手性多孔有机笼用作气相色谱固定相分离手性和非手性化合物

Chiral porous organic cage used as stationary phase for gas chromatographic separation of chiral and achiral compounds

多孔有机笼(POCs)是一种新型的多孔分子材料,具有明确的分子内腔结构、丰富的主客体识别能力和良好的溶解性,因而在分子识别、气体吸附、传感、催化、色谱分离等多个领域受到广泛关注。本文由四(4-醛基苯基)乙烯和(R,R)-1,2-环己二胺通过席夫碱缩合反应合成了一种手性多孔有机笼(CPOC),采用静态涂敷法将其涂敷于毛细管柱内表面制备了气相色谱柱,测试了该柱对有机混合物、异构体以及手性化合物的分离能力。结果显示,该柱可以实现4种有机混合物(正构烷烃、芳香烃、正构醇和Grob混合物)中所有组分的基线分离;同时有9种二取代苯位置异构体以及包括结构异构和顺反异构在内的16种有机异构体在该柱上也获得了较好的分离。更重要的是,该柱还具有优秀的手性拆分性能,有12种手性化合物在该柱上得到了拆分,其中5种手性化合物(3-羟基丁酸乙酯、缬氨酸衍生物、谷氨酸衍生物、1,2-丁二醇二乙酸酯和1,2-环氧丁烷)获得了基线分离。将该柱与商品β-DEX 120柱的拆分效果相比,该柱可以拆分β-DEX 120柱不能拆分的3-羟基丁酸乙酯、缬氨酸衍生物、谷氨酸衍生物、1,2-环氧丁烷、环氧氯丙烷和环氧溴丙烷等6种手性化合物,说明其与β-DEX 120柱具有手性拆分互补性。研究表明,CPOC制备的毛细管柱对手性和非手性化合物都具有良好的分离能力。

Porous organic cages(POCs)are a new type of molecular material.The well-defined cavities,abundant host-guest recognition ability,and good solubility of POCs render them attractive for use in various fields such as molecular recognition,gas adsorption,molecu-lar containers,sensing,catalysis,chromatographic separation.In this study,a chiral POC(CPOC)was synthesized via the Schiff base condensation of 4,4′,4″,4″′-(ethene-1,1,2,2-tetrayl)tetrabenzaldehyde with(R,R)-1,2-cyclohexanediamine.CPOC was characterized using nuclear magnetic resonance(NMR)spectroscopy,Fourier transform-infrared(FT-IR)spec-troscopy,mass spectroscopy(MS),and thermogravimetric analysis(TGA).The FT-IR spec-trum of CPOC showed a strong peak at 1638 cm-1,which was attributed to imine(-C=N-)absorption,as well as absorption peaks at 2928 and 2856 cm-1,which were attributed to the stretching vibrations of-CH2-and-CH-,respectively.MS analysis of CPOC revealed peaks at m/z=18019797,m/z=9019914,and m/z=6016631,corresponding to[M+H]^(+),[M+2H]^(2+),and[M+3H]^(3+),respectively,and indicating a molecular formula of CPOC(C_(126)H_(120)N_(12)).The TGA curve of CPOC indicated high thermal stability up to 360℃;thus,the material is suitable for use as a stationary phase for gas chromatography(GC).CPOC was coa-ted on the inner wall of a capillary column using the static coating method to prepare a GC col-umn.Scanning electron microscopy(SEM)was used to characterize the coating condition of the fabricated column.The SEM images showed that the column had a uniform coating with a thickness of approximately 200 nm.Column efficiency was determined to be 3500 plates/m using n-dodecane as a target at 120℃.The polarity of the CPOC stationary phase was evaluated using McReynolds constants,which were measured using benzene,1-nitropropane,2-pen-tanone,pyridine,and 1-butanol as probe molecules at 120℃.The average McReynolds con-stant was 152,indicating that CPOC is a moderately polar stationary phase.The ability of the column to separate organic mixtures,isomers,and chiral compounds was subsequently investi-gated.All components of the four organic mixtures(n-alkanes,aromatics,n-alcohols,and Grob mixtures)tested achieved baseline separation on the column.In addition,nine positional isomers of disubstituted benzenes were well separated,and seven(o,m,p-nitrotoluene,o,m,p-nitrochlorobenzene,o,m,p-nitrobromobenzene,o,m,p-bromotoluene,o,m,p-dichlo-robenzene,o,m,p-chloroaniline,and o,m,p-bromoaniline)achieved baseline separation.Some polar and apolar structural isomers,such as pentanol,dimethylphenol,dimethylaniline,butanol,and C9 aromatic hydrocarbon isomers,were also well separated on the column.Five cis/trans-isomers(nerol/geraniol,cis/trans-1,3-dichloropropene,cis/trans-1,2,3-trichloro-propene,cis/trans-citral,and cis/trans-decahydronaphthalene)were baseline-separated on the column.More importantly,the column successfully separated 12 chiral compounds,indica-ting good chiral separation ability.Among these chiral compounds,five(ethyl 3-hydroxybu-tyrate,a valine derivative,a glutamic acid derivative,1,2-butanediol diacetate,and 1,2-epoxy-butane)achieved baseline separation.Six of these chiral compounds(ethyl 3-hydroxybutyrate,the valine derivative,the glutamic acid derivative,1,2-epoxybutane,epichlorohydrin,and epi-bromohydrin)could not be separated on aβ-DEX 120 column but were well separated on the developed column.Moreover,the separation efficiency of 1,2-butanediol diacetate and the iso-leucine derivative on this column was better than that on theβ-DEX 120 column.Separation of the glutamic acid derivative and o,m,p-nitrotoluene was performed before and after the column was used for repeated injections to explore its repeatability.The retention times and selectivity observed after 80,160,and 500 injections were nearly unchanged compared with those ob-tained following the first use of the column,indicating that the column has good repeatability.The column was conditioned at 280℃for a certain period to examine its thermal stability.Sep-aration of 3-hydroxybutyrate and o,m,p-nitrochlorobenzene after the column was conditioned at 280℃for 2,4,or 8 h revealed no obvious changes compared with the first use of the col-umn,indicating that the column had good thermal stability.Thus,CPOC is a stationary phase with good application potential for GC.