Researchers Database

Fujii Hiroshi

    Faculty Division of Natural Sciences Research Group of Chemistry Professor
Contact:
fujiicc.nara-wu.ac.jp
Last Updated :2021/09/18

researchmap

Degree

  • Ph.D (Kyoto University), Kyoto University

Research Interests

  • 電子構造 反応性 反応中間体 タンパク質 酵素 金属イオン Electronic Structure Reactivity Reaction intermediate Protein Enzyme Metal ion 

Research Areas

  • Nanotechnology/Materials, Inorganic and coordination chemistry
  • Life sciences, Functional biochemistry

Research Experience

  • Apr. 2014, Nara Women's University, Faculty, Division of Natural Sciences, 教授
  • Apr. 2014, -:Professor, Graduate School of Humanities and Sciences and Department of Chemistry, Biology, and Environment Sciences, Nara Women's University
  • Apr. 2007 Mar. - 2014, :自然科学研究機構岡崎統合バイオサイエンスセンター 准教授
  • 2007 - 2014, :Associate Professor, Okazaki Institute of Integrative Bioscience, National Institutes of Natural Sciences
  • Apr. 2004 Mar. - 2007, :自然科学研究機構岡崎統合バイオサイエンスセンター 助教授
  • 2004 - 2007, :Associate Professor, Okazaki Institute of Integrative Bioscience, National Institutes of Natural Sciences
  • Feb. 2001 Mar. - 2004, :岡崎国立共同研究機構統合バイオサイエンスセンター 助教授
  • 2001 - 2004, :Associate Professor, Center for Integrative Bioscience, Okazaki National Research Institutes
  • Mar. 1998 Jan. - 2001, :岡崎国立共同研究機構分子科学研究所 助教授
  • 1998 - 2001, :Associate Professor, Institute for Molecular Science, Okazaki National Research Institutes
  • Feb. 1994 Feb. - 1998, :山形県テクノポリス財団生物ラジカル研究所 主任研究員
  • 1994 - 1998, :Chief Scientist, Yamagata Technopolis Foundation, Institute for Life Support Technology
  • Nov. 1992 Jan. - 1994, :ミネソタ大学化学科 博士研究員
  • 1992 - 1994, Post-doctoral Fellow, University of Minnesota
  • Apr. 1990 Oct. - 1992, :北海道大学理学部化学科 助手
  • 1990 - 1992, :Assistant Professor, Department of Chemistry, Faculty of Science, Hokkaido University

Education

  • Apr. 1987, Mar. - 1990, Kyoto University, 工学研究科, 分子工学専攻博士後期課程, Japan
  • Apr. 1985, Mar. - 1987, 京都大学大学院, 工学研究科, 分子工学専攻修士課程
  • Apr. 1981, Mar. - 1985, Kanazawa University, Faculty of Engineering, 工業化学科

Published Papers

  • Photo-biohydrogen Production by Photosensitization with Biologically Precipitated Cadmium Sulfide in Hydrogen-Forming Recombinant Escherichia coli

    Yuki Honda; Yuka Shinohara; Motonori Watanabe; Tatsumi Ishihara; Hiroshi Fujii

    Dec. 2020, ChemBioChem., 21, 3389 - 3397

  • Visible light-driven, external mediator-free H2 production by a combination of a photosensitizer and a whole-cell biocatalyst: Escherichia coli expressing [FeFe]-hydrogenase and muturase genes

    Yuki Honda; Yuka Shimonhara; Hiroshi Fujii

    Sep. 2020, Catalysis Science & Technology, 10, 6006 - 6012

  • DFT insight into axial ligand effects on electronic structure and mechanistic reactivity of oxoiron(IV) porphyrin

    Zhifeng Ma; Naoki Nakatani; Hiroshi Fujii; Masahiko Hada

    Jul. 2020, Physical Chemistry Chemical Physics., 22, 12173 - 12179

  • Spectroscopic Evidence for Acid-Catalyzed Disproportionation Reaction of Oxoiron(IV) Porphyrin to Oxoiron(IV) Porphyrin π-Cation Radical and Iron(III) Porphyrin

    Kana Nishikawa; Yuki Honda; Hiroshi Fujii

    Mar. 2020, J. Am. Chem. Soc., 142, 4980 - 4984

  • Effect of External Electric Fields on the Oxidation Reaction of Olefins by Fe(IV)OCl­Porphyrin Complexes

    Zhifeng Ma; Naoki Nakatani; Hiroshi Fujii; Masahiko Hada

    Feb. 2020, Bull. Chem Soc. Jpn., 93, 187 - 193

    Scientific journal

  • Unique Electronic Structures of the Highly Ruffled Hemes in Heme-Degrading Enzymes of Staphylococcus aureus, IsdG and IsdI, by Resonance Raman and Electron Paramagnetic Resonance Spectroscopies

    Satoshi Takahashi; Shusuke Nambu; Toshitaka Matsui; Hiroshi Fujii; Haruto Ishikawa; Yasuhisa Mizutani; Kouhei Tsumoto; Masao Ikeda-Saito

    2020, Biochemistry, 59, 3918 - 3928

  • Dioxygen-Binding in Metalloproteins and Corresponding Models

    Shinobu Itoh; Hiroshi Fujii

    Elsevier, 2020, Comprehesive Coordination Chemsitry III, doi

    In book

  • Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron Porphyrinoid Dimer

    Nozomi Mihara; Yasuyuki Yamada; Hikaru Takaya; Yasutaka Kitagawa; Kazunobu Igawa; Katsuhiko Tomooka; Hiroshi Fujii; Kentaro Tanaka

    © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 5+ , which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 5+ catalyzed ethane oxidation in the presence of H 2 O 2 at a relatively low temperature. The site-selective complexation of 3 5+ with an additional anionic porphyrin (TPPS 4− ) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 5+ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS 4− to 3 5+ enhanced the catalytic activity., 01 Mar. 2019, Chemistry - A European Journal, 25 (13), 3369 - 3375, doi;pubmed;scopus;scopus_citedby

    Scientific journal

  • Small Reorganization Energy for Ligand-Centered Electron-Transfer Reduction of Compound I to Compound II in Heme Model Study

    Nami Fukui; Xiao-Xi Li; Wonwoo Nam; Shunichi Fukuzumi; Hiroshi Fujii

    2019, Inorg. Chem., 58, 8263 - 8266

    Scientific journal

  • Direct Observation of Primary C–H Bond Oxidation by An Oxido-iron(IV) Porphyrin π-Radical Cation Complex in a Fluorinated Carbon Solvent

    Yuma Morimoto; Yuki; Shimaoka, Yuri; Ishimizu; Hiroshi Fujii; Shinobu Itoh

    2019, Angew. Chem. Int. Ed, 58, 10863 - 10866

    Scientific journal

  • Experimental and Theoretical Studies of the Porphyrin Ligand Effect on the Electronic Structure and Reactivity of Oxoiron(IV) porphyrin π-Cation Radical Complexes

    Yuri Ishimizu; Zhifeng Ma; Masahiko Hada; Hiroshi Fujii

    2019, J. Biol. Inrog. Chem., 24, 483 - 494

    Scientific journal

  • Substitution Effects on Olefin Epoxidation Catalyzed by Oxoiron(IV) Porphyrin π-Cation Radical Complexes: A DFT Study

    Zhifeng Ma; Kasumi Ukaji; Naoki Nakatani; Hiroshi Fujii; Masahiko Hada

    2019, J. Cmput. Chem., 40, 1780 - 1788

    Scientific journal

  • Critical factors in determining the heterolytic versus homolytic bond cleavage of terminal oxidants by Iron(III) porphyrin complexes

    Sawako Yokota; Hiroshi Fujii

    Heterolytic versus homolytic cleavage of the metal-bound terminal oxidant is the key for determining the nature of reactive intermediates in metalloenzymes and metal catalyzed oxygenation reactions. Here, we study the bond cleavage process of hypochlorite by iron(III) porphyrin complexes having 4-methoxy-2,6-dimethylphenyl (1), 2,4,6-trimethylphenyl (2), 4-fluoro-2,6-dimethylphenyl (3), 2-chloro-6-methylphenyl (4), 2,6-dichlorophenyl (5), and 2,4,6-trichlorophenyl (6) groups at the meso position. Oxoiron(IV) porphyrin π-cation radical complexes (CompI) are characterized from the reactions of 1-4 with tetra-n-butylammonium hypochlorite (TBA-OCl) in dichloromethane at -80 °C, while oxoiron(IV) porphyrin complexes (CompII) are characterized for 5 and 6 under the same conditions. For all of 1-6, we find the formation of an epoxidation product in good yields from the catalytic reactions with TBA-OCl, suggesting heterolytic cleavages of the O-Cl bonds. CompI of 5 and 6 are reduced to the corresponding CompII by both chloride and hypochlorite, while CompI of 1-4 are not. The reduction reactions with hypochlorite are much faster than those with chloride. These results provide a mechanism where the O-Cl bond of the iron-bound hypochlorite is cleaved heterolytically to form CompI for all of 1-6, but the subsequent reduction reaction with remaining hypochlorite affords CompII for 5 and 6. The E(OCl•/OCl-) value is the boundary to discriminate the identity of the final product: CompI or CompII. Thermodynamic analysis based on the redox potential is successfully applied for explaining the bond cleavage processes of the hypochlorite, hydroperoxide, and tert-butyl peroxide complexes., American Chemical Society, 18 Apr. 2018, Journal of the American Chemical Society, 140 (15), 5127 - 5137, doi

    Scientific journal

  • Preparation, Characterization and Reactivity of a Bis-hypochlorite Adduct of a Chiral Manganese(IV) Salen Complex

    Ikuko Araki; Kaoru Fukui; Hiroshi Fujii

    A bis-hypochlorite adduct of a manganese(IV) salen complex having a chiral (R,R)-cyclohexane-1,2-diamine linkage (2-tBu) is successfully prepared and characterized by various spectroscopic methods. The reactions of 2-tBu with various organic substrates show that 2-tBu is capable of sulfoxidation, epoxidation, chlorination, and hydrogen abstraction reactions. However, the enantioselectivity of the epoxidation reactions by 2-tBu is much lower than that reported for the catalytic reactions by Jacobsen's catalyst. The low enantioselectivity is consistent with a planar conformation of the salen ligand, which is suggested by circular dichroism spectroscopy. This study suggests that 2-tBu is not a reactive intermediate of Jacobsen's enantioselective epoxidation catalysis., American Chemical Society, 19 Feb. 2018, Inorganic Chemistry, 57 (4), 1685 - 1688, doi

    Scientific journal

  • Coexpression of 5-aminolevulinic Acid Synthase Gene Facilitates Heterologous Production of Thermostable Cytochrome P450, CYP119, in Holo Form in Escherichia coli

    Yuki Honda; Ki Nanasawa; Hiroshi Fujii

    2018, ChemBioChem, 19, 2156 - 2159

    Scientific journal

  • Participation of Electron Transfer Process in Rate-Limiting Step of Aromatic Hydroxylation Reactions by Compound I Models of Heme Enzymes

    Maaya Asaka; Hiroshi Fujii

    Hydroxylation reactions of aromatic rings are key reactions in various biological and chemical processes. In spite of their significance, no consensus mechanism has been established. Here we performed Marcus plot analysis for aromatic hydroxylation reactions with oxoiron(IV) porphyrin pi-cation radical complexes (compound I). Although many recent studies support the mechanism involving direct electrophilic attack of compound I, the slopes of the Marcus plots indicate a significant contribution of an electron transfer process in the rate-limiting step, leading us to propose a new reaction mechanism in which the electron transfer process between an aromatic compound and compound I is in equilibrium in a solvent cage and coupled with the subsequent bond formation process., AMER CHEMICAL SOC, Jul. 2016, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 138 (26), 8048 - 8051, doi;web_of_science

    Scientific journal

  • The Origin of Relative Stability of Di-mu-oxo M-M Chiral Salen Complexes [M-M = Ti(TV)-Ti(IV), V(IV)-V(IV), Cr(IV)-Cr(IV), and Mn(IV) Mn(IV)]: A Quantum-Chemical Analysis

    Radhika Narayanan; Archana Velloth; Takuya Kurahashi; Hiroshi Fujii; Masahiko Hada

    Di-mu-oxo dimetal cores can form Binuclear complexes with definite stereochemistries. Recent studies describing the synthesis and evaluation of titanium(IV) and manganese(IV) di-mu-oxo dimetal chiral salen complexes prompted us to explore the corresponding vanadium(IV) and chromium(IV) complexes. We therefore modeled a series of di-mu-oxo dimetal complexes of titanium(IV), vanadium(IV), chromium(IV), and manganese(IV) with tetradentate salen ligands bearing different degrees of steric bulk. Quantum mechanical calculations were conducted to compare the stabilities and molecular structures of these complexes. The results of natural population analysis gave an insight into the charge distribution characteristics of the di-mu-oxo dimetal cores of these complexes. Our calculations showed that the di-mu-oxo dimetal complexes bearing the least sterically encumbered model ligand 1 preferred the M-helical form over the P-helical one. In the titanium(IV) and chromium(IV) complexes containing a practical chiral salen ligand 2, the P-helical form was found to be more stable than the corresponding M-form. In contrast, the corresponding vanadium(IV) and manganese(IV) complexes preferred to exist in the M-helical form. The degree of distortion of the di-mu-oxo dimetal core and the inter ligand interactions were key factors for determining the stability of these complexes., CHEMICAL SOC JAPAN, Apr. 2016, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 89 (4), 447 - 454, doi;web_of_science

    Scientific journal

  • Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation

    Toshitaka Matsui; Shusuke Nambu; Celia W. Goulding; Satoshi Takahashi; Hiroshi Fujii; Masao Ikeda-Saito

    Bacterial pathogens must acquire host iron for survival and colonization. Because free iron is restricted in the host, numerous pathogens have evolved to overcome this limitation by using a family of monooxygenases that mediate the oxidative cleavage of heme into biliverdin, carbon monoxide, and iron. However, the etiological agent of tuberculosis, Mycobacterium tuberculosis, accomplishes this task without generating carbon monoxide, which potentially induces its latent state. Here we show that this unusual heme degradation reaction proceeds through sequential mono- and dioxygenation events within the single active center of MhuD, a mechanism unparalleled in enzyme catalysis. A key intermediate of the MhuD reaction is found to be meso-hydroxyheme, which reacts with O-2 at an unusual position to completely suppress its monooxygenation but to allow ring cleavage through dioxygenation. This mechanistic change, possibly due to heavy steric deformation of hydroxyheme, rationally explains the unique heme catabolites of MhuD. Coexistence of mechanistically distinct functions is a previously unidentified strategy to expand the physiological outcome of enzymes, and may be applied to engineer unique biocatalysts., NATL ACAD SCIENCES, Apr. 2016, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113 (14), 3779 - 3784, doi;web_of_science

    Scientific journal

  • The functional role of the structure of the dioxo-isobacteriochlorin in the catalytic site of cytochrome cd(1) for the reduction of nitrite

    Hiroshi Fujii; Daisuke Yamaki; Takashi Ogura; Masahiko Hada

    Cytochrome cd(1) is a key enzyme in bacterial denitrification and catalyzes one-electron reduction of nitrite (NO2-) to nitric oxide (NO) at the heme d(1) center under anaerobic conditions. The heme d(1) has a unique dioxo-isobacteriochlorin structure and is present only in cytochrome cd(1). To reveal the functional role of the unique heme d1 in the catalytic nitrite reduction, we studied effect of the porphyrin macrocycle on each reaction step of the catalytic cycle of cytochrome cd(1) using synthetic model complexes. The complexes investigated are iron complexes of dioxo-octaethylisobacteriochlorin (1), mono-oxooctaethylchlorin (2) and octaethylporphyrin (3). We show here that the reduction potential for the transition from the ferric state to the ferrous state and the binding constant for binding of NO2- to the ferrous complex increases with a trend of 3 < 2 < 1. However, the reactivity of the ferrous nitrite complex with protons increases in the reversed order, 1 < 2 < 3. We also show that the iron bound NO of the ferric NO complex is readily replaced by addition of 1 equiv. of p-nitrophenolate. These results indicate that the dioxo-isobacteriochlorin structure is superior to porphyrin and mono-oxo-chlorin structures in the first iron reduction step, the second nitrite binding step, and the NO dissociation step, but inferior in the third nitrite reduction step. These results suggest that the heme d(1) has evolved as the catalytic site of cytochrome cd(1) to catalyze the nitrite reduction at the highest possible redox potential while maintaining its catalytic activity., ROYAL SOC CHEMISTRY, 2016, CHEMICAL SCIENCE, 7 (4), 2896 - 2906, doi;web_of_science

    Scientific journal

  • Factors Affecting Hydrogen-Tunneling Contribution in Hydroxylation Reactions Promoted by Oxoiron(IV) Porphyrin pi-Cation Radical Complexes

    Zhiqi Cong; Haruki Kinemuchi; Takuya Kurahashi; Hiroshi Fujii

    Hydrogen atom transfer with a tunneling effect (H-tunneling) has been proposed to be involved in aliphatic hydroxylation reactions catalyzed by cytochrome P450 and synthetic heme complexes as a result of the observation of large hydrogen/deuterium kinetic isotope effects (KIEs). In the present work, we investigate the factors controlling the H-tunneling contribution to the H-transfer process in hydroxylation reaction by examining the kinetics of hydroxylation reactions at the benzylic positions of xanthene and 1,2,3,4-tetrahydronaphthalene by oxoiron(IV) 5,10,15,20-tetramesitylporphyrin pi-cation radical complexes ((TMP+center dot)(FeO)-O-IV(L)) under single-turnover conditions. The Arrhenius plots for these hydroxylation reactions of H-isotopomers have upwardly concave profiles. The Arrhenius plots of D-isotopomers, clear isosbestic points, and product analysis rule out the participation of thermally dependent other reaction processes in the concave profiles. These results provide evidence for the involvement of H-tunneling in the rate-limiting H-transfer process. These profiles are simulated using an equation derived from Bell's tunneling model. The temperature dependence of the KIE values (k(H)/k(D))) determined for these reactions indicates that the KIE value increases as the reaction temperature becomes lower, the bond dissociation energy (BDE) of the C-H bond of a substrate becomes higher, and the reactivity of (TMP+center dot)(FeO)-O-IV(L) decreases. In addition, we found correlation of the slope of the 1n(k(H)/k(D)) - 1/T plot and the bond strengths of the Fe=O bond of (TMP+center dot)(FeO)-O-IV(L) estimated from resonance Raman spectroscopy. These observations indicate that these factors modulate the extent of the H-tunneling contribution by modulating the ratio of the height and thickness of the reaction barrier., AMER CHEMICAL SOC, Oct. 2014, INORGANIC CHEMISTRY, 53 (19), 10632 - 10641, doi;web_of_science

    Scientific journal

  • Theoretical Study of One-Electron Oxidized Mn(III)- and Ni(II)-Salen Complexes: Localized vs Delocalized Ground and Excited States in Solution

    Shinji Aono; Masayuki Nakagaki; Takuya Kurahashi; Hiroshi Fujii; Shigeyoshi Sakaki

    One-electron oxidized Mn(III)- and Ni(II)-salen complexes exhibit unique mixed-valence electronic structures and charge transfer (CT) absorption spectra. We theoretically investigated them to elucidate the reason why the Mn(III)-salen complex takes a localized electronic structure (class II mixed valence compound by Robin Day classification) and the Ni(II)-analogue has a delocalized one (class III) in solution, where solvation effect was taken into consideration either by the three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) method or by the mean-field (MF) QM/MM-MD simulation. The geometries of these complexes were optimized by the 3D-RISM-SCF-U-DFT/M06. The vertical excitation energy and the oscillator strength of the first excited state were evaluated by the general multiconfiguration reference quasi-degenerate perturbation theory (GMC-QDPT), including the solvation effect based on either 3D-RISM-SCF- or MF-QM/MM-MD-optimized solvent distribution. The computational results well agree with the experimentally observed absorption spectra and the experimentally proposed electronic structures. The one-electron oxidized Mn(III) salen complex with a symmetrical salen ligand belongs to the class II, as experimentally reported, in which the excitation from the phenolate anion to the phenoxyl radical moiety occurs. In contrast, the one-electron oxidized Ni(II)-salen complex belongs to the class III, in which the excitation occurs from the doubly occupied delocalized pi(1) orbital of the salen radical to the singly occupied delocalized pi(2) orbital; the pi(1) is a bonding combination of the HOMOs of two phenolate moieties and the pi(2) is an antibonding combination. Solvation effect is indispensable for correctly describing the mixed-valence character, the geometrical distortion, and the intervalence CT absorption spectra of these complexes. The number of d electrons and the d orbital energy level play crucial roles to provide the localization/delocalization character of these complexes., AMER CHEMICAL SOC, Mar. 2014, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 10 (3), 1062 - 1073, doi;web_of_science

    Scientific journal

  • Synthesis, Characterization, and Reactivity of Hypochlorito-Iron(III) Porphyrin Complexes

    H. Fujii; Z. Cong; T. Kurahashi; S. Yanagisawa; T. Ogura

    SPRINGER, Mar. 2014, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, 19, S159 - S159, web_of_science

  • Di-mu-oxo Dimetal Core of Mn-IV and Ti-IV as a Linker Between Two Chiral Salen Complexes Leading to the Stereoselective Formation of Different M- and P-Helical Structures

