Competitive kinetics in free radical reactions of cinnamic acid derivatives. Influence of phenoxyl radicals reactions.
Relative rates of consumption of caffeic, ferulic and sinapic acids by 2,2'-azobis(2-amidine propane) derived peroxyl radicals has been measured in parallel experiments employing a single substrate and in competitive experiments. Rates of consumption measured in independent experiments at low substrate concentrations (first order limit) follow the order: sinapic > ferulic > caffeic. In agreement with this, in competitive experiments employing simultaneously sinapic and caffeic acid the former compound is consumed considerably faster. On the other hand, in competitive experiments employing ferulic and caffeic acids over a wide range of experimental conditions, caffeic acid is consumed considerably faster than ferulic acid, a result that contrasts with that obtained when both compounds are reacted independently. These apparently anomalous results are interpreted in terms of secondary reactions of the phenol-derived radicals. In particular, hydrogen transfer among phenoxyl radicals and the phenols and fast reactions (disproportionation) of caffeic acid derived radicals could explain these discrepancies.
López-Alarcón
Camilo
C
Departamento de Farmacia, Facultad de Química, Pontificia Universidad Católica de Chile, Chile.
Aspée
Alexis
A
Lissi
Eduardo
E
D000975:Antioxidants / Q000737:chemistry; D001667:Binding, Competitive; D001671:Biochemistry / Q000379:methods; D002109:Caffeic Acids / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002934:Cinnamates / Q000737:chemistry* / Q000378:metabolism; D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D017382:Reactive Oxygen Species; D013997:Time Factors
D000975:Antioxidants; D002109:Caffeic Acids; D002934:Cinnamates; D005609:Free Radicals; D010636:Phenols; D017382:Reactive Oxygen Species; C029010:cinnamic acid; C042329:phenoxy radical; D006859:Hydrogen; C040048:caffeic acid