[en] Flavonolignans from silymarin, the standardized plant extract obtained from thistle, exhibit various antioxidant activities, which correlate with the other biological and therapeutic properties of that extract. To highlight the mode of action of flavonolignans as free radical scavengers and antioxidants, 10 flavonolignans, selectively methylated at different positions, were tested in vitro for their capacity to scavenge radicals (DPPH and superoxide) and to inhibit the lipid peroxidation induced on microsome membranes. The results are rationalized on the basis of (i) the oxidation potentials experimentally obtained by cyclic voltammetry and (ii) the theoretical redox properties obtained by quantum-chemical calculations (using a polarizable continuum model (PCM)-density functional theory (DFT) approach) of the ionization potentials and the O-H bond dissociation enthalpies (BDEs) of each OH group of the 10 compounds. We clearly establish the importance of the 3-OH and 20-OH groups as H donors, in the presence of the 2,3 double bond and the catechol moiety in the E-ring, respectively. For silybin derivatives (i.e., in the absence of the 2,3 double bond), secondary mechanisms (i.e., electron transfer (ET) mechanism and adduct formation with radicals) could become more important (or predominant) as the active sites for H atom transfer (HAT) mechanism are much less effective (high BDEs).
Disciplines :
Chemistry Physics
Author, co-author :
Trouillas, P.
Marsal, Philippe
Svobodova, A.
Vostalova, J.
Gazak, R.
Hrbac, J.
Sedmera, P.
Kren, V.
Lazzaroni, Roberto ; Université de Mons > Faculté des Sciences > Service de Chimie des matériaux nouveaux
Duroux, J.L.
Walterova, D.
Language :
English
Title :
Mechanism of the Antioxidant Action of Silybin and 2,3-Dehydrosilybin Flavonolignans: A Joint Experimental and Theoretical Study
Publication date :
07 February 2008
Journal title :
Journal of Physical Chemistry. A
ISSN :
1089-5639
Publisher :
American Chemical Society, Washington, United States - District of Columbia
Volume :
112
Issue :
5
Pages :
1054-1063
Peer reviewed :
Peer Reviewed verified by ORBi
Research unit :
S817 - Chimie des matériaux nouveaux
Research institute :
R400 - Institut de Recherche en Science et Ingénierie des Matériaux
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