Redox mechanisms

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

The variation in the amounts of the high and low spin forms of Fe(III)BLM as a function of pH was determined using esr. 

The Fe(II) complexes of the new bleomycin derivatives, 2-4, were prepared in the presence of the atmosphere by the additTon of Fe(II)(Ci ,04)2 to a 10 3m solution of the bleomycin. The pH was adjusted by addition of small amounts of IM HCt or IM NaOH to the solution containing the complex. No oxidation to Ferill) occurred. 

The dc polarographic studies were carried out in buffered and in unbuffered aqueous solutions. Potentials were referenced against a Ag/AgCt saturated NaCt electrode. The electrochemical assignments and the apparatus used to collect the polarographic data have been previously described (14,15). 

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Hydroperoxides are more widely used as initiators in low temperature appHcations (at or below room temperature) where transition-metal (M) salts are employed as activators. The activation reaction involves electron-transfer (redox) mechanisms ... 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

FIGURE 15.2 Decomposition of peroxides by ions of metals (Redox mechanism). 

Our study was focused on the influence of reducing power on the selective oxidation of H2S over the various transition metal oxides, which would be proceeded by the redox mechanism [5,6]. The redox mechanism and the reducing power [7] in selective oxidation of H2S can be defined as follows ... 

Ammonia and acetic acid in waste water give rise serious pollution problems which bring about eutrophication of rivers, lakes, etc [1, 2]. These have been treated by the conventional method of biological techniques, adsorption, and thermal incineration. A band of researchers have suggested that the ammonia molecules could be transferred to N2 using a photocatalytic redox mechanism as shown follows 4NH3 + 3O2 2N2 + 6H2O. However, it has been... 

From Fig.2 (a), A solid phase transformation fiom hematite, Fc203 to magnetite, Fe304, is observed, indicating that the active sites of the catalj are related to Fc304. Suzuki et. al also found that Fe304 plays an important role in the formation of active centers by a redox mechanism [6]. It is also observed that the hematite itself relates to the formation of benzene at the initial periods, but no obvious iron carbide peaks are found on the tested Li-Fe/CNF, formation of which is considered as one of the itsisons for catalyst deactivation [3,6]. 

Under certain conditions a combination of Pd(II) and Cu(II) in acetic acid oxidises olefins to saturated products which neither reagent produces alone. Although Cu(II) continues to catalyse the production of vinyl acetate through step (46) by a redox mechanism, the following new reaction can be effected... 

Selective oxidation and ammoxldatlon of propylene over bismuth molybdate catalysts occur by a redox mechanism whereby lattice oxygen (or Isoelectronlc NH) Is Inserted Into an allyllc Intermediate, formed via or-H abstraction from the olefin. The resulting anion vacancies are eventually filled by lattice oxygen which originates from gaseous oxygen dlssoclatlvely chemisorbed at surface sites which are spatially and structurally distinct from the sites of olefin oxidation. Mechanistic details about the... 

In the cases of the selective oxidation reactions over metal oxide catalysts the so-called Mars-van Krevelen or redox mechanism [4], involving nucleophilic oxide ions 0 is widely accepted. A possible role of adsorbed electrophilic oxygen (molecularly adsorbed O2 and / or partially reduced oxygen species like C , or 0 ) in complete oxidation has been proposed by Haber (2]. However, Satterfield [1] queried whether surface chemisorbed oxygen plays any role in catalytic oxidation. 

It is well known also that higher alkanes suffer radical gas phase oxidation above 723 K. Therefore, their use requires catalysts active and selective for deNOx at lower temperatures. The mechanism of NOx elimination is still debated a redox mechanism involving Cu ions is probable, and isolated Cu cations exchanged into MFI [4,5] or mordenite [6] have been found to be more active than CuO clusters. It must be emphasized, however, that acid zeolites exhibit good activity at high temperature, and acid mechanisms have been proposed [7-10]. In presence of Cu this acid mechanism disappears probably due to the decrease of the acidity of mordenite upon Cu exchange [6]. According to... 

Reasonable NO conversion can be achieved using n-decane as reductant. In the absence of sulfur dioxide, the catalytic activity is roughly related to the r ucibility of the Cu phase of Cu ions in zeolites the reaction temperature needed to reach 20% NO conversion parallels that of the TPR peak (Table 7). This relation also practically holds for Cu on simple oxides, therefore a redox mechanism in which reduction of Cu + cations is the slow step could account for the results. 

The presence of V V on the surface before catalysis is unessential for catalytic activity. We cannot however rule out an SCR redox mechanism involving VV-V V. ESR and IR results show that the oxidation state of surface vanadium at the reaction temperature is controlled mainly by the composition of the reactant mixture. 

By-products from capture of nucleophilic anions may be observed.53 Phenols can be formed under milder conditions by an alternative redox mechanism.98 The reaction is initiated by cuprous oxide, which effects reduction and decomposition to an aryl radical, and is run in the presence of Cu(II) salts. The radical is captured by Cu(II) and converted to the phenol by reductive elimination. This procedure is very rapid and gives good yields of phenols over a range of structural types. 

