A-Oxy radicals

Figure 4.14 Diagrammatic representation of (a) oxy-radical>mediated S-thioiation and (b) thiol/disulphide-initiated S-thiolation of protein suiphydryl groups. Under both circumstances mixed disuiphides are formed between glutathione and protein thiois iocated on the ion-translocator protein resulting in an alteration of protein structure and function. Both of these mechanisms are completely reversible by the addition of a suitabie reducing agent, such as reduced glutathione, returning the protein to its native form.

In addition to alkyl radicals, other nucleophilic radicals can participate in tin hydride mediated addition reactions (Scheme 31). Phenyl radicals are highly reactive112 but give only modest yields of addition products113 and one suspects that vinyl radicals should behave similarly.114 a-Oxy radicals have been... 

Wunderlich [2] and Nesvadba [3] prepared long alkyl chain 2,2,6,6 tetraalk-ylpiperidine-A -oxy radicals and A-alkoxy derivatives, (11), and (III), respectively, that were effective as polymerization regulators. 

Pryor, W.A. Oxy-radical and related species Their formation, their lifetimes, and their reactions Ann. Rev. Physiol. 48 (1986) 657-667. 

At higher temperature and lower HBr concentrations these two radicals may interconvert to give non-stereospecific products. Cyclopropyl, a-oxy radicals, and vinyl radicals tend to retain configuration and this leads to stereospecificity or stereoselectivity in many of their reactions at sufficiently low temperatures. Reactions of radicals can be very stereoselective when an additional fused ring is formed or when there is strong steric hindrance to one face of a planar radical center. In... 

The mechanism of free radical polymerization of ethylene is outlined m Figure 6 17 Dissociation of a peroxide initiates the process m step 1 The resulting per oxy radical adds to the carbon-carbon double bond m step 2 giving a new radical which then adds to a second molecule of ethylene m step 3 The carbon-carbon bond forming process m step 3 can be repeated thousands of times to give long carbon chains... 

The radical X is formed by homolysis of the X—R bond either thermally or photolytically. In the reactions of alcohols with lead tetraacetate evidence suggests that the X—R bond (X = 0, R = Pb(OAc)3) has ionic character. In this case the oxy radical is formed by a one electron transfer (thermally or photochemically induced) from oxygen to lead. 

A general reaction mechanism for the grafting of MA onto EPM is given in Figure 13.3 [15,16]. Free-radical grafting of MA starts with the decomposition of the radical initiator, usually a peroxide [15,18]. The peroxide decomposes at elevated temperamres into the corresponding oxy radicals, which may further degrade to alkyl radicals and ketones. These oxy and alkyl radicals abstract... 

El-Agamey, A, Cantrell, A, Land, EJ, McGarvey, DJ, and Truscott, TG, 2004a. Are dietary carotenoids beneficial Reactions of carotenoids with oxy-radicals and singlet oxygen. Photochem Photobiol Sci 3, 802-811. 

Kinetic analysis of the results of ketone oxidation in the presence of amine II reveals that the velocity constant of the oxidation of amines by acyl per-oxy radicals must be greater (by a factor of 2 - 3) than that of the interaction of these radicals with the nitroxide-i. In this reaction, acyl peroxy radicals are captured and destroyed by amines. 

D Schulte-Frohlinde, R Anker, E Bothe. In M. A. J. Rogers, E. L. Powers, eds. Oxygen and Oxy-Radicals in Chemistry and Biology. New York Academic Press, 1981, p 61. 

Heating cleaves a weak 0-0 bond homolytically to give two oxy radicals. Fragmentation of the C1-C6 and C9-C14 bonds gives two radicals which recombine to give a cyclic diacyl peroxide. 

The fragment ions at m/z 149, [CgHsOs], and 167, [C8H704], are especially prominent in the El spectra of phthalates. The formation of the [CgHsOs]" ion has initially been attributed to a McLafferty rearrangement followed by loss of an alk-oxy radical and final stabilization to a cyclic oxonium ion. [104] However, it has been revealed that four other pathways in total lead to its formation excluding the above one. [105,106] The two most prominent fragmentation pathways are ... 

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