Language：English   Publisher：RSC Advances  

CH4 conversion is one of the most challenging chemical reactions due to its inertness in terms of physical and chemical properties. We have achieved photo-induced C-H bond breaking of CH4 and successive C-O bond formation to form CH3OH concomitant with HCHO by an organometallic Ru complex with O2

DOI： 10.1039/d2ra01772e

Web of Science

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

Repository Public URL： https://hdl.handle.net/2324/7160910

Language：English   Publishing type：Research paper (scientific journal)  

Publisher：Dalton Transactions  

Hydrogen fuel is a promising alternative to fossil fuel. Therefore, efficient hydrogen production is crucial to elucidate the distinctive reactivities of metal hydride species, the intermediates formed during hydrogen activation/evolution in the presence of organometallic catalysts. This study uses density functional theory (DFT) to investigate the isomerizations and reactivities of three nickel-iron (NiFe) hydride isomers synthesized by mimicking the active center of NiFe hydrogenase. Hydride transfer within these complexes, rather than a chemical reaction between the complexes, converts the three hydrides internally. Their reactivities, including their electron-transfer, hydride-transfer and proton-transfer reactions, are investigated. The bridging hydride complex exhibits a higher energy level for the highest occupied molecular orbital (HOMO) than the terminal hydride during the electron-transfer reaction. This energy level indicates that the bridging hydride is more easily oxidized and is more susceptible to electron transfer than the terminal hydride. Regarding the hydride-transfer reaction between the NiFe hydride complex and methylene blue, the terminal hydrides exhibit larger hydricity and lower reaction barriers than the bridging hydride complexes. The results of energy decomposition analysis indicate that the structural deformation energy of the terminal hydride in the transition state is smaller than that of the bridging hydride complex, which lowers the reaction barrier of hydride transfer in the terminal hydride. To produce hydrogen, the rate-determining step is represented by the protonation of the hydride, and the terminal hydrides are thermodynamically and kinetically superior to the bridging ones. The differences in the reactivities of the hydride isomers ensure the precise control of hydrogen, and the theoretical calculations can be applied to design catalysts for hydrogen activation/production.

DOI： 10.1039/d1dt03582g

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d1cc01611c

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.organomet.0c00565

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0cc04789a

Language：English   Publishing type：Research paper (scientific journal)  

水素の合成や分解を担う３種類の天然ヒドロゲナーゼ酵素の構造をヒントに１つの新しい触媒を開発した。今回開発した触媒は、同じ分子式で構造だけが異なる３種類の異性体によって、３種類のヒドロゲナーゼ酵素のように（i）燃料電池の水素電極の触媒（ii）水素製造の触媒（iii）化学工業の水素化の触媒として働くことを発見した。本研究成果は、これまで不明であったヒドロゲナーゼ酵素の触媒反応と触媒の分子構造との関係を解き明かすことで、次世代のエネルギー源である水素を効率よく利用する道を開いた。

DOI： 10.1126/sciadv.aaz8181

Language：English   Publishing type：Research paper (scientific journal)  

One of the challenges in utilizing hydrogen gas (H₂) as a sustainable fossil fuel alternative is the inhibition of H₂ oxidation by carbon monoxide (CO), which is involved in the industrial production of H₂ sources. To solve this problem, a catalyst that selectively oxidizes either CO or H₂ or one that co-oxidizes H₂ and CO is needed. Recently, a NiIr catalyst [Ni^IICl(X)Ir^IIICl(Ε⁵-C₅Me₅)], (X = N,N′-dimethyl-3,7-diazanonane-1,9-dithiolate), which efficiently and selectively oxidizes either H₂ or CO depending on the pH, has been developed (Angew. Chem. Int. Ed. 2017, 56, 9723-9726). In the present work, density functional theory (DFT) calculations are employed to elucidate the pH-dependent reaction mechanisms of H₂ and CO oxidation catalyzed by this NiIr catalyst. During H₂ oxidation, our calculations suggest that dihydrogen binds to the Ir center and generates an Ir(III)-dihydrogen complex, followed by subsequent isomerization to an Ir(V)-dihydride species. Then, a proton is abstracted by a buffer base, CH₃COO^-, resulting in the formation of a hydride complex. The catalytic cycle completes with electron transfer from the hydride complex to a protonated 2,6-dichlorobenzeneindophenol (DCIP) and a proton transfer from the oxidized hydride complex to a buffer base. The CO oxidation mechanism involves three distinct steps, i.e., (1) formation of a metal carbonyl complex, (2) formation of a metallocarboxylic acid, and (3) conversion of the metallocarboxylic acid to a hydride complex. The formation of the metallocarboxylic acid involves nucleophilic attack of OH^- to the carbonyl-C followed by a large structural change with concomitant cleavage of the Ir-S bond and rotation of the COOH group along the NiIr axis. During the conversion of the metallocarboxylic acid to the hydride complex, intramolecular proton transfer followed by removal of CO₂ leads to the formation of the hydride complexes. In addition, the barrier heights for the binding of small molecules (H₂, OH^-, H₂O, and CO) to Ir were calculated, and the results indicated that dissociation from Ir is a faster process than the binding of H₂O and H₂. These calculations indicate that H₂ oxidation is inhibited by CO and OH^- and thus prefers acidic conditions. In contrast, the CO oxidation reactions occur more favorably under basic conditions, as the formation of the metallocarboxylic acid involves OH^- attack to a carbonyl-C and the binding of OH^- to Ni largely stabilizes the triplet spin state of the complex. Taken together, these calculations provide a rationale for the experimentally observed pH-dependent, selective oxidations of H₂ and CO.

DOI： 10.1021/acs.inorgchem.9b02400

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.inorgchem.9b02704

Language：English   Publishing type：Research paper (scientific journal)  

While hydrogenase and photosystem II enzymes are known to oxidize H₂ and H₂O, respectively, a recently reported iridium aqua complex [Ir^III(η⁵-C₅Me₅){bpy(COOH)₂}(H₂O)]²⁺ is able to oxidize both of the molecules and generate energies as in the fuel and solar cells (Ogo et al. ChemCatChem 2017, 9, 4024-4028). To understand the mechanism behind such an interesting bifunctional catalyst, in the present study, we perform density functional theory (DFT) calculations on the dual catalytic cycle of H₂ and H₂O oxidations by the iridium aqua complex. In the H₂ oxidation, we found that the H-H bond is easily cleaved in a heterolytic fashion, and the resultant iridium hydride complex is significantly stabilized by the presence of H₂O molecules, due to dihydrogen bond. The rate-determining step of this reaction is found to be the H₂O → H₂ ligand substitution with an activation energy of 10.7 kcal/mol. In the H₂O oxidation, an iridium oxo complex originating from an oxidation of the iridium aqua complex forms a hydroperoxide complex, where an O-O bond is formed with an activation energy of 21.0 kcal/mol. Such a relatively low activation barrier is possible only when at least two H₂O molecules are present in the reaction, allowing the water nucleophilic attack (WNA) mechanism to take place. The present study suggests and discusses in detail six reaction steps required for the dual catalytic cycle to complete.

