研究者詳細 - 依馬　正

論文 - 依馬　正

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Carbazole-based BODIPYs with ethynyl substituents at the boron center: Solid-state excimer fluorescence in the VIS/NIR region

Chihiro Maeda, Keiji Nagahata, Tadashi Ema

Organic and Biomolecular Chemistry 15 ( 37 ) 7783 - 7788 2017年

掲載種別：研究論文（学術雑誌）

Carbazole-based BODIPYs 1-6 with several different substituents at the boron atom site were synthesized. These dyes fluoresced in the solid state, and 3a with phenylethynyl groups exhibited a red-shifted and broad fluorescence spectrum, which suggested an excimer emission. Its derivatives 3b-n were synthesized, and the relationship between the solid-state emission and crystal packing was investigated. The X-ray crystal structures revealed cofacial dimers that might form excimers. From the structural optimization results, we found that the introduction of mesityl groups hindered intermolecular access and led to reduced interactions between the dimers. In addition, the red-shifted excimer fluorescence suppressed self-absorption, and dyes with ethynyl groups showed solid-state fluorescence in the vis/NIR region.

DOI： 10.1039/c7ob01473b

Synthetically useful variants of industrial lipases from: Burkholderia cepacia and Pseudomonas fluorescens

Kazunori Yoshida, Masakazu Ono, Takahiro Yamamoto, Takashi Utsumi, Satoshi Koikeda, Tadashi Ema

Organic and Biomolecular Chemistry 15 ( 41 ) 8713 - 8719 2017年

掲載種別：研究論文（学術雑誌）

Industrial enzymes lipase PS (LPS) and lipase AK (LAK), which originate from Burkholderia cepacia and Pseudomonas fluorescens, respectively, are synthetically useful biocatalysts. To strengthen their catalytic performances, we introduced two mutations into hot spots of the active sites (residues 287 and 290). The LPS-L287F/I290A double mutant showed high catalytic activity and enantioselectivity for poor substrates for which the wild-type enzyme showed very low activity. The LAK-V287F/I290A double mutant was also an excellent biocatalyst with expanded substrate scope, which was comparable to the LPS-L287F/I290A double mutant. Thermodynamic parameters were determined to address the origin of the high enantioselectivity of the double mutant. The ΔΔH‡ term, but not the ΔΔS‡ term, was predominant, which suggests that the enantioselectivity is driven by a differential energy associated with intermolecular interactions around Phe287 and Ala290. A remarkable solvent effect was observed, giving a bell-shaped profile between the E values and the log&P or ϵ values of solvents with the highest E value in i-Pr2O. This suggests that an organic solvent with appropriate hydrophobicity and polarity provides the double mutant with some flexibility that is essential for excellent catalytic performance.

DOI： 10.1039/c7ob01823a

Intramolecular Electronic Coupling in the Thiophene-Bridged Carbazole-Based Diporphyrin

Chihiro Maeda, Mototsugu Takata, Asami Honsho, Tadashi Ema

Organic Letters 18 ( 23 ) 6070 - 6073 2016年12月

掲載種別：研究論文（学術雑誌）

The Glaser coupling reaction of ethynyl-substituted carbazole-based isophlorins provided butadiyne-bridged dimers, which were transformed into the thiophene-bridged dimers via the annulation reaction. Oxidation of these isophlorin dimers afforded carbazole-based diporphyrins. Notable electronic interactions in the diporphyrins have been confirmed by means of UV/vis-near-infrared (NIR) absorption spectroscopy, cyclic voltammetry (CV) measurements, and density functional theory (DFT) calculations.

