Superoxide-peroxide

Super-leitfahigkeit, /. superconductivity, -oxyd, n. superoxide (peroxide), -oxyd-bleiche, /. peroxide bleach, superoxydecht, a. fast to peroxide. Super-oxydhydrat, n. hydrated peroxide, -phosphatschlempe, /. a fertilizer made by incorporating superphosphate with molasses residue. 

Byezkowski, J.Z. and Gessner, T. (1987). Asbestos-catalysed oxidation of benzo(a)pyrene by superoxide-peroxidized microsomes. Bull. Environ. Contam. Toxicol. 39, 312-317. 

Oxygen Structural atom of water and most organic molecules in biological systems required for respiration by most organisms. Induces convulsions at high Pojl very toxic as ozone, superoxide, peroxide, and hydroxyl radicals/ ... 

Oxidases catalyze electron transfer to dioxygen, which is reduced to superoxide, peroxide or water.1225-1226 The best characterized example of an oxidase is cytochrome oxidase, the last member of the respiratory chain, which catalyzes the four-electron reduction of dioxygen to water. 

As a first example of the use of reaction mechanism graphs, consider the electrochemistry of molten carbonate fuel cell (MCFC) cathodes. These cathodes are typically nickel-oxide porous electrodes with pores partially filled with a molten carbonate electrolyte. Oxygen and carbon dioxide are fed into the cathode through the vacant portions of the pores. The overall cathodic reaction is 02 + 2C02 + 4e / 2C03=. This overall reaction can be achieved through a number of reaction mechanisms two such mechanisms are the peroxide mechanism and the superoxide-peroxide mechanism, and these are considered next. 

As reaction mechanisms become more complicated, the need for effective graphical depictions increases. To illustrate this, let us consider the superoxide-peroxide mechanism of Adanuvor, White and Appleby (1990).25 The overall reaction for this mechanism is the same as in the previous cases 02 + 2C02 + 4e 2C03. This mechanism consists of seven steps, three of which appear to be the same as in the peroxide mechanism ... 

Figure 5. Superoxide-peroxide reaction mechanism graph notation and symbols as in Figure 4.

Figure 7. Reaction route graphs for the peroxide and superoxide-peroxide mechanisms reaction steps occur on directed edges nodes n, represent the component potentials, the difference between these potentials for adjacent nodes is the affinity of the associated reaction step and terminal nodes are open, intermediate nodes, closed.

Figure 8. Equivalent component-potential reaction route graph for the peroxide and superoxide-peroxide mechanisms.

The reaction route graphs, however, do have certain limitations. It is not in general possible, for example, to depict the physical location of the various reactions and species. It is not easy to distinguish on reaction route graphs that the peroxide ions, which must move across the electrolyte in the peroxide mechanism, exist only on the phase interfaces (gas-electrolyte and electrolyte-solid) in the superoxide-peroxide mechanism. This depiction is one of the strong points for reaction mechanism graphs. 

P-450 is also able to catalyse reductive reactions. Thus if the enzyme becomes activated in the absence of substrate it can react as an oxidase, reducing oxygen to superoxide, peroxide and water. Whether such an uncoupled reaction can occur in vivo, however, is not clear [219], At low concentrations of oxygen, P-450 can act as a reductase. Thus it is able to initiate lipid peroxidation either directly via reduction of lipid hydroperoxides or via reducing CCI4 to CHCI3 [217],... 

It should be noted that when the 0-0 bond is broken, the O2 molecule bound at Fe + receives four electron equivalents and yields a water molecule and an oxide on Fe +, at least, formally. The stable oxygenated form and the unstable peroxide intermediate provide the four-electron reduction of O2 at once. As is well known, if an O2 molecule receives four electrons one at a time, three active oxygen species, superoxide, peroxide, and hydroxyl radical, will be produced during the O2 reduction. Cytochrome c oxidase must reduce O2 totally without releasing these species, which are extremely toxic to the cell. The four-electron reduction of this enzyme may be the strategy of this enzyme for safe O2 reduction (without damaging cells). 

Very ionic compounds are formed with halides, oxides and many complex ions. The heavier elements form superoxides, peroxides and some sub-oxides. Alkalides (containing M- ions) and electrides can be made. 

Induces convulsions at high Po, very toxic as ozone, superoxide, peroxide, and hydroxyl radicals/... 

Note that one oxygen atom is bound to the heme iron and one oxygen atom is associated with Cub. This reaction is a rapid four-electron reduction of O2, bypassing any formation of toxic reactive oxygen species (superoxide, peroxide, hydroxide radical) (see Babcock ). Even though the Fe" " =0 state and Tyr radical that are formed at the catalytic site are reactive, they are bound to the COX and are not released. Note that the formation of Pm just rearranges electrons and protons that are already present at the catalytic site and does not require any additional proton or electron input. 

The true metabolic role of HA per se (and not as mere precursor of other substances such as quinolinic acid and so on) is still awaiting a conclusive definition. However, HA toxicity seems to be related not to the compound itself, but rather to other substances, arising form its (auto)oxidation. As ever, one can speculate about the chemical nature of those species, therefore some evidence exists in favour of the profound involvement of reactive intermediates in dioxygen reduction, namely superoxide, peroxide and hydroxyl, whereas other indications suggest the participation of anthranilyl and/or HA quinoneimine in the toxicity mechanism. 

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