Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography.

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO2-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO2 was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO2-MER microspheres (5 µm) with a pore size of ~1.3 nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO2-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO2-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO2-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO2, commercial C18, ZIC-HILIC, and bare SiO2 columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

Fabrication of microporous organic network@silica composite for high-performance liquid chromatographic separation of drugs and proteins.

Microporous organic networks (MONs) that exhibit good stability and hydrophobicity are promising candidates for performing HPLC separation of small organic compounds. However, their applications in separating large analytes as well as biomolecules are still limited by the microporous nature of MONs. Herein, we demonstrated the fabrication of a MON-functionalized silica (MON@SiO2 ), exhibiting micro and mesopores for the HPLC separations of small drugs as well as large analytes, such as flavones, nonsteroidal anti-inflammatory drugs (NSAIDs), endocrine disrupting chemicals (EDCs), and proteins. MON was successfully modified on SiO2 microspheres to yield the uniform and mono-dispersed MON@SiO2 . The separation mechanisms and performance of the MON@SiO2 packed column were evaluated for a wide range of analytes, including neutral, acidic, basic compounds, drugs, and proteins. Compared with commercial C18 and SiO2 -NH2 packed columns, the proposed MON@SiO2 column afforded superior performance in the separations of flavones, NSAIDs, EDCs, and proteins. Moreover, the MON@SiO2 column also offered good repeatability with intraday RSDs (n = 7) of <0.1%, <2.0%, <2.3%, and <0.7% for the retention time, peak height, peak area, and half peak width, respectively, for separating EDCs. This work proved the potential of using MONs in the HPLC separations of drugs and proteins.

Monomer-mediated fabrication of microporous organic network@silica microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography.

Microporous organic networks (MONs) are promising in high performance liquid chromatography (HPLC) with large specific surface area, good hydrophobicity and stability. However, their superhydrophobic structures restrict MONs-based HPLC only in reversed-phase mode. To decrease the hydrophobicity of pristine MONs and to expand their broad application in HPLC, here we described the monomer-mediated fabrication of core-shell MON-2COOH@SiO2 microspheres for reversed-phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) mixed-mode chromatography for the first time. The -COOH groups were introduced into MONs' skeleton to improve their hydrophilicity and to provide hydrophilic interaction sites. The MON-2COOH was grafted onto silica via a monomer mediated method to produce monodispersed core-shell microspheres. By adjusting the concentration of reactants, the thickness of MON-2COOH shell was easily manipulated. The packed MON-2COOH@SiO2 column showed high resolution and selectivity for separating both hydrophobic (alkylbenzenes, polycyclic aromatic hydrocarbons, anilines and phenols) and hydrophilic (nucleoside and nucleic bases) probes, highlighting the promise of MONs in mixed-mode HPLC. The MON-2COOH@SiO2 column also achieved good separation to sulfonamides, nonsteroidal anti-inflammatory drugs, flavonoids and phenylurea herbicides, and offered better resolution than commercial C18 and pristine SiO2 column. Multiple retention mechanisms were also found on MON-2COOH@SiO2 packed column, underlining the great potential of MONs in mixed-mode HPLC.