Influence of the secondary structure on the AIE-related emission behavior of an amphiphilic polypeptide containing a hydrophobic fluorescent terminal and hydrophilic pendant groups

In this study of the amphiphilic polypeptide TP-PPLG-g-MEO2 containing a hydrophobic tetraphenylthiophene (TP) terminal, with aggregation-induced emission (AIE) properties, and hydrophilic ether side groups, it was found that secondary structures (α-helix, β-sheet and random coil) of the peptide chains affected the AIE-related emission of the TP terminal. The amphiphilic TP-PPLG-g-MEO2, prepared from a ring-opening polymerization and the following click reaction, contained a secondary structure mostly composed of α-helical chains. The main α-helical chain nevertheless can be converted into a β-sheet structure by adding NaCl into the aqueous solution of TP-PPLG-g-MEO2 and by doing so, the solution emission can be enhanced. In addition, the coil chain generated in the alkaline solution was found to emit efficiently with the highest emission intensity among all three conformations. The relationship between the AIE property and the secondary structure of the peptide chains can therefore be evaluated. All three secondary structures were also used as luminescent sensors to test their sensitivity for bovine serum albumin (BSA).