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Showing papers on "Redox published in 1972"


Journal ArticleDOI
TL;DR: The increased reducibility of cy tochrome b induced by antimycin plus oxidant is considered to be the result of two effects: inhibition of oxidation of ferrocytochrome b by ferricytochrome c1 (the effect of antimyzin), and oxidation of the semiquinone form of a two-equivalent redox couple such as ubiquinone/ubiquinol by the added oxidant, leading to a decreased redox potential of the QH

266 citations



Journal ArticleDOI
TL;DR: It is proposed that the redox potentials of many high-potential cytochromes may be accounted for by a local heme environment of low-dielectric constant, characteristic of nonpolar amino-acid side chains, and that this factor may play a dominant role in the determination of the oxidation-reduction properties of these proteins.
Abstract: A method has been described for measurement of the oxidation-reduction potentials of redox couples in nonaqueous solutions. This method has been applied to a study of the effect of a nonpolar environment on the redox potential of a heme complex. A positive potential difference of some 300 mV is observed for the measured redox potentials by comparison with reported values for the corresponding heme complex in aqueous solution. The proposal is made that the redox potentials of many high-potential cytochromes may be accounted for by a local heme environment of low-dielectric constant, characteristic of nonpolar amino-acid side chains, and that this factor may play a dominant role in the determination of the oxidation-reduction properties of these proteins.

174 citations


Journal ArticleDOI
TL;DR: In this article, the open-circuit potentials of quinone/hydroquinone systems measured in 2 N H2SO4 are very close to the values of the redox potentials measured in alcoholic solutions.

147 citations


Book ChapterDOI
TL;DR: The chloroplasts are now accepted as the physiological Hill reaction is the photoreduction of nicotinamide adenine dinucleotide phosphate (NADP).
Abstract: Publisher Summary This chapter discusses the measurement of hill reactions and photoreduction. R. Hill discovered that a leaf homogenate would evolve oxygen when illuminated in the presence of a ferric salt. After the successful preparation of intact chloroplasts, it could be shown that the oxygen evolution system resides in the green particulate fraction obtained from intact chloroplasts by osmotic shock and that the CO 2 -fixation system can be separated from the light-dependent reactions of photosynthesis. The particulate fraction—the thylakoid system of whole chloroplasts is able to catalyze two types of photosynthetic reactions: photophosphorylation and photosynthetic reduction of an electron acceptor concomitant with oxygen evolution. A Hill reaction is defined as the photoreduction of an electron acceptor at the expense of water, which is oxidized to oxygen. The final Hill acceptor in photosynthesis in vivo is CO 2 . The chloroplasts are now accepted as the physiological Hill reaction is the photoreduction of nicotinamide adenine dinucleotide phosphate (NADP). Several redox reactions and redox carriers besides the actual light-accepting pigments are localized in the thylakoid system of the chloroplasts, and participate in photosynthetic NADP reduction at the expense of water photo-oxidation.

83 citations



Journal ArticleDOI
TL;DR: The green complex formed on treating commercial ruthenium trichloride hydrate with acetic acid and sodium acetate in ethanol is shown to be of the basic acetate oxo-centred triangular type with the formula [Ru3O(CO2Me)6-(H2O)3] as mentioned in this paper.
Abstract: The green complex formed on treating commercial ruthenium trichloride hydrate with acetic acid and sodium acetate in ethanol is shown to be of the basic acetate oxo-centred triangular type with the formula [Ru3O(CO2Me)6-(H2O)3](CO2Me). The complex may be cationic, neutral, or anionic depending on the pH of the solution, owing to ionisation of co-ordinated water. The water molecules may be replaced by pyridine to give [Ru3O(CO2Me)6py3]+. Both the aquo and pyridine complexes undergo successive one and two electron reductions to give complexes in which the metal atoms are in formal oxidation states + 2 ⅔ or (III, III, II) and +2 or (II, II, II) respectively. The reduction to the latter state involves loss of the central oxygen atom from the triangle of metal atoms; this atom may be reinserted using molecular oxygen, or more specifically by use of a reagent such as pyridine-N-oxide. In the presence of triphenylphosphine, [Ru3O(CO2Me)(H2O)3]+ gives the reduced species Ru3O(CO2Me)6(PPh3)3. The potentials and reversibility of the redox reactions have been studied electrochemically. Analogous complexes of other carboxylic acids are described. N.m.r., i.r., and electronic absorption spectra of the species are reported.

