Titanium-containing magnetic mesoporous silica spheres: effective enrichment of peptides and simultaneous separation of nonphosphopeptides and phosphopeptides

Protein phosphorylation is a common posttranslational modification, and involved in many cellular processes. Like endogenous peptides, endogenous phosphopeptides contain many biomarkers of preclinical screening and disease diagnosis. In this work, titanium-containing magnetic mesoporous silica spheres were synthesized and applied for effective enrichment of peptides from both tryptic digests of standard proteins and human serum. Besides, the enriched peptides can be further separated into nonphosphopeptides and phosphopeptides by a simple elution. First, titanium-containing magnetic mesoporous silica spheres were synthesized by a sol-gel method and found to have high surface area, narrow pore size distribution, and useful magnetic responsivity. Then, as the prepared material was used for selective capturing of phosphopeptides, it demonstrated to have higher selectivity than commercial titanium dioxide. Moreover, via combination of size-exclusion mechanism, hydrophobic interaction, and affinity chromatography, titanium-containing magnetic mesoporous silica spheres were successfully applied to simultaneously extract and separate nonphosphopeptides and phosphopeptides from standard protein digestion and human serum.     

Boronic acid functionalized Fe3O4 magnetic microspheres for the specific enrichment of glycoproteins

Glycoproteins are useful biomarkers and therapeutic targets for a number of diseases, including infections and cancer. However, identification and isolation of low‐abundant glycoproteins remains a significant challenge that limits their application. Thus, methods of specific and selective glycoprotein enrichment are required. In this study, novel phenylboronic acid functionalized magnetic microspheres were successfully synthesized. Fe₃O₄ microspheres were synthesized by using a hydrothermal method and were coated with tetraethyl orthosilicate using an ultrasonic method to form a core‐shell structure. Compared to the conventional mechanical stirring for 12 h, the ultrasonic method saved about 7 h in processing time, and the home‐made magnetic microspheres had better dispersibility and homogeneity. Subsequently, the magnetic microspheres were modified by addition of an amino group and a carboxyl group, in sequence. Finally, 3‐aminophenylboronic acid, as the functional monomer, was linked to the magnetic microspheres for capturing glycoprotein/glycopeptides. The results of this study indicate that phenylboronic acid functionalized magnetic microspheres show excellent adsorption performance toward glycoprotein/glycopeptides. The maximum absorbing capacity of the microspheres for fetuin was 108 mg/g, and the enrichment efficiency reached 89.7%, indicating their potential to separate and enrich glycoproteins from the complex biological samples.     

Aminopyrene functionalized mesoporous silica for the selective determination of resorcinol

Aminopyrene was convalently anchored onto the surface of mesoporous MCM-41 silica by post-grafting. This organic-inorganic hybrid has been applied as sensing material to phenols determination. Experimental results reveal that the functionalized material presents good sensitivity and selectivity towards resorcinol and can be used for resorcinol determination in water at pH 6.0. The fluorescence intensity of aminopyrene functionalized mesoporous silica decreases proportionally to the logarithm of resorcinol concentration in water. The linear range for resorcinol detection lies in 4.79-163 μM with a detection limit of 2.86 μM (S/N = 3).     

Hydrazide-functionalized magnetic microspheres for the selective enrichment of digested tryptophan-containing peptides in serum

The extreme complexity of protein samples is becoming a great challenge for proteomic analysis, especially for those having large dynamic range of protein abundance. To solve this problem, and to overcome the limitation of the current proteomic technologies, a new method using hydrazide-functionalized magnetic microspheres was established in this study. With this method, tryptophan (Trp)-containing peptides can be selectively and sensitively enriched from complex and low-volume samples. Furthermore, combined with 1D-LC-MS/MS analysis, the strategy was successfully applied to the proteomic study of mouse serum. The proportion of Trp-containing peptides was increased from 19.4% to 80.2% through enrichment, and the complexity of the sample was reduced more than two times. An additional 113 Trp-containing peptides and 48 novel proteins were detected compared to the conventional method. This enrichment method provides a means for identifying more proteins as potential biomarkers in serum and other complex samples.     

