Complex formation of ionic liquid surfactant and β-cyclodextrin

An ionic liquid (IL) surfactant, 1-dodecyl-3-methylimidazolium hexafluorophosphate (C12mimPF6) can form the inclusion complexes (ICs) with β-cyclodextrin (β-CD). The surface tension measurements revealed that there were two kinds of inclusion formations, 1:1 and 1:2 (β-CD/IL) stoichiometry for β-CD-C12mimPF6 ICs. The inclusion complexation interaction was further confirmed by FT-IR spectra. The inclusion compound was also characterized by Powder X-ray diffraction (XRD), 13C CP/MAS NMR, 2D 1H-1H COSY and TGA. The results showed that the host–guest system presented a channel type structure and each glucose unit of β-CD was in a similar environment. Only the tails of C12mimPF6 were included into the cavity of β-CD. The formation mechanism of the β-CD-C12mimPF6 was also discussed. It was suggested that hydrophobicity played a crucial role in supporting the formation of β-CD-C12mimPF6 ICs and hydrogen bonding was dispensable to maintain the channel type crystal structure. The weak hydrophobic driven force made the β-CD-C12mimPF6 unstable, which was reflected by TGA curves. In addition, possible inclusion structures of β-CD-C12mimPF6 were speculated.