Synthesis and properties of GABA-based ionic liquids and deep eutectic solvents

Abstract

GABA-based ionic liquids (ILs) and deep eutectic solvents (DESs) were synthesized and their properties compared with those of ILs and DESs with similar structures. In ILs, using GABA as the anion, [N₄₄₄₄][GABA], [N₂₂₂₄][GABA] and [N₄₄₄₆][GABA] in combination with ammonium, [C₂mim][GABA] in combination with imidazolium and [Ch][GABA] in combination with the biological substance choline were synthesized. Among the ILs under investigation, [N₂₂₂₄][GABA], [N₄₄₄₆][GABA] and [C₂mim][GABA] were liquid at room temperature. In DESs, GABA was used as the hydrogen bond donor and three GABA-based DESs were prepared by combining [Ch][Cl], [L-Car][Cl], and [DL-Car][Cl] as hydrogen bond acceptors. Among these DESs, [L-Car][Cl] : GABA (1:1) and [DL-Car][Cl] : GABA (1:1) were shown to be liquid at room temperature. Comparing the viscosities of the prepared liquids showed that DESs was significantly higher than ILs. The viscosity increase was suggested to be due to the hydrogen bond acceptors of [L-Car][Cl] : GABA (1:1) and [DL-Car][Cl] : GABA (1:1) having carboxyl groups. The toxicity of GABA-based ILs and DESs was investigated using HeLa cells, which showed that their cytotoxicity was similar to or lower than that of GABA alone in HeLa cells.