Chiral self-assembly and water effect on a supramolecular organogel stable towards aqueous interfaces

Abstract

Herein, we report on the stabilizing effect of water and the chiral self-assembly mode of a cholesterol-based low-molecular-weight supramolecular organogelator. Dynamic rheology experiments performed on gels prepared in methanol and methanol–water mixtures showed an enhanced strength and rigidity in the presence of water, in line with the thermal stability previously observed. Morphological characterization experiments (scanning electron microscopy and X-ray powder diffraction) were performed on aerogels obtained after solvent extraction with supercritical CO2. Concentration- and temperature-dependent proton nuclear magnetic resonance and electronic circular dichroism experiments confirmed that the molecules of gelator self-assemble with a dominant right-handed helicity through intermolecular hydrogen bond interactions between the carbamate groups, and that the addition of water does not affect either the mode of assembly or the chirality of the supramolecular structure. Computational simulation experiments allowed us to propose a mode of self-assembly compatible with the experimental results, which involves a unidimensional head-to-tail stacking of molecules. A methanolic gel was successfully used as a molecular template for the in situ hydrolytic sol-gel polymerization of tetraethyl orthosilicate giving rise to silica nanotubes with an internal diameter of 7 nm.