Efficient renewable and non-toxic 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 (DES) with well-known VOCs capture agents like β-cyclodextrin (βCD). Yet, a question arises: does βCD retain its encapsulation ability in DES? Multiple NMR techniques are used here to demonstrate the formation of inclusion complexes of βCD with two VOCs, aniline and toluene, in the pure DES reline and in reline/water mixtures. Complexation-induced chemical shift changes and intermolecular hostguest NOEs in the rotating frame give evidence of a genuine encapsulation in the βCD 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.

Unlike the archetypal deep eutectic solvent (DES) choline chloride:urea (ChCl:U), fundamental knowledge of the intermolecular network in choline acetate (ChOAc) DESs and how they change upon dilution is still missing. Here we jointly use UV resonance Raman (UVRR) and NMR spectroscopy to comparatively explore how the strength and distribution of hydrogen bonding and the solvation of the components are modified in ChOAc:U and ChCl:U with increasing hydration. Overall, Raman and NMR data indicate that ChOAc:U is continuously affected by hydration and, even at low water concentrations, undergoes a breakage of DES–DES interactions, with rapid solvation of the urea portion and full exchange of mobile protons. On the contrary, ChCl:U seems to maintain its structure as small interplays gradually occur between urea in the DES and the surrounding water molecules. The combined approach provides a multifaceted consistent description of the systems, outlining the crucial role of the anion in driving the structure and dynamics of the materials and then yielding valuable data toward the exploitation of DESs as tunable systems.

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The traditional use of organic solvents in various branches of industry is being rethought as these compounds very often display high volatility, toxicity and lipophilicity (related to the ability to interact with biological membranes). More recently, developments in the field of Green Chemistry are focusing on the design of more sustainable and cost-effective solvent alternatives like Ionic Liquids (ILs), bio-based solvents and natural deep eutectic solvents (NADESs). The present study aimed at performing an ecotoxicological screening of 15 NADESs using an extensive set of marine and freshwater bioassays, based on different endpoints as the following: immobilization of the crustacean Daphnia magna, growth inhibition of Raphidocelis subcapitata and of Phaeodactylum tricornutum, larval development alterations on the serpulid Ficopomatus enigmaticus and bioluminescence inhibition of Aliivibrio fischeri. What emerged was a general absence of toxicity of all samples. However, both algal assays showed a certain degree of biostimulation, up to over 100% growth increase in respect to controls with 8 out of 15 compounds tested with Raphidocelis subcapitata. Despite NADESs-induced negligible toxicity effects to invertebrates, encouraging their labelling as “sustainable” solvents, the liability of their intentional or accidental release into aquatic systems may represent a serious risk in terms of ecosystem functioning impairments.

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.