EFFECT OF Cu2+-COMPLEXATION ON THE SCAVENGING ABILITY OF CHRYSIN TOWARDS PHOTOGENERATED SINGLET MOLECULAR OXYGEN (O2(1Δg)). POSSIBLE BIOLOGICAL IMPLICATIONS.

MUÑOZ, VANESA A.; FERRARI, GABRIELA V.; MONTAÑA, MARIA P.; MISKOSKI, SANDRA; GARCÍA, NORMAN A.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2016 vol. 162 p. 597 - 603

1011-1344

Visible-light irradiation of aqueous-ethanolic solutions of riboflavin (Rf) in the individual presence of the flavone chrysin (Chr) and its complex with Cu2+ ([Chr2Cu]; 2:1 L:M) generates singlet molecular oxygen O2(1Δg), that concomitantly interact with both flavone derivatives. Overall (kt ) and reactive (kr) rate constants in the order of 107M-1s-1 were determined for the process. Metal chelation greatly enhances the scavenging ability of [Chr2Cu] towards O2(1g) through a mechanism dominated, in more than 80%, by the physical component. In this way, practically all O2(1Δg) is deactivated by the complex without significant loss of the quencher. The isolated flavone quenches O2(1Δg) in a prevailing reactive fashion. The very low value exhibited by [Chr2Cu] for the kr/kt ratio constitutes a positive quality for antioxidative protectors in biological media, where elevated local concentration and high reactivity of significant molecules make them initial targets for O2(1g) aggression. Finally, two interesting properties in the field of free radicals scavenging by [Chr2Cu] must be mentioned. In first place metal chelation itself, in the obvious sense of free metal ion withdrawal from the oxidizable medium, prevents the initiation of a free radical-mediated oxidation processes through mechanisms of Fenton or lipid peroxidation. In addition, the incorporation of Cu adds to [Chr2Cu] the ability of a free radical scavenger, already described for similar Cu-chelate compounds. This collection of beneficial properties positions the complex as a remarkably promising bioprotector towards ROS-mediated oxidation.A quantification of the efficiency on the initial anti-oxidative effect exerted by Chr and [Chr2Cu] towards tryptophan was carried out. The amino acid is an archetypal molecular model, commonly employed to monitor oxidative degradation of proteinaceous media. It was efficiently photoprotected against O2(1g)-mediated photooxidation by [Chr2Cu].