Redox

About: Redox is a research topic. Over the lifetime, 26853 publications have been published within this topic receiving 862368 citations. The topic is also known as: reduction-oxidation & reduction-oxidation reaction.

Cooperative Bimetallic Redox Reactivity

Abstract: Binucleating ligands possessing contiguous 6-coordinate and 4-coordinate sites are described, and the redox properties of their bimetallic complexes have been investigated. The design of the two parts of these ligands is based on the redox and reactivity patterns of the corresponding monometallic complexes. If the two sites were to behave as they do in the corresponding monometallic complexes, these bimetallic complexes would be expected to bind a substrate, such as dioxygen, and to reduce it by two electrons, one from each metal, as occurs in the respiratory protein, hemerythrin. This was found not to be the case. In these bimetallic complexes, oxidation of one metal leads to the deactivation of the other metal to oxidation. The origins of this mutual deactivation appear to be connected with ligand reorganization, through-bond electronic coupling, and electrostatic interactions between neighboring metals. It is suggested that, in the systems described, ligand reorganization is the dominant deactivating e...

Syngas production from methane and air via a redox process using Ce-Fe mixed oxides as oxygen carriers

Abstract: CeO2, Fe2O3, Fe2O3/Al2O3 and Ce–Fe mixed oxides with different Ce/Fe ratios were prepared and characterized using XRD, Raman, XPS, and H2–TPR techniques. The selective oxidation of methane to syngas using a gas–solid reaction was investigated at 850 °C. For binary Ce–Fe oxides, only small amounts of iron ions could be incorporated into the CeO2 lattice with the superfluous Fe2O3 remaining on the surface of the molecule. Chemical interactions between surface iron sites and the Ce–Fe solid solution strongly enhanced the reducibility of materials. Methane was found to adsorb and activate on the surface iron sites as carbonaceous species and hydrogen. Carbon deposition was selectively oxidized to CO by the release of activated oxygen from the CeO2 lattice. The activation rate of methane was dependent on the quality of dispersion of surface Fe species, while the oxygen mobility of the material dominated the CO formation rate. Hydrothermally prepared Ce0.7Fe0.3O2−δ showed high activity and selectivity during the successive production of syngas using repetitive redox processes (methane reduction/air re-oxidation). Both the dispersion of surface Fe2O3 and the formation of the Ce–Fe solid solution were enhanced by the redox treatment, which made the oxygen carrier more stable.

Mitochondrial copper(I) transfer from Cox17 to Sco1 is coupled to electron transfer.

Abstract: The human protein Cox17 contains three pairs of cysteines In the mitochondrial intermembrane space (IMS) it exists in a partially oxidized form with two S-S bonds and two reduced cysteines (HCox17(2S-S)) HCox17(2S-S) is involved in copper transfer to the human cochaperones Sco1 and Cox11, which are implicated in the assembly of cytochrome c oxidase We show here that Cu(I)HCox17(2S-S), ie, the copper-loaded form of the protein, can transfer simultaneously copper(I) and two electrons to the human cochaperone Sco1 (HSco1) in the oxidized state, ie, with its metal-binding cysteines forming a disulfide bond The result is Cu(I)HSco1 and the fully oxidized apoHCox17(3S-S), which can be then reduced by glutathione to apoHCox17(2S-S) The HSco1/HCox17(2S-S) redox reaction is thermodynamically driven by copper transfer These reactions may occur in vivo because HSco1 can be found in the partially oxidized state within the IMS, consistent with the variable redox properties of the latter compartment The electron transfer-coupled metallation of HSco1 can be a mechanism within the IMS for an efficient specific transfer of the metal to proteins, where metal-binding thiols are oxidized The same reaction of copper-electron-coupled transfer does not occur with the human homolog of Sco1, HSco2, for kinetic reasons that may be ascribed to the lack of a specific metal-bridged protein-protein complex, which is instead observed in the Cu(I)HCox17(2S-S)/HSco1 interaction

Reductive metabolism of the hypoxia marker pimonidazole is regulated by oxygen tension independent of the pyridine nucleotide redox state.

Abstract: 2-Nitroimidazoles, such as pimonidazole, are reduced in cells with low oxygen tension and are, therefore, used as hypoxia markers. However, the effect of the pyridine nucleotide redox state on pimonidazole reduction is not known. Therefore, livers from fed or fasted rats were perfused with oxygen-saturated buffer containing pimonidazole (400 microM) in the presence and absence of an inhibitor of the mitochondrial respiratory chain, potassium cyanide; these treatments were used to modulate the mitochondrial and cytosolic pyridine nucleotide redox states. Pimonidazole-induced increases in oxygen uptake over basal values were as follows: fed, 15.1 +/- 2.4; fasted, 4.2 +/- 0.8; fed + KCN, 32.1 +/- 0.9; fasted + KCN, 0.2 +/- 0.2 micromol x g(-1) x h(-1). However, if NADPH was added in excess, microsomal oxygen uptake due to oxidative metabolism of pimonidazole was independent of treatment. These results indicate that pimonidazole-stimulated O2 uptake, due predominantly to N-oxidation and glucuronidation, is dependent on the NADPH redox state. In contrast, reduced pimonidazole adducts, detected immunochemically, accumulated in pericentral regions in liver. Increasing the NADH redox state by inhibiting the mitochondrial respiratory chain with KCN decreased protein-bound pimonidazole adducts. Concomitantly, the average O2 tension of the liver was increased at least 30%. However, KCN had no effect on total pimonidazole adducts detected by ELISA, although both cytosolic (lactate/pyruvate) and mitochondrial (3-hydroxybutyrate/acetoacetate) NADH redox states were elevated by at least a factor of eight. These results indicate that, unlike oxidative metabolism, the pyridine nucleotide redox state does not determine the rate of reductive metabolism of pimonidazole. Instead, the cellular oxygen tension regulates this process. Therefore, even in cases where the supply of reducing equivalents is increased (e.g., ethanol metabolism), accumulation of the reduced bound product of pimonidazole is oxygen dependent in liver.