Folded-sheet Mesoporous Material Research Articles

Introduction of a Small Amount of Chromium to Enhance the Catalytic Performance of SBA-15 for the Oxidative Dehydrogenation of Isobutane to Isobutene

Various solid oxide catalysts are active for the oxidative dehydrogenation of propane, but achieve yields of less than 2% when these were used for the oxidative dehydrogenation of isobutane to isobutene. An improved isobutene yield of 8% was obtained in the oxidative dehydrogenation of isobutane by using a folded-sheet mesoporous material (FSM-16) and mesoporous molecular sieve (MCM-41), with or without chromium via impregnation or template-ion exchange methods. Further activity enhancement, however, could not be attained. In the present study, chromium cations were introduced into the framework of SBA-15 using a direct synthesis method by mixing chromium nitrate with tetraethylorthosilicate in an aqueous solution with an initial pH of 1.5 and subsequent hydrothermal treatment. Loading the resultant catalyst, SBA-15, with a small amount of chromium (1.84 wt% Cr-SBA-15) increased the isobutene yield (15.4%) at 723 K, while a previous report showed that chromium oxide supported on SBA-15 (CrOx/SBA-15) prepared via incipient wetness impregnation had a lower isobutene yield (11%) at 813 K. To explain this improvement, the catalysts were characterized using X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, and NH3 temperature-programmed desorption. Cr-SBA-15 was found to have a large specific surface area (1,610 m2/g), although the structural and acidic nature of the catalyst was similar to the general properties of other mesoporous silicas. The conversion of Cr3+ species into Cr6+ on Cr-SBA-15 with the large specific surface area could affect the improvement of the oxidative dehydrogenation of isobutane to isobutene.

Role of the Amide Carbonyl Groups in the Nitrile Hydratase Active Site for Nitrile Coordination Using Co(III) Complex with N2S3-type Ligand

Abstract The role of the amide carbonyl oxygens in the nitrile hydratase (NHase) active site for the nitrile coordination to the metal center was studied using a distorted square-pyramidal N2S3-type Co(III) complex at room temperature in the presence of a folded-sheet mesoporous material (FSM) or sodium cation.

Acidic Properties of Various Silica Catalysts Doped with Chromium for the Oxidative Dehydrogenation of Isobutane to Isobutene

Although previous researchers have found that FSM-16 (#16 Folded Sheet Mesoporous material) doped with chromium and related Cr-doped silica catalysts has shown great activity for the oxidative dehydrogenation of isobutane to isobutene, information on the nature of these catalysts is insufficient. For this study, three types of Cr-doped silica catalysts were prepared by applying the template ion exchange method. CrOx/FSM-16 and CrOx/SiO2 were used as references. These catalysts were used for oxidative dehydrogenation, which was then characterized via various techniques. The most active catalyst was Cr-doped silica, which did not have the hexagonal structure that is characteristic of mesoporous FSM-16. Various characterizations showed that the catalytic activity of the Cr-species, stemmed from a weak acidic nature and a redox nature that originated from the combination of silicate and a Cr cation, as opposed to the hexagonal structure and strong acidic nature of FSM-16.

Properties and reactivity of Zr-incorporated folded sheet mesoporous material for alkylation of anisole using tert-butylalcohol

Zr-incorporated Folded Sheet Mesoporous material (FSM-16) with different Si/Zr ratios = 90, 60, 10 have been synthesized by intercalating kanemite using cetyltrimethylammonium bromide (CTMABr) as the intercalating agent and zirconium sulphate precursors as the zirconium source. The resulting samples were characterized by means of inductively coupled plasma (ICP) technique, XRD, BET, TEM, FT-IR, UV–Vis and a temperature–programmed–desorption (TPD) of pyridine. The effect of the Si/Zr molar ratio on the textural properties of Zr-FSM-16 was investigated. The results reveal that the Zr-FSM-16 was successfully synthesized. The catalytic performance was examined in the vapor phase tert-butylation of anisole with tert-butanol at the temperatures between 423 and 523 K under atmospheric pressure. The results indicate that Zr-FSM-16 (10) was found to be more active than its relatives.The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). Maximum conversion of anisole is observed at 473 K and decreased after that with increasing temperature. The influence of molar ratio, influence of temperature, weight hourly space velocity (WHSV) and time on stream on the selectivity of products was investigated and the results are discussed.

