Mechanism of antioxidation and

By the use of certain additives which divert or moderate the degradation reaction. A wide range of antioxidants and stabilisers function by this mechanism (see Chapter 7). 

The use of antioxidants has already been generally described in Chapter 7. The mechanism of oxidation and the effect of antioxidants are altered by the sulphide cross-links and other structures present in the vulcanisate. There are indeed grounds for arguing that a correct choice of curing system is more important than the decision whether or not to incorporate an antioxidant. 

BONDET v, BRAND-wiLLiAMS w and BERSET c (1997) Kiuetics and mechanisms of antioxidant activity using the DPPH- free radical method, Lebensm Wiss Technol, 30, 609-15. 

In summary, therefore, the evidence seems convincing that exercise modifies circulating and tissue concentrations of antioxidants and enzyme activities. It is much less certain that the fatigue or damage to skeletal muscle associated with various forms of excessive or unaccustomed exercise is initiated by free radical-mediated degradation. Considerably more work is required in this area to clarify the underlying pathogenic mechanisms. 

Nagaoka, S. Mukai, K. Itoh, T. Katsumata, S. Mechanism of antioxidant reaction of vitamin E. 2. Photoelectron spectroscopy and ab initio calculation. J. Phys. Chem. 1992, 96, 8184-8187. 

Scheme II.1 Mechanism of antioxidant action. After Grassie and Scott [1]. From N. Grassie and G. Scott, Polymer Degradation and Stabilisation, Cambridge University Press, Cambridge (1988). Reproduced by permission of Cambridge University Press...

Edge, R and TG Truscott. 1997. Prooxidant and antioxidant reaction mechanisms of carotene and radical interactions with vitamins E and C. Nutrition 13(ll/12) 992-994. 

Rottkamp CA, Nunomura A, Hirai K, Sayre LM, Perry G and Smith MA (2000). Will antioxidants fulfill their expectations for the treatment of Alzheimer disease Mechanisms of Ageing and Development, 116, 169-179. 

It was in 1924 when Christiansen [3] put forward the conception of the chain mechanism of oxidation and explained the action of antioxidants via chain termination by the antioxidant [3]. Three years later, Backstrom and coworkers [4—6] experimentally proved the chain mechanism of benzaldehyde oxidation (see Chapter 1) and the mechanism of antioxidant (hydroquinone) action via chain termination. The systematic study of the oxidation kinetics of esters of nonsaturated acids was performed by Bolland and ten Have [7,8], They observed in the kinetic experiments that substrates are oxidized by the chain mechanism with chain propagation via the cycle of reactions (see Chapter 2). 

The mechanism of antioxidant action on the oxidation of carbon-chain polymers is practically the same as that of hydrocarbon oxidation (see Chapters 14 and 15 and monographs [29 10]). The peculiarities lie in the specificity of diffusion and the cage effect in polymers. As described earlier, the reaction of peroxyl radicals with phenol occurs more slowly in the polymer matrix than in the liquid phase. This is due to the influence of the polymeric rigid cage on a bimolecular reaction (see earlier). The values of rate constants of macromolecular peroxyl radicals with phenols are collected in Table 19.7. 

In 1989, we showed [142] that the Fe2+(rutin)2 complex is a more effective inhibitor than rutin of asbestos-induced erythrocyte hemolysis and asbestos-stimulated oxygen radical production by rat peritoneal macrophages. Later on, to evaluate the mechanisms of antioxidant activities of iron rutin and copper-rutin complexes, we compared the effects of these complexes on iron-dependent liposomal and microsomal lipid peroxidation [165], It was found that the iron rutin complex was by two to three times a more efficient inhibitor of liposomal peroxidation than the copper-rutin complex, while the opposite tendency was observed in NADPH-dependent microsomal peroxidation. On the other hand, the copper rutin complex was much more effective than the iron rutin complex in the suppression of microsomal superoxide production, indicating that the copper rutin complex indeed acquired additional SOD-dismuting activity because superoxide is an initiator of NADPH-dependent... 

Despite the conclusions in the cited literature about direct MT interaction with free radicals, the mechanism of MT antioxidant activity remains obscure. Markant and Pallauf [339] concluded that cysteine groups and not zinc are responsible for the inhibition of lipid peroxidation in hepatocytes. Maret and Vallee [340,341] also questioned the possibility of direct scavenging of free radicals by MT and suggested that zinc release is a major mechanism of antioxidant effects of metallothioneins. 

At present, numerous free radical studies related to many pathologies have been carried out. The amount of these studies is really enormous and many of them are too far from the scope of this book. The main topics of this chapter will be confined to the mechanism of free radical formation and oxidative processes under pathophysiological conditions. We will consider the possible role of free radicals in cardiovascular disorders, cancer, anemias, inflammation, diabetes mellitus, rheumatoid arthritis, and some other diseases. Furthermore, the possibilities of antioxidant and chelating therapies will be discussed. 

Bondet V, Brand-Williams W, Berset C. Kinetics and Mechanisms of Antioxidant Activity using the DPPH" Free Radical Method. Food Science and Technology. 1997 30, 609-615. 

Little information about the mechanism of action of flavonoids is anticipated from in vivo studies. The mechanism of catechin and morin seems to be related to an increase of the activity of detoxifying enzymes like glutathione-S-transferase and NADPH quinone reductase [198, 211]. Similarly, EGCG effect at the colonic level is associated to an increase in tissue superoxide dismutase levels, suggesting that it may act through a potentiation of the antioxidative defense [210]. 

Antioxidants for fats and oils function by interfering in the formation of the free radicals that initiate and propagate oxidation. Knowledge of the mechanism of antioxidant performance reinforces several important aspects of antioxidant usage. 

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