69 citations


Journal ArticleDOI
TL;DR: In this article, the electrochemical reactivity of different nitrogen oxides or their absorption products in sulfuric acid was investigated by potential scan measurements at 23°C with platinum electrodes.
Abstract: The electrochemical reactivity of different nitrogen oxides or their absorption products in sulfuric acid was investigated by potential scan measurements. Experiments were carried out at 23°C with platinum electrodes. Among the substances studied only and exhibited well‐defined oxidation and reduction currents. The electrochemical reactions of in were studied in detail by using a rotating disk electrode. Mass transport limited currents were observed for both oxidation and reduction. From the variation of the limiting current with rotation rate the diffusion coefficient of was determined to be .

66 citations


Journal ArticleDOI
TL;DR: In this paper, a mechanism involving the oxidation and reduction of the solid is presented for carbon monoxide oxidation on cerium dioxide, and expressions for the reaction rate and the electrical conductivity of the catalyst are derived from this mechanism.

66 citations


Journal ArticleDOI
TL;DR: The redox potential was found to be better correlated with the disinfecting property of the water than was the amount of available chlorine.
Abstract: The kill of Escherichia coli within 3 min. was studied in chlorine-demand-free water using sodium hypochlorite, monochloramine, dichloramine, halazone, chloramine T, cyanuric acid + sodium hypochlorite and cyanuric acid + monochloramine. The redox potential and the available chlorine were measured. The redox potential was found to be better correlated with the disinfecting property of the water than was the amount of available chlorine. For individual pure chlorine compounds, the measuring of available chlorine showed in general a somewhat better correlation with reduction of the bacteria than the redox potential showed.

53 citations



Journal ArticleDOI
TL;DR: Spinach chloroplasts suspended in a mixture of redox buffers were titrated under anaerobic conditions by adding small amounts of oxidant (potassium ferricyanide) or reductant (reduced methyl viologen) to determine the extent of the low temperature light-induced reduction of C-550 and oxidation of cytochrome b 559.

Journal ArticleDOI
TL;DR: The electron donor sites on the surface of hydrogen Y-zeolite may cover a wide spectrum of energies as discussed by the authors, and two different surface sites are responsible for the reducing properties of HY.


Journal ArticleDOI
TL;DR: There appeared to be a limit to the photocurrent that could be drawn from a membrane at a particular intensity of irradiation; i.e., it did not increase indefinitely with increase of the redox potential gradient.
Abstract: Artificial bileaflet membranes were formed from extracts of chloroplasts. Gradients of a redox potential were created across the membranes by adding various concentrations of ceric-cerous ions, ferric-ferrous ions, and ascorbic acid to the aqueous solutions on either side of the membrane. When a membrane interposed between solutions of different redox potential was irradiated with light, a potential difference of up to 50 mV was recorded. Analysis of the photoresponse allowed its separation into two components: a photoelectromotive driving force dependent upon the redox potential gradient, and a photoconductive pathway dependent upon the amount of light absorbed by the membranes. There appeared to be a limit to the photocurrent that could be drawn from a membrane at a particular intensity of irradiation; i.e., it did not increase indefinitely with increase of the redox potential gradient. Conductance of the photoconductive pathway was independent of temperature. Phycocyanin added to the aqueous solution participated in the photoresponse in a unidirectional manner that suggested facilitation of electron transport from membrane to acceptors in the aqueous solution.

