Article pubs.acs.org/cm
Ordered Mesoporous Alumina with Ultra-Large Pores as an Efficient Absorbent for Selective Bioenrichment Jing Wei,†,‡ Yuan Ren,† Wei Luo,§ Zhenkun Sun,† Xiaowei Cheng,† Yuhui Li,† Yonghui Deng,*,†,⊥ Ahmed A. Elzatahry,¶ Daifallah Al-Dahyan,# and Dongyuan Zhao*,† †
Department of Chemistry, State Key Laboratory of Molecular Engineering of Polymers, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, and iChEM, Fudan University, Shanghai 200433, P. R. China ‡ The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, P. R. China § College of Materials Science and Engineering, Donghua University, Shanghai 201620, P. R. China ⊥ State Key Lab of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, P. R. China ¶ Materials Science and Technology Program, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha 2713, Qatar # Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia S Supporting Information *
ABSTRACT: Alumina has recently turned out to be effective in enrichment of biomacrolecules like phosphopeptides due to its good affinity to phosphor groups. Ordered mesoporous alumina (OMA) materials with high surface areas, regular porous structures, and large pore size are an ideal absorbent for the enrichment of phosphopeptides. Herein, a ligand-assisted solvent evaporation induced coassembly route is developed to synthesize OMA materials with an ultralarge pore size (16.0−18.9 nm) using a highmolecular-weight poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a soft template, aluminum acetylacetonate as a precursor, and tetrahydrofuran as a solvent. The obtained ordered mesoporous alumina shows high surface area (114−197 m2/g), large pore volume (0.16−0.34 cm3/g), and high thermal stability (up to 900 °C). The OMA materials show crystalline γ-Al2O3 frameworks with crystal size of ∼11 nm after calcination at 900 °C in air. Because of their high surface area, ultralarge pore size, and rich Lewis acid sites, the obtained OMA materials are demonstrated to be an excellent bioabsorbent in enriching phosphopeptides selectively from protein digestions with ultralow concentrations (2 × 10−9 M), even from more complex samples from human serum.
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INTRODUCTION Protein phosphorylation is one of the most important and ubiquitous post-translational modifications, and one-third of the proteins expressed in mammalian cells are phosphorylated at serine, threonine, and tyrosine residues.1,2 Mass spectrometry, especially matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), is an important technology for the detection and characterization of protein phosphorylation and phosphopeptides.3−6 However, the signals of phosphopeptides are often suppressed by nonphosphorylated-peptide residues coexisting in the protein digest due to their low abundance in biosamples. The specific enrichment of phosphoproteins, especially those with the low abundance, has been a challenging work in proteomics applications.7,8 The immobilized metal-ion affinity chromatography (IMAC) and metal oxide affinity chromatography (MOAC) methods have been substantially developed as a reliable approach to purify and concentrate the phosphopeptides in the protein digest.9−14 The MOAC method is more promising for the © XXXX American Chemical Society
enrichment of phosphopeptides than IMAC because such metal oxides rely on specific and reversible chemisorption of phosphate groups on their amphoteric surface and have less nonspecific binding.15,16 Various metal oxides have been demonstrated to be able to enrich phosphopeptides based on Lewis acid−base interactions.16−28 Among these metal oxides, alumina has recently been demonstrated to be an efficient sorbent in the enrichment of phosphopeptides due to its good affinity to phosphor groups and excellent selectivity.21,22 The alumina materials were used as an absorbent to fish out phosphopeptides from complicated biosamples after coating (usually aggregated nanoparticles) on various substrates, for example, magnetic particles, and their enrichment capacity still needs to be improved due to the small surface area and low density of adsorption sites. Received: November 26, 2016 Revised: February 11, 2017
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DOI: 10.1021/acs.chemmater.6b05032 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials
Figure 1. Schematic synthesis process of the ordered mesoporous alumina (OMA) materials. Step 1: ligand-assistant solvent evaporation induced coassembly process to form PEO-b-PS/inorganic sol composite micelles with ordered mesostructure using PEO-b-PS as a template, and Al(acac)3 as a precursor. Step 2: the ordered mesostructure of PEO-b-PS/aluminum hydroxides is fixed by the further condensation of inorganic sol after aging at 100 °C. Step 3: the ordered mesostructure of carbon/Al2O3 composites obtained after carbonization in N2. Step 4, OMA materials obtained after calcination in air to remove the protective carbon.
of ordered mesoporous materials with large pore size and various compositions such as silica,42−47 carbon,48−54 and metal oxides.55−57 However, large-pore OMA (pore size >10 nm) has not been reported to date. Herein, we demonstrate a ligand-assisted solvent evaporation induced coassembly route to conveniently synthesize highly OMA materials with an ultralarge pore size using a highmolecular-weight PEO-b-PS as the soft template, aluminum acetylacetonate (abbreviated as Al(acac)3) as a precursor, and tetrahydrofuran (THF) as a solvent. An effective carbon supporting crystallization strategy was employed to convert the as-made mesostructured composites into ordered mesoporous carbon-alumina through pyrolysis treatment in N2 at high temperature, followed by calcination in air to remove the carbon support. The obtained OMA shows an ultralarge pore size (16.0−18.9 nm), high Brunauer−Emmett−Teller (BET) surface area (114−197 m2/g), large pore volume (0.16−0.34 cm3/g), and high thermal stability (up to 900 °C). The OMA synthesized at 900 °C shows well-crystalline structure with uniform γ-Al2O3 nanoparticles (∼11 nm) distributed in the frameworks. Because of their high surface area, ultralarge pore size, and rich Lewis acid sites (0.168 mmol/g), the obtained OMA materials are demonstrated to be an excellent bioabsorbent for selective enrichment of phosphopeptides from phosphopeptide solution with ultralow concentrations (2 × 10−9 M), even from more complex samples of human serum.
Ordered mesoporous alumina (OMA) materials with wellarranged pores and high surface areas have been utilized in many applications such as catalysis and adsorption.29−37 Because of the large pore size and high pore volume, OMA materials could show fast adsorption rate and high loading capacity for binding phosphopeptides. However, there is no work to investigate the application of OMA materials in enrichment of phosphopeptides to date. This is possible due to the difficulty to synthesize OMA materials with a high surface area and large pore size. Usually, ordered mesoporous alumina materials are difficult to be synthesized by using the commercially available surfactants and amphiphilic block copolymers as templates. By carefully optimizing the synthetic conditions (such as humidity, solvent evaporation rate, and acidity), mesoporous alumina has been synthesized by the solvent evaporation induced assembly method.29−37 However, most of the synthesized mesoporous alumina materials show poorly mesostructural regularity and a low degree of crystallization due to the limitation of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-b-PPO-b-PEO) block copolymers as well as the poorly controllable sol−gel process of alumina source. Moreover, these mesoporous alumina materials usually show small pore size (
