Inclusion complex formation of ionic liquids with cucurbit[7]uril studied by competitive binding of methylene blue fluorescent probe

Methylene blue (MB) was used as a fluorescent probe to study the encapsulation of three kinds of 1-butyl-3-methylimidazolium ionic liquids in cucurbit[7]uril (CB7) at pH 3. Addition of ionic liquids to the aqueous solution of MB–CB7 inclusion complexes brought about considerable fluorescence intensity quenching, and it was because that MB was extruded from the cavity of CB7 into the aqueous phase by the ionic liquid. NMR and AM1 semi-empirical calculations indicated that the 1-butyl-imidazolium moiety of ionic liquid was responsible for the complexation with CB7.

Graphical abstractEnergy-minimized structure of C4MIm+–CB7 complex in the ground state was calculated by AM1 method and NMR showed that C4MIm+ was partially included in the hydrophobic core of CB7.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The inclusion of ionic liquids in CB7 were studied by methylene blue as a probe. ► Ionic liquids can extrude methylene blue from CB7 cavity. ► AM1 calculation and NMR indicated the partial inclusion of ionic liquids by CB7.