Iron redox systems

Glass, B.L. Relation between the degradation of DDT and the iron redox system in soils. J. Agric. Food Chem., 20(2) 324-327, 1972. 

The function of the chelator is to complex the ferrous ion and thus limit the concentration of free iron. Redox systems appear very versatile, permitting polymerization at ambient temperatures and the possibility of control of the rate of radical initiation versus polymerization time. This would thus permit control of heal generation and the minimization of reaction time. The use of the redox system ammonium persulfate (2 mmol) together with sodium pyrosulfite (Na S Oj 2.5 mmol) together with copper sulfate (0.002 mmol) buffered with sodium bicarbonate in I liter of water form an effective redox system for vinyl acetate emulsion polymerization. The reaction was started at 25 C and run nonisothermally to 70 C. The time to almost complete conversion was 30 min (Warson, 1976 and Edelhauser, 1975). 

The most common and apparently simple iron redox system would certainly be the hexa-aqua iron (III) complex whose formal reduction potential is reported to be in the range 4-0.74 to 4-0.77 V versus NHE. The kinetic of Fe(H20)6 " reduction has been studied in chloride-free aqueous perchloric solutions at single... 

In the case of the iron redox systems presented here, the most reactive of the nitroaromatic model compounds (4-acetylnitrobenzene) was reduced by only about one order of magnitude faster than the least reactive NAC (2-methylnitrobenzene) whereas there was 4 orders of magnitude difference in the H2S/NOM system. 

The effects of alternating currents are much less of a corrosion danger than those of direct currents. Experiments on steel have shown that during the positive half wave [34-37] only about 1 % contributes to the dissolution of iron according to Eq. (2-21). The remaining 99% is involved in the discharge of capacitances, of redox systems (e.g., Fe /Fe in surface films) or in the evolution of Oj by... 

The presence of sulphonic and carboxylic groups enables the iron ions to be in the vicinity of the cellulose backbone chain. In this case, the radicals formed can easily attack the cellulose chain leading to the formation of a cellulose macroradical. Grafting of methyl methacrylate on tertiary aminized cotton using the bi-sulphite-hydrogen peroxide redox system was also investigated [58]. 

Hence, in the absence of a redox system in solution the anodic reaction of FeS2 yields iron oxide/hydroxide and water-soluble sulfate ions. The compound does not undergo non-oxidative dissolution. 

The classical example of snch a device is a cell where thionine dye is used. Thionine is the oxidizing agent in the reaction T -r e + f TH. Thionine itself is hard to reduce electrochemically. Therefore, the mediating redox system Fe /Fe is used, which functions as an electron shnttle. The excited form of thionine, T, produced under illumination is readily rednced by divalent iron ions ... 

Hard, S. and Kanner, J. (1989). Haemoglobin and myoglobin as inhibitors of hydroxyl radical generation in a model system of iron redox cycle. Free Rad. Res. Commun, 6, 1-10. 

Table 12.29 Reaction paths involved in anthraquinonoid and iron-complex redox systems [214]...

Dining preparation of iron(II) perchlorate, a mixture of iron sulfate and perchloric acid was being strongly heated when a most violent explosion occurred. Heating should be gentle to avoid initiating this redox system. 

E is normally written with a subscript to indicate the two redox states involved. fpe +.Fe. for example, is the electrode potential for the ferrous ion-iron metal system. Note that we expect a different electrode potential if different redox states are involved, so Epe +.Pe Fe +.Fe- th usual practice to write the oxidized form of the couple first. 

It is important to clarify that there have been, in the literature, some examples of electrochemical processes on CNT-modified electrodes on which an apparent electrocatalytic process associated to the CNTs seems to take place (that is from the edge-plane-like sites) where in fact that was not the case. An example is the apparent electrocatalytic oxidation ofhydrazine at MWNTelectrodes [64,65]. Such electrochemical behavior has been demonstrated to be a consequence of iron impurities contained in the CNTs that were responsible for the observed electrocatalytic effects (Figure 3.7). Therefore, caution is needed when reporting catalytic effects of CNTs under a given redox system and a careful comparison vdth, for instance, edge HOPG is mandatory to make sure that the CNTs are the responsible for the electrochemical enhancement. 

In complex 1, the electrons are passed from NADH+H first to FMN (see p. 104) and then on to several iron-sulfur (Fe/S) clusters. These redox systems are only stable in the interior of proteins. Depending on the type, Fe/S clusters may contain two to six iron ions, which... 

In a redox system consisting of a peroxo compound and an iron(II) salt, the initiating radicals are formed by electron transfer from Fe " to the peroxo compound, causing the peroxy link to be cleaved, with simultaneous formation of a radical and an anion. In a second step, the oxidized metal reacts with another hydroperoxide to form a peroxy radical and a proton ... 

The ferrocene/ferrocenium reference redox system at platinum fulfills these requirements fairly well [4-6]. Another system which has been recommended is bis(biphenyl)chromium (0)/bis(biphenyl)chromium (+1) (BCr+ /BCr) [5, 7]. Several other systems have been suggested, and used sporadically, such as cobaltocene/cobaltocenium, tris(2,2 -bipyridine) iron (I)/tris(2,2 -bipyridine) iron (0), Rb+/Rb(Hg), and so on. 

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