Self-assembly behavior of peptide amphiphiles (PAs) with different length of hydrophobic alkyl tails

Amphiphilic peptide and their derivatives, with distinguished advantages over conventional materials, have received extensively research interesting recently. In this work, four peptide amphiphiles (PAs1-4) with different length of hydrophobic alkyl tails (C9 for PA1, C11 for PA2, C13 for PA3, and C15 for PA4) were fabricated and their self-assembly behaviors in aqueous medium at different pHs were investigated systematically. It was found that all the peptide amphiphiles can self-assemble in water at a neutral pH of 7 to form tightly packed nanofibers with a beta-sheet conformation. When altering the solution environment to basic medium (pH 11), due to the strong hydrophobic interaction of long alkyl tails in PA3 and PA4, the fibrous nanostructure self-assembled from PA3 and PA4 was not destroyed. However, the nanofibers self-assembled from PA1 in which the length of alkyl tail was relatively short converted into loose spherical micelles with a beta-sheet conformation. Due to the moderate length of alkyl tail in PA2, both nanofibers and micelles can be formed via the self-assembly of PA2 when increasing the pH of the self-assembling system.