Sugar-integrated gelators of organic solvents - Their remarkable diversity in gelation ability and aggregate structure

Five 1-O-methyl-4,6-O-benzylidene derivatives of the monosaccharides D-glucose, D-galactose, and D-mannose were synthesized. The β-isomer of the D-glucose derivative was sparingly soluble in most organic solvents, whereas the α-isomer of the D-mannose derivative was soluble in many organic solvents. The α-isomer of the D-glucose derivative and the α- and β-isomers of the D-galactose derivative acted as versatile gelators of various organic solvents; this indicates that saccharides are useful as potential templates for the molecular design of chiral gelators. In particular, the two D-galactose-based gelators behaved as "excellent gelators". It is very surprising that a change in the configuration of only one carbon atom results in such a drastic change in the solubility and the gelation properties. The possible relationship between the saccharide structure and the gelation properties is discussed on the basis of FT-IR and ¹H NMR spectroscopic data, differential scanning calorimetric (DSC) measurements, scanning electron microscopy (SEM) observations, and computational studies. FT-IR spectroscopy showed that the gelation properties are related to the formation of "moderate" intermolecular hydrogen bonds. The SEM observations showed that the gelators can form various fibrous structures (straight, puckered, and helical). The present study shows that this saccharide family is a potential combinatorial library of organic gelators and more generally, of molecular assembly systems.