We report the preparation and the study of the properties of novel deep eutectic solvents (DESs) formed by zwitterionic trimethylglicine and high melting point carboxylic acids. These zwitterionic DESs are liquid at room temperature or at temperatures lower than 70 °C and do not have chloride or any metal ions in their composition. These media were characterized in terms of their viscosity, conductivity, density, ionicity (via Walden plots), surface tension and thermal stability. The values observed are similar to other typical DESs, and the mixtures resulted in “poor ionic liquids” in the Walden plot. The values obtained could be correlated to the carboxylic acids' structures. The toxicity of the pure mixtures was evaluated via an FTIR-bioassay on Saccharomyces cerevisiae cells. This method allowed us to define the action of these media as dehydrating agents on eukaryotic model cells, with a mechanism highly correlated with CaCl₂, a well-known dehydrating agent. The Glycolic acid/Trimethylglicine eutectic system can be considered a NADES (Natural Deep Eutectic Solvent) and resulted as the best in our set for many reasons. It is formed by natural, renewable, eco-compatible and cheap compounds (both the molecules can be derived from sugar beet) and it can be used in many applications because it has a low melting point (−36 °C) and it is colorless, and therefore suitable for spectroscopic measurements. For these reasons, the solubility of some α-L-amino acids was investigated in this DES, showing a good solubility for aromatic amino acids, which are normally scarcely soluble in water.

Twelve novel deep eutectic solvents (DESs) were prepared and characterized in this work. They are mixtures of (1S)-(+)-10-camphorsulfonic acid (CSA) and differently structured sulfobetaines (SBs) with aliphatic, aromatic and amphiphilic moieties. They are liquids at room temperature, their melting points span, in fact, from −5° to 19 °C, so we can name these mixtures RTDESs (room temperature deep eutectic solvents). These zwitterionic DESs were characterized in terms of their viscosity, conductivity (and therefore ionicity via Walden plots), density, surface tension and toxicity on eukaryotic model cells. The collected data suggest that the interaction between CSA and the SBs can be ascribed as a hydrogen bond instead of a proton transfer, therefore they are not ionic liquids. To our knowledge, their position on the Walden plot, in the left portion close to the diagonal, has not yet been observed for other DESs or ionic liquid systems and indicates the low ionicity of these mixtures. A FTIR-based bioassay was performed to determine the toxicity of these mixtures on eukaryotic model cells (Saccharomyces cerevisiae). The DESs showed merely a dehydrating effect on the cells, similar to that produced by CaCl₂, a low cell toxicity salt. This supports these DESs as promising green media. Amphiphilic SBs DESs showed a stronger effect on the cells and a structure-activity trend can be described for this class. A preliminary study on the use of these novel DESs as Brønsted catalyst media was accomplished by the use of one of them in chalcone synthesis, which showed promising catalytic and recycling capabilities.