NMR studies on the antiradical mechanism of phenolic compounds towards 2,2-diphenil-1-pycridrazyl radical

Phenolic compounds are the most abundant c1ass of natural antioxidants. These types of compounds are ubiquitous in fruits and vegetables and in plant-derived beverages, such tea and wine, being important constituents of human diet. Recent studies have pointed out particular interest on phenolic type compounds (e.g. flavonoids, catechins, cinnamic and benzoic acid derivatives) with respect not on1y to the organoleptic characteristics of foodstuffs (e.g. flavour, bitterness, astringency) but also to their potential benefits in deleterious oxidative radicalar processes related with human disease (e.g. cancer, atherosc1erosis).l,2 The antioxidant activity of phenolic compounds could be related with their antiradicalar activity and/or with the ability to act as metal ions chelators. Although there is general agreement that catecholic compounds possess radical scavenging properties till now its mechanism of action is not fully understood. The. determination of antiradicalar potency of antioxidants is usually performed using "Trap Assays" from which a screening of their scavenging activity towards different radical species could be obtained. The DPPH method is a non-enzymatic assay widely used for this purpose, in which the reactivity of the tested compounds towards a stable free radicaI2,2-diphenyl-l-picrylhydrazyl (DPPHe ) is measured.3 Following our interest on the antioxidant behaviour of phenolic compounds4 ,5 the mechanism of the antiradicalar activity of ortho-dihydroxy cinnamic acids and 2-styry1chromone derivatives towards DPPHe was studied by NMR spectroscopy.