Masahiro Fujiwara

Photocontrolled reversible release of guest molecules from coumarin-modified mesoporous silica

Since the discovery of MCM-41 more than ten years ago, many investigations have explored the suitability of hexagonal mesoporous silicas for potential practical applications. These range from catalysis and optically active materials to polymerization science, separation technology and drug delivery, with recent successes in the fabrication of hybrid mesoporous organosilicas expected to open up further application possibilities. Because the pore voids of this class of materials exhibit relatively narrow pore size distributions in the range of 2–4 nm in diameter, mesoporous silicas can selectively include organic compounds and release them continuously at a later stage. The functionalization of MCM-41 pore voids with photoactive derivatives provides influence over the materials absorption behaviour, but full control over the release process remains difficult. Here we show that the uptake, storage and release of organic molecules in MCM-41 can be regulated through the photocontrolled and reversible intermolecular dimerization of coumarin derivatives attached to the pore outlets. Successful functionalization requires uncalcined MCM-41 still filled with the template molecules that directed the formation of its pores, to ensure that coumarin derivatives attach preferentially to the pore outlets, rather than their inside walls. We find that this feature and the one-dimensional, isolated nature of the individual pores allow for efficient and reversible photocontrol over guest access to the materials interior.

Shaping liquid on a micrometre scale using microwrinkles as deformable open channel capillaries

Methods of shaping and manipulating liquids on small scales are important for micro-patterning, microfluidics and biosensing, and may provide fundamental insights into phenomena in confined small spaces. Here, we report a simple technique for shaping liquids into micrometre-scale filaments. Microgrooves on microwrinkles generated by thin film buckling on elastic substrates can function as open channel capillaries for liquids with appropriate wettabilities. Tuning the groove depth of the microwrinkles by modulating strain, we explore the capillary action of various liquids in microgrooves, which form liquid filaments emanating from a large reservoir. This behaviour is explained in terms of sinusoidal-geometry-dependent surface energy. Based on this concept, a regular array of liquid filaments can be formed over a large area by a simple coating method, and these filaments can be further reshaped by exploiting strain-induced nonlinear changes in microwrinkle topography. This technology shows promise for applications in micro-patterning, nano- and micro-reactors, and microfluidics.

Measurement of ultrafast dephasing time of Cresyl Fast Violet in cellulose by photon echoes with incoherent light

Ultrafast homogeneous transverse relaxation time (dephasing time) T2 of Cresyl Fast Violet in cellulose has been measured in the S0 ↔ S1 transition by photon echoes with temporally incoherent nanosecond laser pulses. At 10 K, T2 was 0.7 psec when the sample was excited 6250 A near the long-wavelength edge of the absorption band, but it was several tens of femtoseconds at 5940 A. The fact that T2 is shorter at shorter wavelengths can attributed to the intramolecular relaxation of Cresyl Fast Violet molecules. T2 was measured also at 80 and 300 K. At 10 K persistent nonphotochemical holes (PNPH’s) were observed, and the relations between T2 and the shapes of the PNPH’s have been considered.

Dipolar molecules as impellers achieving electric-field-stimulated release.

Here we report the design of a new external electric field-controlled release system using functional dipolar molecules as nanoimpellers. The dipolar molecule 4-(3-cyanophenyl)butylene, which can reorient in response to external electric fields with different frequencies because of its strong inherent dipole moment, was synthesized and grafted onto the inner surfaces of mesopores. Under an alternating electric field, the swinging flexible molecular chains consequently push guest molecules out of the pore voids. This innovative approach to controlled release may provide important application opportunities in tumor treatment with a number of advantages in terms of local release with targetability, external remote control, and the nonelectrochemical nature of the process.

Hydrogenation of CO and CO2 toward methanol, alcohols and hydrocarbons on promoted copper-rare earth oxides catalysts

The recent development of a copper-rare earth oxid catalyst (CuLa2Zr2O7) with cubic pyrochlore structure allows to synthesize alcohols and hydrocarbons from CO + H2 and CO2 + H2 feeds. A good activity in methanol synthesis is obtained by promoting the given catalysts by addition of oxides, e.g., ZnO or ZrO2. C2+ alcohols and C2+ hydrocarbons are formed in the presence of a transition metal promotor like Co. Finally, a composite catalyst prepared by mixing the CuLa2Zr2O7 methanol catalyst with a HY zeolite yields mainly C2+ hydrocarbons.

