Cysteine and pH-Responsive Hydrogel Based on a Saccharide Derivative with an Aldehyde Group

For the development of chemoresponsive hydrogel, a new saccharide-derived hydrogelator 1 methyl-4,6-O-(4'-aldehydephenylidene)-alpha-D-glucopyranoside was synthesized and characterized. The resulting hydrogel not only shows thermal responsiveness but also exhibits cysteine and pH responsiveness due to the presence of aldehyde and acetal groups in 1. The release of guest molecules from the hydrogel of 1 was examined by employing compound 2 (fluorescein disodium) and compound 3 methyl-4,6-O-(2'-pyrenylidene)-alpha-D-glucopyranoside as guest molecules. The results indicate that the release of compound 2 from the hydrogel of 1 is controlled by the diffusion process, while the release of compound 3 from the hydrogel of 1 is facilitated by the presence of cysteine. These results demonstrate (1) the proof of principle to design chemoresponsive gels by incorporating reactive groups into the gelators and (2) it is possible to stimulate the release of guest molecules from hydrogels upon addition of reactive chemicals by manipulating the intermolecular interactions among the hydrogelators and guest molecules.