First Evidence of Cyclodextrin Inclusion Complexes in a Deep Eutectic Solvent

Cyclodextrins (CD) inclusion complexes are generally studied in aqueous solutions or more rarely in the presence of cosolvent.In this study, we investigated the ability of CD to retain their host-guest properties in deep eutectic solvent (DES).Five cyclodextrins were solubilized in choline chloride:urea (ChCl:U) and these new solutions were characterized by measuring the viscosity and density of the different mixture.The heat of dissolution of β-CD in ChCl:U was measured by calorimetry.The dissolution process is exothermic meaning that the interaction between DES and CD are favorable (enthalpy of dissolution of -23.3 J/g).The ability of CDs to form inclusion complexes with various guests in ChCl:U was demonstrated using two different methods: UV-Visible spectroscopy and static headspace gas chromatography.On one hand, the experimental data obtained from the complexation between methyl orange and CDs follows the theoretical fitted curved for 1:1 inclusion complex.On the other hand, the observed volatility reductions of four volatile organic compounds in different mixture of DES/CDs were correlated to the CD/guest formation constant values determined in water.These results will certainly enlarge the application of CD in the DES field.