Investigation of three flavonoids binding to bovine serum albumin using molecular fluorescence technique

The three flavonoids including naringenin, hesperetin and apigenin binding to bovine serum albumin (BSA) at pH 7.4 was studied by fluorescence quenching, synchronous fluorescence and UV–vis absorption spectroscopic techniques. The results obtained revealed that naringenin, hesperetin and apigenin strongly quenched the intrinsic fluorescence of BSA. The Stern–Volmer curves suggested that these quenching processes were all static quenching processes. At 291 K, the value and the order of the binding constant were K_{A (naringenin)}=4.08×10⁴<K_{A (hesperetin)}=5.40×10⁴≈K_{A (apigenin)}=5.32×10⁴ L mol^?1. The main binding force between the flavonoid and BSA was hydrophobic and electrostatic force. According to the Förster theory of non-radiation energy transfer, the binding distances (r₀) were obtained as 3.36, 3.47 and 3.30 nm for naringenin–BSA, hesperetin–BSA and apigenin–BSA, respectively. The effect of some common ions such as Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺ and Ca²⁺ on the binding was also studied in detail. The competition binding was also performed. The apparent binding constant (K′_A) obtained suggested that one flavonoid had an obvious effect on the binding of another flavonoid to protein when they coexisted in BSA solution.