Study On Metal-Organic Frameworks Used As Chiral Stationary Phases In High Performance Liquid Chromatography

Metal-organic frameworks (MOFs) as a new generation of functional molecular materials, have shown intriguing applications in gas storage, catalysis, separation, sensor and many other fields due to their unusual properties, such as high surface area, rich topologies, permanent microporous, availability of outer-surface modification and so on. Being another important section of MOFs, chiral MOFs also have attracted much attention in asymmetric catalysis and separation because of their porous functionalities and chirality. Chiral MOFs are typically used in adsorption separation, while a few of them were reported for chiral stationary phases in chromatography. To the best of our knowledge, there are only three attempts to utilize chiral MOFs in high-performance liquid chromatography (HPLC). Bn-ChirUMCM-1was only used for1-phenylethanol with low resolution,[Zn2(bdc)(L-lac)(dmf)]’DMF (bdc p-benzenedicarboxylic acid, L-lac=L-lactic acid) and (R)-MOF-silica were specially used for chiral alkyl aryl sulfoxides, all of them showed narrow scope in enantioseparations. In order to explore chiral MOFs as a new kind of chiral stationary phases, they were studied for HPLC chiral separation in this dissertation.Chapter one was the preface. Firstly, the basic concepts of chirality, the important of chiral separations and the chiral separation methods were stated. Secondly, HPLC and chiral stationary phases were introduced. Thirdly, the development, synthesis, and application of MOF were reviewed, especially for eanti﹕eparations in chromatography. Finally, the goals and the significances of this dissertation were also illustrated here.An unusual3-D chiral nanoporous MOF was synthesized in chapter2. X-ray powder diffraction and TG analysis of [(CH3)2NH2][Cd(bpdc)1.5]-2DMA (bpdc=4,4-biphenyldicarboxylate, DMA=N,N’-Dimethylacetamide) were employed to demonstrate that DMA molecules can be removed without breaking the open structure. The crystals of [(CH3)2NH2][Cd(bpdc)1.5] with an average size of5μm were obtained by the solvent suspension. Then, the prepared crystals were slurry-packed into a stainless steel empty column under40MPa. Ten racemates including alcohol, phenol, flavone, ketone, and amide etc. were successfully separated on this column. The experimental results showed that [(CH3)2NH2][Cd(bpdc)1.5] possesses excellent recognition ability for various racemates, the enantioseparations on chiral MOFs is practicable, which opens a new gateway in chiral separation science.In chapter3, a chiral MOF [Zn2(D-Cam)2(4,4’-bpy)]n (D-Cam=D-Camphoric acid,4,4’-bpy=4,4’-bipyridine) with2-D homochiral layers was convenient used as chiral stationary phase with suitable particle size and uniform cubic shaped for enantioseparations. The influence of column temperature, analytes mass and flow rate on enantioseparations was discussed. A wide range of enantiomers such as alcohol, aldehyde, phenol, ketone, amide, and chiral drug etc. were successfully separated with lower column pressure. The convenient and optical selectivity on the naturely chiral MOF column can promote the application of chiral MOFs use as stationary phase for chiral discrimination.A homochiral MOF [Cd2(D-cam)3]·2Hdma·4dma·2H2O (dma=dimethylamine) with open chiral channels was synthesized before used as a new chiral stationary phase for high-performance liquid chromatographic enantioseparation in chapter4. Many kinds of enantiomers were successfully separated on [Cd2(D-cam)3]·2Hdma·4dma·2H2O packed column, especially for (±)-1-(1-naphthyl)ethanol with a high resolution (RS=4.55) which possibly make this chiral MOF as a promising candidate for specific separation of some enantiomers. When racemate of (±)-1-(1-naphthyl)ethanol was separated on the packed optical resolution column, the retention and the selectivity of analyte were influenced by the mobile phase composition, column temperature, and analytes mass.Chapter5focused on exploring the chromatographic characteristic of a homochiral MOF [Cu2(D-Cam)2(4,4’-bpy)]n with3-D six-connected self-penetrating architectures for the separations of positional isomers and chiral compounds. Some impact factors (mobile phase composition, column temperature, and analytes mass) for enantioseparations on this chiral column also had been investigated. Fortunately, besides six racemates of alcohol, phenol, and ketone compounds were successfully discriminated by this chiral stationary phase, ten useful positional isomers were also analyzed on this packed column.[Cu2(D-Cam)2(4,4’-bpy)]n exhibited good selectivity for positional isomers and enantiomers. Therefore, it is practicable that the separation of positional isomers and enantiomers are carried out on the chiral MOF column.Chiral MOFs ([{Cu(sala)}n],[Cd(LTP)2]n, y-CD-MOF, and [Zn2(bdc)(L-lac)(dmf)]-DMF) were packed into four stainless steel empty columns, respectively (chapter six). However, those CSPs possessed different chiral property to give different resolution abilities.[{Cu(sala)}n] with3-D chiral channel framework had separated three positional isomers and seven racemates, whereas another MOFs hadn’t separated for the tests. Thus, the chiral MOFs with different composition and structure may lead to different chiral recognition abilities.In order to gain further insight into the enantioseparation of chiral MOFs, chapter seven gave some collection, analysis, and comparison of the data coming from this dissertation, our group’s work and published reports so that the chiral MOFs as stationary phases will further be utilized in the liquid chromatography.