Interaction between ionic liquids and beta-cyclodextrin: a discussion of association pattern.

We report herein the interaction of three ionic liquids, i.e., 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (11), 1-hexyl-2,3-dimethylimidazolium chloride (16), and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (17), with beta-cyclodextrin (beta-CD). For 11 and 16, the 1:1 inclusion complexes were determined and the association constants were estimated through a competitive fluorescence method, conductivity, and (19)F NMR measurements. It was confirmed that the alkyl side chain on the imidazolium ring but not the imidazolium ring itself entered into the cavity of beta-CD. According to the association constants, the sequence of interaction strength of some ILs with beta-CD was obtained. We also found that the cation and the anion in 17 exhibited strong interactions with beta-CD simultaneously. Furthermore, a general interaction pattern of an IL with beta-CD was suggested.