Modulating self-assembly behavior of a salt-free peptide amphiphile (PA) and zwitterionic surfactant mixed system

A salt-free surfactant system formed by a peptide amphiphile with short headgroup (PA, C-16-GK-3) and a zwitterionic surfactant (dodecyldimethylamine oxide, C(12)DMAO) in water has been systematically investigated. The microstructures and properties of C-16-GK-3/C(12)DMAO mixed system were characterized using a combination of microscopic, scattering and spectroscopic techniques, including transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), circular dichroism (CD) and rheological measurements. Rich phase transitions have been observed by adjusting the concentration of C-16-GK-3. Investigation of the hydrogels of C-16-GIC-3/C(12)DMAO with TEM, SEM and AFM showed that all of these hydrogels form nanobelts. The nanobelt formation is performed in a hierarchical manner: beta-sheet peptides and C(12)DMAO first interact each other to form small aggregates, which then arrange themselves to form one dimensional (1D) left-handed ribbons. The ribbons further aggregated into flat and rigid nanobelts. We proposed a mechanism to interpret the self-assembly process according to the specific peptide structure as well as multiple equilibria between the hydrogen bonding interactions between the headgroups of C-16-QC-3, between C(12)DMAO molecules and the headgroups of C-16-GK-3, chirality of the amino acid residues and hydrophobic interactions of the alkyl chains. (C) 2015 Elsevier Inc. All rights reserved.