Journal ArticleDOI
TL;DR: The role of ferredoxin and the interrelationships between photosynthesis, reductant pool and hydrogen metabolism are discussed in the light of recent results obtained by ourselves and other workers.
Abstract: The requirements for activity of blue-green algal nitrogenase have been studied. The optimal concentration ranges for ATP and Na2S2O4 are 2-3 mM and 4-10 mM respectively. A magnesium requirement has been confirmed but the enzyme is not specific for Mg2+, Co2+ and Mn2+ will also support activity but Ca2+, Cu2+ and Zn2+ will not. The partially purified enzyme is soluble and specific activities of 50–100 nmoles C2H4/mg protein/min have been obtained. The biochemical characteristics of the enzyme, as determined in studies using enzyme inhibitors, are similar to those of bacterial and legume nitrogenases in that the enzyme is a metallo-protein containing iron and reduced thiol groups and the redox capacity of the enzyme involves a possible valency change in the iron. The transfer of electrons from H2 via a bacterial hydrogenase has been shown to be mediated, at least in part, by ferredoxin. The role of ferredoxin and the interrelationships between photosynthesis, reductant pool and hydrogen metabolism are discussed in the light of recent results obtained by ourselves and other workers.

Journal ArticleDOI
TL;DR: Light-induced cytochrome oxidations in Chromatium subchromatophore particles were studied in detail and were found to be dependent not only on redox potential, but also on the efficiency of coupling of the redox buffer electrons to the Cytochrome system.

Journal ArticleDOI
TL;DR: In this paper, the influence of equatorial and axial ligands on the half-wave potentials of reversible electron transfers corresponding to formal redox couples CoIII→ CoII, CoII→ CoI, and to one-electron oxidation, in some series of organometallic cobalt chelates was investigated.
Abstract: Polarographic techniques are employed to investigate the electrode processes and to point out the influence of equatorial and axial ligands on the half-wave potentials of reversible electron transfers corresponding to formal redox couples CoIII→ CoII, CoII→ CoI, and to one-electron oxidation, in some series of organometallic cobalt chelates. Free-energy relationships are found between the E½ and the pKa values of the hydrocarbon acid corresponding to the organic group in the axial position, showing that the effect is due to charge donation from the organic group, decreasing the electron affinity of the particle. The change of equatorial ligand has a parallel effect of E½ of both reduction and oxidation waves.

Journal ArticleDOI
TL;DR: The reaction of N-ethylmaleimide and NEMA with OH radicals and H atoms results in NEMA, which is produced from the hydrolysis of NEM at pH > 7.
Abstract: The reaction of $e_{{\rm aq}}^{-}$ , OH radicals and H atoms with N-ethylmaleimide (NEM) and N-ethylmaleamic acid (NEMA, which is produced from the hydrolysis of NEM at pH > 7) were investigated in aqueous solutions. The reaction rate constants, the transient optical absorption spectra and the decay kinetics of the resulting intermediates were obtained. The free radical sensitization reactions of NEM with model compounds were followed by pulse radiolysis. A number of organic free radicals were found to react with NEM by an electron transfer process (oxidation of free radicals) to produce $\cdot {\rm NEM}^{-}$ , and/or by addition to NEM. NEMA, being a poorer oxidizing agent, does not appear to undergo most of these reactions. Electron adducts (e.g., radical anions of pyrimidine bases) were shown to transfer an electron to NEM. Solutes with redox potentials higher than that of NEM, such as menadione and oxygen, were found to be good electron acceptors from ...

Journal ArticleDOI
TL;DR: In this article, it was shown that a transient species, believed to be a ferric ascorbate complex, and exhibiting a broad absorption band with λmax.= 560 nm is formed by a two-step mechanism.
Abstract: The oxidation of ascorbic acid by Fe3+ ion has been studied using the stopped-flow technique in an attempt to detect and study the formation of an intermediate. It has been shown that a transient species, believed to be a ferric ascorbate complex, and exhibiting a broad absorption band with λmax.= 560 nm is formed by a two-step mechanism. Values of 11 ± 6 l mol–1 cm–1 and 0·55 ± 0·4 for the extinction coefficient and formation constant respectively at 25 °C have been obtained for the overall complex formation. At 0 °C, the first step in the reaction is governed by the law, Rate =k[Fe3+][H2A], where k has the value of 30 ± 10 l mol–1 s–1. The probable mechanism of both the complex formation and overall redox reaction are discussed.

