Do Cyclodextrins Encapsulate Volatiles in Deep Eutectic Systems?

Efficient renewable and nontoxic absorbents can now be designed to eliminate air pollutants such as volatile organic compounds (VOCs) from confined atmospheres. New hybrid materials result from the combination of deep eutectic systems (DESs) with well-known VOC capture agents like beta-cyclodextrin (beta CD). However, a question arises: does beta CD retain its encapsulation ability in DESs? Multiple nuclear magnetic resonance (NMR) techniques are used here to demonstrate the formation of inclusion complexes of beta CD with two VOCs, aniline and toluene, in the pure DES reline and in reline/water mixtures. Complexation-induced chemical shift changes and intermolecular host-guest nuclear Over-hauser effects (NOEs) in the rotating frame give evidence of genuine encapsulation in the beta CD cavity, and complementary information on the dynamics of the VOC is gathered via relaxation and diffusion experiments. This work shows how different NMR techniques can contribute to the design of task-specific sustainable materials for absorption/extraction processes.