Trypsin immobilization on mesoporous silica with or without thiol functionalization

The effects of pore size, structure, and surface functionalization of mesoporous silica on the catalytic activity of the supported enzyme, trypsin, were investigated. For this purpose, SBA-15 with 1-dimensional pore arrangement and cubic Ia3d mesoporous silica with 3-dimensional pores were prepared and tested as a support. Materials with varying pore diameters in the range 5–10 nm were synthesized using a non-ionic block copolymer by controlling the synthesis temperature. Thiol-group was introduced to the porous materials via siloxypropane tethering either by post synthesis grafting or by direct synthesis. These materials were characterized using XRD, SEM, TEM, N₂ adsorption, and elemental analysis. Trypsin-supported on the solids prepared was active and stable for hydrolysis of N-α-benzoyl-DL-arginine-4-nitroanilide (BAPNA). Without applying thiol-functionalization, cubic Ia3d mesoporous silica with ca. 5.4 nm average pore diameter was found to be superior to SBA-15 for trypsin immobilization and showed a better catalytic performance. However, enzyme immobilized on the 5% thiol-functionalized SBA-15 prepared by directly synthesis was found to be the most promising and was also found recyclable.     

介孔分子筛SBA-15表面改性对脂肪酶固定化的强化作用

引言 脂肪酶可以催化酯水解或醇解、酯合成、酯交换、多肽合成及高聚物合成等多种有机反应,已被广泛应用于食品、精细化工及制药工业中[1].作为重要的生物催化剂,脂肪酶应用的有效性和经济性很大程度上取决于酶的固定化.     

Synthesis of hexagonal and cubic mesoporous silica using power plant bottom ash

An alkali fusion method was adopted to extract silicate species from coal bottom ash in a power plant and the supernatant solution was used for the synthesis of MCM-41, SBA-15, and SBA-16 mesoporous silica materials. The minor impurities present in the bottom ash were not found to be detrimental to the successful formation of mesoporous silica phases. Additional silica from sodium metasilicate was introduced to improve the textural properties for SBA-15 and SBA-16. According to SEM analyses, particle morphology of the samples gradually approaches those prepared using pure chemical as the amount of external silica source increases. XRD analyses confirmed well-ordered mesostructures in all of these silica materials. N₂ adsorption–desorption isotherms of MCM-41 prepared using bottom ash showed a type IV isotherm with a region of steep increase due to capillary condensation, whilst SBA-15 and SBA-16 showed type IV isotherm with H1 and H2 hysteresis loops, respectively. ²⁷Al MAS NMR analysis of MCM-41 synthesized from the supernatant solution reveals that the extracted Al species from bottom ash were tetrahedrally incorporated in the framework. TEM clearly showed the uniform pore structure of the materials prepared using the industrial waste.     

Performance of organic–inorganic hybrid catalysts based on Ia-3d mesoporous silica

The cubic Ia-3d mesoporous silica with ordered large pores was synthesized from tetraethoxysilane (TEOS) and a small amount of 3-mercaptopropyltorimetoxysilane (MPTS) as the silica sources under the acidic conditions by using triblock copolymer P123 (EO₂₀PO₇₀EO₂₀) as a surfactant. After removal of the surfactant by the solvent extraction method, mercaptopropyl (MP) group (–CH₂CH₂CH₂SH) remained inside pores with a slight loss. The pore diameter of this mesoporous silica was about 5 nm. After converting the MP group to sulfopropyl (SP) group (–CH₂CH₂CH₂SO₃H) by the oxidation with H₂O₂, the amount of organic group was significantly reduced. However, it was possible to introduce additional organic groups by post-synthetic grafting. It was also possible to graft both MP and SP groups at the same time, and cooperative effect was observed in the acid-catalyzed condensation reaction of phenol with acetone. More organics were immobilized to the multi-dimensional cubic Ia-3d structure than the one-dimensional 2d-hexagonal structure. The catalyst having both SH and SO₃H groups showed much higher selectivity for bisphenol A than Amberlyst 15 and Nafion SAC-13, which could be explained by the SH group-assisted mechanism.     

介孔硅SBA-15对水溶液中咪唑基离子液体的吸附性能研究

本文研究了介孔硅SBA-15对水中咪唑基离子液体[Bmim]Cl和[Bmim]OH的吸附行为。合成的SBA-15具有有序的二维六方介孔结构。研究发现升高温度会使SBA-15对离子液体的吸附量降低,吸附过程是放热过程。25℃下将吸附等温数据进行Langmuir和Freundlich方程线性拟合,相比之下Langmuir模型更适合用来描述SBA-15对两种离子液的吸附行为,SBA-15对[Bmim]Cl和[Bmim]OH最大吸附量分别为336.7和467.3mg·g-1。     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

The influence of carbon source on the wall structure of ordered mesoporous carbons

A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N₂ adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors, but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization. The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups and limited graphitizable properties, and in turn medium but almost constant capacitances.     

