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Silica Monoliths (silica + monolith)
Selected AbstractsDevelopment of a silica monolith microbioreactor entrapping highly activated lipase and an experiment toward integration with chromatographic separation of chiral estersJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007Koei Kawakami Abstract Microbioreactors are effective for high-throughput production of expensive products from small amounts of substrates. Lipases are versatile enzymes for chiral syntheses, and are highly activated when immobilized in alkyl-substituted silicates by the sol,gel method. For practical application of sol,gel immobilized lipases to a flow system, a microbioreactor loaded with a macroporous silica monolith is well suited, because it can be easily integrated with a chromatographic separator for optical resolution. We attempted to develop a microbioreactor containing a silica monolith-immobilized lipase. A nonshrinkable silica monolith was first formed from a 4:1 mixture of methyltrimethoxysilane (MTMS) and tetramethoxysilane (TMOS). It was then coated with silica precipitates entrapping lipase, derived from a 4:1 mixture of n -butyltrimethoxysilane (BTMS) and TMOS. As a result, monolith treated with the BTMS-based silicate entrapping lipase exhibited approximately ten times higher activity than nontreated monolith-immobilized lipase derived from the MTMS-based silicate, in transesterification between glycidol and vinyl n -butyrate in isooctane. A commercially available chiral column was connected in series to the monolith microbioreactor, and a pulse of substrate solution was supplied at the inlet of the reactor. Successful resolution of the racemic ester produced was achieved in the chromatographic column. [source] Fe3+ immobilized metal affinity chromatography with silica monolithic capillary column for phosphoproteome analysisPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 3 2007Shun Feng Abstract Immobilized metal affinity chromatography (IMAC) is a commonly used technique for phosphoproteome analysis due to its high affinity for adsorption of phosphopeptides. Miniaturization of IMAC column is essential for the analysis of a small amount of sample. Nanoscale IMAC column was prepared by chemical modification of silica monolith with iminodiacetic acid (IDA) followed by the immobilization of Fe3+ ion inside the capillary. It was demonstrated that Fe3+ -IDA silica monolithic IMAC capillary column could specifically capture the phosphopeptides from tryptic digest of ,-casein with analysis by MALDI-TOF MS. The silica monolithic IMAC capillary column was manually coupled with nanoflow RPLC/nanospray ESI mass spectrometer (,RPLC,nanoESI MS) for phosphoproteome analysis. The system was validated by analysis of standard phosphoproteins and then it was applied to the analysis of protein phosphorylation in mouse liver lysate. Besides MS/MS spectra, MS/MS/MS spectra were also collected for neutral loss peak. After database search and manual validation with conservative criteria, 29 singly phosphorylated peptides were identified by analyzing a tryptic digest of only 12,,g mouse liver lysate. The results demonstrated that the silica monolithic IMAC capillary column coupled with ,RPLC-nanoESI MS was very suitable for the phosphoproteome analysis of minute sample. [source] Capillary electrochromatography with monolithic silica column:,I.ELECTROPHORESIS, Issue 3 2003Preparation of silica monoliths having surface-bound octadecyl moieties, applications to the separation of neutral, charged species, their chromatographic characterization Abstract Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 ,m ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (>,2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160,000 plates/m, a value comparable to that obtained on columns packed with 3 ,m C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio. [source] Silica-Based, Organically Modified Host Material for Waveguide Structuring by Two-Photon-Induced PhotopolymerizationADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Stefan Krivec Abstract The three-dimensional fabrication of optical waveguides has gained increasing interest in recent years to establish interconnections between electrical components on a very small scale where copper circuits encounter severe limitations. In this work the application of optically clear, organically modified porous silica monoliths and thin films as a host material for polymeric waveguides to be inscribed into the solid host structure by two-photon-induced photopolymerization is investigated. Porosity is generated using a lyotropic liquid crystalline surfactant/solvent system as a template for the solid silica material obtained by a sol,gel transition of a liquid precursor. In order to reduce the brittleness of the purely inorganic material, organic,inorganic co-precursor molecules that contain poly(ethylene glycol) chains are synthesized and added to the mixture, which successfully suppresses macroscopic cracking and leads to flexible thin films. The structure of the thus-obtained porous organic,inorganic hybrid material is investigated by atomic force microscopy. It is shown that the modified material is suitable for infiltration with photocurable monomers and functional polymeric waveguides can be inscribed by selective two-photon-induced photopolymerization. [source] Surface interaction of well-defined, concentrated poly(2-hydroxyethyl methacrylate) brushes with proteinsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2007Chiaki Yoshikawa Abstract The interaction of concentrated polymer brushes with proteins was