Complexation of pinosylvin, an analogue of resveratrol with high antifungal and antimicrobial activity, by different types of cyclodextrins.

The complexation of pinosylvin, a potent antimicrobial and antifungal stilbenoid, by cyclodextrins (CDs) is described for first time in this work. Steady-state fluorescence was used to demonstrate that natural (alpha-, beta-, and gamma-CD) and modified (HP-beta-CD, methyl-beta-CD, and ethyl-beta-CD) CDs are able to complex pinosylvin following a 1:1 stoichiometry. However, substantial differences in the strength of the complexation exist between the CDs tested. Although among natural CDs the interaction of pinosylvin with beta-CD was more efficient than with alpha- and gamma-CD, the results show that the complexation constants (K(F)) were higher for all of the modified CDs than for natural CDs, the highest K(F) being that determined for HP-beta-CD-pinosylvin complexes (12112 +/- 761 M(-1)). Moreover, deprotonation of the hydroxyl group of pinosylvin led to a sharp fall in the K(F) values with respect to those observed for the complexes formed between the protonated structure of this stilbenoid and the CDs. Moreover, a pK(a) value is reported for the first time for pinosylvin. Furthermore, when the temperature of the system was increased, a significant drop was observed in the complexation constant values. From these K(F) values and to throw light on the mechanism of pinosylvin affinity for HP-beta-CD, three thermodynamic parameters, DeltaH degrees , DeltaS degrees , and DeltaG degrees , were calculated. The results show that the complexation of pinosylvin by HP-beta-CD is a spontaneous and exothermic process with negative values for entropy changes. Finally, to gain information on the effect of the structure of different compounds belonging to the stilbenoid family on the K(F) values, the complexation of other molecules such as (E)-resveratrol and pterostilbene was studied and compared with the results obtained for the HP-beta-CD-pinosylvin complexes.