Preparation of very reactive thiol-protected gold nanoparticles: revisiting the Brust-Schiffrin method

The preparation and properties of tert-dodecanethiol protected gold nanoparticles amenable to very rapid surface functionalization by associative mechanism is described. The new material can be easily prepared by controlling the reaction time, because only a limited but enough number of tert-dodecanethiol to stabilize the gold clusters is bond to the surface until about an hour. Accordingly, it can be isolated as a solid and handled much like the highly stabilized Brust-Schiffrin analogues, but reacted very rapidly with any molecular species containing one or multiple functional groups such as thiol, disulfide, pyridine, etc. These characteristics are ideal for the preparation of a variety of new organic-inorganic hybrid nanomaterials by coordinative self-assembly. This possibility was illustrated using meso-tetra(4-pyridyl)porphyrin, which promptly bonded to the reactive protected gold nanoparticles generating a solid that can be grown as thin films with layer-by-layer control on a suitably modified surface.     

Characterization of methyl‐substituted polyamides used for reverse osmosis membranes by positron annihilation lifetime spectroscopy and MD simulation

Three kinds of polyamides were synthesized from three diamines and 1,3,5‐benzenetricarbonyl trichloride (TMC). The diamines used were m‐phenylene diamine, N‐methyl‐m‐phenylenediamine, and N,N′‐dimethyl‐m‐phenylenediamine. The average free volume sizes of the polyamides were measured by positron annihilation lifetime spectroscopy (PALS), and the free volume fractions were evaluated by molecular dynamics (MD) simulations. The methyl substitution on amino groups of diamines brought about an increase in interstitial space of molecular chains of the polyamides. In addition, reverse osmosis (RO) membranes were prepared by interfacial polymerization from the three diamines and TMC. The increase in the degree of methyl‐substitution of diamines led to increased chlorine resistance and decreased salt rejections of the polyamide RO membranes. Thus, the methyl‐substitution of diamines significantly influenced membrane performance. The vacancy sizes and fractional volumes in polyamides evaluated by PALS measurement and MD simulation were well correlated with salt rejection of polyamide RO membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Physical Factors Determining Thermal Conductivities of Isotropic Conductive Adhesives

The thermal conductivities of a typical isotropic conductive adhesive (ICA) composed of an epoxy-based binder containing flake-shaped and spherical Ag particles have been studied. The ICA specimens exhibit anisotropy in their thermal conductivities between the vertical and in-plane directions. In addition, their thermal conductivities apparently depend on their thermal history during the curing and subsequent annealing processes, even if they are fully cured during the preliminary curing stage. The thermal conductivities tend to increase with decreasing electrical resistivities. The experimental values for the thermal conductivities of the ICA specimens were apparently higher than␣those predicted using Bruggemann’s equation. Analysis using the Wiedemann–Franz (W–F) law indicates that their thermal conductivities increase with increasing contribution from electrical conduction. In order to discuss the thermal conductivities of ICA specimens that exhibit relatively low electrical resistivities (below 10⁻³ Ω cm), the contribution of the conducting electrons must be included.     

Electrochemical methods coupled with impedance measurement for energy gap study: correlation between the energy states and charge transport properties

The energy states of poly(3-hexylthiophene) (P3HT) polymer films degraded using UV/ozone environment were studied by optical and electrochemical methods. Energy levels of highest occupied and lowest unoccupied molecular orbitals as well as localized states between them were estimated. Electrical properties of polymer films sandwiched between two metal electrodes were investigated for various trap energy distributions. Comparison of the energy states density evaluated by optical/electrochemical methods and estimated from the current-voltage characteristics was carried out to discuss suitability of space-charge limited electrical conduction models for semiconducting polymers.     

Dramatic effect of dispersed carbon nanotubes on the mechanical and electroconductive properties of polymers derived from ionic liquids

Free-radical polymerization of an imidazolium ion-based ionic liquid bearing a methacrylate group, gelling with single-walled carbon nanotubes (SWNTs), allows fabrication of a mechanically reinforced, electroconductive soft material (bucky plastic). A film sample of this material displays an excellent conductivity of 1 S cm(-1) and a 120-fold enhancement of the Young's modulus at a 7 wt % content of SWNTs. The conductivity is temperature-dependent in the range 5-300 K, suggesting that the conductive process involves carrier hopping. Scanning electron and atomic force micrographs of a bucky plastic film display the presence of crosslinked networks consisting of finely dispersed SWNTs. Such nanotube networks, developed in the polymer matrix, likely suppress slipping of entrapped polymer molecules via a strong interfacial interaction and also facilitate intertubular carrier transport. Although a bucky plastic derived from a vinylimidazolium ion-based ionic liquid monomer shows a comparable conductivity to that of the methacrylate version, the film is brittle irrespective of the presence or absence of SWNTs.     

The Role of Reverse Intersystem Crossing Using a TADF-Type Acceptor Molecule on the Device Stability of Exciplex-Based Organic Light-Emitting Diodes

Exciplex system exhibiting thermally activated delayed fluorescence (TADF) holds a considerable potential to improve organic light-emitting diode (OLED) performances. However, the operational lifetime of current exciplex-based devices, unfortunately, falls far behind the requirement for commercialization. Herein, rationally choosing a TADF-type electron acceptor molecule is reported as a new strategy to enhance OLEDs' operating lifetime. A comprehensive study of the exciplex system containing 9,9′,9′′-triphenyl-9H,9′H,9′′H-3,3′:6′,3′′-tercarbazole (Tris-PCz) and triazine (TRZ) derivatives clarifies the relationship between unwanted carrier recombination on acceptor molecules, TADF property of acceptors, and the device degradation event. By employing a proposed “exciton recycling” strategy, a threefold increased operational lifetime can be achieved while still maintaining high-performance OLED properties. In particular, a stable blue OLED that employs this strategy is successfully demonstrated. This research provides an important step for exciplex-based devices toward the significant improvement of operational stability.     

