Superoxide, reactions, with

In the literature there are no quantitative studies on the kinetics and thermodynamics of stoichiometric superoxide reactions with metal centers in general, and metalloporphyrins in particular. More precisely, superoxide concentration and temperature dependent kinetic and thermodynamic measurements were never reported and consequently the rate constants, activation parameters or binding constants for this t5rpe of reactions (Scheme 15) are not known. (The catalytic rate constants for the superoxide disproportionation, i.e., dismutation, by metal complexes are known (see earlier), however in those measurements the concentration of a catalytic amount... 

Table 8. Electrogenerated superoxide reaction with malonate esters ...

Copper in trace amounts can distort the kinetics of superoxide reactions with other compounds, because it effectively catalyses the dismutation reaction [143], Complexation by edta prevents this, as well as the reduction of hydrogen peroxide. Thus, edta protects the bases of DNA against copper-mediated damage [144]. However, edta will not protect if iron is involved, since rates of reaction between this metal complex and oxygen, superoxide or hydrogen peroxide are appreciable. 

AH the peroxides are colorless and diamagnetic when pure. Traces of the superoxide in technical-grade sodium peroxide impart a yellow color. Storage containers must be sealed to prevent reaction with atmospheric carbon dioxide and water vapor. 

Preparation of pure K2O2, Rb202 and CS2O2 by this route is difficult because of the ease with which they oxidize further to the superoxides MO2. Oxidation of the metals with NO has been used but the best method is the quantitative oxidation of the metals in liquid ammonia solution (p. 78). The peroxides can be regarded as salts of the dibasic acid H2O2. Thus reaction with acids or water quantitatively liberates H2O2 ... 

Kurfuerst, M., Ghisla, S., and Hastings, J. W. (1986). Bacterial luciferase intermediates the neutral flavin semiquinone, its reaction with superoxide, and the flavin 4a-hydroxide. Method. Enzymol. 133 140-149. 

In a study directed to the analysis of the role of Fe and the generation of H2O2 in Escherichia coli (McCormick et al. 1998), hydroxyl radicals were specihcally trapped by reaction with ethanol to give the a-hydroxyethyl radical. This formed a stable adduct with a-(4-pyridyl-l-oxide)-iV-t-butyl nitroxide that was not formed either by superoxide or hydroxyl radicals. The role of redox-reactive iron is to use EPR to analyze the EPR-detectable ascorbyl radicals. 

Shimizu, N., Kobayashi, K. and Hayashi, K. (1984). The reaction of superoxide radical with catalase. J. Biol. Chem. 259, 4414-4418. 

We also explored the direct conversion of S-b-tBM to S-b-MA.K. Hydrolysis under basic conditions (KOH in refluxing aqueous THF) was again resulted in unchanged S-b-tBM. The reaction with potassium trimethylsilanolate for 1 hr in refluxing toluene gave very little reaction. Only 10% of the expected amount of potassium was found by ICP, and the NMR and IR spectra were little changed from those of the starting copolymer. This difference in reactivity between S-b-MM and S-b-tBM parallels that observed for the reaction of alkyl methacrylate blocks with potassium superoxide (7-10). 

Fig. 1 Schematic mechanism for the long-distance oxidation of DNA. Irradiation of the anthraquinone (AQ) and intersystem crossing (ISC) forms the triplet excited state (AQ 3), which is the species that accepts an electron from a DNA base (B) and leads to products. Electron transfer to the singlet excited state of the anthraquinone (AQ 1) leads only to back electron transfer. The anthraquinone radical anion (AQ ) formed in the electron transfer reaction is consumed by reaction with oxygen, which is reduced to superoxide. This process leaves a base radical cation (B+-, a hole ) in the DNA with no partner for annihilation, which provides time for it to hop through the DNA until it is trapped by water (usually at a GG step) to form a product, 7,8-dihydro-8-oxoguanine (8-OxoG)...

D. Cocco, L. Calabrese, A. Rigo, F. Marmocchi, and G. Rotitlio, Preparation of selectively metal-free and metal-substituted derivatives by reaction of Cu-Zn superoxide dismutase with diethyldithiocar-bamate. Biochem. J. 199, 675-680 (1981). 

A number of binuclear iron complexes have also been isolated (with a neutral base attached to each metal in an axial position). The iron complexes undergo net two-electron redox reactions with dioxygen to yield products containing two identical low-spin Fe(n) metal sites superoxide or peroxide are simultaneously generated. Remarkably, the reaction can be partially reversed by removal of 02 from the system by, for example, flushing with N2 in a mixed aqueous solvent at 0°C. 

Other cationic surfactants such as TTAB, DTAB, DODAB, STAC, CEDAB, and DDDAB have been used in CL reactions with less frequency. Thus, tetradecyltrimethylammonium bromide [TTAB] has been used to increase the sensitivity of the method to determine Fe(II) and total Fe based on the catalytic action of Fe(II) in the oxidation of luminol with hydrogen peroxide in an alkaline medium [47], While other surfactants such as HTAB, hexadecylpiridinium bromide (HPB), Brij-35, and SDS do not enhance the CL intensity, TTAB shows a maximum enhancement at a concentration of 2.7 X 10 2 M (Fig. 11). At the same time it was found that the catalytic effect of Fe(II) is extremely efficient in the presence of citric acid. With regard to the mechanism of the reaction, it is thought that Fe(II) forms an anionic complex with citric acid, being later concentrated on the surface of the TTAB cationic micelle. The complex reacts with the hydrogen peroxide to form hydroxy radical or superoxide ion on the... 

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