Green Preparation Of Gold/Peptide Nanocomposites By Biomimetic Mineralization Based On Reducing Polypeptides And Its Catalytic Application

Metallic nanomaterials have various microstructure and excellent physical and chemical properties,which are widely used in catalysis,miniaturization device manufacturing,biomedicine and other research fields.In recent years,more and more researchers have begun to prepare novel organic/inorganic composites by biomolecular biomimetic mineralization in a green way.It is worth noting that due to the various physicochemical properties,good biocompatibility and biodegradability of peptide molecules,many researches have been reported on the synthesis of metal/peptide nanocomposites with special structure and function by biomimetic mineralization using peptides or peptide assemblies.However,there are still some problems to be solved in the design,synthesis,regulation and application of these composites.It mainly includes the discovery of gentler and simpler methods for synthesizing composites with special structure and properties,the discovery of the basic law of the effect of physical and chemical properties of peptide molecules on the structure and properties of composite materials,the discovery of effect law of composite structure on catalytic performance and the exploration of potential emerging applications of composite materials.In this paper,according to the characteristics of different amino acids and the structural and functional properties of peptides,gold/peptide nanocomposites were greenly prepared by biomimetic mineralization using the known and designed reducing peptide monomers or assemblies.Specific research contents and results are as follows:1.Amyloid nanofibrils with regular and stable microstructure can bind metal ions and are often used as templates for the preparation of metal/peptide nanocomposites.We chose to fabricate gold/peptide nanocomposites by biomimetic mineralization in a green way using self-assembled nanofibrils from the core assembly sequence h IAPP_20-29（SNNFGAILSS）of human islet amyloid polypeptide（h IAPP）associated human type 2 diabetes mellitus without reducing amino acids.We found that h IAPP_20-29self-assembled to form long fibrils in Milli-Q water.Electrostatic force microscopy（EMF）and Zeta potential results showed that there was a large amount of positive charge on the surface of the long fibrils.The simulation results show that electron transfer can occur between h IAPP_20-29 and HAu Cl₄,leading to the reduction of gold ions to form gold atoms.By mixing h IAPP_20-29 solution with HAu Cl₄ solution and heating reaction,the composite of two-dimensional gold nanosheets and nanofibrils can be obtained.However,HAu Cl₄ cannot be reduced to the two-dimensional gold nanostructure by using the special amino acids contained in the peptide sequence and the amino acid replacement peptides,and the two-dimensional gold nanostructure could not be obtained by adding hole trapping agents in the reaction,indicating that the structure of peptides and charge transformation could determine the formed morphology of gold nanostructures.Finally,we use the gold/peptide nanocomposite prepared by biomimetic mineralization as catalyst.Due to the presence of electroactive polypeptide components,gold/peptide nanocomposites show excellent catalytic effect in the catalytic reduction of p-nitrophenol,and the conversion rate can reach 58.9%when the catalyst concentration is 5μM.The electrochemical sensor constructed by gold/peptide nanocomposites also has a good detection effect on hydrogen peroxide.2.Polypeptides have great advantages in the synthesis of metal/peptide superstructural nanocomposites with customized shape and function.However,there are few researches on the preparation of gold/peptide superstructural nanocomposites by biomimetic mineralization using polypeptides in a green way.The polypeptide（CYYFGAILYY）is designed and synthesized based h IAPP_20-29.The introduction of tyrosine and cysteine endow the polypeptide redox-active properties.Polypeptides could aggregate intoβ-sheet nanofibrils in Milli-Q water.We mixed polypeptide monomer and nanofibril solution with HAu Cl₄ solution,fully reacted under mild conditions,and realized structural regulation of gold/peptide nanocomposites by using different polypeptide structures.It was found that peptide nanofibril materials loaded with gold nanoparticles were obtained after HAu Cl₄ was reduced by self-assembled nanofibrils,and peptide nanomembrane composites loaded with gold nanoparticles were obtained after HAu Cl₄ was reduced by polypeptide monomers.Due to the electroactive polypeptide component,the gold nanostructure with good dispersion and smaller size,more catalytic reaction sites in the gold/peptide nanomembrane composite,which shows the best catalytic effect in the catalytic reduction of p-nitrophenol and peroxidase-like catalytic reactions.Compared with the gold/peptide nanocomposite prepared based on the h IAPP_20-29 fibrils,the gold/peptide nanomembranes are superstructural composites containing more oxidation-reducing polypeptide components,so their catalytic activity is higher.The colorimetric sensor constructed by gold/peptide nanocomposite films material has excellent detection performance and can realize colorimetric detection of low concentration hydrogen peroxide,and the lowest detection concentration of hydrogen peroxide is10μM.3.In order to prepare gold/peptide nanoparticle composites that can be applied in biomedical directions,different concentrations of HAu Cl₄ solution were mixed with antibacterial polypeptide（CWFWKWWRRRRR）monomers solution containing reducing amino acids and positively charged amino acids,which reacted adequately under mild conditions.Polypeptide monomers play a variety of functions in the reaction as dispersant,reducing agent and template.We have achieved structural regulation of gold/peptide nanocomposites by controlling the concentration of HAu Cl₄.At low concentration of HAu Cl₄,granular gold/peptide nanocomposites were obtained,while at high concentration of HAu Cl₄,seaweed-like gold/peptide nanocomposites were obtained.Because of its good dispersibility,small size and more catalytic reaction sites,the catalytic activity of the gold/peptide nanoparticle composite in the peroxidase-like catalyzed reaction is twice that of the seaweed-like gold/peptide nanocomposite.Based on the enzyme-like catalytic activity of gold/peptide nanoparticle composites,which can be applied in catalytic biomedical field.4.We optimized the concentration ratios of the antibacterial peptide（CWFWKWWRRRRR）and HAu Cl₄ to synthesize gold/antimicrobial peptide（Au@AP）nanozymes by biomimetic mineralization,which have the photothermal properties and peroxidase-like catalytic properties.We performed the catalytic antibacterial and removing biofilm experiments using Au@AP nanozymes.The experimental results show that E.colis,S.aureus and S.mutans can be efficiently killed,the lowest antibacterial concentration was 120μM,and the removal efficiency of S.mutans biofilm on tooth surface could reach 78%under the catalytic action of Au@AP nanozymes.According to the results of tooth whitening experiments,teeth contaminated with external pigments can be whitened effectively with the catalytic action of Au@AP nanozymes without damaging tooth enamel.In addition,the results of cytotoxicity and mice experiments indicate that Au@AP nanozymes have good biocompatibility in vitro and in vivo.In conclusion,the Au@AP nanozyme materials prepared by biomimetic mineralization in a green way have great potential in the treatment of oral diseases caused by bacteria.