Superoxide anion radical formation

Treatment with the cells with the redox cycler paraquat, as expected, increased superoxide radical anion formation significantly. Incubation with CML or CasCML resulted in a major decrease of MitoSOX-fluorescent cells in HEK-FL and Caco-2, with CML causing the more explicit effects. Since mitochondrial superoxide anion radical formation in HEK-DC... 

Although this mechanism could explain the inertness of di-t-butyl sulphide towards oxidation due to the absence of a-hydrogen atoms, it was later ruled out by Tezuka and coworkers They found that diphenyl sulphoxide was also formed when diphenyl sulphide was photolyzed in the presence of oxygen in methylene chloride or in benzene as a solvent. This implies that a-hydrogen is not necessary for the formation of the sulphoxide. It was proposed that a possible reactive intermediate arising from the excited complex 64 would be either a singlet oxygen, a pair of superoxide anion radical and the cation radical of sulphide 68 or zwitterionic and/or biradical species such as 69 or 70 (equation 35). 

The elementary reaction step, which involves the formation of singlet oxygen, is a reaction of superoxide anion radicals CO ), which are the reaction intermediates of the above oxidation when performed in an alkaline medium. In the presence of water they may be converted to hydrogen peroxyl radicals HOO as follows ... 

W.H. Orme-Johnson and H. Beinert, Formation of the superoxide anion radical during the reaction of reduced iron-sulfur proteins with oxygen. Biochem. Biophys. Res. Commun. 36, 905-911 (1969). 

In this classical Haber-Weiss cycle iron is being reduced by superoxide anion radical (02T), ascorbic acid or glutathione and subsequently decomposes hydrogen peroxide - formed by spontaneous dismutation of 02T - in the Fenton reaction to produce 0H. This iron-driven 0H formation has a stringent requirement for an available iron coordination site, a sine qua non met not only by hexaaquoiron(III) but by most iron chelates (28). Thus, Fe-EDTA, -EGTA, and -ATP retain a reactive coordination site and catalyze the Haber-Weiss cycle. Phytic acid, however, occupies all available iron coordination sites and consequently fails to support 0H generation (Figure 6). 

Our radiolysis studies also indicate that phosphonates react quite slowly with the superoxide anion radical. Although our studies do not support the formation of radical cations as an initial oxidation step, we cannot rule out the possibility that radical cations are not involved in the oxidation of the C—P bond, as previously proposed [44], It is also possible that more electron-rich organphosphorus compounds or organophosphorus compounds in the adsorbed state may exhibit different redox and hydroxyl radical chemistries than what is observed under pulse radiolysis employing homogeneous conditions. 

Figure 4.75 Formation of free radicals as reactive intermediates responsible for toxicity. The example shown is paraquat, which acquires an electron and in turn produces superoxide anion radical and hydroxyl radical. The small arrow indicates the free radical intermediate (the small dot represents the extra electron).

The reaction between hydroxide ions and ozone leads to the formation of one superoxide anion radical 02° and one hydroperoxyl radical H02°. 

The selectivity of the trap towards hydroxyl radicals was demonstrated by several control experiments using different radicals, showing that the formation of the respective hydroxylation product, 5-hydroxy-6-0-zso-propyl-y-tocopherol (57), was caused exclusively by hydroxyl radicals, but not by hydroperoxyl, alkylperoxyl, alkoxyl, nitroxyl, or superoxide anion radicals. These radicals caused the formation of spin adducts from standard nitrone-and pyrroline-based spin traps, whereas a chemical change of spin trap 56 was only observed in the case of hydroxyl radicals. This result was independent of the use of monophasic, biphasic, or micellar reaction systems in all OH radical generating test systems, the trapping product 57 was found. For quantitation, compound 57 was extracted with petrol ether, separated by adsorption onto basic alumina and subsequently oxidized in a quantitative reaction to a-tocored, the deeply red-colored 5,6-tocopheryldione, which was subsequently determined by UV spectrophotometry (Scheme 23). 

An example of free radical formation is molecular oxygen, which can accept electrons from a variety of sources to produce reactive oxygen species (ROS) such as the superoxide radical, the hydroxyl radical, and the nitric oxide radical. The superoxide anion radical is formed when one electron is taken up by one of the 2p orbitals of molecular oxygen. Certain drugs and other xenobiotics have the capacity to undergo so-called redox cycles, whereby they provide electrons to molecular oxygen and form super oxide. 

In the DV of the parasite, free heme is rapidly converted to hematin, i.e., iron II is oxidized in iron III. During this process, electrons liberated promote the formation of reactive oxygen species (ROS) such as superoxide anion radicals and hydrogen peroxide [160], ROS can cause cellular damage. Hydrogen peroxide may also be used for the peroxidative degradation of heme. In this context, the influence of H2O2 on the redox behavior of FQ and implications for antimalarial activity was questioned. 

For total utilization of oxidant ability of molecular oxygen resulting in the formation of water molecule four electrons should be accepted by the molecule. During step-by-step acceptance of electrons, superoxide anion radical (SAR, I), hydroperoxide (II), and hydroxyl radical (III) are formed in series (Figure 2). 

Polysaccharides that are mainly found in the gel are also a group of compounds that exhibit antioxidant activities. It was demonstrated that APS-1 (mainly composed b mannose glucose in ratio 18 5) was effective in scavenging superoxide anion radical (dose-dependant fashion), hydroxyl radical, suppressed conjugated diene formation from LDL oxidation induced by Cu, and exhibited a protective effect on hydrogen peroxide-induced injury in PC12 cells 64). Also Kardosova et al. (65) showed that in vitro experiments with acidic and neutral polysaccharides were able to prevent lipid peroxidation by scavenging hydroxyl radicals. 

Irradiation of the contact charge transfer complex formed between trans-stilbenes and oxygen molecules in a zeolite NaY matrix at 313 nm leads to generation of the corresponding benzaldehydes in an electron-transfer process from which stilbene cation radicals and superoxide anion radicals arise. By contrast, excitation at 254 nm induces isomerisation and phenanthrene production, but without formation of any oxygenation products. 

Because electron transfer from C02 to oxygen is very rapid, oxygenated aqueous solutions of sodium formate are used to study the superoxide anion radical and its reactions ... 

The second activity commonly referred to as the oxidase activity of CYP450 involves electron transfer from reduced CYP450 to molecular oxygen with the formation of superoxide anion radical and H2O2 (equations 1.2a and 1.2b) ... 

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