Free radicals formation with carbonyl

Heat catalyzes free radical formation in cellulose. Aldehydes form from C2 and C3 hydroxyls. Aldehydes oxidize to carboxyls, and with dehydration, carbon monoxide (CO) and carbon dioxide (C02) form as well as conjugated carbonyl-ethylenic chromophoric groups that selectively absorb blue light and impart yellowness (35). During the induction stage of cellulose oxidation, yellowness may increase steadily with selective carbonyl and ethylene group formation. By artificially aging... 

Benzophenone is a common photosensitiser. Free radical formation by hydrogen abstraction from solvent leads to use in UV-curing applications such as inks, imaging, and clear coatings in the printing industry. By way of contrast, hydroxy benzophenones with the OH group adjacent to the carbonyl are useful photostable UV absorbers because reversible proton transfer is an efficient deactivation route leading to very short lived excited-states. 

In this process, the organic halide is split into an ion and a radical fragment. Free-radical formation by oxidation of molybdenum carbonyl with carbon tetrachloride and carbon tetrabromide has been studied in detail [6]. The overall reaction may be represented as follows ... 

The photooxidation mechanism occurs via free radical mechanism with formation of polymer peroxy and alkoxy radicals and hydroperoxide and carbonyl groups. Formation of these groups was confirmed from IR spectra. 

Upon photolysis of polypropylene hydroperoxide (PP—OOH) a major absorption at 1726 and 1718 cm has been observed in the IR spectrum, which is attributed to the carbonyl groups. Sometimes the macroradical having free radical site reacts with a neighboring newly born hydroperoxide causing the formation of a macroalkoxy radical [116]. 

In earlier studies the in vitro transition metal-catalyzed oxidation of proteins and the interaction of proteins with free radicals have been studied. In 1983, Levine [1] showed that the oxidative inactivation of enzymes and the oxidative modification of proteins resulted in the formation of protein carbonyl derivatives. These derivatives easily react with dinitrophenyl-hydrazine (DNPH) to form protein hydrazones, which were used for the detection of protein carbonyl content. Using this method and spin-trapping with PBN, it has been demonstrated [2,3] that protein oxidation and inactivation of glutamine synthetase (a key enzyme in the regulation of amino acid metabolism and the brain L-glutamate and y-aminobutyric acid levels) were sharply enhanced during ischemia- and reperfusion-induced injury in gerbil brain. 

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