Preparation Of Surface Molecularly Imprinted Polymers On Silica Gel For Chiral Separation Of 1,1’-bi-2-Naphthol Racemates

With a specific molecular recognition ability,molecular imprinted polymers(MIPs)possess a significant amount of three-dimension of structure cavities that are complementary to the template in shape,size,and functional groups.In view of the fact that the conventional molecular imprinting technology is easy to appear the"embedding"phenomenon,the MIPs was employed as the chiral stationary phase for the resolution of enantiomers The surface molecularly imprinted polymers(SMIPs)were prepared by using molecular imprinting technology(MIT)and the coating method(the pre-polymerization was coated on the surface of silica gel).Being the crosslinking agent,ethylene glycol dimethacrylate(EGDMA)was copolymerized with the monomer,acrylamide(AM),in the presence of R-1,1’-Bi-2-naphthol(R-BINOL)as the template molecules on the surface of the silica gel particles by free radical polymerization to produce the SMIPs.SMIPs were used as chiral stationary phase(SMIPs-CSP)for the resolution of BINOL enantiomer by high performance liquid chromatography(HPLC).In order to prepare effective SMIPs,the influence of some primary factors on the chiral recognition ability of SMIPs,such as the type of functional monomer,molar ratio of template/monomer,pre-polymerization temperature,and polymerization temperature,were systematically investigated.SMIPs prepared with molar ratio of the R-BINOL/AM of 1:2 at the pre-polymerization temperature of 20℃and the polymerization temperature of 60℃had the optimal separation effect to the enantiomer separation of BINOL.The separation factor was 4.28.The molecular imprinted polymers were characterized by thermogravimetric analysis(TGA),scanning electron microscope(SEM),fourier transform infrared spectrum(FT-IR).The TG curves of the coated silica gel and SMIP illustrated that the complex coated on the surface of silica gel successfully and SMIP shown a good thermal stability.It could be seen that the surface of silica gel attached a layer of polymer successfully and SMIPs were fragmented from SEM.The FT-IR spectra of SMIPs before elution and SMIPs after elution shown that the naphthol was cleared off completely.The article employed SMIPs as HPLC stationary phase to study the effect of chromatographic conditions on the chirality separation.Within the scope of this study,the best chromatographic condition of SMIPs-CSP for the resolution of BINOL enantiomers as follow:sample concentration,0.6 mg/mL;flow rate,0.07 mL/min;mobile phase acetonitrile/chloroform(90/10,v/v).Under the optimal chromatographic conditions,the highest separation factor of SMIPs-CSP to chiral separation of BINOL enantiomers was 4.28,and the resolution was 1.29.In order to better estimate the binding capacity of SMIPs,the effective number of binding sites(Lt)and dissociation constant(Kdiss)were detected by the frontal analysis.The binding sites of SMIPs-CSP for R-BINOL(L_t=6.68 umol/g)was greater than that for S-BINOL(L_t=3.37 umol/g).The dissociation constant of SMIPs-CSP for R-BINOL(Kdiss=2.90 mmol/L)was less than that for S-BINOL(Kdiss=7.75 mmol/L).The results showed that SMIPs-CSP was specific binding to R-BINOL and had a stronger specific combining ability.