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.