Study On Chiral Metal-Organic Frameworks Used For High-Resolution Gas Chromatography

Metal-organic frameworks (MOFs), also known as coordination polymer, are crystal materials with infinite network structures built from transition metal ions or metal clusters and organic bridging ligands (mostly aromatic acid or alkaline) by the approaches of molecular assembly and crystal engineering. MOFs are a new kind of porous materials being largely researched in recent years, which possess outstanding properties, such as large surface area, highly ordered pore structure and good chemical stability. They have been widely used as gas storage, separation, catalysis, sensor, drug delivery, molecular magnet, nonlinear optical material and composite functional material, etc.With the rapid development of chiral MOF materials, a large number of chiral MOF materials have been synthesized and used for asymmetric catalysis and separation. Although chiral MOFs have been focused on the adsorption separation of chiral compounds, there are a few report of chiral MOFs used as stationary phases. To the best of our knowledge, there has been no attempt to utilize chiral MOFs in gas chromatography.In the dissertation, we synthesized some chiral MOF materials which were used as chiral stationary phases for high-resolution gas chromatographic separations. The main works were as follows:chiral MOF-coated open tubular columns were fabricated by a three-dimensional single-handed helical MOF ([{Cu(sala)}n]), and the separation ability of the [{Cu(sala)}n] was investigated; A three-dimensional open-framework material Co-(D-Cam)1/2(bdc)1/2(tmdpy) with intrinsic chiral topology was prepared and used as stationary phase for separation of chiral compounds in gas chromatography; A three-dimensional MOF with integrated molecular chirality, absolute helicity, and intrinsic chiral topology (Ni(D-cam)(H2O)2) was used as stationary phase for eantioseparations; Studied the open tubular columns prepared with a three-dimensional honeycomb channels with homochiral chains MOF ([Mn3(HCOO)4(D-Cam)]n); Synthesized a porous chiral MOF (InH(D-C10H14O4)2) with anionic-type diamond network and left-handed helical channel structure, it was used for chiral recognition in high-resolution gas chromatographiy; A porous metal membrane for SPE of PAHs was investigated.Part1:PrefaceThe basic concepts of chirality, the important signification of chiral resolution, chiral recognition methods, the development of high-resolution gas chromatography, the capillary gas chromatographic columns and the chiral stationary phases were introduced. The synthetic methods and application of chiral MOF were reviewed, especially for its eantioseparation of chromatography. After stating the development and advantages of SPE technology, we illustrated the purpose and signification of the dissertation.Part2:Chiral MOF [{Cu(sala)}n] for high-resolution gas chromatographic separations.A three-dimensional chiral channel framework which has the formula [{Cu(sala)}n](H2sala=N-(2-hydroxybenzyl)-L-alanine) was synthesized. Four fused-silica open tubular columns with different inner diameters or lengths, including column A (30m×530μm i.d.), column B (30m×250μm i.d.), column C (9m×75μm i.d.) and column D (2m×75μm i.d.), were coated by a dynamic coating method using [{Cu(sala)}n] as stationary phase. The chromatographic properties of four MOF columns (A, B, C, D) were investigated, and their numbers of theoretical plates (plates/m) were1500,2200,3500and3600, respectively. In order to investigate the coating properties of stationary phase on open tubular column inner wall, the cross section and inner surface of open tubular column A were examined by scanning electron microscopy (SEM). The SEM analysis results showed that the fabricated column had an approximately1μm uniformly thick MOF coating on the inner wall. The thermogravimetric analysis (TGA) exhibited that the column was thermally stable below220℃and therefore suitable for GC usage. To evaluate the separation properties of columns, the columns (B, C, D) were used for the separation of various types of organic compounds, including racemates, isomers, alkanes, alcohols and Grob’s test mixture. The experimental results indicate that the stationary phase has excellent selectivity toward isomers, alkanes, and alcohols etc, especially for chiral compounds. Eleven racemates include aldehyde, ketone, organic acid, amino acid and alcohol, were separated at least85%baseline resolution on column D. Comparing to column E fabricated by metal-complex [Cu(sala)]2-2H2O, the chiral recognition ability of MOF was more stronger than that of metal-complex. It demonstrated that the single-handed helical channels of the MOF made a significant contribution to the chiral separation in GC.Part3:A three-dimensional open-framework material Co-(D-Cam)1/2(bdc)1/2-(tmdpy) with intrinsic chiral topology used as stationary phase in gas chromotographyWe report the fabrication of Co(D-Cam)1/2(bdc)1/2(tmdpy)(D-Cam=D-camphoric acid; bdc=1,4-benzenedicarboxylate; tmdpy=4,4’-trimethylenedipyridine)-coated open tubular columns for high-resolution gas chromatographic (GC) separation of chiral compounds. The Co(D-Cam)1/2(bdc)1/2(tmdpy) compound