DOI： 10.1021/acs.inorgchem.9b00307

Language：English   Publishing type：Research paper (scientific journal)  

水素を酸化する酵素「ヒドロゲナーゼ」と水を酸化する酵素「光化学系II」の機能を複合した単一分子触媒を開発し、固体高分子形燃料電池の電極触媒として応用したところ、水素と水を両方燃料にできる電池の作製に成功した。均一系触媒と不均一系触媒の両方の性質を併せ持つ電極触媒の反応メカニズムの解明は極めて困難であるため、密度汎関数理論により、その反応メカニズムの詳細を明らかにした。

DOI： 10.1021/acs.inorgchem.9b00307

Language：English   Publishing type：Research paper (scientific journal)  

The homogeneous catalytic reduction of a polyoxometalate (POM) by hydrogen gas in aqueous media was investigated for the first time by using a [NiRu] hydrogenase model complex (I) under very mild conditions. By bubbling hydrogen gas into the buffer solution containing I and the Dawson-type POM (II_ox), the color of the solution turned from pale yellow to dark blue, suggesting the reduction of II_ox. The catalytic and kinetic studies revealed that I acted as an efficient catalyst to yield one-electron-reduced Dawson-type POM (II_red) with a low energy barrier for activating dihydrogen and reducing II_oxvia a hydride complex of I. The process for the one-electron reduction of II_ox was confirmed by UV-vis spectroscopy, controlled potential electrolysis, and X-ray photoelectron spectroscopy. POM II_red could stably store protons and electrons and release them by addition of oxidants, demonstrating that POMs acted as redox active mediators for transporting protons and electrons from hydrogen gas to acceptors. The recycle study showed that II_ox and II_red could be reduced and oxidized by hydrogen and oxygen gases, respectively, at least five times with >99% yield of reduced species, showing a durable system for extracting protons and electrons from hydrogen gas.

DOI： 10.1039/c9ra04396a

Language：English   Publishing type：Research paper (scientific journal)  

The development of hydrogen fuel cells is greatly hindered by the unwanted generation of H₂O₂ at the cathode. A non-Pt cathode catalyst is now shown to be capable of simultaneously reducing both O₂ and H₂O₂, thus rendering H₂O₂ a useful part of the feed stream. The applicability of this unique catalyst is demonstrated by employing it in a fuel cell running on H₂/CO and O₂/H₂O₂.

DOI： 10.1002/anie.201810270

Language：English   Publishing type：Research paper (scientific journal)  

Oxidative damage of DNA by reactive oxygen species (ROS) is responsible for aging and cancer. Although many studies of DNA damage by ROS have been conducted, there have been no reports of the oxidation of RNA components, such as guanosine monophosphate, by metal-based species in water. Here, we report the first case of oxidation of guanosine monophosphate to 8-oxoguanosine monophosphate by a metal-based oxygen bound species, derived from O
₂
and in water.

DOI： 10.1002/asia.201801267

Language：English   Publishing type：Research paper (scientific journal)  

We report the reactivity of a new Mn^I(cyclam) complex (cyclam: 1,4,8,11-tetraazacyclotetradecane) toward O₂ and H₂O as a model for the photoinhibited species of oxygen-evolving complex (OEC). The reactivity varies according to the number of CO ligands. A Mn^I dicarbonyl complex, [Mn^I(cyclam)(CO)₂]⁺ reacts with O₂, but not with H₂O, to form a bis(μ-oxo)Mn₂^III,IV complex, though a Mn^I tricarbonyl complex, [Mn^I(cyclam)(CO)₃]⁺ does not react with either O₂ or H₂O. Newly synthesized Mn^I(cyclam) dicarbonyl complex was characterized by ESI mass spectrometry, UVvis absorption spectroscopy, IR spectroscopy, and X-ray analysis.

DOI： 10.1246/cl.170869

Language：English   Publishing type：Research paper (scientific journal)  

We report the mechanistic investigation of catalytic H₂ evolution from formic acid in water using a formate-bridged dinuclear Ru complex as a formate hydrogen lyase model. The mechanistic study is based on isotope-labeling experiments involving hydrogen isotope exchange reaction.

DOI： 10.1080/14686996.2017.1379857

Language：English   Publishing type：Research paper (scientific journal)  

本論文では、燃料電池と太陽電池を融合する同一触媒の開発について報告した。次世代の電池として、燃料電池と太陽電池はこれまで別々に開発されてきたが、本研究では、「自然界の水素酵素と光合成の機能を融合した新しい触媒」を開発に成功した。この触媒を用いることで、「水素をエネルギー源として燃料電池が、水と光をエネルギー源として太陽電池が駆動する」ことを見出した。本研究成果はエネルギー研究の分野において格段の発展と波及効果をもたらす可能性が十分に期待できる。

DOI： 10.1002/cctc.201700995

Language：English   Publishing type：Research paper (scientific journal)  

We present a mechanistic investigation for the activation of H₂ and O₂, induced by a simple ligand effect within [NiFe] models for O₂-tolerant [NiFe]hydrogenase. Kinetic study reveals Michaelis-Menten type saturation behaviors for both H₂ and O₂ activation, which is the same behavior as that found in O₂-tolerant [NiFe]hydrogenase. Such saturation behavior is caused by H₂ complexation followed by heterolytic cleavage of H₂ by an outer-sphere base, resulting in the formation of a hydride species showing hydridic character.

DOI： 10.1021/acs.organomet.7b00471

Language：English   Publishing type：Research paper (scientific journal)  

Taking advantage of the outstanding oxygen-sensitive luminescence properties of the previously synthesised Tb(iii) complex [{(^MeMeArO)₃tacn}Ln^III(THF)] (1^Tb, Ln = Tb), herein, we have prepared an oxygen sensor based on 1^Tb embedded in polystyrene film (1^Tb/PS) and found that 1^Tb/PS shows the highest sensitivity (I₀/I₁₀₀ = 14.9) and the fastest response (response/recovery time = 1.9 s/2.9 s), among the lanthanide(iii)-based oxygen sensors with f-f emission. Moreover, we have prepared the lanthanide(iii)-based colorimetric luminescent oxygen sensor (1^TbSm/PS) with green-yellow-red responses, by using 1^Tb and a newly synthesised oxygen-insensitive Sm(iii) complex (1^Sm, Ln = Sm; Φ = 0.010 and τ = 12.2 μs).

DOI： 10.1039/c7dt01388d

Language：English   Publishing type：Research paper (scientific journal)  

The ability to catalyze the oxidation of both H₂ and CO in one reaction pot would be a major boon to hydrogen technology since CO is a consistent contaminant of H₂ supplies. Here, we report just such a catalyst, with the ability to catalyze the oxidation of either or both H₂ and CO, based on the pH value. This catalyst is based on a NiIr core that mimics the chemical function of [NiFe]hydrogenase in acidic media (pH 4–7) and carbon monoxide dehydrogenase in basic media (pH 7–10). We have applied this catalyst in a demonstration fuel cell using H₂, CO, and H₂/CO (1/1) feeds as fuels for oxidation at the anode. The power density of the fuel cell depends on the pH value in the media of the fuel cell and shows a similar pH dependence in a flask. We have isolated and characterized all intermediates in our proposed catalytic cycles.

