Macro-mesoporous organosilica monoliths with bridged-ethylene and terminal-vinyl: High-density click functionalization for chromatographic separation

Characterization of hybrid organo-silica monoliths for possible application in the gradient elution of peptides

We characterized thermally polymerized organo-silica hybrid monolithic capillaries to test their applicability in the gradient elution of peptides. We have used a single-pot approach utilizing 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), ethylene dimethacrylate (EDMA), and n-octadecyl methacrylate (ODM) as functional monomers. The organo-silica monolith containing MPTMS and EDMA was compared with the stationary phase prepared by adding ODM to the original polymerization mixture. Column prepared using a three-monomer system provided a lower accessible volume of flow-through pores, a higher proportion of mesopores, and higher efficiency. We utilized isocratic and gradient elution data to predict peak widths in gradient elution. Both protocols provided comparable results and can be used for peptide peak width prediction. However, applying gradient elution data for peak width prediction seems simpler. Finally, we tested the effect of gradient time on achievable peak capacity in the gradient elution of peptides with a column prepared with a three-monomer system providing a higher peak capacity. However, the performance of hybrid organo-silica monolithic stationary phases in gradient elution of peptides must be improved compared to other monolithic stationary phases. The limiting factor is column efficiency in highly aqueous mobile phases, which needs to be focused on.

Review of recent advances in development and applications of organic-silica hybrid monoliths

Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.

Chromatographic separation of peptides and proteins for characterization of proteomes

Characterization of proteomes aims to comprehensively characterize proteins in cells or tissues via two main strategies: (1) bottom-up strategy based on the separation and identification of enzymatic peptides; (2) top-down strategy based on the separation and identification of intact proteins. However, it is challenged by the high complexity of proteomes. Consequently, the improvements in peptide and protein separation technologies for simplifying the sample should be critical. In this feature article, separation columns for peptide and protein separation were introduced, and peptide separation technologies for bottom-up proteomic analysis as well as protein separation technologies for top-down proteomic analysis were summarized. The achievement, recent development, limitation and future trends are discussed. Besides, the outlook on challenges and future directions of chromatographic separation in the field of proteomics was also presented.

Surface-Charged Hybrid Monolithic Column for MS-Compatible Peptide Separation with High Peak Capacity and Its Application in Proteomic Analysis

For bottom-up proteomics, peptide separation with high peak capacity under MS-compatible conditions is of vital significance to increase proteome coverage. Herein, a surface-charged ethane-bridged hybrid monolithic column was prepared based on the efficient ring-opening reaction of N-methyl-aza-2,2,4-trimethyl-silacyclopentane after C18-functionalization. The existence of secondary amino groups on the surface was beneficial to reduce the secondary interactions of silanol groups and increase peak capacity for peptide separation with MS-compatible mobile phases (e.g., using 0.1% FA as the mobile phase modifier). Such columns offered a 4-fold increase in peak capacity compared with ethane-bridged hybrid monolithic columns without surface charge modification. By a 100 cm length surface-charged ethane-bridged hybrid capillary column, high peak capacity of 700 was achieved within a 240 min gradient for the separation of Hela tryptic peptides with 0.1% FA-containing mobile phases, under the low backpressure of ∼200 bar. On average, 44493 ± 459 peptides corresponding to 5148 ± 47 proteins were identified from 750 ng Hela tryptic digests. Finally, the surface-charged ethane-bridged hybrid monolithic column was successfully applied in the quantitative proteomic analysis of dopaminergic neuron death model of N-methyl-4-phenylpyridinium iodide induced SH-SY5Y cells. These results demonstrated great promise of such surface-charged ethane-bridged hybrid monolithic columns for bottom-up proteomic analysis in complex samples.

