Study On The Recognition Performance Of Chiral Molecule By Polysacch-based Metal-Organic Framework Materials

Chirality is one of the inherent properties of nature.The synthesis,identification and isolation of chiral molecules are some of the most important problems that need to be solved.Chiral amino acids play a very important role in plants and animals,and their conformation can be determined by certain methods to advance the development of materials science,pharmaceutical science and even life science,so chiral identification of amino acids is the most important part of chiral molecule identification.Electrochemical methods have the advantages of low cost,high detection limits and environmental friendliness,and differential pulse voltammetry（DPV）,cyclic voltammetry（CV）and electrochemical impedance are used to characterise their electrochemical properties.This paper focuses on the selection of metal-organic backbone（MOF）materials with high specific surface area and tunable pore size and polysaccharide materials with multiple chiral sites and a wide range of sources to construct electrochemical sensors and to investigate their selectivity for amino acid conformation in three main parts.The identification method we used was mainly electrochemical with the advantages of low cost,high detection limit and greenness to make a scientific judgement on the identification ability of the electrochemical chiral platform it was constructed from.Differential pulse voltammetry（DPV）,cyclic voltammetry（CV）and electrochemical impedance were used to characterise their electrochemical properties,as follows:1.MIL-88（Fe）NH₂was prepared by solvothermal method and then combined with amidation to graft sodium carboxymethyl cellulose（CMC）to MIL-88（Fe）NH₂to form CMC-MIL-88（Fe）chiral composites.Cyclic voltammograms and Nyquist plots showed that the composites had excellent electrochemical properties.The CMC-MIL-88（Fe）was then modified on a glassy carbon electrode（GCE）to probe the ability of CMC-MIL-88（Fe）/GCE to recognise tryptophan in different conformations.Differential pulse voltammetry（DPV）showed that the CMC-MIL-88（Fe）/GCE chiral platform has a stronger recognition of L-tryptophan（L-Trp）due to the difference in spatial site resistance caused by the different configurations.The optimal recognition conditions of the chiral platform were also investigated,as well as its stability and reproducibility,and the structure of both conformations of Trp in human serum and urine was examined to verify its practical application.2.Secondly,the electrochemical chiral platform constructed by the polysaccharide material chitosan（CS）when used as a chiral selector was explored,while carbon quantum dots（CQDs）were also introduced as a substrate material to synergistically exert recognition properties.The chiral recognition performance of the chiral composites for Trp was investigated under two different bonding approaches.One was CQDs/CS,which was synthesised by intermolecular force linkage,and the other was CQDs-CS,which was covalently grafted by amidation reaction.The results showed that CQDs-CS was more sensitive than CQDs/CS for the conformational detection of Trp.The strength of the redox peaks in the CV plots shows that CQDs/CS are more conductive than CQDs-CS,mainly due to the intermolecular forces enhancing the charge transfer rate of the composites.However,from the DPV characterisation,only CQDs-CS has a strong recognition of Trp isomers.We believe that the main reason for this is that CQDs/CS is more prone to decomposition compared to CQDs-CS,leading to the failure of the constructed sensing platform,so CQDs-CS was mainly chosen as the chiral interfacial modification material for the construction of the chiral sensing platform in this part.3.Also,to further investigate the effect of molecular size differences in the modified materials on Trp recognition when MOF materials are used as s-chiral selectors,we used the solvothermal method to prepare Trp isomers with chiral recognition properties using L-proline-functionalised UiO-66-LP.These materials were also characterised by FT-IR,XRD,XPS and SEM.Trp recognition was achieved using the recognition site of L-proline embedded in the UiO-66-LP cage.The results show that UiO-66-LP binds better to D-Trp,while L-Trp binds less well,and therefore L-Trp shows g higher peak currents in the presence of redox probes in solution.