含磺酸基的介孔分子筛SO3H-SBA-15催化合成油酸丁酯

采用水热法直接合成了含磺酸基的介孔分子筛SO3H-SBA-15.以油酸与正丁醇为原料催化合成油酸丁酯,进行了不同催化剂的对比实验以及反应条件包括催化剂用量、反应温度、反应时间、酸醇摩尔比的考察.得到最佳反应条件为：催化剂质量分数为10%,反应温度120 ℃,反应时间3 h,酸醇摩尔比1∶2.     

辣根过氧化物酶在三种孔材料上的在线固定化研究

利用已建立的顺序注射紫外可见分析系统,以硅基介孔材料MCM-41、SBA-15和炭材料XC-72作为载体,研究和比较了辣根过氧化物酶(HRP)在3种无机孔材料上的在线吸附行为。结果表明,HRP在XC-72上的负载量和结合稳定性高于MCM-41和SBA-15,且以XC-72为载体制备的固定化HRP具有较高的活性和良好的操作稳定性。     

含磺酸基介孔分子筛SBA-15-SO3H催化合成油酸乙酯

采用水热法直接合成含磺酸基的介孔分子筛SBA-15-SO₃H。以油酸和乙醇为原料催化合成油酸乙酯，进行了不同催化剂的对比实验以及催化剂组成、反应温度、酸醇物质的量比和催化剂用量等反应条件的考察。得到最佳反应条件：温度130 ℃，n(酸)∶n(醇)=1∶2.5，反应时间4 h，催化剂质量分数为10%。     

Palladium with spindle-like nitrogen ligand supported on mesoporous silica SBA-15: A tailored catalyst for homocoupling of alkynes and Suzuki coupling

A mesoporous silica SBA-15-supported palladium with spindle-like nitrogen donor groups, 1,4-diaza-bicyclo[2.2.2]octane, has been successfully prepared and applied for homocoupling of terminal alkynes. The catalyst exhibited very high activity for terminal alkynes carrying various substitution groups, yields ranging from 70% to 94%, with a significant advantage that air acted as the oxidant. It also showed good reusability, could be easily recovered through filtration and washing, and reused at least five times with virtually no evident loss of catalytic performance. Furthermore, it was also proved to be an effective and air-stable heterogeneous catalyst for Suzuki coupling of aryl halides (X = I, Br) with arylboronic acids. The catalyst was systematically characterized by elemental analysis, X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, nitrogen physical adsorption, Brunauer-Emmett-Teller method and X-ray powder diffraction. The analyses indicated that the mesoporous structure of the materials was retained during the immobilization process.     

Flash induction calcination: A powerful tool for total template removal and fine tuning of the hydrophobic/hydrophilic balance in SBA-15 type silica mesoporous materials

A new rapid calcination method has been used to completely remove the organic template from SBA-15 ordered mesoporous silica, and to preserve a high number of silanol in these materials. This calcination method provided by an induction furnace was found to considerably reduce the calcination time and therefore the energy consumption associated. Moreover, adjustment of both calcination temperature and duration allowed tuning the hydrophobic/hydrophilic balance of the mesoporous SBA-15 silica materials. For comparison, short and long time conventional muffle furnace calcination was performed. The induction calcination was also successfully applied to different type of mesoporous silica materials such as SBA-16 and MCM-41.     

介孔材料SBA-15固定化脂肪酶的研究进展

介孔材料由于其孔道分布有序且孔径均匀等优点而在固定化酶催化领域引起人们的广泛关注.本文综述了新型介孔材料SBA-15对脂肪酶固定化的研究进展.总结了SBA-15的孔径大小、形貌及等电点等因素对脂肪酶固定化的影响.归纳了SBA-15上三种不同固定化方法的优缺点,并介绍了SBA-15固定化脂肪酶在手性拆分、酯水解、酯合成及转醇化反应等领域的应用.最后提出SBA-15固定化脂肪酶在发展过程中存在的问题以及今后的发展趋势.     

