Hisashi Shimakoshi

Kinetic analysis of superoxide anion radical-scavenging and hydroxyl radical-scavenging activities of platinum nanoparticles

There are few reports on the physiological effects of metal nanoparticles (nps), especially with respect to their functions as scavengers for superoxide anion radical (O2(.-)) and hydroxyl radical (.OH). We tried to detect the scavenging activity of Pt nps using a hypoxanthine-xanthine oxidase system for O2(.-) and using a Fenton and a UV/H2O2 system for .OH. Electron spin resonance analysis revealed that 2 nm particle size Pt nps have the ability to scavenge O2(.-) and .OH. The calculated rate constant for the O2(.-)-scavenging reaction was 5.03 +/- 0.03 x 10(7) M (-1) s (-1). However, the analysis of the Fenton and UV/H 2O 2 system in the presence of Pt nps suggested that the .OH-scavenging reaction cannot be determined in both systems. Among particle sizes tested from 1 to 5 nm, 1 nm Pt nps showed the highest O2(.-)-scavenging ability. Almost no cytotoxicity was observed even after adherent cells (TIG-1, HeLa, HepG2, WI-38, and MRC-5) were exposed to Pt nps at concentrations as high as 50 mg/L. Pt nps scavenged intrinsically generated reactive oxygen species (ROS) in HeLa cells. Additionally, Pt nps significantly reduced the levels of intracellular O2(.-) generated by UVA irradiation and subsequently protected HeLa cells from ROS damage-induced cell death. These findings suggest that Pt nps may be a new type of antioxidant capable of circumventing the paradoxical effects of conventional antioxidants.

First example of a rigid (µ-oxo-di-µ-acetato) diiron(III) complex with 1,2-bis[2-di(2-pyridyl)methyl-6-pyridyl]ethane; its efficient catalysis for functionalization of alkanes

The µ-oxo-di-µ-acetatodiiron(III) complex [Fe2(hexpy)(O)-(OCOMe)2][ClO4]2{hexpy = 1,2-bis[2-di(2-pyridyl)-methyl-6-pyridyl]ethane} efficiently catalyses the oxygenation of cyclohexane, methylcyclohexane and adamantane in the presence of m-choloroperbenzoic acid.

New macrocyclic ligands having discrete metal binding sites

Abstract New macrocyclic dinucleating ligands have been easily synthesized by Schiff-base condensation reaction with the appropriate aldehyde and amine using the boric ion template method. The ligands have two N2O2 metal-binding sites which are doubly linked to each other with methylene spacers. The ligands chelate with Co2+, Cu2+ and Ni2+ to form dimetallic compounds in high yields.

Green molecular transformation by a B12-TiO2 hybrid catalyst as an alternative to tributyltin hydride

The B(12)-TiO(2) hybrid catalyst was effectively used for the radical reactions, such as 1,2-migrations of phenyl groups and acyl groups under irradiation by UV light, and the selectivity of the reaction was controlled by the solvent system.

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.

Photophysical and photosensitizing properties of brominated porphycenes.

A heavy atom, bromine, was directly substituted into the porphycene macrocycle to promote intersystem crossing by way of spin-orbit coupling. The singlet oxygen production ability of the porphycene is dramatically enhanced, and the highest value of 0.95 for the quantum yield of singlet oxygen generation (PhiDelta) was obtained for the dibrominated porphycene by visible light excitation.

Electroorganic syntheses of macrocyclic lactones mediated by vitamin B12 model complexes: Part 17. Hydrophobic vitamin B12☆

Abstract The electrolyses of bromoalkyl acrylates were carried out in N,N-dimethylformamide in the presence of a catalytic amount of heptamethyl cobyrinate perchlorate under various reaction conditions. A large-membered cyclic lactone was obtained in a moderate yield. A photo-sensitive intermediate having a cobalt–carbon bond formed during the electrolysis has been characterized using electronic and electrospray ionization mass spectroscopies in the dark. The formation of a cyclic lactone was inhibited by the addition of the spin-trapping reagent, α-phenyl N-(t-butyl)nitrone. Based on various spectroscopic results, the electrolysis proceeds as follows: the Co(II) complex as a catalyst is electrochemically reduced to the Co(I) species, and the corresponding alkylated complex is generated by the reaction of the supernucleophilic Co(I) species with a bromoalkyl acrylate. The alkylated complex is subsequently decomposed to form the substrate radical, and the intramolecular addition of the radical affords the cyclic product. During the catalytic reaction, the cobalt complex repeatedly acts as a mediator.

Syntheses of new water-soluble dicobalt complexes having two cobaltcarbon bonds and their ability for DNA cleavage

Abstract One-pot syntheses of new water-soluble dicobalt complexes having two cobaltcarbon bonds are reported. The complexes were characterized by 1 H NMR and UV–vis spectroscopies as well as ESI-MS. These complexes were photosensitive, and photo-cleavage of the cobaltcarbon bonds upon irradiation with visible light produced methyl radicals which were detected by ESR spin-trapping techniques. The dicobalt complexes exhibited high ability for DNA cleavage in comparison with that for the corresponding monocobalt complex.

Oxygen-Controlled Catalysis by Vitamin B12-TiO2: Formation of Esters and Amides from Trichlorinated Organic Compounds by Photoirradiation

An oxygen switch in catalysis of the cobalamin derivative (B12 )-TiO2 hybrid catalyst for the dechlorination of trichlorinated organic compounds has been developed. The covalently bound B12 on the TiO2 surface transformed trichlorinated organic compounds into an ester and amide by UV light irradiation under mild conditions (in air at room temperature), while dichlorostilbenes (E and Z forms) were formed in nitrogen from benzotrichloride. A benzoyl chloride was formed as an intermediate of the ester and amide, which was detected by GC-MS. The substrate scope of the synthetic strategy is demonstrated with a range of various trichlorinated organic compounds. A photo-duet reaction utilizing the hole and conduction band electron of TiO2 in B12 -TiO2 for the amide formation was also developed.

Electron Transfer in the Supramolecular Donor-Acceptor Dyad of Zinc Porphycene

The electron transfer processes of Zn octaethylporphycene (ZnPcn), a structural isomer of Zn octaethylporphyrin, have been investigated mainly using transient absorption spectroscopy. To form a supramolecular donor-acceptor dyad, imide compounds bearing a pyridine group at the N position of the imides have been used as an acceptor. The N atom of the pyridine ring can coordinate to the central Zn ion of ZnPcn. Formation of a supramolecular donor-acceptor dyad, that is, pentacoordinated ZnPcn, was confirmed by steady-state absorption spectroscopy using toluene as a solvent. Charge separation upon excitation of ZnPcn was indicated by efficient fluorescence quenching, especially when pyromellitic diimide was used as the acceptor. Electron transfer processes were confirmed by subpicosecond transient absorption spectroscopy, in which generation of a radical anion of the acceptor and a radical cation of ZnPcn, which was identified by means of gamma-ray radiolysis, was confirmed. It became clear that the charge separation rate was smaller than that of the corresponding supramolecular dyads of Zn tetraphenylporphyrin and Zn octaethylporphyrin despite a similar driving force. This observation indicates a larger internal reorganization energy and a smaller coupling element of the ZnPcn dyad.