Abstract: Spectrophotometric titrations were performed in aqueous buffer solution(pH=10.5, c=0.025 mol/L) at 25 ℃ to determine the binding constants ofβ-cyclodextrin(β-CD), mono(6-O-α-maltosyl)-β-cyclodextrin(6-G₂-β-CD) and mono[2-O-(2-hydroxypropyl)]-β-cyclodextrin(2-HP-β-CD) with several aliphatic chiral guest molecules using phenolphthalein as a spectral probe. The results obtained indicate that several weak interactions cooperatively contribute to the inclusion complexation of theβ-cyclodextrin hosts and the complex stability is dominated by the size/shape-matching between host and guest. The substituent on the cyclodextrin derivatives changes its original binding ability. For the relatively small guest molecules,i.e., borneol, camphor and menthol, the molecular binding ability is 2-HP-β-CD>β-CD>6-G₂-β-CD. Furthermore, the threeβ-cyclodextrin hosts can also serve as chiral discrimination reagents and afford stronger binding ability toward (+)-isomers. Among them, 2-HP-β-CDgives a moderate enantiometric selectivity of 1.25 for (+)/(-)-camphor.

Key words: β-Cyclodextrin, Phenolphthalein, Aliphatic alcohol, Competitive inclusion, Molecular recognition