title: Free radical scavenging by natural polyphenols: atom versus electron transfer.
abstract: Polyphenols (synthetically modified or directly provided by human diet) scavenge free radicals by H-atom transfer and may thus decrease noxious effects due to oxidative stress. Free radical scavenging by polyphenols has been widely theoretically studied from the thermodynamic point of view whereas the kinetic point of view has been much less addressed. The present study describes kinetic-based structure-activity relationship for quercetin. This compound is very characteristic of the wide flavonoid subclass of polyphenols. H-atom transfer is a mechanism based on either atom or electron transfer. This is analyzed here by quantum chemical calculations, which support the knowledge acquired from experimental studies. The competition between the different processes is discussed in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom- and electron-transfer efficiency. The role of the catechol moiety and the 3-OH group of quercetin as scavengers of different types of free radicals (CH3OO(•), CH3O(•), (•)OH, and (•)CH2OH) is rationalized. Identifying the exact mechanism and accurately evaluating kinetics is of fundamental importance to understand antioxidant behavior in physiological environments.
authors: Laboratoire de Chimie des Substances Naturelles EA-1069, Faculté de Pharmacie, Université de Limoges, 2 rue du Docteur Marcland, Limoges Cedex, France.
authors: Florent
authors: F
authors: Di Meo
authors: Vincent
authors: V
authors: Lemaur
authors: Jérôme
authors: J
authors: Cornil
authors: Roberto
authors: R
authors: Lazzaroni
authors: Jean-Luc
authors: JL
authors: Duroux
authors: Yoann
authors: Y
authors: Olivier
authors: Patrick
authors: P
authors: Trouillas
mesh_terms: D002396:Catechols / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D016166:Free Radical Scavengers / Q000737:chemistry*; D005609:Free Radicals / Q000037:antagonists & inhibitors*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D059808:Polyphenols / Q000737:chemistry*; D011789:Quantum Theory; D011794:Quercetin / Q000737:chemistry*; D012996:Solutions; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D002396:Catechols; D016166:Free Radical Scavengers; D005609:Free Radicals; D059808:Polyphenols; D012996:Solutions; D011794:Quercetin