Sei-ichi Nishimoto

Correlation of the crystal structure of titanium dioxide prepared from titanium tetra-2-propoxide with the photocatalytic activity for redox reactions in aqueous propan-2-ol and silver salt solutions

Titanium dioxide (TiO2) has been prepared by the hydrolysis of titanium tetra-2-propoxide, followed by calcination at various temperatures (Tc) up to 1000 °C. The content and crystallite size of anatase in the TiO2 powders increased upon increasing Tc up to 550 °C. In the Tc range 550–600 °C a mixture of anatase and rutile was obtained. A further increase in Tc resulted in TiO2 of rutile structure only. The photocatalytic activities of these TiO2 powders for redox reactions were evaluated in the following systems: (1) aqueous propan-2-ol solution, (2) aqueous Ag2SO4 solution and (3) aqueous Ag2SO4 solution containing propan-2-ol. The anatase TiO2 showed photocatalytic activity in all these systems, the activity increasing with crystal growth. In aqueous propan-2-ol solution the activity is dramatically enhanced by partial coverage of the TiO2 with platinum black. The photocatalytic activity of the rutile TiO2 powder was comparable to or even greater than that of anatase when the reaction system included the silver salt, but was negligibly small for aqueous propan-2-ol solution regardless of the partial Pt coverage.

Amyloid β-protein (Aβ)1–40 protects neurons from damage induced by Aβ1–42 in culture and in rat brain

Previously, we found that amyloid β‐protein (Aβ)1–42 exhibits neurotoxicity, while Aβ1–40 serves as an antioxidant molecule by quenching metal ions and inhibiting metal‐mediated oxygen radical generation. Here, we show another neuroprotective action of nonamyloidogenic Aβ1–40 against Aβ1–42‐induced neurotoxicity in culture and in vivo. Neuronal death was induced by Aβ1–42 at concentrations higher than 2 μm, which was prevented by concurrent treatment with Aβ1–40 in a dose‐dependent manner. However, metal chelators did not prevent Aβ1–42‐induced neuronal death. Circular dichroism spectroscopy showed that Aβ1–40 inhibited the β‐sheet transformation of Aβ1–42. Thioflavin‐T assay and electron microscopy analysis revealed that Aβ1–40 inhibited the fibril formation of Aβ1–42. In contrast, Aβ1–16, Aβ25–35, and Aβ40–1 did not inhibit the fibril formation of Aβ1–42 nor prevent Aβ1–42‐induced neuronal death. Aβ1–42 injection into the rat entorhinal cortex (EC) caused the hyperphosphorylation of tau on both sides of EC and hippocampus and increased the number of glial fibrillary acidic protein (GFAP)‐positive astrocytes in the ipsilateral EC, which were prevented by the concurrent injection of Aβ1–40. These results indicate that Aβ1–40 protects neurons from Aβ1–42‐induced neuronal damage in vitro and in vivo, not by sequestrating metals, but by inhibiting the β‐sheet transformation and fibril formation of Aβ1–42. Our data suggest a mechanism by which elevated Aβ1–42/Aβ1–40 ratio accelerates the development of Alzheimers disease (AD) in familial AD.

Highly active semiconductor photocatalyst: Extra-fine crystallite of brookite TiO2 for redox reaction in aqueous propan-2-ol and / or silver sulfate solution

Extra-fine crystallite of brookite TiO2, prepared by air oxidation of TiCl3 in aqueous HCl solution, exhibited marked photocatalytic activity for both dehydrogenation of propan-2-ol in aqueous solution and Ag metal deposition in silver sulfate solution.

Formation of a membrane-active form of amyloid β-protein in raft-like model membranes

The conversion of soluble, nontoxic amyloid beta-protein (A beta) to aggregated, toxic A beta rich in beta-sheet structures is considered to be the key step in the development of Alzheimers disease. We have proposed that the aggregation proceeds in the lipid raft containing a ganglioside cluster, the formation of which is facilitated by cholesterol and for which A beta shows a specific affinity. In this study, using fluorescence resonance energy transfer, we found that after A beta binds to raft-like membranes composed of monosialoganglioside GM1/cholesterol/sphingomyelin (1/1/1), the protein can translocate to the phosphatidylcholine membranes to which soluble A beta does not bind. Furthermore, self-quenching experiments using fluorescein-labeled A beta revealed that the translocation process competes with the oligomerization of the protein in the raft-like membranes. These results suggest that the lipid raft containing a ganglioside cluster serves as a conformational catalyst or a chaperon generating a membrane-active form of A beta with seeding ability.

