The binding of kaempferol-3,7-α-L-rhamnopyranoside (KRR) with bovine serum albumin (BSA) was investigated by different spectroscopic methods under simulative physiological conditions. Analysis of ?uorescence quenching data of BSA by KRR at different temperatures using Stern-Volmer methods revealed the formation of a ground state KRR-BSA complex with moderate binding constant of the order 10⁴ L·mol⁻¹. The existence of some metal ions could weaken the binding of KRR on BSA. The changes in the van't Hoff enthalpy (ΔH⁰) and entropy (ΔS⁰) of the interaction were estimated to be −26.53 kJ·mol⁻¹ and 3.33 J·mol⁻¹·K⁻¹ and both hydrophobic and electrostatic forces contributed to stabilizing the BSA-KRR complex. According to the F?ster theory of non-radiation energy transfer, the distance r between the donor (BSA) and the acceptor (KRR) was obtained (r=2.83 nm). Site marker competitive experiments showed that KRR could bind to Site I of BSA. In addition, synchronous fluorescence, UV-Vis absorption and circular dichroism (CD) results indicated that the KRR binding could cause conformational changes of BSA.

Fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) and FT-Raman spectroscopy were employed to analyze the binding of the asiatic acid (AA) to bovine serum albumin (BSA) under simulative physiological conditions. Fluorescence data revealed that the fluorescence quenching of BSA by AA was the result of the formation of BSA-AA complex. The fluorescence quenching mechanism of BSA by AA was a static quenching procedure. According to the Van′t Hoff equation, the thermodynamic parameters enthalpy change (ΔH⁰) and entropy change (ΔS⁰) for the reaction were evaluated to be −12.55 kJ·mol⁻¹ and 67.08 kJ·mol⁻¹, respectively, indicating that hydrophobic and electrostatic interactions played a major role in stabilizing the complex. The influence of AA on the conformation of BSA has also been analyzed on the basis of FT-IR, CD and FT-Raman spectra.

The interaction between xanthoxylin (XT) and bovine serum albumin (BSA) under simulative physiological conditions has been analyzed in detail by various spectroscopic techniques including fluorescence, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy. Fluorescence quenching data revealed that the quenching constants (K) were 3.31×10⁵, 2.03×10⁵ and 0.94×10⁵ L·mol⁻¹ at 286, 298 and 310 K, respectively. Based on the fluorescence results, the fluorescence quenching mechanism of the interaction between XT and BSA has been found to be combined static and dynamic quenching. Thermodynamic parameters ΔH⁰, ΔS⁰ and ΔG⁰ suggested that the hydrophobic force played a main role in binding of XT to BSA. The effect of XT on the conformation of BSA was analyzed by FT-IR spectroscopy and quantitatively calculated from CD spectroscopy with reduction of α-helical content by about 3.9%. In addition, the effect of common ions on the binding constant was also discussed.