Interaction between Ionic Liquids and β-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 F-19 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.