Effect of Water on the Activation Thermodynamics of Deep Eutectic Solvents Based on Carboxybetaine and Choline

Thermodynamic characteristics as well as peculiarities of hydrogen bonding in aqueous solutions of new deep eutectic solvents (DES) based on synthetic carboxybetaine have been studied. Cheap starting reagents (acrylic acid and 2-dimethylaminoethanol), simple preparation, and high yields are the advantages of the proposed betaine. Analyses of the calculated stabilization energies and natural bond orbital delocalization energies revealed the absence of preferential association in aqueous reline solutions tested for the comparative purpose. On the other hand, it was demonstrated that water preferentially associates with betaine molecules as this type of interaction was proved to possess the highest stabilization energy among the considered complexes. These data were used to discuss the anomalous behavior of the experimentally determined enthalpy and entropy factor of a viscous flow. Thus, sharp increase in the values of TΔSA and ΔHA was demonstrated for the betaine-based solutions with 30–40 wt % water. The ...