Keiichi Inukai

Effective encapsulation of laccase in an aluminium silicate nanotube hydrogel

Aluminium silicate nanotubes (ASNT), with a length to width ratio of four, were synthesized from aluminium chloride and sodium silicate, and the ASNT hydrogel was easily prepared by adjusting the pH to 7. The hydrogel nanotube concentration was 1.5 wt%. Laccase, a type of oxidase, was encapsulated during ASNT hydrogel formation. This encapsulation method will have fewer negative effects on the relatively unstable enzyme because of the milder conditions used, which are different from sol–gel silica formation by acidic catalysis using strong acids such as hydrochloric acid. The obtained hydrogels were fully characterized by various methods such as field-emission scanning electron microscopy and Fourier transform infrared spectroscopy. The ASNT-hydrogel encapsulated enzyme worked well; notably, laccase–ASNT hydrogels prepared from the shortest nanotubes exhibited a higher activity than the free laccase in solution because of an improvement in the substrate affinity of the encapsulated enzyme. Tryptophan fluorescence spectroscopy indicated that the highly ordered structure of laccase was not altered once bound to the nanotubes within the hydrogel. Notably, after nine repeated reactions, laccase encapsulated in the ASNT hydrogel retained its activity. The cycle performance of the encapsulated enzyme indicates that no enzyme was released from the ASNT hydrogel. In addition, the laccase–ASNT hydrogel was easily used to prepare transparent thin films on glass cover slips, while still maintaining the enzyme activity. Another oxidase, myoglobin, was also encapsulated in the same type of ASNT hydrogel. Although free myoglobin in solution demonstrated oxidation activity, the activity of the bound protein was remarkably decreased due to changes in its tertiary structure when inside the ASNT hydrogel.

Oxidation of aromatic hydrocarbons with H2O2 catalyzed by a nano-scale tubular aluminosilicate, Fe-containing imogolite

Imogolite is a nano-scale tubular clay mineral with the typical chemical composition (OH)3Al2O3SiOH. The Fe-containing imogolite was synthesized from FeCl3, AlCl3 and Na4SiO4 aqueous solutions. The fibrous morphology observed by AFM in this sample is similar to that of synthetic imogolite. In the catalytic oxidation of aromatic hydrocarbon compounds such as benzene, phenol and chrolobenzene, the aromatic ring was oxidized. When the side-chain is a hydrocarbon group such as methyl, both benzene ring and the side-chain group were oxidized. It was found that the side-chain group was preferentially oxidized.

Aluminum silicate nanotube coating of siloxane-poly(lactic acid)-vaterite composite fibermats for bone regeneration

In our earlier work, a flexible fibermat consisting of a biodegradable composite with soluble silicate species, which has been reported to enhance bone formation, was prepared successfully using poly(L-lactic acid) and siloxane-containing calcium carbonate particles by electrospinning. The fibermat showed enhanced bone formation in an in vivo test. In the present work, to improve the hydrophilicity of skeletal fibers in a fibermat, they were coated with nanotubular aluminum silicate crystals, which have a hydrophilic surface that has excellent affinity to body fluids and a high surface area advantageous for pronounced protein adsorption. The nanotubes were coated easily on the fiber surface using an electrophoretic method. In a conventional contact angle test, a drop of water rapidly penetrated into the nanotube-coated fibermat. The culture test using murine osteoblast-like cells (MC3T3-E1) showed that the cell attachment to the nanotube-coated fibermat at an early stage after seeding was enhanced in comparison with that to the noncoated one. This approach may provide a new method of improving the surface of polymer-based biomaterials.

Synthesis and Applications of Imogolite Nanotubes

Imogolite is a naturally occurring nanotube aluminum silicate. It is classified as a clay mineral, with tube dimensions of about 2 nm in outside diameter, 1 nm in inside diameter, and lengths ranging from tens of nanometers to several micrometers. Imogolite is remarkable not only for its nanoscale fibrous microstructure and its high surface area but also in its ability to adsorb water. So it can be expected to find a wide range of applications. In this chapter, synthesis method for imogolite and applications for anti-dewing materials and heat exchange material in adsorption-type heat pump systems are described.

