Organic-silica Hybrid Monolith Research Articles

Single-step fabrication of a teicoplanin functionalized organic-silica hybrid monolith for enantioseparation by nano-liquid chromatography

A novel teicoplanin functionalized organic-silica hybrid chiral monolithic column was prepared by a facile single-step approach. The conditions for the preparation of the organic-silica hybrid chiral monolithic column were systematically optimized, including the amount of poly (ethylene glycol) (PEG) and urea, the tetramethyl orthosilicate (TMOS)/3-(trimethoxysilyl)-propylmethacrylate (γ-MAPS) ratio (v/v), the content of teicoplanin-2-isocyanatoethyl methacrylate (Tei-ICNEML) monomer, and the reaction temperature and time. The optimum column exhibited satisfactory efficiency, permeability and stability. In order to obtain satisfactory enantioseparation performance, reversed phase (RPM) and polar organic phase (POM) modes were employed, and different experimental conditions were optimized, such as buffer concentration and pH, amount of the organic solvent, concentration and ratio of TEA/HAc, and MeOH/ACN ratio. The stability of the Tei-ICNEML organic-silica hybrid monolithic column was also investigated in both POM and RPM separation modes. Then, this novel monolithic column was successfully applied to achieve the enantioseparation of amino alcohols, N-derivatized amino acids and mandelic acids. 15 out of 20 amino alcohols were baseline separated with good column efficiency in the POM mode, and 3 out of 5 mandelic acids and 5 out of 6 N-derivatized amino acids were baseline separated in the RPM mode.

Synthesis of Hybrid Monolithic Columns Using a Click Chemistry Reaction for Application in Capillary Liquid Chromatography

Hybrid monolithic columns present characteristics of both silica and organic monoliths, such as good mechanical properties, wide pH tolerance, high permeability and stability and little swelling or shrinkage. A common way to prepare this type of material is by using alkoxysilanes and organic monomers via the sol-gel process and click chemistry reactions. In this paper, a co-condensation organic-silica hybrid monolith was prepared based on tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as precursors for the sol-gel process. The hybrid monolithic matrix was modified with dodecanethiol through the thiol-ene click chemistry reaction and the resulting material was compared with a dodecanesilane bonded phase column, in order to evaluate the differences in the chromatographic performance of a stationary phase prepared by a classic reaction or by a thiol-ene click reaction. Additionally, the stability of the thiol-ene column over time was evaluated. The effects of different synthetic proportions were investigated in detail by scanning electron microscopy (SEM), scanning capacitively coupled contactless conductivity detection (sC4D), Fourier-transform infrared spectroscopy (FTIR) and retention behavior in capillary liquid chromatography (cLC). The hybrid monolithic column prepared with dodecanethiol was the best one for the separation of alkylbenzenes and polycyclic aromatic hydrocarbons by cLC-UV.

Preparation of a polyhedral oligomeric silsesquioxanes hybrid monolith via a single-step ring-opening polymerization for pressurized capillary electrochromatography.

An organic-silica hybrid monolith was prepared by a single-step ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS-epoxy), polyethylenimine (PEI), and β-cyclodextrin (β-CD) in a ternary porogenic solvent consisting of polyethylene glycol, 1,4-butanediol, and 1-propanol. The framework of POSS-PEI hybrid monolith could offer well-defined 3D skeleton, while β-CD with the ability of forming a host-guest inclusion complexes with a variety of compounds could show an ability of specific selection. The obtained hybrid monoliths were successfully applied for separation of phenols, benzoic acids, and nucleobases. Especially due to the introduction of β-CD, positional isomers including hydroquinone and resorcinol, o-nitrophenol and p-nitrophenol, as well as p-chlorophenol and o-chlorophenol were baseline separated and the column efficiency reached 82300 plates/m for hydroquinone.

