Synthesis of bitetrathiafulvalenes with FeCl3-mediated homo-coupling of tetrathiafulvalenylmagnesium bromide and formation of nanostructures from bitetrathiafulvalenes having long alkylthio chains

The FeCl₃-mediated homo-coupling of 4,5-bis(alkylthio)-4′-tetrathiafulvalenylmagnesium bromide 5 produced the corresponding bitetrathiafulvalene derivatives 2a-d in moderate yields (25-51%). Bitetrathiafulvalenes 2c and 2d having long alkylthio chains formed nanostructures and showed bulk electric conductivities (σ_rt = 2.6 − 8.0 × 10⁻⁵ S cm⁻¹) in the neutral state owing to the fastener effect. Interestingly, the nanofiber of tetrakis(dodecylthio)bitetrathiafulvalene 2d exhibited a p-type semiconductivity as detected by AFM.     

An efficient synthesis of chiral isoquinuclidines by Diels-Alder reaction using Lewis acid catalyst

The Diels-Alder reaction of 1,2-dihydropyridine derivatives (1-phenoxycarbonyl-1,2-dihydropyridine 1 or 1-methoxycarbonyl-1,2-dihydropyridine 4) with N-acryloyl (1S)-2,10-camphorsultam (1S)-2 {or N-acryloyl (1R)-2,10-camphorsultam (1R)-2} in the presence of Lewis acid, such as titanium tetrachloride, zirconium tetrachloride, and hafnium tetrachloride afforded the endo-cycloaddition product, 2-azabicyclo[2.2.2]octane derivatives in good yields with excellent diastereoselectivity. The absolute stereochemistry assignment of the endo-cycloaddition product (1S)-5a starting from N-acryloyl (1S)-2,10-camphorsultam (1S)-2 has been established to be (1S,4R,7S) and the reaction mechanism was proposed.     

Ultrafast photosynthetic reduction of elemental sulfur by Au nanoparticle-loaded TiO2

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S8) led to the energetically uphill reduction of S8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters (substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.     

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.     

Micellar structures of block‐copolymers with ordered cores in dilute solution as studied by polarized and depolarized light scattering

The hierarchical self‐assembly behaviors of a series of amphiphilic liquid crystalline block copolymers (pEG_mAz_n), consisting of poly(ethylene glycol) (pEG) block and liquid crystalline polymer block (pAz) of poly{11‐[4‐(4‐butylphenylazo) phenoxy]‐undecyl methacrylate} containing an azobenzenzene mesogen, in the selective solvent diethyleneglycol, which is good for pEG block, were studied by polarized and depolarized light scattering. It was found that these copolymers can form micellar particles with internal ordered structures of optical anisotropy. Depending on the relative lengths of the blocks, the obtained micellar structures show optical anisotropies with different geometrical anisotropies. The higher composition of pAz‐core blocks leads to the larger aggregate. The lower‐molecular‐weight copolymers tend to form the long and thin strings, which show rather the larger size with larger aggregation number. Even at the similar composition of pAz‐core block, copolymers with different chain lengths can form the core of the different aggregating structures with the different molecular orientations. It was also found that the addition of a small amount of the surfactant, C₁₂E₂₅, makes the string‐like aggregate shorter. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1333–1343, 2007     

Design of a rate- and time-programming drug release device using a hydrogel: pulsatile drug release from κ-carrageenan hydrogel device by surface erosion of the hydrogel