Novel synthesis of microcrystalline titanium(IV) oxide having high thermal stability and ultra-high photocatalytic activity : thermal decomposition of titanium(IV) alkoxide in organic solvents

Thermal decomposition of titanium(IV) tetra-tert-butoxide (TTB) in inert organic solvents at 573 K yielded microcrystalline anatase (titanium(IV) oxide, TiO2) powders with a crystallite size of ca. 9 nm and a surface area of <100 m2 g-1. Primary and secondary alkoxides of titanium(IV), however, were not decomposed under similar conditions, indicating that the thermal stability of C-O bonds in the alkoxides was a decisive factor for their decomposition. The TiO2 prepared from TTB by this manner was thermally stable upon calcination in air and retained high surface area of ca. 100 m2 g-1 even after calcination at 823 K. The as-prepared TiO2 powders, without calcination, exhibited much higher rate of carbon dioxide formation than any other active photocatalysts such as Degussa P-25 and Ishihara ST-01 in the photocatalytic mineralization of acetic acid in aerated aqueous solutions. The higher activity of the present TiO2 photocatalysts is attributed to both high crystallinity and large surface of the present product. The calcination of the as-prepared TiO2 in air reduced the photocatalytic activity, but it was still higher than the other commercially available TiO2s.

Photocatalytic reaction of neat alcohols by metal-loaded titanium(IV) oxide particles

Abstract The photocatalytic reaction (excitation wavelength, greater than 300 nm) of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO2) was conducted under argon at room temperature. The dehydrogenation products hydrogen (H2) and acetaldehyde (or acetone in the case of 2-propanol) were found in the absence of additives. The corresponding acetals, ethers, and alkanes were obtained by the addition of concentrated hydrochloric acid (HCl). The measurement of the product yields during the post-irradiation dark reaction in the presence of photocatalyst (TiO2) loaded with platinum(IV) oxide (PtO2) revealed that the production of ether and ethane and the regeneration of ethanol proceed by the hydrogenation of acetal over loaded metal, presumably via a hemiacetal intermediate. X-ray diffraction (XRD) analyses showed that the loaded PtO2 is reduced to platinum metal during the course of the photocatalytic reaction. For the production of ether from HCl-acidified ethanol, Pd-loaded catalysts, especially prepared by precipitation—reduction, exhibit the highest activity of several metal-loaded TiO2 catalysts. From XRD and X-ray photoelectron spectroscopy studies of Pd-loaded TiO2 particles, it was shown that the smaller the size of the Pd particles, the higher the selectivity for ether production from the acidified ethanol suspension. The application of this photocatalytic O-alkylation to the synthesis of cyclic ethers was demonstrated.

Ruthenium Complexes with Hydrophobic Ligands That Are Key Factors for the Optical Imaging of Physiological Hypoxia

The phosphorescence emission of ruthenium complexes was applied to the optical imaging of physiological hypoxia. We prepared three complexes with hydrophobic substituents on the phenanthroline ligand and characterized their emission, which was quenched by molecular oxygen. Among the complexes synthesized in this study, a pyrene chromophore-linked ruthenium complex, Ru-Py, exhibited optimal properties for the imaging of hypoxia; the prolonged lifetime of the triplet excited state of the ruthenium chromophore, which was induced by efficient energy distribution and transfer from the pyrene unit, provided the highest sensitivity towards molecular oxygen. The introduction of hydrophobic pyrene increased the lipophilicity of the complex, leading to enhanced cellular uptake. Consequently, the bright phosphorescence of Ru-Py was seen in the cytoplasm of viable hypoxic cells, whereas the signal from aerobic cells was markedly weaker. Thus, we could clearly discriminate between hypoxic and aerobic cells by monitoring the phosphorescence emission. Furthermore, Ru-Py was applied to optical imaging in live mice. An intramuscular injection of Ru-Py successfully visualized ischemia-based hypoxia, which was constructed by leg banding.

