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Kenichi Oyaizu

Publications and source records attributed to Kenichi Oyaizu.

11 recordsLinked to original sources
PubMed2006

Highly stable polymerizable vesicles in anionic surfactant/ammonium salt mixtures in the presence of cross-linking monomers for convenient preparation of hollow nanospheres.

Spontaneous and stable vesicles are formed from vinylbenzyltrimethylammonium chloride (VBTAC) and sodium dodecyl sulfate (SDS) ranging in molar composition from 3:7 to 7:3 in the presence of 30 mol % divinylbenzene (DVB). Dynamic light scattering analysis and transmission electron microscope observations revealed that microparticles with diameters around 120 nm (30%) and 580 nm (70%) were formed. Trapping efficiency of the vesicles examined with D-(+)-glucose amounted to ca. 15%. These vesicles were capable of undergoing polymerization in the presence of water-soluble radical initiators such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride to fix the vesicular structure. Retention of the vesicle size and bimodal size distribution characteristics during the polymerization indicated that intravesicular polymerization prevailed over the intervesicular process. SDS was stably retained in the cross-linked vesicle and was not removed from the vesicle by exhaustive dialysis or ultrafiltration, due to the electrostatic interaction within the cross-linked polymeric framework produced from VBTAC and DVB. The resulting hollow nanospheres are readily redispersed in water without the aid of additional surfactants.

Journal Article↗
PubMed2006

Surface-modified mesoporous silicas as recyclable adsorbents of an endocrine disrupter, bisphenol A.

Surface-modified mesoporous silicas (MSs) were investigated for recyclable adsorption of an endocrine disrupter, bisphenol A (BPA). Surface-modified MSs were prepared by (i) post-synthesis surface modification of MSs using surface hydroxyl groups and organosilanes (m-MS) and by (ii) co-condensation of tetraethoxysilane and the corresponding organosilanes (d-MS). Infrared measurements indicated that organic groups mainly existed on the surface of m-MS, which resulted in a surface characterized by high hydrophobicity. Both organic groups and isolated hydroxyl groups existed on the surface of d-MS, resulting in both hydrophobicity and hydrophilicity on the surface. The amount of BPA adsorbed on surface-modified MSs per organic group was similar for m-MS and d-MS, however, the d-MS established equilibrium for BPA adsorption faster than m-MS, as measured by UV-vis spectra. A larger amount of BPA per surface area could be adsorbed on carbon materials than on the surface-modified MSs, however, the regeneration of carbon materials by washing could not be done easily. The surface-modified MSs retain adsorption capacity for BPA after several regeneration cycles, demonstrating that the surface-modified MSs are effective recyclable adsorbents of the endocrine disrupter, bisphenol A.

Adsorption↗
PubMed2005

Electrochemical synthesis of a polypyrrole thin film with supercritical carbon dioxide as a solvent.

A conductive polypyrrole (PPy) film was successfully synthesized in a homogeneous supercritical carbon dioxide (scCO2)/acetonitrile (AN) system. The occurrence of a homogeneous supercritical state was confirmed by observations of the phase behavior of the system through a high-pressure cell with a viewing window. The concentration of a supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAPF6), significantly changed the phase behavior of the scCO2/AN system. The polymerization rate of the film in that system decreased with further addition of CO2. This result suggested that the low viscosity of scCO2 did not play an important role in improving the growth rate of the PPy film. The low polymerization rate might have been due to the electron-transfer resistance arising from the low dielectric constant of scCO2/AN mixture. The roughness of the film prepared in the homogeneous scCO2/AN system was 1/10 that synthesized in AN itself as a solvent. The slow growth of film and the high diffusion rate of the monomer seemed to account for the smooth flat film formation.

Journal Article↗
PubMed2005

Highly stable gold(III) complex with a hydantoin ligand in alkaline media.

A novel gold(III) complex with a monodentate 5,5-dimethylhydantoin ligand, [Au(dmh)4]-, is square planar in geometry, inert and highly stable in alkaline solutions because of soft acid-base interactions, and electrochemically reduced near -0.3 V vs Ag/AgCl to give a gold(0) film with a high current efficiency.

Journal Article↗
PubMed2004

Micellar cobaltporphyrin nanorods in alcohols.

