Participation of superoxide free radical and Mn2+ in sulfite oxidation

Degradation of an Organic Dye by Bisulfite Catalytically Activated with Iron Manganese Oxides: The Role of Superoxide Radicals

Metal-activated bisulfite systems have been widely used to treat recalcitrant wastewater. However, due to the disadvantages of their narrow effective pH range and difficulty in recovering metal ions, homogeneous systems are severely limited in practical applications. To overcome these problems, Fe/Mn bimetallic catalysts with different molar ratios were prepared using a simple sol-gel method to activate bisulfite. Influential factors, such as catalyst and system types, catalyst dosage, bisulfite concentration, pH value, and bisulfite addition modes, were investigated. The new system exhibited a wide effective pH range and high degradation efficiency, and it was found that the dissolved oxygen content played an important role in the activation system. The radical quenching test showed that a superoxide radical (O2 •-), instead of a hydroxyl radical (HO•) or a sulfate radical (SO4 •-), was the main oxide species for the degradation of rhodamine B (RhB).

DNA damage induced by sulfite autoxidation catalyzed by copper(ii) tetraglycine complexes

Copper(II)/(III) tetraglycine complexes were investigated for their ability to catalyze the autoxidation of sulfite resulting in oxidative DNA damage. The focus of this work is on DNA damage by Cu(III) and oxysulfur radicals formed by the oxidation of S(IV) oxides by dissolved oxygen in the presence of Cu(II) tetraglycine complexes. The results suggest that sulfite is rapidly oxidized by oxygen in the presence of Cu(II) complexes producing Cu(III) tetraglycine, which can be monitored spectrophotometrically at 365 nm. A synergistic effect of Cu(II) with a second metal ion (Ni(II), Co(II) or Mn(II) traces) was observed.

Xanthine oxidase/hydrogen peroxide generates sulfur trioxide anion radical (SO3.-) from sulfite (SO3(2-))

In the presence of hydrogen peroxide (H2O2), xanthine oxidase has been found to catalyze sulfur trioxide anion radical (SO3.-) formation from sulfite anion (SO3(2-)). The SO3.- radical was identified by ESR (electron spin resonance) spin trapping, utilizing 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) as the spin trap. Inactivated xanthine oxidase does not catalyze SO3.- radical formation, implying a specific role for this enzyme. The initial rate of SO3.- radical formation increases linearly with xanthine oxidase concentration. Together, these observations indicate that the SO3.- generation occurs enzymatically. These results suggest a new property of xanthine oxidase and perhaps also a significant step in the mechanism of sulfite toxicity in cellular systems.

Sulfate anion free radical formation by the peroxidation of (Bi)sulfite and its reaction with hydroxyl radical scavengers

The one-electron oxidation of (bi)sulfite is catalyzed by peroxidases to yield the sulfur trioxide radical anion (SO3-), a predominantly sulfur-centered radical as shown by studies with 33S-labeled (bi)sulfite. This radical reacts with molecular oxygen to form a peroxyl radical. The subsequent reaction of this peroxyl radical with (bi)sulfite has been proposed to form the sulfate anion radical, which is nearly as strong an oxidant as the hydroxyl radical. We used the spin trapping electron spin resonance technique to provide for the first time direct evidence for sulfate anion radical formation during (bi)sulfite peroxidation. The sulfate anion radical is known to react with many compounds more commonly thought of as hydroxyl radical scavengers such as formate and ethanol. Free radicals derived from these scavengers are trapped in systems where (bi)sulfite peroxidation has been inhibited by these scavengers.

Free-radical chemistry of sulfite

The free-radical chemistry of sulfite oxidation is reviewed. Chemical transformations of organic and biological molecules induced by sulfite oxidation are summarized. The kinetics of the free-radical oxidations of sulfite are discussed, as are the kinetics of the reactions of the sulfite-derived radicals SO3 and the peroxy derivative SO5 with organic compounds.

Air pollutant sulfur dioxide-induced alterations on the levels of lipids, lipid peroxidation and lipase activity in various regions of the rat brain

The exposure of rats to SO2 (10 p.p.m.) for one hour daily for 30 days caused depletion of total lipids in all brain areas. The contents of phospholipid were elevated in cerebellum and brain stem, but were depleted in cerebral hemisphere. Cholesterol levels showed an increase in various brain regions. On the other hand, gangliosides were increased in cerebellum and brain stem, but were decreased in cerebral hemisphere. Interestingly, cholesterol/phospholipid ratio was increased in different regions of the brain. Lipase activity was elevated in cerebral hemisphere. Lipid peroxidation showed marked increment in whole brain and in all the brain areas studied. The results suggest that SO2-exposure induces degradation of lipids. Interestingly, the lipid contents are affected differentially in the various parts of the brain.