Complex formation of ionic liquid surfactant and β-cyclodextrin

An ionic liquid (IL) surfactant, 1-dodecyl-3-methylimidazolium hexafluorophosphate (C(12)mimPF(6)) can 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) ICs. The inclusion complexation interaction was further confirmed by Fr-IR spectra. The inclusion compound was also characterized by Powder X-ray diffraction (XRD), C-13 CP/MAS NMR, 2D(1)H-H-1 COSY and TGA. The results showed that the host-guest system presented a channel type structure and each glucose unit of beta-CD was in a similar environment. Only the tails of C(12)mimPF(6) were included into the cavity of beta-CD. The formation mechanism of the beta-CD-C(12)mimPF(6) was also discussed. It was suggested that hydrophobicity played a crucial role in supporting the formation of beta-CD-C(12)mimPF(6) ICs and hydrogen bonding was dispensable to maintain the channel type crystal structure. The weak hydrophobic driven force made the beta-CD-C(12)mimPF(6) unstable, which was reflected by TGA curves. In addition, possible inclusion structures of beta-CD-C(12)mimPF(6) were speculated. (c) 2006 Elsevier B.V. All rights reserved.