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a “one-pot” strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.     

Preparation of a multi‐hollow magnetic molecularly imprinted polymer for the selective enrichment of indolebutyric acid

A simple strategy was developed for the preparation of multi‐hollow magnetic molecularly imprinted polymers by incorporating 3‐indolebutyric acid and ferroferric oxide nanoparticles simultaneously into a poly(styrene‐co‐methacrylic acid) copolymer matrix. The as prepared absorbents were characterized using scanning electron microscopy, Fourier‐transform infrared spectroscopy and mercury porosimetry. The adsorption isotherms of indolebutyric acid revealed that there are two types of affinity binding sites in the absorbents. The apparent maximum binding capacity and dissociation constant were 17.88 mg/g and 158.7 μg/mL for high‐affinity binding sites and 9.310 mg/g and 35.04 μg/mL for low‐affinity binding sites, respectively. The results testified that multi‐hollow magnetic molecularly imprinted polymers possessed excellent recognition capacity and fast kinetic binding behavior to the objective molecules due to the high specific surface area as large as 511.3 m²/g. Recoveries of 75.5–86.8% were obtained for the indolebutyric acid spiked at three concentration levels in blank and pear samples.     

Preparation of doxycycline‐imprinted magnetic microspheres by inverse‐emulsion suspension polymerization for magnetic dispersion extraction of tetracyclines from milk samples

A magnetic dispersion extraction method was developed based on a molecularly imprinted magnetic microsphere (MIMM) for the selective clean‐up and enrichment of tetracycline antibiotics from milk samples. The MIMMs were prepared by inverse‐emulsion suspension polymerization, using doxycycline, trimethylolpropane trimethacrylate, acrylamide, methacrylic acid, and surface‐modified Fe₃O₄ as a template molecule, crosslinker, functional monomer, and magnetic component, respectively. Synthesis and extraction conditions were optimized for obtaining excellent affinity and high selectivity. The magnetism, covering amount, and selectivity of the magnetic microspheres were characterized by a vibrating sample magnetometer, thermogravimetric analysis, and a competitive recognition experiment. The MIMMs were applied to separate tetracycline antibiotics from milk samples by magnetic dispersion extraction, and an enrichment factor of 9.28 and a good sample clean‐up were obtained. The average recoveries of four tetracycline antibiotics were obtained in the range of 74.5–93.8% with a precision of 1.2–5.2%. The LODs and LOQs of the proposed method were in the range of 7.4–19.4 and 24.7–64.7 μg/kg, respectively. The results indicated that magnetic dispersion extraction using MIMMs is a powerful tool for food‐sample pretreatment with high selectivity and a simplified procedure.     

Titania coated magnetic mesoporous hollow silica microspheres: fabrication and application to selective enrichment of phosphopeptides

Titania coated magnetic hollow mesoporous silica spheres with high surface area were created, which can be used in efficient and rapid capture of phosphopeptides from peptide mixtures.     

Development of mesoporous TiO2 microspheres with high specific surface area for selective enrichment of phosphopeptides by mass spectrometric analysis

In this study, mesoporous TiO₂ microspheres were synthesized by simple hydrothermal reaction, and successfully developed for phosphopeptides enrichment from both standard protein digestion and real biological sample such as rat brain tissue extract. The mesoporous TiO₂ microspheres (the diameter size of about 1.0 μm) obtained by simple hydrothermal method were found to have a specific surface area of 84.98 m²/g, which is much larger than smooth TiO₂ microspheres with same size. The surface area of mesoporous TiO₂ microspheres is almost two times of commercial TiO₂ nanoparticle (a diameter of 90 nm). Using standard proteins digestion and real biological samples, the superior selectivity and capacity of mesoporous TiO₂ microspheres for the enrichment of phosphorylated peptides than that of commercial TiO₂ nanoparticles and TiO₂ microspheres was also observed. It has been demonstrated that mesoporous TiO₂ microspheres have powerful potential for selective enrichment of phosphorylated peptides. Moreover, the preparation of the mesoporous TiO₂ microspheres obtained by the hydrothermal reaction is easy, simple and low-cost. These mesoporous TiO₂ microspheres with the ability of large scale synthesis can widely be applied for phosphorylated proteomic research.     

