From guest to ligand – A study on the competing interactions of antitumor drug resveratrol with β-cyclodextrin and bovine serum albumin

Interaction between bovine serum albumin (BSA) and resveratrol (RES) included by β-cyclodextrin (β-CD) in Tris–HCl aqueous buffer solutions (pH 7.4) has been investigated by isothermal titration calorimetry (ITC) combined with ultraviolet, fluorescence and circular dichroism spectra analyses. The results indicate that there are two classes of ligand binding sites. The first class of binding is mainly driven by enthalpy, while the second one is driven by both enthalpy and entropy. The secondary structure of BSA in the aqueous system was slightly changed with addition of the drug. Thermodynamic parameters, i.e., equilibrium constants, standard enthalpy changes and the entropy effects for the binding process of RES with BSA were calculated based on the calorimetric data. In fact, due to the poor solubility of RES in aqueous buffer medium, these parameters could not be determined by the employed experimental method without the existence of the CD.