Preparation and rheological characterization of imogolite hydrogels

Imogolite, one of the aluminium silicates, has a nanotube structure and has been known to form gel under alkaline condition. Imogolite nanotubes were synthesized in an acidic solution with various tube lengths by controlling the aging time from 1 d to 14 d. The length of the nanotubes grew from 100 nm to several µm as the aging time. Pure imogolite hydrogels were prepared by applying a salting-outmethod and centrifugation fromits dispersed solutions with various tube lengths and solution pH. Imogolite hydrogel can be classified as the physically cross-linked one; the structure of the gel network is considered to be the entanglements and hydrogen bonding among nanotubes. The theoretical water contents of the prepared hydrogels were calculated as ∼99.7% in average. Gelation percentage significantly increased as the length of imogolite nanotubes. Whereas hydrogel prepared from 4 d aging sample showed the highest storage modulus of ∼970 Pa, it was found that the hydrogel could be prepared in the pH range from 6 to 10. The gel strength reached the highest value of 1000 Pa when the gel was prepared from the imogolite dispersed solution of pH 8. It could be explained by the surface charge variation of the imogolite.

Aluminum Silicate Nanotube Modification of Cotton-Like Siloxane-Poly(L-lactic acid)-Vaterite Composites

In our earlier work, a cotton-like biodegradable composite, consisting of poly(L-lactic acid) with siloxane-containing vaterite, has been prepared by electrospinning. In the present work, the fibers skeleton of the cotton-like composites was modified successfully with imogolite, which is hydrophilic and biocompatible, via a dip process using ethanol diluted solution to improve the cellular initial attachment. Almost no change in the fiber morphology after the surface modification was observed. The surface-modified composite showed the similar calcium and silicate ions releasabilities, for activating the osteoblasts, as an unmodified one. Cell culture tests showed that the initial adhesion of murine osteoblast-like cells on the surface of the fibers was enhanced by surface modification.

Visible Light Responsive Titanium Dioxide Photocatalysts Prepared by Ultraviolet Irradiation

Titanium dioxide photocatalyst films were prepared by dip-coating method using titanium dioxide sol solution in order to research the H2O addition effect on the photocatalytic activities. The sol solution was prepared with titanium tetra-isopropoxide, urea and 2-methoxyethanol, then irradiated ultraviolet light and added distilled H2O. The substrates for the dip-coating were fused silica plates and as-prepared films were dried at 100 °C then annealed at 650 °C. The films prepared by these methods showed visible light absorption in wavelengths longer than 380 nm and accelerated photodegradation of methylene blue by visible light irradiation. Furthermore, the photocatalytic activities of these films were depending on the H2O additions to the sol solution.

Preferential Oxidation of CO over Pt Catalysts Supported on Mesoporous Aluminosilicates in the Presence of H2

. Preferential oxidation (PROX) of CO in the presence of H2 is an important reaction to maintain stable operation of polymer electrolyte fuel cells (PEFCs) since their anode catalyst can be poisoned by trace amount of CO. In this study, we examined PROX reactions mediated by Pt catalysts prepared using several mesoporous silica and aluminosilicate supports such as imogolite (IM), allophane (AP), silica aerogel (SAG), and an amorphous hydroxyl aluminosilicate developed in our research group (HAS). The selectivity of CO oxidation gradually decreased from 80 to 60 % with increasing temperature from 323 to 473 K for Pt/HAS catalyst whereas it increased with temperature from 10 to 40 % for Pt/IM, Pt/AP, Pt/SAG catalysts. These results indicate that Pt supported on HAS may be effective for low-temperature PROX reactions.

CHARACTERIZATION OF A GERMANIUM ANALOG OF THE TUBULAR ALUMINOSILICATE, IMOGOLITE

The imogolite composites in which Si was substituted by Ge (Ge-substituted imogolite) were prepared from a concentrated solution with dissolved GeOz and were characterized by using atomic force microscopy, IR and Raman spectroscopy. IR and Raman spectra of these materials are the same as previous results prepared from a dilute inorganic solution. Thermal transformation of Ge-substituted imogolite was investigated by using thermal analysis, A1 solid-state nuclear magnetic resonance and X-ray diffraction. Two endothermic peaks (110°C and 400°C) and an exothermic peak (906°C) were shown by differential thermal analysis. Ge-substituted imogolite changed into an amorphous phase by dehydration and transformed Al6Gez013 crystals at ca. 900°C. A12Gez07 crystals were formed as a new phase at 1300°C from Ge-substituted imogolite.