Free radical and radiation

Departments of Medicine and Radiology (Free Radical and Radiation Biology Graduate Program), The University of Iowa College of Medicine, and The University of Iowa Holden Comprehensive Cancer Center, Iowa City, lA 52242... 

Harman, D. (1956). Aging A theory based on free radical and radiation chemistry. /. Gerontol. 2, 298-300. 

Harmon, D., Aging A Theory Based on Free Radical and Radiation Chemistry, Toumal of Gerontology VII, 298 (1956). 

I larman, D. 2002. Aging A Hieory Based on Free Radical and Radiation Chemislry. Sci. Aging Knowl. Environ., 2002(37), cpl4—. 

Several groups have studied the copolymerization of 2-methylfuran, and 2,5-dimethylfuran with MA, Copolymerizations may be achieved under both free-radical and radiation ( Co y-source) conditions but fails under ultraviolet radiation even with photosensitizers. 

There is some indication that norbornenecarboxylic acid will also undergo equimolar copolymerization with MA, using both free-radical and radiation ( °Co) initiation.Some decarboxylation, attributed to the norbornenecarboxylic acid, occurs during both polymerizations. The composition of the copolymers is independent of the method of initiation and of the initial comonomer feeds. However, Nyitray and Hardy " claim significant selfaddition of MA may occur from copolymerization of eutectic mixtures of norbornenecarboxylic acid-MA. 

A major complication in applying radiation chemical techniques to ion-molecule reaction studies is the formation of nonionic initial species by high energy radiation. Another difficulty arises from the neutralization of ions, which may also result in the formation of free radicals and stable products. The chemical effects arising from the formation of ions and their reactions with molecules are therefore superimposed on those of the neutral species resulting from excitation and neutralization. To derive information of ion-molecule reactions, it is necessary to identify unequivocally products typical of such reactions. Progress beyond a speculative rationalization of results is possible only when concrete evidence that ionic species participate in the mechanism of product formation can be presented. This evidence is the first subject of this discussion. 

MECHANISMS OF SECONDARY REACTIONS. The primary processes involved in absorption of radiation in polymers lead to the expectation of free radical and ionic mechanisms for the secondary chemical reactions. Electron spin resonance (ESR) spectroscopy has proved extremely valuable for observation of free radical reactions in polymers, where various radicals are stabilized in the solid matrix at different temperatures. 

The fact that acid enhances grafting also indicates the possibility that ionic processes may also contribute to the present grafting mechanism. In this context, acid may be considered to be a catalyst for the cationic process especially since ionising radiation is the initiator for the reaction and both free radicals and ions are known to be species formed from interaction between molecules and such radiation. However, the ionic mechanism for grafting is favoured by anhydrous conditions, thus, in the present system, acid enhancement via the ionic pathway would not appear to be a predominant process. 

In microwave plasma destmction, organic material is channeled through a plasma detector tube where destruction is initiated by microwave radiation-producing electrons. The electrons react with the organic molecules to form free radicals and final simple reaction products such as SO2, CO2, CO, H2O, HPO3, COCI2, and Br2 [60]. In bench-scale tests, the plasma method resulted in extensive detoxification (>99% destmction) for several pesticides, including malathion, phenylmercuric acetate (PMA), and Kepone [55]. 

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