Recognition And Separation Of Amino Acid Enantiomers By Polysaccharides Based Chiral Composites

Chirality is one of the ubiquitous characteristics in nature,and chiral molecules usually exist in the form of two enantiomer.Usually,only one isomer exhibits perfect activity,while the other is not of ideal value and can even cause serious side effects.Amino acids are important substances in protein metabolism and in medicine and food.Therefore,developing efficient methods for chiral recognition and separation of isomers is seen as a challenge.Compared with other traditional recognition and separation methods,electrochemical recognition and membrane separation methods have been widely concerned because of their advantages such as high sensitivity,easy operation,high efficiency and low cost.In this paper,combining with the unique properties of polysaccharides,the electrochemical chiral sensing platform and solid chiral separation membrane were constructed to realize the identification and separation of amino acid isomers.The work of this paper is mainly carried out from the following three aspects:1、Cs@Cu-β-CD was prepared by self-assembly of chitosan（CS）and Cu²⁺modifiedβ-CD（Cu-β-CD）.Subsequently,the electrochemical chiral sensing platform Cs@Cu-β-CD/GCE was constructed and used for the specific recognition of Phe isomers.It was found that CS@Cu-β-CD/GCE showed higher peak current and better recognition efficiency for D/L-Phe,I_D/I_L=2.25,compared with CS/GCE and Cu-β-CD/GCE.Water contact Angle experiments show that the sensor platform has a higher affinity for D-Phe than L-Phe.This is because D-Phe and L-Phe have different configurations,making it easier for the D configuration to pass through the modified layer on the electrode surface to reach the electrode surface.In addition to the matching of cavity size,the-OH on the edge of Cu-β-CD is more likely to form hydrogen bonds with-NH₂ on D-Phe.At the same time,the CS@Cu-β-CD/GCE sensor platform was tested for its specificity,resistance to ion interference,stability and reproducibility.The results show that the CS@Cu-β-CD/GCE electrochemical sensing platform has high specificity,ionic interference resistance,stability and reproducibility.In addition,the incubation time,temperature,pH and concentration of the test solution were optimized.2、In order to improve the conductivity of the electrochemical chiral sensing platform,graphene oxide（GO）with high conductivity was selected as the base material.A chiral electrochemical sensing platform CSR@SPT/GO/GCE was constructed by self-assembly of maize starch（CSR）and sweet potato starch（SPT）to prepare CSR@SPT,which was used for the specific recognition of Phe isomers.The results show that CSR@SPT/GO/GCE has better recognition efficiency and higher peak current than CSR@SPT/GCE,I_L/I_D=3.47.It is proved that the presence of GO greatly improves the conductivity of CSR@SPT/GO/GCE electrochemical sensor platform,thus optimizing the recognition results.In addition,the recognition ability of CSR@SPT/GO/GCE for L-Phe is better than that of D-Phe,indicating that L-Phe and D-Phe have different forces when they combine with chiral composites due to their different spatial configurations.The results of water contact Angle test also support this result from the side.At the same time,the detection conditions were optimized,CSR@SPT/GO/GCE electrochemical sensing platform has excellent reproducibility,stability,ion interference resistance,selectivity.3、In the first two chapters,the chiral electrochemical sensing platform is constructed for the identification of amino acid isomers.However,the separation of amino acid isomers is also important.Therefore,in this chapter,we prepare chiral solid separation membranes by one-pot method for the enantioselective separation of Trp isomers.First,chitosan（CS）is combined with graphene oxide（GO）by an amide reaction,and then Cu-β-CD is introduced by hydrogen bonding to produce CD-CS/GOM.The introduction of bimanual centers can provide more chiral sites.As a base material,GO can provide more chiral loading sites and high throughput due to its unique lamellar structure.The results show that CD-CS/GOM can better pass L-Trp,while D-Trp can hardly pass.The theoretical separation factor can reach 2.35.Because of the different spatial configuration,L-Trp,D-Trp and CD-CS/GOM have different phase and three point interaction forces.It is proved that the chiral solid separation membrane has good selective permeability.In addition,the separation factor was quantitatively calculated by UV absorption spectrum.