Hierarchical self-assembly of amphiphilic peptide dendrons: evolution of diverse chiral nanostructures through hydrogel formation over a wide pH range.

An amphiphilic dendron containing three dendrite L-glutamic acid units and a long alkyl chain was synthesized by a convergent method. It was found that the dendron could form hydrogels over a wide pH range from 2 to 13. Moreover, accompanying the pH change, the compounds self-assembled into various chiral structures: from helical nanotube, helical nanotube with a string of beads, and coiled superhelix to dendrite nanostructures, such as pine, feather, etc. A series of characterizations based on TEM observations, X-ray diffraction and FTIR spectroscopic measurements revealed that the dendron formed a bilayer first and then hierarchically self-assembled into various chiral nanostructures. The four carboxylic acid groups and three amide groups played an important role in the self-assembly. The interaction between the multiamide groups stabilized the bilayer structures, whereas the ionization degree of the carboxylic acids was responsible for the formation of various chiral structures. The work presented a hydrogel system with wide pH adaptability and showed the regulation on chiral structures by simple pH variations.