Masoomeh Shaghaghi - Department of Chemistry, Payame Noor University, P. O. Box ۱۹۳۹۵-۴۶۹۷ Tehran, Iran
Gholamreza Dehghan - Department of Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran
Fatemeh Khajevand - Department of Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran

Chelation therapy has been used to remove toxic metals from the body for a long time. Flavonoids such as quercetin (QUR), a well-known protective antioxidant and free radical scavenger, can bind to metal cations and protect our bodies from toxic metals. In the current study, we used UV–Vis, ۱HNMR, IR, and fluorescence spectroscopic techniques as well as viscosity measurements to investigate the synthesis, characterization, and interaction between Bi(III)-QUR complex and calf thymus DNA (ctDNA) in physiological buffer. The antioxidant activity of the complex was assessed utilizing DPPH and ABTS free radical scavenging, and ferric reducing potential. After chelation of the Bi(III) cation, the antioxidant potential of QUR was reduced. In the presence of ctDNA, the absorption spectrum of Bi(III)-QUR complex was raised, and the fluorescence intensity of Bi(III)-QUR complex was increased. With the addition of the Bi(III)-QUR complex, the relative viscosity of ctDNA rose. These findings indicate that the Bi(III)-QUR complex interacts with ctDNA in a groove-binding mode. The thermodynamic parameters (ΔH, ΔS, and ΔG) of the Bi(III)-QUR complex with ctDNA, as well as well as association constant, Ka, and number of binding sites (n), were assessed from the fluorescence data, indicating that the binding of Bi(III)-QUR complex to ctDNA was primarily driven by hydrophobic interactions.

Flavonoids, Chelation therapy, Bi(III)-quercetin complex, Radical scavenging, Natural products, antioxidant