Copper Ion-controlled Peptide Self-assembly And Peptide-controlled Cuprous Oxide Synthesis

The complexes formed between proteins/peptides and metal ions are ubiquitous in organisms.Many of these complexes play important biological roles in life activities.Such as metalloenzymes coordinate with certain metal ions by non-covalent interactions to realize their catalytic activities.Not all complexes formed by proteins and metal ions benefit for the life,there are many complexes harmful for organisms such as the oligomers formed by amyloid proteins with Zn²⁺,Cu²⁺,or Fe³⁺.The interaction mechanism and mode between proteins or peptides and metal ions have been researched during several decades.A few basic understandings have been concluded.The detailed information about the coordination environment in metalloenzymes and the pathogenic mechanism related with amyloid protein-metal ion complexes can direct to build the functional materials such as artificial enzymes or cure the neurodegenerative diseases.In this research,the hairpin peptides as the model molecules were designed by changing the amino acids sequence in the molecular structure to investigate the effect of molecular structure to the selective coordination between the peptides and metal ions.Other peptides containing histidine residues were used to synthesize cuprous oxide nanoparticles with different morphologies.In this research,the hairpin peptides Ac-VKVKVHVHV^DPPTHVHVKVKV-NH₂?CBHH?and Ac-VKVKVKVKV^DPPTKVKVKVKV-NH₂ were designed and synthesized on the CEM peptide synthesizer.The data obtained from UV-Vis,¹H NMR,and CD indicated that the peptide CBHH coordinated with Cu²⁺by four imidazole groups and then the conformation of CBHH molecules changed to?-sheet from random coil at pH5.But the Ac-VKVKVKVKV^DPPTKVKVKVKV-NH₂ did not coordinate with copper ions when adding equivalent copper ions and the conformation of this peptide kept random coil.These data demonstrated that the coordination between imidazole group and copper ion was very important in conformation transition of peptide CBHH.When addition of Zn²⁺,Ni²⁺,Na⁺,and Ca²⁺into peptide CBHH solution at pH5,the CBHH maintained random coil which indicated the coordination environment occurred in hairpin structure was specifically suitable to copper ion.When CBHH formed?-sheet in the presence of equivalent copper ion at pH5,the fibril was formed by hydrophobic interaction from side chain of valine and intermolecular hydrogen bond from amide in the main chain soon after.Because the copper ion located on the interface between fibril and water,the CuS nucleated at the interface between fibril and water and grew along the fibril when adding Na₂S?the ratio between copper and sulfur=1:1?.The temperature of mixture increased approximately 17°C at 4 mM CuS/CBHH complex structures when the sample exposed at near infrared laser light?808 nm?during 7.5 minutes.The thermal effect of Cu S nanowires was concentration-dependent.Further investigating the effect of molecular structures,the number and species of amino acids in other five hairpin peptides were constant with CBHH,and then the sequence of amino acids in hairpin peptides was adjusted.All six hairpin peptides possessed similar charged situation at pH5 due to similar pKa.The location of histidine residues in peptides could affect the affinity between copper ion and hairpin peptides from isothermal titration calorimetry?ITC?analysis.The order of affinity between copper ion and hairpin peptides was CBHH>KHHK>HHKK>HKKH>KHKH>HKHK.The UV-Vis,¹H NMR,Vis-CD analysis gave the coincident results with ITC data.Both CBHH and KHHK formed stably distorted tetragonal coordination structure with copper ion by four imidazole groups.Other four peptides coordinated with copper ion by two or three imidazole groups so these peptides with1 mM copper ion could not formed hairpin structure.Only 1 mM CBHH and KHHK formed short fibril in the presence 1 mM copper ion.Other four peptides formed disordered aggregation.When peptides and inorganic salts in solution reached to enough high concentration,all six peptides transformed to?-sheet conformation and formed fibril due to the charge screening by negative ions.Other three peptides contained HG12,HG6,and CN225 synthesized were used to direct the growth of cuprous oxide nanostructures.With the imidazole group,amino group,nitrogen from amide,carboxyl group coordinated with copper on?111?crystal planes of cuprous oxide,the?111?crystal planes were stabilized and the crystal grew along<111>crystallographic orientation.The majority of nanoparticle surface synthesized by peptides was?111?crystal plane.The methyl orange was efficiently degraded by cuprous oxide nanoparticles synthesized by peptides.