DOI： 10.1002/anie.201704864

Language：English   Publishing type：Research paper (scientific journal)  

Pyruvate ferredoxin oxidoreductase from Citrobacter sp. S-77 (PFOR_S77) was purified in order to develop a method for acetyl-CoA production. Although the purified PFOR_S77showed high O₂-sensitivity, the activity could be remarkably stabilized in anaerobic conditions. PFOR_S77was effectively immobilized on ceramic hydroxyapatite (PFOR_S77-HA) with an efficiency of more than 96%, however, after encapsulation of PFOR_S77-HA in alginate, the rate of catalytic acetyl-CoA production was highly reduced to 36% when compared to that of the free enzyme. However, the operational stability of the PFOR_S77-HA in alginate hydrogels was remarkable, retaining over 68% initial activity even after ten repeated cycles. The results suggested that the PFOR_S77-HA hydrogels have a high potential for biotechnological application.

DOI： 10.1016/j.biortech.2016.12.051

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.160909

Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://doi.org/10.1016/j.biortech.2016.12.051

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.inorgchem.6b00800

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C6DT01655C

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C6DT01057A

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C6DT01303A

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.150988

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C6CC00059B

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.151029

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.150988

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.150935

Language：English   Publishing type：Research paper (scientific journal)  

We report the first example of a μ-η¹:η¹-N₂ dinuclear Ru^II complex with a polyamine ligand and elucidate the structure by means of X-ray analysis. The N=N stretching vibration has been observed at 1994 cm^-1 by Raman spectroscopy, which is the lowest value of all the known N₂-coordinated RuII complexes. This low value strongly suggests the N=N bond is primed for activation.

DOI： 10.1246/cl.151004

Language：English   Publishing type：Research paper (scientific journal)  

We report the first example of a wholly inorganic mimic of a part of the FeMoco active centre of nitrogenases. We detail the synthesis, characterisation and reactivity of two related, transient hydride-containing inorganic clusters, a dihydride complex and a vinyl monohydride complex, which bear the [Fe₂MoOS₃] portion of FeMoco. The dihydride complex is capable of reducing acetylene to ethylene via the vinyl monohydride complex. In the reaction cycle, a transient low-valent complex was generated by the reductive elimination of H₂ or ethylene from dihydride or vinyl monohydride complexes, respectively.

DOI： 10.1039/c6dt01655c

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a gadolinium(iii) complex that shows blue phosphorescence in the crystalline state at room temperature under air atmosphere; color of the crystals can be changed to pale-green from blue by doping of 1-naphthol.

DOI： 10.1039/c6dt01303a

Language：English   Publishing type：Research paper (scientific journal)  

Dioxygen-tolerant [NiFe] hydrogenases catalyze not only the conversion of H₂ into 2 H⁺ and 2 e^- but also the reduction of O₂ to H₂O. Chemists have sought to mimic such bifunctional catalysts with structurally simpler compounds to facilitate analysis and improvement. Herein, we report a new [NiFe]-based catalyst for O₂ reduction via an O₂ adduct. Structural investigations reveal the first example of a side-on iron(IV) peroxo complex. Dioxygen-tolerant [NiFe] hydrogenases catalyze not only the conversion of H₂ into 2 H⁺ and 2 e^- but also the reduction of O₂ to H₂O. A new [NiFe]-based complex is a synthetic mimic of such hydrogenases and catalyzes O₂ reduction via an O₂ adduct, which was shown to be the first example of a side-on iron(IV) peroxo complex.

DOI： 10.1002/anie.201507022

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents the first dysprosium(iii) complex, [{(^MeMeArO)₃tacn}Dy^III(THF)] (1^Dy), that shows oxygen-sensitive luminescence. The synthesis, structure and oxygen-sensitive luminescence properties of 1^Dy are reported (Φ = 0.050 and τ = 17.7 μs under N₂, Φ = 0.011 and τ = 4.1 μs under O₂ and K_SV = 305 M^-1 in THF; K_SV = 0.0077%^-1 in polystyrene film). The oxygen sensitive mechanism of 1^Dy is discussed based on the photophysical properties of the corresponding gadolinium(iii) complex, [{(^MeMeArO)₃tacn}Gd^III(THF)].

DOI： 10.1039/c6dt01057a

Language：English   Publishing type：Research paper (scientific journal)  

Rod-like millimetre-size crystals of a newly prepared rhodium dithionite complex with n-pentyl moieties bend upon photoirradiation and return to the initial shape upon heating; the roles of the flexible n-pentyl moieties as well as the photoreactive dithionite unit (μ-O₂SSO₂) are disclosed by single crystal X-ray diffraction.

DOI： 10.1039/c6cc00059b

Language：English   Publishing type：Research paper (scientific journal)  

We report the synthesis and characterization of a μ-hydroxo NiRu complex as a model for the active site of (Ni-SIr)_I of [NiFe]hydrogenase. This is the first example of the (Ni-SIr)_I model with a bridging hydroxo ligand between dimetal centers and an available coordination site on Ni center cis to the bridging hydroxo ligand. We have determined the structure of the (Ni-SIr)_I model complex by X-ray analysis and reported reversible switching between the catalytically inactive (Ni-SIr)_I and a catalytically active (Ni-SIr)_II models.

DOI： 10.1016/j.jorganchem.2014.09.025

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201507022.

Language：English   Publishing type：Research paper (scientific journal)  

We report an acid-stable Si oxide-doped Ir oxide film (IrSi oxide film), made by metal organic chemical vapour deposition (MOCVD) of an Ir^V complex for electrochemical water-oxidation. This is a successful improvement of catalytic ability and stability depending upon the pH of Ir oxide by doping of Si oxide. The turnover frequency (TOF) of the electrochemical water-oxidation by the IrSi oxide film is the highest of any Si oxide-doped Ir oxide materials and higher even than that of Ir oxide in acidic media.

DOI： 10.1039/c5cc04286k

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C5CC04286K

Language：English   Publishing type：Research paper (scientific journal)  

DOI： org/10.1246/cl.150155

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a 1,4,7,10-teraazacyclododecane-based tetrakis-phenol as a protonated ligand precursor and its oxygen-sensitive luminescent terbium(iii) complex with an extendable phenol pendant arm (Φ = 0.91 under N₂, Φ = 0.031 under air), in which the potentially N₄O₄-octadentate ligand unprecedentedly coordinates to the Tb³⁺ ion in a N₄O₃-heptadentate fashion.

DOI： 10.1039/c5dt00816f

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C4CC07717B

Language：English   Publishing type：Research paper (scientific journal)  

DOI： org/10.1246/cl.150468

Language：English   Publishing type：Research paper (scientific journal)  

We report the first example of a Ni⁰ precursor that provides a contamination-free (<1%) nickel film by metal-organic chemical vapor deposition (MOCVD) using N₂ as the carrier gas. The structure and physical properties of the Ni₀ precursor and subsequent film are described.

DOI： 10.1246/cl.150155

Language：English   Publishing type：Research paper (scientific journal)  

Here, we report the first Fe-based model for metabolism linking between the dioxygen reduction of respiration and the water oxidation of photosynthesis. The reaction mechanism was investigated by X-ray analysis, UV-vis spectroscopy, and mass spectrometry.

