Katsumi Chikama

Photocatalytic function of a polymer-supported B12 complex with a ruthenium trisbipyridine photosensitizer

The hybrid polymer was synthesized by a radical polymerization of a B(12) derivative and a Ru complex having styrene moieties in each peripheral position, and the hybrid polymer showed photocatalytic activity for molecular transformation with visible light irradiation.

Droplet-size dependence of the electron transfer rate across the single-microdroplet/water interface

Abstract Electron transfer between ferrocene in a single oil droplet and hexacyanoferrate(III) in the surrounding water phase was studied by laser trapping, spectroscopic, and electrochemical techniques. We determined the rate of interfacial electron transfer for an individual droplet and found for the first time that the rate increased with a decreased in the droplet diameter. This particular micrometer size dependence was discussed on the basis of kinetic analysis of the electron transfer rate.

Non-stoichiometric dissolution of lanthanum fluoride (LaF3) and its relevance to a process of ion-selective charge separation at the solid ⋯ solution interface

Abstract The solubilities of lanthanum fluoride (LaF3) powder and single crystals were measured in various aqueous electrolyte solutions. In contrast with the classical assumption of the stoichiometric dissolution of LaF3, it was found that the dissolution of the component cation La3+ was undetectable and the fluoride ion dissolved preferentially: cF−> 3cLa3+ where c is the ion concentration. X-ray photoelectron spectroscopy (XPS) of the LaF3 surface treated with electrolyte solutions corroborated this observation. As a result of the preferential fluoride dissolution, charge separation was expected to occur in such a way that the LaF3 surface would have positively charged “fluoride-vacancies”. This was confirmed by changes in membrane potential as a function of the fluoride dissolution the adsorption of an anionic adsorption marker (eosin Y) on the solid surface. It was also found that the preferential dissolution of fluoride ions was accompanied by simultaneous adsorption of almost the same amount of electrolyte anions (e.g. NO 3−) onto the LaF3 surface. This was confirmed by both solution measurements and surface analysis by diffuse reflectance IR Fourier transform (DRIFT) spectrometry. The result of this anion adsorption was explained in terms of ion exchange to ensure electroneutrality in the bulk of the adjacent electrolyte solution, which would otherwise be violated by the preferential fluoride dissolution. The anionic adsorption marker and DRIFT measurements were used to characterize further the above-mentioned ion exchange and selective uptake of fluoride ions into the “fluoride vacancies”. Release of the adsorbed eosin Y or electrolyte anions, such as NO3−, from the LaF3 surface was found to be induced by F− or OH− ions only. On the basis of this observation, the response mechanism of the fluoride ion-selective electrodes was discussed.

Hydrophobicity/hydrophilicity tunable hyperbranched polystyrenes as novel supports for transition-metal nanoparticles

Development of a new preparative procedure for hyperbranched polystyrene having Cl end groups (HPS-Cl) enables to prepare HPS-NR(3)(+)Cl(-), for which the hydrophobicity/hydrophilicity is tunable by the R groups. The resulting ammonium salts behave as a good support of platinum nanoparticles, which is useful for catalytic biphasic hydrogenation of alkenes.

Water-proton relaxivity of hyperbranched polymers carrying TEMPO radicals

High water‐soluble hyperbranched poly(styrene) (HPS) polymers carrying stable 2, 2, 6, 6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radicals, HPS‐N‐TEMPO, HPS‐Im‐TEMPO, and HPS‐Im‐(TEMPO)2, were prepared in ca. 60% introducing yield. HPS‐N‐TEMPO and HPS‐Im‐TEMPO were determined to be nearly spherical shapes of the diameter of 2.4 ± 0.6 and 2.2 ± 0.6 nm, respectively, by transmission electron microscope (TEM) images. The values of water‐proton relaxivity, r1, at 25 MHz, 0.59 T, and 25 °C were 6.0, 5.2, and 14 mM−1 sec−1 for HPS‐N‐TEMPO, HPS‐Im‐TEMPO, and HPS‐Im‐(TEMPO)2, respectively. The spin‐lattice relaxation time (T1)‐weighted images in phantom were also observed. Copyright

Water- and Organo-Dispersible Gold Nanoparticles Supported by Using Ammonium Salts of Hyperbranched Polystyrene: Preparation and Catalysis

Gold nanoparticles (1 nm in size) stabilized by ammonium salts of hyperbranched polystyrene are prepared. Selection of the R groups provides access to both water- and organo-dispersible gold nanoparticles. The resulting gold nanoparticles are subjected to studies on catalysis in solution, which include reduction of 4-nitrophenol with sodium borohydride, aerobic oxidation of alcohols, and homocoupling of phenylboronic acid. In the reduction of 4-nitrophenol, the catalytic activity is clearly dependent on the size of the gold nanoparticles. For the aerobic oxidation of alcohols, two types of biphasic oxidation are achieved: one is the catalyst dispersing in the aqueous phase, whereas the other is in the organic phase. The catalysts are reusable more than four times without loss of the catalytic activity. Selective synthesis of biphenyl is achieved by the homocoupling of phenylboronic acid catalyzed by organo-dispersible gold nanoparticles.

Fabrication of copper wiring by micro-contact printing method and electroless plating and electroplating

A micro-contact printing (µCP) method has been applied to the fabrication of microstructures and electronics. We have successfully fabricated a copper wiring structure on flexible substrates using a combination of µCP, electroless plating, and electroplating. A nucleating agent ink pattern was printed by µCP onto polyethylene terephthalate, and polyethylene naphthalate. Nickel and copper thin films were electrolessly plated onto the pattern, and used as a conductive layer for subsequent copper electroplating. Copper wiring structures with a half-pitch of a 100 µm and a 250 µm line-and-space pattern, were successfully produced on flexible films at temperatures below 100 °C.