Antioxidant properties of flavonoids

The antioxidant properties of flavonoids are attributable to the ring whose radical has the lower reduction potential. Conjugation between the 2-aryl and the fused benzene rings is very inefficient <96JCS(P2)2497>. 

Epidemiological studies and intervention trials with food and beverages rich in flavonoids are not conclusive although flavonoids were recognized to display numerous antioxidant, anti-inflammatory, anti-tumoral, and anti-microbial activities. The antioxidant capacity of flavonoids has been largely reported in numerous in vitro and ex vivo systems. Numerous reviews "" have been published on the antioxidant properties of flavonoids. Degenerative diseases are largely associated with oxidative mechanisms that may be counteracted by flavonoids. 

Finotti E and Di MajoD. 2003. Influence of solvents on the antioxidant property of flavonoids. Nahrung/Food 47(3) 186—187. 

The spectrum of llavonoid biological effects is very broad the best known are their estrogenic, antitumor, antimicrobial, antiallergic, and antiinflammatory activities (for review, see Cushnie [19]). At least some of these activities are based on non-membrane-related mechanisms, like flavonoid-induced cell cycle arrest. Most of them, however, are claimed in the literature to appear as a consequence of antioxidative properties of flavonoids. 

Different model systems and different methods are used to evaluate the antioxidant properties of flavonoids. The stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), which changes color after being reduced by an antiradical compound, was employed to study the antioxidant properties of isoflavones genistein (42) and daidzein (40), flavones apigenin (23) and lute-... 

Despite the strong evidence ofthe antioxidant properties of flavonoids, demonstrated under in vitro conditions, the putative in-planta function remains unclear (Hernandez et al, 2009). Experimental data suggests that flavonols and flavan-3-ols, may act as antioxidants in plants, but the chemical diversity and complex biochemistry has hindered efforts to establish an unequivocal correlation between the spatiotemporal localization of flavonoids and oxidative stress reactions (Hernandez et al, 2009). 

A significant amount of literature regarding the antioxidant properties of flavonoids and other plant polyphenols is available. As the essence of redox chemistry involves electron transfer, it seems natural that electrochemical detection rivals spectrophotometric detection techniques for the compounds that are supposed to be antioxidants. With the improvements in electrochemical detector geometries and electronics over the last decade, coupled with a requirement for increased sensitivity, the use of electrochemical detectors offers significant additional advantages when combined with the traditional UV-VIS detection in the analysis of flavonoids and other plant polyphenols. ... 

Jovanovic, S.V., Steenken, S., Simic, M.G., and Hara, Y. 1998. Antioxidant properties of flavonoids Reduction potentials and electron transfer reactions of flavonoid radicals, in Flavonoids in Health and Disease, eds., C.A. Rice-Evans and L. Packer, New York Marcel Dekker, Inc., pp. 137-161. 

Flavonoids are widely distributed in fruits and vegetables and are very common nutritional supplements as antioxidants. The results on antioxidant activities of simple catechols provide a useful basis for evaluating results for the many, more complex natural compounds containing the catechol structure, such as the flavonoids, steroidal catechols and hormonal catecholamines. There are several reviews on the antioxidant properties of flavonoids and several reports on experimental " and theoretical evidence linking their antioxidant properties to the catechol moiety usually found in their structure. The basic flavonoid structure (29) is shown in Chart 1, with a few selected examples (30-36) from different groups to illustrate some of the relationships between their detailed structures and related antioxidant properties. Efforts to elucidate these relationships are hampered by their very low solubility in non-polar solvents, and the tendency of some researchers to employ metal ions as initiators of oxidation in aqueous media so that one cannot distinguish between their action as chain-breaking... 

The classical hydrogen-donating antioxidant properties of flavonoids, which are often used as a possible explanation for their biological activity, may, after all, not be the most important determinant for their effects in vivo. This conclusion is tenable when faetors sueh as in vivo metaboUsm and the achieved plasma and tissue coneentrations of flavonoids/metabolites are taken into account. Therefore, the bioaetivity of flavonoids in vivo may rather be supported by their ability to modulate protein fimctions, intracellular cell signaling, and receptor activities on the basis of interactions, for example, with ATP-binding sites and benzodiazepine-binding domains. 

Jovanovic SV, Steenken S, Simic MG, Hara Y. Antioxidant properties of flavonoids Reduction potentials and electron transfer reactions of flavonoid... 

The antioxidant properties of flavonoids have been recognized since the middle of the last century. Quercetin is probably the active compound that gathers all the properties necessary for a powerful antioxidant function, and it is used in moisturizing and anti-aging products. 

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