Yukihiko Ueno

Photoresponsive electrode based on the reaction between oxygen and the excited Ru(bpy)2+3 complex incorporated in a coated Nafion film

Abstract A photoresponsive electrode was prepared by coating a Nafion film on a indium tin oxide (ITO) electrode incorporating the Ru(bpy) 2+ 3 complex in the film. A photocurrent was induced at the coated electrode dipped in an aqueous electrolyte in the presence of oxygen. The action spectrum showed that the photocurrent is based on the reaction between O 2 and the excited Ru complex. Viologen molecules present as a solute or as the second film on the top of the Nafion[Ru(bpy) 2+ 3 ] film increase the induced photocurrent by about a factor of two by working as a mediator between the excited Ru(bpy) 2+ 3 and O 2 .

Synthesis of tetraethylene oxide-organosiloxane hybrid and the linear ionically conductive spectra of its membrane doped with LiCIO4

Abstract Tetraethylene oxide-organosiloxane hybrid (TEOS), a flat membrane, was obtained by mixing solutions of tetraethylene oxide and methyltrichlorosilane in a Teflon vessel. In the frequency spectra of the linear conductivity of the ionically conductive membrane using TEOS as a matrix ( TEOS LiClO 4 ), relaxations associated with the electrode and interfacial polarizations were observed.

Catalytic activity of poly(amino-organosiloxane)s

Abstract The poly(amino-organosiloxane)s (PAOS) form PAOS-Cu( ii ) complexes. The copper catalysed oxidation of ascorbate and hydroquinone by molecular oxygen was studied in the presence of PAOS. It was found that the addition of PAOS enhances the catalytic efficiency of Cu( ii ). The PAOS-Cu( ii ) catalysed reaction, unlike the Cu( ii ) catalysed reaction, becomes zero-order in the substrate concentration at relatively low concentration of substrate and exhibits Michaelis-Menten kinetics, which indicates the existence of a catalyst-substrate complex. This catalytic activity is similar to the poly( l -histidine)-Cu( ii ) catalysed reaction described by Pecht and Levitski. The specific effect of PAOS on the Cu( ii ) catalysed reactions is interpreted by the conformation of PAOS in aqueous solution, which is dependent on the flexibility and hydrophobicity of the PAOS main chain. In order to investigate the conformation of PAOS in aqueous solution, the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate anion was studied, and it was found that the conformation of PAOS is easily controlled by altering the pH, the coordination to Cu( ii ) ions and the hydrophobicity of PAOS.

Oxygenation of 3-methylindole catalyzed by cobalt(II) phthalocyanine attached to polyorganosiloxane Part 2. Mechanism for addition of oxygen to 3-methylindole

Oxygenation of 3-methylindole was catalyzed by cobalt(II)phthalocyanine (Co(II)Pc) attached to polyorganosiloxane. The mechanism for the addition of oxygen to 3-methylindole was examined by means of the reaction rate determined from the amount of oxygen consumption. The reaction rate (V) was given as follows: V = K[3-methylindole] [Co(II)Pc][O2]. 3-Methylindole was concluded to be not only a substrate but also an oxidation inhibitor. The oxygenation was considered to proceed via a radical mechanism.

Esterolyses of p-nitrophenyl esters catalyzed by dialkylaminopyridines attached to polyorganosiloxane

SummaryThe present study describes the preparation of polyorganosiloxanes containing dialkylaminopyridines in their side chains (POS-DAAPs) and the use of them as catalysts for esterolyses of p-nitrophenyl esters of CH3(CH2)nCOOH (n=0–5). The POS-DAAPs (4, 5) were prepared from poly[(3-chlorocarbonylpropyl)methylsiloxane] (PCCPMS, 1) and two pyridine derivatives, such as 4-[(2-hydroxyethyl)methylamino]pyridine (HEMAP, 2) and 4-[4-(2-hydroxyethyl)piperidino]pyridine (HEPP, 3). Pyridyl groups of POS-DAAPs 4 and 5 were partially quaternized with dimethylsulfate (6, 7) in order to carry out esterolysis in homogenious systems. The esterolyses were examined in methanol/tris(hydroxymethyl)-aminomethane-hydrochloric acid buffer solution (vol. ratio 2/1, pH of buffer solution: 7.5) and analyzed following Michaelis-Menten like kinetics. The second-order rate constants (k2/Km) of the esterolyses catalyzed by POSs 6 and 7 were 22–38 fold values of those catalyzed by the corresponding monomolecular catalysts 2 and 3. In addition, the effects of POSs were discussed from the kinetic, thermodynamic, and activation parameters.

