It has a crucial role in anti-inflammatory processes, inhibition of platelet aggregation, and immune enhancement (Bansal et al., 2005) Subsequently, vitamin E ([alpha]-tocopherol) is a chain-breaking antioxidant to inhibit the propagation step where the
alkyl radical reacts with molecular oxygen at a very high rate, giving a peroxyl radical.
Li, "Accurate calculation of the reaction barriers and rate constants of the pyrolysis of
alkyl radicals in the [beta]-position using the isodesmic reaction method," Acta Physico-Chimica Sinica, vol.
This has been attributed to allyl or
alkyl radicals which were formed by chain scission reactions as a result of irradiation and which act as annealable color centers, as discussed, for example, by Martinez-Morlanes et al.
Radical scavenging activity of the plasma and liver in juvenile red seabream fed the experimental diets for 10 wks (1) Diets DDG0 DDG5 DDG10 DDG15 DDG20 DDG25 Plasma DPPH radical 63.7 77.6 77.9 83.7 80.3 84.3
Alkyl radical 93.2 93.9 94.0 94.5 93.6 93.4 Liver DPPH radical 74.2 77.5 79.6 81.3 81.6 81.7
Alkyl radical 74.1 73.0 75.6 71.6 74.3 68.6 SEM p-value Plasma DPPH radical 4.82 0.250
Alkyl radical 0.46 0.092 Liver DPPH radical 1.80 0.226
Alkyl radical 3.55 0.454 DDG distillers dried grain; SEM, standard error of mean; DPPH, 1, 1- Diphenyl-2-picryl-hydrazyl.
In the first place, they combine with
alkyl radicals at the diffusion limit of reaction velocities [17].
VTEOS conversions declined in the presence of this antioxidant, since chain-breaking donors quench alkoxy and
alkyl radicals first by hydrogen atom donation, and subsequently through rapid radical termination processes [16].
The formate radical will liberate [CO.sub.2] and an
alkyl radical will result.
The loss of terminal-C=C and the high levels of crosslinking achieved indicate that
alkyl radical fragmentation ([r.sub.6]) was not a dominant reaction in the chemistry of this LLDPE resin.
Certain azo compounds such as azobisisobutyronitrile can also photolytically cleave, forming two
alkyl radicals and nitrogen gas.
This new approach exploits the regioselectivity of functionalized nitroxyls such as acryloyloxy-2,2,6,6-tetramethylpipcridinc-/V-oxyl (AOTEMPO) for trapping of
alkyl radicals by combination as opposed to C=C bond addition [19].
By using density functional theory method, the structures and electronic states of
alkyl radicals (R, [C.sub.n][H.sub.2n+1], n = 1-4) added to [C.sub.20] fullerenes were investigated [1].
Trace olefin formation on the other hand may be attributed to the cleavage of
alkyl radicals at the adjacent C H bonds [20].
The following reaction at a propagation stage proceeds much slower--alkyl peroxy radicals take hydrogen from hydrocarbons and form alkyl hydro peroxides (ROOH) and new
alkyl radicals (Rx):
Crosslinking of chains result from the combination of secondary
alkyl radicals, whereas chain scission or molecular weight loss is generally attributed to the fragmentation of tertiary
alkyl radicals (1), (2).