Preparation of porous polylactide microspheres by emulsion‐solvent evaporation based on solution induced phase separation

Porous polylactide (PLA) microspheres were fabricated by an emulsion‐solvent evaporation method based on solution induced phase separation. Scanning electron microscopy (SEM) observations confirmed the porous structure of the microspheres with good connectivity. The pore size was in the range of decade micrometers. Besides large cavities as similarly existed on non‐porous microspheres, small pores were found on surfaces of the porous microspheres. The apparent density of the porous microspheres was much smaller than that of non‐porous microspheres. Fabrication conditions such as stirring rate, good solvent/non‐solvent ratio, PLA concentration and dispersant (polyvinyl alcohol, PVA) concentration had an important influence on both the particle size and size distribution and the pore size within the microspheres. A larger pore size was achieved at a slower stirring rate, lower good solvent/non‐solvent ratio or lower PLA concentration due to longer coalescence time. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface‐imprinted magnetic nanoparticles for the selective enrichment and fast separation of fluoroquinolones in human serum

Surface enrofloxacin‐imprinted magnetic nanoparticles were prepared for the selective recognition and fast separation of fluoroquinolones in human serum by surface‐initiated reversible addition fragmentation chain transfer polymerization. The surface morphology and imprinted behavior were investigated and optimized. The living/controlled nature of reversible addition‐fragmentation chain transfer polymerization reaction allowed the successful construction of well‐defined imprinted polymer layer outside the Fe₃O₄ core. Such molecularly imprinted polymers exhibited superparamagnetic properties and specific recognition toward fluoroquinolones. Combined with reversed‐phase high‐performance liquid chromatography, the prepared molecularly imprinted polymers were used for the selective enrichment and analysis of fluoroquinolones in human serum samples. The recoveries of four fluoroquinolones were 86.8–95.3% with relative standard deviations of 2.0–6.8% (n  = 3). Such magnetic molecularly imprinted polymers have great prospects in the separation and enrichment of trace analysts in complex biological samples.     

Preparation of magnetic core mesoporous shell microspheres with C18-modified interior pore-walls for fast extraction and analysis of phthalates in water samples

In this study, core-shell magnetic mesoporous microspheres with C18-functionalized interior pore-walls were synthesized through coating Fe(3)O(4) microspheres with a mesoporous inorganic-organic hybrid layer with a n-octadecyltriethoxysilane (C18TES) and tetraethyl orthosilicate (TEOS) as the silica source and cetyltrimethylammonia bromide (CTAB) as a template. The obtained C18-functionalized Fe(3)O(4)@mSiO(2) microspheres possess numerous C18 groups anchored in the interior pore-walls, large surface area (274.7 m(2)/g, high magnetization (40.8 emu/g) and superparamagnetism, uniform mesopores (4.1 nm), which makes them ideal absorbents for simple, fast, and efficient extraction and enrichment of hydrophobic organic compounds in water samples. Several kinds of phthalates were used as the model hydrophobic organic compounds to systematically evaluate the performance of the C18-functionalized Fe(3)O(4)@mSiO(2) microspheres in extracting hydrophobic molecules by using a gas chromatography-mass spectrometry. Various parameters, including eluting solvent, the amounts of absorbents, extraction time and elution time were optimized. Hydrophobic extraction was performed in the interior pore of magnetic mesoporous microspheres, and the materials had the anti-interference ability to macromolecular proteins, which was also investigated in the work. Under the optimized conditions, C18-functionalized Fe(3)O(4)@mSiO(2) microspheres were successfully used to analyze the real water samples. The results indicated that this novel method was fast, convenient and efficient for the target compounds and could avoid being interfered by macromolecules.     