On-line trapping/capillary hydrophilic-interaction liquid chromatography/mass spectrometry for sensitive determination of RNA modifications from human blood

RNA modification has recently been proposed to play important roles in biological regulation. The detection and quantification of RNA modifications generally are challenging tasks since most of the modifications exist in low abundance in vivo. Here we developed an on-line trapping/capillary hydrophilic-interaction liquid chromatography/electrospray ionization-mass spectrometry (on-line trapping/cHILIC/MS) method for sensitive and simultaneous quantification of RNA modifications of N6-methyladenosine (m6A) and 5-methylcytosine (5-mC) from human blood. The hydrophilic organic-silica hybrid monolith was prepared using sol-gel combined with “thiol-ene” click reaction for the separation of nucleosides. A poly(MAA-co-EGDMA) monolithic capillary was used as the on-line trapping column. With the developed on-line trapping/cHILIC/MS analytical platform, the detection limits of m6A and 5-mC can reach to 0.06 fmol and 0.10 fmol. We then investigated the contents of m6A and 5-mC in human blood RNA from healthy persons at the age of 6–14 and 60–68 years. Our results showed that both m6A and 5-mC contents were significantly decreased in elder persons, suggesting the RNA modifications of m6A and 5-mC are correlated to aging.

Preparation of Organic-Silica Hybrid Monolith with Anion Exchange/Hydrophilic Interaction Mixed-Mode Via Epoxy–Amine Ring-Opening Polymerization Using Polyethylenimine as Functional Monomer

Polyethylenimine (PEI) and 2,4,6,8-tetramethyl-2,4,6,8-tetrakis(propyl glycidyl ether)cyclotetrasiloxane (POSS–epoxy) were used as precursors for the preparation of organic-silica hybrid monolithic columns (PEI–POSS monolith) via epoxy–amine ring-opening polymerization (ROP). The high density of amine groups in PEI provides rich chromatographic interaction sites for the polar or acidic analytes in hydrophilic interaction (HILIC) and weak anion exchange (WAX) mechanisms. The column preparation conditions, such as the porogens, solvent and reaction temperature, were systematically investigated according to the morphology, permeability and column efficiency. The separation mechanisms of HILIC and WAX were evaluated with neutral polar compounds and halogen benzoic acids. Owing to the existence of reactive amine groups on the matrix surface, the PEI–POSS monolith is also an ideal starting material for the preparation of HILIC or strong anionic exchange (SAX) stationary phases by modification. The modification of PEI–POSS monoliths with iodomethane or bromoacetic acid via the nucleophilic substitution reaction could achieve the retention mechanisms of SAX or zwitterionic HILIC, respectively.

Histidine-modified organic-silica hybrid monolithic column for mixed-mode per aqueous and ion-exchange capillary electrochromatography.

A novel organic-silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed-mode per aqueous and ion-exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro-osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water-rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed-mode mechanism of hydrophobic and ion-exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine-modified organic-silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.

Aptamer-based organic-silica hybrid affinity monolith prepared via “thiol-ene” click reaction for extraction of thrombin

A novel strategy for preparing aptamer-based organic-silica hybrid monolithic column was developed via “thiol-ene” click chemistry. Due to the large specific surface area of the hybrid matrix and the simplicity, rapidness and high efficiency of “thiol-ene” click reaction, the average coverage density of aptamer on the organic-silica hybrid monolith reached 420pmolμL−1. Human α-thrombin can be captured on the prepared affinity monolithic column with high specificity and eluted by NaClO4 solution. N-p-tosyl-Gly-Pro-Arg p-nitroanilide acetate was used as the sensitive chromogenic substrate of thrombin. The thrombin enriched by this affinity column was detected with a detection of limit of 0.01μM by spectrophotometry. Furthermore, the extraction recovery of thrombin at 0.15μM in human serum was 91.8% with a relative standard deviation of 4.0%. These results indicated that “thiol-ene” click chemistry provided a promising technique to immobilize aptamer on organic–inorganic hybrid monolith and the easily-assembled affinity monolithic material could be used to realize highly selective recognition of trace proteins.

