Peptide Self-assembly And Directed Synthesis & Assembly Of Platinum Nanocrystals

The synthesis and assembly of Pt NCs have attracted much more interest because of remarkably distinct properties and application potentials in catalysis. Because peptides have many compositions and active groups, and are degradable, biologically active, biocompatible, specific recognizable, could be used in biological and medical fields, and especially some amphiphilic peptides could self-assemble to nanostructures with a variety of morphologies, scientists have been trying to synthesize and assemble Pt NCs with peptides in the hope of obtaining more functional and adjustable nanomaterials. So in this subject, the stabilization mechanism to Pt NCs of a genetic peptide, named P7 A with a sequence of TLHVSSY, the self-assembly mechanism of Aβ(16-22), and peptide directed Pt NCs non-template-based assembly to supraarchitectures or template-based assembly to 1D nanoassemblies were investigated. The mainly results are as follows:(1) The mechanism of peptide stabilizing Pt NCs and mediating Pt NCs non-template-based assemblyThe mechanism of P7 A derived from phage display technology capable of stabilizing ultrasmall Pt NCs was investigated. Our work revealed that P7 A could adsorb onto the ultrasmall Pt NCs through its N-terminal and side-chain active groups(including amino, hydroxyl and imizadole ring), leaving its C-terminal carboxyl group free and supplying electrostatic repulsive interactions to stabilize Pt NCs. Through modulating the colloidal dispersion pH to control the protonation extent of the carboxyl groups, reversible, regularly edge-to-edge distanced supraarchitectures were assembled from P7 A capped ultrasmall Pt NCs.Further through amidating the C-terminal carboxyl groups of P7 A to synthesize its derivative peptide P7A-NH2 as the capping agent, the core/shell supraspheres could be assembled from P7A-NH2 capped ultrasmall Pt NCs. Through controlling the concentration of P7A-NH2 to modulate the reaction rate of the limiting step, other supraarchitectures with morphologies different from supraspheres could be assembled. With the help of the hydrophilicity of P7A-NH2, these supraspheres could selectively wet and spread on the mica surface to form an ultrathin film, while sustain the whole on HOPG surface.(2) The mechanism of amphiphilic peptide self-assembly and morphology modulationsThrough N-terminal acetylation and C-terminal amidation to block the amino and carboxyl charged groups, the electrostatic repulsion could be selectively decreased, and the self-assembled narrower nanofibers from unblocked Aβ(16-22) could be modulated to wider nanoribbons self-assembled from blocked ones. And further through adjusting the solution pH to change the charge properties of Aβ(16-22), the diameters of the self-assembled nanostructures could be finely modulated.Through replacing the Phe(s) in blocked Aβ(16-22) with Cha, Phg or Chg, the hydrophobic, aromatic and steric interactions could be well refined, and the roles of Phe side chain in Aβ(16-22) self-assembly were investigated. The results showed that, through replacing FF to(Cha)(Cha),(Phg)(Phg) and(Chg)(Chg), the laminate aggregation forces(aromatic interactions, steric complementary) would be decreased with different extent, and the self-assembled nanostructures would be transformed to nanotubes, nanofibrils or much narrower nanoribbons from original wider nanoribbons. And further through replacing either F to(Phg)F or F(Phg) with Phg, the twisted nanoribbons or nanofibrils could be self-assembled. However, when replacing the 20 th A to F, the peptide FFF self-assembled to the narrowest nanofibrils rather than more wider nanoribbons, showing that the hydrophobic interactions is the principal driving force in Aβ(16-22) self-assembly.In one word, there is an equilibrium between the laminate aggregation forces(aromatic interactions, steric complementary) and the laminate twisting forces(hydrophobic interactions, electrostatic repulsive interactions and steric hindrance), which leads to the blocked Aβ(16-22) self-assembled to nanoribbons. As long as disturbing the equilibrium, the self-assembled morphologies of Aβ(16-22) would be modulated.(3) Peptide directed assembly of 1D Pt nanoassemblies and modulating the characteristicsWith the nanofibrils self-assembled from an Aβ(16-22)-like ultrashort peptide I3 K as the templates, through adding K2PtCl4 as precursor and NaBH4 as reductant--in situ synthesis strategy, 1D continuous Pt nanoassemblies could be assembled. Further introducing P7 A as the capping agent, 1D Pt nanoarrays distributed with regularly interparticle-distanced NCs could then be assembled. These 1D Pt nanostructures exhibited distinct electrocatalytic properties, showing the better catalytic performance to the DMFC anode electro-oxidation reaction of the 1D continuous Pt nanoassemblies. In addition to the better electrocatalytic properties, the new electrocatalysts have higher tolerance to poisoning intermediates than the commercial Pt black control.When concentrating P7 A capped ultrasmall Pt NCs and adding them into I3 K self-assembled nanofibrils--post conjugation synthesis strategy, 1D Pt nanoassemblies with discrete NCs sprinkled around I3 K nanofibrils were assembled. Furthermore, the assembly characteristics, such as small Pt NC nanoclusters or isolated Pt NCs as the assembly units, could be well tuned through precipitation-redispersion or ultrafiltration enrichment approach.