Nitrile Hydration by Co(III) Complex with Oxygenated S Atoms Inserted into Mesoporous Silica

Three octahedral Co(III) complexes with N2S2 coordination donors at the equatorial plane and two molecules of tert-butylisocyanide at axial sites were prepared to investigate the hydration of acetonitrile, propionitrile, benzonitrile, and acrylonitrile. The complexes are different in the oxidation state of the coordinated sulfurs; two thiolates (–S; 1), two sulfenates (–SO; 2), and two sulfinates (–SO2; 3). The hydration of the nitriles to their corresponding amides was observed only in the reaction system including 2, indicating that the sulfenate group is essential for the generation of the hydration activity in the series. In order to avoid the deactivation of catalyst 2 by decomposition, it was inserted into the mesopores in the folded sheet mesoporous material (FSM). Indeed, the thermal stability of 2 increased and the reaction turnover number somewhat improved, but the catalyst eluted out from the pores because the electrostatic interaction between silanol groups and polar groups of 2 weakened in an aqueous solution.

Detection of hetero-proteins–mesoporous silica assembly by BRET

The assembly of a hetero-protein (Renilla reniformis luciferase (Rluc) and a green fluorescence protein (sGFP)) encapsulated in folded-sheet mesoporous material with 7.1 nm pore diameter (FSM7.1), which was used for studying protein-protein interactions in pores of mesoporous silica, has been confirmed by the detection of bioluminescence resonance energy transfers (BRET).

Molecular states of prednisolone dispersed in folded sheet mesoporous silica (FSM-16)

Modes of molecular interaction between prednisolone and mesoporous materials have been investigated by the technique of solid-state NMR. Folded sheet mesoporous material (FSM-16) was used as host material and prednisolone was used as guest molecule. A suspension of FSM-16 in prednisolone dichloromethane solution was evaporated to prepare the evaporated samples. 13C NMR spectroscopy was used as well as powder X-ray diffractometry and differential scanning calorimetry. Crystalline behavior of prednisolone disappeared in the evaporated samples, indicating the monomolecular dispersion of prednisolone in FSM-16 matrices. NMR peak shifts and broadening could be attributed to the molecular interaction between the A ring of prednisolone and FSM-16. Thermal properties of prednisolone were investigated after heat treatment of the evaporated samples. The results indicated that the thermal stability of the dispersion made from FSM-16 of large pore size was superior to that from FSM-16 of small pore size. Hydrocortisone was used to compare the dispersion state with prednisolone. It was suggested that the double bond at the C-1 and C-2 positions of prednisolone might play an important role in the process of adsorption of prednisolone to FSM-16.

Catalase encapsulated in mesoporous silica and its performance

Catalase was confined in a nanospace of about 7 nm in diameter in mesoporous silica (FSM; folded-sheet mesoporous material), forming a catalase-FSM conjugate. That the enzyme was encapsulated in the pores of mesoporous materials was proven by the direct visualization technique. The catalase-FSM showed not only an activity similar to that of the native catalase in the decomposition of H 2O 2 but also much higher stability: specifically, the catalase immobilized in FSM still retained its original activity after being applied 50 times to the decomposition, whereas the native lost its activity after 20 times recycling. Furthermore, the catalase-FSM showed catalase activity even in an organic media in which the native catalase had almost no catalytic activity.

