Physicochemical study of the complexation of pterostilbene by natural and modified cyclodextrins.

In this paper, the interaction between pterostilbene and cyclodextrins (CDs) is described for the first time using steady-state fluorescence. It was seen that pterostilbene forms a 1:1 complex with all of the natural (alpha-, beta-, and gamma-CDs) and modified (HP-beta-CD, methyl-beta-CD, and ethyl-beta-CD) CDs tested. Among natural CDs, the interaction of pterostilbene with beta-CD was the most efficient. However, all of the modified CDs showed higher complexation constants (K(F)) than beta-CD. The highest K(F) was found for HP-beta-CD (17520 +/- 981 M(-1)), in which its value showed a strong dependence upon pH in the region where the pterostilbene begins the deprotonation of its hydroxyl group. Moreover, the values of K(F) decreased as the system temperature increased. To obtain information on the mechanism of pterostilbene affinity for CD, the thermodynamic parameters of the complexation (DeltaH degrees , DeltaS degrees , and DeltaG degrees ) were studied. Finally, a comparison of the K(F) values obtained for three types of stilbenes revealed that both the stoichiometry and the K(F) values of the complex are dependent upon the structure of the guest molecule. While the trans-resveratrol-HP-beta-CD and pterostilbene-HP-beta-CD complexes showed a 1:1 stoichiometry with a higher K(F) value for the trans-resveratrol-HP-beta-CD complexes, trans-stilbene showed a 1:2 stoichiometry.