    Takuya Kurahashi; Masahiko Hada; Hiroshi Fujii

    Because of restricted rotational freedom along the metal-metal axis, a di-mu-oxo dimetal core could be an excellent building block to create dinuclear compounds with well-defined stereochemistry, but their stereoselective synthesis remains a challenge. We herein report the formation of di-mu-oxo dimanganese(IV) complexes with tetradentate salen ligands bearing different degrees of steric bulk, in order to study stereochemical aspects of the dimerization reaction that potentially generates multiple stereoisomers. Xray crystallography shows that the di-mu-oxo dimanganese(IV) complex with salen, where salen is (R,R)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, adopts a unique structure in which two salen complexes are arranged in an M-helical fashion. According to the solution study using H-1, H-2 NMR, and circular dichroism spectroscopies, the dimerization reaction is highly diastereoselective in the presence of the tert-butyl group at the 3/3' position as a determinant steric factor. In contrast, the di-mu-oxo dititanium(IV) complex with the same salen ligand was previously reported to afford an opposite P-helical dimer. The present DFT study clarifies that a less-covalent Ti-O bonding causes a distortion of the di-mu-oxo dititanium(IV) core structure, generating a completely different framework for interligand interaction. The present study provides a solid basis to understand the stereochemistry for the formation of the di-mu-oxo dimetal core., AMER CHEMICAL SOC, Jan. 2014, INORGANIC CHEMISTRY, 53 (2), 1070 - 1079, doi;web_of_science

    Scientific journal

  • Oxygen-Atom Transfer from Iodosylarene Adducts of a Manganese(IV) Salen Complex: Effect of Arenes and Anions on I(III) of the Coordinated Iodosylarene

    Chunlan Wang; Takuya Kurahashi; Kensuke Inomata; Masahiko Hada; Hiroshi Fujii

    This paper reports preparation, characterization, and reactivity of iodosylarene adducts of a manganese(IV) salen complex. In order to systematically investigate steric and electronic factors that control reactivity and selectivity, we prepared iodosylarene adducts from iodosylbenzene, iodosylmesitylene, 2,4,6-triethyliodosylbenzene, and pentafluoroiodosylbenzene. We also investigated the effect of anions on I(III) by using chloride, benzoate, and p-toluenesulfonate. Spectroscopic studies using H-1 NMR, electron paramagnetic resonance, infrared spectroscopy, and electrospray ionization mass spectrometry show that these iodosylarene adducts are manganese(IV) complexes bearing two iodosylarenes as external axial ligands. Reactions with thioanisole under the pseudo-first-order conditions show that the electron-withdrawing pentafluorophenyl group and the p-toluenesulfonate anion on I(III) significantly accelerate the oxygen-atom transfer. The high reactivity is correlated with a weakened I-OMn bond, as indicated by IR spectroscopy and mass spectrometry. Stoichiometric reactions with styrenes show that both enantioselectivity and diastereoselectivity are dependent on the arenes and anions on I(III) of the coordinate iodosylarenes. Notably, the pentafluorophenyl group and the p-toluenesulfonate anion suppress the cis-to-trans isomerization in the epoxidation of cis-beta-methylstyrene. The present results show that iodosylarene adducts of manganese(IV) salen complexes are indeed active oxygen-atom-transfer reagents and that their reactivity and selectivity are regulated by steric and electronic properties of the arenes and anions on I(III) of the coordinated iodosylarenes., AMER CHEMICAL SOC, Aug. 2013, INORGANIC CHEMISTRY, 52 (16), 9557 - 9566, doi;web_of_science

    Scientific journal

  • Unique Ligand-Radical Character of an Activated Cobalt Salen Catalyst That Is Generated by Aerobic Oxidation of a Cobalt(II) Salen Complex

    Takuya Kurahashi; Hiroshi Fujii

    The Co(salen)(X) complex, where salen is chiral N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine and X is an external axial ligand, has been widely utilized as a versatile catalyst. The Co(salen)(X) complex is a stable solid that has been conventionally described as a Co-III(salen)(X) complex. Recent theoretical calculations raised a new proposal that the Co(salen)(H2O)(SbF6) complex contains appreciable contribution from a Co-II(salen(circle+)) electronic structure (Kochem, A.; Kanso, H.; Baptiste, B.; Arora, H.; Philouze, C.; Jarjayes, O.; Vezin, H.; Luneau, D.; Orb, M.; Thomas, F. Inorg. Chem. 2012, 51, 10557-10571), while other theoretical calculations for Co(salen)(Cl) indicated a triplet Co-III(salen) electronic structure (Kemper, S.; Hrobarik, P.; Kaupp, M.; Schlorer, N. E. J. Am. Chem. Soc. 2009, 131, 4172-4173). However, there have been no experimental data to evaluate these theoretical proposals. We herein report key experimental data on the electronic structure of the Co(salen)(X) complex (X = CF3SO3-, SbF6-, and p-MeC6H4SO3-). The X-ray crystallography shows that Co(salen)(OTf) has a square-planar N2O2 equatorial coordination sphere with OTf as an elongated external axial ligand. Magnetic susceptibility data indicate that Co(salen)(OTf) complexes belong to the S = 1 spin system. H-1 NMR measurements provide convincing evidence for the Co-II(salen(circle+))(X) character, which is estimated to be about 40% in addition to 60% Co-III(salen)(X) character. The CH2Cl2 solution of Co(salen)(X) shows an intense near-IR absorption, which is assigned as overlapped transitions from a ligand-to-metal charge transfer in Co-III(salen)(X) and a ligand-to-ligand charge transfer in Co-II(salen(circle+))(X). The present experimental study establishes that the electronic structure of Co(salen)(X) contains both Co-II(salen(circle+))(X) and Co-III(salen)(X) character., AMER CHEMICAL SOC, Apr. 2013, INORGANIC CHEMISTRY, 52 (7), 3908 - 3919, doi;web_of_science

    Scientific journal

  • 酸化反応に関わる金属酵素からみた生物無機化学の展望

    藤井 浩

    2013, 錯体化学会誌, 62

  • Synthesis, Characterization, and Reactivity of Hypochloritoiron(III) Porphyrin Complexes

    Zhiqi Cong; Sachiko Yanagisawa; Takuya Kurahashi; Takashi Ogura; Satoru Nakashima; Hiroshi Fujii

    A hypochloritoiron(III) porphyrin species has been proposed as a key intermediate in an antimicrobial defense system in neutrophils and in hemecatalyzed chlorination reactions. We report herein the preparation, spectroscopic characterization, and reactivity of the bis(hypochlorito)iron(III) porphyrin complex [(TPFP)Fe-III(OC1)(2)](-) (1) and the imidazole-hypochloritoiron complexes (TPFP)Fe-III(OC1)(1-R-Im) [R = CH3 (2), H (3), CH2CO2H (4)], in which TPFP is 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinate. The structures of 1-4 were confirmed by absorption, H-2 and F-19 NMR, EPR, and resonance Raman spectroscopy and electrospray ionization mass spectrometry at low temperature. The reactions of 1 and 2 with various organic substrates show that 1 and 2 are capable of chlorination, sulfoxidation, and epoxidation reactions and that 1 is much more reactive with these substrates than 2., AMER CHEMICAL SOC, Dec. 2012, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (51), 20617 - 20620, doi;web_of_science

    Scientific journal

  • Comparative Spectroscopic Studies of Iron(III) and Manganese(III) Salen Complexes Having a Weakly Coordinating Triflate Axial Ligand

    Takuya Kurahashi; Hiroshi Fujii

    We thoroughly compared spectroscopic and magnetic properties of mononuclear iron(III) and manganese(III) complexes with symmetric and nonsymmetrical salen ligands, in order to investigate the relation between spectroscopic properties and electronic structures. Magnetic susceptibility and dual-mode electron paramagnetic resonance data show the assignment of [Fe-III(salen)(OTf)] and [Mn-III(salen)(OTf)] as high-spin S = 5/2 and S = 2 electronic configurations, respectively, irrespective of the electron-donating properties and symmetry of the salen ligand. Further insights into electronic structures of central metal are obtained from H-2 NMR spectra of selectively deuterated complexes, in which [Fe-III(salen)(OTf)] and [Mn-III(salen)(OTf] exhibit well-resolved paramagnetic NMR signals of quite different shift patterns, due to the presence or absence of the unpaired electron in the d(x2-y2) orbital expected for S = 5/2 iron(III) or S = 2 manganese(III) centers., CHEMICAL SOC JAPAN, Sep. 2012, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 85 (9), 940 - 947, doi;web_of_science

    Scientific journal

  • Effect of the Axial Ligand on the Reactivity of the Oxoiron(IV) Porphyrin pi-Cation Radical Complex: Higher Stabilization of the Product State Relative to the Reactant State

    Akihiro Takahashi; Daisuke Yamaki; Kenichiro Ikemura; Takuya Kurahashi; Takashi Ogura; Masahiko Hada; Hiroshi Fujii

    The proximal heme axial ligand plays an important role in tuning the reactivity of oxoiron(IV) porphyrin pi-cation radical species (compound I) in enzymatic and catalytic oxygenation reactions. To reveal the essence of the axial ligand effect on the-reactivity, we investigated it from a thermodynamic viewpoint. Compound I model complexes, (TMP+center dot)(FeO)-O-IV(L) (where TMP is 5,10,15,20-tetrarnesitylporphyrin and TMP+center dot is its pi-cation radical), can be provided with altered reactivity by changing the identity of the axial ligand, but the reactivity is not correlated with spectroscopic data (nu(Fe=O), redox potential, and so on) of (TMP+center dot)(FeO)-O-IV(L). Surprisingly, a clear correlation was found between the reactivity of (TMP+center dot)(FeO)-O-IV(L) and the Fe-II/Fe-III redox potential of (TMP)(FeL)-L-III, the final reaction product. This suggests that the thermodynamic stability of (TMP)(FeL)-L-III is involved in the mechanism of the axial ligand effect. Axial ligand-exchange experiments and theoretical calculations demonstrate a linear free-energy relationship, in which the axial ligand modulates the reaction free energy by changing the thermodynamic stability of (TMP)Fe-III(L) to a greater extent than (TMP+center dot)(FeO)-O-IV(L). The linear free energy relationship could be found for a wide range of anionic axial ligands and for various types of reactions, such as epoxidation, demethylation, and hydrogen abstraction reactions. The essence of the axial ligand effect is neither the electron donor ability of the axial ligand nor the electron affinity of compound I, but the binding ability of the axial ligand (the stabilization by the axial ligand). An axial ligand that binds more strongly makes (TMP)Fe-III(L) more stable and (TMP+center dot)(FeO)-O-IV(L) more reactive. All results indicate that the axial ligand controls the reactivity of compound I (the stability of the transition state) by the stability of the ground state of the final reaction product and not by compound I itself., AMER CHEMICAL SOC, Jul. 2012, INORGANIC CHEMISTRY, 51 (13), 7296 - 7305, doi;web_of_science

    Scientific journal

  • Coordination and Electronic Structure of Ruthenium(II)-tris-2,2 '-bipyridine in the Triplet Metal-to-Ligand Charge-Transfer Excited State Observed by Picosecond Time-Resolved Ru K-Edge XAFS

    Tokushi Sato; Shunsuke Nozawa; Ayana Tomita; Manabu Hoshino; Shin-ya Koshihara; Hiroshi Fujii; Shin-ichi Adachi

    Time-resolved X-ray absorption spectra of photoexcited nithenium(H)-tris-2,2'-bipyridine ([Ru-II(bpy)(3)](2+) in the triplet metal-to-ligand charge transfer ((MLCT)-M-3) state are measured and analyzed to investigate transient structural changes directly related to the photophysical properties of the complex. The results from visible (400 rim) and UV (267 nm) excitation indicate that electrostatic interaction between the oxidized Ru atom and the reduced bipyridine ligand is the dominant factor affecting the Ru-N bond contraction. This thus leads to two groups of Ru ligand distances, one exhibiting the ground-state Ru-N distance and another yielding a slightly decreased Ru-N distance due to the localized MLCT excited state. The EXAFS analysis of the photoexcited complex was analyzed toward one single Ru-N distance., yielding a contraction of 0.04 (0.01) angstrom with an increased DW factor (corresponding to a 0.05 angstrom mean increase)., AMER CHEMICAL SOC, Jul. 2012, JOURNAL OF PHYSICAL CHEMISTRY C, 116 (27), 14232 - 14236, doi;web_of_science

    Scientific journal

  • Formation of Iron(III) meso-Chloro-isoporphyrin as a Reactive Chlorinating Agent from Oxoiron(IV) Porphyrin pi-Cation Radical

    Zhiqi Cong; Takuya Kurahashi; Hiroshi Fujii

    Iron(III) isoporphyrin, a tautomer of porphyrin with a saturated meso carbon, is one of the isoelectronic forms of oxoiron(IV) porphyrin pi-cation radical, which is known as an important reactive intermediate of various heme enzymes. The isoporphyrin has been believed to be incapable of catalyzing oxygenation and oxidation reactions. Here, we report that an oxoiron(IV) porphyrin pi-cation radical can be converted to iron(III) meso-chloro-isoporphyrin in the presence of trifluoroacetic acid and chloride ion. More importantly, this study shows the first evidence that iron(III) meso-chloro-isoporphyrin is an excellent reactive agent for chlorinating aromatic compounds and olefins. The results of this study suggest that the mechanism involves electrophilic chlorination of substrate with iron(III) meso-chloro-isoporphyrin., AMER CHEMICAL SOC, Mar. 2012, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (10), 4469 - 4472, doi;web_of_science

    Scientific journal

  • Structure and Reactivity of an Iodosylarene Adduct of a Manganese(IV)-Salen Complex

    Chunlan Wang; Takuya Kurahashi; Hiroshi Fujii

    WILEY-V C H VERLAG GMBH, 2012, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 51 (31), 7809 - 7811, doi;web_of_science

    Scientific journal

  • Solid-state O-17 NMR and computational studies of terminal transition metal oxo compounds

    Jianfeng Zhu; Takuya Kurahashi; Hiroshi Fujii; Gang Wu

    We report solid-state NMR characterization of the O-17 (I = 5/2) chemical shift and quadrupole coupling tensors in two terminal oxo compounds, O-17 Ti(IV)(TMP) and O-17 Cr(IV)(TMP), in which TMP is 5,10,15,20-tetramesitylporphyrin and the oxo ligand is enriched by O-17 (ca. 40%). This is the first time that O-17 NMR tensors are determined for this important class of compounds. The O-17 nuclei in the O Ti and O Cr triple bonds are found to exhibit very large chemical shift anisotropies but rather small O-17 quadrupole coupling constants. Terminal oxo compounds represent one of the rare cases where the atomic nucleus under study simultaneously experiences a highly anisotropic magnetic shielding environment, but a highly symmetrical electric field distribution. The solid-state O-17 NMR data are consistent with solid-state C-13, N-15 and P-31 NMR results on carbido, nitrido and phosphido compounds. The density functional theory (DFT) computations using the zeroth-order regular approximation (ZORA) to account for spin-orbital relativistic effects reproduce the experimental O-17 NMR results reasonably well. DFT computations also reveal the origins at the molecular orbital level of the observed O-17 NMR properties for terminal oxo compounds., ROYAL SOC CHEMISTRY, 2012, CHEMICAL SCIENCE, 3 (2), 391 - 397, doi;web_of_science

    Scientific journal

  • Redox Potentials of Oxoiron(IV) Porphyrin pi-Cation Radical Complexes: Participation of Electron Transfer Process in Oxygenation Reactions

    Akihiro Takahashi; Takuya Kurahashi; Hiroshi Fujii

    The oxoiron(IV) porphyrin pi-cation radical complex (compound I) has been identified as the key reactive intermediate of several heme enzymes and synthetic heme complexes. The redox properties of this reactive species are not yet well understood. Here, we report the results of a systematic study of the electrochemistry of oxoiron(IV) porphyrin pi-cation radical complexes with various porphyrin structures and axial ligands in organic solvents at low temperatures. The cyclic voltammogram of (TMP)Fe(IV)O, (TMP = 5,10,15,20-tetramesitylporphyrinate), exhibits two quasi-reversible redox waves at E(1/2) = 0.88 and 1.18 V vs SCE in dichloromethane at similar to 60 degrees C. Absorption spectral measurements for electrochemical oxidation at controlled potential clearly indicated that the first redox wave results from the (TMP)Fe(IV)O/[TMP(+circle))Fe(IV)O](+) couple. The redox potential for the (TMP)Fe(IV)O/[(TMP(+circle))Fe(IV)O](+) couple undergoes a positive shift upon coordination of an anionic axial ligand but a negative shift upon coordination of a neutral axial ligand (imidazole). The negative shifts of the redox potential for the imidazole complexes are contrary to their high oxygenation activity. On the other hand, the electron-withdrawing effect of the meso-substituent shifts the redox potential in a positive direction. Comparison of the, measured redox potentials and reaction rate constants for epoxidation of cyclooctene and demethylation of N,N-dimethylanilines enable us to discuss the details of the electron transfer process from substrates to the oxoiron(IV) porphyrin pi-cation radical complex in the oxygenation mechanisms., AMER CHEMICAL SOC, Aug. 2011, INORGANIC CHEMISTRY, 50 (15), 6922 - 6928, doi;web_of_science

    Scientific journal

  • One-Electron Oxidation of Electronically Diverse Manganese(III) and Nickel(II) Salen Complexes: Transition from Localized to Delocalized Mixed-Valence Ligand Radicals

    Takuya Kurahashi; Hiroshi Fujii

    Ligand radicals from salen complexes are unique mixed-valence compounds in which a phenoxyl radical is electronically linked to a remote phenolate via a neighboring redox-active metal ion, providing an opportunity to study electron transfer from a phenolate to a phenoxyl radical mediated by a redox-active metal ion as a bridge. We herein synthesize one-electron-oxidized products from electronically diverse manganese(III) salen complexes in which the locus of oxidation is shown to be ligand-centered, not metal-centered, affording manganese(III) phenoxyl radical species. The key point in the present study is an unambiguous assignment of intervalence charge transfer bands by using nonsymmetrical salen complexes, which enables us to obtain otherwise inaccessible insight into the mixed-valence property. A d(4) high-spin manganese (III) ion forms a Robin Day class II mixed-valence system, in which electron transfer is occurring between the localized phenoxyl radical and the phenolate. This is in clear contrast to a d(8) low-spin nickel(II) ion with the same salen ligand, which induces a delocalized radical (Robin Day class III) over the two phenolate rings, as previously reported by others. The present findings point to a fascinating possibility that electron transfer could be drastically modulated by exchanging the metal ion that bridges the two redox centers., AMER CHEMICAL SOC, Jun. 2011, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133 (21), 8307 - 8316, doi;web_of_science

    Scientific journal

  • Oxidation of Chloride and Subsequent Chlorination of Organic Compounds by Oxoiron(IV) Porphyrin pi-Cation Radicals

    Zhiqi Cong; Takuya Kurahashi; Hiroshi Fujii

    WILEY-BLACKWELL, 2011, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 50 (42), 9935 - 9939, doi;web_of_science

    Scientific journal

  • 高酸化サレン錯体を鍵とする不斉酸化触媒や金属酵素の機能発現機構の研究

    藤井 浩; 倉橋 拓也

    2011, 錯体化学会誌, 57, 57 - 66, doi

  • Unique Properties and Reactivity of High-Valent Manganese-Oxo versus Manganese-Hydroxo in the Salen Platform

    Takuya Kurahashi; Akihiro Kikuchi; Yoshitsugu Shiro; Masahiko Hada; Hiroshi Fujii

    To gain an understanding of oxidation reactions by Mn(III)(salen), a reaction of Mn(III)(salen) with m-chloroperoxybenzoic acid in the absence of a substrate is investigated. UV-vis, perpendicular- and parallel-mode electron paramagnetic resonance, and X-ray absorption spectroscopy show that the resulting solution contains Mn(IV)(salen)(O) as a major product and Mn(IV)(salen)(OH) as a minor product. Mn(IV)(salen)(O) readily reacts with 4-H-2,6-tert-Bu(2)C(6)H(2)OH (homolytic bond dissociation energy of an OH bond, BDE(OH) = 82.8 kcal mol(-1)), 4-CH(3)CO-2,6-tert-Bu(2)C(6)H(2)OH (BDE(OH) = 83.1 kcal mol(-1)), and 4-NC-2,6-tert-Bu(2)C(6)H(2)OH (BDE(OH) = 84.2 kcal mol(-1)) at 203 K, following second-order rate kinetics. Mn(IV)(salen)(OH) reacts with 4-CH(3)CO-2,6-tert-Bu(2)C(6)H(2)OH (BDE(OH) = 83.1 kcal mol(-1)) much more slowly under identical conditions than Mn(IV)(salen)(O) and does not react with 4-NC-2,6-tert-Bu(2)C(6)H(2)OH (BDE(OH) = 84.2 kcal mol(-1), suggesting that the thermodynamic hydrogen-atom-abstracting ability of Mn(IV)(salen)(OH) is about 83 kcal mol(-1). The rate constant for reactions of Mn(IV)(salen)(OH) with phenols is not dependent on the concentration of phenols, suggesting that Mn(IV)(salen)(OH) might bind phenols prior to the rate-limiting oxidation reactions. Quantum chemical calculations are carried out for Mn(IV)(salen)(O) and Mn(IV)(salen)(OH), both of which well reproduce the extended X-ray absorption fine structures as well as the electronic configurations. It is also indicated that protonation of Mn(IV)(salen)(OH) induces a drastic electronic structural change from manganese(IV) phenolate to a manganese(III) phenoxyl radical, which is also consistent with the experimental observation., AMER CHEMICAL SOC, Jul. 2010, INORGANIC CHEMISTRY, 49 (14), 6664 - 6672, doi;web_of_science

    Scientific journal

  • Resonance Raman Study of a High-valent Fe=O Porphyrin Complex as a Model for Peroxidase Compound II

    Hirohito Ishimaru; Hiroshi Fujii; Takashi Ogura

    Resonance Raman spectroscopy is applied to a Fe-IV oxo porphyrin with imidazolate as the axial ligand. The v(Fe=O) mode is observed at 792 cm(-1), which is 23 cm(-1) lower than that of the analogous 1-methylimidazole complex and similar to that of horseradish peroxidase compound II (787 cm(-1)) at alkaline pH, for which presence of an anionic histidine was previously postulated. This study thus provides a useful model compound of horseradish peroxidase compound II., CHEMICAL SOC JAPAN, Apr. 2010, CHEMISTRY LETTERS, 39 (4), 332 - 333, doi;web_of_science

