Gelation behavior and supramolecular chirality of a BTA derivative in a deep eutectic solvent

As novel solvents, deep eutectic solvents (DESs) are non-toxic, easily producible and biocompatible, which is attractive for eutectogel fabrication. In this work, a benzene 1,3,5-tricarboxamide (BTA) derivative (substituted by three hexanoic acid) was selected to prepare a supramolecular gel in a suitable DES composed of choline chloride and phenylacetic acid molecules. The obtained eutectogel exhibited higher stability than that produced in conventional solvents. The gel microstructure was composed of spiral fiber networks as confirmed from atomic force microscopy and scanning electron microscopy observations. Macroscopic chirality was therefore recognized by the circular dichromatic spectrum, though such a supramolecular chiral signal was random. To explore the gelation mechanism, the effect of BTA derivative molecular structure change was systematically investigated. With the help of Fourier transform infrared spectroscopy and powder X-ray diffraction, the gel formation was attributed to the π-π stacking of adjacent BTA molecules and the three-fold hydrogen bond between amide groups or the hydrogen bond between carboxylic groups. Furthermore, the directional hydrogen bonds between BTA and solvent molecules induced their aggregate to form one-dimensional fibers, which were either left- or right-handed. The obtained results not only extend the gel systems in DESs, but also help design the supramolecular chirality from non-chiral molecules.