Profiling of cis-diol-containing nucleosides and ribosylated metabolites by boronate-affinity organic-silica hybrid monolithic capillary liquid chromatography/mass spectrometry.

RNA contains a large number of modified nucleosides. In the metabolic re-exchange of RNA, modified nucleosides cannot be recycled and are thus excreted from cells into biological fluids. Determination of endogenous modified nucleosides in biological fluids may serve as non-invasive cancers diagnostic methods. Here we prepared boronate-affinity organic-silica hybrid capillary monolithic column (BOHCMC) that exhibited excellent selectivity toward the cis-diol-containing compounds. We then used the prepared BOHCMC as the on-line solid-phase microextraction (SPME) column and developed an on-line SPME-LC-MS/MS method to comprehensively profile cis-diol-containing nucleosides and ribosylated metabolites in human urine. Forty-five cis-diol-containing nucleosides and ribosylated metabolites were successfully identified in human urine. And five ribose conjugates, for the first time, were identified existence in human urine in the current study. Furthermore, the relative quantification suggested 4 cis-diol-containing compounds (5′-deoxy-5′-methylthioadensine, N4-acetylcytidine, 1-ribosyl-N-propionylhistamine and N2,N2,7-trimethylguanosine) increased more than 1.5 folds in all the 3 types of examined cancers (lung cancer, colorectal cancer, and nasopharyngeal cancer) compared to healthy controls. The on-line SPME-LC-MS/MS method demonstrates a promising method for the comprehensive profiling of cis-diol-containing ribose conjugates in human urines, which provides an efficient strategy for the identification and discovery of biomarkers and may be used for the screening of cancers.

Preparation of polyhedral oligomeric silsesquioxane based hybrid monoliths by thiol-ene click chemistry for capillary liquid chromatography.

A facile organic-silica hybrid monolith was prepared by a thiol-ene click reaction of polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) with 1,4-bis(mercaptoacetoxy) butane (BMAB) using toluene and dodecanol as a porogenic system. The effects of the ratio of POSS-MA-BMAB and porogenic solvents and click reaction temperature on the morphology, permeability and column performance of the resulting POSS-BMAB hybrid monoliths were studied in detail. A uniform monolithic network with a high porosity was obtained. The POSS-BMAB hybrid monolith exhibited good permeability and high thermal and mechanical stability. A series of test compounds, including alkylbenzenes, polycyclic aromatic hydrocarbon, phenols and, anilines were used to evaluate the retention behaviors of the POSS-BMAB hybrid monolith in capillary liquid chromatography. The prepared POSS-BMAB hybrid monolith exhibited typical reversed-phase chromatographic behavior toward neutral solutes. The minimum plate height of this hybrid monolith was determined as 12.6 and 13.7 μm for thiourea and benzene, respectively. These results demonstrate that thiol-ene click chemistry can provide a facile and robust approach for the preparation of a POSS-based hybrid monolith.

Improved sulfoalkylbetaine‐based organic‐silica hybrid monolith for high efficient hydrophilic interaction liquid chromatography of polar compounds

A novel sulfoalkylbetaine-based zwitterionic organic-silica hybrid monolith was synthesized by using 3-dimethyl-(3-(N-methacrylamido) propyl) ammonium propane sulfonate (DMMPPS, neutral sulfoalkyl-betaine monomer). The added amount of zwitterionic monomer was significantly increased when DMMPPS was used instead of the conventionally used acidic sulfoalkyl-betaine monomer, that is, the N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine, and this led to a significantly improved hydrophilicity of the monolith. The DMMPPS-based organic-silica hybridmonolith exhibited good mechanical stability and excellent separation performance. About ∼20 mμ plate height (corresponding to column efficiency of ∼50,000 plates/m) was obtained for nucleoside at the linear velocity of 1 mm/s. The proposed monolithic column was successfully applied to separate purines/pyrimidines, nucleotides, and tryptic digest of bovine hemoglobin in a nano-HILIC mode, and the results demonstrated that such monolith has the potential for separation of a variety of hydrophilic substances.

