Cluster aggregation of water-based deep eutectic solvents in water and evaluation of their cytotoxicity

• Clusters of water-based DESs ( aquo DESs) are observed by diluting them in water. • Glycolic acid/water; betaine/water; choline chloride/water are the analyzed aquo DESs. • The water dilutions provoke viscosity reduction of the liquids. • The DESs’ structures are preserved until high water dilutions, about 50–60 % w/w. • The cytotoxicity of the aquo DESs dilutions is very low and dependent on the non-water components only. Deep Eutectic Solvents (DESs) are emerging in the recent literature as promising environmentally friendly liquids in different topics, finding fruitful applications as substitutes to common volatile organic solvents. In this work a study of cluster formation of water-based DESs in water dilutions is presented. The three analysed mixtures are: glycolic acid/water (GA/H 2 O); betaine/water (TMG/H 2 O), choline chloride/water (ChCl/H 2 O). Ionic conductivity, viscosity, ultrasound spectroscopy and NMR techniques showed the presence of aggregates of aquo DESs in water dilutions. These aggregates are present in the solutions until values about 50% w/w of added water, showing the presence of water-in-water structured systems. Moreover, taking into account the convenient disposal as water dilution of a DES, the cytotoxicity of these dilutions was evaluated on Caco2 model cells, showing the effect to be related only to the non-water components of these liquids. The water dilutions of water-based DESs have a great relevance for their applications, because their physical properties can be modulated as needed preserving their DESs’ identities.