Photocatalytic activity of titanium(IV) oxide prepared from titanium(IV) tetra-2-propoxide: reaction in aqueous silver salt solutions

Abstract Titanium(IV) oxide TiO 2 ) powders were prepared by hydrolysis of titanium(IV) tetra-2-propoxide and subsequent calcination at various temperatures T c up to 1073 K. The transformation of crystal structure from anatase to rutile was observed at T c ≈873 K along with a drastic decrease in specific surface area. This led to a decrease in the amount of both surface hydroxyls and Ag + adsorbed ([Ag + ] ad ) from an aqueous silver nitrate solution. For each powder, [Ag + ] ad increased with pH of the suspension. Deposition of silver metal onto the TiO 2 surface and evolution of molecular oxygen (O 2 ) were observed by photoirradiation (at greater than 300 nm) on TiO 2 suspended in a silver sulfate solution at room temperature. The overall stoichiometry of [4Ag + +2H 2 O = 4Ag+O 2 +4H + ] was obtained from the results of irradiation of 1 h for each TiO 2 powder. The initial rate of this photocatalytic reaction was evaluated from the amount of photodeposited silver during several photoirradiation durations of less than 5 min, and compared with [Ag + ] ad . The lower photocatalytic activity of TiO 2 of lower T c , despite larger [Ag + ] ad , was caused by the signficant surface recombination of photoexcited electrons and positive holes, depressing the substantial rate of reduction of adsorbed Ag + .

Catalytic and photocatalytic decomposition of ozone at room temperature over titanium(IV) oxide

Dark and photoinduced decomposition of ozone (O3, ca. 80 ppm) in air over various titanium(IV) oxide (TiO2) powders has been studied with a flow-type reactor (1.5 dm3 min–1) at room temperature. The ozone decomposition in the dark was attributed to catalysis by TiO2. The catalytic activity, evaluated from % decrease in O3 concentration, increased with the increase in the specific surface area of TiO2 and also in the amount of surface hydroxyls. The fact that substitution of hydroxyls with fluoride anions reduced the activity of TiO2(Merck, anatase) to less than half, suggested a mechanism including O3 decomposition on the surface hydroxyls. A TiO2 powder, contaminated with sulfate anion, exhibited a catalytic activity lower than expected from the specific surface area, but increased more than three-fold by washing with aqueous alkaline solution to eliminate sulfate anions and recover hydroxyls. The O3 decomposition under irradiation (>200 nm) occurred not only by direct photolysis of O3 adsorbed on the TiO2 surface (mainly by 254 nm irradiation), but also by a photocatalytic reaction initiated by absorption of photons by TiO2 at <ca. 400 nm, as well as the dark catalytic decomposition. The O3 decomposition via the photocatalytic reaction was evaluated separately by cutting off the light of wavelength <290 nm. The photocatalytic activity of TiO2 was independent of the specific surface area, but dependent on its crystal structure. The photocatalytic activity of TiO2 was independent of the specific surface area, but dependent on its crystal structure. The photocatalytic activity increased in the order anatase anatase–rutile mixture < rutile. The mechanism of these O3 decomposition processes has been discussed.

Importance of the amorphous fraction of polypropylene in the resistance to radiation-induced oxidative degradation

Abstract Radiation-induced oxidative degradation of two types of polypropylene (PP-A and PP-B) and of their blends in sheet form was studied in air with irradiation doses up to 10 Mrad. The elongation at break (γB) scarcely changed with irradiation dose below a critical value (Dc), but decreased drastically on irradiation a little in excess of Dc. The critical dose (Dc) increased rapidly with increasing amorphous fraction (fa) of the polypropylene, the relationship being expressed by an empirical equation, 33·5. The G values (3·1) for main-chain scission obtained for the irradiation of PP-A and PP-B in air were almost equal. The oxidation yield (Yox), defined as the amount of ketones produced per gram of polymer, depends on both the total dose of irradiation (D) and the amorphous fraction (fa) according to the relationship, 11·4 fa3·0D1·3. On the basis of these results, the important role of the amorphous fraction (fa) of polypropylene resin in its resistance to radiation-induced oxidative degradation is discussed.