    Scientific journal

  • Direct Probing of Spin State Dynamics Coupled with Electronic and Structural Modifications by Picosecond Time-Resolved XAFS

    Shunsuke Nozawa; Tokushi Sato; Matthieu Chollet; Kouhei Ichiyanagi; Ayana Tomita; Hiroshi Fujii; Shin-ichi Adachi; Shin-ya Koshihara

    The first direct observation of the transient spin-state in a disordered magnetic system with time-resolved XAFS is reported. By observing the evolution of the Fe(II) 1s -3d transition, the spin crossover transition from the (1)A(1) low spin state to (5)T(2) high spin state has been directly observed on a picosecond time scale. Moreover, observation of the transient spin state with time-resolved XAFS allows for the investigation of the variations in the electronic state and molecular structure. This unique experimental technique probes the excited states involved in the ultrafast photoinduced reactions in disordered magnetic systems., AMER CHEMICAL SOC, Jan. 2010, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132 (1), 61 - +, doi;web_of_science

    Scientific journal

  • Paramagnetic C-13 and N-15 NMR Analyses of the Push and Pull Effects in Cytochrome c Peroxidase and Coprinus cinereus Peroxidase Variants: Functional Roles of Highly Conserved Amino Acids around Heme

    Daisuke Nonaka; Hiroyuki Wariishi; Karen G. Welinder; Hiroshi Fujii

    Paramagnetic C-13 and N-15 nuclear magnetic resonance (NMR) spectroscopy of heme-bound cyanide ((CN)-C-13-N-15) was applied to 11 cytochrome e peroxidase (UP) and Coprinus cinereus peroxidase (CIP) mutants to investigate contributions to the Push and Pull effects of conserved amino acids around heme. The C-13 and N-15 NMR data for the distal His and Arg mutants indicated that distal His is the key amino acid residue creating the strong pull effect and that distal Arg assists. The Mutation of distal Trp of CcP to Phe, the amino acid at this position in CIP, changed the push and pull effects so they resembled those of CIP, whereas the mutation of distal Pile of CIP to Trp changed this mutant to become CcP-like. The C-13 NMR shifts for the proximal Asp mutants clearly showed that the proximal Asp-His hydrogen bonding strengthens the push effect. However, even in the absence of a hydrogen bond, the push effect of proximal His in peroxidase is significantly stronger than in globins. Comparison of these NMR data with the Compound I formation rate constants and crystal Structures Of these mutants showed that (1) the base catalysis of the distal His is more critical for rapid compound I Formation than its acid catalysis, (2) the primary function of the distal Arg is to maintain the distal heme pocket in favor of rapid Compound I formation via hydrogen bonding, and (3) the push effect is the major contribution to the differential rates of compound I formation in wild-type peroxidases., AMER CHEMICAL SOC, Jan. 2010, BIOCHEMISTRY, 49 (1), 49 - 57, doi;web_of_science

    Scientific journal

  • Critical Role of External Axial Ligands in Chirality Amplification of trans-Cyclohexane-1,2-diamine in Salen Complexes

    Takuya Kurahashi; Masahiko Hada; Hiroshi Fujii

    A series of Mn(IV)(salen)(L)(2) complexes bearing different external axial ligands (L = Cl, NO(3), N(3), and OCH(2)CF(3)) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that Mn(IV)(salen)(OCH(2)CF(3))(2) and Mn(IV)(salen)(N(3))(2) adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for Mn(IV)(salen)(Cl)(2). The CH(2)Cl(2) solution of Mn(IV)(salen)(L)(2) shows circular dichroism of increasing intensity in the order L = Cl < NO(3) << N(3) < OCH(2)CF(3), which indicates Mn(IV)(salen)(L)(2) adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in Mn(IV)(salen)(L)(2) to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation., AMER CHEMICAL SOC, Sep. 2009, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 131 (34), 12394 - 12405, doi;web_of_science

    Scientific journal

  • Catalytic Reactivity of a Meso-N-Substituted Corrole and Evidence for a High-Valent Iron-Oxo Species

    Amanda J. McGown; William D. Kerber; Hiroshi Fujii; David P. Goldberg

    It is shown that an iron(III) meso-N-substituted corrole (TBP(8)Cz)Fe(III) (1) (TBP(8)CZ = octakis(4-tert-butylphenyl)corrolazinato), is a potent catalyst for the oxidation of alkenes in the presence of pentaflouroiodosylbenzene (C(6)F(5)IO) as oxidant. In the case of cyclohexene, complex 1 performs on a par with one of the best porphyrin catalysts ((TPPF(20))FeCl), exhibiting rapid turnover and a high selectivity for epoxide (CzFe(III)/C(6)F(5)IO/cyclohexene (1:100:1000) in CH(2)Cl(2)/CH(3)OH (3:1 v:v) gives 33 turnovers of epoxide.in <2 min). Reaction rates for 1 are greatly enhanced compared to other Fe or Mn corroles under similar catalytic conditions, consistent with an increase in the electrophilicity of a high-valent iron-oxo intermediate induced by meso-N substitution. Reaction of dark-green 1 (lambda(max) = 440, 611, 747 nm) under single-turnover-ike conditions at -78 degrees C leads to the formation of a new dark-brown species (2) (lambda(max) = 396, 732, 843 nm). The Fe(III) complex 1 is restored upon the addition of 2 equiv of ferrocene to 2, or by the addition of 1 equiv of PPh(3), which concomitantly yields OPPh(3). In addition, complex 2 reacts with excess cyclohexene at -42 degrees C to give 1. Complex 2 was also characterized by EPR spectroscopy, and all of the data are consistent with 2 being an antiferromagnetically coupled iron(IV)-oxo pi-cation-radical complex. Rapid-mixing stopped-flow UV-vis studies show that the low-temperature complex 2 is generated as a short-lived intermediate at room temperature., AMER CHEMICAL SOC, Jun. 2009, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 131 (23), 8040 - 8048, doi;web_of_science

    Scientific journal

  • Effect of Imidazole and Phenolate Axial Ligands on the Electronic Structure and Reactivity of Oxoiron(IV) Porphyrin pi-Cation Radical Complexes: Drastic Increase in Oxo-Transfer and Hydrogen Abstraction Reactivities

    Akihiro Takahashi; Takuya Kurahashi; Hiroshi Fujii

    To study the effect of axial ligands on the electronic structure and reactivity of compound I of peroxidases and catalases, oxoiron(IV) porphyrin pi-cation radical complexes with imidazole, 2-methylimidazole, 4(5)-methylimidazole, and 3-fluoro-4-nitrophenolate as the axial ligands were prepared by ozone oxidation of iron(III) complexes of 5,10,15,20-tetramesitylporphyrin (TMP) and 2,7,12,17-tetramethyl-3,8,13,18-tetramesitylporphyrin (TMTMP). These complexes were fully characterized by absorption, H-1, H-2, and F-19 NMR, electron paramagnetic resonance (EPR), and electrospray ionization mass spectrometry (ESI-MS) spectroscopy. The characteristic absorption peak of compound I at approximately 650 nm was found to be a good marker for estimation of the electron donor effect from the axial ligand. The axial ligand effect did not change the porphyrin pi-cation radical state, the a(2u) state of the TMP complexes, or the a,, radical state of both the TMTMP complexes and compound 1. The ferryl iron and porphyrin pi-cation radical spins were effectively transferred into the axial ligands for the a2u complexes but not for the a,, complexes. Most importantly, the reactivity of the oxoiron(IV) porphyrin pi-cation radical complex was drastically increased by the imidazole and phenolate axial ligands. The reaction rate for cyclooctene epoxidation was increased 100- to 400-fold with axial coordination of imidazoles and phenolate. A similar increase was also observed for the oxidation of 1,4-cyclohexadiene, N, N-dimethyl-p-nitroaniline and hydrogen peroxide. These results suggest extreme enhancement of the reactivity of compound I by the axial ligand in heme enzymes. The functional role of axial ligands on the compound I in heme enzymes is discussed., AMER CHEMICAL SOC, Mar. 2009, INORGANIC CHEMISTRY, 48 (6), 2614 - 2625, doi;web_of_science

    Scientific journal

  • Paramagnetic C-13 and N-15 NMR Analyses of Cyanide- ((CN)-C-13-N-15-) Ligated Ferric Peroxidases: The Push Effect, Not Pull Effect, Modulates the Compound I Formation Rate

    Daisuke Nonaka; Hiroyuki Wariishi; Hiroshi Fujii

    Paramagnetic C-13 and N-15 NMR spectroscopy of home-bound cyanide ((CN)-C-13-N-15) was utilized to quantitatively distinguish the electron donor effect (the push effect) from the proximal histidine and hydrogen-bonding effect (the pull effect) from the distal amino acid residues in cytochrome c peroxidase (CcP), ascorbate peroxidase (APX), lignin peroxidase (LiP), and manganese peroxidase (MnP). Paramagnetic C-13 NMR signals of heme-bound (CN)-C-13-N-15 of these peroxidases were observed in a wide range, -3501 ppm (CcP), -3563 ppm (APX), -3823 ppm (MnP), and -3826 ppm (LiP), while paramagnetic N-15 NMR signals of those were detected in a narrow range, 574 ppm (ARP), 605 ppm (CcP), 626 ppm (LiP), and 654 ppm (MnP). Detailed analysis, combined with the previous results for horseradish peroxidase and Arthromyces ramosus peroxidase, indicated that the push effect is quite different among these peroxidases while the pull effect is similar. More importantly, a strong correlation between the C-13 NMR shift (the push effect) and the compound I: formation rate was observed, indicating that the push effect causes a variation in the compound I formation rate. Comparison of the C-13 and N-15 NMR results of these peroxidases with their crystal structures suggests that the orientation of the proximal imidazole plane to the heme N-Fe-N axis controls the push effect and the compound I formation rate of peroxidase., AMER CHEMICAL SOC, Feb. 2009, BIOCHEMISTRY, 48 (5), 898 - 905, doi;web_of_science

    Scientific journal

  • Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy

    Tokushi Sato; Shunsuke Nozawa; Kohei Ichiyanagi; Ayana Tomita; Matthieu Chollet; Hirohiko Ichikawa; Hiroshi Fujii; Shin-ichi Adachi; Shin-ya Koshihara

    An experimental set-up for time-resolved X-ray absorption spectroscopy with 100 ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented., WILEY-BLACKWELL PUBLISHING, INC, Jan. 2009, JOURNAL OF SYNCHROTRON RADIATION, 16, 110 - 115, doi;web_of_science

    Scientific journal

  • ENDOR Study of Oxoiron(IV) Porphyrin pi-Cation Radical Complexes as Models for Compound I of Heme Enzymes

    Akihiro Takahashi; Yasunori Ohba; Seigo Yamauchi; Hiroshi Fujii

    Electron nuclear double resonance (ENDOR) spectroscopy of oxoiron(IV) porphyrin pi-cation radical complexes with pyrrole beta-substituted porphyrins is reported. Hyperfine coupling constants (A(H)) of the pyrrole beta-methyl groups were determined. Comparison of the A H values with those of compound I of peroxidase and catalase indicated the a(Iu) porphyrin pi-cation radical states of these compound I., CHEMICAL SOC JAPAN, Jan. 2009, CHEMISTRY LETTERS, 38 (1), 68 - 69, doi;web_of_science

    Scientific journal

  • 100-picosecond Time-resolved X-ray Absorption Fine Structure of Fe-II(1,10-phenanthroline)(3)

    Tokushi Sato; Shunsuke Nozawa; Kouhei Ichiyanagi; Ayana Tomita; Hirohiko Ichikawa; Matthieu Chollet; Hiroshi Fujii; Shin-ichi Adachi; Shin-ya Koshihara

    Studying photo-induced molecular dynamics in liquid with sub-nanosecond time-resolution and sub-Angstrom spatial resolution gives information for understanding fundamental chemical process in the photo-induced cooperative phenomena of molecular systems and also for developing new materials and devices. Here, we present time-resolved Xray absorption fine structure on the spin-crossover complex Fe-II tris-(1,10-phenanthroline) dissolved in aqueous solution. We utilized femtosecond laser at 400nm pulse for excitation and 100ps X-ray pulse for probe., IOP PUBLISHING LTD, 2009, LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3), 148, 012035, doi;web_of_science

    International conference proceedings

  • Chiral distortion in a Mn(IV)(salen)(N(3))(2) derived from Jacobsen's catalyst as a possible conformation model for its enantioselective reactions

    Takuya Kurahashi; Hiroshi Fujii

    The Mn(IV)(salen)(N(3))(2) complex (3) from Jacobsen's catalyst is synthesized, and the X-ray crystal structures of 3 as well as the starting Mn(III)(salen)(N(3))(CH(3)OH) complex (2) are determined in order to investigate the conformation of the high-valent Mn(IV)(salen) molecule in comparison with that of Mn(III)(salen). The asymmetric unit of the crystal of 3 contains four complexes, all of which adopt a nonplanar stepped conformation effectively distorted by the chirality of the diimine bridge. The asymmetric unit of 2 also contains four complexes. Two of them show a stepped conformation of a lesser degree, but the other two adopt a bowl-shaped conformation. Comparison of the structural parameters shows that the Mn center in 3 is coordinated from both sides by two external axial N(3) ligands with significantly shorter bond lengths, which could induce greater preference for the stepped conformation in 3. The CH(3)CN solution of 3 shows circular dichroism with a significantly strong band at 275 nm as compared to 2, suggesting that 3 may adopt a more chirally distorted conformation also in solution. The circular dichroism spectrum of 3 is slightly altered with isodichroic points from 298 to 253 K and shows no further change at temperatures lower than 253 K, suggesting that the solution of 3 contains an equilibrium between two conformers, where a low-energy conformer with more chiral distortion is predominantly favored even at room temperature. Complexes 2 and 3 are thoroughly characterized using various techniques including cyclic voltammetry, magnetic susceptibility, UV-vis, electron paramagnetic resonance, (1)H NMR, infrared spectroscopy, and electrospray ionization mass spectrometry., AMER CHEMICAL SOC, Sep. 2008, INORGANIC CHEMISTRY, 47 (17), 7556 - 7567, doi;web_of_science

    Scientific journal

  • Effect of a tridentate ligand on the structure, electronic structure, and reactivity of the copper(I) nitrite complex: Role of the conserved three-histidine ligand environment of the type-2 copper site in copper-containing nitrite reductases

    Masato Kujime; Chiemi Izumi; Masaaki Tomura; Masahiko Hada; Hiroshi Fujii

    It is postulated that the copper(I) nitrite complex is a key reaction intermediate of copper containing nitrite reductases (Cu-NiRs), which catalyze the reduction of nitrite to nitric oxide (NO) gas in bacterial clenitrification. To investigate the structure-function relationship of Cu-NiR, we prepared five new copper(I) nitrite complexes with sterically hindered tris(4-imidazolyl)carbinois [Et-TIC = tris(1-methyl-2-ethyl-4-imidazolyl)carbinol and iPr-TIC = tris(1-methyl-2-isopropyl-4-imidazolyl)carbinol] or tris(1-pyrazolyl)methanes [Me-TPM = tris(3,5-dimethyl-1-pyrazolyl) methane; Et-TPM = tris(3,5-diethyl-1-pyrazolyl) methane; and iPr-TPM = tris(3,5-diisopropyl-1-pyrazolyl) methane]. The X-ray crystal structures of all of these copper(II) nitrite complexes were mononuclear eta(1)-N-bound nitrite complexes with a distorted tetrahedral geometry. The electronic structures of the complexes were investigated by absorption, magnetic circular dichroism (MCD), NMR, and vibrational spectroscopy. All of these complexes are good functional models of Cu-NiR that form NO and copper(II) acetate complexes well from reactions with acetic acid under anaerobic conditions. A comparison of the reactivity of these complexes, including previously reported (iPr-TACN)Cu(NO(2)) [iPr-TACN = 1,4,7-triisopropyl-1,4,7-triazacyclononane], clearly shows the drastic effects of the tridentate ligand on Cu-NiR activity. The copper(I) nitrite complex with the Et-TIC ligand, which is similar to the highly conserved three-histidine ((HiS)(3)) ligand environment in the catalytic site of Cu-NiR, had the highest Cu-NiR activity. This result suggests that the (HiS)(3) ligand environment is essential for acceleration of the Cu-NiR reaction. The highest Cu-NiR activity for the Et-TIC complex can be explained by the structural and spectroscopic characterizations and the molecular orbital calculations presented in this paper. Based on these results, the functional role of the (HiS)(3) ligand environment in Cu-NiR is discussed., AMER CHEMICAL SOC, May 2008, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 130 (19), 6088 - 6098, doi;web_of_science

    Scientific journal

  • Transient intermediates from Mn(salen) with sterically hindered mesityl groups: Interconversion between Mn-IV-phenolate and Mn-III-phenoxyl radicals as an origin for unique reactivity

    Takuya Kurahashi; Akihiro Kikuchi; Takehiko Tosha; Yoshitsugu Shiro; Teizo Kitagawa; Hiroshi Fujii

    In order to reveal structure-reactivity relationships for the high catalytic activity of the epoxidation catalyst Mn(salen), transient intermediates are investigated. Steric hindrance incorporated to the salen ligand enables highly selective generation of three related intermediates, O = Mn-IV(salen), HO-Mn-IV(salen), and H2O-Mn-III(salen(+center dot)), each of which is thoroughly characterized using various spectroscopic techniques including UV-vis, electron paramagnetic resonance, resonance Raman, electrospray ionization mass spectrometry, H-2 NMR, and X-ray absorption spectroscopy. These intermediates are all one-electron oxidized from the starting Mn-III(salen) precursor but differ only in the degree of protonation. However, structural and electronic features are strikingly different: The Mn-O bond length of HO-Mn-IV(salen) (1.83 angstrom) is considerably longer than that of O = Mn-IV(salen) (1.58 angstrom); the electronic configuration of H2O-Mn-III(salen(+center dot)) is Mn-III-phenoxyl radical, while those of O = Mn-IV(salen) and HO-Mn-IV(salen) are Mn-IV-phenolate. Among O = Mn-IV(salen), HO-Mn-IV(salen), and H2O-Mn-III(salen(+center dot)), only the O = Mn-IV(salen) can transfer oxygen to phosphine and sulfide substrates, as well as abstract hydrogen from weak C-H bonds, although the oxidizing power is not enough to epoxiclize olefins. The high activity of Mn(salen) is a direct consequence of the favored formation of the reactive O = Mn-IV(salen) state., AMER CHEMICAL SOC, Mar. 2008, INORGANIC CHEMISTRY, 47 (5), 1674 - 1686, doi;web_of_science

    Scientific journal

  • 2. 金属酵素の反応中間体の電子状態・構造解析

    藤井 浩; 城 宜嗣

    2008, 固体物理, 43 (11), 7 - 18

  • Activation parameters for cyclohexene oxygenation by an oxoiron(IV) porphyrin pi-cation radical complex: Entropy control of an allylic hydroxylation reaction

    Akihiro Takahashi; Takuya Kurahashi; Hiroshi Fujii

    Activation parameters for epoxidation and allylic hydroxylation reactions of cyclohexene with (FeO)-O-IV(TMP)Cl center dot+ (1) were determined. Within the experimental temperature range, the epoxidation reaction was enthalpy-controlled (i.e., Delta H-double dagger > -T Delta S-double dagger), while the allylic hydroxylation reaction was entropy-controlled (i.e., -T Delta S-double dagger > Delta H-double dagger). An unexpectedly large contribution of the entropy term for the allylic hydroxylation reaction indicated that the free energy of activation, Delta G(double dagger), rather than the activation energy, E-a, should be used to discuss the reaction mechanism and chemoselectivity. The results of this study bring caution to previous density functional theory studies, in which the reaction mechanism and chemoselectivity are evaluated from calculated E-a., AMER CHEMICAL SOC, Aug. 2007, INORGANIC CHEMISTRY, 46 (16), 6227 - 6229, doi;web_of_science

    Scientific journal

  • Cu-63 NMR spectroscopy of Copper(I) complexes with various tridentate ligands: CO as a useful Cu-63 NMR probe for sharpening Cu-63 NMR signals and analyzing the electronic donor effect of a ligand

    Masato Kujime; Takuya Kurahashi; Masaaki Tomura; Hiroshi Fujii

    Cu-63 NMR spectroscopic studies of copper(I) complexes with various N-donor tridentate ligands are reported. As has been previously reported for most copper(I) complexes, Cu-63 NMR signals, when acetonitrile is coordinated to copper(I) complexes of these tridentate ligands, are broad or undetectable. However, when CO is bound to tridentate copper(I) complexes, the Cu-63 NMR signals become much sharper and show a large downfield shift compared to those for the corresponding acetonitrile complexes. Temperature dependence of Cu-63 NMR signals for these copper(I) complexes show that a quadrupole relaxation process is much more significant to their Cu-63 NMR line widths than a ligand exchange process. Therefore, an electronic effect of the copper bound CO makes the Cu-63 NMR signal sharp and easily detected. The large downfield shift for the copper(I) carbonyl complex can be explained by a paramagnetic shielding effect induced by the copper bound CO, which amplifies small structural and electronic changes that occur around the copper ion to be easily detected in their Cu-63 NMR shifts. This is evidenced by the correlation between the Cu-63 NMR shifts for the copper(I) carbonyl complexes and their nu(CO) values. Furthermore, the Cu-63 NMR shifts for copper(I) carbonyl complexes with imino-type tridentate ligands show a different correlation line with those for amino-type tridentate ligands. On the other hand, C-13 NMR shifts for the copper bound (CO)-C-13 for these copper(I) carbonyl complexes do not correlate with the nu(CO) values. The X-ray crystal structures of these copper(I) carbonyl complexes do not show any evidence of a significant structural change around the Cu-CO moiety. The findings herein indicate that CO complexation makes Cu-63 NMR spectroscopy much more useful for Cu(I) chemistry., AMER CHEMICAL SOC, Jan. 2007, INORGANIC CHEMISTRY, 46 (2), 541 - 551, doi;web_of_science

