Synergistic Interactions between Antioxidants

The efficiency of the antioxidant will depend on the ratio of the rates of Reaaion 2.10 to those for Reactions 2.11 and 2.12. A compound that is capable of reducing the antioxidant radical (A ) back to the parent compound (AH) will compete with Reactions 2.11 and 2.12, and so increase the efficiency of peroxyl radical scavenging (Reaction 2.10). In addition, the steady-state concentration of the antioxidant wiU be maintained at its initial concentration for a longer period and this should also result in more efficient suppression of the peroxidation reaction. The net result of these effects will be a synergistic enhancement of antioxidant activity. 

In satisfying these criteria it is clear that a balance must be struck between a sufficiendy rapid rate for Reaction 2.10 while minimizing the rates of Reactions 2.11 and 2.12. This could be achieved by decreasing the reactivity of the antioxidant by sterically hindering the functional group donating the hydrogen atom. 

In the case of a-tocopherol and probucol it is possible to demonstrate synergy between these antioxidants and the water-soluble antioxidant ascorbate in both model 

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The above result, that the antioxidant response in two-stage hydroprocessed oils is clearly better than in solvent-refined base stocks, has recently been confirmed [76]. It was demonstrated that phenolic-based formulations, blended into two-stage hydroprocessed oils, gave the greatest oxidative stability when total and polynuclear aromatics were lowest. Most fully formulated turbine oils make use of the synergistic interaction between phenolic and aminic antioxidants, see Reaction (4.70). Thus, depending on the performance requirements and the base oil composition, phenol/amino ratios of 1 1 to 4 1 are used [77],... 

Aside from statistical considerations, biological interactions between the different antioxidants may explain the lack of effect of vitamin C on risk in some instances. Experiments have demonstrated synergistic interactions involving antioxidant regeneration (Gey et ai, 1993). In CHD, accelerated lipoprotein peroxidation was observed without regeneration of vitamin E, presumably caused by vitamin C (Bowry et al, 1992). 

These results suggest that the antioxidant activity of some tested extracts might be attributed to the presence of non-phenohc compounds. Nevertheless, it should be taken into consideration that individual phenohcs may have distinct antioxidant activities there may be antagonistic or synergistic interactions between phenolics and other compounds like carbohydrates, proteins, etc. (Odabasoglu et al. 2005). 

The synergistic effect observed in the presence of all three antioxidants implies that there is an interaction between the individual antioxidant components. The direct interaction of the a-tocopherol radical and ascorbic acid is already well established (Bisby and Parker 1995) and a study by Mayne and Parker (1989) on chicks deficient in vitamin E and selenium showed that the... 

At present, considerable interest is drawn to the use of natural mixtures of antioxidants isolated from various vegetable materials. Some authors claim that such mixtures manifest stronger antioxidant effects than individual components due to synergistic interactions. It is of course quite possible, but it should be noted that synergistic interactions are not a single mechanism of the interaction between components for example, the simultaneous presence of the antioxidant and prooxidant flavonoids might diminish summary antioxidant effect of the mixture. Furthermore, natural mixtures contain, as a rule, some unknown compounds, which affect the summary effect by unknown manner. 

Interaction Between Vitamin E- Radicals and Ascorbate. Vitamin E and ascorbate probably act synergistically (55) that is, vitamin E acts as the primary antioxidant (particularly in biomembranes) and the resulting vitamin E- radical then reacts with ascorbate to regenerate vitamin E. That such a reaction can occur was subsequently demonstrated (56), and the reaction rate (/c42 1.55 0.2 X 10 was... 

The cooperative interaction between two or more antioxidants (or antioxidant fimctions) that enhances the stabilization of a polymer by more than the sum of the individual effects of the antioxidants is referred to as synergism. Often, the overall effectiveness of the synergistic system is much greater than can be achieved by either of the antioxidants, even at higher concentration, and hence the practical importance of synergism. Synergism can result from the combined action of two... 

In considering the possible choices of pigment and/or UV stabiliser systems for sunlight protection, it has to be remembered that many PE, and all PP, contain thermal antioxidants, and it is known that interactions can occur between antioxidants, UV stabilisers, and pigments. These interactions may either be synergistic or antagonistic in terms of the weathering life of the polymer. 

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