At x=l, the redox reaction was very slow and the UV-VIS absorption showed no change with time. The orange - yellowish color persisted for weeks, indicating that there was little or no reduction (i.e., poor conversion) of Cr(VI). At x=4 or more, development gf blue color occurred instantly, which is evidence of CrCHgOJg production via the acidic redox mechanism. At x=2 to 3, the green color of dated Cr(III) developed in minutes, followed by gelation of the polymer. 

Palozza, P, S Serini, A Torsello et al. 2003. Beta-carotene regulates NF-kappa B DNA-binding activity by a redox mechanism in human leukemia and colon adenocarcinoma cells. J Nutr 133 381-388. 

However, recently, several other non-redox mechanisms have been implicated in the modulation of cell growth by carotenoids, which include the direct modulation of the expression of proteins and transcription factors involved in cell proliferation, differentiation and apoptosis. 

This review reports the more recent evidence for the ability of P-carotene and other carotenoids to modulate cell signaling related to cell growth and implicated in a lot of pathological events, including cancer, inflammation, and atherosclerosis by both redox and non-redox mechanisms. 

Palozza, P. 2005. Can beta-carotene regulate cell growth by a redox mechanism An answer from cultured cells. Biochim Biophys Acta 1740 215-221. 

Palozza, P., Serini, S., Di Nicuolo, R et al. 2001b. Mitogenic and apoptotic signaling by carotenoids Involvement of a redox mechanism. IUBMB Life 52 77-81. 

A redox mechanism. An oxidized form of a more efficient component of a synergic mixture is reduced by the presence of a less reactive component. Example aromatic amines + phenols. 

The effect of ionizing radiation on molecular or ionic solids is to eject electrons, which often subsequently react at sites in the material well removed from the residual electron-loss centre. These electron-loss and electron-gain centres, or breakdown products thereof, are paramagnetic and have been extensively studied by e.s.r. spectroscopy. Results for a wide range of organo metals both as pure compounds and as dilute solid solutions are used to illustrate this action. Aspects of the electronic structures of these centres are derived from the spectra and aspects of redox mechanisms are discussed. 

Reductive and oxidative transformations of small ring compounds form the basis of a variety of versatile synthetic methods which include functionalization and carbon skeleton construction. Redox mechanisms of organotransition metal compounds play an important role in inducing or catalyzing specific reactions. Another useful route in this area is based on one-electron redox reactions. The redox tautomerism of dialkyl phosphonate also contributes to the efficiency of the reductive transformation of small ring compounds. This review summarizes selective transformations which have a high potential for chemical synthesis. 

Mechanism 3 involves NiOH in at least three reactions, and Ni(OH)2 as the active Ni reactant in solution. Since increasing the concentration of the complex-ant(s) in solution will reduce the concentration of both unhydrolyzed and hydrolyzed metal ions, arguments of complexation cannot be readily employed to either support or discount this mechanism. However, it has been this author s experience in formulating electroless Co-P solutions with various complexants for Co2+ that improper complexation which results in even a faint precipitate of hydrolyzed cobalt ions yields an inactive electroless Co-P solution. Furthermore, anodic oxidation of hypo-phosphite at Ni anodes does not proceed at a significant rate under conditions where the surface is most probably covered with a passive film of nickel oxide [48], e.g. NiO.H20, which would be expected to oxidize the reducing agent via a cyclic redox mechanism. 

The dissociation of iron from a tetradentate siderophore complex is more rapid than from the analogous hexadentate system (3). This may be a reason for some organisms to produce tetradentate siderophores instead of hexadentate siderophores despite the concentration effect noted in Section III. A. As was illustrated in Fig. 19, it is also thermodynamically easier to reduce iron(III) in tetradentate complexes than hexadentate complexes, making it easier to induce release of iron from the complex by a redox mechanism. 

Yoneyama H, Tsuda R, Nishida K, Kuwabata S (1993) Proceedings of the 5th International Symposium on Redox Mechanisms and Interfacial Properties of Molecules of Biological Importance, Schultz E, Taniguchi I (eds), The Electrochemical Society, Pennington NJ, USA... 

Eisenberg et ah—the redox mechanistic perspective over Rh and Pt/Sn systems. The term redox mechanism in catalysis is used to describe cases where the catalyst itself undergoes changes in oxidation state during the course of the mechanism. It does not refer to the oxidation state changes of reactants, products, or associated intermediates, although associated intermediates are often involved in the course of the mechanism. 

B. Better tools available, but no consensus on mechanism or active site—1980 to 2006. Rhodes et al.291 published a comprehensive review on the heterogeneously catalyzed water-gas shift mechanism in 1995. Included in that discussion was the copper/zinc oxide/alumina system. The conclusion was that this system appears to be constructed of small metallic islands of copper resting on a zinc oxide alumina phase. Zinc oxide may exert some impact on catalytic activity, but it was suggested in the review that the contribution is small. It was indicated that strong evidence exists to support either a formate or a redox mechanism, and the authors even suggest the possibility that both mechanisms might occur, though insufficient data exist to determine which mechanism predominates. 

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