Hybrid Monolith Research Articles

Roles of Divinylbenzene Co‐Cross‐Linker in a Threefold Cross‐Linked Polystyrene–Phosphine Hybrid Monolith: Impact of Cross‐linking Degree on Catalytic Performance

AbstractContinuous‐flow organic transformations using immobilized catalysts are crucial for green and sustainable chemistry. Cross‐linked polymer ligands offer high stability, ease of recovery through filtration, and thus enhance performance in continuous‐flow reactions via transition‐metal catalysis. Additionally, the cross‐linking structure of the polymer support creates a unique reaction platform that controls the coordination behavior of the supported ligands and stabilizes the metal catalysts. However, insights into the material‐based design for preparing highly active and durable immobilized metal catalysts are still limited. In this report, we propose a straightforward approach to boost both selective mono‐coordination and effective stabilization of metal complexes. We developed threefold cross‐linked polystyrene‐triphenylphosphine hybrid monoliths with cross‐linking structures adjusted by varying the content of divinylbenzene as co‐cross‐linker. The coordination behaviors and metal‐support interactions of these monoliths were evaluated, highlighting the importance of co‐cross‐linker content in site‐isolating phosphine units and stabilizing metal centers via arene‐metal interactions on the polystyrene network. By optimizing the cross‐linking structure, the monolith catalysts demonstrated exceptionally high catalytic activity and durability in Pd‐catalyzed C−Cl transformations, such as Suzuki–Miyaura cross‐couplings and Buchwald‐Hartwig aminations in continuous flow. This underscores the utility of our monolith system in challenging transition‐metal catalysis.

A novel halloysite nanotubes-based hybrid monolith for in-tube solid-phase microextraction of polar cationic pesticides

The accurate determination of polar cationic pesticides in food poses a challenge due to their high polarity and trace levels in complex matrices. This study hypothesized that the use of halloysite nanotubes (HNTs) can significantly enhance the extraction efficiency and sensitivity of these analytes because of their rich hydroxyl groups and cation exchange sites. Therefore, we chemically incorporated HNTs with organic polymer monoliths for in-tube solid-phase microextraction (SPME). This novel hybrid monolith extended service life, improved adsorption capacity, and exhibited excellent extraction performance for polar cationic pesticides. Based on these advancements, a robust and sensitive in-tube SPME-HILIC-MS/MS method was constructed to determine trace levels of polar cationic pesticides in complex food matrices. The method achieved limits of detection of 1.9, 2.1, and 0.1 μg/kg for maleic hydrazide, amitrole, and cyromazine, respectively. The spiked recoveries in five food samples ranged from 80.2 to 100.8%, with relative standard deviations below 10.7%.

Aptamer based hybrid monolithic pipette tips supported by melamine sponge for enrichment of proteins

BackgroundThe convenient preparation and application of functionalized organic-inorganic hybrid monolithic materials have obtained substantial interest in the pretreatment of complex samples by solid-phase extraction (SPE). Compared to the in-tube solid-phase microextraction in fused-silica capillaries, micro SPE in plastic pipette tips have fascinating merits for the easily operated enrichment of trace target analytes from biological samples. However, the poor compatibility of organic-inorganic hybrid monoliths with plastics leads to the rare appearance of commercial hybrid monolithic pipette tips (HMPTs). Therefore, how to synthesize the organic-inorganic hybrid monolithic materials with better extraction performance in plastic pipette tips becomes a challenge. ResultsWe develop a facile and cheap strategy to immobilize organic-inorganic hybrid monoliths in pipette tips. Melamine sponge was employed as the supporting skeleton to in situ assemble amine- and thiol-bifunctionalized hybrid monolithic material via “one pot” in a pipette tip, and gold nanoparticles (GNPs) and thiol-modified aptamer against human α-thrombin were sequentially attached to the hybrid monolith within the HMPTs. The average coverage density of the aptamer with GNPs as an intermediary reached as high as 818.5 pmol μL−1. The enriched thrombin concentration was determined by a sensitive enzymatic chromogenic assay with the limit of detection of 2 nM. The extraction recovery of thrombin at 10 nM in human serum was 86.1 % with a relative standard deviation of 6.1 %. This proposed protocol has been applied to the enrichment and determination of thrombin in real serum sample with strong anti-interference ability, low limit of detection and high recovery. SignificanceThe amine- and thiol-bifunctionalized HMPTs prepared with sponge as the skeleton frame provided a novel substrate material to decorate aptamers for efficient enrichment of proteins. This enlightens us that we can take advantage of the tunability of sponge assisted HMPTs to produce and tailor a variety of micro SPE pipette tips for broader applications on the analysis of trace targets in complex biological, clinic and environmental samples.

