Yoshio Hisaeda

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.

Electrochemical reactions mediated by vitamin B12 derivatives in organic solvents

Abstract Vitamin B 12 enzymes, involving the cobalt species as a catalytic center, mediate various isomerization reactions accompanied by carbon-skeleton rearrangements. In order to simulate the catalytic functions of vitamin B 12 as exerted in the hydrophobic active sites of enzymes concerned, we have been dealing with hydrophobic vitamin B 12 derivatives, which have ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B 12 . In this work, the carbon-skeleton rearrangements as mediated by hydrophobic vitamin B 12 derivatives were investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides with various electron-withdrawing groups were carried out, and the electrochemical carbon-skeleton rearrangements proceeded effectively via formation of anionic intermediates. These reactions can also be applied to the ring-expansion reactions. We have prepared a novel vitamin B 12 derivative, [Cob(II)7Phe(OBzl)]ClO 4 , having phenylalanine residues on the peripheral side chains. [Cob(II)7Phe(OBzl)]ClO 4 effectively catalyzed 1,2-migration of the carboxylic ester in 1-bromo-2,2-bis(ethoxycarbonyl)propane at −1.0 V vs. SCE under irradiation conditions. A strapped hydrophobic vitamin B 12 was prepared in order to change the enantioselectivity, and the controlled-potential electrolysis of a racemic alkyl halide was carried out in the presence of vitamin B 12 derivatives. Product analyses and computational calculations suggested that the stability of alkylated complexes dominated the enantioselectivity of reduction products.

The electroreduction of carbon dioxide by macrocyclic cobalt complexes chemically modified on a glassy carbon electrode

Abstract Various macrocyclic cobalt complexes were chemically bonded to a glassy carbon (GC) electrode, on which CO 2 , electroreduction was carried out to give CO in aqueous phosphate buffer solution of pH 6.3. The macrocyclic cobalt complexes were naphthalocyanato cobalt(II), phthalocyanato cobalt(II), dibromo(11-hydroxyimino-4,10-dipropyl-5,9-diazatrideca-4,9-diea-3-one oximato) cobalt(III) (denoted as CoDO), two kinds of hydrophobic vitamin B 12 s (heptamethyl cobyrinate perchlorate and heptapropyl cobyrinate perchlorate 5,10,15,20-tetraphenylporphyrinato cobalt(II), and 5,10,15,20-tetrakis (4-methoxyphenyl)porphyrinato cobalt(II). Their redox potentials Co(I)/Co(II) are in the above order from positive to negative potentials in a 0.05 M TBAP DMSO solution, being between -0.23 and -1.0 V (SCE). These complexes were chemically bonded to GC through -CONH-pyridine which locates perpendicularly to a planar semi-planar complex structure, where the N of the pyridine forms a coordinate bond with the Co atom of the above complexes as a fift ligand. The catalytic activity for hydrogen evolution in aqueous solution was observed to be high on Co naphthalocyanine and C phthalocyanine modified GC electrodes; the latter gave H 2 evolution at the most positive potentials among the Co complexes employee. When the lower potential limit in cyclic voltammetry became less than the hydrogen evolution potential, in the reverse positive-going sweep, and anodic lump current was oberved at -0.35 ∼ -0.78 V, which is assigned to a cobalt hydride oxidation process; the hydrid is suggested to form when hydrogen evolution takes place, and the hump disappeared after the introduction of CO 2 into the solution, was observed that the Co complex chemically bonded on GC can give CO from CO 2 only at relatively low overvoltages, except for CoDO which was not able to reduce CO 2 ; phthalocyanato cobalt(II) gave CO at E = − 1.0V (0.26 V as overvoltage) at 20% current efficiency. The highest CO current efficiency was observed in the case of tetraphenyl-porphyrinato cobalt(II) chemically modified GC.

Chiral recognition and chiral sensing using zinc porphyrin dimers

Abstract The chiral zinc porphyrin dimer linked by the ( S )-NMe 2 or ( R )-2,2′-dimethoxy-1,1′-binaphthyl tightly binds diamines via a zinc–nitrogen coordinated ditopic interaction. In particular, the zinc porphyrin displays excellent enantioselectivity towards Lys. The D / L selectivity is determined to be 11–12 for the lysine derivatives. The achiral zinc porphyrin dimers linked by biphenyl unit exhibit a significantly induced CD in the Soret region in the presence of chiral diamines such as lysine amides and cystine diesters, indicating that the chirality of the amino acid derivatives can be monitored upon the complexation with the achiral zinc porphyrin dimer. These results conclude that the zinc porphyrin dimers linked by rigid spacers may be good receptors to discriminate two enantiomers or monitor the absolute configuration of a diamine.

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.

Meso-Unsubstituted Iron Corrole in Hemoproteins: Remarkable Differences in Effects on Peroxidase Activities between Myoglobin and Horseradish Peroxidase

Myoglobin (Mb) and horseradish peroxidase (HRP) were both reconstituted with a meso-unsubstituted iron corrole and their electronic configurations and peroxidase activities were investigated. The appearance of the 540 nm band upon incorporation of the iron corrole into apoMb indicates axial coordination by the proximal histidine imidazole in the Mb heme pocket. Based on (1)H NMR measurements using the Evans method, the total magnetic susceptibility of the iron corrole reconstituted Mb was evaluated to be S = 3/2. In contrast, although a band does not appear in the vicinity of 540 nm during reconstitution of the iron corrole into the matrix of HRP, a spectrum similar to that of the iron corrole reconstituted Mb is observed upon the addition of dithionite. This observation suggests that the oxidation state of the corrole iron in the reconstituted HRP can be assigned as +4. The catalytic activities of both proteins toward guaiacol oxidation are quite different; the iron corrole reconstituted HRP decelerates H(2)O(2)-dependent oxidation of guaiacol, while the same reaction catalyzed by iron corrole reconstituted Mb has the opposite effect and accelerates the reaction. This finding can be attributed to the difference in the oxidation states of the corrole iron when these proteins are in the resting state.

Multicomponent molecular puzzles for photofunction design: Emission color variation in lewis acid-base pair crystals coupled with guest-to-host charge transfer excitation

Simple yet ubiquitous multimolecular assembly systems with color-tunable emissions are realized by cooperative electron donor-acceptor interactions, such as the boron-nitrogen (B-N) dative bond as a Lewis acid-base pair and charge transfer (CT) interactions. These are ternary-component systems consisting of a naphthalenediimide derivative (NDI), tris(pentafluorophenyl)borane (TPFB), and aromatic molecules (guest) with an NDI:TPFB:guest ratio of 1:2:2. The crystal shows guest-dependent color-tunable emissions such as deep blue to orange when a guest molecule of benzene is replaced with other π-conjugated systems. A good correlation between the emission wavelength and ionization potential of the guest and electronic structure calculations indicated that the emission is due to the CT transition from the guest to the NDI. The present study suggests that a rational solution of multcomponent molecular puzzles would be useful for obtaining novel photofunctional solid-state systems.

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.