Inclusion complexes of β-cyclodextrin with ionic liquid surfactants

The three kinds of ionic liquid (IL) surfactants, 1-dodecyl-3-methylimidazolium hexafluorophosphate (C-12-mimPF(6)), 1-tetradecyl-3-methylimidazolium hexafluorophosphate (C(14)mimPF(6)), and 1-hexadecyl-3-methylimidazolium hexafluorophosphate (C(16)mimPF(6)), were used to form the inclusion complexes (ICs) with beta-cyclodextrin (beta-CD). The surface tension measurements revealed that there were two kinds of inclusion formations, 1:1 and 1:2 (beta-CD/IL) stoichiometry for beta-CD-C(12)mimPF(6) and beta-CD-C(14)mimPF(6) ICs, and only 1:1 stoichiometry for beta-CD-C(16)mimPF(6) ICs. These inclusion compounds were further characterized by XRD, C-13 CP/MAS NMR, H-1 NMR, rotating frame nuclear Overhauser effect spectroscopy (ROESY), and thermogravimetry (TGA). The results showed that these ICs were fine crystalline powder. The host-guest system presented a channel-type structure, and each glucose unit of beta-CD was in a similar environment. It was suggested that hydrophobicity played a crucial role in supporting the formation of ICs. The decomposition temperature of these ICs was lower than those of their precursors. Furthermore, the possible inclusion structures were also speculated. These inclusion behaviors are likely to be used to recover ILs in the process of their preparation.