Superoxide elimination

Dias RMB, Vieira AJSC (1997) Substituent effect on superoxide elimination from peroxyl radicals of adenine and methylated derivatives. J Photochem Photobiol AChem 117 217-222 Didenko YT, Nastish DN, Pugach SP, Polovinka YA, Kvochka VI (1994) The effect of bulk solution temperature on the intensity and spectra of water sonoluminescence. Ultrasonics 32 71-76 Dillon D, Combes R, McConville M, Zeiger E (1992) Ozone is mutagenic in Salmonella. Environ Mol Mutagen 19 331-337... 

Evidence for this type of superoxide elimination exists in similar non-a-hydroxyl systems [70], with rates apparently varying across a wide range. Thus, the half-time of reaction (43) is 30 xs [71] whereas that of reaction (44) is at least three orders of magnitude longer [72]. 

The OH-adduct radicals of the pyrimidines react with oxygen at close to diffusion-controlled rates, yielding the corresponding peroxyl radicals. In basic solutions, but also in neutral solutions provided that these peroxyl radicals have a sufficiently long lifetime, the C(5)-OH,C(6)-peroxyl radicals can undergo superoxide elimination after deprotonation at N(l) [reactions (26) and (27)]... 

Details of this kind of superoxide elimination, including die determination of the p Ta value of the peroxyl radical, have been elucidated in a very similar system, glycine anhydride [43]. An isopyrimidine (see below) is formed in reaction (27). 

In acid solutions, but also in neutral solutions at high steady-state radical concentrations, the superoxide elimination becomes too slow compared with the bimolecular decay of these peroxyl radicals [reactions (28)-(31)]. This leads to a very different product distribution, as seen in Table 5. There is evidence that in their bimolecular decay peroxyl radicals can give rise to the formation of oxyl radicals which may undergo fragmentation (see, e.g., [37, 38]) [e.g., reaction (30)], leading to products with the pyrimidine cycle destroyed (e.g., l-N-formyl-5-hydroxyhydantoin. Other pyrimidine-ring cleavage reactions are conceivable but at present not supported by product data). 

When H2O2 is a necessary component of a luminescence system, it can be removed by catalase. If a luminescence system involves superoxide anion, the light emission can be quenched by destroying O2 with superoxide dismutase (SOD). The ATP cofactor usually present in the fresh extracts of the fireflies and the millipede Luminodesmus can be used up by their spontaneous luminescence reactions, eventually resulting in dark (nonluminous) extracts containing a luciferase or photoprotein. The process is, however, accompanied by a corresponding loss in the amount of luciferin or photoprotein. The use of ATPase and the elimination of Mg2+ in the extract may prevent such a loss. 

Adults require 1-2 mg of copper per day, and eliminate excess copper in bile and feces. Most plasma copper is present in ceruloplasmin. In Wilson s disease, the diminished availability of ceruloplasmin interferes with the function of enzymes that rely on ceruloplasmin as a copper donor (e.g. cytochrome oxidase, tyrosinase and superoxide dismutase). In addition, loss of copper-binding capacity in the serum leads to copper deposition in liver, brain and other organs, resulting in tissue damage. The mechanisms of toxicity are not fully understood, but may involve the formation of hydroxyl radicals via the Fenton reaction, which, in turn initiates a cascade of cellular cytotoxic events, including mitochondrial dysfunction, lipid peroxidation, disruption of calcium ion homeostasis, and cell death. 

In contrast, antioxidant enzymes can efficiently counteract all UV-induced ROS (Aguilera et al. 2002). These enzymes are represented by superoxide dismutase (SOD), catalase and glutathione peroxidase as well as those involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, mono-dehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. One of the most important classes of antioxidant enzymes is the SOD family, which eliminate noxious superoxide radical anions. Different metalloforms of SOD exist (Fe, Mn, CuZn and Ni), which due to their intracellular localisation protect different cellular proteins (Lesser and Stochaj 1990). 

Reactions of potassium superoxide solubilized in apolar solvents with crown ethers (see Oxidation reactions, p. 356) are also frequently accompanied by elimination reactions. Thus, in DMSO solution, secondary alkyl bromides only yield olefins when treated with the K02 complex of dicyclohexyl-18-crown-6 (Johnson et al., 1978). Scully and Davis (1978) have studied the elimination of HC1 from N-chloramines with 18-crown-6-solubilized K02, KOH, and KOAc in ether solution (27). High yields of aldimines were obtained with K02,... 

It is generally agreed that the CL obtained with Inminol (124) is based on the series of transformations shown in Scheme 3, where the analyte (oxidant) as such or in combination with a catalyst prodnces a free radical (125), which in him captnres a superoxide anion to yield an endoperoxide (126), which on elimination of N2 prodnces an excited intermediate (127), which finally settles down to the 3-aminophthalate ion (128) on emission of a photon. A hnear correlation may be established between the intensity of the CL emission and the concentration of the analyte. ... 

Yoshizaki, F., T. Komatsu, K. Inoue, R. Kanari, T. Ando, and S. Hisamichi. Survey of crude drugs effective in eliminating superoxides in blood plasma of mice. Int J Pharmacog 1996 34(4) 277-282. 

Product of NADPH oxidase reaction NADPH provides the reducing equivalents for phagocytes in the process of eliminating invading microorganisms. NADPH oxidase uses molecular oxygen and NADPH to produce superoxide radicals, which in turn can be converted to peroxide, hypochlorous acid, and... 

The majority of the published electrochemical studies involving hydroxides have been conducted in the NaOH-KOH eutectic (49.0-51.0 mol%, mp = 170°C). This eutectic mixture can be used at temperatures considerably below those of the individual salts pure NaOH and KOH melt at 318 and 400°C, respectively. Water, oxygen, and carbon dioxide are the major impurities in molten hydroxides. The various procedures for removing these contaminants have been summarized [34]. Water can be eliminated by passing dry inert gas over the melt when it is heated to about 450 or 500°C heating the melt to these temperatures also leads to the thermal decomposition of peroxide and superoxide contaminants [34] ... 

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