Autooxidation of ascorbic acid

It is known that the redox potential of the Fe+3/Fe+2 pair can vary by complexing ligands (27). EDTA reduces the redox potential of Fe+2 (28) and this increases the rate constant transfer of the electron from Fe+2 to H202, which is formed during autooxidation of ascorbic acid (29), and decomposition of the latter to H0-. However, at low pH 3-4, EDTA was found to inhibit ascorbic acid oxidation by ferric ions (29). Thus, the form the metal chelate takes, as a function of pH, plays a key role in its effectiveness as a catalyst. Cupric ions are known to accelerate ascorbic acid oxidation however, EDTA inhibits its catalytic effect at both neutral and low pH (24). 

Phenanthroline in the presence of heavy metals acts as an activator of the polymerization of vinyl compounds - and other olefins. " It also assists the dimerization of olefins in the presence of titanium catalysts. - It enhances the metal catalyzed oxidation of ascorbic acid and dimethyl sulfoxide. On the other hand, on its own it can inhibit several polymerization processes. - It also stabilizes butadiene and isoprene and prevents their dimerization. It prevents peroxide formation in ether, inhibits the vinylation of alcohol and stabilizes cumyl chloride. It accelerates the vulcanization of diene rubbers and copolymers. 1,10-Phenanthroline catalyzes the autooxidation of linoleic and ascorbic acids in the absence of metals. ... 

Akbiyik T, Sonmezoglu 1, Gu9ld K, Tor I, Apak R (2012) Protection of ascorbic acid from copper(ll)-catalyzed oxidative degradation in the presence of fruit acids citric, oxalic, tartaric, malic, malonic, and fumaric acids. Int J Food Prop 15 398 11 Smith TD (1967) Effect of nitrate on the autooxidation of tin(ll) in citric acid solutions. Austr J Chem 20 15-19... 

In connection with the antioxidant properties of L-ascorbic acid and its stability, many kinetic and mechanistic studies have been performed. For instance, it has been shown a role as a radical scavenger in the autooxidation of methyl linoleate, and its synergistic effect when used with vitamin E.362 The photooxidation,363 superoxide-mediated oxidations,364 reactions with radicals,365 and the influence of other agents, including ultrasound and y-rays,366 have been reported. 

Systematic examination of the catalytic properties of dimeric complexes was initiated shortly after the identification of dinuclear iron sites in metalloenzymes. The first report of a reactive dimeric system came from Tabushi et al. in 1980, who examined the catalytic chemistry of [Fe3+(salen)]20, 1 (salen is N,N -(salicylaldehydo)-l,2-ethylenediamine) (12). They reported interesting stereoselectivity in the oxidation of unsaturated hydrocarbons with molecular oxygen in the presence of mercaptoethanol or ascorbic acid and pyridine as a solvent ([l]<<[alkane]<<[2-mercaptoethanol]). With adamantane as substrate, they observed the formation of a mixture of (1- and 2-) adamantols and adamantanone (Table I) (12). Both the relative reactivity between tertiary and secondary carbons (maximum value is 1.05) and final yield ( 12 turnovers per 12 hr) were dependent on the quantity of added 2-mercaptoethanol. Because autoxidation of adamantane gave a ratio of 3°/2° carbon oxidation of 0.18-0.42, the authors proposed two coexisting processes autooxidation and alkane activation. 

Fukuzawa, K., Chida, H., Akira,T., and Tsukatani, H. (1981), Autooxidative effect of a-tocopherol incorporation into lecithin hposomes on ascorbic acid Fe++-induced lipid peroxidation, Arch. Biochem. Biophys., 206,173-180. 

Recent studies in biological systems have revealed the presence of a variety of compounds of many structural types that appear to function as antioxidants. The plant kingdom is especially rich in these materials (Larson, 1988). They include flavonoids and other phenolic compounds, alkaloids and other amines, reduced sulfur compounds, uric acid, ascorbic acid. Vitamin E, carotenoids, and many other substances. Often, their principal mechanism of action appears to be the quenching of peroxy radicals, removing them from the autooxidation chain. Vitamin E, for example, reacts with these radicals in a manner entirely analogous to that of BHT ... 

Imanaga, Y., 1955a, Autooxidation of L-ascorbic acid and imidazole nucleus. I. The effects of imidazole derivatives on the autooxidation of L-ascorbic acid, J. Biochem. 42 657-668. 

Quinone conjugation to proteins occurs readily in vivo, and thus, autooxidation of DOPAC and other endogenous catechol-containing compounds could be an important component of protein modification. Indeed, the DOPAC quinone produced from autooxidation is responsible for the irreversible inhibition of [ H] spiperone binding to neuronal dopamine D2 receptors. Ascorbic acid and dithiothreitol can prevent this inhibition (Cammack et al, 1991b). 

---