Estudos de complexos metálicos contendo a quercetina como ligante

Abstract

Polyphenolic compounds are very abundant in nature, being found in fruits and vegetables, green and black tea, oils, wines and chocolate. Within this class of compounds stand out flavonoids, substances that are made up of C 6 -C 3 -C 6 units in which C 6 is an aromatic ring. In the literature, several studies demonstrate that these compounds have antioxidant and cytoprotective properties. Among those flavonoids with antioxidant activity, we can highlight quercetin. This compound is the main flavonoid present in the human diet, and it can coordinate with metallic ions, increasing its antioxidant property. In order to contribute to a better understanding of the coordination of quercetin to metals, compounds were prepared from reactions of quercetin with Fe(II), Cu(II) and Zn(II), in stoichiometric ratios of 1:1 and 1:2 (metal:ligand). The compounds were characterized by ultraviolet-visible electron spectroscopy, infrared vibrational spectroscopy, hydrogen nuclear magnetic resonance spectrometry ( 1 H NMR), in addition to conductivity measurement in solution, thermal analysis and cyclic voltammetry. The results indicate that four complexes were formed, however none of them in the desired stoichiometry. In one case, Cu(II) favored the quercetin oxidation reaction. Cyclic voltammetry data indicated a significant modification in the oxidation potentials of the compounds with coordination.