Alkoxy Tail Length Dependence of Gelation Ability and Supramolecular Chirality of Sugar-Appended Organogelators

A series of sugar-appended organogelators, 4-(4'-alkoxyphenyl)phenyl-beta-O-D-glucoside (GBCn, where n = 1-12 denotes the number of carbon atom in the tail), are synthesized to elucidate the effect of terminal chain length on their gelation and chiral expression abilities in gels. In the mixture of H2O/dioxane (60/40 v/v), GBCn undergoes a phasic evolution of precipitation-solution-gel-precipitation-gel as its tail length increases from n = 1, 2, 3-6, and 7-10 to 11-12, respectively. Helical ribbons are observed in gels, but platelet-like structures are the dominant morphologies in the systems that precipitation happens. Combinatory analyses of microscopic, spectroscopic, and diffraction results reveal that the self-assembly into interdigitated bilayer structures of GBCn is driven by hydrogen bondings of sugar heads, pi-pi interactions of biphenyl rods, and hydrophobic interactions of alkoxy tails. The helical-morphology formation is caused by the significant steric repulsion between chiral moieties on the condition of the disordering or the size of alkoxy chains reaching the threshold of helical twisting and bending.