Interaction of pyrogallol red with peroxyl radicals. A basis for a simple methodology for the evaluation of antioxidant capabilities.
A competitive method to evaluate the reactivity of highly reactive antioxidants is reported. Pyrogallol red (PGR) and AAPH (2,2'-azo-bis-(2-amidinopropane) dihydrochloride) were employed as target-molecule and peroxyl radical source, respectively. In the zero-order kinetic limit in PGR, the dependence of the ratio R(o)/R (where R(o) is the rate of the process in the absence of additive and R is the rate of the process in the presence of additive) upon the additive concentration (Stern-Volmer like plots) was studied. Various polyphenols (n=10) and ascorbic acid (AA) were tested as additives. In PGR protection by AA, was observed a neat induction time, associated to the total protection of the target molecule. On the other hand, the experiments that were carried out in presence of phenolic compounds allowed a relative evaluation of their reactivity towards peroxyl radicals. This reactivity follows the order quercetin > gallic acid > Trolox > kaempferol. Data obtained employing quercetin and Trolox are compatible with a competitive protection by these antioxidants. Due to the high reactivity of PGR towards peroxyl radicals and its high extinction coefficient at long wavelengths, it is a very suitable molecule to be employed as target in the evaluation of the free radical scavenging capability of very reactive phenolic compounds.
López-Alarcón
Camilo
C
Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla.
Lissi
Eduardo
E
D000578:Amidines / Q000737:chemistry; D000975:Antioxidants / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D005419:Flavonoids / Q000737:chemistry; D016166:Free Radical Scavengers / Q000737:chemistry; D007700:Kinetics; D016877:Oxidants / Q000737:chemistry; D010545:Peroxides / Q000737:chemistry*; D011748:Pyrogallol / Q000031:analogs & derivatives* / Q000737:chemistry; D011794:Quercetin / Q000737:chemistry
D000578:Amidines; D000975:Antioxidants; D004396:Coloring Agents; D005419:Flavonoids; D016166:Free Radical Scavengers; D016877:Oxidants; D010545:Peroxides; D011748:Pyrogallol; C049375:perhydroxyl radical; C058731:pyrogallol sulfonphthalein; C046728:2,2'-azobis(2-amidinopropane); D011794:Quercetin