Development of Low-Molecular-Mass Organogelators: Synthesis and Physical Properties of N-Linear Saturated Fatty Acyl-GABAs and Their Ester Derivatives.

Abstract

We determined that compounds in which γ-aminobutyric acid (GABA) and linear saturated fatty acids of various lengths are amide-bonded, as found in the human brain, have the ability to gelate organic solvents. We also synthesized compounds of these GABA derivatives attached to 1,5-anhydro-d-glucitol (1,5-AG) or d-glucopyranose (Glc) via ester linkages, and these compounds were also found to be able to gelate organic solvents. From the comparative experiments of gelation using various lengths of N-linear saturated fatty acyl-GABAs and their ester derivatives, it was determined that the compound of N-tetradecanoic acyl-GABA bonded to 1,5-AG via ester linkage (C14GABA-AG) had a particularly high gel hardness and could gelate various organic solvents. Furthermore, field-emission scanning electron microscopy observations revealed the formation of a fibrous structure, which encapsulates the organic solvent and forms a gel. A variable-temperature Fourier transform infrared spectroscopy analysis revealed that the alkyl chains of N-linear saturated fatty acyl-GABAs are packed with an all-trans conformation, whereas the alkyl chains of the ester compounds attached to 1,5-AG or Glc are slightly skewed from the all-trans conformation due to the intermolecular hydrogen bonding of the amide groups. Here, we report the synthesis and analysis of N-linear saturated fatty acyl-GABA derivatives and the gelation mechanism.