Electrostatic Interaction Induced Peptides Amphiphiles Coassembly

Peptide and peptide based biomaterials have showed important application potential in various areas such as cell culture because of its excellent biocompatibility and abundant self-assembly features.Coassembly of two kinds of peptides would further improve the properties and functions of assemblies on the basis of self-assembly.And it has gradually attracted researchers' interests.Both lipopeptides and peptide amphiphiles are amphiphiles like traditional surfactants.In this thesis,we have designed and synthesized a positively charged lipopeptide C16K2-NH2 and a negatively charged C16E2-NH2,and studied the coassembly behavior of them by electrostatic attraction according to the principle of sufactants mixing.On the basis of coassembly results,we added a light responsive functional group on the alky chain of lipopeptide,and studied coassembly behavior of the modified lipopeptide with other amphiphilic molecules with and without UV light.Both TEM(Transmission Electron Microscopy)and AFM(Atomic Force Microscope)results revealed that C16K2-NH2 and C16E2-NH2 coassembled into distorted long fibers through the electrostatic attraction between amino and carboxyl on side chains on each kind of molecules below their each critical aggregation concentrations.CD(Circular Dichroism)results showed that these coassemblies adopted the secondary structure of ?-sheet.Adjusting the concentration ratio of the lipopeptides,pH as well as salt(NaCl)concentration could effectively adjust the coassembly process and phase behavior.The sceening effects of NaCl reduced the ? potential of the assembled nanofibers and thus affected its colloidal stability and aggregation behavior.Adjusting pH changed the dissociation or protonation degree of charged aminio acid residues,and thus affected the molecular ratio in the coassemblies.The mixing concentrations changed the molecular ratio in coassemblies directly,and also changed the charges of fiber.Thus it regulated the electrostatic interactions between molecules,so the solution phase behavior and coassembly process also changed accordingly.In molecular self-assembly,the introduction of light-responsive groups helps to manipulate the structure,property and function of self-assembly.We designed and synthesized photosensitive anionic peptide amphiphile AzoE2-NH2 by introducing azobenzene group in the hydrophobic aliphatic chain of C16E2-NH2.Then we studied the coassembly behavior of AzoE2-NH2 with the cationic short peptide Ac-L3K-NH2.Morphology characterization results showed AzoE2-NH2 and Ac-L3K-NH2 self-asssembled to random aggregators and spheres respectively.When mixing them together,long nanofibers were formed through the electrostatic attraction.The ultraviolet spectrum proved that azobenzene changed structure from trans-to cis-after UV-irradiation.However,the morphology of the nanofibers didn't change obviously because of their strong electrostatic attraction and hydrogen interaction between molecules in the coassemblies.