One-pot preparation of bi-functional POSS-based hybrid monolith via photo-initiated polymerization for isolation of extracellular vesicles

Extracellular vesicles (EVs) are important participants in numerous pathophysiological processes, and could be used as valuable biomarkers to detect and monitor various diseases. However, facile EV isolation methods are the essential and preliminary issue for their downstream analysis and function investigation. In this work, a polyhedral oligomeric silsesquioxanes (POSS) based hybrid monolith combined metal affinity chromatography (MAC) and distearoyl phospholipid ethanolamine (DSPE) function was developed via photo-initiated thiol-ene polymerization. This synthesis process was facile, simple and convenient, and the obtained hybrid monolith could be applied to efficiently isolate EVs from bio-samples by taking advantages of the specific bond of Ti4+ and phosphate groups on the phospholipid membrane of EVs and the synergistic effect of DSPE insertion. Meanwhile, the eluted EVs could maintain their structural integrity and biological activity, suggesting they could be used for downstream application. Furthermore, 75 up-regulated proteins and 56 down-regulated proteins were identified by comparing the urinary EVs of colorectal cancer (CRC) patients and healthy donors, and these proteins might be used as potential biomarkers for early screening of CRC. These results demonstrated that this hybrid monolith could be used as a simple and convenient tool for isolating EVs from bio-samples and for wider applications in biomarker discovery.

Mixed-mode chromatographic performance using nicotinic acid-functionalized chito-oligosaccharide-bonded Ti/Si hybrid monolithic capillary columns.

This article describes the fabrication of porous nicotinic acid-functionalized chito-oligosaccharide-bonded titania/silica hybrid monoliths (TiO2/SiO2@ChO-N) through a co-gelation sol-gel process. A capillary monolith with a well-defined and homogeneous structure was obtained by controlling the hydrolysis speed of titanium alkoxides in a sol mixture by using glycerol and acetylacetone. As a result of the functionalization with chito-oligosaccharides (ChO)-modified nicotinic acid, the obtained stationary phase provides superior physiochemical properties, such as a cationic hydrophilic surface, porosity, and mechanical strength. Scanning electron microscope and attenuated total reflectance-infrared spectroscopy were used to characterize the functionalized monolithic columns. The produced capillary columns showed high chromatographic performance with acceptable selectivity for charged analytes as well as organic polar compounds such as nucleic bases, nucleosides, carbamate pesticides, and strobilurinfungicides. The obtained results also indicated that the functionalized ChO's amino, amide, hydroxyl, and pyridinium ring moieties served as hydrophilic electrostatic traps for charged substances, in addition tostroing π-π interaction with the carbamate pesticides and strobilurin fungicides analytes via hydrogen bonding.

Sheltering Mono-P-Ligated Metal Complexes in Porous Polystyrene Monolith: Effect of Aryl Pendant Stabilizers on Catalytic Durability.

Metal centers that can generate coordinatively unsaturated metals in accessible and stable states have been developed using synthetic polymers with sophisticated ligand and scaffold designs, which required synthetic efforts. Herein, we report a simple and direct strategy for producing polymer-supported phosphine-metal complexes, which stabilizes mono-P-ligated metals by modulating the electronic properties of the aryl pendant groups in the polymer platform. A three-fold vinylated PPh3 was copolymerized with a styrene derivative and a cross-linker to produce a porous polystyrene-phosphine hybrid monolith. Based on the Hammett substituent constants, the electronic properties of styrene derivatives were modulated and incorporated into the polystyrene backbone to stabilize the mono-P-ligated Pd complex via Pd-arene interactions. Through NMR, TEM, and comparative catalytic studies, the polystyrene-phosphine hybrid, which induces selective mono-P-ligation and moderate Pd-arene interactions, demonstrated high catalytic durability for the cross-coupling of chloroarenes under continuous-flow conditions.

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.

