Spectroscopic investigation of the interaction between chrysin and bovine serum albumin

The interaction of chrysin with bovine serum albumin (BSA) in physiological buffer solution (pH 7.4) was studied by fluorescence, UV/vis absorption and resonance light scattering (RLS) spectroscopy. The experimental results showed that there was a strong fluorescence quenching of BSA by chrysin. The probable quenching mechanism of fluorescence of BSA by chrysin was a static quenching by forming the BSA–chrysin complex. The addition of increasing chrysin to BSA solution led to the gradual enhancement in RLS intensity, implying the formation of an aggregate in solution. The binding constants K and number of binding sites n of chrysin with BSA were obtained by fluorescence quenching method. The thermodynamic parameters of the interaction of chrysin with BSA were measured according to the van’s Hoff equation. The enthalpy change (ΔHθ) and the entropy change (ΔSθ) were calculated to be 39.19 kJ mol−1, 211.91 J mol−1 K−1 respectively, which indicated that the interaction between chrysin and BSA was driven mainly by hydrophobic interaction. The binding was shown to be spontaneous at the standard state because the changes in standard Gibbs free energy (ΔGθ) values were negative. The binding distance of chrysin from the tryptophan residue in BSA was calculated to be 2.44 nm based on the Förster theory of non-radiation energy transfer. The results of synchronous fluorescence spectra demonstrated that chrysin induced a conformational change of BSA. In addition, the effect of some inorganic ions on the binding constants of chrysin with BSA was also investigated.