Channels Of MCM-41 Research Articles

Biotinylated MCM-41 channels as a sensing element in planar bilayer lipid membranes

Mesoporous silica MCM-41 and biotinylated MCM-41 (biotin-MCM-41) channels were incorporated into planar bilayer lipid membranes (BLMs). The BLMs containing MCM-41 and biotin-MCM-41 exhibited a marked shift in the chord current, often accompanied by rectangular, channel-like currents, which were ascribable to ion translocation through the pores of MCM-41. The penetration of lipid molecules into the pores of biotin-MCM-41 was indicated by fluorometric measurements with rhodamine B-tagged lipid. The ion transport, through MCM-41 and biotin-MCM-41 channels, was symmetrical with respect to the applied voltage. When biotinylated MCM-41 was incorporated into BLMs, the integrated current decreased with an increase in the concentration of avidin ranging from 2.9 pM to 1.5 nM for the micro BLMs formed by the tip–dip method and from 1.5 to 15 nM for the BLM formed by the folding method. Bovine serum albumin (BSA) did not induce any changes in the integrated currents, showing the selective recognition of avidin by the biotin sites of MCM-41 channels in the BLM. The present results show the potential of biotin-MCM-41 channels as a sensing element that exhibit the on/off gating of ion transport for ion-channel sensors.

A new and easy method for anchoring manganese salen on MCM-41

This work reports a new method to covalently attach manganese salophen complex onto MCM-41, using a diisocyanate as a binder. The prepared catalyst was tested on the liquid phase limonene oxidation reaction. Diluted t-Butyl hydroperoxide was used as oxygen supplier. Limonene oxide, carveol and carvone are formed, but the main product obtained was a polymer. The preservation of the MCM-41 channel system was checked by X-ray diffraction and nitrogen adsorption analysis. The use of the same catalyst sample in four consecutive experiments, without loss of activity, is a confirmation of the success of the anchoring process.

New theoretical insights into epoxidation of alkenes by immobilized Mn-salen complexes in mesopores: Effects of substrate, linker and confinement

The origin of enantioselectivity in the epoxidation reaction of cis- and trans-methylstyrene, catalyzed by anchored oxo-Mn V-salen into MCM-41 channels, is investigated by applying density functional calculations in combination with molecular mechanics methodologies. The calculations provide new insights on the importance of electronic and steric effects of the salen ligand, substrate, immobilizing linker and MCM-41 confinement. Based on the assumption that the formation of a radical intermediate is the key step along the reaction path, the calculations are performed on a catalytic surface with triplet spin-state, comprising no Mn-salen spin-crossing. We rationalize the effect of immobilization and show how that correlates with the linker and substrate choices. We show that although a trans-substrate has a higher level of asymmetric induction to the immobilized Mn-salen complex than that to a homogeneous catalyst, the reaction path is more in favor of the cis-substrate. The MCM-41 channel reduces the energy barriers and enhances the enantioselectivity by influencing geometrical distortions of the Mn-salen complex.

Microwave-assisted immobilization of metallophthalocyanines in mesoporous channels of MCM-41

Metallophthalocyanines have been assembled in MCM-41 channels by microwave irradiation of a mixture of ion-exchanged MCM-41, and 1,2-dicyanobenzene under solvent-free conditions in a considerably short period of time. The prepared materials have been characterized by diffuse reflectance UV-vis spectroscopy, X-ray powder diffraction XRD, differential scanning calorimetry DSC, and Brunauer-Emmett-Teller BET nitrogen adsorption desorption techniques. The X-ray diffraction and Brunauer-Emmett-Teller results showed that the textural properties of MCM-41 were preserved during microwave irradiation.

Quantitative incorporation of Pt nanoparticle by coordination of Pt precursor with APTMS-anchored SiMCM-41

