Sharp-pH-Sensitive Amphiphilic Polypeptide Micelles with Adjustable Triggered pHs by Salts via the Hofmeister Effect

Supramolecular self-assembly of polymeric molecules for sharp-pH-sensitive (SPS) nanoparticles is an especially important application in biology. Here, amphiphilic polypeptide copolymers are synthesized and spontaneously assembled to micelles in aqueous solution, and protonation of the tertiary amine groups in the side-chain of the copolymer under weak acid causes the micelle disassembly, which is sharp-pH-sensitive, and the responsive pHs can be adjusted by adding salts. Size and morphologic change of the polymeric micelles are characterized by means of dynamic lighting scattering, transmission electron microscope (TEM), and atomic force microscope (AFM) in sequential pH alterations. It is found that the Hofmeister ions play a key factor in controlling the subtle interaction of different noncovalent bonds among polypeptide molecules during their self-assembly or disassembly. The physical property exploration of the SPS micelles may provide a new chance for the development of dynamic, complex nanostructures in various pH-responsive applications.