possesses a three-dimensional framework containing enantiopure building blocks embedded in intrinsically chiral topological nets. In this study, two fused-silica open tubular columns with different inner diameters and lengths were prepared by a dynamic coating method using Co-(D-Cam)1/2(bdc)1/2(tmdpy) as the stationary phase. The chromatographic properties of the two columns were investigated using n-dodecane as the test compound at120℃. The number of theoretical plates (plates/m) of the two metal-organic framework (MOF) columns was1450and3100, respectively. The separation properties were evaluated using racemates, isomers, alkanes, alcohols, and Grob’s test mixture. The experimental results showed that the stationary phase has excellent selectivity and also possesses good recognition ability toward these organic compounds, especially chiral compounds. Part4:Three-dimensional open-framework material Ni(D-cam)(H2O)2with integration of molecular chirality, absolute helicity and intrinsic chiral topology used as stationary phase in gas chromotographyBy using enantiopure D-camphoric acid as organic ligand, a three-dimensional open-framework material Ni(D-cam)(H2O)2with integration of molecular chirality, absolute helicity and intrinsic chiral topology was synthesized. Column A (30m×250μm i.d.) and column B (2m×75μm i.d.) coated by Ni(D-cam)(H2O)2were prepared The cross section and inner surface of open tubular column A were examined by SEM, and the thermally stable of these columns were tested by TGA. The column B was used for the separation of various types of organic compounds, it showed that the stationary phase possessed good separation ability, especially for chiral compounds, such as aldehyde, organic acid, alcohol and amino acid. Therefore, the stationary phase has a good prospect of application as a new type of GC stationary phase due to its good film-forming property, high thermal stability and excellent separation performance.Part5:Chiral MOF [Mn3(HCOO)4(D-Cam)]n with honeycomb channels for high-resolution gas chromatographic separationsIn this part, chiral MOFs [Mn3(HCOO)4(D-Cam)]n with honeycomb channels was used as stationary phase for column A (30m×250μm i.d.) and column B (5m×75μm i.d.) in high-resolution gas chromatography. We investigate the coating properties of stationary phase by SEM on open tubular column inner wall and the thermally stable by TGA. Some racemates, alkanes and isomers were used as targets for separation on column B. The experimental results showed that the stationary phase also possessed good separation ability toward these organic compounds.Part6:A porous chiral MOF InH(D-C10H14O4)2with diamond network and left-handed helical channel for high-resolution gas chromatographic enantioseparat-ionsA porous chiral metal-organic framework InH(D-C10H14O4)2(D-C10H14O4= D-(+)-camphoric acid) with diamond network and a left-handed helical channel assembled from D-(+)-camphoric acid was used as chiral stationary phase in GC. InH(D-C10H14O4)2-coated open tubular columns with different inner diameters or lengths were prepared by a dynamic coating method for high-resolution GC separation of various types of organic compounds, including racemates, isomers, alkanes, alcohols and Grob’s test mixture. Their column efficiency, polarity and selectivity were studied. The experimental results gave that the stationary phase had excellent selectivity and also possessed good recognition ability toward these organic compounds, especially for chiral compounds.Part7:Porous metal membranes for solid-phase extraction of polycyclic aromatic hydrocarbonsSolid-phase extraction (SPE) is one of the most important techniques for sample preparation, purification, concentration, and cleanup. Membrane made from synthetic organic polymers, cellulose, or glass fibers are used for sample pretreatment. However, in previous reports there are no porous metal membranes for solid-phase extraction. In this work, we report that porous metal membrane, the metal filters in HPLC, was used as a novel kind of solid-phase extraction adsorbent material for the extraction of polycyclic aromatic hydrocarbons (PAHs). To evaluate the performance of the porous metal membrane for SPE, naphthalene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, perylene and benzo(a)pyrene were selected for investigation. Several conditions that affected the extraction efficiency such as the extraction time, the concentration of NaCl, the extraction temperature and the agitation speed were examined. The experimental result indicates that the porous metal membrane possesses high adsorption ability to the tested PAHs. In the optimum conditions, the detection limits of the developed method were in the range of0.03-0.082μg L-1(S/N=5), and the excellent linear correlation between peak area and the concentration of PAHs over the range of0.1-60μg L-1. The precisions (RSD) for five replicate extractions of the PAHs from sample solution were in the range of2.6-5.0%. The recoveries of the PAHs of tap water and river water samples spiked with9PAHs (20ug L-1of each individual PAH) ranged from83.0%to112.5%. The porous metal membrane is durable, simple, inexpensive, reproducible and high adsorption ability for the SPE of PAHs.