Deep eutectic systems from betaine and polyols – Physicochemical and toxicological properties

Abstract

The tailor-made versatility of deep eutectic systems (DES) has opened promising future perspectives for their applications in industry, to complement or even replace some of the already existing processes. Although there has been an active and considerable effort by the scientific community to characterize these systems, their toxicity towards different living organisms has not yet been thoroughly investigated. In this work, different mixtures of betaine with glycerol, propylene glycol, ethylene glycol, and their mixtures with water, were prepared and characterized in terms of density, viscosity, and polarity. Additionally, DES effects were also evaluated on a human intestinal epithelial cell model (Caco-2), towards a Gram-positive (Staphylococcus aureus) and a Gram-negative (Escherichia coli) bacterium, and on wheat (Triticum aestivum) seeds. Results showed that the physicochemical properties of the DES tested, namely density and viscosity, could be tuned not only through the hydrogen bond donor, but also by changing temperature or the water content. Polarity was also considerably affected by the water content of the system. Additionally, although DES presented different responses towards different organisms, generally, the systems presented a low toxicity profile, which could be substantially reduced by increasing their water content. These findings suggest that the DES studied can be minimally toxic, with easily tunable properties, which reinforces the prospect of using this kind of systems in the field of green technologies.