High Power Density of a Hydrogen Peroxide Fuel Cell Using Cobalt Chlorin Complex Supported on Carbon Nanotubes as a Noncorrosive Anode.

Hydrogen peroxide fuel cells (HPFCs) have attracted much attention due to their simple one-compartment structures and high availability under harsh conditions such as an anaerobic environment; however, catalysis improvement is strongly demanded for both anodes and cathodes in terms of activity and durability. Herein, we report the high catalytic activity of CoII chlorin [CoII(Ch)] for hydrogen peroxide (H2O2) oxidation with a low overpotential (0.21 V) compared to that of the CoII phthalocyanine and CoII porphyrin complexes, which have previously been reported as active anode catalysts. Linear sweep voltammograms and differential pulse voltammograms of the CoII complexes (CoIIL) and the corresponding ligands clearly showed that the CoIIIL species are the active species for H2O2 oxidation. Then, one-compartment HPFCs were constructed with CoII(Ch) supported on multiwalled carbon nanotubes (CNTs) as the anode together with FeII3[CoIII(CN)6]2 supported on CNTs as the cathode. The maximum power density of the HPFCs reached 151 µW cm-2 with an open circuit potential of 0.33 V when the coverage of CNT surfaces with CoII(Ch) exceeded ∼60% at the anode.

Selective Crystallization of Linkage Isomers, [RhIII(NCS)(SCN)5]3- and [RhIII(SCN)6]3-, to Investigate Structural Trans Influence and Thermal Stability.

Linkage isomers of homoleptic complexes, [RhIII(SCN)6]3- and [RhIII(NCS)(SCN)5]3-, formed in aqueous solution were successfully separated by employing methyltriphenylphosphonium (MePPh3+) and 1-ethylquinolinium (EtQu+) ions as countercations, respectively. The single-crystal X-ray analysis of (MePPh3)3[RhIII(SCN)6] (1) indicated that all of the SCN- ligands coordinate to the RhIII ion by S atoms with an octahedral symmetry, where the average bond length of Rh-S is 2.374(7) Å. On the other hand, the RhIII ion of (EtQu)3[RhIII(NCS)(SCN)5]·H2O (2) is coordinated by five S atoms and one N atom of the SCN- ligands with a C4v symmetry. Structural trans influence was observed in the shorter bond length of Rh-S at the trans position of Rh-N. The Rh-S bond length is 2.3398(13) Å significantly shorter than those of 1 by ca. 0.04 Å, although DFT calculations based on the crystal structures indicated that the effective bond order of Rh-N is higher than those of Rh-S. Thermal stability examination by thermogravimetric and differential thermal analyses (TG/DTA) and IR spectroscopy indicated that the linkage isomerization of [RhIII(SCN)6]3- to [RhIII(NCS)(SCN)5]3- proceeded after melting around 174 °C. These results clearly indicate that [RhIII(NCS)(SCN)5]3- is thermodynamically more stable than [RhIII(SCN)6]3- in solid states, although further linkage isomerization hardly occurs.

Synergistic Effect of FeII and MnII Ions in Cyano-Bridged Heterometallic Coordination Polymers on Catalytic Selectivity of Benzene Oxygenation to Phenol.

A cyano-bridged heterometallic coordination polymer with partial deficiencies of CN- ligands, [MnII(H2O)8/3]3/2[FeII(CN)5(NH3)], forms open metal sites both on MnII and FeII ions by liberation of monodentate ligands such as NH3 and H2O. [MnII(H2O)8/3]3/2[FeII(CN)5(NH3)] exhibits high catalytic activity and selectivity of benzene oxygenation to phenol in the presence of m-chloroperoxybenzoic acid as an oxidant. The postcatalytic spectroscopy of [MnII(H2O)8/3]3/2[FeII(CN)5(NH3)] and catalysis comparison with a physical mixture of [MnII(H2O)3]2[FeII(CN)6] and [Fe(H2O)3/2]4/3[Fe(CN)6], which has open metal sites on both MnII and Fe ions separately, indicated that the high activity resulted from high oxidation ability and phenol adsorption ability of FeII and MnII ions, respectively.

High quantum yield photochemical water oxidation using a water-soluble cobalt phthalocyanine as a homogenous catalyst.