DOI： 10.1246/cl.150468

Language：English   Publishing type：Research paper (scientific journal)  

We report the decomposition of formic acid to hydrogen and carbon dioxide, catalysed by a NiRu complex originally developed as a [NiFe]hydrogenase model. This is the first example of H₂ evolution, catalysed by a [NiFe]hydrogenase model, which does not require additional energy.

DOI： 10.1039/c4cc05911e

Language：English   Publishing type：Research paper (scientific journal)  

This communication presents a new terbium(III) complex that shows the highest luminescence quantum yield among the oxygen-sensitive lanthanide complexes (Φ = 0.91 under N₂, Φ = 0.054 under air).

DOI： 10.1039/c4cc07717b

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/C4CC07717B

Language：English   Publishing type：Research paper (scientific journal)  

Herein, we report the first crystal structure of a monomeric p-semiquinonato d-block complex and its reactivity toward dioxygen, closely associated with a biological system of an oxygen evolving centre of photosystem II.

DOI： 10.1039/c4cc06055e

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A new class of efficient catalyst, the Rh(I) complex [(η⁵-C₅Me₅)Rh^I(bpy)] (1; bpy = 2,2′-bipyridine), for the C-F bond hydrogenolysis of fluoroaromatics (C₆F₅CF₃, C₆F₆, C₆F₅H, and C₆F₅CH₃) is presented. The best turnover number of 380 for C₆F₆ is afforded by using 0.1 mol % of 1, 0.8 MPa of H₂, and 2 equiv of Et₂NH in CH₃CN at 25 °C. The successful isolation of the C-F bond cleavage product [(η⁵-C₅Me₅)Rh^III(bpy)(C₆F₅)](F) as a plausible intermediate of the catalytic hydrogenolysis of C₆F₆ by 1 is also described.

DOI： 10.1021/om500647h

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Reported herein is an electrode for dihydrogen (H₂) oxidation, and it is based on [NiFe]Hydrogenase from Citrobacter sp. S-77 ([NiFe] _S77). It has a 637 times higher mass activity than Pt (calculated based on 1 mg of [NiFe]_S77 or Pt) at 50 mV in a hydrogen half-cell. The [NiFe]_S77 electrode is also stable in air and, unlike Pt, can be recovered 100% after poisoning by carbon monoxide. Following characterization of the [NiFe]_S77 electrode, a fuel cell comprising a [NiFe] _S77 anode and Pt cathode was constructed and shown to have a a higher power density than that achievable by Pt.

DOI： 10.1002/anie.201404701

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

水素と酸素から電気を作る燃料電池は、排出物として水しか生成しないクリーンな発電装置である。燃料電池はその構造によって数種類に分類され、なかでも低温作動や小型軽量化が可能な固体高分子形燃料電池（polymer electrolyte fuel cell、PEFC）は、家庭用、携帯用、自動車用電源に適している。しかし、PEFCの電極触媒は枯渇資源で高価な白金触媒であり、その代替触媒の開発が行われてきたが、未だに白金に代わる実用触媒の開発には至っていない。本研究では、水素極（水素から電子を取り出す電極）の脱白金触媒として水素酸化酵素であるヒドロゲナーゼを用いたPEFCを初めて作製し、それらの発電実験に成功した。本研究で使用したヒドロゲナーゼS–77（当研究室で新規に探索・精製・単離）は、これまでのヒドロゲナーゼよりも高活性かつ頑丈であり、PEFCの作動条件でも十分にその機能を発揮できる。ヒドロゲナーゼS–77の単位重量あたりの水素酸化活性は、白金触媒に対して637倍であることを明らかにした。

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We propose a model for the water-oxidation and recovery systems of the oxygen-evolving complex (OEC) of the photosystem II (PSII) enzyme. The whole system is constructed from two catalytic cycles, conducted as a tandem reaction: (i) a water-oxidation loop uses cerium(iv) ammonium nitrate as an oxidant to activate a dimanganese complex for water-oxidation and thereby liberate a molecule of O₂ and (ii) a recovery loop begins with photoinhibition of the dimanganese complex but then uses O₂ to reactivate the manganese centre. The net result is a catalytic water-oxidation catalyst that can use self-generated O₂ for recovery.

DOI： 10.1039/c3dt52846d

Language：English   Publishing type：Research paper (scientific journal)  

We report the synthesis of mononuclear nonheme manganese(V)oxo complexes in aqueous acetonitrile solution from the reaction of manganese(III) complexes using hydrogen peroxide as an oxidant for the first time. A crystal structure of chloro derivative of manganese(V)oxo complex and its reactivity toward 3,5-di-tert-butyl-catechol are also reported.

DOI： 10.1246/cl.140376

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We provide confirmation of our proposed design principles for a H ₂ activation catalytic cycle by constructing a new catalyst. We have been able to obtain a crystal structure to confirm our proposition that a reduced, dinuclear species stores electrons from hydrogen molecules in a metal-metal bond.

DOI： 10.1002/ejic.201300049

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

From blue to red: The structure and luminescence properties of the gadolinium(III) complex 1 were investigated. Reversible switching of the luminescence of 1 in THF at room temperature by alternating light irradiation and O₂ exposure is presented, during which the emission color changes as shown in the picture. Light-induced phosphorescence of 1 plays a key role in this behavior.

DOI： 10.1002/anie.201303137

Language：English   Publishing type：Research paper (scientific journal)  

The first example of monooxygenation by a high-valent Mn^IV complex with a peroxide is described. A key Mn^IV acylperoxo intermediate, which uses m-chloroperoxybenzoic acid as the oxygen donor, is directly observed by electro-spray ionization mass spectrometry and resonance Raman spectroscopy.

DOI： 10.1039/c3cc43447h

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We report the successful increase in performance of a fuel cell based on organometallic catalysis. An organometallic [Ni^IIRu^IV] peroxo complex functions as cathode catalyst and was designed following mechanistic consideration of the cell. It was confirmed that the organometallic [Ni^IIRu^IV] peroxo catalyst could function in the fuel cell with a 240% increase in power output over our previous systems. This organometallic catalyst can act in both solid and solution phases and allows observation of the mechanism, hence providing us further opportunity for future improvement.

DOI： 10.1002/cctc.201200595

Language：English   Publishing type：Research paper (scientific journal)  

ニッケル・鉄ヒドロゲナーゼは、常温・常圧という温和な条件下で触媒的に水素を酸化する酵素である。多くの研究グループが、ニッケル・鉄ヒドロゲナーゼの機能モデル錯体の開発を試みてきたが、これまで達成されることはなかった。本研究では、世界で初めて常温・常圧で水素をヘテロリティックに活性化し、水素を酸化できるニッケル・鉄モデル錯体の開発に成功した。その反応中間体であるヒドリド錯体の構造は、X線構造解析をはじめとする種々の分光学的測定によって決定された。

Language：English   Publishing type：Research paper (scientific journal)  

Chemists have long sought to mimic enzymatic hydrogen activation with structurally simpler compounds. Here, we report a functional [NiFe]-based model of [NiFe]hydrogenase enzymes. This complex heterolytically activates hydrogen to form a hydride complex that is capable of reducing substrates by either hydride ion or electron transfer. Structural investigations were performed by a range of techniques, including x-ray diffraction and neutron scattering, resulting in crystal structures and the finding that the hydrido ligand is predominantly associated with the Fe center. The ligand's hydridic character is manifested in its reactivity with strong acid to liberate H2.

