Free Radicals and Oxygen

Free radical species are inherently unstable by virtue of their single unpaired electron, thus tending to be highly reactive and transient, usually existing only at very low steady state concentrations (1 nM-100 pM). The single electron product of molecular oxygen, the superoxide anion radical (O ) is one of the more stable radical species. 

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Methionine is the major precursor in the biochemical pathway to ethylene (9). Ethylene is formed from carbons 3 and 4 of methionine which is degraded in reactions possibly involving free radicals and oxygen (9). Recently Adams and Yang (10,11) identified S-adenosylmethionine (SAM) and 1-aminocyclopropane-l-carboxylic acid (ACC) as intermediates in the pathway from methionine to ethylene. The sequence of reactions in the pathway... 

As one might expect, a different picture emerges for the thermooxidative stability as reflected in the results of TO and ITG tests performed in air. The participation of oxygen in the overall degradation process leads to the intermediacy of imidazole free radicals and oxygenated free radicals with concomitant chain scission and the net result is a rather catastrophic weight loss observed as the test temperature approaches the 450-500 C level. The representative TG thermograms of Hg. 7, obtained in air, Dlustrate this trend... 

K.B. Patel, R.L. Willson (1973). Semiquinone free radicals and oxygen. Pulse radiolysis study of one electron transfer equilibria. J. Chem. Soc., Faraday Trans. 1, 69, 814-825. 

The process of polymer degradation is always accompanied by a parallel competitive process of crosslinking which results in the formation of a microgel. The crosslinking depends on numerous factors such as the structure of the macro-radicals, the cage effect, the presence of various free radicals and oxygen, and the concentration of the polymers in solution. 

Free radicals (R, ROO% etc.) can be defined as any chemical species having one or more unpaired electrons, a wide definition that covers hydrogen atoms, transitions metals, the oxygen molecule itself, etc. One of the major areas in which carbon free radicals and oxygen free radicals are involved is lipid oxidation that determines the quality and shelf life of foods. Oxidative rancidity leads to the production of spoiled off-flavor products and is commonly associated with the organoleptic appraisal of food products. ... 

Bodwell W. Ischemia, reperfusion and reperfiision injury Role of oxygen free radicals and oxygen free radical scavengers. J Cardiovasc Nurs 1989 4 25-32. 

When benzene is oxidized by Fenton s reagent in the presence of air or oxygen, the only detectable organic product is phenol (that is, equation 76) whereas in the absence of air both phenol and diphenyl are produced (31). This oxygen effect may be due to the interaction of free phenyl radicals with oxygen, forming free radical peroxides, and ultimately phenol, in the presence of ferrous ion. The reaction between free radical and oxygen therefore appears to be faster than the dimerization of the free radical (31). 

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