Is there depth to eutectic solvents?

We define an empirical descriptor of eutectic depth that allows an easy comparison between mixtures of distinct chemical nature. The molecular origin of the large melting point de-pressions observed for deep eutectic solvents (DESs) is discussed through the examples of three well-studied mix-tures: urea + choline chloride, ethylene glycol + choline chlo-ride and (-)-menthol + thymol. We show that the link between the state-of-the-art knowledge of the DES liquid microstructure and its macroscopic properties is still missing. We call for the experimental quantification of the observed balance between interactions and disorder at the molecular level and the sub-sequent incorporation of this data in thermodynamic models. This would facilitate the calculation and prediction of solvation properties and eutectic depth.