Facile preparation of organic-silica hybrid monolith for capillary hydrophilic liquid chromatography based on “thiol-ene” click chemistry

In this work, a one-step approach to facile preparation of organic–inorganic hybrid monoliths was successfully developed. After vinyl-end organic monomers and azobisisobutyronitrile (AIBN) were mixed with hydrolyzed tetramethoxysilane (TMOS) and 3-mercaptopropyltrimethoxysilane (MPTMS), the homogeneous mixture was introduced into a fused-silica capillary for simultaneous polycondensation and “thiol-ene” click reaction to form the organic-silica hybrid monoliths. By employing this strategy, two types of organic-silica hybrid monoliths with positively charged quaternary ammonium and amide groups were prepared, respectively. The functional groups were successfully introduced onto the monoliths during the sol–gel process with “thiol-ene” click reaction, which was demonstrated by ζ-potential assessment, energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR) spectroscopy. The porous structure of the prepared monolithic columns was examined by scanning electron microscopy (SEM), nitrogen adsorption–desorption measurement, and mercury intrusion porosimetry. These results indicate the prepared organic-silica hybrid monoliths possess homogeneous column bed, large specific surface area, good mechanical stability, and excellent permeability. The prepared monolithic columns were then applied for anion-exchange/hydrophilic interaction liquid chromatography. Different types of analytes, including benzoic acids, inorganic ions, nucleosides, and nucleotides, were well separated with high column efficiency around 80,000–130,000plates/m. Taken together, we present a facile and universal strategy to prepare organic-silica hybrid monoliths with a variety of organic monomers using one-step approach.

Polyhedral oligomeric silsesquioxane (POSS)-based multifunctional organic–silica hybrid monoliths

A facile polyhedral oligomeric silsesquioxane (POSS)-based hybrid monolith with multiple mechanisms was developed by an in situ polymerization. High mechanical stability and good separation capabilities to polar and hydrophobic analytes were successfully achieved. An ideal versatile organic-silica hybrid monolith was presented for easy access to the efficient separation of various analytes.

Facile Preparation of Zwitterionic Organic-Silica Hybrid Monolithic Capillary Column with an Improved “One-Pot” Approach for Hydrophilic-Interaction Liquid Chromatography (HILIC)

A simple single-step thermal-treatment "one-pot" approach for the preparation of organic-silica hybrid capillary monolithic columns is described. In this improved method, the cross-linker vinyltrimethoxysilane (VTMS) was replaced by 3-methacryloxypropyltrimethoxysilane (γ-MAPS), which is more active in polymerization reactions, and only one thermal treatment step was required in the preparation of hybrid monoliths. Two zwitterionic organic-silica monolithic columns were successfully synthesized by using [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (MSA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) as the organic monomers. The effects of the tetramethoxysilane (TMOS)/γ-MAPS molar ratio, content of monomer, composition of porogenic solvent, and reaction temperature on the morphologies of the hybrid monoliths were investigated. The MSA-silica and MPC-silica hybrid monolithic columns exhibited good permeability and good mechanical stability. The monolithic columns were used for the separation of polar compounds by capillary hydrophilic-interaction chromatography (cHILIC). A typical HILIC retention mechanism was observed at higher organic solvent contents (>50% ACN). The MSA monoliths were further investigated in the separation of various neutral, basic, and acidic analytes, as well as small peptides, by capillary liquid chromatography (cLC), and high efficiency and satisfactory reproducibility were achieved. In addition, the analysis of a tryptic digest of bovine serum albumin (BSA) by cLC tandem mass spectrometry (cLC-MS/MS) with an MSA monolith further demonstrated its potential in the separation of biological samples.