The quantitative incorporation and high dispersion of platinum nanoparticles into MCM-41 has been carried out by the coordination between Pt(IV) ion and APTMS-anchored MCM-41. Before and after calcination of Pt/APTMS/MCM41 samples, the Pt content in samples was evaluated from home-made photoacoustic spectrometer (PAS). The PAS bands at 350 nm and 450 nm can be assigned to d–d transition bands of Pt complexes. By increasing the concentration of Pt solution, the PAS intensity of Pt/APTMS/MCM41 was increased proportionally up to 1.0×10−2 M, and remained constant above 1.0×10−2 M. It can be attributed to the saturation of Pt content within Pt/APTMS/MCM41. The Pt content in the saturated Pt/APTMS/MCM41 was 8.5 wt% (the theoretical value), 9.7 wt% (measured by EDX) and 9.2 wt% (measured by ESCA), respectively. This indicates that the content of Pt precursor within MCM-41 could be controlled by the concentration of Pt precursor solution. The PAS intensity of calcined Pt/APTMS/MCM41's in H2 flow was increased up to 1.0×10−2 M and remained nearly constant above 1.0×10−2 M. Therefore, we suggest that the formation of Pt complexes with APTMS-anchored MCM-41 made it possible to incorporate quantitatively Pt nanoparticles in the range of 0.5–9.2 wt% within MCM-41 channels.

Solid state fluorescence of a 3,4,9,10-perylenetetracarboxylic diimide derivative encapsulated in the pores of mesoporous silica MCM-41

This work describes the encapsulation of N, N′-bis(2-phosphonoethyl)-3,4,9,10-perylenetetracarboxylic diimide (PPDI), a water-soluble perylene dye, in the channels of mesoporous silica MCM-41. The incorporation of the dye was achieved by stirring MCM-41 with aqueous solutions of PPDI. The solid material obtained by this process exhibited a red fluorescence. Diffuse reflectance and emission spectra of the fluorescent powder suggested a highly organized arrangement with the PPDI molecules self-assembled in a 1D stack inside the channels of the mesoporous silica. The new materials described here have potential applications as nanoscale optoelectronic devices, such as conducting nanowires and fluorescent gas sensors.

Effect of Hydrophobic Modification on Sustained-Release Properties of Alachlor/MCM-41

The herbicide of alachlor was incorporated into the channels of MCM-41-type mesoporous silica (M41) by using an impregnation wetness method. Surface hydrophobic modification of the assembly of alachlor-MCM-41 (Ach/M41),via a gas-solid reaction with 1,1,1,3,3,3-hexamethyldisilazane (HMDS),gave rise to an efficient sustained-release system (Ach/TMS-M41). The resulting Ach/TMS-M41 not only retained high alachlor loading capacity but also possessed prolonged alachlor release time. The characterization results of XRD,nitrogen adsorption/desorption,FT-IR,and TG analysis showed that the M41 retained its structural integrity during the alachlor-loading process and alachlor was dispersed completely in the channels of MCM-41 with a mass ratio of alachlor [m(alachlor)/m(alachlor-MCM-41)] as high as 0.381 g·g-1 (mass fraction 27.6%). The release properties of Ach/M41 and Ach/TMS-M41 in water were investigated. 62% and 38.1% of alachlor were released from Ach/M41 and Ach/TMS-M41 after 6 days,respectively,which indicated that hydrophobic modification of MCM-41 was conducive to sustained-release of alachlor. Furthermore,the framework of the mesoporous silica protected the encapsulated alachlor against ultraviolet light irradiation.

Anchoring manganese acetylacetonate complex on MCM-41: Catalytic testing on limonene oxidation

Abstract This work reports the results of limonene oxidation in the liquid phase, over manganese acetylacetonate anchored onto MCM-41. Diluted t-butyl hydroperoxide is used as oxidant. Limonene oxide, carveol and carvone are formed, but the main product obtained is a polymer. The preservation of the MCM-41 channel system upon anchoring was checked by transmission electron microscopy (TEM), X-ray diffraction and nitrogen adsorption analysis. The complex anchoring was succeeded, since the catalyst could be used in four consecutive experiments. The maximum TOF values obtained for each run are similar and no significant metal complex leaching was observed (3% after the 4th run).

Loading and delivery of sertraline using inorganic micro and mesoporous materials

Sertraline hydrochloride (designated as sertraline from now on) is an antidepressive drug with unpleasant effects in the gastric tract. Therefore, improved means of delivery allowing for a more controlled and efficient release were looked for. Two different porous materials, montmorillonite-K10 and MCM-41, were chosen as hosts. The drug was intercalated in the interlayer spacing of the clay by cation exchange and was loaded inside the MCM-41 channels by pore volume impregnation means. Spectroscopic evidence (UV/vis, FTIR, powder X-ray diffraction (XRD) and 13C CP/MAS and 29Si CP/MAS and MAS solid-state NMR), as well as elemental analysis, complemented by DFT calculations, demonstrated the presence of sertraline in the composite materials. The release processes were monitored under in vitro conditions using a simulated body fluid. The release profile from the clay is fast, indicating that a concentration peak is reached in a short period of time, while the release profile from MCM is slower but lasts longer. These differences are discussed on the basis of different therapeutic indications for both materials.

