Abstract:

In the present study, the interactions between bovine serum albumin (BSA) and four caffeoylquinic acid (CQA)
derivatives (5-CQA, 3,4-diCQA, 3,5-diCQA and 4,5-diCQA) isolated from the leaves of Ilex kudingcha C. J. Tseng were
investigated by fluorescence spectroscopy under simulated physiological condition (pH 7.4 and 310 K). The binding
parameters were calculated according to modified Stern-Volmer equation, and the thermodynamic parameters were
determined by the van’t Hoff equation. The results showed that CQA derivatives interacted with BSA, and the binding
constants were ranked in the following order: 3,4-diCQA > 3,5-diCQA > 4,5-diCQA > 5-CQA, suggesting that the addition
of caffeoyl moiety significantly increased the binding capacity. Thermodynamic analysis showed that the ΔH and ΔS values
were both positive and the ΔG was negative, indicating that the interaction process was spontaneous, and hydrophobic
force might be primarily responsible for the interaction. In addition, the conformational change of BSA was observed by
3D fluorescence and synchronous fluorescence spectra, indicating that the interaction between CQA and BSA was achieved
through the binding of CQA to the tryptophan and tyrosine residues of BSA.

Key words: Kudingcha, caffeoylquinic acid, bovine serum albumin, fluorescence spectroscopy, interaction