New sugar-based gelators with an amino group, the gelatin ability of which is remarkably reinforced by the hydrogen bond and the metal coordination

Three sugar-integrated gelators bearing a p-aminophenyl group which are expected to exert a hydrogen-bonding effect and a metal coordination effect on the gelation ability were synthesised. -D-Galactose-based 2b was only soluble or precipitated and -D-glucose-based 4b gelated only two of 15 solvents tested herein whereas -D-glucose-based 1b acted as an excellent gelator which could gelate 8 solvents. The sol–gel phase-transition temperature (Tgel) values for 1b were higher by 41–78 °C than those for -D-glucose-based 1a bearing a p-nitrophenyl group. The spectral studies indicated that this gel reinforcement is due to the hydrogen-bonding interaction including the amino group. The Tgel values for the ethanol gel of 1b were markedly improved by the addition of AgNO3, CoCl2 or CdCl2. The detailed examination of a 1b + CoCl2 gel system in ethanol showed that the gel is stabilised by the cross-link of 1b molecules by the Co(II)–amino group interaction. This is the first and a convenient method for the metal reinforcement of organic gels

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. \u