Scavenging mechanisms

The hterature suggests that more than one mechanism may be operative for a given antiozonant, and that different mechanisms may be appHcable to different types of antiozonants. All of the evidence, however, indicates that the scavenger mechanism is the most important. All antiozonants react with ozone at a much higher rate than does the mbber which they protect. The extremely high reactivity with ozone of/)-phenylenediamines, compared to other amines, is best explained by their unique abiUty to react ftee-tadicaHy. The chemistry of ozone—/)-PDA reactions is known in some detail (30,31). The first step is beheved to be the formation of an ozone—/)-PDA adduct (32), or in some cases a radical ion. Pour competing fates for dissociation of the initial adduct have been described amine oxide formation, side-chain oxidation, nitroxide radical formation, and amino radical formation. 

Chemical antiozonants have been developed to protect rubber against ozone under such dynamic conditions. Several mechanisms have been proposed to explain how chemical antiozonants protect rubber. The scavenging mechanism, the protective film mechanism, or a combination of both are nowadays the most accepted mechanisms. 

The scavenging mechanism states that antiozonants function by migrating towards the surface of the rubber and, due to their exceptional reactivity towards ozone, scavenge the ozone before it can react with the rubber [60]. The scavenging mechanism is based on the fact that all antiozonants react much more rapidly with ozone than do the double bonds of the rubber molecules. This fact distinguishes antiozonants from antioxidants. 

Ruhlin, D.E. and Owen, R.M. (1986) The rare earth element geochemistry of hydrothermal sediments from the East Pacific Rise Examination of a seawater scavenging mechanism. Geochim. Cosmochim. Acta, 50, 393-400. 

Ahnfelt-Ronne, 1., Nielsen, O.H., Christensen, A., Langholz, E., Binder, V. and Riis, P. (1990). Clinical evidence supporting the radical scavenger mechanism of 5-aminosalicylic acid. Gastroenterology 98, 1162-1169. 

It is amply clear from the foregoing discussion that several of the naturally produced and artificially injected radionuclides are removed from sea water to sediments on short time scales, but the questions of their removal sites and principal scavenging mechanism are still wide open. It is likely that a systematic study of the interrelation of particulate phase activities with various components and properties of suspended solids in the ocean may help resolve some of these questions. 

Leuenberger C, Ligocki MP, Pankow JF. 1985. Trace organic compounds in rain. 4. Identities, concentrations and scavenging mechanisms for phenols in urban air and rain. Environ Sci Technol... 

Radionuclides with half-lives of minutes to hours would be useful in studying atmospheric precipitation scavenging mechanisms since their half-lives are of the same order of magnitude as the time scale on which... 

Flavonoids have the ability to act as antioxidants by a free radical scavenging mechanism with the formation of less reactive flavonoid phenoxyl radicals [Eq. (1) and (2)]. On the other hand, through then-known chelating ability these compounds may inactivate transition metals ions (iron, copper), thereby suppressing the superoxide-driven Fenton Reaction, Eqs. (3) and (4), which is currently believed to be the most important route to activate oxygen species [51]. 

Waychunas, G.A., Kim, C.S. and Banfield, J.F. (2005) Nanoparticulate iron oxide minerals in soils and sediments unique properties and contaminant scavenging mechanisms. Journal of Nanoparticle Research, 7(4-5), 409-33. 

Increasing evidence indicates that diet/nutrition plays an important role in modulating the action and/or metabolism of a number of chemicals, drugs and environmental pollutants. Nutrients are essential for all fundamental cellular processes. The nutritional status of the affected subject may, therefore, influence cellular susceptibility to the effect of xenobiotics, including those from cigarette smoke. While the precise role of vitamin E in cellular metabolism is not yet clear, the vitamin may protect essential cellular components from the adverse effects of xenobiotics either via a free radical scavenging mechanism or as a component of the cell membrane (10-11). Administration of vitamin E has been shown to lessen the toxicity of a variety of compounds (12-16). 

Afanas ev, I.B., Dorozhko, A.I., Brodskii, A.V., Kostyuk, V.A., and Potapovitch, A.1.1989. Chelating and free radical scavenging mechanisms of inhibitory action of rutin and quercetin in lipid peroxidation. Biochem. Pharmacol. 38, 1763-1769. 

It is not known how much of the oxygen consumption of the cell is turned over to generating reactive oxygen species, but the figure is thought to be between 2% (Chance et al. 1979) and 0.2% (St-Pierre et al. 2002 Staniek and Nohl 2000). The cell has very efficient scavenging mechanisms, and so these figures may be underestimates. 

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