pH- and thermo-induced morphological changes of an amphiphilic peptide-grafted copolymer in solution

A pH-responsive amphiphilic poly(N-isopropylacrylamide) (PNIPAm) was synthesized by grafting on a peptide (Leu-Lys)8. The grafted content of the copolymer was 12 mol%. We investigated the pH- and thermo-induced conformational and morphological changes of the grafted copolymer and found small globular aggregates below and above the coil-to-globule transition temperature of the main chain under acidic conditions. However, under basic conditions, the peptide graft chains formed a stable β-sheet structure above the transition temperature. Under basic conditions and at high temperature, the main chains formed a globular conformation, and the deprotonated peptides formed intermolecular hydrogen bonds between the copolymer chains. This pH- and thermo-induced conformational transition resulted in the formation of large aggregates. These results imply that the morphology of this grafted copolymer can be controlled by multiple stimuli.