    Scientific journal

  • Trigonal-bipyramidal geometry induced by an external water ligand in a sterically hindered iron salen complex, related to the active site of protocatechuate 3,4-dioxygenase

    Takuya Kurahashi; Kenji Oda; Manabu Sugimoto; Takashi Ogura; Hiroshi Fujii

    A unique distorted trigonal-bipyramidal geometry observed for the non-heme iron center in protocatechuate 3,4dioxygenase (3,4-PCD) was carefully examined utilizing a sterically hindered iron salen complex, which well reproduces the endogenous His(2)Tyr(2) donor set with water as an external ligand. X-ray crystal structures of a series of iron model complexes containing bis(3,5-dimesitylsalicylidene)-1,2-dimesitylethylenediamine indicate that a distorted trigonal-bipyramidal geometry is achieved upon binding of water as an external ligand. The extent of a structural change of the iron center from a preferred square-pyramidal to a distorted trigonal-bipyramidal geometry varies with the external ligand that is bound in the order Cl << EtO < H2O, which is consistent with the spectrochemical series. The distortion in the model system is not due to steric repulsions but electronic interactions between the external ligand and the iron center, as evidenced from the X-ray crystal structures of another series of iron model complexes with a less-hindered bis(3-xylylsalicylidene)-1,2-dimesitylethylenediamine ligand, as well as by density functional theory calculations. Further spectroscopic investigations indicate that a unique distorted trigonal-bipyramidal geometry is indeed maintained even in solution. The present model study provides a new viewpoint that a unique distorted trigonal-bipyramidal iron site might not be preorganized by a 3,4-PCD protein but could be electronically induced upon the binding of an external hydroxide ligand to the iron(III) center. The structural change induced by the external water ligand is also discussed in relation to the reaction mechanism of 3,4-PCD., AMER CHEMICAL SOC, Sep. 2006, INORGANIC CHEMISTRY, 45 (19), 7709 - 7721, doi;web_of_science

    Scientific journal

  • C-13 and N-15 NMR studies of iron-bound cyanides of heme proteins and related model complexes: Sensitive probe for detecting hydrogen-bonding interactions at the proximal and distal sides

    Hiroshi Fujii; Tadashi Yoshida

    Studies of the C-13 and N-15 NMR paramagnetic shifts of the iron-bound cyanides in the ferric cyanide forms of various heme proteins containing the proximal histidine and related model complexes are reported. The paramagnetic shifts of the C-13 and N-15 NMR signals of the iron-bound cyanide are not significantly affected by the substitution of the porphyrin side chains. On the other hand, the paramagnetic shifts of both the C-13 and N-15 NMR signals decrease with an increase in the donor effect of the proximal ligand, and the C-13 NMR signal is more sensitive to a modification of the donor effect of the proximal ligand than the N-15 NMR signal. With the tilt of the iron-imidazole bond, the paramagnetic shift of the C-13 NMR signal increases, whereas that of the N-15 NMR signal decreases. The hydrogen-bonding interaction of the iron-bound cyanide with a solvent decreases the paramagnetic shift of both C-13 and N-15 NMR signals, and the effect is more pronounced for the N-15 NMR signal. Data on the C-13 and N-15 NMR signals of iron-bound cyanide for various heme proteins are also reported and analyzed in detail. Substantial differences in the C-13 and N-15 NMR shifts for the heme proteins can be explained on the basis of the results for the model complexes and structures around the heme in the heme proteins. The findings herein show that the paramagnetic shift of the C-13 NMR signal of the iron-bound cyanide is a good probe to estimate the donor effect of the proximal imidazole and that the ratio of N-15/C-13 NMR shifts allows the hydrogen-bonding interaction on the distal side to be estimated., AMER CHEMICAL SOC, Aug. 2006, INORGANIC CHEMISTRY, 45 (17), 6816 - 6827, doi;web_of_science

    Scientific journal

  • O-17 NMR study of oxo metalloporphyrin complexes: Correlation with electronic structure of M=O moiety

    H Fujii; T Kurahashi; T Tosha; T Yoshimura; T Kitagawa

    O-17 NMR spectroscopy of oxo ligand of oxo metalloporphyrin can be considered as an excellent means to derive information about structure, electronic state, and reactivity of the metal bound oxo ligand. To show the Utility Of O-17 NMR spectroscopy of oxo ligand of oxo metalloporphyrin. O-17 NMR spectra of oxo ligands of dioxo ruthenium(VI), oxo chromium(IV), and oxo titanium(IV) porphyrins are measured. For all oxo metalloporphyrins, well-resolved O-17 NMR signals are detected in far high frequency region. The O-17 NMR signal of the metal bound oxo ligand shifts high frequency in order of Ru(VI) < Ti(IV) < Cr(IV), thus the O-17 NMR chemical shift does not directly correlate with the oxo-transfer reactivity, Ti(IV) < Cr(IV) < Ru(VI). On the other hand, the O-17 NMR shift of oxo ligand correlates with the bond strength of metal-oxo bond. This suggests that the O-17 NMR signal of metal bound oxo ligand is a sensitive probe to study the nature of metal-oxo bond in oxo metalloporphyrin. The effect of the electron-withdrawing meso-substituent on the O-17 NMR shift of the oxo ligand is also investigated. With increase in the electron-withdrawing effect of the meso-substituent, the O-17 NMR signal of the oxo ligand of oxo chromium(IV) porphyrin shifts high frequency while that or dioxo ruthenium(VI) porphyrin hardly change resonance position. The changes in metal-oxo bonds induced by the electron-withdrawing meso-substituent are discussed on the basis of the O-17 NMR shifts, the strengths of the metal-oxo bonds, and the oxo-transfer reaction rates. (c) 2006 Elsevier Inc. All rights reserved., ELSEVIER SCIENCE INC, Apr. 2006, JOURNAL OF INORGANIC BIOCHEMISTRY, 100 (4), 533 - 541, doi;web_of_science

    Scientific journal

  • Roles of the herne distal residues of FixL in O-2 sensing: A single convergent structure of the heme moiety is relevant to the downregulation of kinase activity

    A Tanaka; H Nakamura; Y Shiro; H Fujii

    FixL is a heme-based O-2 sensor, in which the autophosphorylation is regulated by the binding of exogenous ligands such as O-2 and CN-. In this study, mutants of the heme distal Arg200, Arg208, Ile2O9, Ile210, and Arg214 residues of SmFixL were characterized biochemically and physicochemically, because it has been suggested that they are significant residues in ligand-linked kinase regulation. Measurements of the autoxidation rate, affinities, and kinetics of ligand binding revealed that all of the above residues are involved in stabilization of the O-2-heme complex of FixL. However, Arg214 was found to be the only residue that is directly relevant to the ligand-dependent regulation of kinase activity. Although the wild type and R214K and R214Q mutants exhibited normal kinase regulation, R214A, R214M, R214H, and R214Y did not. C-13 and N-15 NMR analyses for (CN-)-C-13-N-15 bound to the truncated heme domains of the Arg214 mutants indicated that, in the wild type and the foregoing two mutants, the heme moiety is present in a single conformation, but in the latter four, the conformations fluctuate possibly because of the lack of an interaction between the iron-bound ligand and residue 214. It is likely that such a rigid conformation of the ligand-bound form is important for the downregulation of histidine kinase activity. Furthermore, a comparison of the NMR data between the wild type and R214K and R214Q mutants suggests that a strong electrostatic interaction between residue 214 and the iron-bound ligand is not necessarily required for the single convergent structure and eventually for the downregulation of FixL., AMER CHEMICAL SOC, Feb. 2006, BIOCHEMISTRY, 45 (8), 2515 - 2523, doi;web_of_science

    Scientific journal

  • Spectroscopic characterization of reaction intermediates in a model for copper nitrite reductase

    M Kujime; H Fujii

    WILEY-BLACKWELL, 2006, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 45 (7), 1089 - 1092, doi;web_of_science

    Scientific journal

  • O-2- and H2O2-dependent verdoheme degradation by heme oxygenase - Reaction mechanisms and potential physiological roles of the dual pathway degradation

    T Matsui; A Nakajima; H Fujii; KM Matera; CT Migita; T Yoshida; M Ikeda-Saito

    Heme oxygenase (HO) catalyzes the catabolism of heme to biliverdin, CO, and a free iron through three successive oxygenation steps. The third oxygenation, oxidative degradation of verdoheme to biliverdin, has been the least understood step despite its importance in regulating HO activity. We have examined in detail the degradation of a synthetic verdoheme IX alpha complexed with rat HO-1. Our findings include: 1) HO degrades verdoheme through a dual pathway using either O-2 or H2O2; 2) the verdoheme reactivity with O-2 is the lowest among the three O-2 reactions in the HO catalysis, and the newly found H2O2 pathway is similar to 40-fold faster than the O-2-dependent verdoheme degradation; 3) both reactions are initiated by the binding of O-2 or H2O2 to allow the first direct observation of degradation intermediates of verdoheme; and 4) Asp(140) in HO-1 is critical for the verdoheme degradation regardless of the oxygen source. On the basis of these findings, we propose that the HO enzyme activates O-2 and H2O2 on the verdoheme iron with the aid of a nearby water molecule linked with Asp140. These mechanisms are similar to the well established mechanism of the first oxygenation, meso-hydroxylation of heme, and thus, HO can utilize a common architecture to promote the first and third oxygenation steps of the heme catabolism. In addition, our results infer the possible involvement of the H2O2-dependent verdoheme degradation in vivo, and potential roles of the dual pathway reaction of HO against oxidative stress are proposed., AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, Nov. 2005, JOURNAL OF BIOLOGICAL CHEMISTRY, 280 (44), 36833 - 36840, doi;web_of_science

    Scientific journal

  • Oxidizing intermediates from the sterically hindered iron salen complexes related to the oxygen activation by nonheme iron enzymes

    T Kurahashi; Y Kobayashi; S Nagatomo; T Tosha; T Kitagawa; H Fujii

    Oxidizing intermediates are generated from nonheme iron(III) complexes to investigate the electronic structure and the reactivity, in comparison with the oxoiron(IV) porphyrin pi-cation radical (compound 1) as a heme enzyme model. Sterically hindered iron salen complexes, bearing a fifth ligand Cl (1), OH2 (2), OEt (3), and OH (4), are oxidized both electrochemically and chemically. Stepwise one-electron oxidation of 1 and 2 generates iron(Ill)mono- and diphenoxyl radicals, as revealed by detailed spectroscopic investigations, including UV-vis, EPR, Mossbauer, resonance Raman, and ESIMS spectroscopies. In contrast to the oxoiron(IV) formation from the hydroxoiron(III) porphyrin upon one-electron oxidation, the hydroxo complex 4 does not generate oxoiron(IV) species. Reaction of 2 with mCPBA also results in the formation of the iron(Ill)-phenoxyl radical. One-electron oxidation of 3 leads to oxidative degradation of the fifth DO ligand to liberate acetaldehyde even at 203 K. The iron(Ill)phenoxyl radical shows high reactivity for alcoxide on iron(III) but exhibits virtually no reactivity for alcohols including even benzyl alcohol without a base to remove an alcohol proton. This study explains unique properties of mononuclear nonheme enzymes with Tyr residues and also the poor epoxidation activity of Fe salen compared to Mn and Cr salen compounds., AMER CHEMICAL SOC, Oct. 2005, INORGANIC CHEMISTRY, 44 (22), 8156 - 8166, doi;web_of_science

    Scientific journal

  • Synthesis of sterically hindered tris(4-imidazolyl)carbinol ligands and their copper(I) complexes related to metalloenzymes

    M Kujime; H Fujii

    Tris(4-imidazolyl)carbinol, which has close coordination environment to the active site of metalloenzymes, has not been utilized as a biomimetic ligand because of its instability. We have synthesized stable tris(4-imidazolyl)carbinol derivatives having a methyl group as the NH protective group and a bulky substituent on the imidazole ring for stabilizing reactive species bound to the metal center. These ligands provide stable monomeric copper(l) complexes whose coordination environment are very close to the active site of metalloenzymes. (c) 2005 Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2005, TETRAHEDRON LETTERS, 46 (16), 2809 - 2812, doi;web_of_science

    Scientific journal

  • Essential amino acid residues controlling the unique regioselectivity of heme oxygenase in Pseudomonas aeruginosa

    H Fujii; XH Zhang; T Yoshida

    AMER CHEMICAL SOC, Apr. 2004, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126 (14), 4466 - 4467, doi;web_of_science

    Scientific journal

  • A superoxo-ferrous state in a reduced oxy-ferrous hemoprotein and model compounds

    R Davydov; JD Satterlee; H Fujii; A Sauer-Masarwa; DH Busch; BM Hoffman

    Cryoreduction of the [FeO2](6) (n = 6 is the number of electrons in 3d orbitals on Fe and pi* orbitals on O-2) dioxygen-bound ferroheme through gamma irradiation at 77 K generates an [FeO2](7) reduced oxy-heme. Numerous investigations have examined [FeO2](7) centers that have been characterized as peroxo-ferric centers, denoted [FeO2](per)(7), in which a ferriheme binds a dianionic peroxo-ligand. The generation of such an intermediate can be understood heuristically if the [FeO2](6) parent is viewed as a superoxo-ferric center and the injected electron localizes on the O-O moiety. We here report EPR/ENDOR experiments which show quite different properties for the [FeO2](7) centers produced by cryoreduction of monomeric oxy-hemoglobin (oxy-GMH3) from Glycera dibranchiata, which is unlike mammalian "globins" in having a leucine in place of the distal histidine; of frozen aprotic solutions of oxy-ferrous octaethyl porphyrin; and of the oxy-ferrous complex of the heme model, cyclidene. These [FeO2](7) centers are characterized as "superoxo-ferrous" centers ([FeO2](sup)(7)), With nearly unit spin density localized on a superoxo moiety which is end-on coordinated to a low-spin ferrous ion. This assignment is based on their g tensors and O-17 hyperfine couplings, which are characteristic of the superoxide ion coordinated to a diamagnetic metal ion, and on the absence of detectable ENDOR signals either from the in-plane N-14 ligands or from an exchangeable H-bond proton. Such a center would arise if the electron that adds to the [FeO2](6) superoxo-ferric parent localizes on the Fe ion, to make a superoxo-ferrous moiety. Upon annealing to T > 150 K, the [FeO2](sup)(7) species converts to peroxo/hydroperoxo-ferric ([FeO2H](7)) intermediates. These experiments suggest that the primary reduction product is [FeO2](sup)(7) and that the internal redox transition to [FeO2](per)(7)/[FeO2H](7) states is driven at least in part by H-bonding/proton donation by the environment., AMER CHEMICAL SOC, Dec. 2003, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 125 (52), 16340 - 16346, doi;web_of_science

    Scientific journal

  • Kinetic isotope effects on the rate-limiting step of heme oxygenase catalysis indicate concerted proton transfer/heme hydroxylation

    R Davydov; T Matsui; H Fujii; M Ikeda-Saito; BM Hoffman

    AMER CHEMICAL SOC, Dec. 2003, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 125 (52), 16208 - 16209, doi;web_of_science

    Scientific journal

  • Stereo selectivity of each of the three steps of the heme oxygenase reaction: Hemin to meso-hydroxyhemin, meso-hydroxyhemin to verdoheme, and verdoheme to biliverdin

    XH Zhang; H Fujii; KM Matera; CT Migita; DY Sun; M Sato; M Ikeda-Saito; T Yoshida

    Heme oxygenase catalyzes the regiospecific oxidation of hemin to biliverdin IXalpha with concomitant liberation of CO and iron by three sequential monooxygenase reactions. The alpha-regioselectivity of heme oxygenase has been thought to result from the regioselective oxygenation of the heme alpha-meso position at the first step, which leads to the reaction pathway via meso-hydroxyheme IXalpha and verdoheme IXalpha intermediates. However, recent reports concerning heme oxygenase forming biliverdin isomers other than biliverdin IXalpha raise a question whether heme oxygenase can degrade meso-hydroxyhemin and isomers other than the alpha-isomers. In this paper, we investigated the stereoselectivity of each of the two reaction steps from meso-hydroxyhemin to verdoheme and verdoheme to biliverdin by using a truncated form of rat heme oxygenase-1 and the chemically synthesized four isomers of meso-hydroxyhemin and verdoheme. Heme oxygenase-1 converted all four isomers of meso-hydroxyhemin to the corresponding isomers of verdoheme. In contrast, only verdoheme IXalpha was converted to the corresponding biliverdin IXalpha. We conclude that the third step, but not the second, is stereoselective for the alpha-isomer substrate. The present findings on regioselectivities of the second and the third steps have been discussed on the basis of the oxygen activation mechanisms of these steps., AMER CHEMICAL SOC, Jun. 2003, BIOCHEMISTRY, 42 (24), 7418 - 7426, doi;web_of_science

    Scientific journal

  • Preparation of artificial metalloenzymes by insertion of chromium(III) Schiff base complexes into apomyoglobin mutants

    M Ohashi; T Koshiyama; T Ueno; M Yanase; H Fujii; Y Watanabe

    WILEY-V C H VERLAG GMBH, 2003, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 42 (9), 1005 - +, doi;web_of_science

    Scientific journal

  • EPR characterization of the heme oxygenase reaction intermediates and its implication for the catalytic mechanism

    M Ikeda-Saito; H Fujii

    Heme oxygenase (HO) catalyzes the regiospecific degradation of heme to biliverdin by using three O-2 molecules and seven electrons. The enzyme binds one equivalent of heme to form the heme complex, and electron donation initiates the three stepwise oxygenase reactions through the two novel heme derivatives, alpha-hydroxyheme and verdoheme, during which CO and free Fe are also produced. EPR has been used to study electronic and coordination structures of the HO catalytic intermediates, including the ferric hydroperoxo active species generated by one-electron reduction of the ferrous oxy form. A combination of the novel characteristics of the reaction intermediates and the protein environment are responsible for the unique HO enzyme catalytic mechanism., AMER CHEMICAL SOC, 2003, PARAMAGNETIC RESONANCE OF METALLOBIOMOLECULES, 858, 97 - 112, web_of_science

    Scientific journal

  • Superpenetration of a high energy Q(Q)over-bar bound state through random color fields

    H Fujii; T Matsui

    The transmission amplitude of a color dipole through a random external color field is computed in the eikonal approximation in order to study the absorption of high energy quarkonium by nuclear target. It is shown that the internal color state of the dipole becomes randomized and all possible color states are eventually equi-partitioned, while the probability of finding a color singlet bound state attenuates not exponentially, but inversely proportional to the distance L of the random field zone which the dipole has traveled. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, Oct. 2002, PHYSICS LETTERS B, 545 (1-2), 82 - 90, web_of_science

    Scientific journal

  • C-13 NMR signal detection of iron-bound cyanide ions in ferric cyanide complexes of heme proteins

    H Fujii

    AMER CHEMICAL SOC, May 2002, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 124 (21), 5936 - 5937, doi;web_of_science

    Scientific journal

  • Electronic structure and reactivity of high-valent oxo iron porphyrins

    H Fujii

    High valent oxo iron porphyrins have been prepared and characterized as models for compounds-I and compounds-II in heme enzymes. In this review, we survey studies of high valent oxo iron porphyrin complexes. Spectroscopic properties and reactivities of oxo iron(IV) porphyrin pi-cation radical complexes are summarized. Electron-withdrawing effects of meso-substituents and pyrrole beta-substituents on the electronic structure of oxo iron(IV) porphyrin pi-cation radicals are discussed. The effect of the axial ligand is also reviewed. Isoelectronic forms of oxo iron(IV) porphyrin pi-cation radical are reviewed. We have summarized the synthesis and characterization of oxo iron(IV) porphyrins as models for compounds-II. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE SA, Mar. 2002, COORDINATION CHEMISTRY REVIEWS, 226 (1-2), 51 - 60, doi;web_of_science

    Scientific journal

  • Catalytic mechanism of heme oxygenase through EPR and ENDOR of cryoreduced oxy-heme oxygenase and its Asp 140 mutants

    R Davydov; Kofman, V; H Fujii; T Yoshida; M Ikeda-Saito; BM Hoffman

    Heme oxygenase (HO) catalyzes the O-2- and NADPH-cytochrome P450 reductase-dependent conversion of heme to biliverdin, Fe, and CO through a process in which the heme participates both as a prosthetic group and as a substrate. In the present study, we have generated a detailed reaction cycle for the first monooxygenation step of HO catalysis, conversion of the heme to alpha-meso-hydroxyheme. We employed EPR (using both O-16(2) and O-17(2)) and H-1, N-14 ENDOR spectroscopies to characterize the intermediates generated by 77 K radiolytic cryoreduction and subsequent annealing of wild-type oxy-HO and D140A, F mutants. One-electron cryoreduction of oxy-HO yields a hydroperoxoferri-HO with g-tensor, g = [2,37, 2.187, 1.924]. Annealing of this species to 200 K is accompanied by spectroscopic changes that include the appearance of a new H-1 ENDOR signal, reflecting rearrangements in the active site. Kinetic measurements at 214 K reveal that the annealed hydroperoxoferri-HO species, denoted R, generates the ferri-alpha-meso-hydroxyheme product in a first-order reaction. Disruption of the H-bonding network within the distal pocket of HO by the alanine and phenylalanine mutations of residue D140 prevents product formation. The hydroperoxoferri-HO (D140A) instead undergoes heterolytic cleavage of the O-O bond, ultimately yielding an EPR-silent compound II-like species that does not form product. These results, which agree with earlier suggestions, establish that hydroperoxoferri-HO is indeed the reactive species, directly forming the alpha-meso-hydroxyheme product by attack of the distal OH of the hydroperoxo moiety at the heme alpha-carbon., AMER CHEMICAL SOC, Feb. 2002, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 124 (8), 1798 - 1808, doi;web_of_science