We demonstrated high catalytic activity (TON = 670, TOFmax = 2.7 s-1) of a water-soluble cobalt phthalocyanine complex (CoPcTS, PcTS = phthalocyaninetetrasulfonate) for visible light-driven photochemical water oxidation and investigated its reaction mechanism by electrochemical and spectroscopic measurements.

Tuning Oxygen Reduction Catalysis of Dinuclear Cobalt Polypyridyl Complexes by the Bridging Structure.

The four-electron oxygen reduction reaction (4e--ORR) is the mainstay in chemical energy conversion. Elucidation of factors influencing the catalyst's reaction rate and selectivity is important in the development of more active catalysts of 4e--ORR. In this study, we investigated chemical and electrochemical 4e--ORR catalyzed by Co2(µ-O2) complexes bridged by xanthene (1) and anthracene (3) and by a Co2(OH)2 complex bridged by anthraquinone (2). In the chemical ORR using Fe(CpMe)2 as a reductant in acidic PhCN, we found that 1 showed the highest initial turnover frequency (TOFinit = 6.8 × 102 s-1) and selectivity for 4e--ORR (96%) in three complexes. The detailed kinetic analyses have revealed that the rate-determining steps (RDSs) in the catalytic cycles of 1-3 have the O2 addition to [CoII2(OH2)2]4+ as an intermediate in common. In the only case that complex 1 was used as a catalyst, kcat depended on proton concentration because the reaction rate of the O2 addition to [CoII2(OH2)2]4+ was so fast as compared to that of the concerted PCET process of 1. Through X-ray, Raman, and electrochemical analyses and stoichiometric reactions, we found the face-to-face structure of 1 characterized by a slightly flexible xanthene was advantageous in capturing O2 and stabilizing the Co2(µ-O2) structure, thus increasing both the reaction rate and selectivity for 4e--ORR.

Photochemical Water Oxidation Using a Doubly N-Confused Hexaphyrin Dinuclear Cobalt Complex.

A doubly N-confused hexaphyrin dinuclear cobalt complex (Co2DNCH) is revealed as an efficient water oxidation catalyst, outperforming the mononuclear cobalt porphyrin with the same aryl group as those in Co2DNCH. By photoirradiation of a water/acetone-d6 (9:1) mixture containing Co2DNCH, [RuII(bpy)3]2+, and S2O82- as the water oxidation catalyst, photosensitizer, and sacrificial electron acceptor, respectively, with visible light, O2 was obtained as the maximum with turnover number = 1200, turnover frequency = 3.9 s-1, and quantum yield = 0.30.

Highly stable chemisorption of dyes with pyridyl anchors over TiO2: application in dye-sensitized photoelectrochemical water reduction in aqueous media.

A polypyridyl ruthenium sensitizer possessing pyridyl anchors (Ru-py) forms much stronger chemical linkages to TiO2 surfaces compared to the conventional carboxylate and phosphonate ones. A highly stable dye-sensitized photoelectrochemical cell for water reduction is successfully demonstrated using this technique.

Improving the robustness of cobalt porphyrin water oxidation catalysts by chlorination of aryl groups.

The water oxidation (WO) activity of a chlorinated cobalt tetraphenylporphyrin (CoClPS), possessing Cl atoms on the 2,6-positions of the aryl groups, shows higher resistance to attack by singlet oxygen, in situ generated during photochemical WO using Ru(bpy)3(2+) and S2O8(2-) with the turnover frequency (TOF) and turnover number (TON) reaching 1.7 s(-1) and 836, respectively.

Photochemical Water Oxidation Catalyzed by a Water-Soluble Copper Phthalocyanine Complex.

Copper tetrasulfonatophthalocyanine (CuPcTS) is reported to serve as a catalyst for photochemical water oxidation via a radical coupling mechanism. Chloride greatly inhibits the water oxidation rate as a result of axial chloride binding to CuPcTS, preventing formation of the Cu oxyl or hydroxyl intermediate required for O-O bond formation.

Improving singlet oxygen resistance during photochemical water oxidation by cobalt porphyrin catalysts.

