Solvent and pH Effects on the Antioxidant Activity of Caffeic and Other Phenolic Acids
Citations Over TimeTop 10% of 2006 papers
Abstract
The antioxidant activity of several phenolic acids and esters has been investigated both in organic solutions and in large unilamellar phosphatidylcholine vesicles. In solution these compounds behaved as good antioxidants, with the exception of protocatechuic acid, due to the presence of the catechol moiety. Because their antioxidant activity followed an inverse dependence on the magnitude of their O-H bond dissociation enthalpies (BDE), the key mechanism of the chain-breaking action was attributed to hydrogen atom transfer (HAT) from the phenolic OH to peroxyl radicals. In unilamellar vesicles the antioxidant activity was strongly dependent on the pH of the buffer solution. In acid media (pH 4) all of the examined phenolic acids or esters behaved as weak inhibitors of peroxidation, whereas, with increasing pH, their antioxidant activity increased substantially, becoming comparable to or even better than that of Trolox. At pH 8 they also gave rise to lag phases 2-3 times longer than that of Trolox. The increased activity being observed in proximity of the pK(a) value corresponding to the ionization of one of the catecholic hydroxyl groups, this effect has been attributed to the high antioxidant activity of the phenolate anion.
Related Papers
- → Commonly used food antioxidants: a comparative study in dispersed systems(2003)61 cited
- → Synthesis and Antioxidant Activity Evaluation of Trolox Derivatives(2020)2 cited
- → New insights into the antioxidant activity of Trolox in o/w emulsions(2010)21 cited
- → Hydrogen bonding and crystal packing trends in tetraalkylammonium halide—catechol complexes: synthesis, spectroscopic and crystal structure studies of Me4NC1—catechol, Et4NCl—catechol, Et4NBr—catechol and Pr4NBr—catechol complexes(1986)15 cited
- → Synthetic mimics of tyrosinase: catechols from ortho-, meta- and para-substituted phenols and copper(I) complexes(1995)10 cited