    Scientific journal

  • A trigonal-bipyramidal ferric aqua complex with a sterically hindered salen ligand as a model for the active site of protocatechuate 3,4-dioxygenase

    H Fujii; Y Funahashi

    WILEY-V C H VERLAG GMBH, 2002, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 41 (19), 3638 - 3641, doi;web_of_science

    Scientific journal

  • ヘムオキシゲナーゼによる酸素活性化 金属酵素の反応場と機能の関わり

    藤井 浩

    2002, 化学工業, 53, 18 - 24

  • A role for highly conserved carboxylate, aspartate-140, in oxygen activation and heme degradation by heme oxygenase-1

    H Fujii; XH Zhang; T Tomita; M Ikeda-Saito; T Yoshida

    Heme oxygenase (HO) catalyzes the oxygen-dependent degradation of heme to biliverdinIX alpha, CO, and free iron ion via three sequential monooxygenase reactions. Although the distinct active-site structure of HO from cytochrome P450 families suggests unique distal protein machinery to activate molecular oxygen, the mechanism and the key amino acid for the oxygen activation have not been clear. To investigate the functionality of highly conserved polar amino acids in the distal helix of HO-1, we have prepared alanine mutants: T135A, R136A, D140A, and S142A, and found drastic changes in the heme degradation reactions of D140A. In this paper, we report the first evidence that D140 is involved in the oxygen activation mechanism in HO-1. The heme complexes of HO mutants examined in this study fold and bind heme normally. The pK(a) values of the iron-bound water acid autoxidation rates of the oxy-form are increased with R136A, D140A, and S142A mutations, but are not changed with T135A mutation. As the wild-type, T135A, R136A, and S142A degrade heme to verdohemeIX alpha with H2O2 and to biliverdinIXa with the NADPH reductase system. On the other hand, D140A heme complex forms compound II with H2O2, and no heme degradation occurs. For the NADPH reductase system, the oxy-form of D140A heme complex is accumulated in the reaction, and only 50% of heme is degraded. The stopped flow experiments suggest that D140A cannot activate iron-bound dioxygen and hydroperoxide properly. To investigate the carboxylate functionality of D140, we further replaced D140 with glutamic acid (D140E), phenylalanine (D140F), and asparagine (D140N). D140E degrades heme normally, but D140N shows reactivity similar to that of D140A. D140F loses heme degradation activity completely. All of these results indicate that the carboxylate at position 140 is essential to activate the iron-bound dioxygen and hydroperoxide. On the basis of the present findings, we propose an oxygen activation mechanism involving the hydrogen-bonding network through the bridging water and D140 side chain., AMER CHEMICAL SOC, Jul. 2001, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 123 (27), 6475 - 6484, doi;web_of_science

    Scientific journal

  • Participation of carboxylate amino acid side chain in regiospecific oxidation of heme by heme oxygenase

    H Zhou; CT Migita; M Sato; DY Sun; XH Zhang; M Ikeda-Saito; H Fujii; T Yoshida

    AMER CHEMICAL SOC, Aug. 2000, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 122 (34), 8311 - 8312, doi;web_of_science

    Scientific journal

  • Spin distribution in low-spin (meso-tetraalkylporphyrinato)iron(III) complexes with (d(xz),d(yz))(4)(d(xy))(1) configuration. Studies by H-1 NMR, C-13 NMR, and EPR spectroscopies

    T Ikeue; Y Ohgo; T Saitoh; M Nakamura; H Fujii; M Yokoyama

    H-1 NMR, C-13 NMR, and EPR studies of a series of low-spin (meso-tetraalkylporphyrinato)iron(III) complexes, [Fe(TRP)(L)(2)]X where R = Pr-n,Pr-c, and Pr-i and L represents axial ligands such as imidazoles, pyridines, and cyanide, have revealed that the ground-state electron configuration of [Fe((TPPrP)-P-n)(L)(2)]X and [Fe((TPrP)-Pr-c)(L)(2)]X is presented either as the common (d(xy))(2)(d(xz),d(yz))(3) or as the less common (d(xz),d(yz))(4)(d(xy))(1) depending on the axial ligands. The ground-state electron configuration of the isopropyl complexes [Fe(Tt-PrP)(L) (2)]X is, however, presented as (d(xz),d(yz))(4)(d(xy))(1) regardless of the kind of axial ligands. In every case, the contribution of the (d(xz),d(yz))(4)(dxy)(1) state to the electronic ground state increases in the following order: HIm < 4-Me2NPy < 2-MeIm < CN- < 3-MePy < Py < 4-CNPy. Combined analysis of the C-13 and (HNMR)-H-1 isotropic shifts together with the EPR S values have yielded the spin densities at the porphyrin carbon and nitrogen atoms. Estimated spin densities in [Fe((TPrP)-Pr-i)(4-CNPy)(2)](+), which has the purest (d(xz),d(yz))(4)(d(xy))(1) ground state among the complexes examined in this study, are as follows: meso-carbon, +0.045; alpha-pyrrole carbon, +0.0088; beta-pyrrole carbon, -0.00026; and pyrrole nitrogen, +0.057. Thus, the relatively large spin densities are on the pyrrole nitrogen and meso-carbon atoms. The result is in sharp contrast to the spin distribution in the (d(xy))(2)(d(xz,)d(yz))(3) type complexes; the largest spin density is at the beta-pyrrole carbon atoms in bis(1-methylimidazole)(meso-tetraphenylporphyrinato)iron(III), [Fe(TPP)(1-MeIm)(2)](+), as determined by Goff. The large downfield shift of the meso-carbon signal, delta +917.5 ppm at -50 degrees C in [Fe((TPrP)-Pr-i)(4-CNPy)(2)](+), is ascribed to the large spin densities at these carbon atoms. In contrast, the large upfield shift of the alpha-pyrrole carbon signal, delta -293.5 ppm at the same temperature, is caused by the spin polarization from the adjacent meso-carbon and pyrrole nitrogen atoms., AMER CHEMICAL SOC, May 2000, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 122 (17), 4068 - 4076, doi;web_of_science

    Scientific journal

  • Electron spin-echo envelope modulation spectral properties of amidate nitrogen coordinated to oxovanadium(IV) ion

    K Fukui; H Fujii; H Ohya-Nishiguchi; H Kamada

    Electron spin-echo envelope modulation (ESEEM) measurements have been performed for a VO2+-amidate complex, [(VO)-O-IV(hybeb)](2-) (H(4)hybeb = 1,2-bis(2-hydroxybenzamido)benzene). ESEEM spectroscopic properties of the amidate N-14 nucleus have been characterized for the first time (\ A(iso)\ = 6.70 MHz; e(2)qQ/h = 2.5 MHz, eta = 0.04) to provide a basis for the studies of vanadium-peptide interactions. The electronic structure of the amidate nitrogen is discussed., CHEMICAL SOC JAPAN, Mar. 2000, CHEMISTRY LETTERS, (3), 198 - 199, doi;web_of_science

    Scientific journal

  • Resonance raman spectra of legitimate models for the ubiquitous compound I intermediates of oxidative heme enzymes

    K Czarnecki; Kincaid, JR; H Fujii

    AMER CHEMICAL SOC, Sep. 1999, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 121 (34), 7953 - 7954, doi;web_of_science

    Scientific journal

  • Post-assembly insertion of metal ions into thiol-derivatized porphyrin monolayers on gold

    N Nishimura; M Ooi; K Shimazu; H Fujii; K Uosaki

    The insertion of metal ions into thiol-derivatized free-base porphyrin monolayers pre-assembled on gold has been conducted by refluxing the metal ion solution in which the monolayer-coated gold electrode was immersed. The extent of the metal insertion was estimated from the decrease in the N1s peak in X-ray photoelectron spectra (XP spectra) assigned to the pyrrole nitrogen which binds a hydrogen atom. The insertion of Co(II) was completed by refluxing for 3 h. Although the extent of the metal insertion for the same reflux time depends on the metal ion used, the insertion of several ions including Mn(II), Fe(II), Ni(II), Cu(II) and Zn(II) was possible. Besides XP spectra, the metal insertion was confirmed by the electrocatalytic activity of the monolayers for the reduction of molecular oxygen. The structural characterization has proved that the monolayer is stable during the reflux;; neither desorption nor change in the orientation of the porphyrin molecules took place. Compared to the commonly used self-assembly of the pre-metalated porphyrins, this post-assembly metal insertion method has an advantage because neither intra nor intermolecular coordinations of the thiol functionality to the central metal ion take place, thus avoiding the unexpected disorder in the monolayer such as the formation of a multilayer, the blocking of the electrocatalytically active central metal ion and the loss of the anchoring functionality or thiol. (C) 1999 Elsevier Science S.A. All rights reserved., ELSEVIER SCIENCE SA, Sep. 1999, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 473 (1-2), 75 - 84, doi;web_of_science

    Scientific journal

  • Electron configuration of ferric ions in low-spin (dicyano)(meso-tetraarylporphyrinato)iron(III) complexes

    M Nakamura; T Ikeue; A Ikezaki; Y Ohgo; H Fujii

    The electron configuration of a series of low-spin (dicyano){meso-tetrakis(2,4,6-trialkylphenyl)porphyrinato}iron(III) complexes, [Fe(R-TPP)(CN)(2)](-) where R = Me, Et, or Pr-i, together with the parent [Fe(TPP)(CN)(2)](-), has been examined in dichloromethane-methanol solution by H-1 NMR, C-13 NMR, and EPR spectroscopies. While the ferric ion of [Fe(TPP)(CN)(2)](-) has shown a common (d(xy))(2)(d(xz),d(yz))(3) configuration, the ferric ions of the alkyl-substituted complexes [Fe(R-TPP)(CN)(2)](-) have exhibited the preference of a less common (d(xz),d(yz))(4)(d(xy))(1) configuration. Spectroscopic characteristics of the complexes in which ferric ions take the (d(xz),d(yz))(4)(d(xy))(1) configuration are (i) axial type EPR spectra, (ii) downfield shifted pyrrole and meta signals in H-1 NMR spectra, and (iii) downfield shifted meso-carbon signals in C-13 NMR spectra. Occurrence of the less common (d(xz),d(yz))(4)(d(xy))(1) configuration in [Fe(R-TPP)(CN)(2)](-) has been ascribed to the electronic interaction between iron (d(pi)) and cyanide (p(pi)*) orbitals. The interaction stabilizes the d(pi) orbitals and induces (d(xz),d(yz))(4)(d(xy))(1) configuration. Since the electron configuration of (dicyano){meso-tetrakis(2,6-dichlorophenyl)porphyrinato}iron(III), [Fe(Cl-TPP)(CN)(2)](-), which carries bulky electronegative chlorine atoms at the ortho positions, is presented as a common (d(xy))(2)(d(xz),d(yz))(3), the less common (d(xz),d(yz))(4)(d(xy))(1) configuration in [Fe(R-TPP)(CN)(2)](-) can be ascribed, at least partially, to the electron-donating ability of the meso-aryl groups., AMER CHEMICAL SOC, Aug. 1999, INORGANIC CHEMISTRY, 38 (17), 3857 - 3862, doi;web_of_science

    Scientific journal

  • Molecular oxygen oxidizes the porphyrin ring of the ferric alpha-hydroxyheme in heme oxygenase in the absence of reducing equivalent

    CT Migita; H Fujii; KM Matera; S Takahashi; H Zhou; T Yoshida

    Heme oxygenase catalyzes the regiospecific oxidative degradation of iron protoporphyrin IX (heme) to biliverdin, CO and Fe, utilizing molecular oxygen and electrons donated from the NADPH-cytochrome P-450 reductase. The catalytic conversion of heme proceeds through two known heme derivatives, alpha-hydroxyheme and verdoheme. In order to assess the requirement of reducing equivalents in the second stage of heme degradation, from alpha-hydroxyheme to verdoheme, we have prepared the alpha-hydroxyheme complex with rat heme oxygenase isoform-1 and examined its reactivity with molecular oxygen in the absence of added electrons. Upon reaction with oxygen, the majority of the alpha-hydroxyheme in heme oxygenase is altered to a species which exhibits an optical absorption spectrum with a broad Soret band, along with the minority which is converted to verdoheme. The major product species, which is electron paramagnetic resonace-silent, can be recovered to the original alpha-hydroxyheme by addition of sodium dithionite. We have also found that oxidation of the alpha-hydroxyheme-heme oxygenase complex by ferricyanide or iridium(IV) chloride yields a species which exhibits an optical absorption spectrum and reactivity similar to those of the main product of the oxygen reaction. We infer that the oxygen reaction with the ferric alpha-hydroxyheme-heme oxygenase complex forms a ferric-porphyrin cation radical. We conclude that in the absence of reducing agents, the oxygen molecule functions mainly as an oxidant for the porphyrin ring and has no role in the oxygenation of alpha-hydroxyheme. This result corroborates our previous conclusion that the catalytic conversion of alpha-hydroxyheme to verdoheme by heme oxygenase requires one reducing equivalent along with molecular oxygen. (C) 1999 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, Jul. 1999, BIOCHIMICA ET BIOPHYSICA ACTA-PROTEIN STRUCTURE AND MOLECULAR ENZYMOLOGY, 1432 (2), 203 - 213, doi;web_of_science

    Scientific journal

  • Insensitivity of vanadyl-oxygen bond strengths to radical type ((2)A(1u) vs (2)A(2u)) in vanadyl porphyrin cation radicals

    K Czarnecki; LM Proniewicz; H Fujii; D Ji; RS Czernuszewicz; Kincaid, JR

    Resonance Raman (RR) spectra are reported for vanadyl octaethylporphyrin, OV(OEP), tetramesityltetramethylporphyrin, OV(TMTMP), and tetramesitylporphyrin, OV(TMP), and their corresponding pi-cation radicals obtained by chemical and electrochemical oxidation. The behavior of the nu(2) RR porphyrin "marker band", which moves to higher frequency upon oxidation of the OV(OEP) and OV(TMTMP) and to lower frequency for OV(TMP), shows that the resultant cation radicals have predominantly (2)A(1u) and (2)A(2u) ground states, respectively. In contrast to earlier work (Macor, K. A.; Czernuszewicz, R. S.; Spiro, T. G. Inorg. Chem. 1990, 29, 1996), it is demonstrated here that the shift of the nu(V=O) is insensitive to radical type, behavior which is in agreement with similar studies of the ferryl analogues (Czarnecki, K.; et al. J. Am. Chem. Soc. 1996, 116, 2929 and 4680). It is suggested that the observed downshifts of the nu(V=O) previously reported for RR spectra of vanadyl porphyrin pi-cation radicals, relative to their neutral parents, are most reasonably ascribed to trans oxo ligand coordination (most probably a water molecule) during low-temperature electrochemical oxidation of the neutral species., AMER CHEMICAL SOC, Apr. 1999, INORGANIC CHEMISTRY, 38 (7), 1543 - 1547, doi;web_of_science

    Scientific journal

  • High-spin (meso-Tetraalkylporphyrinato)iron(III) complexes as studied by X-ray crystallography, EPR, and dynamic NMR spectroscopies

    T Ikeue; Y Ohgo; A Uchida; M Nakamura; H Fujii; M Yokoyama

    H-1 NMR spectra of a series of high-spin (meso-tetraalkylpsrphyrinato)iron(III) chlorides, [Fe(TRP)Cl] where R - Me, Et, Pr, or Pr-i, have been measured at various temperatures in CD2Cl2 solution. In the case of the Et,Pr, and Pr-i complexes, either the methyl or the methylene signal split into two signals with equal integral intensities at low temperature. In contrast, the Me complex did not show any splitting even at -100 degrees C. The results have been ascribed to the hindered relation of the meso-alkyl groups about C-meso-C-alpha bonds. The activation free energies for rotation have been determined as 8.0 (-72 degrees C), 8.5 (-60 degrees C), and 8.9 (-62 degrees C) kcal . mol(-1) for the Et, Pr, and Pr-i complexes, respectively, at coalescence temperatures given in parentheses. The small activation free energy for rotation of the isopropyl groups observed in the present system is explained in terms of the nonplanarity of the porphyrin ring, which has been verified both by the X-ray crystallographic analysis and by the EPR spectrum taken in a frozen CH2Cl2-toluene solution. The success in observing the hindered rotation of less bulky primary alkyl groups such as ethyl and propyl groups at an easily accessible temperature range is attributed to the large difference in chemical shifts of the mutually exchanging protons, ca. 3500 Hz in the case of the Et complex, caused by the paramagnetism of the five-coordinated ferric porphyrin complexes., AMER CHEMICAL SOC, Mar. 1999, INORGANIC CHEMISTRY, 38 (6), 1276 - 1281, doi;web_of_science

    Scientific journal

  • Cobalt porphyrin heme oxygenase complex. EPR evidences for the distal heme pocket hydrogen bonding

    H Fujii; Y Dou; H Zhou; T Yoshida; M Ikeda-Saito

    AMER CHEMICAL SOC, Aug. 1998, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 120 (32), 8251 - 8252, doi;web_of_science

    Scientific journal

  • Cu-63 NMR study of copper(I) carbonyl complexes with various hydrotris(pyrazolyl)borates: Correlation between Cu-63 chemical shifts and CO stretching vibrations

    S Imai; K Fujisawa; T Kobayashi; N Shirasawa; H Fujii; T Yoshimura; N Kitajima; Y Moro-oka

    Copper(I) carbonyl complexes with a series of hindered L-R1,L-R2 ligands (L: hydrotris(pyrazolyl)borate, R1 and R2 are substituents at the 3- and 5-positions of the pyrazole ring, respectively), (LCuCO)-Cu-R1,R2 [R1, R2 = Me, Me (1), i-Pr, i-Pr (2), t-Bu, Me (3), t-Bu, i-Pr (4), Ph, i-Pr (5), Ph, Ph (6)1 have been synthesized and characterized by]H NMR and IR spectroscopy and elemental analysis. The molecular structures of 3 and 6 have been determined by X-ray crystallography. The electronic structures of copper(I) sites are characterized by means of Cu-63 NMR spectroscopy and by the C=O stretching vibration. The sharp Cu-63 NMR signals are observed for (LCuCO)-Cu-R1,R2 complexes in toluene at room temperature. The Cu-63 NMR Signals of copper(I) complexes with alkyl-substituted ligands (1-4) are observed in lower field than those of the phenyl derivatives (5, 6) correlating with the electron-density at the copper center. This argument is supported by the good correlation between the delta((CU)-C-63) value and C=O stretching vibration which is a sensitive indicator of the extent of back-donation of the Cu d electrons to the antibonding C=O orbitals., AMER CHEMICAL SOC, Jun. 1998, INORGANIC CHEMISTRY, 37 (12), 3066 - 3070, doi;web_of_science

    Scientific journal

  • Electron configuration and spin distribution in low-spin (meso-tetraalkylporphyrinato)iron(III) complexes carrying one or two orientationally fixed imidazole ligands

    M Nakamura; T Ikeue; H Fujii; T Yoshimura; K Tajima

    To understand the orientation effect of coordinated imidazole ligands, a series of low spin (tetraalkylporphyrinato)-iron(III) complexes, [Fe(TRP)(L)(2)](+) and [Fe(TRP)(L)(CN)], carrying at least one orientationally fixed imidazole (L) have been prepared. The H-1 NMR pyrrole signals of a series of [Fe(TRP)(2-MeIm)(2)](+) have shown considerable downfield shifts as the meso substituent becomes bulkier, from -30.4 (R = H) to +5.6 ppm (R = Pr-i) at -71 degrees C. These complexes have exhibited four pyrrole signals at lower temperature due to the hindered ligand rotation. The spread of the pyrrole signals decreases from 9.4 (Me) to 8.2 (Et) and then to 5.7 (Pr-i) ppm. The downfield pyrrole signals together with the small spread in [Fe((TPrP)-Pr-i)(2-MeIm)(2)](+) are in sharp contrast to the other low-spin complexes with orientationally fixed imidazole ligands; the chemical shifts and spreads of the pyrrole signals in [tetrakis(2,4,6-trialkylphenyl)porphyrinato]iron(III) complexes [Fe(R-TPP)(2-MeIm)(2)](+) (R = Me, Et, Pr-i) are ca. -20 and ca. 9 ppm, respectively, at -71 degrees C. The EPR spectra of a series of [Fe(TRP)(2-MeIm)(2)](+) were then taken at 4.2 K. While the R = H, Me, and Et complexes have shown so-called "large g(max) type" spectra as in the case of [Fe(R-TPP)(2-MeIm)(2)](+), the Pr-i complex has exhibited an "axial type" spectrum. The result indicates that the electron configuration of the ferric ion of [Fe((TPrP)-Pr-i)(2-MeIm)(2)](+) is presented by the unusual (d(xz), d(yz))(4)- (d(xy))(1) in contrast to the other low-spin complexes where ferric ions have the (d(xy))(2)(d(xz), d(yz))(3) configuration. When one of the 2-MeIm ligands in [Fe(TRP)(2-MeIm)(2)](+) is replaced by CN-, not only the Pr-i but also the Me and Et complexes have shown the (d(xz), d(yz))(4)(d(xy))(1) configuration as revealed from the EPR spectra. The pyrrole signals of the Pr-i complex [Fe((TPrP)-Pr-i)(2-MeIm)(CN)] have been observed at 12.2, 14.1, 14.8, and 16.2 ppm at -71 degrees C. Thus, the spread is only 4.0 ppm. The value is quite different from that of the corresponding [Fe(Me-TPP)(2-i(P)rIm)(CN)] where the spread reaches as much as 11.4 ppm. On the basis of these results, it is concluded that the spin distribution on the pyrrole beta-carbons in the complexes with (d(xz), d(yz))(4)(d(xy))(1) is rather homogeneous even if the coordinated imidazole is orientationally fixed. On the contrary, the fixation induces a larger asymmetric spin distribution on these carbons in the complexes with (d(xy))(2)(d(xz), d(yz))(3) configuration., AMER CHEMICAL SOC, May 1998, INORGANIC CHEMISTRY, 37 (10), 2405 - 2414, doi;web_of_science

