Synthesis Of Chiral Materials Based On Chiral Metal-organic Skeletons And Their Electrochemical Recognition

Chirality is a common phenomenon in nature,and chiral recognition plays an important role in many fields.Amino acids are the substances from which life originates and are the most basic units that make up proteins.Research with amino acids has not only contributed to the development of life sciences,but also to the study of chiral recognition.Compared with traditional chiral recognition methods,electrochemical chiral recognition has the advantages of low price,simple operation,fast detection speed and high sensitivity,thus has become a hot research topic.Metal organic frameworks(MOFs)are widely used due to their high enantiomeric purity,high structural homogeneity and modularity,available porosity and diverse functionality.Chiral metal organic frameworks(CMOFs)have large porosity as well as tunable structures,which have many promising applications in the field of chiral recognition.CMOFs have chiral characteristics as well as high stability,providing a good platform for electrochemical chiral sensors.In this paper,we combined the advantages of CMOFs to construct an electrochemical chiral sensor and successfully achieved the chiral recognition of amino acid enantiomeric isomers.There are three main sections:1:Preparation of CMOF using in situ substitution of ligands.D-histidine(D-His)by in situ substitution of 2-methylimidazole(Hmim)above ZIF-8,formation of a chiral metal-organic framework based on ZIF-8(D-His-ZIF-8).Electrochemical tests were conducted on D-His-ZIF-8,and cyclic voltammetry and Nyquist charts show that D-His-ZIF-8 had poor electrochemical performance.Kochen Black(KB)is a conductive carbon black material that requires only a small amount of addition to achieve high electrical conductivity.Cyclic voltammetry(CV)and impedance plots(EIS)show that the electron transfer capacity of KB is much higher than that of D-His-ZIF-8.Significantly improved electrochemical performance can be observed when KB was added to D-His-ZIF-8 as a substrate material.KB/D-His-ZIF-8 was used to construct an electrochemical sensing platform for the recognition of tryptophan(Trp)isomers.The results showed that the binding ability of KB/D-His-ZIF-8 to L-tryptophan(L-Trp)was stronger than that of D-tryptophan(L-Trp),which was due to the different spatial stereoisomerism between L-Trp and D-Trp.In addition,the recognition effect of other amino acid enantiomers was compared,and the efficiency of the recognition of the Trp enantiomer was the highest,and the electrochemical sensor had good stability and anti-interference ability.KB/D-His-ZIF-8 also enables the detection of Trp isomers in real samples.2: The KB/D-His-ZIF-8 synthesized in the first part of the work has been effective in the recognition of Trp,and CMOF has a tunable topology as well as a high stability.However,the poor electrochemical properties of uncalcined CMOF lead to its limited use,and the addition of the substrate material,although it will improve the electrical conductivity,and will make its otherwise regular shape irregular.Therefore,the induction of optically active polymers in the chiral nanochannels or pores of CMOF provides a new idea for the synthesis of chiral materials.Encapsulation of unmodified polyaniline chains(PANI)in chiral nanochannels induces chiral transfer to PANI chains by induction.When the framework structure of D-His-ZIF-8 was disrupted,the chiral polyaniline chain(c-PANI)released from the chiral channel of D-His-ZIF-8 remained chiral.The c-PANI chain was shown to have good electrical conductivity and excellent recognition of Trp by electrochemical tests.In addition,the chiral recognition effects of other amino acids were compared.3: There are many ways to improve the electrical conductivity of MOFs,and addition of metal particles(MNPs)can also effectively improve the electrochemical properties of uncalcined MOFs.Therefore,in this chapter,the noble metal Au NPs was chosen to be loaded to improve the electrochemical performance of MOF.The D-His-ZIF-8 prepared in Chapter 1 was used as a chiral recognition center on the surface of which Au NPs were loaded to enhance the electrical conductivity of the material.However,the Au NPs loaded on the surface are easy to fall off during the experiment,and a "protective shell" is created on the surface to prevent the Au NPs from falling off,and a sandwich material D-His-ZIF-8@Au@ ZIF-8 was formed.The presence of the "sandwich layer" of Au NPs can be clearly observed by transmission electron microscopy(TEM).The electrochemical sensing interface constructed by sandwich materials has optimal recognition of phenylalanine enantiomer(Phe)compared to other amino acids.