Preparation of magnetic molecularly imprinted polymers for the rapid and selective separation and enrichment of perfluorooctane sulfonate

As a persistent organic pollutant, perfluorooctane sulfonate has drawn a great worldwide attention. In this contribution, a novel material of magnetic molecularly imprinted polymers, based on perfluorooctane sulfonate, as a template, molecule was prepared. The magnetic molecularly imprinted polymers were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and vibrating sample magnetometry. The adsorption isotherm was measured, and adsorption kinetic tests were conducted. The adsorbents possess high recognition ability (2.460 mg/g) and short adsorption equilibration time (60 min). Besides, they show good specificity and good reusability with the adsorption capacities of adsorbent toward perfluorooctane sulfonate decreasing less than 3% after five adsorption–desorption cycles. The magnetic molecularly imprinted polymers were used successfully in the separation and enrichment of perfluorooctane sulfonate in real water sample and exhibited good prospects in environmental treatment and monitoring.     

Succinic acid functionalized magnetic mesoporous silica for the magnetic assisted separation of uranium from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - The magnetite embedded mesoporous silica was prepared and functionalized with succinic acid, (abbreviated as Fe-MCM-SUC) for targeted adsorption...     

Preparation of magnetic chitosan microspheres and its applications in wastewater treatment

The methods of preparation of magnetic chitosan microspheres have been introduced. In addition, their applications in the wastewater treatment, based on different kinds of wastewater, have been reviewed, and their mechanisms have been discussed. Supported by the Key Natural Science Foundation of China (Grant No. 50633030)     

Application of ionic‐liquid‐supported magnetic dispersive solid‐phase microextraction for the determination of acaricides in fruit juice samples

In this study, ionic liquid (IL) supported magnetic dispersive solid‐phase microextraction was developed and a systematic investigation was conducted on imidazolium ILs for their extraction performance. This nano‐based pretreatment procedure was then applied for the determination of acaricides in fruit juice samples for the first time. A feature of this technique is that the commonly laborious chemical modification of magnetic nanoparticles (MNPs) was skillfully circumvented. Because of the combination of ILs, dispersive liquid–liquid microextraction, and dispersive MNP solid‐phase microextraction, the extraction efficiency can be significantly improved using commercial MNPs. Parameters of the extraction method were investigated by one‐factor‐at‐a‐time approach. The optimal experimental conditions were as follows: emulsification for 2 min by sonication with the addition of 50 μL [C₆MIM][NTf₂] in the dispersive liquid–liquid microextraction step and vortexing for 90 s after adding 40 mg spherical barium ferrite nanoparticles (20 nm). The desorption time was 2 min. Good linearity (0.5–500 ng/mL) and detection limits within the range of 0.05–0.53 ng/mL were achieved. The application of the proposed method was demonstrated by the analysis of real fruit juice samples, in which recoveries between 85.1 and 99.6% were obtained.     

Preparation and separation properties of oxalylurea‐bridged silica membranes

Two new bridged alkoxysilanes, bis(triethoxysilylalkyl)‐N,N′‐oxalylureas (alkyl = methyl or n‐propyl), bearing a highly rigid and polar oxalylurea unit in the bridges, were employed as precursors of bridged silica membranes. The gas and water separation performance of the membranes prepared from the precursors using the sol–gel process was investigated. Interestingly, the membrane properties depended on the alkyl chain length. The membrane containing methylene units (alkyl = methyl) was porous and rather hydrophilic but the other with longer propylene units (alkyl = n‐propyl) was non‐porous and more hydrophobic. High H₂/SF₆ gas permeance ratios of 3100 and 1700, and NaCl rejections of 89 and 85% for 2000 ppm aqueous NaCl were obtained using the membranes containing methyl and n‐propyl, respectively. The membrane with alkyl = methyl also showed a high CO₂/N₂ permeance ratio of 20.6 at 50°C. These results indicate the potential applications of the membranes as gas and water separation materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of catecholamines in urine using aminophenylboronic acid functionalized magnetic nanoparticles extraction followed by high‐performance liquid chromatography and electrochemical detection

