Fabrication, Characterization, and In Vitro Testing of Quercetin–Copper(II) Complex

Quercetin is a biologically active and widely used dietary flavonoid with robust antioxidant and chelating effects. However, due to its lesser solubility, it has poor bioavailability, which results in limited medicinal effects. This study synthesized quercetin–metal complexes, which enhanced the medicinal properties and bioavailability of quercetin. Quercetin–copper (Cu) complexes were fabricated by using copper sulfate and copper chloride in the Quercetin/Cu ratios of 1:2 and 1:1, respectively. Furthermore, Cu complexes with quercetin extracted from onion peels or standard quercetin were obtained. The current research also sought to assess the bioavailability as well as antibacterial and antioxidant properties. Spectrophotometry revealed that better complexes were prepared with a ratio of 1:2 as compared to 1:1. Copper chloride and copper sulfate showed no significant (p < 0.05) effects on complex formation. These metal complexes had a considerable impact on Bacillus subtilis (Gram⁺) as compared to Escherichia coli (Gram^–). The pharmacokinetic parameters indicated that the oral bioavailability of quercetin–Cu(II) complexes was significantly enhanced as compared to pure quercetin. The results of this study suggested the successful formation of quercetin–metal complexes, which markedly increased the bio-availability of quercetin.