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

The rotational dynamics of the mixture composed of the deep eutectic solvent (DES) reline, and the macrocyclic oligosaccharide beta-cyclodextrin (beta CD) 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 beta CD in different ways. The findings are consistent with beta CD 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 beta CD within the DES/beta CD/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.