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.