3D porous alumina/graphene hybrids prepared by atomic layer deposition and their performance for water treatment

Metal / carbon hybrids have impressive potential of applications in many fields: catalysis, energy conversion and storage, environmental. However, further efforts are needed to achieve a better control of homogeneity of the metal oxide deposit on the carbon surface to provide reliable synthesis approaches of metal / carbon hybrids. In this work, atomic layer deposition is used to prepare 3D porous alumina / reduced graphene oxide hybrid monoliths. We show that atomic layer deposition, even though rarely reported to prepare metal oxide / carbon hybrids, allows a conformal coating onto the graphene nanosheet surface. In-depth advanced characterization have been performed thanks to a coupled approach consisting of the preparation of lamellas of the porous hybrid by means of focused ion beam and their analysis by transmission electron microscopy. A good accessibility of the alumina precursors to the internal surface of the prepared 3D porous carbon monoliths was evidenced. The alumina / graphene hybrid prepared with 50 cycles of ALD deposit has a surface as high as 284 m2/g. As a proof-of-concept for the interest of the designed hybrids, they are tested for the removal of Congo red, a standard organic dye pollutant. 87 and 98 % of Congo red removal were reached at the first and the second step of adsorption proving the good adsorption performance and reusability ability of the de designed hybrid adsorbents. We believe that such multi-porous 3D alumina / graphene macrostructures that offers a favorable accessibility to the adsorption sites open interesting potentialities for pollution remediation applications.

Enhancing Top-Down Characterization of Membrane Proteoforms with C8-Functional Amine-Bridged Hybrid Monoliths.

Comprehensive characterization of membrane proteins at the level of proteoforms in complex biological samples by top-down mass spectrometry (MS) is of vital importance in revealing their precise functions. However, severe peak broadening in the separation of hydrophobic membrane proteins, caused by resistance to mass transfer and strong adsorption on separation materials, leads to MS spectra overlap and signal suppression, which makes against the in-depth research on membrane proteoforms. Herein, C8-functional amine-bridged hybrid monoliths with an interconnected macroporous structure were developed by the in situ one-step sol-gel reaction of triethoxy(octyl)silane and bis[3-(trimethoxysilyl)propyl]amine in capillaries. Due to the unique macroporous structure and bridged secondary amino groups in the framework, the monolith possessed reduced resistance to mass transfer, low nonspecific adsorption, and electrostatic repulsion to membrane proteins. These features tremendously alleviated peak broadening in the separation of membrane proteins, thus outperforming traditional reversed-phase columns in top-down characterization of membrane proteoforms. With this monolith, a total of 3100 membrane proteoforms were identified in the mouse hippocampus, representing the largest membrane proteoform database obtained by top-down analysis so far. The identified membrane proteoforms revealed abundant information, including combinatorial post-translational modifications (PTMs), truncation, and transmembrane domains. Furthermore, the proteoform information was integrated into the interaction network of membrane protein complexes involved in oxidative phosphorylation processing, opening up new opportunities to uncover more detailed molecular basis and interaction in the biological processes.

Enhanced performance of ZIF-8 nanocrystals hybrid monolithic composites via an in-situ growth strategy for efficient capillary microextraction of perfluoroalkyl phosphonic acids

Enrichment of perfluoroalkyl phosphonic acids (PFPAs) is of great significance and challenging for environmental monitoring, due to their toxic and persistent nature, highly fluorinated character as well as low concentration. Herein, novel metal-organic frameworks (MOFs) hybrid monolithic composites were prepared via metal oxide-mediated in situ growth strategy and utilized for capillary microextraction (CME) of PFPAs. A porous pristine monolith was initially obtained by copolymerization of the zinc oxide nanoparticles (ZnO-NPs)-dispersed methacrylic acid (MAA) with ethylenedimethacrylate (EDMA) and dodecafluoroheptyl acrylate (DFA). Afterwards, nanoscale-facilitated transformation of ZnO nanocrystals into the zeolitic imidazolate framework-8 (ZIF-8) nanocrystals was successfully realized via the dissolution-precipitation of the embedded ZnO-NPs in the precursor monolith in the presence of 2-methylimidazole. Experimental and spectroscopic results (SEM, N2 adsorption-desorption, FT-IR, XPS) revealed that the coating of ZIF-8 nanocrystals significantly increased the surface area of the obtained ZIF-8 hybrid monolith and endowed the material abundant surface-localized unsaturated zinc sites. The proposed adsorbent showed highly enhanced extraction performance for PFPAs in CME, which was mainly ascribed to the strong fluorine affinity, Lewis acid/base complexing, anion-exchange, and weakly π-CF interaction. The coupling of CME with LC-MS enables effective and sensitive analysis of ultra-trace PFPAs in environment water and human serum. The coupling method demonstrated low detection limits (2.16–4.12 ng L−1) with satisfactory recoveries (82.0–108.0%) and precision (RSDs ≤6.2%). This work offered a versatile route to design and fabricate selective materials for emerging contaminant enrichment in complicated matrices.

