Metal-triggered supramolecular hydrogels based on bipyridine ligand possessing hydrazine moieties with metal ions

Bipyridine-based gelator 1 having two D-alanine units was prepared, and its gelation ability was evaluated in the presence of Co(NO3)(2) and AgNO3 in water. Gelator 1 could gelate H2O in the presence of Co(NO3)(2) or AgNO3 (1.0 equiv.) in water. Gelator 1 formed a 2:1 (1:Co2+) octahedral complex with Co2+, whereas it formed a 2:1 (1:Ag+) tetrahedral complex with Ag+. The metallosupramolecular hydrogel with Co2+ assembled into a left-handed helical fiber, whereas that with Ag+ assembled into a nanorod structure. H-1 NMR and FTIR analyses revealed that pi-pi stacking and intermolecular hydrogen bonds acted as the driving force for the formation of the supramolecular nanoarchitectures. Furthermore, to characterize the viscoelastic properties of hydrogels, rheology experiments were conducted at 25 degrees C, including time, strain, and frequency sweeps.