DOI： 10.1126/science.1231345

Language：English   Publishing type：Research paper (scientific journal)  

We present two closely related series of a [NiFe] hydrogenase analogue. Based on a [NiRu] core, these complexes demonstrate inactivity, H₂ activation, or O₂ activation depending only on the nature of the Ru-coordinated aromatic ligand. It is demonstrated that even small changes made to this aromatic ligand can modulate the catalytic activity of the complex. Structural, electrochemical, kinetic, and thermodynamic studies reveal that differences in activation and binding modes of the substrates, combined with differences in σ donation and lability of the aromatic ligands, result in abrupt changes in catalytic activity.

DOI： 10.1021/om300833m

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Herein, we report a [NiRu] biomimetic system for O ₂-tolerant [NiFe]hydrogenases and demonstrate that electron donation to the [NiRu] center can switch the system between the activation of H ₂ and O ₂ through simple ligand effects by using hexamethylbenzene and pentamethylcyclopentadienyl ligands, respectively. Furthermore, we present the synthesis and direct observations of a [NiRu]-peroxo species, which was formed by the oxygenation of a Ni-SIa model [NiRu] complex, that we propose as a biomimetic analogue of O ₂-bound species (OBS) of O ₂-tolerant [NiFe]hydrogenases. The [NiRu]-peroxo complex was fully characterized by X-ray analysis, X-ray photoelectron spectroscopy (XPS), mass spectrometry, and ¹H NMR spectroscopy. The OBS analogue was capable of oxidizing p-hydroquinone and sodium borohydride to turn back into the Ni-SIa model complex.

DOI： 10.1002/asia.201101020

Language：English   Publishing type：Research paper (scientific journal)  

The structure of a neutral five-coordinated organoruthenium( 0) complex [(η ⁶-C ₆Me ₆)Ru ⁰(bpy)] (1, bpy: 2,2′-bipyridine) was determined by X-ray diffraction analysis. The solvent-induced reversible color change based on the interconversion between the purple Ru ⁰ complex 1 and a yellow Ru ^IIhydride complex [(η ⁶-C ₆Me ₆)Ru ^II(bpy)H] ⁺ is presented.

DOI： 10.1246/cl.2012.650

Language：English   Publishing type：Research paper (scientific journal)  

A Rh ^III monohydride terpyridine complex undergoes reductive elimination of H ₂ in CH ₃CN to form a dinuclear Rh ^II complex with a metal-metal bond. Kinetic studies have revealed that the conversion from the monohydride species to the dinuclear species with evolution of H ₂ obeys first-order kinetics and have determined the kinetic deuterium isotope effect value to be 2.0. We discuss the mechanism for the reductive elimination of H ₂ from rhodium hydride species.

DOI： 10.1021/om2009759

Language：English   Publishing type：Research paper (scientific journal)  

Reductive activation of O ₂ by H ₂ with rhodium terpyridine complexes in H ₂O and CH ₃CN is described and the mechanism is fully elucidated. The rhodium complex extracts electrons from H ₂ and reductively activates O ₂ to form a peroxo active intermediate. This intermediate is able to oxidise triphenyl phosphine to triphenyl phosphine oxide. A model system constructed in CH ₃CN provides isolable analogues of catalytic intermediates in H ₂O, allowing a detailed look at each step in the catalytic cycle.

DOI： 10.1039/c1dt11599e

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We report the synthesis of a mer-triaqua Rh ^III complex using terpyridine as a meridional tridentate ligand. This is the first example of a structurally characterized six-coordinated mertriaqua complex for any second- or third-row element from the main transition-metal groups (groups 511). This is also the first example of a structurally characterized mer-triaqua complex with terpyridine for any transition metal. Acid dissociation constants, pK _a1 and pK _a2, of the triaqua complex are determined to be 3.0 and 6.9, respectively.

DOI： 10.1246/cl.2012.116

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： DOI: 10.1039/c1dt11599e

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

This review discusses the development of aqueous phase, homogeneous, transfer hydrogenation catalysis. Transfer hydrogenation catalysts, based on Ru, Ir and Rh, reduce organic substrates in water by assisting the transfer of hydrogen from simple donor species. These catalysts are expected to have significant benefits when compared with organic phase catalysts, including greater activity, greater selectivity and smaller environmental impact. They will therefore be expected to make a significant contribution to homogeneous catalysis and 'green chemistry'. Here, we comprehensively examine these catalysts, paying special attention to structural features.

DOI： 10.1039/c1dt10544b

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c1dt11454a

Language：English   Publishing type：Research paper (scientific journal)  

We propose a modified mechanism for the inhibition of [NiFe]hydrogenase ([NiFe]H ₂ase) by CO. We present a model study, using a NiRu H ₂ase mimic, that demonstrates that (i) CO completely inhibits the catalytic cycle of the model compound, (ii) CO prefers to coordinate to the Ru ^II center rather than taking an axial position on the Ni ^II center, and (iii) CO is unable to displace a hydrido ligand from the NiRu center. We combine these studies with a reevaluation of previous studies to propose that, under normal circumstances, CO inhibits [NiFe]H ₂ase by complexing to the Fe ^II center.

DOI： 10.1021/ic200965t

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/b921273f

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/b926061g

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/b918940h

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2010.128

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2010.130

Language：English   Publishing type：Research paper (scientific journal)  

A (μ-η²:η²-peroxo)dicopper(II) complex, [Cu₂(H-L)(O₂)]²⁺ (1-O₂), supported by the dinucleating ligand 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl] benzene (H-L) is capable of initiating C-H bond activation of a variety of external aliphatic substrates (SH_n): 10-methyl-9,10-dihydroacridine (AcrH₂), 1,4-cyclohexadiene (1,4-CHD), 9,10-dihydroanthracene (9,10-DHA), fluorene, tetralin, toluene, and tetrahydrofuran (THF), which have C-H bond dissociation energies (BDEs) ranging from ∼75 kcal mol^-1 for 1,4-CHD to ∼92 kcal mol^-1 for THF. Oxidation of SH _n afforded a variety of oxidation products, such as dehydrogenation products (SH_(n-2)), hydroxylated and further-oxidized products (SH_(n-1)OH and SH_(n-2)=O), dimers formed by coupling between substrates (H_(n-1)S-SH_(n-1)) and between substrate and H-L (H-L-SH_(n-1)). Kinetic studies of the oxidation of the substrates initiated by 1-O₂ in acetone at -70°C revealed that there is a linear correlation between the logarithms of the rate constants for oxidation of the C-H bonds of the substrates and their BDEs, except for THF. The combination of this correlation and the relatively large deuterium kinetic isotope effects (KIEs), k₂^H/k₂^D (13 for 9,10-DHA, ≳29 for toluene, and ∼34 for THF at -70°C and ∼9 for AcrH₂ at -94°C) indicates that H-atom transfer (HAT) from SH_n (SD_n) is the rate-determining step. Kinetic studies of the oxidation of SH_n by cumylperoxyl radical showed a correlation similar to that observed for 1-O₂, indicating that the reactivity of 1-O₂ is similar to that of cumylperoxyl radical. Thus, 1-O ₂ is capable of initiating a wide range of oxidation reactions, including oxidation of aliphatic C-H bonds having BDEs from ∼75 to ∼92 kcal mol^-1, hydroxylation of the m-xylyl linker of H-L, and epoxidation of styrene (Matsumoto, T.; et al. J. Am. Chem. Soc. 2006, 128, 3874).