Toward the preparation of a nanocomposite material through surface initiated controlled/“living” radical polymerization of styrene inside the channels of MCM-41 silica

A hybrid organic–inorganic material was prepared by surface initiated controlled/“living” radical polymerization (CRP) of styrene in the internal space of a MCM-41 silica. The inorganic precursor was synthesized, via sol–gel, using tetraethoxysilane and cetyltrimethylammonium bromide, in the presence of ammonia and ethanol to induce the formation of submicrometric spherical particles. After characterization by powder X-ray diffraction (XRD), transmission electron micrography (TEM), scanning electron micrography (SEM), N2 adsorption and titration of the surface silanol groups, the mesoporous silica was functionalized through a 3-step grafting process, in order to link the nitroxide initiator to the inorganic matrix (TEMPO-MCM-41). The anchorage of the TEMPO-based initiator was checked by diffuse reflectance infrared spectroscopy (DRIFT-IR). Experimental data confirmed that the styrene polymerization occurred inside the MCM-41 channels system.

Tungstophosphoric acid supported over zirconia in mesoporous channels of MCM-41 as catalyst in veratrole acetylation

Tungstophosphoric acid (TPA) over zirconia dispersed uniformly in mesoporous silica (MS) channels of MCM-41 and MCM-48 were synthesized and tested for their catalytic activity in veratrole acetylation. Catalysts with different TPA loadings (5–50 wt.%) on 22.4 wt.%ZrO 2/MCM-41 and 15 wt.%TPA on different zirconia loadings (10–70 wt.%)/MCM-41 were prepared and calcined at 1123 K. The physico-chemical characterization of the supported catalysts was done by powder X-ray diffraction (XRD), surface area measurement (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed-infrared (FT-IR) spectroscopy, UV–vis diffuse reflectance spectra, Temperature programmed desorption (TPD) of ammonia, FT-IR pyridine adsorption and 31P cross polarization-magic angle spinning (CP-MAS) NMR spectroscopy. The mesoporous silica supports play an important role in stabilizing catalytically active TPA along with tetragonal phase of zirconia. Among the catalysts, 15 wt.%TPA/22.4 wt.%ZrO 2/MCM-41 calcined at 1123 K was found to have highest acidity and at least four times more active than neat 15 wt.%TPA/ZrO 2 in veratrole acetylation to acetoveratrone by acetic anhydride. Reaction conditions were evaluated with 15 wt.%TPA/22.4 wt.%ZrO 2/MCM-41 calcined at 1123 K to get higher conversion of acetic anhydride to acetoveratrone. The reaction was found to be heterogeneously catalyzed and no contribution from homogeneous (leached) TPA into the medium under the reaction conditions.