    Scientific journal

  • Identification of histidine 45 as the axial heme iron ligand of heme oxygenase-2

    K Ishikawa; KM Matera; H Zhou; H Fujii; M Sato; T Yoshimura; M Ikeda-Saito; T Yoshida

    A truncated, soluble, and enzymatically active form of human heme oxygenase-2 (Delta HHO2) was expressed in Escherichia coli, To identify the axial heme ligand of HO-2, His-45 to Ala (Delta H45A) and His-152 to Ala (Delta H152A) mutants have been prepared using this expression system. Delta H45A could form a 1:1 complex with hemin but was completely devoid of the heme degradation activity, A 5-coordinate-type ferrous NO EPR spectrum was ob served for the heme-Delta H45A complex, The Delta H152A mutant was expressed as an inclusion body and was recovered from the lysis pellet by dissolution in urea followed by dialysis. The solubilized fraction obtained, however, was composed of a mixture of a functional enzyme and an inactive fraction. The inactive fraction was removed by Sephadex G-75 column chromatography since it eluted out of the column at the void volume, The gel filtration-purified Delta H152A exhibited spectroscopic and enzymatic properties identical to those of wild-type. We conclude, in contrast to the previous reports (McCoubrey and Maines (1993) Arch. Biochem. Biophys. 302, 402-408; McCoubrey, W, K., Jr., Huang, T, J., and Maines, M. (1997) J. Biol, Chem. 272, 12568-12574), that His 45, but not His-152, in heme oxygenase isoform-a is the proximal ligand of the heme and is essential for the heme degradation activity of the enzyme, His-152 appears to play a structural role in stabilization of the heme oxygenase protein., AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, Feb. 1998, JOURNAL OF BIOLOGICAL CHEMISTRY, 273 (8), 4317 - 4322, doi;web_of_science

    Scientific journal

  • Raman signature of the Fe2O2 "diamond" core

    EC Wilkinson; YH Dong; Y Zang; H Fujii; R Fraczkiewicz; G Fraczkiewicz; RS Czernuszewicz; L Que

    We report the resonance Raman (RR) spectra of iron complexes containing the Fe-2(mu-O)(2) core. Frozen CH3CN solutions of the (FeFeIV)-Fe-III intermediate [Fe-2(mu-O)(2)L-2](ClO4)(3) (where L = TPA, 5-Me-3-TPA, 5-Me-2-TPA, 5-MeTPA, 5-Et-3-TPA, or 3-Me-3-TPA) show numerous resonance-enhanced vibrations, and among these, an oxygen-isotope-sensitive vibration around 667 cm(-1) that shifts ca. 30 cm(-1) when the samples are allowed to exchange with (OH2)-O-18, and whose Raman shift does not vary with methyl substitution of the TPA ligand. Spectra of iron-isotope-substituted samples of [Fe-2(mu-O)(2)(L)2(])(ClO4)(3) (Fe-54 and Fe-57 for L = TPA, and Fe-54 and Fe-58 for L = 5-Me-3-TPA) show that this vibration is also iron-isotope sensitive. These isotopic data taken together strongly suggest that this vibration involves motion of the Fe-2(mu-O)(2) core that is isolated from motions of the Ligand. A frozen CH3CN solution of the diiron(III) complex [Fe-2(mu-O)(2)(6-Me-3-TPA)(2)](ClO4)(2) shows one intense resonance-enhanced vibration at 692 cm(-1) that shifts -30 cm(-1) with O-18 labeling. Normal coordinate analysis of the Fe-2(mu-O)(2) core in [Fe-2(mu-O)(2)(5-Me-3-TPA)(2)](ClO4)(3) supports the assignment of the Fermi doublet centered around 666.2 cm(-1) as an A(1) vibration of this core. Furthermore, we propose that this unique feature found in the region between 650 and 700 cm(-1) is indicative of a diamond core structure and is the Raman signature of an iron cluster containing this core., AMER CHEMICAL SOC, Feb. 1998, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 120 (5), 955 - 962, doi;web_of_science

    Scientific journal

  • The oxygen and carbon monoxide reactions of heme oxygenase

    CT Migita; KM Matera; M Ikeda-Saito; JS Olson; H Fujii; T Yoshimura; H Zhou; T Yoshida

    The O(2) and CO reactions with the heme, alpha-hydroxyheme, and verdoheme complexes of heme oxygenase have been studied, The heme complexes of heme oxygenase isoforms-1 and -2 have similar O(2) and CO binding properties. The O(2) affinities are very high, KO(2) = 30-80 mu M(-1), which is 30-90-fold greater than those of mammalian myoglobins, The O(2) association rate constants are similar to those for myoglobins (k(O2)', = 7-20 mu M(-1) s(-1)), whereas the O(2) dissociation rates are remarkably slow (k(O2) = 0.25 s(-1)), implying the presence of very favorable interactions between bound O(2) and protein residues in the heme pocket, The CO affinities estimated for both isoforms are only 1-6-fold higher than the corresponding O(2) affinities. Thus, heme oxygenase discriminates much more strongly against CO binding than either myoglobin or hemoglobin. The CO binding reactions with the ferrous alpha-hydroxyheme complex are similar to those of the protoheme complex, and hydroxylation at the alpha-meso position does not appear to affect the reactivity of the iron atom. In contrast, the CO affinities of the verdoheme complexes are >10,000 times weaker than those of the heme complexes because of a 100-fold slower association rate constant (k(CO)' approximate to 0.004 mu M(-1) s(-1)) and a 300-fold greater dissociation rate constant (k(CO) approximate to 3 s(-1)) compared with the corresponding rate constants of the protoheme and alpha-hydroxyheme complexes, positive charge on the verdoporphyrin ring causes a large decrease in reactivity of the iron., AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, Jan. 1998, JOURNAL OF BIOLOGICAL CHEMISTRY, 273 (2), 945 - 949, doi;web_of_science

    Scientific journal

  • Heme oxygenase: A central enzyme of oxygen-dependent heme catabolism and carbon monoxide synthesis

    M Ikeda-Saito; H Fujii; KM Matera; S Takahashi; CT Migita; DL Rousseau; T Yoshida

    Heme oxygenase (IIO) catalyzes the regiospecific degradation of heme to biliverdin-alpha by using O-2 and electrons donated by NADPH cytochrome P-450 reductase. The enzyme binds one equivalent of heme to form the heme-enzyme complex, and electron donation initiates the three stepwise oxygenase reactions through the two novel heme derivatives, alpha-hydroxyheme and verdoheme, during which CO and iron-biliverdin-alpha are produced; heme participates both as a prosthetic group and as a substrate. Electronic states, coordination structures, and reactivities of the HO complexes with heme, alpha-hydroxyheme, and verdoheme have been studied. The proximal iron ligand has been identified as a neutral imidazole of His-25 and the presence of a distal base has been established. Conversion to alpha-hydroxyheme is the step responsible for the regiospecificity. alpha-Hydroxyheme reveals its ferrous neutral radical state as a key property of its reactivity. Requirement of O-2 and one reducing equivalent for the conversion of ferric alpha-hydroxyheme to verdoheme has been determined. The positive charge on the macrocycle causes unique characteristics of the verdoheme complex. Combination of the novel characteristics of the catalytic intermediates and the protein environment appears to be responsible for the unique HO enzyme function., SPRINGER-VERLAG TOKYO, 1998, OXYGEN HOMEOSTASIS AND ITS DYNAMICS, 1, 304 - 314, web_of_science

    International conference proceedings

  • Heme degradation mechanism by heme oxygenase: Conversion of alpha-meso-hydroxyheme to verdoheme IX alpha

    H Fujii; KM Matera; S Takahashi; CT Migita; H Zhou; T Yoshida; M Ikeda-Saito

    Heme oxygenase (HO) is a microsomal enzyme that catalyzes the degradation of iron protoporphyrin IX theme) to biliverdin IXalpha through two novel heme derivatives, alpha-meso-hydroxyheme and verdoheme IXalpha. Using the recombinant HO protein and chemically synthesized alpha-hydroxyheme and verdoheme, we have elucidated HO-catalyzed heme degradation mechanisms. Heme in HO is first hydroxylated to form alpha-meso-hydroxyheme via a ferric hydroperoxide intermediate that is produced by the one-electron reduction of ferrous oxy-complex. The hydrogen bond between iron-bound dioxygen and a protein moiety may play an important role in the dioxygen reduction and regiospecific hydroxylation processes. We have shown that one electron as well as one molecular oxygen are required to degrade alpha-meso-hydroxyheme to verdoheme IXalpha and that two alternative degradation pathways are probable: ferric and ferrous. We propose here a degradation mechanism whereby the ferrous pi-neutral radical formed from ferric alpha-meso-hydroxyheme by an intramolecular electron transfer reacts with superoxide, which is produced from the reduction of dioxygen by ferric or ferrous alpha-meso-hydroxyheme to form verdoheme: IXalpha and CO. We also propose the degradation mechanism of verdoheme IXalpha to biliverdin IXalpha via dioxygen activation processes on verdoheme iron., SPRINGER-VERLAG TOKYO, 1998, OXYGEN HOMEOSTASIS AND ITS DYNAMICS, 1, 315 - 321, web_of_science

    International conference proceedings

  • Imidazole and p-nitrophenolate complexes of oxoiron(IV) porphyrin pi-cation radicals as models for compounds I of peroxidase and catalase

    H Fujii; T Yoshimura; H Kamada

    AMER CHEMICAL SOC, Dec. 1997, INORGANIC CHEMISTRY, 36 (27), 6142 - 6143, doi;web_of_science

    Scientific journal

  • Change in electron configuration of ferric ion in bis(cyanide)(meso-tetraalkylporphyrinatoiron(III)), [Fe(TRP)(CN)(2)](-), caused by the nonplanarity of the porphyrin ring

    M Nakamura; T Ikeue; H Fujii; T Yoshimura

    The synthesis and characterization of a series of bis(cyanide) (meso-tetraalkylporphyrinatoiron(III)), [Fe(TRP)(CN)(2)](-) where R is H, Me, Et, and Pr-i, are reported. The H-1 NMR spectrum of the unsubstituted [Fe(THP)(CN)(2)](-) shows a pyrrole signal at delta = -23.19 ppm (-25 degrees C) in CD2Cl2, which is quite typical as a low spin ferric complex. As the bulkiness of the meso substituent increases, the pyrrole signal moves to lower magnetic field; 0.34, -2.26, and 11.94 ppm for [Fe(TMeP)(CN)(2)](-), [Fe(TEtP)(CN)(2)](-), and [Fe((TPrP)-Pr-i)(CN)(2)](-), respectively. Corresponding to the pyrrole proton signal, the cyanide carbon signal also exhibits a large downfield shift. The difference in chemical shifts between [Fe(THP)(CN)(2)](-) and [Fe((TPrP)-Pr-i)(CN)(2)](-) reaches as much as 1443 ppm at -25 degrees C. The substituent dependent phenomena are also observed in EPR spectra taken in frozen CH2Cl2 solution at 4.2 K. While the unsubstituted complex gives a so called large g(max) type signal at 3.65, the alkyl substituted complexes exhibit axial type spectra; the EPR parameters for [Fe((TPrP)-Pr-i)(CN)(2)](-) are g(perpendicular to) = 2.43 and g(parallel to) = 1.73. These results clearly indicate that the electronic ground state changes from the usual (d(xy))(2)(d(xz), d(yz))(3) to the unusual (d(xz), d(yz))(4)(d(xy))(1) as the substituent becomes bulkier. Analysis of the EPR g values reveals that the orbital of the unpaired electron has more than 90% d(xy) character in the alkyl substituted complexes. The unusual electron configuration is ascribed to the destabilization of d(xy) orbital and/or stabilization of d(xz) and d(yz) orbitals caused by the S-4 ruffled structure of the alkyl substituted porphyrin ring. Thus, in a strongly ruffled low spin complex such as [Fe((TPrP)-Pr-i)(L)(2)](+/-), electron configuration of iron is presented by (d(xz), d(yz))(4)(d(xy))(1) regardless of the kind and basicity of the axial ligand (L). In fact, low spin bis(pyridine) complex [Fe((TPrP)-Pr-i)(Py)(2)](+) gives a pyrrole signal at quite a low field, delta = +16.4 ppm at -87 degrees C, which is actually the lowest pyrrole signal ever reported for the low spin ferric porphyrin complexes. Correspondingly, the EPR spectrum taken at 77 K showed a clear axial type spectrum, g(perpendicular to) = 2.46 and g(parallel to) = 1.59. In every case examined, (d(xz)d(yz))(4)(d(xy))(1) ground state is more or less stabilized by the addition of methanol as exemplified by the further downfield shift of the pyrrole proton and cyanide carbon signals together with the smaller EPR g(perpendicular to) values. The methanol effect is explained in terms of the stabilization of d(xz) and d(yz) relative to d(xy) due to the hydrogen bond formation between coordinated cyanide and methanol., AMER CHEMICAL SOC, Jul. 1997, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 119 (27), 6284 - 6291, doi;web_of_science

    Scientific journal

  • ESR studies of oxochromium(V) porphyrin complexes: Electronic structure of the Cr-V=O moiety

    H Fujii; T Yoshimura; H Kamada

    ESR spectra of oxochromium(V) porphyrins were obtained to investigate the electronic structure of the Cr-V=O moiety. At room temperature, the chlorooxochromium(V) meso-tetramesitylporphyrin complex 1-Cl exhibits an isotropic ESR signal, split into nine signals due to hyperfine coupling with four equivalent N-14, at g = 1.982. A small isotropic satellite signal, split into a quartet due to hyperfine coupling by the Cr-53 isotope is also observed. At 77 K, 1-Cl shows an anisotropic ESR signal with g(parallel to) = 1.986 and g(perpendicular to) = 1.980 and small satellite g(parallel to) signals arising from hyperfine coupling with the Cr-53 isotope. The ESR parameters of 1-Cl, obtained from ESR spectral simulation, show that the pi-bonding character of the Cr-V=O bond is not as strong as that of the Cr-V=N bond. To explore substituent effects on the bond character of the Cr-V=O moiety, ESR spectra of perchloratooxochromium(V) porphyrins having various electronegative substituents were recorded. With an increase in electronegativity of the meso-substituent, the gi value and the Cr-53 hyperfine coupling constant (/a(Cr-53)/) are increased. These changes suggest an increase in the ct-bonding character of the Cr-V=O moiety with an increase in the electronegativity of the meso-substituent. Furthermore, the hyperfine coupling constant of the oxo ligand, /a(O-17)/, obtained from ESR spectra of O-17-labeled oxochromium(V) porphyrin is increased with an increase in electronegativity of the meso-substituent. This indicates that the radical character of the oxo ligand is increased by the electronegative meso-substituent. These data suggest that the pi-antibonding orbital of Cr=O is destabilized with an increase in electronegativity of the meso-substituent, which may facilitate bond breaking of the Cr=O moiety in an epoxidation reaction., AMER CHEMICAL SOC, Mar. 1997, INORGANIC CHEMISTRY, 36 (6), 1122 - 1127, doi;web_of_science

    Scientific journal

  • Regioselective pyrrole synthesis from asymmetric beta-diketone and conversion to sterically hindered porphyrin

    H Fujii; T Yoshimura; H Kamada

    The condensation of asymmetric beta-diketones with alpha-oximinoacetoacetate esters affords pyrroles regioselectively. The mechanism of the regioselectivity is studied using C-13-NMR spectroscopy. Pyrrole having a neopentyl group at the 4-position is synthesized by the method, and further converted to a steric hindered porphyrin in good yield. (C) 1997 Elsevier Science Ltd., PERGAMON-ELSEVIER SCIENCE LTD, Feb. 1997, TETRAHEDRON LETTERS, 38 (8), 1427 - 1430, doi;web_of_science

    Scientific journal

  • Resonance Raman spectroscopic characterization of alpha-hydroxyheme and verdoheme complexes of heme oxygenase

    S Takahashi; KM Matera; H Fujii; H Zhou; K Ishikawa; T Yoshida; M IkedaSaito; DL Rousseau

    Heme oxygenase (HO) is the microsomal enzyme that catalyzes the oxidative degradation of protoheme (iron protoporphyrin IX) and the generation of carbon monoxide. The enzyme converts protoheme into biliverdin through two known heme derivatives, alpha-hydroxyheme and verdoheme. To: gain insight into the degradation mechanisms of the two intermediates, the resonance Raman spectra were observed for alpha-hydroxyheme and verdoheme complexes of HO and compared with those of apomyoglobin (ape-Mb) complexes. The ferrous alpha-hydroxyheme complexed with both HO and apo-Mb shows a resonance Raman spectral pattern similar to that of the protoheme complexes. On the contrary, the ferric alpha-hydroxyheme and ferrous verdoheme complexes of HO and ape-Mb show atypical Raman patterns, which are interpreted as the result of the symmetry lowering of the porphyrin-conJugated pi-electron system. The comparison of the resonance Raman spectra of the verdoheme, complexed with HO and ape-Mb with those of the five- and six-coordinate model complexes of verdoheme shows that the ferrous forms of the verdoheme-protein complexes are six-coordinate. The Fe-CO and Fe-CN stretching frequencies of ferrous verdoheme compounds are distinct from those of ferrous heme compounds. It is inferred that the positive charge of the verdoheme ring possesses some of the charge density on the iron atom, causing unique characteristics of the iron ligand stretching vibrations and altered ligand binding properties., AMER CHEMICAL SOC, Feb. 1997, BIOCHEMISTRY, 36 (6), 1402 - 1410, doi;web_of_science

    Scientific journal

  • Change in electron configuration of ferric ion in bis(cyanide)(meso-tetraalkylporphyrinato)iron(III)), [Fe(TRP)(CN)2]-, caused by the nonplanarity of the porphyrin ring

    M. Nakamura; T. Ikeue; H. Fujii

    1997, J. Inorg. Biochem, 67, 128, doi

  • Resonance Raman spectrum of a (2)A(1u) ferryl porphyrin pi-cation radical

    K Czarnecki; LM Proniewicz; H Fujii; Kincaid, JR

    Resonance Raman spectra are reported for the iron complex of tetramethyltetramesitylporphine (TMTMP) in its ferric, ferryl, and ferryl pi-cation forms. For comparison, the spectra of the copper complex and its corresponding pi-cation radical are included. Vibrational assignments have been made based on depolarization ratio measurements and isotopic frequency shifts associated with methine deuteration. The observed behavior of the v(2) and v(11) RR ''marker bands'', which shift to higher frequency upon oxidation of the macrocycle, is consistent with previously reported NMR studies wherein these radicals were shown to have predominately (2)A(1u) ground states. The v(Fe-O) stretching modes of the ferryl species (both five- and six-coordinate) and (OFeTMTMP(.+))(ClO4-) are identified by their O-16/O-18 isotope shifts. This is the first observation of the v(Fe-O) mode for a (2)A(lu), type ferryl pi-cation radical. Its frequency (833 cm(-1)) is virtually identical with that of the corresponding derivative of nzeso-tetramesitylporphyrin (TMP), (O=FeTMP(+))(ClO4-), a (2)A(2u), radical, which exhibits its v(Fe-O) mode at 835 cm(-1). These data imply that the v(Fe-O) modes of ferrylporphyrin pi-cation radicals are rather insensitive to radical type ((2)A(lu) vs (2)A(2u))-behavior which is surprisingly different from the previously observed sensitivity of the v(V-O) modes of corresponding vanadylporphyrin pi-cation radicals., AMER CHEMICAL SOC, May 1996, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 118 (19), 4680 - 4685, doi;web_of_science

    Scientific journal

  • ESR studies of A(1u) and A(2u) oxoiron(IV) porphyrin pi-cation radical complexes. Spin coupling between ferryl iron and A(1u)/A(2u) orbitals

    H Fujii; T Yoshimura; H Kamada

    This study shows the ESR spectra of oxoiron(IV) porphyrin pi-cation radicals of 1-8 in dichloromethane-methanol (5:1) mixture. We reported in a previous paper that oxoiron(IV) porphyrin pi-cation radicals of 1-4 are in an a(1u) radical state while those of 5-8 are in an a(2u) radical. The ESR spectra (g(perpendicular to)(eff) similar to 3.1 and g(parallel to)(eff) similar to 2.0) for the a(1u) radical complexes, 1-4, appear quite different from those reported previously for the oxoiron(IV) porphyrin pi-cation radical of 5 (g(y) = 4.5, g(x) = 3.6, and g(z) = 1.99). The unique ESR spectra of the a(1u) radical complexes rather resemble those of compound I from Micrococcus lysodeikticus catalase (CAT) and ascorbate peroxidase (ASP). This is the first examples to mimic the ESR spectra of compound I in the enzymes. From spectral analysis based on a spin Hamiltonian containing an exchange interaction, the ESR spectra of 1-4 can be explained as a moderate ferromagnetic state (J/D similar to 0.3) between ferryl S = 1 and the porphyrin pi-cation radical S' = 1/2. The magnitudes of zero-field splitting (D) for ferryl iron and isotropic J value, estimated from the temperature-dependence of the half-saturation power of the ESR signals, are similar to 28 and similar to+8 cm(-1)) respectively. A change in the electronegativity of the beta-pyrrole substituent hardly changes the ESR spectral feature while that of the meso-substituent slightly does owing to the change in the E/D value. On the basis of the present ESR results, we propose the a(1u) radical state for compound I of CAT and ASP., AMER CHEMICAL SOC, Apr. 1996, INORGANIC CHEMISTRY, 35 (8), 2373 - 2377, doi;web_of_science

    Scientific journal

  • Oxygen and one reducing equivalent are both required for the conversion of alpha-hydroxyhemin to verdoheme in heme oxygenase

