Theoretical Study On Structure And Growth Mechanism Of Protected Precious Metals Nanoclusters By Ligand

Ligand-protected noble metal clusters have unique optical absorption and excitation properties,and there are some novel applications.Polypeptide ligands protect precious metal clusters,have better biocompatibility,and have important application potentials in fields such as energy catalysis,bioimaging,and targeted drug delivery.Among them,the performance of ligands to protect copper clusters is also very bright.In recent years,ligand-protected noble metal clusters have made outstanding contributions in their synthesis methods and applications.However,it is not clear that the basic evolution of the cluster’s growth and evolution mechanism,catalytic reaction path,how the ligand affects and structure.In this work,we used density functional theory(DFT)method to study the structure and growth process of ultra-small sized Cu_n cluster(n=3-10)coated by amino acids.Cysteine could bond well to noble metal clusters and effectively coat the noble metal clusters.So cysteine works as the amino acid ligand to protect Cu clusters here.First,we optimized the initial structures of Cu_n core(n=3-10)and Cysteine-Cu_n(Cys-Cu_n)cluster(n=3-10),respectively.Then,we analyzed the characteristics of the series of energy optimized structure,and tried to find the growth mechanism from their evolutions.Second,we predicted the Cys binding sites by calculating the FuKui indices and established the relationship between the physicochemical properties and the growth mechanism of Cys-Cu_n cluster(n=3-10).Third,the electronic structure properties were studied for Cu_n core(n=3-10)and Cys-Cu_n cluster(n=3-10)to analyze influences of Cys ligand on Cu_n core(n=3-10).The results are analyzed as follows.(1)Cu_n core(n=3-6)grows in the form of a unique isosceles triangle in the Cys-Cu_n(n=3-6)growth process.(2)Cys ligand binding site on Cun core(n=3-10)could be well predicted by the nucleophilic FuKui index F~+(x).(3)As for n=3-6,the position of the Cys bond coincides with the position of the vertex of the isosceles triangle.As for n=7,Cys binds to the apex of the pentagonal bipyramid structure.As for n=8-10,the Cys is more likely bonding with the atom which destroy the pentagon in the pentagonal bipyramid structure.(4)The coating Cys ligand could regulate HOMO-LUMO gap of the original cluster sensitively.As a result,we found the basic growth mechanisms of Cu_n core(n=3-10)and Cys-Cun(n=3-10),and established the relationship between these growth mechanisms and their physicochemical properties(electronic gaining or losing ability).Thus,this work provided theoretical support for the cluster designs with specific physicochemical properties by regulating their growth processes.