Interaction Between Isoquercitrin and Bovine Serum Albumin by a Multispectroscopic Method

ABSTRACT

The interaction of isoquercitrin and bovine serum albumin (BSA) was investigated by means of fluorescence spectroscopy (FS), resonance light scattering spectroscopy (RLS), and ultraviolet spectroscopy (UV). The apparent binding constants (K _a) between isoquercitrin and BSA were 5.37 × 10⁵ L mol^?1 (293.15 K) and 2.34 × 10⁵ L mol^?1 (303.15 K), and the binding site values (n) were 1.18 ± 0.03. According to the Förster theory of non-radiation energy transfer, the binding distances (r) between isoquercitrin and BSA were 1.94 and 1.95 nm at 293.15 K and 303.15 K, respectively. The experimental results showed that the isoquercitrin could be inserted into the BSA, quenching the inner fluorescence by forming the isoquercitrin–BSA complex. The addition of increasing isoquercitrin to BSA solution leads to the gradual enhancement in RLS intensity, exhibiting the formation of the aggregate in solution. It was found that both static quenching and non-radiation energy transfer were the main reasons for the fluorescence quenching. The entropy change and enthalpy change were negative, which indicated that the interaction of isoquercitrin and BSA was driven mainly by van der Waals interactions and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative.