indicated that in milk and saliva the oxidation of thiocyanate to a bacterial inhibitor was likely to predominate over the oxidation of NADH.