A new method was developed for the simultaneous determination of three catecholamines in urine using aminophenylboronic acid functionalized magnetic nanoparticles extraction followed by high‐performance liquid chromatography with electrochemical detection. Novel aminophenylboronic acid functionalized magnetic nanoparticles were prepared by multi‐step covalent modification, and characterized by transmission electron microscopy, Fourier‐transformed infrared spectroscopy, X‐ray diffraction, and vibrating sample magnetometry. With the help of the high affinity between the boronate and cis‐diol group, the particles were used for the highly selective separation and enrichment of three major catecholamines, norepinephrine, epinephrine, and dopamine. Effects of the pH of the feed solution, the extraction time, the composition of the buffer solution, the amount of the magnetic particles, the elution conditions, and the recycling of aminophenylboronic acid functionalized magnetic nanoparticles were explored. Under the optimized conditions, 13–17‐fold enrichment factors were obtained. The linear ranges were 0.01–2.0 μg/mL for the studied analytes. The limits of detection and quantification were in the range of 2.0–7.9 and 6.7–26.3 ng/mL, respectively. The relative recoveries were in the range of 92–108%, with intraday and interday relative standard deviations lower than 6.8%. This method was successfully applied to analysis of catecholamines in real urine.     

Preparation of polypropylene microspheres for selective laser sintering via thermal‐induced phase separation: Roles of liquid–liquid phase separation and crystallization

Although selective laser sintering (SLS) has been widely applied in many fields, more research work is needed to develop proper polymer microspheres for SLS. Thermal‐induced phase separation (TIPS) is a facile way but rarely reported to prepare the polymer microspheres. The roles of liquid–liquid phase separation (LLPS) and crystallization in the TIPS process are not clear. In this study, proper polypropylene (PP) microspheres for SLS are successfully prepared via TIPS with xylene. The diameters and morphologies of these PP microspheres can be regulated easily by changing the PP concentration and the quench temperature. The large undercooling drives the solution into the metastable LLPS region and produces PP microspheres with smooth surfaces. The PP crystallization occurs both on the LLPS interface and inside the polymer‐rich phase when the solution is quenched to a temperature near the binodal line, and the tiny bent lamellae are formed on the microsphere surface. At higher temperature only PP crystallization occurs, which results in the formation of PP particles consisting of packed lamellae. The PP microspheres prepared here are suitable for SLS and promote the development of SLS potentially. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 320–329     

Simple enrichment of thiol‐containing biomolecules by using zinc(II)–cyclen‐functionalized magnetic beads

A simple and efficient method based on magnetic‐bead technology has been developed for the enrichment of thiol‐containing biomolecules, such as l ‐glutathione and cysteine‐containing peptides. The thiol‐binding site on the bead is a mononuclear complex of zinc(II) with 1,4,7,10‐tetraazacyclododecane (cyclen); this is linked to a hydrophilic cross‐linked agarose coating on a particle that has a magnetic core. All steps for the thiol‐affinity separation are conducted in aqueous buffers with 0.10 mL of the magnetic beads in a 1.5 mL microtube. The entire separation protocol for thiol‐containing compounds, from addition to elution, requires less than one hour per sample, provided the buffers and the zinc(II)–cyclen‐functionalized magnetic beads have been prepared in advance. The thiol‐affinity magnetic beads are reusable at least 15 times without a decrease in their thiol‐binding ability, and they are stable for six months at room temperature.