The Ensemble of Hetero-Proteins in Inorganic Nanochannels

The assembly and proper alignment of two heterofluorescent proteins (sGFP and DsRed) in the mesoporous channels of ethanol-treated FSM6.2 (a folded-sheet mesoporous material with a pore diameter of 6.2 nm) was confirmed using a fluorescence resonance energy transfer (FRET) technique. The sGFP-DsRed-FSM6.2 conjugate showed a large decrease in the emission of donor (sGFP) fluorescence, indicating that the conjugate functions as an energy transfer system through the combination of the two heteroproteins, due to the successful encapsulation of the sGFP-DsRed pairs in the mesopores. Fluorescence spectral analysis demonstrated that the proteins were highly dispersed and homogeneously encapsulated in the mesopores of FSM6.2, even at high concentration, although they spontaneously aggregated and showed a red shift in solution at the concentration corresponding to that in the conjugate. Furthermore, an increase in the amount of sGFP and DsRed adsorbed to the pores of FSM6.2 led to a decrease in the distance between these proteins, resulting in enhancement of FRET efficiency.

Encapsulation of Hemoglobin in Mesoporous Silica (FSM)—Enhanced Thermal Stability and Resistance to Denaturants

Hemoblogin (Hb), which is a typical oligomeric protein, was introduced into the pores of mesoporous silica (FSM: folded-sheet mesoporous material) that had a diameter of 7.5 nm. Soret CD spectra of Hb-FSM-7.5 conjugates showed a peak that was identical to that of free Hb. This suggests that Hb retained its highly ordered structure in the mesoporous silica. In addition, the UV-visible absorption spectrum showed that Hb had an increased resistance to heat denaturation in the silica. Even after heat treatment at 85 degrees C, Hb-FSM-7.5 retained its ligand-binding activity. The stability of Hb-FSM-7.5 was examined further by measuring its peroxidase-like activity. Encapsulation of Hb resulted in the retention of activity in the presence of high NaCl or Gdn-HCl levels. This suggests that encapsulation prevented dissociation and denaturing. Thus, it seems that the mesopores created a favorable environment for the oligomeric protein to perform its function, even under harsh conditions.

Effective immobilization of subunit protein in mesoporous silica modified with ethanol

Ethoxylated FSM-type mesoporous silica (folded-sheet mesoporous material) with a pore diameter of 6.2 nm (FSM6.2) remarkably enhances rigidly of the structure in aqueous solutions. The esterified material could be used successfully as an adsorbent to accommodate subunit protein, methemoglobin (Fe(3+)). Furthermore, methemoglobin (Fe(3+)) in the pores of ethoxy-FSM is maintained a peroxidase activity similar to the native, indicating methemoglobin retains its fore subunit structure in the pores of FSM6.2.

Phytol‐modified heme in mesoporous silica: Conjugates as models of hemoproteins

A ferriprotoporphyrin, hemin (Fe(3+)), modified with 3,7,11,15-tetramethyl-2-hexadecen-1-ol, phytol, was adsorbed in nano-spaces of about 4 nm in diameter in mesoporous silica (FSM; folded-sheet mesoporous material) forming a phytol-modified hemin (Fe(3+))-FSM nano-conjugate. The properties and the structure of the conjugate were studied by UV-visible light absorption, IR absorption spectroscopy, and a nitrogen adsorption isotherm. Although the hemin without phytol could not be adsorbed to the mesoporous silica, modification with phytol imparted preferential adsorption properties. The conjugate was not only stable but also had a peroxidase-like activity in a 0.1% hydrogen peroxide solution, while free hemin in the solution was easily destroyed. The hemin (Fe(3+)) in the FSM was reduced to heme (Fe(2+)) by hydrazine. The phytol-modified heme (Fe(2+))-FSM conjugate formed an O(2)-heme complex with a superoxide type structure, resembling oxyhemoglobin or oxymyoglobin, which has not been previously observed for free heme in solution. The addition of carbon monoxide or nitrogen monoxide to the phytol-modified heme (Fe(2+))-FSM conjugate caused the formation of CO- or NO-heme complex in the nano-spaces of the FSM. These properties are attributed not only to the Fe-complex but also to the cooperative functions of the heme with mesoporous silica, resembling properties of a natural heme-protein conjugate; hemoglobin or peroxidase. These results are an elegant example of biomimetic nano-technology.

