Silica-based Cellulose Dichloro-Phenylcarbamate Hybrid Chiral Stationary Phase For Enantioseparation

Enantiomers of drugs have different pharmacological activities,toxic and side effects,so the separation of chiral drugs has always been a research hotspot in the field of medicine.Chromatography resolution is one of the most widely used methods to separate enantiomers,especially the liquid chromatography resolution based on chiral stationary phase(CSP)of cellulose has been recognized by virtue of its high efficiency,high speed and wide range of chiral recognition.For this enantiomerseparation method,the core and key point is preparation of CSP.At present,traditional cellulose derivatives CSPs prepared by coating or immobilizing the chiral recognizers onto the surface of macro-porous silica gel have low loading capacity due to the limited specific surface area of silica gel.As for the coating-type stationary phase,narrow mobile phase selection range is unfavorable for chiral resolution.By contrast,organic-iorganic hybrids materials can regulate the properties of the obtained materials by adjusting the proportion of the precursors,which may provide a direction for the preparation of novel CSP to solve the problems of the traditional stationary phase.In this work,we used 3,5-dichlorophenylcarbamate as the derivatization reagent to modify the hydroxyl group of microcrystalline cellulose,a novel organic-inorganic hybrid cellulose derivative CSP was obtained based on sol-gel chemistry.Its chiral recognition ability was also investigated to evaluate the performance,and the specific work is as follows.1.Study on the preparation of hybrid cellulose CSP.Firstly,cellulose 3,5-dichlorophenylcarbamate bearing a small amount of 3-(triethoxysilyl)propy1 groups(2 w.t%)was synthesized by cellulose hydroxyl derivatization reaction.The synthesized sample was used as organic precursor and cross-linked with the inorganic precursor tetraethyl orthosilicate(TEOS)to prepare silica-based cellulose 3,5-dichlorophenyl carbamate spherical particle with high specific surface area(502 m2/g)and narrow pore size distribution(4 nm)via sol-gel method.29Si CP/MAS NMR,FT-IR,TGA,SEM and EDX analysis methods were performed to verify that the hybrid CSP can meet the general requirements for chromatographic packing materials.2.Study on the forming mechanism of hybrid spherical particle.The effect of factors in sol-gel process including the type of surfactant,surfactant concentration,aging time,pH,the amount of cellulose derivative and TEOS on microspheres surface morphology and organic-inorganic ratio of microspheres were investigated,which can provide a new pathway for preparation of hybrid cellulose derivative CSPs.It was found that a large number of microspheres can be formed in the presence of cationic surfactants C18TAC under acidic conditions,and the proportion of organic and inorganic contents of the hybrid microspheres can be regulated by adjusting the addition of chiral organic precursor and inorganic silane precursor.3.Study on the resolution performance of the hybrid chiral microspheres.After sieving and end-capping,the hybrid microspheres were packed into a stainless-steel column(150 mm × 4.6 mm)by a slurry method and the home-made hybrid chromatographic column was obtained.Furthermore,seven typical chiral compounds were used to evaluate the enantioseparation ability of hybrid CSPs by HPLC,and the loading capacity of the hybrid CSP was also evaluated by two enantiomers trans-1,2-diphenyloxirane and 2-phenylcyclohexanone.The results showed that six of these enantiomers can be separated and baseline separation can be achieved on the hybrid chromatographic column,especially for trans-1,2-diphenyloxirane and 2-phenylcyclohexanone(the selectivity reach up to 1.65 and 1.44,respectively),which demonstrate that the hybrid CSPs exhibited comparable and even better chiral recognition abilities and loading capacity compared with immobilized-type CSP and commercially available Chiralpak IC.Besides,the robust solvent tolerance of the home-made hybrid chromatographic column in the mobile phase containing 0.5%trifluoroacetic acid and chloroform(n-hexane/isopropanol/trifluoroacetic acid(or chloroform)=90/10/0.5,v/v/v)futher demonstrate the great potential of the hybrid chiral stationary phase in industrial applications.4.Preparation of hybrid chiral microspheres by microfluidic method.Taking wide particle size distribution of hybrid microspheres synthesized by sol-gel method into account,we prepared monodisperse spherical particles with a particle size distribution of 2-5 ?m by droplet microfluidic technology.The results indicated that monodisperse hybrid microspheres with controllable particle size can be prepared by adjusting the composition and flow of the continuous and disperse phases.