Supramolecular Organogelation Directed by Weak Noncovalent Interactions in Palmitoylated 1,5-Anhydro-d-Glucitol Derivatives

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

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.

Supramolecular fibrous gels with helical pitch tunable by polarity of alcohol solvents

A sugar-based, low-molecular-weight gelator 16AG, can gelatinize primary alcohols by forming supramolecular fibers. We obtained non-helical, tape-like fibers in methanol and ethanol but helical fibers in alcohols with at least three carbons. The pitch of the helical fibers became shorter with increasing carbon number.

Protonation-Triggered Supramolecular Gel from Macrocyclic Diacetylene: Gelation Behavior, Topochemical Polymerization, and Colorimetric Response

Supramolecular gels originating from the hierarchical self-assembly of low molecular weight organic molecules is a strongly emerging field of advanced material research for the fabrication of soft functional materials. Herein, a novel supramolecular gel was fabricated through the protonation-triggered unidirectional self-assembly of pyridine-attached macrocyclic diacetylene (PyMCDA). Basic nitrogen of a pyridine ring with a strong affinity toward proton transforms the neutral PyMCDA into gelator in its protonated pyridinium salt form (PyMCDA-H⁺), which further evolves to nano-fibrillar networks to yield a supramolecular gel. Under the irradiation of UV light, the white color gel turned to a robust covalently cross-linked blue-phase PDA gel. Interestingly, polymeric PyMCPDA-H⁺ gel exhibits a naked-eye detectable reversible blue-red colorimetric response for alternating acid/base (H₂SO₄/NH₄OH) and colorimetric sensitivity toward selected anions: CH₃COO^-, CN^-, HCOO^-, and CH₃CH₂COO^-. It is with the hope that this work point toward the utility and versatility of macrocyclic PDAs for constructing chromogenic supramolecular gels for their possible use in sensing systems.