Preparation Of Surface Molecularly Imprinted Polymers Coating On Silica-gel For Chiral Separation Of 1,2-diphenylethylenediamine Racemates

The optically pure 1,2-diphenylethylenediamine?DPEN?enantiomer with C₂-axis symmetry is an important chiral ligand and chiral agent.Because of its different chiral recognition effects on biological macromolecules during electrochemical immunostimulation,DPEN molecules?1R,2R-and 1S,2S-?have been widely used in the aspect of bioanalysis and the acquisition of different configurations of DPEN is of great significance.Molecularly imprinted technology?MIT?has been widely studied and applied in molecular recognition and preferential adsorption due to this high selectivity for the template molecules.However,this method also had some disadvantages,such as a slow mass transfer,i.e.,time-consuming,and has a poorchiral recognition.For these problems,an MIP coated silica gel?SMIPs?was prepared in this study by the in-situ copolymerization of MAA with ethylene glycol dimethacrylate?EGDMA?in the presence of R-DPEN as the template on the surface of the silica gel,and the resulting materials were employed as the adsorbent and CSPs for the research on adsorption properties and the chiral separation by HPLC of racemic DPEN.The prepared SMIPs were characterized by the scanning electron microscopy?SEM?and the thermogravimetric analysis?TGA?.The results showed that the surface of the coated silica gel was rough and the thermal mass loss curves of the silica gel and the eluted SMIPs before and after the polymerization occurred significant mass loss,and the weight loss ratio of the coated silica gel reached 38.13%.The comparative analysis of SMIPs before and after elution was carried out by Fourier transform infrared spectroscopy?FT-IR?.In this paper,the adsorption capacity as the objective function,the preparation of SMIPs and adsorption conditions were systematically investigated.The experimental results show that SMIPs prepared with molar ratio of the R-DPEN/MAA of 1/4?mol/mol?mixing 2h in the acetonitrile and used n-hexane/chloroform?6/1,v/v?as adsorption solvent adding the amount of adsorbent 30mg and the initial concentration of 100mg/L adsorpting of 90 min in15?,under this adsorption conditions,The SMIPs has the best adsorption properties,the maximum adsorption reached 7.97mg/g.Compared with the non-imprinted polymers?SNIPs?and pure silica(Q_R-DPEN=2.67mg/g and Q_R-DPEN=1.17mg/g)as adsorbents,the SMIPs has more better adsorptive effect.The influence of the chromatographic conditions such as the kind of mobile phase,flow rate,column temperature and the mobile phaseon composition were systematically investigated in this article.As the result,the SMIPs got the highest separation factor???resolution?Rs?under the chromatographic conditions:mobile phase,n-hexane/chloroform?6/1,v/v?;flow rate,0.1 mL/min;column temperature,15?.The best?and Rs reached 2.52and 1.72 respectively and successfully achieved the baseline separation of The DPEN enantiomers.The equilibrium adsorption isotherms and kinetic models were also used to analyze the kinetics and thermodynamics of the adsorption process of the prepared SMIPs.The results show that the adsorption processes of SMIPs were more in line with the Freundlich adsorption isothermal model and quasi-second-order kinetic model and the correlations of linear fit were R₂=0.9903 and R₂=0.9896,respectively.