| Metal-organic Frameworks(MOFs)are three-dimensional porous materials formed by coordination bonds between inorganic ligands and metal ions which are widely used in separation,catalysis,drug targeted transport and other fields by virtue of their adjustable pore size,large specific surface area and good structural stability.Chiral Metal-organic Frameworks(CMOF)with chiral microenvironments can be synthesized by using chiral substances as inorganic ligands or post-modification of MOFs.These materials have great application potentials in asymmetric catalysis and enantiomer resolution.At present,many CMOFs and composites composed of CMOF have been reported and applied to chiral resolution.Although CMOF has the important application in the field of chiral separation,the specific mechanism of host-guest molecular recognition between CMOF and enantiomer remains unclear.In order to obtain chiral functional materials with excellent recognition performance,the study of the separation mechanism is undoubtedly very important.However,theoretical calculation based on Density Functional Theory(DFT)is still an important means to study the action mechanism of chiral adsorption materials due to the lag of instrument conditions or non-popular of some technical methods.With the rapid development of costly research equipments,some cutting-edge technologies can accurately capture the weak signals of changes in functional groups and bond energy.The interactions between the materials and isomers can be directly observed,and then the in-depth study of the interaction and adsorption mechanisms can be promoted.Therefore,it is expected to reveal the interaction and recognition mechanisms between the novel chiral functional materials and isomers by combining cutting-edge instrument technologies with theoretical calculation.In view of this,three kinds of chiral MOF materials have been designed and synthesized.Their separation performances were also investigated.Combined the cutting-edge technologies with quantum chemical theoretical calculation,their chiral recognition mechanisms were further explored.The main contents are as follows:1.Using D-Histidine as the chiral source,ZIF-L was endowed with chiral by the post synthesis modification.A nitrogen rich chiral metal organic framework material D-His-ZIF-L(DHZL)was synthesized in pure water.The performance of DHZL was verified by enantioselective capture of 1,1’-bi-2-naphthol(BINOL)racemate.The results showed that DHZL had good specific recognition performance for S-BINOL,with an enantiomeric excess(ee)value of 60.5%under optimal conditions.With DHZL as chiral transfer reagent,the chiral recognition mechanism was investigated by solid-state nuclear magnetic resonance carbon spectroscopy(13C CP MAS NMR),solid-state nuclear magnetic resonance nitrogen spectroscopy(15N CP MAS NMR)and X-ray photoelectron spectroscopy(XPS).The results showed that after DHZL combined with S-enantiomer,the peaks corresponding to the chiral carbon and the carbon of imidazole ring in the 13C CP MAS NMR full spectra,exhibited obvious up-field and down-field shifts,indicating that a strong hydrogen bond interaction andπ-π interaction exsited between S-BINOL and DHZL.In addition,after DHZL was loaded with S-BINOL,the clear nitrogen splitting signal in 15N CP MAS NMR and the positive shifts of binding energy for nitrogen atom in XPS further confirmed the specific recognition performance of DHZL for S-enantiomer.At the same time,the control experiment also verified the importance of chiral microenvironment in DHZL.2.Using L-phenylalanine with multi-step derivatization as chiral ligand,a chiral Cu-MOF was synthesized by solvothermal synthesis in an atmospheric reaction kettle.The chiral separation performance of alcohol racemates(naphthylethanol and phenylethanol)and amino acid racemates(leucine and alanine)were studied.The results showed that Cu-MOF can specifically recognize S-1-(1-naphthyl)-ethanol,and the ee value is 99.35%,which is much higher than the other three types of racemates.Based on the excellent chiral recognition performance of Cu-MOF for S-1-(1-naphthyl)-ethanol,the chiral recognition mechanism was experimentally clarified by means of 13C CP MAS NMR,XPS and Raman spectroscopy and so on.The results showed that the peaks corresponding to chiral carbon and carbon near chiral carbon in 13C CP MAS NMR spectra exhibited obvious up-field shift after Cu-MOF combined with S-enantiomer.Due to the interaction between host and guest,the binding energy of oxygen and nitrogen atoms increased significantly.In addition,compared the chiral separation results of phenylethanol,leucine and alanine racemates with 1-(1-naphthyl)-ethanol,the effects of the size and interaction sites for guest molecules on chiral separation were explained.On this basis,DFT theoretical calculation and simulation provided the theoretical support for the chiral separation mechanism.3.A core-shell nanocomposite Au-NRs@Cu2C2D with CMOF functionalization and good water dispersion was synthesized by in-situ growth method,the thickness of chiral Cu2C2D on the surface was about 2.5 nm.The morphology,optical properties,SERS enhancement effect,stability and repeatability of the composite were studied by various characterization methods.The results showed that the SERS signal of the functional composite Au-NRs@Cu2C2D was obvious,and this nano particle also had the inherent chiral microenvironment of the CMOF material.On this basis,based on the dispersive Solid Phase Extraction and Surface Enhanced Raman Scattering technology,a method for the detection of ultra-trace D-lactic acid was established,with a minimum detection limit of 10-12 mol·L-1.It was further applied to the detection of D-lactic acid in the fecal samples of patients with Atopic Dermatitis.The above experimental results were verified by recovery experiment,and the average recycling rate was 99.53%.This method does not need to derivatize D-lactic acid,and the detection method is convenient and fast with the wide linear range and high sensitivity. |
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