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.
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