THE CHEMISTRY OF. .. Antioxidants

Other Important Radical Reactions 487 THE CHEMISTRY OF... Antioxidants 489 THE CHEMISTRY OF... Ozone Depletion and Chlorofluorocarbons (CFCs) 490... 

In this conversion, one molecule of j8-carotene yields two of vitamin A a- and y-carotene give only one. Vitamin A is important not only in vision but in many other ways as well. For example, young animals whose diets are deficient in vitamin A fail to grow. Vitamin A, jS-carotene, and vitamin E ( The Chemistry of... Antioxidants, Section 10.12) are also important lipid-soluble antioxidants. 

The chemistry of antioxidant activity of nitrite is complex and not completely understood. Although much of the literature evidence for this activity is based on the notoriously imreliable TBA test (see Chapter 5), there is more specific evidence based on GC volatile analyses indicating significant reduction of hexanal and other decomposition products of polyunsaturated fatty acids. A number of mechanisms have been suggested for the antioxidant activity of nitrite it inhibits heme-catalysed lipid oxidation by forming a complex with the iron porphyrins, stabilizes the polyunsaturated lipids in membranes, chelates catalytic metals, forms inactive complexes with nonheme iron and copper, or low molecular weight iron fractions, produces... 

Kamal-Eldin, A. Appelqvist, L. A. The chemistry and antioxidant properties of tocopher-ols and tocotrienols. Lipids 1996, 31, 671-701. 

A few other successful 13C 1-NMR determinations should be mentioned. Hunt et al. [28] used 13C NMR to characterise fractions of extracted analytes of PAG and sorbitan ester samples and identified Irganox 1010. H and 13C NMR have been used to identify the main organic components of a breathable diaper back-sheet as LLDPE and pentaerythritol tetra-octyl ester (PETO) [233]. The equally present AOs Irganox 1010 and Irgafos 168 were not detected without extraction. Barendswaard et al. [234] have reported fully assigned 13C solution spectra of these two antioxidants. Chimas-sorb 944 in a polyamide matrix can be determined by H or 13C 1-NMR using solvents such as formic acid, trifluoroacetic acid or trifluoroethanol [235], Both H and 13C NMR have been used to follow the chemistry of a bis-phenoxidemethylaluminum complex (reaction product of BHT and trimethylaluminum) by exposure in air. Pierre and van Bree [216] also used 13C NMR to... 

Prior RL, Wu X, Schaich K. Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements. Journal of Agricultural and Food Chemistry. 2005 53(10) 4290-4302. 

Radicals control the chemistry of the upper atmosphere, where they contribute to the formation and decomposition of ozone. Radicals also play a role in our daily lives, sometimes a destructive one. They are responsible for the rancidity of foods and the degradation of plastics in sunlight. Damage from radicals can be delayed by an additive called an antioxidant, which reacts rapidly with radicals before the radicals have a chance to do their damage. It is believed that human aging is partly due to the action of radicals, and antioxidants such as vitamins C and E may delay the process (see Box 2.1). 

M. Namiki, Chemistry of Maillard reactions recent studies on the browning reaction mechanism and the development of antioxidants and mutagens, Adv. Food Res., 1988,38, 115-183. 

Some sulfated galactans, or products of their partial depolymerization, exhibit antioxidant activity.684,685 The chemistry of radical scavenging effects is not very clear, especially taking into account the fact that several products of chemical modifications of natural polysaccharides, such as oversulfated, phosphorylated, acety-lated and phthaloylated derivatives, may demonstrate stronger antioxidant activity than the raw material.685-688... 

Kamal-Eldin A and Appelqvist LA (1996) The chemistry and antioxidant properties of tocopherois and tocotrienois. Lipids 31,671-701. 

Attachment of B ansformation Products of Stabilizers. Up-to-date knowledge dealing with the chemistry of transformation products of phenolic [6, 15, 17, 20] and aromatic aminic [16, 43, 230] antioxidants and photoantioxidants based on hindered piperidines [10] indicates the possibility of attaching compounds having structures of quinone imine or quinone methide, or of radical species like cyclohexadienonyl, phenoxyl, aminyl or nitroxide to polymeric backbones. These reactions proceed mostly via reactivity of macroalkyl radicals derived fi-om stabilized polymers. Various compounds modelling this reactivity have been isolated [19, 230]. These results are of importance mainly for the explanation of mechanisms of antioxidant activity [6, 22, 24]. 

The fundamental aspects of structure-reactivity relationships in radiation-induced oxidation of substituted benzenes, bimolecular free electron transfer on the femtosecond time scale, the chemistry of sulfur-centered radicals and the radiolysis of metalloproteins are discussed in succeeding chapters. The effects of the direct and indirect mechanisms of radiation-induced DNA damage are discussed individually in two complementary chapters. The last chapter highlights the application of radiation chemical techniques to antioxidant research. 

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