Studies of the interaction between apigenin and bovine serum albumin by spectroscopic methods

The interaction between apigenin (Ap) and bovine serum albumin (BSA) in physiological buffer (pH = 7.4) is investigated by fluorescence quenching technique and UV-vis absorption spectra. The results reveal that Ap could strongly quench the intrinsic fluorescence of BSA. The quenching mechanism of Ap for BSA varies with the change of Ap concentration. when Ap concentration is lower, it is a static quenching procedure, when Ap concentration is higher, a combined quenching (both static and dynamic) would operate. The apparent binding constants Ka and number of binding sites n of Ap with BSA are obtained by fluorescence quenching method. The thermodynamic parameters, enthalpy change (ΔrHm and entropy change (ΔrSm), are calculated to be −15.382 kJ mol−1 K−1 < 0 and 104.888 J mol−1 K−1 > 0, respectively, which indicate that the interaction of Ap with BSA is driven mainly by hydrogen bonding and hydrophobic interactions. The distance r between BSA and Ap is calculated to be 1.89 nm based on Förster’s non-radiative energy transfer theory. The results of synchronous fluorescence spectra show that binding of Ap with BSA cannot induce conformational changes in BSA.