Iron redox reactions

Electron exchange of iron(II-III) tends to be more reversible than is electron exchange between nitrogen, sulfur, or carbon states. Iron redox reactions occur in soils without enzymatic catalysis. The Fe(II) minerals in parent material rocks oxidize spontaneously, though slowly, in aerobic soils. The electron availability for subsequent Fe redox reactions in soils is determined by microbial oxidation of carbon compounds. The reduction of Fe(III) in acid solutions is... 

It was determined that these ceriporic acids suppressed iron redox reactions to attenuate OH production by the Fenton reaction in the presence of iron reductants such as hydroquinone and cysteine. It was proposed that the suppression of the cellulolytic active oxygen species, OH, by this metabolite contributes to the selective lignin-degradation with a minimum loss of cellulose. The absolute configuration of ceriporic acids, their stereoselective biosynthetic pathway and the diversity of their metabolites have been largely discussed. 

In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation state are reduced, for example, in the following redox reaction between fe + and oxalic acid, H2C2O4, iron is reduced since its oxidation state changes from -1-3 to +2. 

Molybdenum. Molybdenum is a component of the metaHoen2ymes xanthine oxidase, aldehyde oxidase, and sulfite oxidase in mammals (130). Two other molybdenum metaHoen2ymes present in nitrifying bacteria have been characteri2ed nitrogenase and nitrate reductase (131). The molybdenum in the oxidases, is involved in redox reactions. The heme iron in sulfite oxidase also is involved in electron transfer (132). 

Phthalocyanines are excellent lubricants at temperatures of 149—343°C (191). Combinations with other lubricants, like grease, molybdenum, or tungsten sulfides, have found appHcations in the automotive industry or professional drilling equipment (192—195). Further uses include indicators for iron(Il), molybdenum(V), and uranium(IV) (196) or redox reactions (197), medical appHcations like hemoglobin replacements (198) or sterilisation indicators (199), or uses like in gas filters for the removal of nitrogen oxides from cigarette smoke (200). 

Redox reactions occur in the reduction of ores (metal oxides) into pure metals and the corrosion (oxidation) of pure metals in the presence of oxygen and water. Rusting iron, 4Fe + 30, + 611,0 —> 4Fe(OH), is a good example of metal oxidation. Strong oxidizing agents can be used as antiseptics (hydrogen peroxide, Fd,0,) or bleaches (sodium hypochlorite, NaOCl). 

One of the most used systems involves use of horseradish peroxidase, a 3-diketone (mosl commonly 2,4-pentandione), and hydrogen peroxide." " " Since these enzymes contain iron(II), initiation may involve decomposition of hydrogen peroxide by a redox reaction with formation of hydroxy radicals. However, the proposed initiation mechanism- involves a catalytic cycle with enzyme activation by hydrogen peroxide and oxidation of the [3-diketone to give a species which initiates polymerization. Some influence of the enzyme on tacticity and molecular... 

High levels of chelant or oxygen affect the redox tendencies of iron-oxygen reactions and permit the liberation of Fe2+ ions (corrosion) from a metal surface and their subsequent chelation, thus preventing the formation or repair of blanketing ferric oxides, hydroxides, or a passivated magnetite film. 

CODH/ACS is an extremely oxygen-sensitive protein that has been found in anaerobic microbes. It also is one of the three known nickel iron-sulfur proteins. Some authors would consider that there are only two, since the CODH and ACS activities are tightly linked in many organisms. However, there is strong evidence that the ACS and CODH activities are associated with different protein subunits and the reactions that the two enzymes catalyze are quite different. CODH catalyzes a redox reaction and ACS catalyzes the nonredox condensation of a methyl group, a carbonyl group, and an organic thiol (coenzyme A). 

C04-0039. Predict whether or not a reaction will occur, and if a reaction does take place, write the half-reactions and the balanced redox reaction (a) a strip of nickel wire is dipped in 6.0 M HCl (b) aluminum foil is dipped in aqueous CaCl2 (c) a lead rod is dipped in a beaker of water (d) an iron wire is immersed in a solution of silver nitrate. 

Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

Redox reactions can proceed by direct transfer of electrons between chemical species. Examples include the rusting of iron and the metabolic breakdown of carbohydrates. Redox processes also can take place by indirect electron transfer from one chemical species to another via an electrical circuit. When a chemical reaction is coupled with electron flow through a circuit, the process is electrochemical. Flashlight batteries and aluminum smelters involve electrochemical processes. 

The difficulty in recognizing redox reactions is illustrated by two of the reactions that occur during the extraction of iron from iron ores, a process that we describe in detail in Chapter 20 ... 

The first reaction is a redox reaction because the oxidation number of carbon increases (oxidation), and that of iron decreases (reduction). 

The corrosion of iron occurs particularly rapidly when an aqueous solution is present. This is because water that contains ions provides an oxidation pathway with an activation energy that is much lower than the activation energy for the direct reaction of iron with oxygen gas. As illustrated schematically in Figure 19-21. oxidation and reduction occur at different locations on the metal surface. In the absence of dissolved ions to act as charge carriers, a complete electrical circuit is missing, so the redox reaction is slow, hi contrast, when dissolved ions are present, such as in salt water and acidic water, corrosion can be quite rapid. 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

C20-0073. Draw a crystal field splitting diagram that illustrates the electron transfer reaction of the simple iron redox protein shown in Figure 20-29a. 

Corrosion, a type of redox reaction, can cause cars and buildings to rust. Rusting happens when iron is oxidized by oxygen in the air. This process happens when —... 

Absorption of americium is greater in iron deficient animals than in iron replete adult animals (Sullivan and Ruemmler 1988 Sullivan et al. 1986) (see Section 3.4.1.2). Concurrent oral exposure to Fe3+ and americium also appears to increase the absorption of ingested americium the latter effect may result from redox reactions in the gastrointestinal tract catalyzed by Fe3+ (Sullivan et al. 1986). These differences are accounted for in the discussions and dosimetric/metabolic models of the ICRP (1989, 1993) and the NEA (1988). 

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