Facile separation of cinnamyl acetate and cinnamaldehyde based on host-guest complexation with -cyclodextrin

A selective inclusion of cinnamyl acetate (CAc) is observed during the complexation of CAc and cinnamaldehyde (CA) with -cyclodextrin (-CD) in aqueous solution. To demonstrate the potential application of -CD for the separation of CAc and CA, the preferential affinity of -CD for CAc over CA was studied from conformational and thermodynamic points of view. Determination of the complexation geometries, performed by 1H and 2D (XRD), confirmed the inclusion capacity of the -CD cavity for CAc and CA. From the stability constants measured by ultraviolet-visible (UV-Vis) spectroscopy and thermodynamic parameters measured by isothermal titration microcalorimetry, it was found that compared to CA, hydrophobic and hydrogen bonding interactions jointly promote CAc to form a more stable -CD binding complex with 1:1 stoichiometry. Furthermore, the higher binding affinity of -CD for CAc (over CA) was investigated theoretically in terms of binding energy and inclusion geometries. The separation of the equimolar CAc-CA mixture was achieved by inclusion complexation in -CD aqueous solution. The effects of the experimental conditions, such as the polarity of the solvent and guest/host molar ratio, on separation performance were investigated. Under the optimized conditions, the selective inclusion procedure exhibited a CAc/CA separation factor of 3.5, which remained stable after five cycles, indicating that -CD is a highly reusable host material.