New sugar-based gelators bearing a p-nitrophenyl chromophore: Remarkably large influence of a sugar structure on the gelation ability

Three sugar-integrated gelators bearing a p-nitrophenyl group as a chromophore were synthesised. D-Mannose-based compound 3 was too soluble in most organic solvents to act as a gelator whereas D-galactose-based compound 2 was sparingly soluble in most organic solvents. D-Glucose-based compound 1 was moderately soluble and acted as an excellent gelator, gelating 10 solvents tested. The possible correlation between the gelation ability and the gelator structure is discussed on the basis of the intermolecular hydrogen-bonding interactions detectable by FT-IR spectroscopy. CD spectral measurements showed that the p-nitrophenyl groups in the gel fibrils of 1 are stacked in the clockwise direction [i.e., with (R)-helicity]. SEM observation of the xerogels showed that in most cases the gelator forms a three-dimensional network with 30-100 nm frizzled fibrils. Only when they were prepared from the methylcyclohexane solution, was the helical structure (although in part) observed.