Ionic liquid assisted in situ growth of nano-confined ionic liquids/metal-organic frameworks nanocomposites for monolithic capillary microextraction of microcystins in environmental waters

A facile in-situ ionothermal synthesis strategy for fabrication of ionic liquids/metal−organic frameworks (MOFs) (ILs@ZIF-8) nanocomposites hybrid monolith has been proposed to facilitate highly effective capillary microextraction (CME) of ultra-trace microcystins (MCs) in environmental waters. The ZnO nanoparticles (ZnO-NPs) were initially introduced into a precursor polymer monolith, and acted as the metal sources and anchoring seeds to construct ILs@ZIF-8 nanocomposites hybrid monolith via a nanoparticle-directed in-situ growth route in confined imidazolium ionic liquids. Detailed characterization based on scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption-desorption isotherms confirmed that both the morphology and porous structure of ZIF-8 were finely tuned by the incorporation of ILs, which acted as solvents and structure directing agent. The confinement of ILs in ZIF-8 framework endows the ILs@ZIF-8 hybrid monolith additional adsorption sites and satisfied water stability for the synergistic enhancement of adsorption efficiency of MCs via multiple interactions (including π-π stacking, hydrogen bonding, hydrophobic and electrostatic interactions). Coupling ILs@ZIF-8 hybrid monolith-based CME to LC-MS enabled an efficient and sensitive analysis of MCs in surface waters with ultra-low detection limits (LOD ≤ 1.4 ng L−1) and satisfactory recoveries (70.2%−107.0%). This study showed great potential for feasible design and fabrication of ILs@MOFs composites with synergistic and tunable structures toward efficient sample preparation applications.

Online highly selective recognition of domoic acid by an aptamer@MOFs affinity monolithic column coupled with HPLC for shellfish safety monitoring.

Enabling cost-effective safety monitoring of shellfish is an important measure for the healthy development of the coastal marine economy. Herein, a new aptamer@metal-organic framework (MOF)-functionalized affinity monolithic column was proposed and applied in selective in-tube solid-phase microextraction (IT-SPME) coupled with HPLC for the accurate recognition of domoic acid (DA) in shellfish. Using a surface engineering strategy, ZIF-8 MOF was grown in situ inside the poly(epoxy-MA-co-POSS-MA) hybrid monolith. A high BET surface area and abundant metal reactive sites of the MOF framework were obtained for anchoring massive aptamers with terminal-modified phosphate groups. Various characterizations, such as SEM, elemental mapping, XRD, and BET, were performed, and the affinity performance was also studied. The presence of a massive amount of aptamers with a super coverage density of 3140 μmol L-1 bound on ZIF-8 MOF activated a high-performance bionic-affinity interface, and perfect specificity was exhibited with little interference of tissue matrixes, thus assuring the highly selective capture of DA from the complex matrixes. Under the optimal conditions, DA toxins in shellfish were detected with the limit of detection (LOD) of 7.0 ng mL-1 (equivalent to 14.0 μg kg-1), representing a 5-28 fold enhancement in detection sensitivity over traditional SPE or MIP adsorbents reported previously. The recoveries of fortified mussel and clam samples were achieved as 91.8 ± 1.2%-94.1 ± 1.9% (n = 3) and 91.2 ± 1.1%-94.5 ± 3.6% (n = 3), respectively. This work sheds light on a cost-effective method for online selective IT-SPME and the accurate monitoring of DA toxins using an aptamer@MOF-mediated affinity monolith system coupled with the inexpensive HPLC-UV technique.

