Light- and pH-Controlled Hierarchical Coassembly of Peptide Amphiphiles

The coassembly behavior of peptide amphiphiles (PAs) C₄-Bhc-EE-NH₂ and C₁₄-FKK-NH₂ has been investigated by transmission electron microscopy, atomic force microscopy, fluorescence microscopy, circular dichroism, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance. These two PAs coassembled into nanofibers by electrostatic and π-π stacking interactions at a low concentration and further aggregated into nanofiber bundles via charge complementation on the surface of nanofibers. As the charge number varied with pH, the bundles could be disassembled/assembled with pH regulation. More interestingly, as C₄-Bhc-EE-NH₂ was a photodegradable molecule, the bundles could also be responsive to both ultraviolet (UV) and near-infrared (NIR) light. In contrast to the reversible pH-dependent response, the light responses were irreversible as C₄-Bhc-EE-NH₂ broke under UV or NIR radiation. The highlight of this article is that structural changes were realized for control at the aggregate level, not only at the molecular level. With this inspiration, we hope that we can support the novel biomaterial construction and exploitation of new functions of biomaterials.