DOI： 10.1021/acs.orglett.6b03054

Solvent-Free Benzoin and Stetter Reactions with a Small Amount of NHC Catalyst in the Liquid or Semisolid State

Tadashi Ema, Yoshiko Nanjo, Sho Shiratori, Yuta Terao, Ryo Kimura

Organic Letters 18 ( 21 ) 5764 - 5767 2016年11月

掲載種別：研究論文（学術雑誌）

The intermolecular or intramolecular asymmetric benzoin reaction was catalyzed by a small amount of N-heterocyclic carbene (NHC) (0.2-1 mol %) under solvent-free conditions. The solvent-free intramolecular asymmetric Stetter reaction also proceeded efficiently with NHC (0.2-1 mol %). In some cases, even solid-to-solid or solid-to-liquid conversions took place with low catalyst loading (0.2-1 mol %).

DOI： 10.1021/acs.orglett.6b03115

Theoretical Study on Highly Active Bifunctional Metalloporphyrin Catalysts for the Coupling Reaction of Epoxides with Carbon Dioxide

Jun ya Hasegawa, Ray Miyazaki, Chihiro Maeda, Tadashi Ema

Chemical Record 16 ( 5 ) 2260 - 2267 2016年10月

掲載種別：研究論文（学術雑誌）

Highly active bifunctional metalloporphyrin catalysts were developed for the coupling reaction of epoxides with CO2 to produce cyclic carbonates. The bifunctional catalysts have both quaternary ammonium halide groups and a metal center. To elucidate the roles of these catalytic groups, DFT calculations were performed. Control reactions using tetrabutylammonium halide as a catalyst were also investigated for comparison. In the present article, the results of our computational studies are overviewed. The computational results are consistent with the experimental data and are useful for elucidating the structure–activity relationship. The key features responsible for the high catalytic activity of the bifunctional catalysts are as follows: 1) the cooperative action of the halide anion (nucleophile) and the metal center (Lewis acid); 2) the near-attack conformation, leading to the efficient opening of the epoxide ring in the rate-determining step; and 3) the conformational change of the quaternary ammonium cation to stabilize various anionic species generated during catalysis, in addition to the robustness (thermostability) of the catalysts.

DOI： 10.1002/tcr.201600053

Color-Tunable Solid-State Fluorescence Emission from Carbazole-Based BODIPYs

Chihiro Maeda, Takumi Todaka, Tomomi Ueda, Tadashi Ema

Chemistry - A European Journal 22 ( 22 ) 7508 - 7513 2016年5月

掲載種別：研究論文（学術雑誌）

Several carbazole-based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1-position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1, 2 a, and 3-6. The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1, 2 a, and 3-5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (ΦF) in the solid state, therefore boron complexes of the carbazole-benzothiazole hybrids 2 b-f, which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal-packing analyses, and the dyes exhibited color-tunable solid-state fluorescence.

DOI： 10.1002/chem.201505150

Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide

Chihiro Maeda, Junta Shimonishi, Ray Miyazaki, Jun Ya Hasegawa, Tadashi Ema

Chemistry - A European Journal 22 ( 19 ) 6556 - 6563 2016年5月

掲載種別：研究論文（学術雑誌）

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500h-1 at 170°C) at an initial CO2 pressure of 1.7MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20°C); and was applicable to a broad range of substrates, including terminal and internal epoxides. In a fix! Bifunctional metalloporphyrins act as catalysts for the formation of cyclic carbonates from epoxides and CO2 (see scheme). A comparison of the catalytic activities shows the superior performance of meta-substituted catalysts. A robust zinc(II) porphyrin with eight nucleophiles at the meta positions shows the highest catalytic activity and a broad substrate scope, including terminal and internal epoxides.

DOI： 10.1002/chem.201600164

Determination of enantiomeric excess of carboxylates by fluorescent macrocyclic sensors

Ali Akdeniz, Tsuyoshi Minami, Sagiri Watanabe, Maki Yokoyama, Tadashi Ema, Pavel Anzenbacher

