Synthesis, Self-Assembly And Interfacial Adsorption Behavior Of Surfactant-like Peptides

As a promising approach to fabricating novel materials and devices on the nanoscale, short peptide self-assembly has been extensively explored over the past few decades. Because of their unique features such as biocompatibility and biological modifications, peptide-based self-assembled have been found applications in the delivery of drugs, nano-technology, bio-materials. Surfactant-like peptides have been reported to self-assemble efficiently into various nanostructures, including fibers, tapes, tubes, and spheres. In this paper, we designed a series of surfactant-like peptides and studied their self-assembly. We described the dynamic self-assembly processes of peptide surfactants in aqueous solution. Our results have revealed interesting transitions in structure and dynamics of peptide molecular self-assembly. We also studied the adsorption of surfactant-like peptides at the hydrophilic and hydrophobic solid/water interface. The main conclusions are listed as follows:From a combined AFM, TEM, and CD study of a series of surfactant-like peptides AmK(m=3,6 and 9), we show that structural transitions (sheets, fibers,worm-like micelles, and short rods) can be induced by increasing the length of the hydrophobic peptide region. The trend can be interpreted using the molecular packing theory developed to describe surfactant structural transitions, but decreased CAC, and increased electrostatic interaction associated with increasing the peptide hydrophobic chain need to be taken into account appropriately. Dynamic processes of molecular self-assembly from two surfactant-like peptides A6K and A9K have been investigated. Aggregated peptide stacks were formed during the first hour of solution preparation, followed by their assembly into short nanofibrillar segments in the 24 hour period. The alignment of short nanofibers into mature long ones then occurred, with final lengths extended to several microns but with diameters remaining fixed at 5-8 nm. Even after a week, gaps or joints still remained in the mature nanofibers. In contrast, A9K self-assembled into smaller nanorods with diameters of around 3-4 nm and lengths mostly within about 100 nm. The entire self-assembling process was completed within the first hour and there were few further morphological variations afterwards.The changed of two surfactant-like peptides A6K and A9K self-assembly in different pH values, temperature and ionic strength have been studied. The structure of peptides is sensitive to the changes of pH, temperature, ionic strength. With the weak non-covalent interaction including the electrostatic interaction, intermolecular hydrogen bond and the interaction of hydrophobic tail, they could self-assembled into the nano-structure and they harmonize with each other. The interactions of hydrophobic tail play a major role in the stability of the surfactant-like peptides self-assembly process.We have focus on the interfacial adsorption of two surfactant-like peptides A6K and A9K, at the hydrophilic and hydrophobic solid/water interface. The A6K achieved its steady adsorption at the concentration of 0.5 mM while the A9K achieved its stead adsorption at the concentration of 0.05 mM on hydrophilic solid/liquid interface. At the concentration of surfactant-like peptide below the CAC, the single molecule of them is adsorbed on the interface. While above the CAC, A6K and A9K are self-assemble into nano-structure and monolayer adsorption on hydrophilic solid/liquid interface. On the hydrophobic solid/liquid interface, A6K self-assembled into nanofibers and monolayer adsorption. While the self-assembled structures of A9K changed by hydrophobic interfacial properties and double-layer adsorbed on it.The hydrophobic tail played a major role in the surfactant-like peptides self-assembly, the dynamic process of self-assembly, self-assembly stability and adsorption on different solid/liquid interface. Through the research, we illustrated the mechanism of surfactant-like peptides self-assembly and adsorption on different solid/liquid interface. Our results showed electrostatic attraction was important for initiating the adsorption and hydrophobic interaction was more dominant in determining the equilibrated amount of adsorption.