Michel Hocquaux

Antioxidant activity of flavonoids: Efficiency of singlet oxygen (1Δg) quenching

Flavonoids, polyphenolic pigments widely present in plants, have been reported to act as scavengers of various oxidizing species. However, most often an overall antioxidant effect was measured. In this paper we report the results of a systematic study of the reactivity of 13 selected flavonoids (from the flavonol, flavone, flavanone and flavane families) with singlet oxygen (1O2(1 delta g)) in order to establish a structure-activity relationship. The rate constants of the chemical reaction of these flavonoids with 1O2(k r) and their rate constants of 1O2 physical quenching (kq) have been determined by kinetic measurements and near-IR singlet oxygen luminescence. The efficiency of the physical quenching is mainly controlled by the presence of a catechol moiety on ring B, whereas the structure of ring C (particularly the presence of a hydroxyl group activating the double bond) is the main factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity scale is dominated by kq, which is in general higher than kr. (+)-Catechin is the most efficient quencher of the series.

Activité anti-oxydante de flavonoïdes réactivitë avec le superoxyde de potassium en phase hétérogène

Abstract Oxidation of flavonols by potassium superoxide (KO2) in heterogeneous aprotic media yields acids and aldehydes by opening of ring C, if the latter contains an ethylenic double bond substituted by an OH group. A mechanism is proposed for this reaction. Other flavonoids like flavones, flavans and flavanones induce only the disproportionation of superoxide anion, without undergoing further oxidation; these flavonoids are therefore anti-oxidants of particular interest.

Réactivité du superoxyde de Potassium en phase hétérogéne: Oxydation de naphtalénedios en naphtoquinones hydroxylées

Abstract Oxidation of dihydronaphthalenes by potassium superoxide (KO2) in heterogeneous aprotic media yields mono- or dihydroxynaphthoquinones, depending on the relative position of the hydroxy groups on the naphthalene moiety. The reaction proceeds mainly at the solid-liquid interface and naphthoquinones can be obtained with good yields.

Oxydation des tetralones par le superoxyde de potassium solubilise par ether-couronne

Resume α and β-tetralones are oxidised in tetrahydrofuran solution by means of potasssium superoxide with crown-ether to give 2-hydroxy-1,4 naphtoquinone with fair to good yields.

Differenciation entre les dihydroxy-2,5 et -3,5 naphtoquinones-1,4 par resonance magnetique nucleaire du 13C et 1H, et heteronucleaire a deux dimensions.

Resume 1 H and 13 C NMR, as well as two-dimensional correlation 13 C/ 1 H experiments were used to characterise unequivocally two isomeric naphthoquinones, 2,5-dihydroxy and 3,5-dihydroxy-1,4-naphthoquinones.

Exemple de réaction à l'interface solide-liquide: oxydation de naphtalènediols par le superoxyde de potassium

Abstract The oxidation of 1,2 and 1,3-dihydroxynaphtalenes with potassium superoxide in aprotic media is a heterogeneous to reaction at the solid-liquid interface, leading to the 2-hydroxy-1,4-naphtoquinone with good yields even if the addition of crown-ether is omitted.

Oxydation du naphtalènediol-1,5 par le superoxyde de potassium en phase hétérogène

Abstract The oxydation of 1,5-dihydroxynaphthalene by potassium Superoxide is essentially an interfacial solid/liquid reaction, which leads to 2,5- and 3,5-dihydroxy-1,4-naphthoquinones. The reaction proceeds in two steps through the formation of 5-hydroxy-1,4-naphthoquinone. The mechanism of the reaction is discussed.