Preparation and electrorheology of new mesoporous polypyrrole/MCM-41 suspensions

Encapsulation or self-assembly of conducting polymer within the channels of mesoporous silica is one of the ways to prepare new nanostructured materials [1]. The resulting materials may have unique nanostructures and properties controlled by host-guest interactions, as well as new potential applications, such as in nano-scale electronic, optical devices [2] and electrorheological (ER) fluids [3]. For example, stabilization of conducting polyaniline filaments with mobile charge carriers in mesoporous silica (MCM-41) represents a step toward the design of nanometer electronic devices [4]. In this area, Qiu [5] et al. found the impedance of polyaniline/SBA-15 (SBA-15 is another kind of mesoporous silica with larger pore size and thicker pore wall compared to MCM-41) composites more sensitive to humidity than that of bulk polyaniline, and Choi et al. [3] reported a composite material with conducting polyaniline in MCM-41 channels showing interesting ER properties. Of conducting polymers, polypyrrole (PPy) as a promising conducting polymer has been widely studied because of its high polarizability, superior conductivity and electrorheological properties [6, 7]. Accordingly, incorporation of PPy in the pores of mesoporous silica is worth investigating, as it can be beneficial for further exploring electronic characteristics and applications of the resultant composite. On the other hand, ER fluids as one of the most promising smart materials for potential industrial applications have received wide interest. Recently, many studies on dry-based ER fluids have been reported, for example, polyaniline/BaTiO3 [8], polypyrrole/clay [9], polyaniline/clay [10] and polyaniline/MCM-41 [11] particles have been adopted as the dispersed phase of ER fluids. In this work, a new type of anhydrous ER material based on conducting polypyrrole confined in MCM-41 channels was prepared and its ER behavior was also investigated for the first time. The preparation of mesoporous silica (MCM41) followed the method described in literature [12]. To synthesize PPy/MCM-41 nanocomposite, the calcined MCM-41 was vacuumed at 200 C for 4 h to remove air and water from the channels. Then the MCM-41 host was suspended above the pyrrole monomer in a flask under vacuum at room temperature for 24 h. The MCM-41 containing pyrrole was immersed in an aqueous solution of FeCl3 AE 6H2O with continuous stirring in an ice bath for 24 h. The PPy/MCM-41 was washed with de-ionized water and acetone, and dried at 40 C under vacuum. For ER behavior investigation, the PPy/MCM-41 particles were further dried at 120 C and dispersed in silicone oil to form 10 wt.% suspension. Schematic of the synthesis of PPy/MCM-41 nanocomposite and ER tests are shown in Fig. 1. FT-IR spectra were obtained on Nicolet Magna-550 spectrometer. N2 adsorption/desorption isotherms were measured using Micromeritics ASAP 2010 system. High resolution transmission electron micrographs (HRTEM) were taken on a JEM 2100 F electron microscope. Scanning electron microscopy (SEM) was conducted on a JEOL JSM-6360 LV electron microscope. Measurements Q. Cheng AE Y. He AE C. Li Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, 200237 Shanghai, China

Speciation of CuO in MCM-41 during oxidation of naphthalene

By extended X-ray absorption fine structural (EXAFS) spectroscopy, copper oxide clusters with a square-plane structure are found in the channels of mesoporous molecular sieve MCM-41. Bond distances of Cu–O and Cu–Cu are 1.90 and 2.80 Å, respectively. Oxidation of naphthalene at 723 K for 4 h in MCM-41 leads to structural perturbation of the clusters (e.g., Cu–O: −0.02 Å and Cu–Cu: +0.02 Å) with little change in their coordination numbers.

Extraction of Nanosize Copper Pollutants with an Ionic Liquid

Speciation and possible reaction paths of nanosize copper pollutants extracted with a RTIL (room-temperature ionic liquid ([C4mim][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate)) have been studied in the present work. Experimentally, in a very short contact time (2 min), 80-95% of nanosize CuO as well as other forms of copper (such as nanosize Cu, Cu2+, or Cu(II)(ads) (in the channels of MCM-41)) in the samples could be extracted into the RTIL. The main copper species extracted in the RTIL as observed by XANES (X-ray absorption near edge structure) were Cu(II). Existence of Cu-N bondings with coordination numbers (CNs) of 3-4 for copper extracted in the RTIL was found by EXAFS (extended X-ray absorption fine structural) spectroscopy. Interestingly, chelation of Cu(II) with 1-methylimidazole (MIm) in the RTIL during extraction was also observed by 1H NMR (nuclear magnetic resonance). At least two possible reaction paths for the rapid extraction of nanosize copper pollutants with the RTIL might occur: (1) an enhanced dissolution of nanosize CuO (to form Cu2+) and (2) formation of [Cu(MIm)4(H2O)2]2+ that acted as a carrier of copper into the RTIL matrix.

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Abstract Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH4). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.

Nanowires of iron oxides embedded in SiO2 templates

To attain the complete filling of the channels of MCM-41 with magnetite and maghemite, we have tried out an alternative method to the incipient wetness impregnation. The mesoporous material was instilled with a Fe-carrying organic salt after subjecting the matrix to a silylation treatment. Thus, a solid of 7.7 wt.% iron-loaded MCM-41 was obtained. Different subsequent thermal treatments were used to produce γ-Fe2O3 or Fe3O4. The Mossbauer and magnetic results show that after this method, the as-prepared composite displays a size-distribution of magnetic particles. It is mainly made up of fine particles that display a super paramagnetic relaxation at room temperature and get blocked at ≈2 K for the AC susceptibility time-scale measurements both for γ-Fe2O3 and Fe3O4 particles. For both samples, about 24% of larger iron-containing phases are magnetically blocked at room temperature. For the Fe3O4 particles, this fraction undergoes the Verwey transition at about 110K; in addition, there is a minor Fe(III) fraction that remains paramagnetic down to 4.2 K.