Enabling the production of solar fuels on a global scale through artificial photosynthesis requires the development of water oxidation catalysts with significantly improved stability. The stability of photosystems is often reduced owing to attack by singlet oxygen, which is produced during light harvesting. Here, we report photochemical water oxidation by CoFPS, a fluorinated Co-porphyrin designed to resist attack by singlet oxygen. CoFPS exhibits significantly improved stability relative to its non-fluorinated analogue, as shown by a large increase in turnover numbers. This increased stability results from resistance of CoFPS to attack by singlet oxygen, the formation of which was monitored in situ by using 9,10-diphenylanthracene as a chemical probe. Dynamic light scattering (DLS) confirms that CoFPS remains homogeneous, proving its stability during water oxidation catalysis.

Mechanism of water oxidation by non-heme iron catalysts when driven with sodium periodate.

Iron tris(2-methylpyridyl)amine (TPA) and iron 1-(bis(2-methylpyridyl)amino)-2-methyl-2-propanoate (BPyA) salts are characterized as water oxidation catalysts (WOCs) using sodium periodate. Under the conditions used, these complexes serve as homogeneous WOCs as demonstrated via kinetic analysis and dynamic light scattering (DLS). The Fe(BPyA) salt serves as both a mononuclear and dinuclear catalyst, with the mononuclear form showing higher catalytic activity. Based on the H/D kinetic isotope effect and pH dependence, the rate determining step (RDS) in water oxidation (WO) by Fe(BPyA) is nucleophilic attack by water during O-O bond formation. In contrast, Fe(TPA) shows complex kinetic behavior due to the formation of multiple oxidation states of the complex in solution, each of which exhibits catalytic activity for WO. The RDS in WO by Fe(TPA) follows an equilibrium established between monomeric and dimeric forms of the catalyst. Under acidic conditions formation of the monomer is favored, which leads to an increase in the WO rate.

Cobalt porphyrins as homogeneous catalysts for water oxidation.

Three water-soluble cobalt porphyrins have been investigated as water oxidation catalysts via photo-initiation using Ru(II)(bpy)3(2+)/Na2S2O8. The pH dependence of the turnover frequency revealed maximum activity at pH 11. Based on the second order dependence on catalyst concentration for the rate of water oxidation, we suggest a bimolecular radical coupling process as the rate determining step.

The physical ability of elderly female Japanese patients with cerebrovascular disease correlates with telomere length in their peripheral blood leukocytes.

BACKGROUND AND AIMS: The telomere length of peripheral blood leukocytes has been reported to be inversely correlated with many kinds of pathophysiological conditions. However, correlations between telomere length in peripheral blood leukocytes and patients' physical ability are not known. METHODS: To address this problem, the physical ability of patients with cerebrovascular disease admitted to the chronic disease ward of Kyushu University Hospital was assessed with the Barthel index (BI) and the telomere length of their peripheral blood leukocytes was determined. RESULTS AND CONCLUSIONS: Women exhibited a significant correlation between the Barthel score and the expression of long telomeres (>9.4 Kb), in contrast with men who revealed no such correlation. The physical ability of older women was positively correlated with the lengths of their somatic telomeres. Among the BI items, the scores of more difficult physical performances tended to correlate with the presence of terminal restriction fragments longer than 9.4 Kb.

The physical ability of Japanese female elderly with cerebrovascular disease correlates with the telomere length and subtelomeric methylation status in their peripheral blood leukocytes.

BACKGROUND: The telomere length and subtelomeric methylated status of peripheral blood leukocytes have been reported to be correlated with many kinds of pathophysiological conditions. However, the correlation between the telomeric parameters and patients' physical ability is not known. OBJECTIVE: This study aims to study how telomeric parameters, including telomere length and the subtelomeric methylation status of peripheral blood leukocytes, are associated with the physical inability of patients with cerebrovascular disease and its improvement by inpatient rehabilitation. METHODS: The physical ability of female patients with cerebrovascular disease admitted in the chronic disease ward of Kyushu University Hospital was assessed using the Barthel index, and the telomeric parameters in their peripheral blood leukocytes were determined by Southern blotting with methylation-sensitive and -insensitive isoschizomers. RESULTS: The patients revealed a significant correlation between Barthel score and the mean telomere length and expression of long telomeres (> 9.4 kb). Improvement of the Barthel index of patients during admission was correlated not to telomere length, but to subtelomeric hypermethylation of long telomeres. CONCLUSIONS: The physical ability of patients was positively correlated with the lengths of their somatic telomeres, and the recovery potential of physical ability was associated with the subtelomeric hypermethylated status stabilizing long telomeric structure.