Molecular breeding of Aspergillus kawachii overproducing cellulase and its application to brewing barley shochu

In order to improve fermentation of barley without addition of commercial cellulase, a white koji mold, Aspergillus kawachii IFO4308, was transformed with the egl1 gene encoding endoglucanase I (EGI) of Trichoderma viride and the endogenous cekA gene encoding endoglucanase (CekA). Transformants with egl1 under the control of the strong glaA promoter produced EGI in both submerged and solid-state cultures. However, the EGI produced in solid-state culture was unstable due to the acidic condition of this culture. A transformant N10 with two additional copies of the cekA gene exhibited endoglucanase activities against carboxymethyl-cellulose, which are 21- and 1.8-fold higher than that of the wild-type (wt) strain when the cells were cultivated in submerged and solid-state cultures, respectively. Cultivation of strain N10 in steamed barley for preparing koji followed by fermentation with Saccharomyces cerevisiae resulted in improved fermentation assessed based on higher productions of ethanol, amino acids, and organic acids, the reduction of residual sugar, and the low viscosity of barley mash. The overall fermentation result for the transformant carrying cekA was comparable with that for the wt strain using commercial cellulase. These results demonstrate that acquisition of only two-fold CekA activity by A. kawachii in the solid-state culture allows us to improve the brewing of barley shochu.     

Fucoxanthin Prevents Pancreatic Tumorigenesis in C57BL/6J Mice That Received Allogenic and Orthotopic Transplants of Cancer Cells

Fucoxanthin (Fx) is a marine carotenoid with anti-inflammatory and anti-cancer properties in various animal models of carcinogenesis. However, there is currently no information on the effects of Fx in animal models of pancreatic cancer. We investigated the chemopreventive effects of Fx in C57BL/6J mice that received allogenic and orthotopic transplantations of cancer cells (KMPC44) derived from a pancreatic cancer murine model (Ptf1a^Cre/+; LSL-kras^G12D/+). Using microarray, immunofluorescence, western blot, and siRNA analyses, alterations in cancer-related genes and protein expression were evaluated in pancreatic tumors of Fx-administered mice. Fx administration prevented the adenocarcinoma (ADC) development of pancreatic and parietal peritoneum tissues in a pancreatic cancer murine model, but not the incidence of ADC. Gene and protein expressions showed that the suppression of chemokine (C-C motif) ligand 21 (CCL21)/chemokine receptor 7 (CCR7) axis, its downstream of Rho A, B- and T-lymphocyte attenuator (BTLA), N-cadherin, αSMA, pFAK(Tyr³⁹⁷), and pPaxillin(Tyr³¹) were significantly suppressed in the pancreatic tumors of mice treated with Fx. In addition, Ccr7 knockdown significantly attenuated the growth of KMPC44 cells. These results suggest that Fx is a promising candidate for pancreatic cancer chemoprevention that mediates the suppression of the CCL21/CCR7 axis, BTLA, tumor microenvironment, epithelial mesenchymal transition, and adhesion.     

A Comparative Study of Organic Cobalt Complex Catalysts for Oxygen Reduction in Polymer Electrolyte Fuel Cells

Reduction of platinum catalysts loading is a central issue in polymer electrolyte fuel cells. As alternatives for platinum, some organic metal chelate compounds are tested as cathode catalysts, such as cobalt aza-complexes or cobalt complexes possessing aminophenyl moieties featured as Co-N₄ or Co-N₂O₂ chelate structures. The way of immobilization of catalysts on the graphite surface influences their stability as well as the performance of oxygen reduction. Heat-treated catalysts supported on graphite at 600°C show much better oxygen reduction abilities than as-received metal complexes. The original chemical structure of metal complexes affects crucially the catalytic ability, though initial structures of molecules are no more intact after the heat treatment. The catalytic activity of these complexes may originate from the central chelate unit CoN₄ on the carbon substrate, and this unit is assumed to constitute the basic coordination site for an oxygen molecule. Electropolymerized catalysts impart a high level of oxygen reduction ability, probably due to the improved molecular orientation for oxygen coordination and formation of good chelate sites on the graphite surface.     

Status of engineering design of liquid lithium target in IFMIF-EVEDA

In International Fusion Materials Irradiation Facility (IFMIF), intense neutron flux (4.5 × 10¹⁷ n/m² s) with a peak energy of 14 MeV are produced by means of two deuteron beams with a total current of 250 mA and maximum energy of 40 MeV that strike a liquid Li target circulating in a Li loop. Major design requirement is to provide a stable Li jet at a speed of 10–20 m/s with a surface wave amplitude on the Li flow less than 1 mm for handling of an averaged heat flux of 1 GW/m² under a continuous 10 MW deuterium beam deposition. The target system consists of a target assembly, a replaceable back-plate, a Li main loop and a Li purification loop. In July 2007, Engineering Validation and Engineering Design Activities (EVEDA) started under Broader Approach. In this paper, status of the engineering design of the IFMIF Li target system performed in 2007/2008 is described. The future EVEDA tasks to develop the target system are also summarized.