Linear and nonlinear conductive spectra of ion-conducting polymers

The linear and nonlinear complex conductivities have been measured as a function of frequency for the polyethylene oxide modified by the addition of SiO/sub 2/, or doped with LiClO/sub 4/. The observed spectra exhibit marked conductive relaxation, suggesting the existence of different conduction processes in the low-frequency regions. It was found that combinations of the linear and nonlinear conductivities as given by the dynamic percolation theory allow estimates of a hopping distance without any additional assumptions. It was also suggested that the elementary process of the ion transport in the ion-conducting polymers was caused by ion hopping between available sites, and therefore, the typical size of a cluster of available sites is about 4 nm.

Nonlinear conductive spectra of ion-conducting polymers

An ion-conducting polymer, tetraethylene oxide-organosiloxane (TEOS) copolymer, was synthesized and the linear and nonlinear complex conductivities were measured as a function of frequency. Observed spectra were reproduced by taking into account the interfacial and electrode polarizations. The most important findings are the very large dielectric relaxation strength and the very long hopping distance in noncrystalline ion-conductivity polymers. The large relaxation strength suggests that the TEOS Li/sup -/ comprises an inhomogeneous system consisting of highly conductive and less conductive regions. It is speculated that such inhomogeneity governs the conduction mechanisms of the ionic conductor and results in a very long hopping distance. A combination of linear and nonlinear DC conductivities leads to a hopping distance of 200 nm.<<ETX>>

Oxidation of 3-methylindole catalyzed by cobalt(II)phthalocyanines covalently bound to polyorganosiloxane

Two kinds of cobalt(II)phthalocyanines covalently bound to polyorganosiloxane (POS) were prepared to be applied as catalysts for the oxidation of 3-methylindole in organic solvents. The catalytic activity of the POS whose carboxyl residues were methyl-esterified was high compared with that of the POS which has carboxyl residues. The former polymeric atalyst exhibited higher catalytic activity than monomolecular phthalocyanine, indicating an appearance of effects of polymer chains. The factors which influence the catalytic oxidation, e.g., polymer conformations, basicity of solvents, and equilibrium involving phthalocyanine monomer and the dimer, are discussed. It has become apparent that polymer conformation influences catalytic activity and that the catalytic activity of the POS, whose main chains are mobile, is high.

Synthesis of silica gels containing imidazole groups and their binding affinity for methyl orange in water

Abstract Silica gels containing imidazole groups or hexyl groups whose compositions are well controlled have been prepared. The imidazole group in the gel was quaternized with C 4 H 9 Br, C 6 H 13 Br or C 12 H 25 Br to obtain gels that are charged and have an alkyl chain. Their binding affinities for methyl orange in water were then investigated. We aimed to clarify the relation between the structure of the gel and its binding behaviour for small molecules in water. So the binding affinities of the unquaternized and quaternized gels were compared for methyl orange in water at various temperatures and we obtained the thermodynamic parameters for this binding. It was found that in silica gel the alkyl chain that is bound chemically to the charged site is very efficient for binding the dye in water.

Liquid crystalline side-chain polysiloxanes containing mesogenic groups attached by esterification

SummaryLiquid crystalline side-chain polysiloxanes were prepared without metal complex catalyst. Mesogenic groups such as cholesteryl, 4-cyano-4′-biphenyl and 4-methoxy-4′-biphenyl group were introduced into polysiloxane by esterification and from DSC measurements they were compatible with other liquid crystalline polysiloxanes reported previously.