title: A comparative photochemical study on the behavior of 3,3'-dihydroxyflavone and its complex with La(III) as generators and quenchers of reactive oxygen species.
abstract: A 1:1 complex between 3,3'-dihydroxyflavone (DHF) and La(III) (DHF-La(III)) is formed in methanolic solution with the relatively high apparent stability constant value of 2.3×10(6) and a calculated standard entropy change of 88.2 J mol(-1) K(-1), both at 25 °C. The photophysical properties of the complex and the free flavonoid are discussed in comparison to the well known related compound 3-hydroxyflavone. The ligand photogenerates O2((1)Δg) by energy transfer from its excited triplet state ((3)DHF(*)) to dissolved ground state oxygen, with a quantum yield of 0.13. (3)DHF(*) is quenched by La(III) with a rate constant close to the diffusion-controlled value. The respective abilities of the free flavonoid and DHF-La(III) as quenchers of the riboflavin-photogenerated reactive oxygen species singlet molecular oxygen (O2((1)Δg)) and superoxide radical anion (O2(-)) have been investigated. Both individual compounds were photoirradiated with visible light in the presence of the flavin as the only light-absorbing compound. A detailed kinetics and mechanistic study employing polarographic monitoring of oxygen uptake and time resolved detection of O2((1)Δg) phosphorescence indicates that DHF and the complex react with O2((1)Δg) and O2(-) by a non simple mechanism. The former deactivates O2((1)Δg) in a predominant physical fashion, a fact that constitutes a desirable property for antioxidants. It was found that metal chelation greatly enhances the ability of DHF as an overall O2((1)Δg) quencher.
authors: Area de Química Física, Universidad Nacional de San Luis, 5700 San Luis, Argentina.
authors: Gabriela V
authors: GV
authors: Ferrari
authors: M Paulina
authors: MP
authors: Montaña
authors: Frida C D
authors: FC
authors: Dimarco
authors: Nora B
authors: NB
authors: Debattista
authors: Nora B
authors: NB
authors: Pappano
authors: Walter A
authors: WA
authors: Massad
authors: Norman A
authors: NA
authors: García
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D005419:Flavonoids / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D015394:Molecular Structure; D017382:Reactive Oxygen Species / Q000737:chemistry*; D012256:Riboflavin / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D005419:Flavonoids; D028581:Lanthanoid Series Elements; D017382:Reactive Oxygen Species; D012256:Riboflavin; C041477:3-hydroxyflavone