Change of catalytic properties of FeZnO/zeolite composite catalyst in the hydrogenation of carbon dioxide

Abstract The hydrogenation of carbon dioxide was examined using the composite catalysts which were obtained by the physical mixing of Fe ZnO and HY zeolite. Fe ZnO was a typical F-T (Fischer-Tropsch) catalyst and Fe ZnO/HY is a composite catalyst which is able to induce a combined methanol synthesis and MTG (Methanol-to-Gasoline) reaction. To study these unique catalytic behaviors of Fe ZnO/HY, the adsorption and the dissociation of carbon monoxide on Fe ZnO as well as TPR measurements were carried out. Fe ZnO is able to produce hydrocarbons by F-T reaction and methanol. In the absence of zeolite, Fe ZnO exerts its ability for F-T reaction. However, HY diminishes the activity for F-T reaction and hydrocarbons were obtained via methanol formed over the modified Fe ZnO

Subpicosecond photon echoes by using nanosecond laser pulses

Abstract Subpicosecond time resolutions have been obtained in photon echoes when a sample was excited by two nanosecond dye laser pulses with a smooth and broad spectrum. The dye laser was pumped by second harmonics of a Q-switched Nd:YAG laser, and the pulse width was 10 ns. The sample was 3% Nd3+-doped silicate glass, and the center frequency of the dye laser was tuned at 5910 A on resonance with the 4I 9 2 ↔ 2G 7 2 , 4G 5 2 transition of Nd3+. The homogeneous transverse relaxation time T2 was measured to be 91 ps at 10 K in agreement with the previous measurements by picosecond pulses.

Formation of titanium tert-butylperoxo intermediate from cubic silicon–titanium complex with tert-butyl hydroperoxide and its reactivity for olefin epoxidation

Abstract Epoxidation of olefins by tert -butyl hydroperoxide (TBHP) was effectively catalyzed by a cubic silicon–titanium μ-oxo-complex, which is obtained from a bulky silanetriol and titanium alkoxides. The stoichiometric reaction of the complex with TBHP in the absence of olefin formed a novel complex as white solid. The comparison of this product with analogous complexes in 1 H and 13 C NMR spectra indicated that the titanium tert -butylperoxo complex; this kind of intermediate is considered to be active for epoxidation in titanium-based catalysts, was first isolated. This titanium peroxo complex reacted with cyclohexene to produce cyclohexene oxide without additional oxidant accompanying the formation of titanium tert -butoxide. All pathways of the catalytic cycle of the epoxidation using titanium catalysts were verified experimentally.

Preparation of Hierarchical Architectures of Silica Particles with Hollow Structure and Nanoparticle Shells: A Material for the High Reflectivity of UV and Visible Light

Silica microcapsules (silica hollow particles) are readily prepared by a single step of the interfacial reaction method, where a W/O/W emulsion is employed effectively. This is a simple (one-step process), inexpensive approach (silica source is sodium silicate) to producing hollow silicas. The addition of NaCl to the sodium silicate solution as the inner water phase of the W/O/W emulsion plainly influenced the shell structure of the silica hollow particles. The increase of the addition of NaCl expanded the size of the mesopores in their silica shell, which reached to macropores (>50 nm). The nanoparticles in the shells of some silica hollow particles attained approximately 200-400 nm in size, which is comparable to the wavelengths of UV and visible light. According to the diffuse reflection spectra of the silica hollow particles in powder form, these particles showed the high reflection of UV and visible light, which increased with added NaCl in the preparation process of the interfacial reaction method. The reflectance of a silica hollow particle from 300 to 800 nm in wavelength was over 90%, which was significantly higher than a common solid (not hollow) silica gel. In addition, even the reflectance of UV light shorter than 300 nm in wavelength was greater than 60%. These characteristic reflections in a wide range of wavelengths were caused by both nanoparticle shells whose sizes are comparable with the wavelength of light and the hollow structures of the main micrometer-sized particles.

A simple preparation method of epoxy resin/silica nanocomposite for Tg loss material

Nanocomposite materials of epoxy resin and silica were prepared by a simple procedure wherein diglycidyl ethers of bisphenol-A (DGEBA) as the pre-polymer of epoxy resin, tetraethoxysilane (TEOS) as silica source, and hexahydrophthalic anhydride (HHPA) were mixed together and heated at 170 °C in a sealed autoclave. HHPA played two roles in this reaction system: one role is as a well-known curing reagent of epoxy resin; the other is as the condensation reagent of alkoxysilane, since transesterification promotes this reaction. These two reactions occurred simultaneously in homogeneous solution, and organic–inorganic composite materials were readily obtained. Field emission SEM/EDX images showed that silica particles of nano size (below 50 nm) were included in the epoxy resin matrix. Some of these epoxy resin/silica nanocomposite materials displayed high thermal stability. When DGEBA bearing about three bisphenol-A units and five molar equivalents of TEOS were reacted, the obtained composite displayed no Tg point below 300 °C in the DSC (differential scanning calorimetry) thermogram. This high thermal stability is likely to be derived from the interaction of hydroxyl groups of DGEBA with silica.