DOI： 10.1021/ja809822c

Language：English   Publishing type：Research paper (scientific journal)  

Structural analysis of the resting state of [NiFe]hydrogenase ([NiFe]H ₂ase) shows that the active site has a characteristic bis(μ-thiolato)NiFe unit, where the Ni atom and the Fe atom are bridged by an undetermined oxygen-bearing ligand. This ligand probably derives from the aqueous solvent and is therefore most likely to be H₂O, OH ^- or O^2-. Here, we compare the reactivities of a NiFe and a NiRu complex when bearing either acetonitrile or aqueous ligands and demonstrate the critical role of an aqueous ligand in hydrogenase and its mimics. We also make observations on the necessity of organometallic metal-carbon bonds to the supporting frameworks.

DOI： 10.1039/b819395a

Language：English   Publishing type：Research paper (scientific journal)  

In the nick(el) of time: Bis(μ-oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H₂O₂, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3. Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ - η²: η² - peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.

DOI： 10.1002/anie.200900222

Language：English   Publishing type：Research paper (scientific journal)  

The mechanism of extraction of electrons from H₂ catalyzed by hydrogenases has proven challenging to elucidate. Catalytic extraction of electrons from H₂ has been achieved by use of a low-valent Ni ^IRu^I complex [Ni^I(μ-SR)₂Ru ^I(η⁶-C₆Me₆)]{μ-SR) ₂ = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)-1,3- propanediamine) as the active catalyst with evolution of H₂ under ambient conditions. The electrons extracted from H₂ have been used for a catalytic reduction of Cu²⁺ to Cu⁰ with the NiRu complexes.

DOI： 10.1246/cl.2008.970

Language：English   Publishing type：Research paper (scientific journal)  

The pH-dependent hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes and hydrogenation of the carbonyl compounds have been investigated with water-soluble bis(μ-thiolate)(μ-hydride)NiRu complexes, Ni^II(μ-SR)₂(μ-H)Ru^II {(μ-SR)₂ = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)-1, 3-propanediamine}, as functional models for [NiFe]hydrogenases. In acidic media (at pH 4-6), the μ-H ligand of the Ni^II(μ-SR) ₂(μ-H)Ru^II complexes has H⁺ properties, and the complexes catalyse the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes. A mechanism of the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes through a low-valent Ni^I(μ-SR)₂Ru^I complex is proposed. In contrast, in neutral-basic media (at pH 7-10), the μ-H ligand of the Ni ^II(μ-SR)₂(μ-H)Ru^II complexes acts as H^-, and the complexes catalyse the hydrogenation of carbonyl compounds.

DOI： 10.1039/b807555g

Language：English   Publishing type：Research paper (scientific journal)  

Reaction of copper(II) complex 1^X supported by the tridentate bis(pyridylmethyl)amine ligand containing m-substituted phenyl groups at the 6-positions of the pyridine rings (L^X) with H₂O₂ in the presence of triethylamine (NEt₃) in acetone generates a copper(II)-alkylperoxo species 2^X [2-hydroxy-2-hydroperoxypropane (HHPP) adduct]. The alkylperoxo intermediate 2^X undergoes an efficient aromatic ligand hydroxylation reaction, producing a phenolate complex 4^X via another intermediate 3^X. Kinetic studies on the aromatic hydroxylation process are reported together with spectral characterization of 2^X.

DOI： 10.1021/ja071623g

Language：English   Publishing type：Research paper (scientific journal)  

New hexadentate dinucleating ligands having a xylyl linker, X-L-R, were synthesized, where X-L-R = 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2,4,6-trimethybenzene (Me₂-L-Me) and 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]-2-fluorobenzene (H-L-F). They form dinuclear copper(I) complexes, [Cu₂(X-L-R)]²⁺ (Me₂-L-Me (1) and H-L-F (2)). The copper(I) complexes in acetone at -78 °C react with O₂ to produce intra- and intermolecular (μ-η²:η²-peroxo)dicopper(II) species depending on the concentrations of the complexes: both complexes generate intramolecular (μ-η²:η²-peroxo)dicopper(II) species [Cu₂(O₂)(X-L-R)]²⁺ (1-O₂ and 2-O₂) at the concentrations below ∼5 mM, whereas at ∼60 mM, both complexes produce intermolecular (μ-η²:η²-peroxo)dicopper(II) species, which were confirmed by the electronic and resonance Raman spectroscopies. The electronic spectrum of 1-O₂ in acetone at concentrations below ∼5 mM showed an absorption band at (λ_max = 442 nm, ε = 5600 M^-1 cm^-1) assignable to the π_σ^*(O-O)-to-Cu(II) ((d x² - y² + d x² - y²) component) LMCT transition in addition to an intense band attributable to the π_σ^*(O-O)-to-Cu(II) ((d x² - y² - d x² - y²) component) LMCT transition (λ_max = 359 nm, ε = 21000 M^-1 cm^-1), indicating that the (μ-η²:η²-peroxo)Cu(II)₂ core of 1-O₂ takes a butterfly structure. Decomposition of 1-O₂ resulted in hydroxylation of the 2-position of the xylyl linker with 1,2-methyl migration (NIH shift), suggesting that the hydroxylation reaction proceeds via a cationic intermediate as proposed for closely related (μ-η²:η²-peroxo)Cu(II)₂ complexes having a xylyl linker. Kinetic study of the decomposition (hydroxylation of the xylyl linker) of 1-O₂ suggests that a stereochemical effect of the methyl group in the 2-position of the xylyl linker has a significant influence on a transition state for decomposition (hydroxylation of the xylyl linker).

DOI： 10.1016/j.jorganchem.2006.05.068

Language：English   Publishing type：Research paper (scientific journal)  

Stepwise down : Reaction of[Cu(Me₂-tpa)]⁺ (tpa = bis(6-methyl-2-pyridylmethyl) (2-pyridylmethyl)amine) with H₂O ₂ results in regioselective oxidation of a methyl group of the Me₂-tpa ligand to produce an alkylperoxocopper(II) complex [Cu(Me-tpa-CH₂OO)]⁺ as a reaction intermediate, which undergoes further decomposition to give aldehyde and alcohol copper(I) complexes as well as alkoxo- and carboxylatocopper(II) complexes (see scheme; blue N, green Cu, red O). (Chemical Equation Presented).

DOI： 10.1002/anie.200602477

Language：English   Publishing type：Research paper (scientific journal)  

A discrete (μ-η²:η²-peroxo)Cu(II)₂ complex, [Cu₂(O₂)(H-L)]²⁺, is capable of performing not only intramolecular hydroxylation of a m-xylyl linker of a dinucleating ligand but also intermolecular epoxidation of styrene via electrophilic reaction to the C=C bond and hydroxylation of THF by H-atom abstraction.

