Effect of Water on Deep Eutectic Solvent/β-Cyclodextrin Systems

Abstract

The rotational dynamics of the mixture composed of the deep eutectic solvent (DES) reline, and the macrocyclic oligosaccharide β-cyclodextrin (βCD) is investigated at the molecular level by NMR relaxation spectroscopy with and without known amounts of water. The progressive addition of water affects the rotational motion of the DES and βCD in different ways. The findings are consistent with βCD interacting primarily with the added water and reline preserving some degree of residual molecular network. Combining in this way the features of the individual components in the mixture may be highly advantageous for future applications. As a proof-of-concept for the encapsulation capacity of βCD within the DES/βCD/H2O mixture, the formation of an inclusion complex with the nonsteroidal anti-inflammatory drug piroxicam is demonstrated through NMR chemical shifts variation and intermolecular host–guest NOEs in the rotating frame.

Furfural and 5‐Hydroxymethylfurfural Production from Sugar Mixture Using Deep Eutectic Solvent/MIBK System

“…Interestingly, an upfield shift of the HDO signal was observed when the dilution of DES was increased (Figure 4). This is contrary to what was observed forF ChCl/urea and ChCl/1,2‐propanediol DESs [20,29,32] . However, a similar yet unexplained upfield shift was observed with ChCl/diethylene glycol DES [23] .…”

“…This is contrary to what was observed forF ChCl/urea and ChCl/ 1,2-propanediol DESs. [20,29,32] However, a similar yet unexplained upfield shift was observed with ChCl/diethylene glycol DES. [23] In this study authors represent that the components of DESs can facilitate hydrogen bonding among water molecules or between water and DES molecules.…”

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] .…”

Effect of Water on a Hydrophobic Deep Eutectic Solvent

“…In this case, the 13 C T 1 relaxation time dependence on the rotational correlation time τ c is given by the Bloembergen–Purcell–Pound theory (BPP; see eq S15 ) by 1/ T 1 = A 0 Z (τ c ), where Z (τ c ) is a second-order function of τ c , and A 0 depends only on the local geometry and the properties of the nuclei. 115 − 117 The rotational correlation time measures the rate at which the correlation between the molecular orientations decays with time and can roughly be identified as the time the molecule needs to rotate approximately 1 radian. The most effective relaxation occurs when the field fluctuations occur approximately at the nuclear Larmor frequency, corresponding to the maximum of the function Z (τ c ).…”