Encapsulation of Myoglobin with a Mesoporous Silicate Results in New Capabilities

A metmyoglobin (Fe3+), an oxidized form of myoglobin (Fe2+), was confined in nanospaces of about 4 nm in diameter in mesoporous silica (FSM; folded-sheet mesoporous material), forming a metmyoglobin (Fe3+)-FSM nanoconjugate. The spectral characteristics of metmyoglobin (Fe3+)- and myoglobin (Fe2+)-FSM show an absorption curve quite similar to that of native metmyoglobin, indicating that myoglobin retains its higher-order structure in the pores of FSM. The metmyoglobin (Fe3+)-FSM conjugate had not only a peroxidase-like activity in the presence of hydrogen peroxide (a hydrogen acceptor) and 2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfomic acid (ABTS) or guaiacol (a hydrogen donor) but also an advanced molecular recognition ability enabling it to distinguish between ABTS and guaiacol. Furthermore, the metmyoglobin (Fe3+)-FSM showed the peroxidase-like activity even in an organic media using benzoyl peroxide as the hydrogen acceptor and leucocrystal violet as the hydrogen donor. The simple immobilization of metmyoglobin (Fe3+) into FSM results in enhanced catalytic activity in organic media compared to that of native metmyoglobin (Fe3+).

Rapid adsorption and entrapment of benzoic acid molecules onto mesoporous silica (FSM-16)

Changes in the molecular state of benzoic acid (BA) in the presence of folded sheet mesoporous material (FSM-16), which has uniformly sized cylindrical mesopores and a large surface area, were assessed with several analyses. When BA was blended with FSM-16 for 5 min (BA content=30%), the X-ray diffraction peaks of BA crystals disappeared, suggesting an amorphous state. Fluorescence analysis of the mixture showed a new fluorescence emission peak for BA at 386 nm after mixing with FSM-16. Fluorescence lifetime analysis of the BA component in the mixture at 386 nm showed a longer lifetime in comparison with that of BA crystals. The solid-state 13C CP/MAS and PST/MAS NMR spectra of the mixture with FSM-16 showed a significantly different spectral pattern from the mixture with nonporous glass, whose NMR spectra were identical to those of BA crystals. These results indicate that BA molecules disperse quickly into the hexagonal channels of FSM-16 by a simple blending procedure and adsorbed BA molecules had clearly different physicochemical properties to BA crystals.

Nanoscale Organization of Chlorophyll a in Mesoporous Silica: Efficient Energy Transfer and Stabilized Charge Separation as in Natural Photosynthesis

Chlorophyll a molecules were adsorbed to mesoporous silica (FSM: folded-sheet mesoporous material) to form a chlorophyll−FSM conjugate capable of nanometer-scale interaction between chlorophyll a molecules as seen in a living plant leaf. The chlorophyll a molecules introduced into nanopores of FSM-22 (with a pore diameter of 4 nm) exhibited a red shift in the absorption peak and showed efficient excitation energy transfer from the shorter to the longer wavelength forms as characterized by the fast transient phase of 38 ps detected in the decay-associated spectrum (DAS) analysis of the fluorescence decay. Illumination of the chlorophyll−FSM-22 conjugate with visible light generated a stable chlorophyll a cation radical in the electron spin resonance (ESR) measurement, although the illumination of free chlorophyll a in solution produced almost no cation signal. The physiological function of the chlorophyll−FSM conjugate intercalated with ruthenium oxide (RuO2) was explored as chlorophyll−FSM exhibited the photoinduced ability to catalyze the reduction of DCIP (an electron carrier). The mesoporous silica−chlorophyll conjugate in an appropriate system thus produced a solar energy conversion system enabling fast energy transfer and stable charge separation, presumably by producing the appropriate interaction of pigments as occurs in living photosynthetic apparatus.