Chemical Science 7 ( 3 ) 2016 - 2022 2016年3月

掲載種別：研究論文（学術雑誌）

Chiral fluorescent chemosensors featuring macrocycles comprising BINOL auxiliary and an array of hydrogen bond donors were synthesized. To enhance fluorescence of the chemosensors, conjugated moieties were attached to the 3,3′-positions of the BINOL auxiliary. The resulting chemosensors recognize a number of carboxylates, namely, enantiomers of ibuprofen, ketoprofen, 2-phenylpropanoate, mandelate, and phenylalanine in a stereoselective fashion. Depending on the structure of the chemosensor, the presence of carboxylate yields fluorescence quenching or amplification. This information-rich signal can be used to determine the identity of the analyte including the sense of chirality. Quantitative experiments were performed aimed at analysis of enantiomeric excess of chiral carboxylates. The quantitative analysis of enantiomeric composition of ibuprofen, ketoprofen, and phenylalanine shows that the sensors correctly identify mixtures with varying enantiomeric excess and correctly predict the enantiomeric excess of unknown samples with error of prediction <1.6%.

DOI： 10.1039/c5sc04235f

Carbazole-Based Boron Dipyrromethenes (BODIPYs): Facile Synthesis, Structures, and Fine-Tunable Optical Properties

Chihiro Maeda, Takumi Todaka, Tadashi Ema

Organic Letters 17 ( 12 ) 3090 - 3093 2015年6月

掲載種別：研究論文（学術雑誌）

Carbazole-based BODIPYs were synthesized in three steps using an organometallic approach consisting of sequential Ir-catalyzed borylation, Suzuki-Miyaura coupling, and boron complexation. Various substituents were introduced into the carbazole moiety, and large substituent effects were confirmed by means of absorption spectroscopy, cyclic voltammetry, and DFT calculations. Dibenzocarbazoles were also converted into the corresponding BODIPYs.

DOI： 10.1021/acs.orglett.5b01363

Quaternary ammonium hydroxide as a metal-free and halogen-free catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide

Tadashi Ema, Kazuki Fukuhara, Takashi Sakai, Masaki Ohbo, Fu Quan Bai, Jun Ya Hasegawa

Catalysis Science and Technology 5 ( 4 ) 2314 - 2321 2015年4月

掲載種別：研究論文（学術雑誌）

Tetrabutylammonium hydroxide (TBAH) and other quaternary ammonium hydroxides catalyzed the cycloaddition of CO2 to epoxides under solvent-free conditions to give cyclic carbonates. When TBAH was exposed to CO2, TBAH was converted into tetrabutylammonium bicarbonate (TBABC), which was a catalytically active species. A D-labeled epoxide and an optically active epoxide were used to study the reaction mechanism, which invoked three plausible pathways. Among them, path A seemed to be predominant; the bicarbonate ion of TBABC attacks the less hindered C atom of the epoxide to generate a ring-opened alkoxide intermediate, which adds to CO2 to give a carbonate ion, and the subsequent cyclization yields a cyclic carbonate. Density functional theory (DFT) calculations successfully delineated the potential energy profile for each reaction pathway, among which path A was the lowest-energy pathway in accordance with the experimental results. The tetrabutylammonium (TBA) cation carries the positive charges on the H atoms, but not on the central N atom, and the positively charged H atoms close to the central N atom form an anion-binding site capable of stabilizing various anionic transition states and intermediates.

DOI： 10.1039/c5cy00020c

Bifunctional catalysts based on m-phenylene-bridged porphyrin dimer and trimer platforms: Synthesis of cyclic carbonates from carbon dioxide and epoxides

Chihiro Maeda, Tomoya Taniguchi, Kanae Ogawa, Tadashi Ema

Angewandte Chemie - International Edition 54 ( 1 ) 134 - 138 2015年1月

掲載種別：研究論文（学術雑誌）

Highly active bifunctional diporphyrin and triporphyrin catalysts were synthesized through Stille coupling reactions. As compared with a porphyrin monomer, both exhibited improved catalytic activities for the reaction of CO2 with epoxides to form cyclic carbonates, because of the multiple catalytic sites which cooperatively activate the epoxide. Catalytic activities were carefully investigated by controlling temperature, reaction time, and catalyst loading, and very high turnover number and turnover frequency were obtained: 220000 and 46000 h-1, respectively, for the magnesium catalyst, and 310000 and 40000 h-1, respectively, for the zinc catalyst. Results obtained with a zinc/free-base hybrid diporphyrin catalyst demonstrated that the Br- ions on the adjacent porphyrin moiety also function as nucleophiles.

