Inclusion of the Phytoalexin <i>trans</i>-Resveratrol in Native Cyclodextrins: A Thermal, Spectroscopic, and X-Ray Structural Study

• Main Authors: Laura Catenacci, Milena Sorrenti, Maria Cristina Bonferoni, Lee Hunt, Mino R. Caira
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Molecules
• Subjects: cyclodextrin; <i>trans</i>-resveratrol; inclusion complexes; thermal analysis; x-ray structure
• Online Access: https://www.mdpi.com/1420-3049/25/4/998

The aim of the study was to determine the feasibility of complexation between the antioxidant <i>trans</i>-resveratrol (RSV) and underivatized cyclodextrins (CDs) using a variety of preparative methods, including physical mixing, kneading, microwave irradiation, co-evaporation, and co-precipitation techniques. Products were characterized using differential scanning calorimetry (DSC), simultaneous thermogravimetric/DSC analysis (TGA/DSC), Fourier transform infrared (FT-IR) spectroscopy, and powder X-ray diffraction (PXRD). With &#945;-CD and RSV, sample amorphization was revealed by PXRD and FT-IR, but no definitive inclusion complexation was evident. Similar results were obtained in attempts to complex RSV with &#946;-CD. However, complex formation between &#947;-CD and RSV was evident from observation of an endo-/exothermic effect appearing in the DSC trace of the product from kneading and was further corroborated by FT-IR and PXRD methods. The latter technique indicated complexation unequivocally as the diffraction peak profile for the product matched that for known isostructural &#947;-CD complexes. Single crystal X-ray analysis followed, confirming the predicted complex between &#947;-CD and RSV. A combination of ¹H NMR and TGA data yielded the complex formula (&#947;-CD)₃&#183;(RSV)₄&#183;(H₂O)₆₂. However, severe disorder of the RSV molecules prevented their modeling. In contrast, our previous studies of the inclusion of RSV in methylated CDs yielded crystals with only minor guest disorder.