Cobalt(II) meso-tetrakis(4-hexadecylamidophenyl)porphyrin self-assembles in ethanol/1-propanol 2/1 (v/v) to form a rodlike micelle with nanoscale dimensions; the nanorod is a face-to-face aggregate having a hydrophobic corona around a polar core and is thus characterized as a reverse micelle.

Journal Article↗
PubMed2003

Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions.

Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.

Journal Article↗
PubMed2003

The first oxovanadium ring in [[O[double bond]V(salen)]2(mu-F)][VO(salen)][BF4].(CH2Cl2)x crystals.

The crystal structure of [{O=VV(salen)}2(mu-F)][VIVO(salen)][BF4].(CH2Cl2)x revealed a hollow cavity with a diameter of 5.3 A that penetrates through the crystal, and a remarkable cyclic chain of the [VO(salen)] unit, a motif that has never been fashioned from oxometal building blocks. These features endow the crystal with a molecular sievelike property for the rapid, reversible, and size-selective absorption of guest CH2Cl2 molecules.

Journal Article↗
PubMed2003

Coordination of BF(4)(-) to oxovanadium(V) complexes, evidenced by the redox potential of oxovanadium(IV/V) couples in CH(2)Cl(2).

The oxidation of oxovanadium(IV) complexes [LV(IV)O] (L = tetradentate Schiff-base ligands such as N,N'-ethylenebis(salicylideneaminate)(2-) (salen) and N,N'-2,2-dimethylpropylenebis(salicylideneaminate)(2-) (salpn)) to [LV(V)O](+), believed to be responsible for the voltammetric response near 0.6 V vs Ag/AgCl in CH(2)Cl(2) in the presence of tetrabutylammonium tetrafluoroborate as a supporting electrolyte, is in fact coupled to a homogeneous process where [LVO](+) coordinates BF(4)(-) to form a neutral complex formulated as [LVOBF(4)]. The formation constants for [VO(salen)BF(4)] and [VO(salpn)BF(4)] are evaluated to be K(salen)(-)(1) = 1.1 x 10(2) M(-)(1) and K(salpn)(-)(1) = 1.4 x 10 M(-)(1), respectively. Crystal structure of [VO(salen)BF(4)] reveals that one of the fluorine atoms in BF(4)(-) is so close to the vanadium(V) atom as to be practically bound in the solid state.

Journal Article↗
PubMed1999

Catalysis of the Electroreduction of O(2) to H(2)O by Vanadium-salen Complexes in Acidified Dichloromethane.

Addition of stoichiometric quantities of trifluoromethanesulfonic (triflic) acid to solutions of V(IV)O(salen) (H(2)salen = N,N '-ethylenebis(salicylideneamine)) in dichloromethane produces the &mgr;-oxo dinuclear vanadium(IV) complex [(salen)V(IV)OV(IV)(salen)](2+) ([V(IV)OV(IV)](2+)). Addition of significant excesses of triflic acid converts the dimer into [V(IV)(salen)](2+). In dichloromethane solutions containing 0.1 M tetrabutylammonium tetrafluoroborate, the [V(IV)OV(IV)](2+) complex undergoes disproportionation and dissociation reactions to produce a solution containing an equimolar mixture of V(IV)O(salen), [V(III)(salen)](+), and [V(IV)OV(V)](3+). The oxophilic [V(III)(salen)](+) complex reacts with O(2) to accomplish a four-electron reduction of O(2): 2[V(III)(salen)](+) + O(2) --> 2[V(V)O(salen)](+). These reactions can be exploited to carry out catalytic electroreductions of O(2) to H(2)O in acidified dichloromethane solutions of V(IV)O(salen) at unusually positive potentials.

Journal Article↗
PubMedDate not supplied

Liposomal surface-loading of water-soluble cationic iron(III) porphyrins as anticancer drugs.

A novel design of anticancer drug delivery system, based on an electrostatic binding of negatively charged liposomes and cationic metalloporphyrins under physiological conditions, is reported. A lack of cytotoxicity of the iron(III) porphyrin-loaded liposomes and an efficient generation of a toxic hydroxyl radical (OH*) from a superoxide anion radical (O2-*) through the iron(III)-catalyzed dismutation and the Fenton-like reaction allow for a targeted necrosis of tumor cells where the concentration of O2-* is locally increased as a result of the reduced activity of superoxide dismutase and catalase in these cells.

Animals↗