Highly Bioactive Elastomeric Hybrid Nanoceramics for Guiding Bone Tissue Regeneration

Conventional bioactive ceramic implants possess high osteogenic ability but exhibit poor machinability and brittleness, which limit their wide applications. In this study, we report an elastomeric machinable bioactive nanoceramic-based hybrid membrane that is formed by nanohydroxyapatite-reinforced hybrid matrix (poly(dimethylsilicone)-bioactive glass-poly(caprolactone) (nHA-PBP)) using a modified sol-gel process. The hybrid matrix is composed of elastomeric polydimethylsiloxane and bioactive glass nanogel. The effect of the nHA contents (0, 20, 30, 40 and 50 wt%) on the physicochemical structure and biomineralization activity of PBP hybrid membranes is investigated systematically. The results show that nHA-PBP hybrid membranes containing more than 20 wt% nHA exhibit the highest apatite-forming bioactivity due to the optimized hydroxyapatite crystalline phase. NHA-PBP implants with nHA also show good elastomeric mechanical behavior and foldable mechanical properties. Furthermore, the study of the in vitro cellular biocompatibility suggests that the nHA-PBP hybrid monoliths can enhance osteoblast (MC3T3-E1) attachment and proliferation. The biomimetic hybrid composition, crack-free monolith structure, and high biological activity of apatite formation make the nHA-PBP hybrid membrane a prospective candidate in the application of bone tissue regeneration.

Self-assembly preparation of Zn2+ -immobilized silica hybrid monolith and application in solid-phase micro-extraction of β-agonists.

Exploiting adsorbents with highly efficient extraction performance is of great promise for extracting small organic molecules from biological samples. In this work, a novel Zn2+ -immobilized chitosan@silica hybrid monolith was prepared through a simple self-assembly Zn2+ -immobilization process. Exploited as an adsorbent in solid-phase micro-extraction for extracting trace β-agonists, the monolith exhibited high extraction efficiencies for salbutamol, clenbuterol, and ractopamine with the enrichment factors approaching 120, 85, and 52, respectively. These could be attributed to the effective interaction between Zn2+ ions and the target molecule via coordination or other intermolecular interactions. Under optimized extraction operations, a sensitive determination was successfully developed coupling with high-performance liquid chromatography-ultraviolet detection. The linear range was 0.17-58.8, 0.12-68.5, and 0.18-65.5ng/ml for salbutamol, clenbuterol, and ractopamine. The limits of detection of the β-agonists were from 0.04 to 0.07ng/ml, and the limits of quantification were from 0.12 to 0.18ng/ml. The recoveries of spiking in mutton samples were observed in the range of 85.9%-95.7%, with relative standard deviations<8.0% (n=3). Application tests demonstrated this newly developed determination was practical, accurate, and convenient for detecting trace content β-agonists in meat.

A Hydrophilic Strong Anion-Exchange Hybrid Monolith for Capillary Liquid Chromatography

A hydrophilic strong anion-exchange monolithic hybrid column was prepared by in-capillary coating 5-µm bare silica particles with the copolymers of methacryloxyethyltrimethyl ammonium chloride and pentaerythritol triacrylate in the presence of a porogen consisting of water, methanol, and cyclohexanol. The composition of the porogen and the concentration of the monomers were investigated and selected. The resulting column was characterized. The column had an uniform pore structure and could withstand a back pressure up to 3500 psi. Its permeability was comparable to that of packed columns and the swelling-shrinking behaviour negligible. Its hydrophobicity could be suppressed at acetonitrile concentrations above 40% (v/v) and the minimum theoretical plate height was about 10 µm for BrÑ. The column-to-column relative standard deviations (RSDs) were 2.2% and 3.5% (n = 9) and the batch-to-batch RSDs were 2.4% and 5.5% (n = 3) for k and H values, respectively. The column exhibited a remarkable performanceforthe separation of inorganic anions, organic weak acids, phenols, and nucleotides.

Front Cover: Assembly‐In‐Foam Approach to Construct Nanodiamond/Carbon Nanotube Hybrid Monolithic Carbocatalysts for Direct Dehydrogenation of Ethylbenzene to Styrene (Eur. J. Inorg. Chem. 26/2022)

Front Cover: Assembly‐In‐Foam Approach to Construct Nanodiamond/Carbon Nanotube Hybrid Monolithic Carbocatalysts for Direct Dehydrogenation of Ethylbenzene to Styrene (Eur. J. Inorg. Chem. 26/2022)

Evaluation of the potential of a 3D-printed hybrid zeolite 13X/activated carbon material for CO2/N2 separation using electric swing adsorption

