Reactions with superoxide anion

Detecting luminescence in the near-inffared region (700-900 nm) is advantageous as there is minimal absorption by other biomolecules. Thus, a near-infrared chemiluminescent probe should be important as a reporter molecule for many analytical applications. Herein, I present the synthesis and luminescence properties of chemiluminescent probes that emit the near-infrared light by reaction with superoxide anions. 

T. Odajima and I. Yamazaki, Myeloneperoxidase of the leukocyte of normal blood. 3. The reaction of ferric myeloperoxidase with superoxide anion. Biochim. Biophys. Acta. 284, 355-359 (1972). 

Lombard M, Fontecave M, Touati D, Niviere V. 2000. Reaction of the desulfoferre-doxin from Desulfovibrio baarsii with superoxide anion. Evidence for a superoxide reductase activity. J Biol Chem 275 115-21. 

In this type of spin traps, 5,5-dimethyl-l-pyrroline-Af-oxide (DMPO) deserves particular mention. DMPO is widely employed as a spin trap in the detection of transient radicals or ion-radicals in chemical and biological systems (see, e.g., Siraki et al. 2007). Characteristic ESR spectra arising from the formation of spin adducts are used for identification of specific spin species. In common opinion, such identification is unambiguous. However, in reactions with superoxide ion (Villamena et al. 2004, 2007b), carbon dioxide anion-radical (Villamena et al. 2006), or carbonate anion-radical (Villamena et al. 2007a), this spin trap gives rise to two adducts. Let us consider the case of carbonate anion-radical. The first trapped product arises from direct addition of carbonate anion-radical, second adduct arises from partial decarboxylation of the first one. Scheme 4.25 illustrates such reactions based on the example of carbonate anion-radical. 

Recently, sulfinyl and sulfonyl peroxy radical intermediates 6a and 6b have been prepared by the reactions of aryl sulfinyl or sulfonyl chloride with superoxide anion radical, respectively. These peroxy intermediates show strong oxidizing abilities in various oxidations. This chapter will describe the properties and applications of a variety of sulfur and phosphorus peroxy compounds in oxidation reactions. For a more complete picture, readers should consult the original papers cited in the areas that most interest them. 

Biotransformation pathways of nitroaromatic compounds are believed to result from nitroreductases that have the ability to use nitro as either one- or two-electron acceptors. One-electron acceptance by the nitro compounds results in the production of the nitro radical-anion. This nitro radical-anion becomes one of the most aggressive species in biological systems because of its reaction on endogenous molecules (DNA bases) and its well-known catalytic ability to transfer one electron to molecular oxygen with superoxide anion formation. 

CIII may also be formed through reactions different from those of the perox-idasic cycle described above (a) oxygenation of Fe11 porphyrin or (b) reaction of FeIU porphyrin (GS) with superoxide anion (Fig. 11.1). Rate constants for these reactions are compiled in Table 11.1. 

Shimizu N, Kobayashi K, Hayashi K (1989) Kinetics of the reaction of superoxide anion with ferric horseradish peroxidase. Biochim Biophys Acta 995 133-137... 

Kobayashi, K., Iwamoto, T., and Honda, K. (1994) Spectral intermediate in the reaction of ferrous cytochrome P450c lm with superoxide anion, Biochem. Biophys. Res. Commun. 201,1348-1355. 

Reactions of hydrogen peroxide with proteins are generally slower than those with superoxide anion. H2O2 reacts with heme proteins, producing theFe(IV)-oxo... 

However, as we will see later on, other modes of evolution of the primary intermediate radical ions can be suggested to explain some oxidation reactions mediated by electron-transfer processes. In fact, several exceptions to the Foote s BQ-controlled photooxygenation procedure have been reported during the last years on several electron-rich substrates. Thus, the involvement of superoxide ion, as an oxygen active species, in all of the DCA-sensitized photooxygenations, remains questionable [96,105,112,115,128]. Schaap and co-workers [98] recorded under inert atmosphere the characteristic ESR spectrum of the (DCA ) radical anion. On the other hand, the involvement of aryl-olefin radical cations and their reactions with superoxide ion was easily observed by quenching experiments with compounds exhibiting lower oxidation potentials than those of aryl-olefins [85, 95, 98],... 

In many papers the term "superoxide" (HOO ) is used simultaneously with "superoxide anion radicals" (Oa )- However, this is under the physiological conditions incorrect The pKa value of this acid-base equilibrium is 4.8 [227] and, therefore, there is only a very small contribution of HOO at physiological pH (7.4). Therefore, the term "superoxide anion radical" should be exclusively used. The superoxide anion radical is both, a one-electron oxidant and a one-electron reductant. The reactions of O2 with many different biological substrates were studied in detail by the radiation chemists and a summary of the obtained second order rate constants is provided in [228]. However, not a single carbohydrate is mentioned in this comprehensive survey since no reaction could have been observed [229]. 

In the presence of metals, such as iron, hydrogen peroxide reacts with superoxide anion to produce hydroxyl radicals (OH ) and singlet oxygen ( O2) by the reaction shown below ... 

Dehydroascorbic acid is an unstable 1,2-diketone, which readily reacts with superoxide anions to give a dioxetane radical anion and a dianion. This then decomposes to oxalic and threonic acid anions together with triplet oxygen molecules. Several standard reactions are also sununarized in Scheme 7,2.12. 

Despite their increasing biological importance, reactions of superoxide anion and of its acidic form, hydroperoxyl radical, with proteins, are little understood. More generally speaking, the chemical basis of biological role of superoxide is still questioned (88). 

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