Physicochemical properties of poly(ethylene oxide)-based composite polymer electrolytes with a silane-modified mesoporous silica SBA-15

Mesoporous silica SBA-15 was surface-modified by γ-glycidoxypropyltrimethoxy silane (GPTMS), and novel poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPE) using the silane-modified SBA-15 (SBA-15-GPTMS) as filler were prepared and characterized. The results of the low-angle X-ray diffraction (XRD) patterns and Fourier-transform infrared (FT-IR) spectroscopy indicated that GPTMS has been successfully attached to the surface of SBA-15 with a high degree of mesoscopic hexagonal pore structure. The incorporation of SBA-15-GPTMS in the PEO-LiClO₄ matrix effectively reduced the PEO crystallinity and obviously improved the conductivity and electrochemical stability of the CPEs. The CPE with 10 wt.% SBA-15-GPTMS provided the highest conductivity among all the tested CPEs, about 2-3 orders of magnitude higher than that of the PEO-LiClO₄ matrix below the melting temperature of PEO. The reasons that the CPEs using SBA-15-GPTMS as filler showed higher conductivity than that with SBA-15 were discussed.     

Syntheses and application of silica monolith with bimodal meso/macroscopic pore structure

A route to synthesize porous materials with a bimodal macro/mesoscopic pore system has been investigated in this work. Polystyrene with sub-micrometer size was used as a template in the synthesis. The resulting mesoporous silica wall replicated inversely the morphology of polystyrene template and had highly ordered three-dimensional arrays of macro pores. Large and moldable meso/macro porous silica monoliths could be obtained in centimeter scale by using monodispersed polystyrene beads and PEO-PPO-PEO/SBA-15 sol solutions. These bimodal structured porous silicates have been used as supports for asymmetric kinetic resolution of racemic epoxides to synthesize optically pure epoxide.     

Alginate/protamine/silica hybrid capsules with ultrathin membranes for laccase immobilization

A novel type of core–shell capsules with ultrathin alginate/protamine/silica (APSi) hybrid membranes are successfully fabricated through a coextrusion minifluidic approach and a biosilicification method for immobilization of laccase. The ultrathin membranes were beneficial to the mass transfer across the capsule membranes, and the silica layer on the outer surface was efficient to inhibit the swelling of the capsule membranes. The immobilizing yield was considered to be 100% because all the enzyme molecules were encapsulated inside the capsules through the proposed method, and the laccase activity immobilized in APSi capsules was 61.8 mmol·g^–1·min^–1. The thermal, pH and storage stabilities of the immobilized laccase in APSi capsules were determined in comparison with free laccase. The stability of encapsulated laccase was significantly improved, which was as high as 67% after 20 days. The residual relative activity of encapsulated laccase remained 45% after 10 cycles. © 2012 American Institute of Chemical Engineers AIChE J, 59: 380–389, 2013     

One-dimensional crosslinked enzyme aggregates in SBA-15: Superior catalytic behavior to conventional enzyme immobilization

α-Chymotrypsin (CT) and lipase (LP) were immobilized in SBA-15 mesoporous silica by crosslinking adsorbed enzymes. This simple approach resulted in one-dimensional crosslinked enzyme aggregates (CLEAs) in the linear pore channels of SBA-15, which was very effective in preventing the enzyme leaching and consequently improving the enzyme stability. Both CLEAs of CT and LP showed negligible activity decrease under harsh shaking condition for one week while the conventional approaches including adsorption and covalent attachment resulted in more than 50–90% enzyme inactivation under the same condition. This effective stabilization results from the bent pore structure of SBA-15 with a high aspect ratio, which prevents the leaching of one-dimensional CLEAs and thereby achieves the higher enzyme loading capacity. Along with the higher specific activity than that of adsorbed enzymes, this CLEA approach is much simpler than that of covalent attachment by obviating the tedious processes for silica functionalization and enzyme attachment.     

Immobilization of Co(III) using tethered cyclam ligand on SBA-15 mesoporous silica for aerial oxidation of ethylbenzene

Cyclam type macrocyclic ligand was tethered onto mesoporous silica surface through N-functionalization of the cyclam. The mesoporous silica was synthesized directly with in-built chloropropyl functional group by applying microwave synthesis approach and the cyclam ligand was tethered via the surface substitution reaction of the chloro group. The tethered cyclam ligand was proven to facilely accommodate Co(III) cation into its cavity. This Co(III)cyclam-functionalized mesoporous silica showed good catalytic activity in the aerial oxidation of ethylbenzene to give acetophenone as the major product, which exceeded 60%. The presence of pyridine ligand which bounded to the axial sites of the tethered Co(III)cyclam complex enhanced the activity of the catalyst with sustaining the selectivity.