Journal ArticleDOI
TL;DR: In this article, the structure and some reactions of the cobalt(II), nickel(II, and copper(II) compounds of several tricyclic quadridentate di-anionic Schiff's base ligands derived from o-aminobenzaldehyde and various diamines were investigated.
Abstract: An investigation is reported of the structure and some reactions of the cobalt(II), nickel(II), and copper(II) compounds of several tricyclic quadridentate di-anionic Schiff's base ligands derived from o-aminobenzaldehyde and various diamines. The ligands are 1,2-bis-(o-iminobenzylideneamino)ethane (aben), 1,2-bis-(o-iminobenzyl-ideneamino)propane (abpn), 1,3-bis-(o-iminobenzylideneamino)propane (abtn), and 1,2-bis-(o-iminobenzylideneamino)phenylene (abphen). The physicochemical data presented are supplementary to that of two recent papers in proving a four co-planar co-ordination polyhedron in the metal(II) compounds. In addition, a polarographic study of the redox behaviour of these compounds indicates that all should have chemically accessible higher oxidation states. Attempts to prepare the nickel and copper oxidation products of the type [M(L)X](X= Br, I) gave only amorphous solids which have not been characterised. But the crystalline compounds [Co(L)X](X= Cl, Br, I) which were readily isolated, are unique examples of paramagnetic cobalt(III) compounds with nitrogen-donor ligands. A square-pyramidal five-co-ordinate structure is postulated. These compounds react in donor solvents such as pyridine to form six-co-ordinate diamagnetic species of the type [Co(L)(solvent)X]. The crystalline diamagnetic compound [Co(aben)(py)Cl] has been isolated, and evidence is given for an equilibrium in the solutions in donor solvents between the diamagnetic and paramagnetic species.


Journal ArticleDOI
TL;DR: In this article, the applicability of the pulse radiolysis technique for understanding the election transfer mechanism in redox proteins is presented, and it is also suggested that the observed redox reactivity of the protein is correlated to its structural features.
Abstract: The applicability of the pulse radiolysis technique for understanding the election transfer mechanism in redox proteins is presented. It is also suggested that the observed redox reactivity of the protein is correlated to its structural features.

Journal ArticleDOI
TL;DR: In this paper, the possibility of titrations with iron (II) sulphate in a strongly alkaline medium of mannitol has been studied, and the formal redox potential values of the redox system of the complex were measured, in their dependence on the potassium hydroxide concentration.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the role of guanosine concentration in the photodynamic degradation of DNA and showed that only the oxidized radical of thiopyronin is affected by guanosines.
Abstract: — The thiopyronin-sensitized photooxidation of guanosine was investigated, using flash photolysis techniques. The reaction kinetics of three short-lived intermediates (the triplet state, the reduced radical, and the oxidized radical) were followed by spectroscopy. The influence of guanosine concentration on the reaction rate shows that only the oxidized radical (reaction 7) of thiopyronin is affected by guanosine. This suggests that the primary step in the photodynamic destruction of DNA is the oxidation of guanosine by the oxidized radical of thiopyronin (reaction 9). This mechanism is discussed in terms of the redox potentials of the donor and the acceptor for three different cases: (1) where the oxidation potential of the donor is more negative than that of the triplet state, the acceptor being the triplet state (FT); (2) where the oxidation potential of the donor is between the potentials of the triplet state and the oxidized radical, the acceptor being the oxidized radical (Fox); and (3) where the oxidation potential of the donor is more positive than the reduction potential of both the triplet state and the oxidized radical; in this case no electron exchange takes place. The thiopyronin-guanosine system is an example of the second case.

Journal ArticleDOI
TL;DR: In this paper, the kinetics of the electrochemical oxidation of NO2− ion dissolved in DMSO has been studied on Pt electrodes at temperature ranging from 25 to 44°C, by means of potentiostatic E/I curves and by relaxation techniques.

Journal ArticleDOI
TL;DR: The dependence of the initial rate on the catalyst amount has been studied both for the oxidation and the decomposition reactions in liquid phase using manganese dioxide as a catalyst.

Journal ArticleDOI
TL;DR: Short fragments of the photochemical electron transfer chain of photosynthesis were reproduced in aqueous detergent solutions or in organic solvents, and the photodisaggregation of chlorophyll was observed.

Journal ArticleDOI
TL;DR: The results contradict an earlier reported suggestion that leghaemoglobin functions at low pH values as a vigorous electron donor capable of producing atomic hydrogen.