Inclusion Complexation Behaviors of 3-Tigloyl-Azadirachtol with β-Cyclodextrin Derivatives

A series of β-cyclodextrin/3-tigloyl-azdirachtol inclusion complexes were prepared from β-cyclodextrin, heptakis( 2,3,6-tri-O-methyl)-β-cyclodextrin, mono(6-ethylene-diamino-6-deoxy)-β-cyclodextrin and mono(6-diethylenetriamino- 6-deoxy)-β-cyclodextrin with 3-tigloyl-azdirachtol (azadirachtin B, AZ-B) in ca. 90%, and their inclusion complexation behaviors were investigated by means of UV/Vis, 1H NMR and 2D NMR spectroscopy. The results showed that the AZ-B could be efficiently encapsulated in the cyclodextrin cavity in aqueous solution to produce complexes that were more stabilized than free AZ-B. Furthermore, the water solubility of AZ-B was obviously increased to high levels up to 4-6.3 mg/ml (calculated as AZ-B) after inclusion complexation with cyclodextrins. This satisfactory water solubility and high stability of the cyclodextrin-AZ-B complexes will be potentially useful, for their application as biopesticide and herbal medicine or healthcare products. The enhanced binding ability of cyclodextrins toward AZ-B was discussed from the viewpoint of the size/shape-fit concept and multiple recognition mechanism between host and guest.