Synergistic Assembly Of Cationic Peptides And Polyoxometalates

The electrostatic assembly of cationic peptides and anionic guests has vast potentials in constructing the novel self-assembly structures and developing functional integrated materials.Especially the electrostatic system of cationic peptides and polyoxometalates(PMs)has made great progress in the field of biomedicine and catalysis.However,some problems still need to be solved in urgent: 1)The assembled structure is single,the degree of order is not high,and the controllability is poor;2)The research on the relationship between the assembled structure and the assembled driving forces is not in-depth;3)How to make use of the advantages of the two parties to develop functional coordination new materials.In this dissertation,through optimal design for the cationic peptides,the controllable construction of the ordered assemblies in aqueous solution based on cationic peptide/PMs was realized via ionic self-assembly(ISA)strategy,we have a deep understanding of the relationship between the assembled structures and driving forces.The multivalent nanofibers were applied in antibacterial field by using the multivalent effect of the surface of the assemblies.The reversible information writing and erasing stimuli-responsive gels were constructed by using the redox properties of PMs.First,the 1D multivalent nanofibers with well-dispersion in aqueous solution were obtained based on the multivalent electrostatic interactions between cationic peptides and PMs,and then further expanded their applications in improving the antimicrobial activity and biological stability of short peptides.At first,the aromatic amino acid containing azobenzene group was designed and synthesized,and a series of facial amphiphilic short peptides with alternating sequence of azobenzene residues and lysine residues were synthesized by traditional fmoc solid phase peptide synthesis method,and then were complexed with PMs in aqueous solution via ISA strategy.CD spectra indicated that the peptide changed from random coil conformation to ?-sheet conformation with adding the PMs,and the TEM data showed that the peptide changed from irregular nanospheres to well-separated 1D nanofibers after mixing with PMs.Zeta-potential data showed that the stable nanofibers with well dispersion can be obtained due to the presence of high density of lysine groups on the surface of nanofibers.The antibacterial activity of cationic short peptide was enhanced by the high binding capacity of the high density lysine groups on the surface of nanofibers with bacterial membrane.The stability of cationic peptides in human serum was increased due to the active sites of cationic peptides were embedded in the assemblies,which can reduce the contact with enzyme.Second,by controlling the hydrophobicity and length of cationic peptides,the assembly process of cationic peptides and PMs with various sizes were studied in detail,so we have a deep understanding of the driving forces and mechanism of assembly process.At first,a series of facial amphiphilic short peptides with lysine residues were designed and synthesized,and then complexed with various PMs in aqueous solution via ISA strategy.CD data indicated that the PMs can induce the peptide changed from random coil conformation to ?-sheet conformation.TEM and AFM images demonstrated that the morphology and stability of the self-assembled nanostructures are attributed to the balance relationship of several competitive driving forces: intermolecular hydrogen-bonds,hydrophobic and/or ?-? stacking interactions,the steric hindrance of PMs,and the electrostatic repulsion of the peptides.1D nanostructures could be constructed by increasing the intermolecular hydrogen-bonds,hydrophobic and/or ?-? statcking interactions of peptide molecules or decreasing the sizes of PMs;the stable nanostructures in aqueous solution could be obtained by decreasing the electrostatic repulsion of peptides.These results provide a new way to control the ISA behavior between cationic peptides and PMs.Third,based on the understanding of the driving forces and mechanism of assembly between cationic peptides and PMs,through further optimization of cationic peptides and the rational screening of PMs,the helical self-assembly of PMs in aqueous solution was realized,and controlling the chirality and pitch of the assembled structures.At first,a series of facial amphiphilic short peptides with lysine residues were designed and synthesized,and then complexed with PMs in aqueous solution via the ISA strategy.TEM results show that L type ionic assembly complex formed the left-handed helical nanofibers,and the D type ionic assembly complex formed the right-handed helical nanofibers.The helical pitch of nanofibers will be increased by decreasing the hydrophobicity of peptides or increasing the size of PM clusters because of the loose stacking of peptide molecules.In addition,the helical assembly of other PMs was also realized by the cationic peptides tuned two PMs co-assembly strategy.Fourth,combining the self-assembly ability of peptides with the redox activity of PMs,the reversible information writing and erasing stimuli-responsive gels were constructed based on the cationic peptides and PMs.We also focus on the facial amphiphilic short peptides and PMs,and the stable hybrid gels were obtained via solvent exchanged strategy(water and ethanol).CD spectra showed that these peptides adopted both ?-sheet and random-coil conformation within the hybrid gels.TEM and SEM images revealed that the PMs acting as nanosized cross-linkers to drive the cationic peptides co-assembly into nanospheres first,then these nanospheres accumulated together to form large sheet-like structures,which further interconnected into continuous 3D network structures.In addition,the PMs also endowed the hybrid gels with reversible photo-and electro-chromic properties,and the non-fluid gel matrix acted as a colour acceptor and depositor.Information writing and erasing were reversible,which was demonstrated by repeated photo or electric stimuli.These results indicate that the hybrid gels with dual-chromogenic properties have potential applications in information storage and optical-electrical switching materials.In conclusion,through optimal design for the cationic peptides and screening of the PMs,we have a deep understanding of the driving forces and mechanism of synergistic assembly of cationic peptides and PMs in aqueous solution.The nanofibers and helical nanofibers were constructed.The nanofibers were applied in improving the antibacterial activity and biological stability of cationic short peptides,and the construction of reversible information writing and erasing stimulus-responsive gel materials.