DOI： 10.1021/ja058117g

Language：English   Publishing type：Research paper (scientific journal)  

Schizophyllans carrying poly(N-substituted-acrylamidej-branches were synthesized from native schizophyllan through Ce(IV)-initiated radical homo- or co-polymerization of N-iso-propyl- and N-sec-butyl-acryl-amide. A series of structural analyses including elemental analysis, gel permeation chromatography, ¹H NMR, and enzymatic degradation using β-1,3-glucanase revealed that schizophyllans (150 kDa) bearing long poly(N-substituted- acrylamide)-branches (ca. 290 kDa) are obtained. These SPG-conjugates form macromolecular complexes with certain homopolynucleotides such as poly(C), poly(dA), and poly(A) and then efficiently co-precipitate them on heating. For example, schizophyllan carrying poly(N-iso-propylacrylamide)-branches can selectively recover poly(C) from a mixture of poly(C) and poly(U) by simple heating (36°C) followed by centrifugation. HPLC analysis of the recovered polynucleotide revealed the high poly(C)-selectivity (poly(C):poly(U) = 95:5). Similarly, schizophyllan carrying more hydrophobic poly(N-iso-propylacrylamide- co-N-sec-butylacrylamide)-branches precipitates at lower temperature (ca. 20°C) and is applicable to isolation of poly(A) that forms less stable macromolecular complexes with SPG and SPG-derivatives (the dissociation temperatures are around 30°C).

DOI： 10.1295/polymj.37.177

Language：English   Publishing type：Research paper (scientific journal)  

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4- imidazolylmethyl)amine. Reaction of a bis(μ-hydroxo)dicopper(II) complex, [Cu₂(L3)₂(OH)₂]²⁺ (1), with H ₂O₂ in acetonitrile at -40 °C generated a (μ-1,1-hydroperoxo)dicopper(II) complex [Cu₂(L3) ₂(OOH)(OH)]²⁺ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu₂(μ-1,1- OOH)(μ-OH) core and each copper has a square pyramidal structure having an N₃O₂ donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu ₂(μ-1,1-OOH)(μ-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and ¹⁶O/¹⁸O exchange reactions in 2 compared to that in 1 and stabilizes the Cu ₂(μ-1,1-OOH)(μ-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 °C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]⁺ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 °C gave a complex having a hydroxylated ligand [Cu₂(L3)(L3-OH)(OH) ₂]²⁺ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 °C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in ∼80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (μ-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.

DOI： 10.1021/ja047437h

Language：English   Publishing type：Research paper (scientific journal)  

A new water-soluble carbohydrate-containing "nonionic" homooxacalix[3]arene (2) was synthesized. 2 could solubilize [60]fullerene (C₆₀) into water and the resultant complex acted as an efficient DNA photocleaving reagent.

DOI： 10.1246/cl.2005.308

Language：English   Publishing type：Research paper (scientific journal)  

Schizophyllans carrying β-lactoside and α-mannoside appendages were prepared from native schizophyllan through NaIO₄ oxidation followed by reductive amination using aminoethyl-β-lactoside and α-mannoside, respectively. The resulting schizophyllans form stable macromolecular complexes with polynucleotides, such as poly(C) and poly(dA). Specific affinity between these macromolecular complexes and saccharide-binding proteins was demonstrated by surface plasmon resonance and agarose gel staining assays. β-Lactoside-appended schizophyllan enhanced an antisense activity in hepatocytes which express lactoside-binding proteins on their cell surfaces.

DOI： 10.1039/b412124b

Language：English   Publishing type：Research paper (scientific journal)  

Single-walled carbon nanotubes can be entrapped within a helical superstructure composed of schizophyllan bearing lactoside-appendages to show an excellent water-solubility as well as a specific lectin-affinity.

DOI： 10.1039/b407409b

Language：English   Publishing type：Research paper (scientific journal)  

A β-(1 → 3)-D-glucan schizophyllan (SPG) forms a stoichiometric complex with some polynucleotides. This communication describes our attempt to apply the SPG complex to deliver CpG DNA to endosomes to enhance cytokine secretion. To increase cellular uptake, we introduced spermine, arginine-glycine-aspartic acid tripeptide, octaarginine, or cholesterol to the SPG side chain. The chemically modified SPG showed essentially no cytotoxicity. When CpG DNA complex made therefrom was exposed to macrophages, dramatic enhancement in the cytokine secretion was observed. It increased 5-10 times from the naked dose and 100 times from the background. This performance promises that SPG can be an excellent carrier for CpG DNA.

DOI： 10.1021/ja031978+

Language：English   Publishing type：Research paper (scientific journal)  

Schizophyllan is a natural β-(1→3)-D-glucan existing as a triple helix in water and as a single chain in dimethylsulfoxide (DMSO), respectively. As we already reported, when some homo-phosphodiester polynucleotide (for example, poly(dA) or poly(C)) is added to the schizophyllan/DMSO solution and subsequently DMSO is exchanged for water, the single chain of schizophyllan forms a complex with the polynucleotide. Furthermore, we have already demonstrated that one of the potential applications of this novel complex is an antisense-oligonucleotide (AS ODN) carrier. This work describes a versatile and universal modification technique which enables us to introduce various functional groups only to the side chain of schizophyllan. This technique consists of periodate oxidation of the glucose side chain (it does not react with the main chain because of the absence of the 1,2-diol group in β-(1→3)-glucan) and subsequent introduction of the functional groups into the formyl terminate. In the present work, the introduced functional groups were spermine, octa-arginine (R8), arginine-glycine-aspartic acid tripeptide (RGD) and some amino or α-amino acid compounds. Using these compounds, we made the complexes and carried out an in vitro antisense assay for them, administrating a phosphorothioate AS ODN to the melanoma A375 or leukemia HL-60 cell lines to depress their c-myb mRNA. When we used the R8 or RGD modified schizophyllan as the antisense carrier, the antisense effect was most enhanced among others. Their superiority can be ascribed to enhancement of endocytosis due to these functional peptides. Furthermore, the cytotoxicity for these two modified schizophyllans was negligibly as small as the natural (unmodified) schizophyllan. One of the peculiar features of our system is that the complex (i.e., carrier+AS ODN) is charged negatively in total, which is different from the conventional systems. The present work has thus clarified that schizophyllan can act as a new potential candidate for AS ODN carriers.

DOI： 10.1016/j.bbagen.2003.10.019

Language：English   Publishing type：Research paper (scientific journal)  

The water solubility of curdlan was enhanced by partial sulfation at O-6. Circular dichroism measurements suggest that the sulfated curdlan with the degree of substitution (DS) from 0 to 8.7mol% forms macromolecular complexes with polycytidylic acid (poly(C)). Although the thermal stability of the complexes decreased with increase in DS, this could be overlapped by addition of NaCl in the concentration above that of serum. The results clearly indicate that the drawback arising from the electrostatic repulsion between the anionic charges can be partially compensated by the presence of salt. Furthermore, the polynucleotide chain complexed with the sulfated curdlan was protected from the enzymatic hydrolysis, corroborating the assumption that the sulfated curdlan has an ability to bind poly(C).

DOI： 10.1016/j.carres.2003.09.022

Language：English   Publishing type：Research paper (scientific journal)  

A schizophyllan (β-1,3-glucan) derivative carrying lactose-appendages prepared by reductive amination can form stable macromolecular complexes with polynucleotides, shows excellent affinity with a lactose-binding lectin, and effectively mediates gene transfection into hepatocytes.

