Synthesis, structural elucidation and antiradical activity of a copper (II) naringenin complex

Coupling the extraction and derivatization of flavonoids to the Citrus processing industry is attractive from both the environmental and economic points of view. In the present work, the flavonoid naringin, obtained by "green" extraction with a water:ethanol mixture from waste grapefruit industry, was hydrolyzed to obtain naringenin. This flavonoid was used to synthesize the complex trans-di(aqua) bis(7-hydroxy-2-(4-hydroxyphenyl)-4-oxo-5-chromanolato) copper (II). This compound was characterized by spectroscopic techniques (UV/Vis, IR, Raman, NMR and EPR), and by thermal analysis (TG and DSC). Then, a monocrystal of the complex obtained by dissolution and recrystallization in DMF was analyzed by single crystal X-ray diffraction. This is the first report of the crystal structure of a Citrus flavonoid complex. Additionally, its antiradical activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) was determined and compared with that for naringenin, demonstrating that coordination to copper enhances the antiradicalar activity of naringenin. According to the Mulliken population analysis conducted, by copper favors the delocalization and stabilization of the produced radical, since it acts as an electronic density acceptor.