Optically functional nanocomposites with poly(oxyethylene)-based di-ureasils and mesoporous MCM-41

Di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid structure (di-ureasil) was incorporated into the hexagonal array of one-dimensional channels of mesoporous silica MCM-41. X-ray diffraction, nitrogen adsorption–desorption, Fourier transform mid-infrared spectroscopy, 29Si and 13C nuclear magnetic resonance, transmission electron microscopy and photoluminescence results demonstrate the interaction (covalent grafting and impregnation) between the di-ureasil structure and the silanol groups of the MCM-41 channels, preserving their integrity. The composites are photoluminescent displaying the intrinsic green emission of MCM-41 superposed to the blue and purplish-blue di-ureasil components. Time-resolved spectroscopy provides further support from energy transfer between the mesopourous silica and the di-ureasil matrix.

Evidence of Nanoconfinement Effects of MCM-41 on Propylene Polymerization Catalyzed by MCM-41 Supported Metallocene Catalyst in the Presence and Absence of β-Cyclodextrin

Propylene polymerization was carried out with MCM-41 supported rac-Et(Ind)2ZrCl2 catalysts, in the presence and absence of beta-cyclodextrin. The resultant PP was studied by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Through comparison of the results, it was found that the channels of MCM-41 could act as a nanoreactor of propylene polymerization and the polypropylene (PP) contained in the channels had noncrystal structure. However, the PP could grow out of the channels and form some crystals after the active sites on the surface of MCM-41 were destroyed. This showed that the channels of MCM-41 had great confinement effects on propylene polymerization.

Oxidation of cyclooctane over Mn(TMPyP) porphyrin-exchanged Al,Si-mesoporous molecular sieves of MCM-41 and SBA-15 type

Mn(TMPyP) metalloporphyrin catalysts supported on aluminated MCM-41 and SBA-15 mesoporous silicas were investigated in the liquid phase oxidation of cyclooctane with molecular oxygen (as air) without the use of sacrificial co-reductant. Cyclooctanone and cyclooctanol were the only reaction products, the first one appearing in overwhelming majority. The activity of the catalysts increased with the increasing pore size of the support, which pointed to the existence of diffusion limitations within the pore inner space. An exceptionally high selectivity to cyclooctanone observed for the MCM-41-derived catalysts, as opposed to SBA-15-based ones and to homogeneous oxidation process, is tentatively interpreted in terms of steric effect due to the suppression of the hydroperoxide intermediate formation in relatively narrow channels of MCM-41. Catalysts show good stability in the reaction conditions.

Organometallic Rhodium Complexes Encapsulated in Mesoporous Molecular Sieves

Rh(III) complexes both dimmer [Cp * RhCl]2(l-Cl)2 and monomer ([RhCp * (S)3] 2+ ) were encapsulated into MCM-41 channels. All silica MCM-41 molecular sieve and aminosililated MCM-41 matrix were used for rhodium complexes accommodation. Reactivity of Cp * rhodium complexes encapsulated in meso structure was estimated on the grounds of their susceptibility to interaction with CO molecules resulting in the formation of carbonyl complexes. Formation of Cp * Rh carbonyls was recorded by means of FTIR spectra. It was found that accommodation of Rh(III) complexes in MCM-41 molecular sieves activated the complex and led to the formation of Rh(III)Cp * carbonyls as a result of contact with CO. Contact of rhodium (III) complexes encapsulated in MCM-41 matrix with CO did not result in rhodium (III) reduction, whereas in the presence of amine groups in aminosililated MCM-41 the reduction of Rh(III) to Rh(I) occurred relatively easily and formation of Cp * Rh(CO)2 complex containing Rh(I) was noted. Encapsulated rhodium complexes showed some activity in methanol carbonylation reaction carried out under heterogeneous conditions. For the most active catalyst the amount of methyl acetate reached about 8 mol.%, however, deactivation of catalyst occurred and after 2 h on stream methyl acetate was not found in the product.