Molecular recognition study of beta-cyclodextrin and its two derivatives with some aliphatic guests by competitive inclusion method

Spectrophotometric titrations were performed in aqueous buffer solution(pH = 10. 5, c = 0. 025 mol/L) at 25 degreesC to determine the binding constant s of beta -cyclodextrin(beta -CD), mono(6-O-alpha -maltosyl)-beta -cyclodex trin (6-G(2)-beta -CD) and mono[2-O-(2-hydroxypropyl)]-beta -cyclodextrin ( 2-HP-beta -CD) with several aliphatic chiral guest molecules using phenolph thalein as a spectral probe. The results obtained indicate that several wea k interactions cooperatively contribute to the inclusion complexation of th e beta -cyclodextrin hosts and the complex stability is dominated by the si ze/shape-matching between host and guest. The substituent on the cyclodextr in derivatives changes its original binding ability. For the relatively sma ll guest molecules, i. e. , borneol, camphor and menthols the molecular bin ding ability is 2-HP-beta -CD>beta -CD>6-G(2)-beta -CD. Furthermore, the th ree beta -cyclodextrin hosts can also serve as chiral discrimination reagen ts and afford stronger binding ability toward (+)-isomers. Among them, 2-HP -beta -CD gives a moderate enantiometric selectivity of i, 25 for (+)/(-)-c amphor.