Interaction between Ionic Liquids and β-Cyclodextrin: A Discussion of Association Pattern

Abstract

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.

Secondary assembly mechanism of cyclodextrin based on LiNTf2@β-CD system

“…Our research group has been investigating the supramolecular interaction pattern between ionic liquids (ILs) and CDs [37][38][39][40], and constructed vesicles and supramolecular hydrogel between ILs and CDs [41,42]. In our previous studies about the interaction between the IL 1-alkyl-3-methylimidazolium-bis(trifluoromethylsulfonyl) imide (C n mimNTf 2 ) and b-CD, we reported that NTf 2 -could form inclusion complex with b-CD in the diluted aqueous solution [38,39].…”

The joint effects of room temperature ionic liquids and ordered media on fluorescence characteristics of estrogens in water and methanol

“…If one of them interacts with b-CD very weakly, 1:2 inclusion complexes should be minimal and 1:1 inclusion complexes are dominant. However, if both the cation and anion of an IL strongly interact with b-CD, 1:2 inclusion complexes are prominent [40,41]. According to the above analyses, RTILs have a strong possibility of being incorporated into the hollow b-CD cavity, which decreases the incorporation of EE2 or E2 into b-CD.…”

“…In this investigation, we only detected one fluorescent peak for the analyte, and thus conclude that a complex rather than a mixture was formed. In addition to the above analysis, previous literature reported that the stoichiometry of the inclusion complex could be judged by surface tension measurements [38,39] and structural characterization by means of FTIR, 1 H NMR and SEM techniques [40,41]. Guest molecules with long hydrophobic chains provided convincing evidence for penetration into the CD cavity and showed a 1:2 stoichiometry [42].…”

“…At the maximum excitation wavelength of 276 nm, no changing phenomena were observed for the emission maxima shape at ca. 430 nm for neat [C 8 the similar size of the b-CD cavity and imidazolium cation play an important role in the complexation process [41]. The building block structure of the C 16 TPB@2b-CD complex was found in aqueous solution, which can form a sheet-like hydrogel with multiresponsive properties [43].…”

Supramolecular Structures in the Presence of Ionic Liquids

“…Thus, the study on this topic is important. Various methods have been applied to investigate the interaction between ILs and CDs, such as the solubility , infrared spectroscopy (Li et al, 2007c), ultra-violet spectroscopy, XRD (Gao et al, 2006c;Gao et al, 2005a;Li et al, 2007c), conductivity (Amajjahe & Ritter, 2008b;He et al, 2009), TGA (Gao et al, 2006c;Gao et al, 2005a;Li et al, 2007c), affinity CE (ACE) (Francois et al, 2007), NMR (Amajjahe & Ritter, 2008b;Gao et al, 2006c;He et al, 2009;Li et al, 2007c), fluorescence competition (He & Shen, 2008;He et al, 2009), microcalorimetry (Amajjahe et al, 2008;Amajjahe & Ritter, 2008b;, surface tension measurements (Gao et al, 2006c) and so on. By these methods, the formation constants of ICs, the stoichiometry for ILs and CDs can be obtained.…”