Sheng-Ming Xie

Chiral metal-organic frameworks for high-resolution gas chromatographic separations.

Chiral metal-organic framework coated open tubular columns are used in the high-resolution gas chromatographic separation of chiral compounds. The columns have excellent selectivity and also possess good recognition ability toward a wide range of organic compounds such as alkanes, alcohols, and isomers.

Homochiral Porous Organic Cage with High Selectivity for the Separation of Racemates in Gas Chromatography

Porous organic molecular cages as a new type of porous materials have attracted a tremendous attention for their potential applications in recent years. Here we report the use of a homochiral porous organic cage (POC) (CC3-R) diluted with a polysiloxane (OV-1701) as a stationary phase for high-resolution gas chromatography (GC) with excellent enantioselectivity. A large number of optical isomers have been resolved without derivatization, including chiral alcohols, diols, amines, alcohol amines, esters, ketones, ethers, halohydrocarbons, organic acids, amino acid methyl esters, and sulfoxides. Compared with commercial β-DEX 120 and Chirasil-L-Val columns, the CC3-R coated capillary column offered more preeminent enantioselectivity. In addition, CC3-R also exhibits good selectivity for the separation of isomers, linear alkanes, alcohols, and aromatic hydrocarbons. The excellent resolution ability, repeatability, and thermal stability make CC3-R a promising candidate as a novel stationary phase for GC. The study described herein first proves useful commercially. This work also indicates that porous organic molecular materials will become more attractive in separation science.

Enantioselective chromatographic resolution using a homochiral metal–organic framework in HPLC

A homochiral MOF was used as a new chiral stationary phase and had an excellent recognition ability for various racemates in HPLC. The results indicated that the optical selectivity of the natural chiral MOF column is practical in HPLC, which promotes the application of chiral MOFs for enantioseparation.

Novel inorganic mesoporous material with chiral nematic structure derived from nanocrystalline cellulose for high-resolution gas chromatographic separations.

Chiral nematic mesoporous silica (CNMS) has attracted widespread attention due to some unique features, such as its nematic structure, chirality, large pore size, high temperature resistance, low cost, and ease of preparation. We first reported the use of CNMS as a stationary phase for capillary gas chromatography (GC). The CNMS-coated capillary column not only gives good selectivity for the separation of linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and isomers but also offers excellent enantioselectivity for chiral compounds. Compared with enantioseparations on commercial β-DEX 120 and Chirasil-l-Val columns, a CNMS-coated capillary column offers excellent enantioselectivity, chiral recognition complementarity, and the separation of analytes within short elution times. It can also be potentially applied in high-temperature GC at more than 350 °C. This work indicates that CNMS could soon become very attractive for separations.

Porous Chiral Metal-Organic Framework InH(D-C10H14O4)2 with Anionic-Type Diamond Network for High-Resolution Gas Chromatographic Enantioseparations

Metal-organic frameworks have large surface area, highly ordered pore structure and good chemical stability. In this study, a porous chiral metal-organic framework InH(D-C10H14O4)2(D-C10H14O4 = D-(+)-camphoric acid) with 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 Grobs test mixture. Their column efficiency, polarity, and selectivity were studied. The experimental results show that the stationary phase has excellent selectivity and also possesses good recognition ability toward these organic compounds, especially for chiral compounds.

Experimental comparison of chiral metal-organic framework used as stationary phase in chromatography

Chiral metal-organic frameworks (MOFs) are a new class of multifunctional material, which possess diverse structures and unusual properties such as high surface area, uniform and permanent cavities, as well as good chemical and thermal stability. Their chiral functionality makes them attractive as novel enantioselective adsorbents and stationary phases in separation science. In this paper, the experimental comparison of a chiral MOF [In₃O(obb)₃(HCO₂)(H₂O)] solvent used as a stationary phase was investigated in gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). The potential relationship between the structure and components of chiral MOFs with their chiral recognition ability and selectivity are presented.

Chiral 3D Open‐Framework Material Ni(D‐cam)(H2O)2 Used as GC Stationary Phase

Metal-organic frameworks (MOFs) have been explored for analytical applications because of their outstanding properties such as high surface areas, flexibility and specific structure features, especially for chromatography application in recent years. In this work, a chiral MOF Ni(D-cam)(H2O)2 with unusual integration of molecular chirality, absolute helicity, and 3-D intrinsic chiral net was chosen as stationary phase to prepare Ni(D-cam)(H2O)2-coated open tubular columns for high-resolution gas chromatographic (GC) separation. Two fused-silica open tubular columns with different inner diameters and lengths, including column A (30 m × 250 µm i.d.) and column B (2 m × 75 µm i.d.), were prepared via a dynamic coating method. The chromatographic properties of the two columns were investigated using n-dodecane as the analyte at 120 °C. The number of theoretical plates (plates/m) of the two metal-organic framework (MOF) columns was 1300 and 2750, respectively. The racemates, isomer and linear alkanes mixture were used as analytes for evaluating the separation properties of Ni(D-cam)(H2O)2-coated open tubular columns. The results showed that the columns offered good separations of isomer and linear alkanes mixture, especially racemates.

A chiral porous organic cage for molecular recognition using gas chromatography

Molecular organic cages as shape-persistent organic molecules with permanent and accessible cavities have attracted a lot of interest because of their importance as host-guest systems. Herein, we report a chiral porous organic cage (POC) CC9 diluted with a polysiloxane OV-1701 to fabricate a CC9-coated capillary column, which was used for the high-resolution gas chromatographic separation of organic compounds, including positional isomers and racemates. On the CC9-coated capillary column, a large number of racemic compounds such as chiral alcohols, esters, ethers and epoxides can be resolved without derivatization. By comparing the chiral recognition ability of the CC9-coated column with the commercially available β-DEX 120 column and the POC CC3-R coated column recently reported by our group, the CC9-coated column offered good resolution during the separation of some racemates, that were not separated using the β-DEX 120 column or POC CC3-R coated column. Therefore, the CC9-coated column can be complementary to the β-DEX 120 column and CC3-R coated column. The results indicated that the CC9-coated column exhibited great potential for application in the separation of positional isomers and enantiomers with great selectivity, high resolution and good reproducibility.

Highly selective separation of enantiomers using a chiral porous organic cage

Porous solids composed of shape-persistent organic cage molecules have attracted considerable attention due to their important applications such as molecular separation, heterogeneous catalysis, and gas storage. In this study, an imine-linked porous organic cage (POC) CC10 diluted with a polysiloxane OV-1701 was explored as a novel stationary phase for high-resolution gas chromatography (GC). A wide variety of enantiomers belonging to different classes of organic compounds have been resolved on the coated capillary column, including chiral alcohols, esters, ketones, ethers, halohydrocarbons, epoxides, and organic acids. The fabricated column complements to commercial β-DEX 120 column and our recently reported CC3-R column for separating enantiomers, which indicates that the excellent chiral recognition ability of CC10 is not only interesting academically, but also has potential for practical application. In addition, CC10 also exhibits good selectivity for the separation of n-alkanes, n-alcohols, Grob mixture, and positional isomers. This work also indicates that this type of chiral POCs will become a new class of chiral selector in the near future.

Chiral separation of D,L-mandelic acid through cellulose membranes.

This work reports the chiral separation of D,L-mandelic acid with cellulose membranes. Cellulose was chosen as membrane material because it possesses multichiral carbon atoms in its molecular structure unit. The flux and permselective properties of membrane using aqueous solutions of D,L-mandelic acid as feed solution was studied. The top surface and cross-section morphology of the resulting membrane were examined by scanning electron microscopy. When the membrane was prepared with 8.1 wt % cellulose and 8.1 wt % LiCl in the DMA casting solution, and the operating pressure and feed concentration of racemate were 0.0125 MPa and 0.5 mg/ml, respectively, over 90% of enantiomeric excess could be obtained. This is the first report that the cellulose membrane is used for isolating the optical isomers of D,L-mandelic acid. Chirality, 2011.