Study of the complexation of resveratrol with cyclodextrins by spectroscopy and molecular modeling

Abstract

In present work the complexation of Res with two kinds of cyclodextrins (CDs), native β-cyclodextrin (β-CD) and modified hydroxypropyl-β-cyclodextrin (HP-CD), have been investigated by fluorescence spectroscopy, 1H-NMR spectroscopy and molecular modeling methods. The stoichiometric ratios, inclusion constants and thermodynamic parameters have been determined by the fluorescence data. In all cases 1:1 inclusion complexes are formed. The inclusion ability of HP-CD is larger than that of β-CD. Both inclusion processes have negative ∆G, negative ∆H and positive ∆S. Thermodynamic analysis suggests that Van der Waals force of guest-host interactions and the release of high-enthalpy water molecules from the cavity of CDs play important roles in driving complex formation. The study of molecular modeling shows that part of the A-ring and the B-ring of Res are placed in the cavity of β-CD, and the hydroxyl groups are projected outside. As for Res in HP-CD, the B-ring of Res is included in the cavity of HP-CD, and part of the A-ring is pointed outside. 1H-NMR spectroscopy results show that H2, H3, H4 and H5 protons of Res are more affected by the complexatin, indicating that they are located inside the torus of CDs, which are in agreement with the result of the molecular modeling.