Spectroscopic investigation on interaction of the bioactive component dl-tetrahydropalmatine to bovine serum albumin

The binding of dl-tetrahydropalmatine (dl-THP) with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, synchronous fluorescence and UV–vis absorption spectroscopy under physiological conditions. The spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of bovine serum albumin by dl-THP was dynamic quenching mechanism, and the hydrophobic interaction was the predominant intermolecular force stabilizing the complex. The binding sites number n and apparent binding K were obtained at various temperatures. The thermodynamic parameters were calculated according to the Vant’t Hoff equation and the result indicated that ΔH0 and ΔS0 are positive value 133.34 kJ mol−1 and 519.13 J mol−1K−1, respectively. The distance r between dl-THP and the protein was evaluated according to the theory of Forster energy transfer. The results of synchronous fluorescence spectra and UV–vis absorption spectra show that the conformation of BSA has been changed at the presence of dl-THP.