    KM Matera; S Takahashi; H Fujii; H Zhou; K Ishikawa; T Yoshimura; DL Rousseau; T Yoshida; M IkedaSaito

    Heme oxygenase is a central enzyme of heme degradation and associated carbon monoxide biosynthesis. We have prepared the alpha-hydroxyheme-heme oxygenase complex, which is the first intermediate in the catalytic reaction. The active site structure of the complex was examined by optical absorption, EPR, and resonance Raman spectroscopies. In the ferric form of the enzyme complex, the heme iron is five coordinate high spin and the alpha-hydroxyheme group in the complex assumes a structure of an oxophlorin where the alpha-meso hydroxy group is deprotonated. In the ferrous form, the alpha-hydroxy group is protonated and consequently the prosthetic group assumes a porphyrin structure. The alpha-hydroxyheme group undergoes a redox-linked conversion between a keto and an enol form. The ferric alpha-hydroxyheme reacts with molecular oxygen to form a radical species. Reaction of the radical species with a reducing equivalent yields the verdoheme-heme oxygenase complex. Reaction of the ferrous alpha-hydroxyheme-heme oxygenase complex with oxygen also yields the verdoheme-enzyme complex. We conclude that the catalytic conversion of ferric alpha-hydroxyheme to verdoheme by heme oxygenase requires molecular oxygen and one reducing equivalent., AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, Mar. 1996, JOURNAL OF BIOLOGICAL CHEMISTRY, 271 (12), 6618 - 6624, doi;web_of_science

    Scientific journal

  • Formation and characterization of thiol-derivatized zinc(II) porphyrin monolayers on gold

    K Shimazu; M Takechi; H Fujii; M Suzuki; H Saiki; T Yoshimura; K Uosaki

    Self-assembled monolayers of two kinds of thiol-derivatized porphyrins, which differ in the number of alkanethiol side chain, have been constructed on Au. X-ray photoelectron, visible and Fourier transform infrared spectra confirmed that surface structure was approximately the same as anticipated; porphyrin molecules having a single chain are somewhat tilted against surface normal, and porphyrins with four chains are oriented coplanar., ELSEVIER SCIENCE SA LAUSANNE, Feb. 1996, THIN SOLID FILMS, 273 (1-2), 250 - 253, doi;web_of_science

    Scientific journal

  • Synthesis and characterization of a binuclear porphyrin complex as a model for heme a(3)-Cu-B site of cytochrome c oxidase

    H Fujii; T Yoshimura; H Kamada

    A binuclear complex, 1, involving copper and heme complexes is synthesized and characterized by paramagnetic H-1-NMR, FAB mass, and ESR spectroscopies. These measurements indicate a fairly weak magnetic interaction between iron and copper ions when a bridge ligand is absent., CHEMICAL SOC JAPAN, 1996, CHEMISTRY LETTERS, (8), 581 - 582, doi;web_of_science

    Scientific journal

  • A HIGH-VALENT NONHEME IRON INTERMEDIATE - STRUCTURE AND PROPERTIES OF [FE-2(MU-O)(2)(5-ME-TPA)(2)](CLO4)(3)

    YH DONG; H FUJII; MP HENDRICH; RA LEISING; GF PAN; CR RANDALL; EC WILKINSON; Y ZANG; L QUE; BG FOX; K KAUFFMANN; E MUNCK

    In our efforts to model the oxygen activation chemistry of methane monooxygenase (MMO) and the R2 protein of ribonucleotide reductase (RNR), we have discovered a transient green species (3) in the reaction of H2O2 with a (mu-oxo)diiron(III) TPA complex (TPA = tris(2-pyridylmethyl)amine). Our studies show that the precursor to 3 is [Fe2O(TPA)(2)(OH)(H2O)](ClO4)(3) (2a), which can be obtained by the treatment of [Fe2O(TPA)(2)(H2O)(ClO4)]-(ClO4)(3) (1) With an equivalent of base. Crystallographic studies show that 1 has a nearly linear (mu-oxo)diiron(III) core with terminal aqua and perchlorato ligands (angle Fe-(mu-O)-Fe = 174.1(4)degrees), while 2c, the 5-Et-TPA analogue of 2a, has a bent (mu-oxo)diiron(III) core that is supported by an H3O2- bridge, The presence of an H3O2- bridge in the latter is indicated by the short O-O separation (2.464(9) Angstrom), the Fe-Fe distance of 3.346(9) Angstrom, and the Fe-(mu-O)-Fe angle of 136.3(3)degrees. Thus treatment of 1 with an equivalent of base results in the replacement of the bound perchlorate with hydroxide and the bending of the Fe-O-Fe unit to form 2, That the bent Fe-O-Fe core persists in solution is indicated by its UV-vis features and NMR spectra that reflect distinct TPA coordination modes about the individual iron sites. The green intermediate 3 is generated by the reaction of 2, [Fe2O(L)(2)(OH)(H2O)](ClO4)(3) (L = TPA, 5-Me-TPA, and 5-Et-TPA), with H2O2 in CH3CN at -40 degrees C; when 5-Me-TPA is used as the tripodal ligand, 3b can be isolated as a solid upon standing overnight at -40 degrees C. Complex 3b exhibits electronic absorption features at 366 (epsilon = 7900 M(-1) cm(-1)) and 616 nm (epsilon = 5200 M(-1) cm(-1)) and an S = 3/2 EPR spectrum with g values at 4.45, 3.90, and 2.01. It exhibits one sharp Mossbauer doublet with Delta E(Q) = 0.49 mm/s and delta = 0.12 mm/s at 100 K, which accounts for 90% of the iron in the solid. Elemental analysis and electrospray ionization mass spectrometry show that 3b is a dinuclear complex best formulated as [Fe-2(O)(2)(5-Me-TPA)(2)](ClO4)(3). This dinuclear formulation is corroborated by magnetic susceptibility measurements showing that 3b has a high-temperature moment of 3.9 mu(B)/2Fe, corresponding to the 5 = 3/2 center observed by EPR. The formula for 3b suggests two unique properties: (a) that it has an Fe-2(mu-O)(2) core, and (b) that it is formally (FeFeIV)-Fe-III. The presence of an Fe-2(mu-O)(2) core in 3b is indicated by its EXAFS spectrum, which requires the inclusion of an Fe scatterer at 2.89 Angstrom for a satisfactory fit. It is further supported by the observation of resonance-enhanced Raman features at 676 and 656 cm(-1) (both of which shift to 634 cm(-1) with added (H2O)-O-18), which are associated with an Fe2O2 breathing mode by analogy to those observed for Mn2O2 complexes. The high-valent nature of 3b is corroborated by the ca. 3 eV upshift of its higher X-ray absorption K-edge relative to that of 2b and the reduction of 3b to the diiron(III) state at -40 degrees C by chemical (ferrocene titration) and cyclic voltammetric (E(1/2) = 0.96 V vs NHE) methods. Thus, 3b represents a bis(mu-oxo)-diiron complex with a formally (FeFeIV)-Fe-III valence state. Complex 3b has an unusual electronic structure. EPR, magnetization, and Mossbauer studies show that 3b has an S = 3/2 ground state with a large and nearly axial zero-field splitting, D = 35 +/- 15 cm(-1) and E/D = 0.04. The Mossbauer data show that 3 contains two equivalent iron sites which have unusually small magnetic hyperfine interactions, A = (-7.8, -7.9, -6.5) MHz. A variety of exchange coupling models are considered to describe the electronic properties of 3b; these include (FeFeIII)-Fe-III sites coupled to a ligand radical and valence-delocalized (FeFeIV)-Fe-III centers. Among the models considered, the only one that could possibly explain the observed site equivalence, isomer shift, and other properties consists of a valence-delocalized low-spin (S = 1/2) Fe-III-low-spin (S = 1) Fe-IV pair coupled by Heisenberg as well as double exchange; however, detailed theoretical studies of double exchange interactions involving low-spin iron sites are required before such an assignment can be made. Whatever its electronic structure, 3b is the only well-characterized high-valent nonheme iron species that is derived from the reaction of H2O2 and a (mu-oxo)diiron(III) complex. As such, it is relevant to the transient species observed in the oxidation chemistry of MMO and RNR R2, and provides a synthetic example of how a high-valent state can be attained in a nonheme environment., AMER CHEMICAL SOC, Mar. 1995, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 117 (10), 2778 - 2792, doi;web_of_science

    Scientific journal

  • STUDIES ON THE IRON(II) MESO-OXYPORPHYRIN PI-NEUTRAL RADICAL AS A REACTION INTERMEDIATE IN HEME CATABOLISM

    MORISHIMA, I; H FUJII; Y SHIRO; S SANO

    The electronic structure of iron(III) meso-hydroxyporphyrin (2a) dissolved in pyridine was characterized by NMR, ESR, and optical absorption spectroscopies. It was found that the meso hydroxyl group of 2a is fully deprotonated in pyridine solution, and the resultant compound is in a quantum mixing state of the iron(III) meso-oxyporphyrin (2b) and the iron(II) porphyrin pi-neutral radical (2c) states, i.e., the resonance structure of 2b and 2c. Deprotonation of the meso hydroxyl group and coordination of the axial ligands are both essential for the generation of this unique electronic structure. The population of 2b and 2c in the mixing state is modulated by the basicity of the axial ligands. as was manifested by the drastic NMR and ESR spectral changes upon varying the pyridine derivatives as the ligands. Because 2c is highly reactive with O-2 to form verdoheme, while 2a and 2b are unreactive, the formation of the pi-radical character is essential in heme breakdown. Thus, wt discussed the electronic structure of meso-hydroxyheme in relation to the reaction of heme catabolism., AMER CHEMICAL SOC, Mar. 1995, INORGANIC CHEMISTRY, 34 (6), 1528 - 1535, doi;web_of_science

    Scientific journal

  • CARBOXYLATOIRON(II) AGGREGATES - A NOVEL FE-4(II) COMPLEX WITH THREEFOLD SYMMETRY

    S MENAGE; H FUJII; MP HENDRICH; L QUE

    VCH PUBLISHERS INC, Sep. 1994, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH, 33 (15-16), 1660 - 1662, web_of_science

    Scientific journal

  • CHARACTERIZATION OF HIGH-VALENT IRON PORPHYRIN IN CATALYTIC REACTION BY IRON(III) TETRAPENTAFLUOROPHENYLPORPHYRIN

    H FUJII

    High valent species formed from iron(III) meso-tetra-(pentafluorophenyl)porphyrin was first prepared in dichloromethane and characterized by low-temperature UV-vis absorption spectra, proton NMR and ESR. These measurements showed the formation of oxo iron(IV) porphyrin pi-cation radical, not iron(V) porphyrin., CHEMICAL SOC JAPAN, Aug. 1994, CHEMISTRY LETTERS, (8), 1491 - 1494, doi;web_of_science

    Scientific journal

  • EFFECTS OF THE ELECTRON-WITHDRAWING POWER OF SUBSTITUENTS ON THE ELECTRONIC-STRUCTURE AND REACTIVITY IN OXOIRON(IV) PORPHYRIN PI-CATION RADICAL COMPLEXES

    H FUJII

    The effects of the electron-withdrawing power of the substituents bound to a porphyrin ring on the electronic structures and the reactivities of oxoiron(IV) porphyrin pi-cation radical complexes were studied by using 2,7,12,17-tetramethyl-3,8,13,18-tetraarylporphyrins (aryl = (1) mesityl, (2) 2-chloro-6-methylphenyl, (3) 2,6-dichlorophenyl, or (4) 2,4,6-trichlorophenyl) and tetrakis-5,10,15,20-tetraarylporphyrins (aryl = (5) mesityl, (6) 2-chloro-6-methylphenyl, (7) 2,6-dichlorophenyl, or (8) 2,4,6-trichlorophenyl). The electronic structures of oxoiron(IV) porphyrin pi-cation radicals were investigated by low-temperature UV-visible absorption spectroscopy and proton NMR measurements. The absorption spectra of oxoiron(IV) porphyrin pi-cation radicals of compounds 1-4 changed with an increase of the electron-withdrawing power of ring substituents, while those of compounds 5-8 did not. Proton NMR measurements demonstrated that oxoiron(IV) porphyrin pi-cation radicals of compounds 1-4 have an a1u radical character and that those of compounds 5-8 are better described as an a2u radical species. The reactivities of oxygen atoms of oxoiron(IV) porphyrin pi-cation radicals were examined by competitive epoxidation of cyclohexene by two oxoiron(IV) porphyrin pi-cation radicals with different radical orbital occupancies or oxidation potentials. The oxygen atom with the higher oxidation potential was more reactive than that with the lower oxidation potential. Furthermore, the oxygen atom with the a1u radical state was almost as reactive as that with the a2u radical state. The results indicate that the reactivity of the oxygen atom of the oxoiron(IV) porphyrin pi-cation radical depends on its oxidation potential and is not affected by the a1u/a2u orbital occupancy., AMER CHEMICAL SOC, Jun. 1993, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 115 (11), 4641 - 4648, doi;web_of_science

    Scientific journal

  • CHARACTERIZATION AND INTRAMOLECULAR SPIN COUPLING OF A MONOMERIC A1U COPPER(II) PORPHYRIN PI-CATION RADICAL

    H FUJII

    The intramolecular magnetic interaction between copper(II) and a1u porphyrin radical spins in [Cu(TMTMP.)]-[SbCl6] (TMTMP. = pi-cation radical of 2,7,12,17-tetramethyl-3,8,13,18-tetramesitylporphyrin) was investigated by using ESR measurements in frozen dichloromethane and by solid magnetic susceptibility measurements. The monomeric nature of [Cu(TMTMP.)][SbCl6] at low temperature was confirmed by low-temperature UV-visible absorption spectral measurements. The radical orbital occupancy of [Cu(TMTMP.)][SbCl6] was examined by use of hyperfine-shifted deuterium NMR resonances, which showed characteristics of an a1u radical state. The ESR spectrum of [Cu(TMTMP.)][SbCl6] afforded signals having characteristics of a monomeric triplet state; i.e., the signal was separated into a four-line component from the interaction of a single copper(II) center and a pair of signals in high field. The temperature dependence of the ESR spectra of [Cu(TMTMP.)][SbCl6] signifies the S = 0 ground state (antifeffomagnetic). The solid magnetic susceptibility measurements for [Cu(TMTMP.)][SbCl6] demonstrated antiferromagnetic coupling between copper(II) and a1u radical spins with J = -120 cm-1. Antiferromagnetic coupling in [Cu(TMTMP.)][SbCl6] can be explained by the spin density at the pyrrole nitrogen atom in the a1u radical orbital., AMER CHEMICAL SOC, Mar. 1993, INORGANIC CHEMISTRY, 32 (6), 875 - 879, doi;web_of_science

    Scientific journal

  • PREPARATION AND CHARACTERIZATION OF AN A1U OXOIRON(IV) PORPHYRIN PI-CATION-RADICAL COMPLEX

    H FUJII; K ICHIKAWA

    AMER CHEMICAL SOC, Mar. 1992, INORGANIC CHEMISTRY, 31 (6), 1110 - 1112, doi;web_of_science

  • NMR-STUDIES OF IRON(II) NITROSYL PI-CATION RADICALS OF OCTAETHYLCHLORIN AND OCTAETHYLISOBACTERIOCHLORIN AS MODELS FOR REACTION INTERMEDIATE OF NITRITE REDUCTASE

    S OZAWA; H FUJII; MORISHIMA, I

    Chemical oxidation of iron(II) nitrosyl complexes of octaethylchlorin (OEC) and octaethylisobacteriochlorin (OEiBC) yielded iron(II) nitrosyl pi-cation radicals. The pi-cation radicals afforded well-resolved hyperfine-shifted NMR resonances characteristic of an a2-pi-radical state. Non-Curie law behavior of the deuterium NMR resonances was interpreted in terms of a valence isomerization from the chlorin pi-cation radical to the FeIINO+ chlorin complex due to ligation of SbF6- to the iron of the pi-cation radical as well as a magnetic interaction between the NO and pi-radical spins in (OEiBC)FeIINO pi-cation radical. This valence isomerization was confirmed by variable-temperature electronic absorption spectral measurements. Furthermore, ligation of imidazole to the pi-cation radicals caused valence isomerization to yield (OEC)FeII(NO+)(Im) and (OEiBC)FeII(NO+)(Im) complexes., AMER CHEMICAL SOC, Feb. 1992, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 114 (5), 1548 - 1554, doi;web_of_science

    Scientific journal

  • SPIN COUPLING IN FERRIC PORPHYRIN AND CHLORIN PI-CATION-RADICAL COMPLEXES

    S NAKASHIMA; H OHYANISHIGUCHI; N HIROTA; H FUJII; MORISHIMA, I

    The ferric porphyrin pi-cation-radical complexes (OEP.)Fe(III)(CIO4)2 (1) (OEP. = monoanion of octaethylporphyrin) and (OEP.)FE(III)Cl]SbCl6[ (2) and the ferric chlorin pi-cation-radical complexes (OEC.)Fe (III)(ClO4)2 (3) (OEC. = monoanion of octaethylchlorin), (OEC.)Fe (III)Cl[SbCl6] (4), and (TPC.)Fe (III)Cl[SbCl6] (5) (TPC. = monoanion of tetraphenylchlorin) were examined in microcrystalline form by magnetic susceptometry over a range of 1.6 K to room temperature at an applied field. The effective magnetic moments of the two six-coordinate complexes, 1 and 3, were in reasonable agreement with simulation in which an S = 5/2 iron ion antiferromagnetically couples with an s = 1/2 porphyrin (or chlorin) pi-radical by weak exchange interaction. In the five-coordinate complexes, 2, 4, and 5, the results of the magnetic susceptibility measurements are consistent with the calculations based on the model that the S = 5/2 iron ion antiferromagnetically couples with the s = 1/2 pi-radical with energies of -8 cm-1 for 2, -20 cm-1 for 4, and -85 cm-1 for 5. Thus the ground states of all these complexes measured are of total spin S(T) = 2. The difference in the magnitude of the antiferromagnetic coupling between the five-coordinate complexes and the six-coordinate complexes is reasonably explained by the difference of the symmetry of the radical orbitals: A1u symmetry of OEP, OEC, and TPC complexes. From these results A1u symmetry for the radical orbitals in horseradish peroxidase compound 1 (HRP compound 1) and myeloperoxidase compound I (MPO compound I) is proposed., AMER CHEMICAL SOC, Dec. 1990, INORGANIC CHEMISTRY, 29 (26), 5207 - 5211, doi;web_of_science

    Scientific journal

  • NMR-STUDIES OF METALLOPORPHYRIN RADICALS - IRON(II) OXOPHLORIN RADICAL FORMED FROM IRON(III) MESO-HYDROXYOCTAETHYLPORPHYRIN

    MORISHIMA, I; H FUJII; Y SHIRO; S SANO

    AMER CHEMICAL SOC, Jun. 1986, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 108 (13), 3858 - 3860, doi;web_of_science

  • Meso-Substitution Activates Oxoiron(IV) Porphyrin π-Cation Radical Complex More Than Pyrrole-ß -Substitution for Atom Transfer Reaction

    Nami Fukui; Kanako Ueno; Masahiko Hada; Hiroshi Fujii

    Mar. 2021, Inorg. Chem., 60, 3207 - 3217

    Scientific journal

  • Synthesis, Characterization and Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complexes bearing Cationic N-Methyl-2-pyridinium Group

    Yuna Suzuki; Masahiko Hada; Hiroshi Fujii

    Jul. 2021, J. Inorg. Biochem., 111542

    Scientific journal

  • Significant Solvent Effetc on Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex: Activation in n-Alkane Solvent

    Kanako Ueno; Yuri Ishimizu; Hiroshi Fujii

    Jul. 2021, Inorg. Chem., 60, 9243 - 9247

    Scientific journal

MISC

  • High-Spin Fe(IV)-Oxo Porphyrin Complexes in Epoxidation Reaction of Olefin : A CASPT2 Study

    UKAJI Kasumi; ABE Minori; HADA Masahiko; FUJII Hiroshi

    High-valent iron (IV)-oxo porphyrin π-cation radical species (P+・) FeIV = O are known as an active intermediate in various enzymatic reactions of cytochrome P450s. In epoxidation reactions catalyzed by these species, potential surfaces between reactant and product are connected by the intersystem crossing. In this report, CASPT2, SO-CASPT2 and SAC-CI calculations were carried out to analyze low-lying doublet, quartet, and sextet electronic ground and excited states in an expoxidation reaction of olefin catalyzed by Cl−(P+・) FeIV = O. In both CASPT2 and SAC-CI calculations, we obtained the quartet and sextet ground states of Cl−(P+・) FeIV = O and Cl (P) FeIII respectively as suggested experimentally., Society of Computer Chemistry, Japan, 2014, Journal of Chemical Software, 13 (3), 167 - 168, doi;cinii_articles

  • レーザーパンプ・X線プローブ法によるRu錯体の光励起状態の構造観測

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 腰原伸也; 藤井浩; 足立伸一

    12 Jan. 2013, 日本放射光学会年会・放射光科学合同シンポジウム予稿集, 26th, 96, j_global;url

  • レーザーパンプ・X線プローブ法によるRu錯体の光励起状態の構造観測

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 腰原伸也; 藤井浩; 足立伸一

    2013, 物構研サイエンスフェスタ要旨集, 1st, 43, j_global;url

  • ピコ秒時間分解XAFSによる[RuII(bpy)3]2+3MLCT状態の観測

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 腰原伸也; 藤井浩; 足立伸一

    2012, PFシンポジウム要旨集, 29th, 66, j_global;url

  • [Ru(bpy)3]2+の100ピコ秒時間分解XAFS

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 腰原伸也; 藤井浩; 足立伸一

    12 Mar. 2010, 日本化学会講演予稿集, 90th (2), 268, j_global;url

  • [Ru(bpy)3]2+の100ps時間分解XAFS

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 腰原伸也; 藤井浩; 足立伸一

    2010, PFシンポジウム要旨集, 27th, 89, j_global;url

  • [Ru(bpy)3]2+の時間分解XAFS

    佐藤篤志; 野澤俊介; 富田文菜; 星野学; 星野学; 腰原伸也; 腰原伸也; 藤井浩; 足立伸一

    2010, 分子科学討論会講演プログラム&要旨(Web), 4th, ROMBUNNO.3B13 (WEB ONLY), j_global;url

  • ピコ秒時間分解XAFSを用いたFe(II)スピンクロスオーバー錯体における光誘起スピン転移・構造変化ダイナミクスの研究

    野澤俊介; 野澤俊介; 佐藤篤志; 佐藤篤志; 佐藤篤志; 一柳光平; 一柳光平; MATTHIEU Chollet; MATTHIEU Chollet; 富田文菜; 富田文菜; 藤井浩; 足立伸; 足立伸; 腰原伸也; 腰原伸也

    2009, 分子科学討論会講演プログラム&要旨(Web), 3rd, ROMBUNNO.1B14 (WEB ONLY), j_global;url

  • 100ピコ秒時間分解XAFSを用いた鉄(II)スピンクロスオーバー錯体における光誘起構造転移のダイナミクスの観測

    野澤俊介; 佐藤篤志; 一柳光平; MATTHIEU Chollet; 富田文菜; 市川広彦; 藤井浩; 足立伸一; 腰原伸也

    05 Aug. 2008, 配位化合物の光化学討論会講演要旨集, 21st, 58 - 59, j_global;url

  • Effect of axial ligand on compound I model complexes related to catalase and peroxidase

    Akihiro Takahashi; Takuya Kurahashi; Hiroshi Fujii

    PHARMACEUTICAL SOC JAPAN, 2008, YAKUGAKU ZASSHI-JOURNAL OF THE PHARMACEUTICAL SOCIETY OF JAPAN, 128, 48 - 48, web_of_science

    Summary international conference

  • A sterically hindered salen iron complex as a model for active sites of mononuclear non-heme iron enzymes

    H Fujii; T Kurahashi; T Ogura

    ELSEVIER SCIENCE INC, Jul. 2003, JOURNAL OF INORGANIC BIOCHEMISTRY, 96 (1), 133 - 133, web_of_science

    Summary international conference

  • Formation of a pure and an admixed intermediate spin complex in saddle-shaped six-coordinated iron(III) porphyrins.

