Study of the interaction between baicalin and bovine serum albumin by multi-spectroscopic method

The interaction of baicalin and bovine serum albumin (BSA) was investigated using fluorescence spectroscopy (FS), resonance light scattering spectroscopy (RLS), and ultraviolet spectroscopy (UV). The apparent binding constants (Ka) between baicalin and BSA were 1.67 x 10(6) (22 degrees C) 1.98 X 10(6) (32 degrees C) and 2.01 x 10(6) (42 degrees C), and the binding sites values (n) were 1.33 +/- 0.01. According to the Forster theory of nonradiation energy transfer, the binding distances (r) between baicalin and BSA were 1.94, 1.95 and 1.96 nm at 22, 32, and 42 degrees C, respectively. The experimental results showed that the baicalin could be inserted into the BSA, quenching the inner fluorescence by forming the baicalin-BSA complex. The addition of increasing baicalin 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 positive, which indicated that the interaction of baicalin and BSA was driven mainly by hydrophobic forces. The process of binding was a spontaneous process in which Gibbs free energy change was negative. (c) 2007 Elsevier B.V. All rights reserved.