DOI： 10.1039/b313426a

Language：English   Publishing type：Research paper (scientific journal)  

Schizophyllan (SPG), a β-1,3-glucan polysaccharide which is known to form macromolecular complexes with certain polynucleotides, was modified by a reductive amination method with α-amino acids (Arg, Lys, and Ser). The thermal stability of the complexes as estimated by T_m was enhanced in SPG-Arg and SPG-Lys conjugates which have pI values higher than the pH of the medium (8.0). The T_m shift increased with the increase in the percentage of α-amino acid introduced and the highest T_m values attained were 64°C for SPG-Arg conjugate and 62°C for SPG-Lys conjugate, which are higher by 13 and 11°C, respectively, than those of the unmodified SPG+poly(C) complex. In the SPG-Ser conjugate with a pI lower than the medium pH (8.0), the T_m values decreased with an increase in the percentage of Ser. Formation of the macromolecular complex was no longer detected above 13.2% Ser. The findings indicate that the T_m values are easily controllable by the type and percentage of the introduced α-amino acids. We believe, therefore, that the present conjugates, consisting of naturally originated SPG and α-amino acids, provide an important lead for developing nontoxic artificial vectors and to control the affinity with polynucleotides in response to medium pH and temperature.

DOI： 10.1016/S0045-2068(03)00020-8

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：The Magellan Sutera Resort, Sabah, Malaysia with online   Country：Malaysia  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡、九州大学病院キャンパス   Country：Japan  

Event date： 2022.6

Language：Japanese  

Venue：オンライン   Country：Japan  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Other  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Other  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Other  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学（黒髪南地区）+ オンライン   Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Online Webinar   Country：Other  

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンラインシンポジウム   Country：Japan  

世界的に脱炭素社会への移行が進む中で、メタンはシェールガス革命以降、ブリッジ・エネルギーとして役割が期待されている。最近では、メタンは再生可能エネルギーであるバイオマスから製造されることから、カーボン・ニュートラル社会の実現に向けたキープレーヤーとしての役割を期待されている。しかし、メタンはその物理化学的性質から、物質変換が最も難しい不活性分子の１つである。本研究では、そのような変換の難しいメタンに対して、光エネルギーを有機化学錯体にインプットしてメタノールに変換する新しい触媒反応を見出した。

Event date： 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：オランダ、デルフト、Delft University of Technology (TU Delft)   Country：Netherlands  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：台湾、新竹、National Chiao Tung University   Country：Taiwan, Province of China  

Event date： 2018.7 - 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：日本、宮城、仙台国際センター   Country：Japan  

Event date： 2017.9

Language：English   Presentation type：Oral presentation (general)  

Venue：札幌、北海道大学   Country：Japan  

Event date： 2017.2

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京、東京ビッグサイト   Country：Japan  

Event date： 2017.2

Language：English   Presentation type：Oral presentation (general)  

Venue：日本、福岡、九州大学 I2CNER   Country：Japan  

Event date： 2016.12

Language：English   Presentation type：Oral presentation (general)  

Venue：ニュージーランド、オークランド、The University of Auckland   Country：New Zealand  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡、福岡大学   Country：Japan  

Event date： 2016.7

Language：English   Presentation type：Oral presentation (general)  

Venue：フランス、ブレスト、Le Quartz Convention Center   Country：France  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪、大阪大学吹田キャンパス   Country：Japan  

Event date： 2016.2

Language：English   Presentation type：Oral presentation (general)  

Venue：日本、福岡、九州大学 I2CNER   Country：Japan  

Event date： 2015.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本、熊本大学   Country：Japan  

Event date： 2015.2

Language：English  

Venue：日本、福岡、I2CNER Hall   Country：Japan  

Event date： 2014.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫、書写山円教寺会館   Country：Japan  

Event date： 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：シンガポール、Suntec Shingapore Convention & Exhibition Centre   Country：Singapore  

Event date： 2014.1

Language：English  

Venue：日本、福岡、I2CNER Hall   Country：Japan  

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：アメリカ、イリノイ、イリノイ大学   Country：Japan  

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡、福岡市産学連携交流センター   Country：Japan  

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山大学   Country：Japan  

Event date： 2012.7

Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2011.9 - 2011.10

Presentation type：Oral presentation (general)  

Venue：岡山理科大学   Country：Japan  

Event date： 2010.12

Presentation type：Symposium, workshop panel (public)  

Venue：アメリカ、ハワイ、ホノルル   Country：United States  

水素社会の到来が迫ってきているが、枯渇資源である白金が未だ最も優れた水素活性化触媒である。水素社会実現のためには、白金の代替触媒の開発が必須である。自然界にはニッケル・鉄ヒドロゲナーゼと呼ばれる水素活性化酵素が存在する。この酵素は水中・常温・常圧で水素を活性化し、水素からの電子抽出を触媒する。しかし、この有用なニッケル・鉄ヒドロゲナーゼの構造・機能を、人工的に再現できたモデル錯体はこれまで報告されていない。本研究では、ニッケル・ルテニウム触媒を用いてその構造・機能を再現することに成功し、これまで知られていなかった水素活性化のメカニズムを解明することに成功した。

Event date： 2010.9

Presentation type：Oral presentation (general)  

Venue：日本、大阪、大阪国際交流センター   Country：Japan  

火力発電と原子力発電に替わる次世代発電システムとして、排出物が水のみであるクリーンな水素燃料電池が期待されている。燃料電池の電極触媒には白金が最適であるが、白金は枯渇資源であるため、白金の代替触媒の開発が求められている。自然界にはニッケル・鉄ヒドロゲナーゼと呼ばれる水素活性化酵素が存在する。この酵素は水中・常温・常圧で水素を活性化し、水素からの電子抽出を触媒する。しかし、この有用なニッケル・鉄ヒドロゲナーゼの構造・機能を、人工的に再現できたモデル錯体はこれまで報告されていない。本研究では、ニッケル・ルテニウム触媒を用いてその構造・機能を再現することに成功した。

Event date： 2009.11

Presentation type：Symposium, workshop panel (public)  

Venue：日本、佐賀、唐津ロイヤルホテル   Country：Japan  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

本総説は化学（化学同人）に掲載されたものである。要旨は下記の通りである。
水素-水素結合（H-H結合）を切断する触媒が新しく開発された。金属酵素であるヒドロゲナーゼをモデルに五つの水素活性化戦略を打ち立て、ヒドリドイオンから電子を取り出すことに初めて成功した。その戦略とは？

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

福岡市産学連携交流センターにおいて、施設見学会「水素エネルギー研究最前線についての講演と燃料電池の実験」を行った。水素社会の到来が刻々と迫ってきているが、枯渇資源である白金が未だ最も優れた水素活性化触媒である。水素社会実現のためには、白金の代替触媒の開発が必須である。自然界にはニッケル・鉄ヒドロゲナーゼと呼ばれる水素活性化酵素が存在し、この酵素は水中・常温・常圧で水素を活性化し、水素からの電子抽出を触媒する。本施設見学会では、本研究室で水素活性化酵素を範として開発した新規水素活性化分子触媒について解説し、燃料電池を参加者と一緒に実際に組み立て発電実験を行い、燃料電池の仕組みについて説明した。

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture