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Author(s): Nayan Xu [sup.1], Baoyan Yuan [sup.1], Cong Hu [sup.1], Yunyan Yu [sup.1], Nan Fu [sup.1], Junhui Zhang [sup.1], Shengming Xie [sup.1], Liming Yuan [sup.1] Author Affiliations: (1) grid.410739.8, 0000 [...], As a new type of multifunctional material, metal-organic frameworks (MOFs) have a wide application prospect in the field of chiral separation. In this study, a homochiral MOF [Ni(S-mal)(bpy)].sub.n was synthesized by the reaction of S-malic acid (S-mal) and 4,4'-bipyridine (bpy) with nickel acetate. The homochiral MOF [Ni(S-mal)(bpy)].sub.n was explored as a new chiral stationary phase for HPLC separation of racemic compounds using n-hexane-isopropanol as a mobile phase. A series of racemic compounds were separated on this column. The results showed that the homochiral MOF column exhibited good chiral recognition ability toward six racemic compounds including amlodipine, ibuprofen, flurbiprofen, propranolol hydrochloride, chlorphenamine maleate and 1-p-chlorobenzyl-ethanol. The homochiral MOF column also offered good reproducibility and stability for the enantioseparation.

The chiral covalent-organic framework (CCOF) is a new kind of chiral porous material, which has been broadly applied in many fields owing to its high porosity, regular pores, and structural adjustability. However, conventional CCOF particles have the characteristics of irregular morphology and inhomogeneous particle size distribution, which lead to difficulties in fabricating chromatographic columns and high column backpressure when the pure CCOFs particles are directly used as the HPLC stationary phases. Herein, we used an in situ growth strategy to prepare core–shell composite by immobilizing MDI-β-CD-modified COF on the surface of SiO2-NH2. The synthesized MDI-β-CD-modified COF@SiO2 was utilized as a novel chiral stationary phase (CSP) to explore its enantiomeric-separation performance in HPLC. The separation of racemates and positional isomers on MDI-β-CD-modified COF@SiO2-packed column (column A) utilizing n-hexane/isopropanol as the mobile phase was investigated. The results demonstrated that column A displayed remarkable separation ability for racemic compounds and positional isomers with good reproducibility and stability. By comparing the MDI-β-CD-modified COF@SiO2-packed column (column A) with commercial Chiralpak AD-H column and the previously reported β-CD-COF@SiO2-packed column (column B), the chiral recognition ability of column A can be complementary to that of Chiralpak AD-H column and column B. The relative standard deviations (RSDs) of the retention time and peak area for the separation of 1,2-bis(4-fluorophenyl)-2-hydroxyethanone were 0.28% and 0.79%, respectively. Hence, the synthesis of CCOFs@SiO2 core–shell composites as the CSPs for chromatographic separation has significant research potential and application prospects. [ABSTRACT FROM AUTHOR]

A new facile strategy was designed to prepare the phenyboronic acid-functionalized Fe3O4 magnetic nanoparticles (Fe3O4@PBA) via direct silanization and thiol-ene click chemistry for the selective adsorption of ortho-dihydroxy-containing compounds. The three kinds of Fe3O4@PBA nanoparticles obtained showed excellent adsorption capacity and selectivity for ortho-dihydroxy-containing compounds including adenosine and o-dihydroxybenzene. Among them, the Fe3O4@MPS@MPBA exhibited the highest adsorption capacity and selectivity for adenosine and o-dihydroxybenzene, followed by Fe3O4@MPTES@AAPBA and Fe3O4@MPTES@VPBA. A synthesis method of superparamagnetic and boronate affinity nanocomposites with mild reaction conditions and simple process has been developed, which also provides a novel way for the synthesis of other types of enrichment materials of ortho-dihydroxy-containing compounds. [ABSTRACT FROM AUTHOR]

A homochiral metal–organic framework (MOF) comprising [Co(L)(bpe) 2 (H 2 O) 2 ]·H 2 O was prepared using (1R,2R)-(−)-1,2-cyclohexanedicarboxylic acid (H 2 L) and 1,2-bis(4-pyridyl)-ethylene as organic ligands. The homochiral MOF [Co(L)(bpe) 2 (H 2 O) 2 ]·H 2 O was explored as chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) separation of racemates. Nine racemates including naphthol, alcohol, diol, amine, ketone, ether and organic acid were well separated on the homochiral MOF [Co(L)(bpe) 2 (H 2 O) 2 ]·H 2 O column (250 mm long × 4.6 mm i.d.). The relative standard deviation for five replicate separations of 1,1′-bi-2-naphthol is 0.69% for the retention time, indicating that the good reproducibility and stability of the homochiral MOF column for HPLC enantioseparation. The results indicated that the homochiral MOF as CSP is practical, which promotes the application of homochiral MOFs in HPLC. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. Chirality 26:27-32, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Chiral metal-organic frameworks (MOFs) have aroused great attention in the chiral separation field based on their excellent characteristics, including abundant topological structures, large surface area, adjustable pore/channel sizes, multiple active sites, and good chemical stability. However, the irregular morphology and nonuniformity of the synthesized MOF particles cause low column efficiency and high column backpressure for MOF-packed columns, which significantly affects their separation performance. Herein, we prepared a homochiral d-his-ZIF-8@SiO 2 composite by growing of d-his-ZIF-8 on the carboxylic-functionalized SiO 2 microspheres via a simple one-pot synthesis approach. The d-his-ZIF-8@SiO 2 core-shell microspheres with uniform particles and narrow size distribution were applied as the chiral stationary phase (CSP) for enantioseparations in HPLC. Various racemates were separated on the d-his-ZIF-8@SiO 2 -packed columns with n -hexane/isopropanol as the mobile phase. Eighteen racemates including alcohol, phenol, amine, ketone, and organic acid were well resolved on the homochiral d-his-ZIF-8@SiO 2 CSP. The d-his-ZIF-8@SiO 2 core-shell microspheres' CSP possesses an excellent chiral resolution ability toward various racemic compounds with good reproducibility and stability. Hence, the fabrication of chiral MOF@SiO 2 core-shell microspheres is an effective strategy to improve the application of homochiral MOFs as CSPs in the field of chromatography.

Molecular organic cage compounds have attracted considerable attention due to their potential applications in gas storage, catalysis, chemical sensing, molecular separations, etc. In this study, a homochiral pentyl cage compound was synthesized from a condensation reaction of ( S , S )-1,2-pentyl-1,2-diaminoethane and 1,3,5-triformylbenzene. The imine-linked pentyl cage diluted with a polysiloxane (OV-1701) was explored as a novel stationary phase for high-resolution gas chromatographic separation of organic compounds. Some positional isomers were baseline separated on the pentyl cage-coated capillary column. In particular, various types of enantiomers including chiral alcohols, esters, ethers and epoxides can be resolved without derivatization on the pentyl cage-coated capillary column. The reproducibility of the pentyl cage-coated capillary column for separation was investigated using nitrochlorobenzene and styrene oxide as analytes. The results indicate that the column has good stability and separation reproducibility after being repeatedly used. This work demonstrates that molecular organic cage compounds could become a novel class of chiral separation media in the near future.

Metal-organic frameworks (MOFs) as a new generation of functional molecular materials, have broad application prospects in enantioselective catalysis and chiral separation areas due to their unusual properties, such as high surface area, rich topologies, permanent microporous, availability of outer-surface modification and so on. A single-handed helical three-dimensional metal-organic framework material [{Cu(sala)}n] (H2sala=N-(2-hydroxybenzyl)-L-alanine) was incorporated with peramylated β-cyclodextrin for the preparation of novel capillary gas chromatography stationary phase. To investigate whether the use of a chiral MOF can enhance enantioseparation on peramylated β-cyclodextrin, three chiral columns were fabricated using different stationary phases for comparison, including column A ([{Cu (sala)}n]), column B (peramylated β-cyclodextrin) and column C ([{Cu(sala)}n]+peramylated β-cyclodextrin). The results of comparing the resolving abilities of the three columns for the same chiral compounds demonstrated that column C showed better enantioselectivity and higher resolution. The use of MOF [{Cu(sala)}n] can improve enantioseparation on peramylated β-cyclodextrin.