Assessment of the interaction between fraxinellone and bovine serum albumin by optical spectroscopy and molecular modeling methods

The interaction of fraxinellone with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, ultraviolet–visible (UV–vis) absorbance, Fourier transform infrared (FT-IR) spectroscopy, and protein-ligand docking studies. The results suggested that the quenching of BSA fluorescence by fraxinellone was a static process. The binding constant Ka at 298 K was calculated to be 6.61×104 L mol−1, and the number of binding sites n were given. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), at different temperatures were −66.22 kJ mol−1 and −129.77 J mol−1 K−1, respectively. Fraxinellone was bound to BSA in site I, and the distance between fraxinellone and BSA was 2.31 nm, as calculated based on the Förster theory of non-radiation energy transfer. Moreover, the obtained UV–vis, synchronous fluorescence, and FT-IR spectra demonstrated that the BSA microenvironment and secondary structure were modified in the presence of fraxinellone. The molecular modeling results are consistent with the displacement and binding mode studies conducted.