DOI： 10.1002/anie.201409729

Chemical modification of lipase for rational enhancement of enantioselectivity

Tadashi Ema, Hiroki Inoue

Chemistry Letters 44 ( 10 ) 1374 - 1376 2015年

掲載種別：研究論文（学術雑誌）

Chemical modifications of the I287C mutant of a Burkholderia cepacia lipase afforded various I287C-X conjugates, among which I287C-PAA bearing an N-phenylacetamide (PAA) moiety showed excellent enantioselectivity and catalytic activity for secondary alcohols. Site-directed chemical modifications are powerful tools to control enantioselective biocatalysis.

DOI： 10.1246/cl.150667

Bifunctional porphyrin catalysts for the synthesis of cyclic carbonates from epoxides and CO <inf>2</inf> : Structural optimization and mechanistic study

Tadashi Ema, Yuki Miyazaki, Junta Shimonishi, Chihiro Maeda, Jun Ya Hasegawa

Journal of the American Chemical Society 136 ( 43 ) 15270 - 15279 2014年10月

掲載種別：研究論文（学術雑誌）

We prepared bifunctional Mg II porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO 2 . The activities of 1d, 1h, and 1i, which have Br - , Cl - , and I - counteranions, respectively, increased in the order 1i < 1h < 1d. Catalysts 1d and 1j-m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst 1d, we synthesized Mg II porphyrin 1o with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h -1 ). The catalytic mechanism was studied by using 1d. The yields were nearly constant at initial CO 2 pressures in the 1-6 MPa range, suggesting that CO 2 was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO 2 , probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO 2 . Experiments with 18 O-labeled CO 2 and D-labeled epoxide suggested that the catalytic cycle involved initial nucleophilic attack of Br - on the less hindered side of the epoxide to generate an oxyanion, which underwent CO 2 insertion to afford a CO 2 adduct; subsequent intramolecular ring closure formed the cyclic carbonate and regenerated the catalyst. Density functional theory calculations gave results consistent with the experimental results, revealing that the quaternary ammonium cation underwent conformational changes that stabilized various anionic species generated during the catalytic cycle. The high activity of 1d and 1o was due to the cooperative action of the Mg II and Br - and a conformational change (induced-fit) of the quaternary ammonium cation.

DOI： 10.1021/ja507665a

Recent progress in catalytic conversions of carbon dioxide

Chihiro Maeda, Yuki Miyazaki, Tadashi Ema

Catalysis Science and Technology 4 ( 6 ) 1482 - 1497 2014年6月

Chemical fixation of carbon dioxide (CO2), which is an inexpensive and renewable carbon source, is becoming more and more important. The development of both new reactions and new catalysts is needed to overcome the kinetic and thermodynamic stability of CO2. Organic and metal catalysts with unique and excellent activity and selectivity have been developed for various chemical conversions of CO2. In this perspective, we provide an overview of the recent progress in this field, classifying it into several categories, where each research is concisely summarized one by one using a single reaction scheme, a representative catalyst structure, and/or a catalytic cycle. This journal is © the Partner Organisations 2014.

DOI： 10.1039/c3cy00993a

Selective anion sensing by chiral macrocyclic receptors with multiple hydrogen-bonding sites

Tadashi Ema, Keiichi Okuda, Sagiri Watanabe, Takayuki Yamasaki, Tsuyoshi Minami, Nina A. Esipenko, Pavel Anzenbacher

Organic Letters 16 ( 5 ) 1302 - 1305 2014年3月

掲載種別：研究論文（学術雑誌）

Chiral macrocycles featuring sulfonamide and/or amide groups as anion-binding sites were synthesized. X-ray crystal structures and DFT calculations have shown that they adopt different conformations that may lead to unique binding behavior. Indeed, various anions could be sensed by their colorimetric and/or fluorescence signal output. The chiral macrocycles showed chiral recognition for chiral anions. Furthermore, a multisensor array with two or four chiral receptors discriminated seven phosphate anions (AMP, ADP, ATP, CMP, GMP, Pi, and PPi) with 100% classification accuracy. © 2014 American Chemical Society.

