Redox

About: Redox is a research topic. Over the lifetime, 26853 publications have been published within this topic receiving 862368 citations. The topic is also known as: reduction-oxidation & reduction-oxidation reaction.

Effects of Fulvic Acid on Fe(II) Oxidation by Hydrogen Peroxide

Abstract: Iron redox cycling can catalyze the oxidation of humic substances and increase the rate of oxygen consumption in surface waters rich in iron and organic carbon. This study examines the role of Fenton`s reaction [oxidation of Fe(II) by hydrogen peroxide] in this catalytic cycle. A number of competing processes were observed in model systems containing dissolved Fe, hydrogen peroxide, and Suwannee River fulvic acid. First, the effective rate constant of Fenton`s reaction increased with increasing fulvic acid concentration, indicating the formation Fe(II)-fulvate complexes that react more rapidly with hydrogen peroxide than Fe(II)-aquo complexes. This effect was significant at pH 5 but negligible at pH 3. A second effect was scavenging of the HO{sup .} radical produced in Fenton`s reaction by fulvic acid, forming an organic radical. The organic radical reduced oxygen to HO{sub 2}{sup .}/O{sub 2}{sup .-}, which then regenerated hydrogen peroxide by reaction with Fe(II). Finally, Fe(III) was reduced by a dark reaction with fulvic acid, characterized by an initially fast reduction followed by slower processes. The behavior of Fe(II) and hydrogen peroxide over time in the presence of fulvic acid and oxygen could be described by a kinetic model taking all of these reactions into account. The netmore » result was an iron redox cycle in which hydrogen peroxide as well as oxygen were consumed (even though direct oxidation of Fe(II) by oxygen was not significant), and the oxidation of fulvic acid was accelerated. 56 refs., 7 figs., 1 tab.« less

Glutathione as an Antioxidant and Regulatory Molecule in Plants Under Abiotic Stress Conditions

Abstract: The glutathione (GSH)/glutathione disulfide (GSSG) redox couple is involved in several physiologic processes in plants under both optimal and stress conditions. It participates in the maintenance of redox homeostasis in the cells. The redox state of the GSH/GSSG couple is defined by its reducing capacity and the half-cell reduction potential, and differs in the various organs, tissues, cells, and compartments, changing during the growth and development of the plants. When characterizing this redox couple, the synthesis, degradation, oxidation, and transport of GSH and its conjugation with the sulfhydryl groups of other compounds should be considered. Under optimal growth conditions, the high GSH/GSSG ratio results in a reducing environment in the cells which maintains the appropriate structure and activity of protein molecules because of the inhibition of the formation of intermolecular disulfide bridges. In response to abiotic stresses, the GSH/GSSG ratio decreases due to the oxidation of GSH during the detoxification of reactive oxygen species (ROS) and changes in its metabolism. The lower GSH/GSSG ratio activates various defense mechanisms through a redox signalling pathway, which includes several oxidants, antioxidants, and stress hormones. In addition, GSH may control gene expression and the activity of proteins through glutathionylation and thiol-disulfide conversion. This review discusses the size and redox state of the GSH pool, including their regulation, their role in redox signalling and defense processes, and the changes caused by abiotic stress.

Structural biology of copper trafficking.

Abstract: 1.1. Background The use of copper in biological systems coincides with the advent of an oxygen atmosphere about 1.7 billion years ago. The presence of O2 both allowed the oxidation of insoluble Cu(I) to the more soluble and bioavailable Cu(II) and led to the requirement for a redox active metal with potentials in the 0-800 mV range. Not only did copper meet this need, but the oxidation of Fe(II) to the insoluble Fe(III) form rendered the use of iron more energetically expensive.1-5 As a result, copper plays a key role in many proteins that react with O2. Generally, O2-reactive centers are mononuclear (type 2), dinuclear (type 3), or trinuclear (type 2 and type 3). Well studied mononuclear copper enzymes include the monooxygenases dopamine-β-hydroxylase and peptidylglycine α-hydroxylating monooxygenase as well as oxidases that also contain organic cofactors, such as amine, galactose, and lysyl oxidases.6 Dinuclear copper proteins include the O2 carrier hemocyanin and enzymes like tyrosinase and catechol oxidase.7 Copper also plays a key role in numerous electron transfer proteins. Mononuclear type 1 (blue copper) centers are found in proteins such as plastocyanin and azurin.8 The multicopper oxidases like laccase, ascorbate oxidase, and ceruloplasmin contain both a catalytic trinuclear type 2/type 3 site and an electron transfer type 1 site.9,10 The classification of copper centers into types is derived from optical and electron paramagnetic resonance (EPR) spectroscopic properties, and there are some notable exceptions, including the cysteine-bridged dinuclear CuA electron transfer site in cytochrome c oxidase11 and nitrous oxide reductase, the tetranuclear catalytic CuZ center in nitrous oxide reductase,12 and the proposed catalytic copper center in particulate methane monooxygenase.13-15 The same redox properties that render copper useful in all these metalloproteins can lead to oxidative damage in cells. Reaction of Cu(I) with hydrogen peroxide and re-reduction of Cu(II) by superoxide via Fenton and Haber-Weiss chemistry yields hydroxyl radicals that can damage proteins, lipids, and nucleic acids.16 Thus, intracellular copper concentrations must be controlled such that copper ions are provided to essential enzymes, but do not accumulate to deleterious levels. In humans, deficiencies in copper metabolism are linked to diseases such as Menkes syndrome, Wilson disease, prion diseases, and Alzheimer’s disease.17 Several classes of proteins, including membrane transporters,18-20 metallochaperones,21,22 and metalloregulatory proteins,23,24 are implicated in copper homeostasis. These proteins have two functions. First, they ensure that copper is provided to the correct proteins and cellular compartments for necessary activities. Second, these proteins detoxify excess copper. Just as copper-containing proteins and enzymes are found in all kingdoms of life, members of these groups of homeostatic proteins are also widespread,5 and have been structurally and biochemically characterized from eukaryotes and prokaryotes.

Electron Transfer between Glucose Oxidase and Electrodes via Redox Mediators Bound with Flexible Chains to the Enzyme Surface

Abstract: : Electrical communication between redox centers of glucose oxidase and vitreous carbon electrodes is established through binding to oligosaccharides, at the periphery of the enzyme, ferrocene functions pendant on flexible chains. Communication is effective when the chains are long (>10 bonds), but when the chains are short (<5 bonds). When attached to long flexible chains the peripherally bound relays penetrate the enzyme to a sufficient depth to reduce the electron transfer distances between a redox center of the enzyme and the relay and between the relay and electrode, thereby increasing the rate of electron transfer.

An investigation of titanium dioxide photocatalysis for the treatment of water contaminated with metals and organic chemicals

Abstract: Laboratory experiments were performed to investigate TiO 2 photocatalysis for treating water contaminated with dissolved metals (Ag, Au, Cd, Cr, Cu, Hg, Ni, and Pt) and a variety of organics (e.g., methanol, formic acid, salicylic acid, EDTA, phenol, and nitrobenzene). It was found that only those metals with half-reaction standard reduction potentials more positive than 0.3 V (vs normal hydrogen electrode) can be treated using TiO 2 as the photocatalyst. Kinetic data illustrating the synergism between oxidation and reduction are presented. Experiments using singly substituted benzenes as electron donors show that the rate of reduction of Cr(VI) is correlated with Hammett a constants