Zeolite13X is known for its higher CO2 adsorption capacity. The use of monolithic shaped materials allows a process with a lower pressure drop than traditionally packed beds, increasing the energy efficiency of the process. Additive manufacturing is an alternative for developing hierarchically structured adsorbent materials with improved geometries. In this study, the potential of a hybrid monolith with electrically conductive properties was assessed for CO2capture by applying an Electrical Swing Adsorption process. Themonolith was obtained by direct ink writing. In addition to the zeolite13X (47.5 %wt.), activated carbon (47.5 %wt.) was used to provide electrical conductivity to the material. Carboxymethylcellulose was used as a binder/plasticizer to assist in writing and provide mechanical stability. The properties of the monolith were analyzed by several techniques and were compared with its raw adsorbent materials. CO2and N2adsorption equilibrium properties and the adsorption dynamics were also evaluated to test the performance of the monolith in capturing CO2. During these tests, electrification to regenerate the structured adsorbent was used.Considering a stream with a molar fraction of 0.15 ofCO2and 0.85 of N2at 1 bar,the monolith presents a CO2/N2selectivity of 30.7. The application of electric current increased the monolith temperature due to the Joule heating effect and demonstrated the efficiency in achieving a faster regeneration of the adsorbent. The cyclic stability of the monolith was also evaluated in this work. This study proves the potential of using direct ink writing to produce structured adsorbent materials for CO2capture using an electric swing adsorption process.

Assembly‐In‐Foam Approach to Construct Nanodiamond/Carbon Nanotube Hybrid Monolithic Carbocatalysts for Direct Dehydrogenation of Ethylbenzene to Styrene

AbstractSustainable nanocarbon catalysts have made measurable progress in ethylbenzene direct dehydrogenation (DDH). Thanks for the distinctive physical and chemical properties of Nanodiamond (ND), the considerable attention have been paid to diverse catalytic transform processes involving the DDH reaction. However, the powder‐form carbon cannot be directly used in fixed‐bed reactors owing to the resulting huge pressure drop. Herein, inspired by the ship‐in‐boat strategy, we present an ingenious assembly‐in‐foam approach for the preparation of a novel hybrid structured monolithic catalyst featuring an aerogel of sulfur‐doped nanodiamonds/carbon nanotubes hybrid within the macropores of SiC foam (ND−CNT−SDS/SiC) by heating the freeze‐dried macroporous hybrid gels composed of CNT, ND, and SDS in N2 atmosphere. Owing to the promoted NDs dispersion, strengthened mass transfer, and sulfur‐doping, the nanodiamonds/carbon nanotube hybrid foam monolithic catalyst exhibits a terrific catalytic performance with high stability for energy‐saving styrene production from DDH of ethylbenzene reaction, as well as overcoming the shortcomings of application of powder‐formed nanocarbon in heterogeneous catalysis. Furthermore, the emerging Assembly‐in‐Foam way for preparing nanocarbons‐based foam monolithic catalyst towards diverse chemical processes has been paved.

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.

C18-Functionalized Amine-Bridged Hybrid Monoliths for Mass Spectrometry-Friendly Peptide Separation and Highly Sensitive Proteomic Analysis.

For proteomic analysis based on mass spectrometry (MS), high-performance peptide separation under MS-friendly conditions is of importance. To this end, a novel kind of amine-bridged hybrid monolith was developed by the sol-gel reaction of bis[3-(trimethoxysilyl)propyl]amine and allyltrimethoxysilane, followed by "thiol-ene" click functionalization of C18 groups. With the secondary amino groups bridged in the framework, the nonspecific adsorption from silanol groups could be decreased, so that peptide peak tailing under MS-friendly conditions was reduced, and half peak width was narrowed. Furthermore, such materials were facilely in situ prepared in the very narrow bore capillary with low backpressure for proteomic analysis of limited amounts of samples. Finally, 16,692 unique peptides corresponding to 3698 protein groups could be averagely identified from 10 ng Hela cell digests in a single 65 min run, and 5257 peptides corresponding to 1062 protein groups could be averagely identified from 200 pg digests in a single 60 min run. Such high sensitivity could be attributed to the decreased nonspecific adsorption, the narrowed peak width, and the miniaturization of the column. It is shown that such monoliths are promising for highly sensitive proteomic analysis, including single-cell proteomics.