We have found that a repetitive pulsatile drug release with a certain time interval is observed from a monolithic hydrogel device by surface erosion of the hydrogel. As a model system of pulsatile drug release, dibucaine hydrochloride and κ-carrageenan hydrogel were chosen as a drug and a device, respectively. Electrostatic interactions between dibucaine hydrochloride and κ-carrageenan polymer segments are strong, since dibucaine hydrochloride is positively charged and each disaccharide repeating unit of κ-carrageenan chains has one sulfate group. Dibucaine hydrochloride was loaded into the hydrogel by immersing dry κ-carrageenan hydrogel disks in a dibucaine hydrochloride solution for 24 h. The pulsed release of dibucaine hydrochloride from the device was observed every 50 min between 30 and 250 min after the release starts. The weight of κ-carrageenan hydrogel decreases in an oscillatory manner with time in distilled water. The oscillatory changes observed in the hydrogel weight in distilled water are considered to be caused by influx and efflux of water molecules into and from the surface and core of the hydrogel and by polymer liberation from the hydrogel. This phenomenon was well explained by our kinetic model [Colloids and Surfaces B 8 (1996) 93–100]. The time interval between pulses observed in drug release coincides with that observed in the oscillatory weight change of the hydrogel. From these, it was concluded that the pulsatile release of dibucaine hydrochloride from the device was caused by the pulsatile liberation of swollen κ-carrageenan hydrogel from the surface of the device.     

Mössbauer study on characterization of Co[Fe(CN)5NH3 \cdot x H2O

The electronic states of Fe atoms in Co[Fe(CN)₅NH₃ H₂O were studied by means of ⁵⁷Fe Mössbauer spectroscopy. The Mössbauer spectra of Co[Fe(CN)₅NH₃ 6H₂O show the coexistence of mixed valences for the Fe atoms and a magnetic relaxation at 4 K. When water molecules were removed, electron transfer from Co to Fe occurred.     

Microelectrochemical approach to induce local cell adhesion and growth on substrates

The nature of an albumin-coated substrate that blocks protein adsorption and cell adhesion was rapidly switched to cell-adhesive by exposure to an oxidizing agent such as HBrO. This finding has enabled cellular pattern drawing even on a single-cell level by closely scanning a microelectrode above the substrate and electrochemically producing the agent at the tip of the electrode. The present microelectrochemical cell patterning is applicable even for a previously cell-patterned substrate and for a grooved substrate. These unique technical features will have impacts on a variety of cell-based studies that require the analysis of heterotypic cell-cell interactions and cellular arrangement on an uneven surface such as semiconductor devices.     

Hydrogen bonding effects on the surface structure and photoelectrochemical properties of nanostructured SnO2 electrodes modified with porphyrin and fullerene composites

Hydrogen bonding effects on surface structure, photophysical properties, and photoelectrochemistry have been examined in a mixed film of porphyrin and fullerene composites with and without hydrogen bonding on indium tin oxide and nanostructured SnO2 electrodes. The nanostructured SnO2 electrodes modified with the mixed films of porphyrin and fullerene composites with hydrogen bonding exhibited efficient photocurrent generation compared to the reference systems without hydrogen bonding. Atomic force microscopy, infrared reflection absorption, and ultraviolet-visible absorption spectroscopies and time-resolved fluorescence lifetime and transient absorption spectroscopic measurements disclosed the relationship between the surface structure and photophysical and photoelectrochemical properties relating to the formation of hydrogen bonding between the porphyrins and/or the C60 moieties in the films on the electrode surface. These results show that hydrogen bonding is a highly promising methodology for the fabrication of donor and acceptor composites on nanostructured semiconducting electrodes, which exhibit high photoelectrochemical properties.     

Antioxidant action by gold-PAMAM dendrimer nanocomposites

Gold-dendrimer nanocomposites were prepared in the presence of poly(amidoamine) (PAMAM) dendrimer (generation 3, 3.5, 5, and 5.5) via reduction of HAuCl4 with sodium borohydride. The average particle size of the gold nanoparticles was independent of the dendrimer concentration, ranging between 3.0 and 4.3 nm in diameter. The catalytic activities of the gold-dendrimer nanocomposites upon elimination of hydroxyl radicals formed in an H2O2/FeSO4 system were examined using a spin-trapping method. The gold-dendrimer nanocomposites exhibited high catalytic activities which were hardly affected by the concentration and the generation of the dendrimer except PAMAM dendrimer 3.5. The highest activity for the gold-PAMAM dendrimer 3.5 nanocomposites was 85 times that of ascorbic acid.