Iron-dependent oxidative process

The obliteration of these iron-dependent oxidative processes by phytate suggests that this ubiquitous and abundant plant component functions as a natural antioxidant, preventing oxidative damage during storage of seeds. Surface treatment with phytic acid of various fruits and vegetables preserved their color, texture and flavor (7). Thus, dietary phytate may be a superior substitute for presently employed food preservatives, many of which pose significant health hazards. Additional applications of phytic acid are summarized in a recent review (34). 

Thus, superoxide itself is obviously too inert to be a direct initiator of lipid peroxidation. However, it may be converted into some reactive species in superoxide-dependent oxidative processes. It has been suggested that superoxide can initiate lipid peroxidation by reducing ferric into ferrous iron, which is able to catalyze the formation of free hydroxyl radicals via the Fenton reaction. The possibility of hydroxyl-initiated lipid peroxidation was considered in earlier studies. For example, Lai and Piette [8] identified hydroxyl radicals in NADPH-dependent microsomal lipid peroxidation by EPR spectroscopy using the spin-trapping agents DMPO and phenyl-tcrt-butylnitrone. They proposed that hydroxyl radicals are generated by the Fenton reaction between ferrous ions and hydrogen peroxide formed by the dismutation of superoxide. Later on, the formation of hydroxyl radicals was shown in the oxidation of NADPH catalyzed by microsomal NADPH-cytochrome P-450 reductase [9,10]. 

Iron(III) hydroxide [1309-33-7], FeH02, is a red-brown amorphous material that forms when a strong base is added to a solution of an iron(III) salt. It is also known as hydrated iron(III) oxide. The fully hydrated Fe(OH)3 has not been isolated. The density of the material varies between 3.4-3.9 g/cm, depending on its extent of hydration. It is insoluble in water and alcohol, but redissolves in acid. Iron(III) hydroxide loses water to form Fe203. Iron(III) hydroxide is used as an absorbent in chemical processes, as a pigment, and in abrasives. Salt-free iron(III) hydroxide can be obtained by hydrolysis of iron(III) alkoxides. 

In most industrial processes, copper is produced from the ore chalcopyrite, a mixed copper-iron sulfide mineral, or from the carbonate ores azurite and malachite. The extraction process depends on the chemical compositions of the ore. The ore is crushed and copper is separated by flotation. It then is roasted at high temperatures to remove volatile impurities. In air, chalcopyrite is oxidized to iron(ll) oxide and copper(ll) oxide ... 

Iron needs to be removed by an oxidation process and filtered off. Iron levels of 1 to 10 ppm can often be found in subsurface waters and this may rise to perhaps 25 ppm in seriously anaerobic water usually sulfides are also present. Both iron and manganese can present problems if present in cooling water, and it is necessary to confirm whether some or all of the iron found has originated from the makeup supply or if it is an indicator of corrosion within the system itself. Ferrous (Fe2+) and ferric (Fe3+) iron may be present in the cooling water depending on the pH. At a pH level of 8.5 or more all the iron will be in the ferric form, usually as a colloidal precipitate. 

Iron and manganese can have different oxidation states, depending on the redox conditions of the environment. Iron(II) compounds, however, are only stable under anaerobic conditions they transform iron(III) compounds on the effect of air and groundwaters (pH = 6-8), therefore, the interfacial processes of iron(II) oxides and hydroxide can play a smaller role under environmental conditions. (Note The iron(II) of silicates can also transform into iron(III) during weathering.)... 

Extensive studies have been made of the oxidations of all the halides by hydrogen peroxide. Mellor in 1904 was already able to cite fourteen investigations of kinetics of the hydrogen peroxide-hydrogen iodide reaction including studies of the temperature dependence of the rates and the kinetic form of catalysis by salts of molybdenum and iron. Since the processes (1) and (2)... 

A group of cytochromes (labeled a, b, and c, depending on their spectra) serve as oxidation-reduction agents, converting the energy of the oxidation process into the synthesis of adenosine triphosphate (ATP), which makes the energy more available to other reactions. Copper is also involved in these reactions. The copper cycles between Cu(II) and Cu(I) and the iron cycles between Fe(nl) and Fe(II) during the reactions. Details of the reactions are available in other sources. ... 

The electrochemical properties of the clathrochelate Ca-nonsymmetric FeDnD 3-n(BX)2 and Ca-nonsymmetric FeD3(BX)(BY) tris-dioximates and their dependence on electronic characteristics of the substituents in the dioximate fragments and ones at capping atoms are discussed in Refs. 64 and 68. Table 36 lists the E1/2 and the Tomes criterion values for these complexes. As seen from this table, the oxidation process for most of the boron-capped iron(II) clathrochelates is reversible or quasi-reversible. 

The electrochemical behaviour of the ribbed-functionalized iron(II) [65, 68] and ruthenium(II) [78] clathrochelates with alkylamine, thioaryl, thioalkyl, phenoxyl and crown ether substituents in a-dioximate fragments was characterized by E1/2 values for Fe3+/2+ and Ru3+/2+ couples (Table 37). The Tomes criterion values of most complexes exhibited reversible or quasi-reversible anodic processes. Moreover, the quasi-reversible oxidation processes are accompanied by the formation of insoluble products followed by passivation of the working electrode. The Ev2 values depend on the electron-donating properties of the substituents in the ribbed fragments. The correlations of E1/2 values for Ru3" 2+ and Fe + 2+ couples with these substituents Hammet s Opara constants were observed in Refs. 65, 68, and 78. These correlations are rather qualitative, but they enable one to conclude that ruthenium complexes are less sensitive to the change of substituents in dioximate fragments. There was no correlation between the Em values and the inductive Taft s (cr,) constants for substituents in dioximate fragments. 

NO was shown by Kanner et al. [120] to inhibit iron-catalysed oxidation reactions by binding to ferrous complexes. It was also shown that NO inhibited the superoxide driven Fenton reaction which, in the presence of iron, generates hydroxyl radical (OH) in vitro. By adding varying amounts of NO to a Fenton reaction process the hydroxylation of benzoic acid was reduced. This demonstrates that depending on the fluxes of the different reactive species, NO may have an antioxidant capability. 

The silica may also be contaminated by metallic impurities such as aluminum, nickel, and iron, depending on the synthesis of the silica or the manufacturing process. These metals may be present either in the form of oxides and hydrous oxides or through oxygen bonds attached to an Si atom [3]. The metal impurities may also have an effect on the chromatography, causing peak tailing due to complexation with the trace metal impurities. The acidity of the surface silanols is increased with the presence of these metal impurities. 

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