Antioxidants oxidation potential

Carotenoids (Car) are known antioxidants. Extensive electrochemical studies in solution have established the low oxidation potentials and demonstrated the formation in various media of carotenoid... 

The multichannel coulometric detection system serves as a highly sensitive tool for the characterization of antioxidant phenolic compounds because they are electroactive substances that usually oxidize at low potential. The coulometric efficiency of each element of the array allows a complete voltammetric resolution of analytes as a function of their oxidation potential. Some of the peaks may be resolved by the detector even if they coelute (Floridi and others 2003). 

The competition between antioxidant and prooxidant activity of flavonoids depends firstly on their chemical structure. If we suppose that the oxidation of flavonoids (Reaction (17)) takes place by one-electron transfer mechanism, then it must depend on the capacity of flavonoids to donate an electron, i.e., on their one-electron oxidation potentials. 

Kotamraju, S., Matalon, S., Matsunaga, T., Shang, T., Hickman-Davis, J. M., and Kalyanaraman, B. (2006). Upregulation of immunoproteasomes by nitric oxide Potential antioxidative mechanism in endothelial cells. Free Radio. Biol. Med. 40,1034—1044. 

The importance of cell death mediated by oxidative damage has led to the popularity of antioxidants as potential therapeutics. A variety of naturally occurring (vitamin C, vitamin E) and synthetic (lazaroids) antioxidants have been smdied as possible remedies for a wide variety of ailments. Large doses of vitamin E have been studied as a putative therapy in Alzheimer s disease, functioning through the inhibition of amyloid-induced oxidative destruction of neuronal membranes within the brain. 

Antioxidants are very effective in stabilizing products undergoing a free-radical mediated chain reaction. These products possess lower oxidation potentials than the active drug. Ideally, antioxidants are stable over a wide pH range and remain soluble in the oxidized form, colorless, and nontoxic. A listing of commonly used antioxidants can be found in Table 3. 

Phenolic substances are for the most part readily oxidized at a graphite electrode. The oxidation potentials for phenols vary widely with structure, and some (hydroquinones and catechols) are far more readily oxidized than others (cresols). Many compounds of biological interest (catecholamines, pharmaceuticals, plant phenolics) [32] and industrial interest (antioxidants, antimicrobials, agricultural chemicals) [33] are phenolic, and trace determination based on LCEC is now quite popular. 

Potential/time relation informs about kinetics of antioxidant oxidation. Table 27.5 displays semi-oxidation periods and average constants of oxidation rate for main antioxidants. 

Unsaturated and Vulcanized Rubbers. Oxidation occurs most readily at polymers with structural double bonds, such as natural rubber, polybutadiene, or polyisoprene. Aromatic amines and sterically hindered phenols are effective antioxidants. From the rubber antioxidants, 96.8 million pounds were amines, and 20 million pounds were phenols. Amines act also as antiozonants whereas phenols are not effective. Furukawa shows that amines have a lower oxidation potential which is a prerequisite for antiozonant action. 

As a measure of the activity of antioxidants and antiozonants, oxidation potential has been used (3, 15, 16, 19). Compounds having an oxidation potential lower than 0.44 volt seem to be effective as antiozonants (20), whereas good antioxidants are known to have the potentials between 0.7 and 0.9 volt (16). The Hiickel molecular orbital calculations... 

This paper shows that Fukui s theory is plausible for interpreting the presence of the optimum oxidation potentials for amines to be effective as antioxidants or antiozonants. 

Figure 1 shows the correlation between the relative tensile strength (TS)/(TS)0 or the time, tc, for the crack formation of NR gum vulcanizates and the oxidation potential of the amines employed as the stabilizer. The antioxidant or antiozonant activity of amine first increases with increasing oxidation potential and reaches a maximum at about 0.4 or 0.25 volt, beyond which the ability decreases with the increase in the potential. 

These results lead us to conclude that some amines are effective as both antioxidants and antiozonants for rubber, and their efficiencies depend on their oxidation potentials. The optimum potentials of amines exist at about 0.4 volt for antioxidants and 0.25 volt for antiozonants. 

As is shown in Figure 3 the highest occupied energy level is found to parallel well the oxidation potential in aniline and p-phenylenediamine derivatives. To elucidate the existence of the optimum oxidation potentials for antioxidation and antiozonization, the reactivity indices Sr and S for radical and nucleophilic reactions have been used. These are ... 

The relationships of oxidation potential to radical reactivity index Sr and nucleophilic reactivity index Sn illustrated in Figure 4 are very similar to those with antioxidation and antiozonization, where the maximum values were observed at 0.4 and 0.25 volt. Therefore, antioxidation seems to proceed by a radical mechanism in contrast to the nucleophilic type of antiozonization. Indeed, the antioxidation effect of amines toward NR, SBR, BR, and HR is well correlated with radical reactivity as shown in Figures 5-8. The protection of SBR solution by amines from oxidative degradation and the termination of chain reaction in the oxygen-Tetralin system are also shown as functions of Sr in Figures 9 and 10. 

The thermal stability of nitromethane can be improved by adding a small amount of boric acid. It reduces the tendency of nitromethane to decompose on distillation (Lippincott [23]). The addition of a small amount (0.2-1.0%) of phenolic antioxidants, such as hydroquinone, has also been suggested, i.e. substances having a critical oxidation potential as low as the air oxidation potential of a- naphthol (Senkus [24]). 

As part of a study on antioxidants the halfwave oxidation potential of phenothiazine at a wax-impregnated graphite electrode was determined and the value -f- 239 (mv SCE) was found. 

Garcinia madruno (Kunth) Hanunel (aerial parts leaves and branches) Flavanone-(I-3,II-S)-flavones Morelloflavone (159) volkensiflavone (154). (I-3, II-8)-flavone Amentoflavone (1). Antioxidant activity Inhibitory LDL oxidation potential and free radical stabilization capacity of the biflavonoid fraction. Osorio et al., 2009[198]. 

By polarographic measurements, Baltes (1964) calculated the following normal oxidation potentials, in connection with a comparison of the antioxidant properties of the tocopherols a-tocopherol 4-754 mV P-tocophcrol 4-824 mV 7-tocopherol 4-829 mV S-tocopherol 4 886 mV. 

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