Marie-Thérèse Maurette

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.

VOC photodegradation at the gas–solid interface of a TiO2 photocatalyst: Part I: 1-butanol and 1-butylamine

Abstract The gas–solid heterogeneous photocatalytic oxidation of 1-butanol and 1-butylamine in air was investigated using supported TiO2 as a catalyst. The supported catalyst was prepared using a sol–gel method and irradiated employing two different light sources, a medium pressure mercury lamp or a xenon-chloride excimer lamp. The experimental set-up was especially designed for generating a gas stream containing stable and defined concentrations of the model pollutants. The gas stream at the reactor exit was analyzed on line by gas chromatography and the structures of the intermediates were established by gas chromatography coupled with mass spectrometry. Six major intermediates (butanal, butanoic acid, 1-propanol, propanal, ethanol and ethanal) were identified in the case of the photocatalytic degradation of 1-butanol. 1-Butylamine was less efficiently adsorbed on the catalyst and its degradation was slower. Three intermediates could be identified in this case (N-butylidene-1-butylamine, N-ethylidene-1-butylamine and N–butylformamide). Based on these results, a degradation mechanism is proposed for both compounds. Mineralization could be achieved under various conditions of concentrations and flow rates and was confirmed by infrared spectroscopy.

Photocatalytic degradation of 2,4-dihydroxybenzoic acid in water: efficiency optimization and mechanistic investigations

Abstract The experimental design and response surface methodologies have been applied to the investigation of the TiO 2 -photocatalytic degradation of 2,4-dihydroxybenzoic acid (DHBA) in aqueous solutions. It has been shown that a quadratic polynomial model may be used to assess adequately the efficiency of the photocatalytic degradation as a function of DHBA and TiO 2 concentrations. Moreover, the study of response surfaces leads to optimal conditions for investigating the catalyst efficiency. A degradation mechanism involving the cleavage of the DHBA aromatic ring at an early stage of the reaction is proposed. Such a mechanism accounts for the absence of any aromatic intermediate in the degradation process.

Hydrogen peroxide evolution during V-UV photolysis of water

Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.

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.

Chemical and photechemical reactivity in micellar media and microemulsions IV: concentration effects on isophorone dimerization

Abstract A study of concentration effects in isophorone photodimerization shows the importance not only of interfacial processes but also of selective extraction of the reactants and products. From this work, another feature can be pointed out: microemulsification is a general phenomenon and microemulsions containing a polar component as the “oil” can be prepared.

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.

Chemical and photochemical reactivity in micellar media and microemulsions VII- Effect of the interface on the reactivity of excited states

Abstract Study of the photodimerization of coumarin in micellar media and microemulsions shows that the orientation and the concentration of molecu- les in the interfacial film can favor reactions involving just one of the excited states (the singlet state in this case).

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.

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.