Photostabilized chlorophyll a in mesoporous silica: adsorption properties and photoreduction activity of chlorophyll a.

Chlorophyll a was adsorbed to mesoporous silica (FSM, folded-sheet mesoporous material) to form a chlorophyll-FSM conjugate, in which a nanometer-scale interaction between chlorophyll a molecules resembles a living plant leaf. The mesopores of FSM acted as nanoscale spaces not only for an interaction between chlorophyll molecules and the silica support but also for a nanoscale interaction between the absorbed chlorophyll molecules. These interactions contribute to photostability. An increase in the amount of chlorophyll adsorbed to the pores of FSM leads to an enhancement of the photostability accompanied by a shift in the absorbance maximum to a longer wavelength. The physiological function of the chlorophyll-FSM conjugate was explored as chlorophyll-FSM exhibited the photoinduced ability to catalyze the reduction of methyl viologen (an electron carrier). The evolution of hydrogen gas was observed for 14 h without deterioration when an aqueous suspension containing chlorophyll-FSM, methyl viologen, 2-mercaptoethanol (an electron donor), and platinum was illuminated with visible light.

Further stabilization of earthworm serine protease by chemical modification and immobilization.

Earthworm serine protease is more stable and is less affected by organic solvents and detergent than other proteases. However, it is inactivated, probably by autolysis, at 60 degrees C or above under alkaline conditions. Further stabilization was managed by chemical modification of the enzyme with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and phenylglyoxal to protect the activity from the autolytic inactivation. Stabilization was possible also under acidic conditions, in which the stability of the enzyme was rather low, by immobilization with folded sheet mesoporous material. Thus, further stabilization of the enzyme has been achieved by chemical modification or immobilization.

Adsorption Selectivity of FSM-16 for Several Organic Compounds

A folded-sheet mesoporous material (FSM-16) was prepared, and its adsorption selectivity for several organic compounds (p-nitrophenol, toluene, n-heptane, benzene, cyclohexane, and o-dichlorobenzene) was studied. The adsorbed amounts of these compounds were measured by batch operation in liquid phase. The p-nitrophenol in aqueous solution was hardly adsorbed into FSM-16, but toluene (in n-heptane solvent) and benzene (in n-heptane solvent or cyclohexane solvent) were adsorbed into FSM-16. The adsorption capacity of these preferentially adsorbed components into FSM-16 was higher than that into commercial adsorbents (13X zeolite and silica gel) because of the higher pore volume of FSM-16. The results obtained by the column method showed that FSM-16 column was useful for separating organic compounds.

New Pulp Biobleaching System Involving Manganese Peroxidase Immobilized in a Silica Support with Controlled Pore Sizes

Attempts have been made to use manganese peroxidase (MnP) for chlorine-free pulp biobleaching, but they have not been commercially viable because of the enzyme's low stability. We developed a new pulp biobleaching method involving mesoporous material-immobilized manganese peroxidase from Phanerochaete chrysosporium. MnP immobilized in FSM-16, a folded-sheet mesoporous material whose pore size is nearly the same as the diameter of the enzyme, had the highest thermal stability and tolerance to H(2)O(2). MnP immobilized in FSM-16 retained more than 80% of its initial activity even after 10 days of continuous reaction. We constructed a thermally discontinuous two-stage reactor system, in which the enzyme (39 degrees C) and pulp-bleaching (70 degrees C) reactions were performed separately. When the treatment of pulp with MnP by means of the two-stage reactor system and alkaline extraction was repeated seven times, the brightness of the pulp increased to about 88% within 7 h after completion of the last treatment.