Assembly and Evolution of Gemini-Type Peptide Amphiphile with a Di-Lysine Spacer

Peptide amphiphiles (PAs) can self-assemble into a variety of supramolecular structures with excellent biofunctions. However, their assembly with time has rarely been observed and reported. Here, we find that a novel gemini-type PA [12-(Lys)₂-12], taking two lysine (Lys) groups as the spacer, shows an obvious assembly and evolution process with time. Driven by the strong hydrophobic interaction between the alkyl chains as well as the electrostatic force and hydrogen bonding among the peptide spacers, the 12-(Lys)₂-12 molecules first self-assemble into vesicles and then transform into fibrils, ribbons, and belts with time. If replacing the -(Lys)₂- spacer with four lysine groups [-(Lys)₄-] or two glutamic acid groups [-(Glu)₂-], the PA molecules do not show the aggregate growth with time. This indicates that the lysine structure and its length are important structural factors contributing to the dynamic aggregate evolution behavior. More interestingly, this assembly and evolution behavior is highly dependent on 12-(Lys)₂-12 concentration. Only in the proper concentration region (0.5-0.7 mM), the self-assembly displays the aggregate growth with time. At lower or higher concentrations, the aggregate growth is largely delayed or inhibited. Moreover, we also find that the aggregate growth of 12-(Lys)₂-12 is related to the fibril solubilization temperature ( T_f→s). The faster aggregate growth occurs when the temperature is much lower than T_f→s. This work gains new insights into the evolution of the self-assembling structures of peptide amphiphiles.