chromatographically investigated. By the use of surface-initiated atom transfer radical polymerization, a low-polydispersity poly(2-hydroxyethyl methacrylate) (PHEMA) was densely grafted onto the inner surfaces of silica monoliths with mesopores of about 50 and 80 nm in mean size. The graft density reached 0.4,0.5 chains/nm2. The 80-nm-mesopore monolithic column with the concentrated PHEMA brush was characterized through the elution of low-polydispersity pullulans with different molecular weights, clearly showing two modes of size exclusion, that is, one by the mesopores and the other by the brush phase. The latter mode gave a sharp separation with a critical molecular weight (size-exclusion limit) of about 1000. This molecular size of pullulan was comparable to the distance between the nearest-neighbor graft points. The elution behaviors of five proteins of different sizes (bovine serum thyroglobulin, bovine serum immunoglobulin G, bovine serum albumin, horse heart myoglobin, and bovine serum aprotinin) were studied with this PHEMA-grafted column. The smallest protein, aprotinin, with a pullulan-reduced molecular weight slightly larger than the critical value of 1000, was eluted much behind the corresponding pullulan, and this indicated that it barely got into the brush layer, suffering from a strong affinity interaction within the brush. On the other hand, the other four larger proteins were eluted at the same elution volumes as the equivalent pullulans, and this meant that they were perfectly excluded from the brush layer and separated only in the size-exclusion mode by the mesopores without an affinity interaction with the brush surface. This excellent inertness of the concentrated brush in the interaction with the large proteins should afford the system long-term stability against biofouling. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4795,4803, 2007 [source] Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6 2006Anne Galarneau Abstract Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (,1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the micrometer scale. We developed a synthesis strategy to control the particle morphology of MTS using the concept of pseudomorphic transformation. Pseudomorphism was recognized in the mineral world to gain a mineral that presents a morphology not related to its crystallographic symmetry group. Pseudomorphic transformations have been applied to amorphous spherical silica particles usually used in chromatography as stationary phases to produce MTS with the same morphology, using alkaline solution to dissolve progressively and locally silica and reprecipitate it around surfactant micelles into ordered MTS structures. Spherical beads of MTS with hexagonal and cubic symmetries have been synthesized and successfully used in HPLC in fast separation processes. MTS with a highly connected structure (cubic symmetry), uniform pores with a diameter larger than 6 nm in the form of particles of 5 ,m could compete with monolithic silica columns. Monolithic columns are receiving strong interest and represent a milestone in the area of fast separation. Their synthesis is a sol-gel process based on phase separation between silica and water, which is assisted by the presence of polymers. The control of the synthesis of monolithic silica has been systematically explored. Because of unresolved yet cladding problems to evaluate the resulting macromonoliths in HPLC, micromonoliths were synthesized into fused-silica capillaries and evaluated by nano-LC and CEC. Only CEC allows to gain high column efficiencies in fast separation processes. Capillary silica monolithic columns represent attractive alternatives for miniaturization processes (lab-on-a chip) using CEC. [source] A computational study of the porosity effects in silica monolithic columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10-11 2004Piotr Gzil Abstract We report on a theoretical study of the influence of the through-pore porosity on the main chromatographic performance parameters (reduced theoretical plate height, flow resistance, and separation impedance) of silica monoliths. To investigate this problem devoid of any structural uncertainties, computer-generated structural mimics of the pore geometry of silica monolithic columns have been studied. The band broadening in these synthetic monoliths was determined using a commercial Computational Fluid Dynamics (CFD) software package. Three widely differing external porosities (, = 0.38, , = 0.60, and , = 0.86) are considered and are compared on the basis of an identical intra-skeleton diffusivity (D s = 5×10,10m2/s), internal porosity (,int = 0.5), and for the same phase retention factor (k ´ = 1.25). Since the data are obtained for perfectly ordered structures, the calculated plate heights and separation impedances constitute the ultimate performance ever to be expected from a monolithic column. It is found that, if silica monoliths could be made perfectly homogeneous, domain size-based reduced plate heights as small as h min , 0.8 (roughly independent of the porosity) and separation impedances as small as Emin , 130 (, = 0.60) and Emin , 40 (, = 0.86) should be achievable with pure water as the working fluid. The data also show that, although the domain size is a much better reduction basis than the skeleton size, the former is still not capable of bringing the van Deemter curves of different porosity columns into perfect agreement in the C term dominated velocity range. It is found that, in this range, large porosity monoliths can be expected to yield smaller domain size-based reduced plate heights than small porosity monoliths. [source] | |||||||||||||