Showing papers by "André M. Braun published in 1993"
3,257 citations
TL;DR: 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 were reported in this paper.
Abstract: 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.
228 citations
87 citations
TL;DR: In this paper, a new Xe-excimer light source was used for the oxidative degradation of 4-chlorophenol (4-CP) in aqueous solution.
Abstract: A new Xe-excimer light source has been used for the oxidative degradation of 4-chlorophenol (4-CP) in aqueous solution. Owing to the very high absorption cross-section of water at the wavelength of excitation (172 nm), degradation of the organic substrate is initiated by hydroxyl radicals generated by water photolysis. Neither oxygen concentration, nor the presence of carbonates or nitrates affects the rate of 4-CP degradation; however, maximum oxygen concentration is required for higher rates of mineralization of organic carbon. Kinetic investigations are based on 4-CP, TOC and Cl − analysis. VUV photolysis as a means of oxidative degradation of organic pollutants in aqueous systems is showing the potential to compete with other photochemical oxidative processes.
71 citations