Contribution of the "Click Chemistry" Toolbox for the Design, Synthesis, and Resulting Applications of Innovative and Efficient Separative Supports: Time for Assessment

The last two decades have seen the rapid expansion of click chemistry methodology in various domains closely related to organic chemistry. It has notably been widely developed in the area of surface chemistry, mainly because of the high-yielding character of reactions of the "click" type. Especially, this powerful chemical reaction toolbox has been adapted to the preparation of stationary phases from the corresponding chromatographic supports. A plethora of selectors can thus be immobilized on either organic, inorganic, or hybrid stationary phases that can be used in different chromatographic modes. This review first highlights the few different chemical ligation strategies of the "click" type that are up to now mainly devoted to the development of functionalized supports for separation sciences. Then, it gives in a second part an up-to-date survey of the different studies dedicated to the preparation of click chemistry-based chromatographic supports while highlighting the powerful and versatile character of the "click" ligation strategy for the design, synthesis, and developments of more and more complex systems that can find promising applications in the area of analytical sciences, in domains as varied as enantioselective separation, glycomics, proteomics, genomics, metabolomics, etc.

Ethane-Bridged Hybrid Monolithic Column with Large Mesopores for Boosting Top-Down Proteomic Analysis

Top-down proteomics is challenged by the high complexity of biological samples. The coelution of intact proteins results in overlapped mass spectra, and hence, an increased peak capacity for protein separation is needed. Herein, ethane-bridged hybrid monoliths with well-defined large mesopores were successfully prepared based on the sol-gel condensation of 1,2-bis(trimethoxysilyl)ethane and tetramethoxysilane, followed by two-step base etching of the Si-O-Si domain while maintaining the Si-C-C-Si domain in the structure. Relatively homogeneous macropores of 1.1 μm and large mesopores of 24 nm were obtained, permitting fast mass transfer of large molecules and efficient diffusion without obstruction. The use of less hydrophobic C1 ligand further sharpened the peak shape and improved peak capacity. A 120 cm-long capillary column was used for top-down proteomic analysis of E. coli lysates under low backpressure with 16 MPa. High peak capacity of 646 was achieved within 240 min gradient. With MS/MS analysis, 959 proteoforms corresponding to 263 proteins could be unambiguously identified from E. coli lysates in a single run. Furthermore, to illustrate the separation performance for large proteoforms, such monoliths were applied to top-down analysis of the SEC fraction of E. coli lysates with Mw ranging from 30 to 70 kDa. With highly effective separation, 347 large proteoforms with Mw higher than 30 kDa were detected in the single 75 min run. These results showed great potential for top-down proteomic analysis in complex samples.

Monolithic Materials-Based RPLC-MS for Proteoform Separation and Identification

High-performance separation of proteoforms plays an important role in top-down proteomic ananlysis due to high complexity of the proteome. To this end, the functionalized ethylene-bridged hybrid monolithic materials have been developed for reversed-phase liquid chromatographic separation of proteoforms followed by online combination with high-resolution mass spectrometry (MS) for top-down proteomic analysis. Such monoliths have advantages of homogenously distributed functional groups in the framework, good chemical stability, and high permeability and, thus, show high resolution, good reproducibility, and low backpressure for proteoform separation. This chapter describes in detail the preparation of such monoliths and online combination with high-resolution MS for proteoform separation and identification.

High stability amino-derived reversed-phase/anion-exchange mixed-mode phase based on polysilsesquioxane microspheres for simultaneous separation of compound drugs

A series of amino-derived mixed-mode chromatographic stationary phases were synthesized based on porous mercaptopropyl-functionalized polysilsesquioxane mesoporous microspheres synthesized by a co-condensation of methyltrimethoxysilane (MTMS) and mercaptopropyltrimethoxysilane (MPTMS). Through controlling the ratio of MTMS and MPTMS, the modified stationary phases with different amino densities were prepared by a "thiol-ene" click chemistry reaction. The morphology, pore structure, and functional groups of the microspheres were characterized by scanning electron microscope (SEM), nitrogen adsorption-desorption test, Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and zeta potential, respectively. The chromatographic behavior of the stationary phases was evaluated by using alkylbenzene homologs and inorganic anions as probes. The mixed-mode retention behavior and separation mechanisms for neutral, alkaline, and acidic drugs on the prepared column had been systematically studied by changing the value of pH, ionic, and solvent strength of the mobile phase. Compared with the silica-based amino-bonded column (S-NH₂), the synthesized organosilica phase exhibited higher hydrothermal stability and longer service life under high alkaline conditions. The newly synthesized phase was successfully applied to the simultaneous separation of the multiple substances in compound drugs.

