Redox intermediates

Perhaps this may be considered in relation to the suggestion of Kellermeyer et al. (K5) that the drugs involved are transformed in vivo to redox intermediates. Furthermore, the reducing capacity of RBC was shown to be a function of GSH content. Reduction of this capacity by intravenous infusion of sodium thiosulfate solution reflects changes in the intracellular oxidation-reduction system of glutathione, the oxidized form being favored (Cl, S9). 

These findings lead to (he conclusion that the reduction of MHb by its reductase requires a natural cofactor, which is abolished during the purification procedure and can be replaced by methylene blue (G5, H22, H23, K8, K14). Since methylene blue and the other effective dyes are redox intermediates, it is obvious that the postulated cofactor interacts in the electron transport sequence of the MHbR reaction (H23). This is confirmed by the finding that oxygen and cytochrome c serve as well as terminal electron acceptor as does MHb (H22, H23, K14). Nevertheless, it had been possible to separate a cytochrome c reductase from MHbR in yeast extracts (A6). 

Teixeira, M., Moura, L, Xavier, A. V, Moura, J. J., LeGall, J., DerVartanian, D. V., Peck, H. D., Jr and Huynh, B. H. (1989) Redox intermediates of Desulfovibrio gigas [NiFe] hydrogenase generated under hydrogen. Mosshauer and EPR characterization of the metal centers. J. Biol. Chem., 264, 16435-50. 

The oxidation state of iron may be either + 2 or + 3 and the importance of the Cytochrome lies in their ability to act as redox intermediates in electron transfer. 

The kinetics of the oxidation of Cr(III) and Cu(I) have been discussed before. Cr(VI) is reduced by dissolved organic matter, the slow re-oxidation resulting in a large enough ti for an existence of Cr(III). Also the existence of Cu(I) in seawater is a steady state between the reduction- and back-oxidation reactions. The lifetime is dependent on pH, PC>2, complexing ligands and redox intermediates such as H2O2 (Moffet and Zika, 1983). 

Flavoproteins play varied roles as coenzymes in biochemical processes. They serve as key intermediates in electron transport between those systems, such as the cytochromes, that carry one electron at a time and the two-electron transfers involved in the redox chemistry of organic-substrate metabolism. Flavins such as FMN or FAD (Figure 2) are designed structurally and electronically to stabilize both one- and two-electron redox intermediates. Thus, the one-electron reduction of... 

Jakopitsch C, Vlasits J, Wiseman B et al (2007) Redox intermediates in the catalase cycle of catalase-peroxidases from Synechocystis PCC 6803, Burkholderia pseudomallei, and Mycobacterium tuberculosis. Biochemistry 46 1183-1193... 

An understanding of the H202-dependent deactivation mechanism or heme peroxidases in structural terms requires detailed structures for the redox intermediates. The three dimensional structure of CIII at atomic levels by X-ray diffraction crystallography has been achieved by the use two different experimental strategies. 

This then seems to be a case in which an element has assumed an unstable oxidation state as a redox intermediate simply because no easier path is available for a reaction that- is, none the less, very favorable energetically. 

Pandelia ME, Fourmond V, Tron-Infossi P, et al. Membrane-bound hydrogenase I from the hyperthermophilic bacterium Aquifex aeolicus enzyme activation, redox intermediates and oxygen tolerance. J Am Chem Soc. 2010 132(20) 6991-7004. 

FIGURE 6. Schematic representation of the catalytic reaction cycle in flavocytochrome b2. Five redox intermediates of FCB2 during the oxidation of one molecule of lactate at a steady-state turnover rate of 100 sec and the reduction of two molecules of cytochrome c at the rate of 200sec° are shown. Step 4 is the rate limiting step in the steady state and the maximal rates of some of the other electron transfer steps are indicated. Reproduced from Daff et al., 1996 with permission. 

Figure 16.2 The redox intermediate, nitrite (N02 ), occupies a central position in the marine N-cycle. Shown are the various processes that are either sources or sinks for N02. Abbreviations include (clockwise from top) ANR = assimilatory nitrate reduction, Nit = nitrification, photolysis = UV-driven photocatalysis, DNR/DN = dissimilatory nitrate reduction/denitrification, ANR and Nit = as above, Anammox = Anaerobic ammonium oxidation.

Rotaxane 40 (Figure 4.18) was synthesised since it was reasoned that it might be possible to prolong the lifetime of any redox intermediate by the incorporation of terminal redox-active stoppers. The presence of the latter may provide a means of facilitating spatial separation of the primary redox changes. Preliminary cyclic voltammetry studies indicated that the 7t-radical dialkoxybenzene cation, formed by excitation of the charge-transfer complex, should favour oxidation of one of the... 

In both cases the primary redox intermediates A stable products. 

In a number of cases, redox intermediates are rather unstable, and the equilibria are best described in terms of multi-electron transfers although, mechanistically, they most probably involve sequential one-electron transfers. A prime example is permanganate, Mn04 , which in neutral solution can be reduced to Mn02 with an uptake of three electrons, and in acidic solution to Mn2+accordingto... 

The electrocatalytic oxidation of organic molecules has been studied very extensively using various supports and adatoms. There are several proposed mechanisms in the literature to interpret the role of adatoms. It is assumed, for instance, that adatoms block the poison formation not leaving enough space for these reactions. According to another hypothesis, adatoms act as redox intermediates. Independently from the explanation, it is a fact that very often a significant enhancement of the catalytic activity can be observed and these results could provide very useful information for liquid-phase catalytic reactions.60... 

The actual electronic structure of (RSSR) is especially interesting. Key feature is a 2o/10 bond between the two sulfur atoms, rendering [RS.. SR]-an even more appropriate and informative notation.55,56 While further details on this three-electron bond will be dealt with in the odd electron bonds section vide infra), the following is of immediate interest. The combined effect of the two bonding o-electrons and the one antibonding a electron affords a formal bond order of 1/2. This, in turn, provides the rationale for the above equilibrium and relative ease of redissociation of the newly formed sulfur-sulfur bond. The same [RS. . SR] species is, incidentally, formed in the reduction of disulfides by hydrated electrons. Thiyl radicals and disulfide radical anions thus are two conjugate forms of the one-electron redox intermediate between thiols and disulfides. 

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