First Evidence of Cyclodextrin Inclusion Complexes in a Deep Eutectic Solvent

Abstract

Supramolecular host−guest inclusion complexes based on cyclodextrins (CDs) are generally studied in aqueous solutions or more rarely in the presence of a cosolvent. In this study, we investigate for the first time the ability of CDs to retain their host−guest properties in deep eutectic solvents (DESs). Five cyclodextrins were solubilized in mixtures of choline chloride:urea (ChCl:U), and these new solutions were characterized by measuring their viscosity and density as a function of temperature. The heat of dissolution of β-CD in ChCl:U was measured by calorimetry. The dissolution process is exothermic meaning that the interaction between ChCl:U and CD is 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 a 1:1 inclusion complex. On the other hand, the observed volatility reductions of four volatile organic compounds in different mixtures of ChCl:U:CD were correlated to the CD/guest formation constant values determined in water. These results will certainly contribute to enlarging the applications of CDs in the DES field.

Do Cyclodextrins Encapsulate Volatiles in Deep Eutectic Systems?

“…It has been recently observed using static headspace gas chromatography (SH-GC), that association constant for the VOC/βCD of in reline are lower than the corresponding values in water. 26 However, it should be noted that also in reline/H 2 O mixtures studied here, toluene binds more strongly to βCD than aniline, which is in agreement with data from the literature. Moreover, the value found here for βCD/toluene complex is higher than the one calculated by SH-GC (79 M -1 vs 11 M -1 ).…”

Determination of Binding Strengths of Host‐Guest Complexes in Deep Eutectic Solvents Using Spin Probe Methodology

“…With large cavity of γ‐CD, in DES, desolvation effects on both rate constants account for a K eq very similar to that measured in water when using BTBN as spin probe. With small cavity of β‐CD, complexation of BTBN in DES is significantly depressed although still maintained, as previously observed with VOC [8–10] …”

“…Probing the binding properties of macrocycles in DES is not as straightforward as in aqueous environments or traditional organic solvents. The combination of high ionic strength and viscosity of the solvent does not allow an easy use of traditional 1 H NMR and isothermal titration calorimetry (ITC) for quantitative measure of binding and very few data on complexation in DES are available in literature [8–10] . In particular, affinity constants for the complexation of methyl orange or volatile organic compounds (VOC) by different CDs were measured by UV‐Vis, [8] static headspace gas chromatography (SH‐GC) [8] and DOSY NMR experiments [9–10] .…”

Diffusivity of α-, β-, γ-cyclodextrin and the inclusion complex of β-cyclodextrin: Ibuprofen in aqueous solutions; A molecular dynamics simulation study

“…Since the inclusion complex formation is the core phenomenon in these applications, it has been the main focus of numerous scientific studies [5] , [17] , [18] , [19] , [20] , [21] , [22] . In most of these studies, the stability of the host-guest complex is studied by using either experimental or simulation techniques [5] , [18] , [20] , [23] , [24] , [25] , [26] , [27] , [28] , [29] . Although in various applications of CDs such as controlled drug-delivery [24] , [30] , [31] , [32] mass transport can play an important role, it has not been as widely studied as the binding properties of the inclusion complexes.…”