Experimental and theoretical study of the stability of the complex Fisetin‐Cu(II) and a comparative study of free ligand and complex interaction with molecular singlet oxygen

MUÑOZ, VANESA A.; DIMARCO PALENCIA, FRIDA C.D.; SANCHO, MATIAS I.; SANDRA, MISKOSKI; GARCÍA, NORMAN A.; FERRARI, GABRIELA V.; MONTAÑA, M. PAULINA

PHOTOCHEMISTRY AND PHOTOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2020

0031-8655

In this work the flavonol Fisetin was selected in order to study its reactivity against Cu(II), a metal ionof interest in biological media and industry. The stoichiometry and apparent formation constant of thecomplex in ethanolic medium at 25ºC were evaluated using spectrophotometric techniques. Theresulting stoichiometry was a 1:1 ligand:metal complex and a log K=5.17±0.12 was determined. Sincetwo possible chelation sites can be proposed for the complex formation quantum chemistrycalculations were performed on these structures. Calculations suggest that the hydroxyl-keto site ismore stable for the complex formation than the catechol site.Flavonoids could exert protection against oxidative damage caused by reactive oxygen species andthis biological activity could be affected by chelation with metal ions. This led us to perform a studyon the interaction of both, free flavonoid and complex, with reactive oxygen species. Our resultsshowed both compounds quench molecular singlet oxygen photogenerated with visible light, mainlyin a physical fashion. In order to analyze a possible protective effect of flavonoid and its complexagainst oxidative damage in biological environments the amino acid tryptophan was selected as amodel oxidation system. Free flavonoid does not have a marked protective effect whereas its complexshowed a relevant protective effect.