Copolymerization of Mesoporous Styrene-Bridged Organosilica Nanoparticles with Functional Monomers for the Stimuli-Responsive Remediation of Water

For every mass product, there are problems associated with the resulting waste. Residues of hormones in urine cannot be removed sufficiently from wastewater, and this has undesired consequences. An ideal adsorbent would take up the impurity, enable a simple separation and recyclability. Polymer colloids with high affinity towards the drug, accessible porosity, high surface area, and stimuli-responsive properties would be candidates, but such a complex system does not exist. Here, porous vinyl-functionalized organosilica nanoparticles prepared from a styrene bridged sol-gel precursor act as monomers. Initiation of the polymerization at the pore walls and addition of functional monomers result in a special copolymer, which is covalently linked to the surface and covers it. An orthogonal modification of external surface was done by click attachment of a thermoresponsive polymer. The final core-shell system is able to remove quantitatively hydrophobic molecules such as the hormone progesterone from water. A change of temperature closes the pores and induces the aggregation of the particles. After separation one can reopen the particles and recycle them.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.

Well-Defined Materials for High-Performance Chromatographic Separation

Chromatographic separation has been widely applied in various fields, such as chemical engineering, precision medicine, energy, and biology. Because chromatographic separation is based on differential partitioning between the mobile phase and stationary phase and affected by band dispersion and mass transfer resistance from these two phases, the materials used as the stationary phase play a decisive role in separation performance. In this review, we discuss the design of separation materials to achieve the separation with high efficiency and high resolution and highlight the well-defined materials with uniform pore structure and unique properties. The achievements, recent developments, challenges, and future trends of such materials are discussed. Furthermore, the surface functionalization of separation ma-terials for further improvement of separation performance is reviewed. Finally, future research directions and the challenges of chromatographic separation are presented.

Bridged Hybrid Monolithic Column Coupled to High-Resolution Mass Spectrometry for Top-Down Proteomics

Top-down mass spectrometry (MS)-based proteomics has become a powerful tool for comprehensive characterization of intact proteins. However, because of the high complexity of the proteome, highly effective separation of intact proteins from complex mixtures prior to MS analysis remains challenging. Monolithic columns have shown great promise for intact protein separation due to their high permeability, low backpressure, and fast mass transfer. Herein, for the first time, we developed bridged hybrid bis(triethoxysilyl)ethylene (BTSEY) monolith with C8 functional groups (C8@BTSEY) for highly effective protein separation and coupled it to high-resolution MS for identification of intact proteins from complex protein mixtures. We have optimized mobile phase conditions of our monolith-based reverse-phase chromatography (RPC) for online liquid chromatography (LC)-MS analysis and evaluated separation reproducibility of the C8@BTSEY column. We further assessed the chromatographic performance of this column by separating a complex protein mixture extracted from swine heart tissue. Using our monolithic column (i.d. 100 μm × 35 cm), we separated over 300 proteoforms (up to 104 kDa) from 360 ng of protein mixture in an 80 min one-dimensional (1D) LC run. The highly effective separation and recovery of intact proteins from this monolithic column allowed unambiguous identification of ∼100 proteoforms including a large protein, αactinin2 (103.77 kDa), by online 1D LC-MS/MS analysis for the first time. As demonstrated, this C8@BTSEY column is reproducible and effective in separation of intact proteins, which shows high promise for top-down proteomics.