    M Nakamura; T Ikeue; T Yamaguchi; Y Ohgo; H Fujii

    AMER CHEMICAL SOC, Mar. 2000, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 219, U822 - U822, web_of_science

    Summary international conference

  • Electron configuration of ferric ions in low spin (meso-tetraaryl porphyrinato)iron(III) complexes.

    M Nakamura; A Ikezaki; T Ikeue; Y Ohgo; H Fujii

    AMER CHEMICAL SOC, Mar. 1999, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 217, U1053 - U1053, web_of_science

    Summary international conference

  • Homogeneous spin distribution in pyrrole beta-carbons in low spin meso-tetraalkylporphyrinatoiron(III) carrying cyanide and rotationally fixed imidazole ligands.

    M Nakamura; T Ikeue; Y Ohgo; H Fujii; T Yoshimura

    AMER CHEMICAL SOC, Sep. 1997, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 214, 281 - INOR, web_of_science

    Summary international conference

  • Change in electronic configuration of ferric ion in low spin porphyrin complexes caused by the nonplanarity of the porphyrin ring.

    M Nakamura; T Ikeue; Y Ohgo; H Fujii; T Yoshimura

    AMER CHEMICAL SOC, Sep. 1997, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 214, 413 - INOR, web_of_science

    Summary international conference

  • Conversion of alpha-hydroxyhemin to verdoheme in heme oxygenase.

    KM Matera; S Takahashi; H Fujii; H Zhou; K Ishikawa; T Yoshimura; DL Rousseau; T Yoshida; M IkedaSaito

    CELL PRESS, Feb. 1996, BIOPHYSICAL JOURNAL, 70 (2), WP342 - WP342, web_of_science

    Summary international conference

  • IRON(II)-OXOPHLORIN RADICAL, A KEY INTERMEDIATE OF THE HEME CATABOLISM, IS A RESONANCE HYBRID OF IRON(III)-MESO-OXYHEME ANION

    MORISHIMA, I; H FUJII; Y SHIRO

    ELSEVIER SCIENCE BV, Jun. 1987, RECUEIL DES TRAVAUX CHIMIQUES DES PAYS-BAS-JOURNAL OF THE ROYAL NETHERLANDS CHEMICAL SOCIETY, 106 (6-7), 334 - 334, web_of_science

    Summary international conference

Books etc

  • 錯体化合物辞典

    (, Range: FeN4OCl)

    朝倉書店, 2019

  • Heme Peroxidases

    Royal Society of Chemistry, 2016

  • クライトン「生物無機化学」

    東京化学同人, 2016

  • フロンティア 生物無機化学

    三共出版, 2016

  • 化学実験テキスト 第4版(下)

    奈良女子大学理学部化学生命環境学科化学コース, 2015

  • Paramagnetic Resonance of Metallobiomolecules, ACS Book Series 858

    American Chemical Society, 2003

  • Paramagnetic Resonance of Metallobiomolecules, ACS Book Series 858

    American Chemical Society, 2003

  • Metal-Oxo and Metal-Peroxo Species in Catalytic Oxidations, Structure & Bonding 97

    Springer, 2000

  • Metal-Oxo and Metal-Peroxo Species in Catalytic Oxidations, Structure & Bonding 97

    Springer, 2000

  • Oxygen Homeostasis and Its Dynamics

    Springer, 1997

  • Oxygen Homeostasis and Its Dynamics

    Springer, 1997

Presentations

  • シトクロムP450の反応活性種のモデル錯体を用いたベンジル位水酸化反応の速度論的研究

    日本化学会第98回春期年会, 2018

  • 鉄4価オキソポルフィリン錯体における不均化反応の研究

    日本化学会第98回春期年会, 2018

  • 鉄3価ヘム次亜塩素酸錯体のO-Cl結合開裂に対する配位子の効果

    日本化学会第97回春期年会, 2017

  • 鉄4価ポルフィリンπカチオンラジカルによるオレフィンエポキシ化反応における電子移動過程への寄与について

    日本化学会第97回春期年会, 2017

  • Participation of Electron-Transfer process in Aromatic Hydroxylation Reactions by Heme Enzymes

    International Symposium on Reactive Intermediates and Unusual Molecules, 2017

  • 鉄3価ヘム次亜塩素酸錯体のOCl結合開裂に対する配位子の効果

    第11回バイオ関連化学シンポジウム, 2017

  • マンガン4価サレン錯体の配位子置換による構造 の研究

    第67回錯体化学討論会, 2017

  • ヘム錯体のポルフィリン配位子及び軸配位子が 鉄の電子状態に及ぼす効果について

    第67回錯体化学討論会, 2017

  • 鉄4価オキソポルフィリンπ-カチオンラジカルが触 媒するオレフィンのエポキシ化反応の電子移動過 程の寄与について

    第67回錯体化学討論会, 2017

  • 疎水性反応空間を有するポルフィリン錯体の合成

    第50回酸化反応討論会, 2017

  • 鉄4価オキソポルフィリンπ-カチオンラジカル錯体における配位子の構造と反応性の関係

    第50回酸化反応討論会, 2017

  • Participation of Electron-Transfer process in Aromatic Hydroxylation Reactions by Heme Enzymes

    International Symposium on Reactive Intermediates and Unusual Molecules, 2017

  • マンガン4価サレン次亜塩素酸イオン付加錯体の反応性の研究

    日本化学会第96回春期年会, 2016

  • 鉄(Ⅲヘム次亜塩素酸錯体の反応性に対する配位子の電子吸引性効果

    日本化学会第96回春期年会, 2016

  • 鉄4価オキソ鉄ポルフィリンπカチオンラジカルと芳香環の反応および反応機構

    日本化学会第96回春期年会, 2016

  • 鉄4価オキソ鉄ポルフィリンπカチオンラジカル錯体のポルフィリンラジカル軌道が反応性に及ぼす影響

    日本化学会第96回春期年会, 2016

  • The Functional Role of the Dioxo-isobacteriochlorin Structure of the Catalytic Site of Cytochrome cd1 in Nitrite Reduction

    42nd International Conference on Coordination Chemistry, 2016

  • 鉄3価ヘム次亜塩素酸錯体の反応性に対するポルフィリン配位子と軸配位子の効果

    第66回錯体化学討論会, 2016

  • Compound Iモデル錯体を用いたチトクロームP450の芳香環水酸化反応の反応機構の研究

    第66回錯体化学討論会, 2016

  • 鉄4価オキソポルフィリンπ-カチオンラジカル錯体における配位子の構造と反応性の関係

    第49回酸化反応討論会, 2016

  • マンガン4価サレン次亜塩素酸イオン付加錯体の同定と反応性の研究

    第49回酸化反応討論会, 2016

  • Mechanism of Aromatic Hydroxylation Reactions by Compound I of Cytochrome P450

    8th Asian Biological Inorganic Chemistry Conference (Asbic8), 2016

  • The Functional Role of the Dioxo-isobacteriochlorin Structure of the Catalytic Site of Cytochrome cd1 in Nitrite Reduction

    42nd International Conference on Coordination Chemistry, 2016

  • Mechanism of Aromatic Hydroxylation Reactions by Compound I of Cytochrome P450

    8th Asian Biological Inorganic Chemistry Conference (Asbic8), 2016

  • ハロパーオキシダーゼの活性反応中間体の研究

    分子研研究会「生物無機化学の最先端と今後の展望」, 2015

  • 酵素モデル金属錯体を用いた金属酵素の機能発現機構の研究

    第52回錯体化学若手の会・近畿支部勉強会, 2015

  • Role of the Heme Axial Ligand on the Reactivity of High-Valent Oxoiron(IV) Porphyrin Intermediate

    227th Electrochemistry Society Meeting, 2015

  • Mechanism of Aromatic Hydroxylation by Cytochrome P450 Compound I Model Complexes

    RIKEN Symposium "Metals in Biology" in Wako, 2015

  • How does the Heme Axial Ligand Controles the Reactivity of High-velent oxoiron intermediates?

    IUPAC-2015, 2015

  • Preparation, characterization and Reactivity of Iron(III) Porphyrin Hypochlorite Complexes as Models for Reactive Intermediates in Haloperoxidase

    ChemComm Symposium, 2015

  • How does the axial ligand control the reactivity of high-valent metal oxo complex?

    2nd Japan-Germany Joint Symposium, 2015

  • 高原子価オキソ鉄ポルフィリン錯体による芳香族水酸化反応の反応機構の研究

    第65回錯体化学討論会, 2015

  • ミエロペルオキシダーゼの活性反応中間体としての鉄(Ⅲ)ヘム次亜塩素酸錯体の反応性の研究

    第48回酸化反応討論会, 2015

  • Compound Iモデル錯体を用いたチトクロームP450による芳香環水酸化反応の反応機構の研究

    第48回酸化反応討論会, 2015

  • マンガン4価サレン次亜塩素酸イオン付加錯体の合成と反応性の研究

    第48回酸化反応討論会, 2015

  • Molecular Mechanism of Heme Axial Ligand for Controlling the Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex

    Pacifichem2015, 2015

  • Electronic Structure of One-electron Oxidized Mixed-Valence Metal Salen Complexes

    Pacifichem2015, 2015

  • Role of the Heme Axial Ligand on the Reactivity of High-Valent Oxoiron(IV) Porphyrin Intermediate

    227th Electrochemistry Society Meeting, 2015

  • Mechanism of Aromatic Hydroxylation by Cytochrome P450 Compound I Model Complexes

    RIKEN Symposium "Metals in Biology" in Wako, 2015

  • How does the Heme Axial Ligand Controles the Reactivity of High-velent oxoiron intermediates?

    IUPAC-2015, 2015

  • Preparation, characterization and Reactivity of Iron(III) Porphyrin Hypochlorite Complexes as Models for Reactive Intermediates in Haloperoxidase

    ChemComm Symposium, 2015

  • How does the axial ligand control the reactivity of high-valent metal oxo complex?

    2nd Japan-Germany Joint Symposium, 2015

  • Molecular Mechanism of Heme Axial Ligand for Controlling the Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex

    Pacifichem2015, 2015

  • Electronic Structure of One-electron Oxidized Mixed-Valence Metal Salen Complexes

    Pacifichem2015, 2015

  • Functional Role of Heme Axial Ligand on the Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex

    8th International Conference on Porphyrins and Phthalocyanines, 2014

  • Hypochlorito-rion(III) Porphyrin Complexes as Models for Reaction Intermediates of Catalytic and Biological Reactions

    41st International Conference on Inorganic Chemistry, 2014

  • 鉄3価ポルフィリン-次亜塩素酸イオン付加錯体の反応性に関する研究

    第64回錯体化学討論会, 2014

  • 鉄3価ヘム-次亜塩素酸錯体の反応性制御機構の研究

    第47回酸化反応討論会, 2014

  • Functional Role of Heme Axial Ligand on the Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex

    8th International Conference on Porphyrins and Phthalocyanines, 2014

  • Hypochlorito-rion(III) Porphyrin Complexes as Models for Reaction Intermediates of Catalytic and Biological Reactions

    41st International Conference on Inorganic Chemistry, 2014

  • ハロペルオキシダーゼの活性反応中間体としての鉄3価ヘム次亜塩素酸錯体の電子構造と反応性

    第40回生体分子科学討論会, 2013

  • Synthesis, Characterization, and Reactivity of Hypochlorite-Iron(III) Porphyrin Complexes

    16th International Conference on Bioinorgnaic Chemsitry, 2013

  • 鉄3価ヘム次亜塩素酸イオン付加錯体の合成、電子構造、反応性

    第63回錯体化学討論会, 2013

  • Structure and Reactivity of Iodosylarene Adduct of Manganese(IV) Salen Complex

    4th Asian Conference on Coordination Chemistry, 2013

  • 高原子価鉄オキソ錯体による酸化反応と反応性制御機構

    第46回酸化反応討論会, 2013

  • Synthesis, Characterization, and Reactivity of Hypochlorite-Iron(III) Porphyrin Complexes

    16th International Conference on Bioinorgnaic Chemsitry, 2013

  • Structure and Reactivity of Iodosylarene Adduct of Manganese(IV) Salen Complex

    4th Asian Conference on Coordination Chemistry, 2013

  • カチオン性ポルフィリン錯体の合成と反応性に関する研究

    鈴木 優菜; 本田 裕樹; 藤井 浩

    第53回酸化反応討論会, 07 Nov. 2020

  • マンガン5価オキソポルフィリンモノ錯体の合成と反応性の研究

    加藤木優里; 本田裕樹; 藤井 浩

    日本化学会第100回春季年会, 23 Mar. 2020

  • Light-driven and mediator-free hydrogen evolution using a combination of a photosensitizer and recombinant Esherichia coli whole-cell biocatalyst

    Yuki Honda; Yuka Shinohara; Hiroshi Fujii

    日本化学会第100回春季年会, 23 Mar. 2020

  • ヘム錯体による末端酸化剤の O-X 結合開裂過程の制御機構

    藤井 浩; 横田 紗和子; 柳井 佳苗

    第52回酸化反応討論会, 19 Nov. 2019

  • シトクロム P450 の反応中間体モデル錯体による C-H 結合の水酸化反応の反応機構

    岡田 沙樹; 本田 裕樹; 藤井 浩

    第52回酸化反応討論会, 09 Nov. 2019

  • Coumpound I モデル錯体の反応性に対する溶媒効果の研究

    上野 夏奈子; 石水 友梨; 本田 裕樹; 藤井 浩

    第52回酸化反応討論会, 09 Nov. 2019

  • シトクロム P450 の活性部位のモデル錯体の反応性

    竹田 彩乃; 本田 裕樹; 藤井 浩

    第52回酸化反応討論会, 09 Nov. 2019

  • Studies on the disproportionation reaction of iron(IV) oxo porphyrin complexes

    Kana Nishikawa; Yuki Honda; Hiroshi Fujii

    第69回錯体化学討論会, 22 Sep. 2019

  • 水溶性ヘム錯体による末端酸化剤の結合開裂過程の解 明と触媒反応の応用

    柳井 佳苗; 本田 裕樹; 藤井 浩

    第69回錯体化学討論会, 22 Sep. 2019

  • シトクロムP450活性部位のモデル錯体の合成の研究

    竹田 彩乃; 本田 裕樹; 藤井 浩

    第69回錯体化学討論会, 21 Sep. 2019

  • Compound-Iモデル錯体の反応性に対する溶媒効果の研究

    上野 夏奈子; 石水 友梨; 本田 裕樹; 藤井 浩

    第69回錯体化学討論会, 21 Sep. 2019

  • 鉄4価オキソポルフィリン錯体の不均化反応の研究

    西川 佳那; 本田 裕樹; 藤井 浩

    第13回バイオ関連化学シンポジウム, 05 Sep. 2019

  • What is an essential factor for determining the bond cleavage process of heme-bound terminal oxidant?

    Hiroshi Fujii

    he First Asian Conference on Porphyrins, Phthalocyanines and Related Materials, 25 Aug. 2019

  • Heterolytic versus Homolytic Bond Cleavage of Hypochlorite by Iron(III) Porphyrin Complexes

    Hiroshi Fujii

    International Conference on Bioinspired Small Molecule Activation, 07 Jun. 2019

  • シトクロムP450 compound Iによる芳香族水酸化の反応選択性についての研究

    奥泉 園子; 本田 裕樹; 藤井 浩

    日本化学会第99春季年会, 16 Mar. 2019

  • Critical Factors in Determining the Reactivity of Hypochlorite Adducts of Metal Complexes

    Hiroshi Fujii

    9th Asian Biological Inorganic Chemistry Conference (Asbic9), 09 Dec. 2018, 14 Dec. 2018

  • ヘム錯体による次亜塩素酸の結合開裂過程の研究 酸化剤の結合開裂過程を支配するものはなにか?

    藤井 浩

    第59回錯体化学若手の会・近畿支部勉強会, 10 Nov. 2018

  • sMMOを模倣したN架橋二核鉄ポルフィリン錯体の合成と反応性

    武藤 晴香; 本田 裕樹; 藤井 浩

    第51回酸化反応討論会, 01 Nov. 2018, 02 Nov. 2018

  • 鉄4価オキソポルフィリンπ-カチオンラジカルが触 媒するオレフィンのエポキシ化反応の反応機構について

    石水 友梨; 藤井 浩

    第51回酸化反応討論会, 01 Nov. 2018, 02 Nov. 2018

  • シトクロムP450によるアルカン水酸化反応の反応機構

    岡田 沙樹; 本田 裕樹; 藤井 浩

    第51回酸化反応討論会, 01 Nov. 2018, 02 Nov. 2018

  • シトクロムP450の反応活性種による芳香族化合物酸化反応の解析

    奥泉 園子; 本田 裕樹; 藤井 浩

    第51回酸化反応討論会, 01 Nov. 2018, 02 Nov. 2018

  • 鉄4価オキソポルフィリンπ-カチオンラジカル錯体による酸化反応の反応機構

    岡田 沙樹; 本田 裕樹; 藤井 浩

    第12回バイオ関連化学シンポジウム, 09 Sep. 2018, 11 Sep. 2018

  • シトクロムP450の反応活性種が触媒する芳香族水酸化反応に関する研究

    奥泉 園子; 本田 裕樹; 藤井 浩

    第12回バイオ関連化学シンポジウム, 09 Sep. 2018, 11 Sep. 2018

  • Marcus Theory Analysis of Aromatic Hydroxylation and Epoxidation Reactions by Compound I Model Complexes

    Hiroshi Fujii

    International Symposium on Recent Advances in Bioinspired Molecular Catalysis, 04 Aug. 2018, 05 Aug. 2018

  • Heterolytic versus Homolytic Bond Cleavage of Hypochlorite by Iron Porphyrin Complexes

    Hiroshi Fujii

    43rd International Conference on Coordination Chemistry, 31 Jul. 2018, 04 Aug. 2018

  • Disproportionation of Metal(IV) Oxo Complexes

    Kana Nishikawa; Yuki Honda; Hiroshi Fujii

    43rd International Conference on Coordination Chemistry, 31 Jul. 2018, 04 Aug. 2018

  • ポルフィリン配位子が鉄3価5配位ヘムの中間スピン状態に及ぼす影響について

    難波 照代; 小林 康浩; 瀬戸 誠; 藤井 浩

    第68回錯体化学討論会, 28 Jul. 2018, 30 Jul. 2018

  • 金属4価オキソ ポルフィリン錯体における不均化反応とオキソ配位子のpKaの研究

    西川 佳那; 本田 裕樹; 藤井 浩

    第68回錯体化学討論会, 28 Jul. 2018, 30 Jul. 2018

  • Participation of Electron-Transfer Process in Aromatic Hydroxylation Reactions by Heme Enzymes

    Hiroshi Fujii

    10th International Conference on Porphyrins and Phthalocyanines, 01 Jul. 2018, 06 Jul. 2018

  • Participation of Electron-Transfer Processes in Oxygenation Reactions by High-valent Iron Porphyrin Complxes

    Hiroshi Fujii

    13th International Symposium on Activation of Dioxygen and Homogeneous Oxidation Catalysis, 26 Jun. 2018

  • Participation of Electron-Transfer Process in Aromatic Hydroxylation Reactions by Heme Enzymes

    Hiroshi Fujii

    2018 Korea-Taiwan-Japn Bioinorganic Chemistry Symposium, 31 May 2018

  • What is an essential factor for determining the bond cleavage process of hemebound terminal oxidant?

    Hiroshi Fujii

    11th International Conference on Porphyrins and Phthalocyanines, 28 Jul. 2021

Association Memberships

  • 日本化学会

  • アメリカ化学会

  • 錯体化学会

  • 日本化学会生体関連化学部会



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