DOI： 10.1021/ol403643d

Synergistic effect of quaternary ammonium hydroxide and crown ether on the rapid and clear dissolution of cellulose at room temperature

Tadashi Ema, Takuzo Komiyama, Satomi Sunami, Takashi Sakai

RSC Advances 4 ( 5 ) 2523 - 2525 2014年

Robust porphyrin catalysts immobilized on biogenous iron oxide for the repetitive conversions of epoxides and CO<inf>2</inf> into cyclic carbonates

Tadashi Ema, Yuki Miyazaki, Tomoya Taniguchi, Jun Takada

Green Chemistry 15 ( 9 ) 2485 - 2492 2013年9月

掲載種別：研究論文（学術雑誌）

Metalloporphyrins were immobilized on biogenous iron oxide (BIO) produced by iron-oxidizing bacteria, Leptothrix ochracea. These organic-inorganic hybrid materials were used as immobilized catalysts for the synthesis of cyclic carbonates from epoxides and CO2 under solvent-free conditions. ZnII porphyrin immobilized via four tetraalkylammonium bromide groups showed high catalytic activity and reusability at a catalyst loading of 0.1 mol%. The product was obtained in 99% yield after nine times reuse, and the substrate scope was broad. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3gc41055b

Multifunctional macrocyclic receptors as templates for aromatic amino acids: A rare example of a highly selective multi-input multi-output chemo-"Logic Gate"

Caterina Fraschetti, Antonello Filippi, Maria Elisa Crestoni, Tadashi Ema, Maurizio Speranza

ChemPlusChem 78 ( 9 ) 979 - 987 2013年9月

掲載種別：研究論文（学術雑誌）

Proton-bound [M×H×G]+ diastereomeric complexes between some chiral aromatic amino acids or dipeptides(G) and a chiral multifunctional macrocyclic receptor (M=Chirabite-A) undergo, in the gas phase, highly selective substitution and addition reactions by amines, such as 2-aminobutane and piperidine. All the [M×H×G]+ complexes follow time-dependent monoexponential decays. In some cases, the kinetic curves exhibit a plateau revealing the presence of unreactive [M×H×G] + structures. In them, the amino acid is accommodated in the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to G=dipeptides or monofunctional amines, which then can be readily released from [M×H×G]+. When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the macrocycle cavity, it saves the canonical structure and can be readily displaced by the amine. The Chirabite-A may act as an efficient template for aromatic amino acids by releasing them or not depending upon the amino acid configuration and the basicity of the amine. These unique properties confer to the gas-phase diastereomeric [M×H×G]+ complexes the features of multi-input multi-output chemo-"logic gates". © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/cplu.201300086

Unexpected behavior of diastereomeric ions in the GasPhase: A stimulus for pondering on ee measurements by ESI-MS

Caterina Fraschetti, Antonello Filippi, Maria Elisa Crestoni, Tadashi Ema, Maurizio Speranza

Journal of the American Society for Mass Spectrometry 24 ( 4 ) 573 - 578 2013年4月

掲載種別：研究論文（学術雑誌）

The most common protocols for the quantitative determination of the enantiomeric excess (ee) of raw mixtures by ESI-MS reveal inadequate in cases where the distribution of diastereomeric derivatives diverges from the ee of original solutions. This phenomenon is attributable to a matrix effect, i.e.; to the stereospecific formation of high order noncovalent adducts in the ESI droplets, which alters the actual availability of the diastereomeric species under MS analysis. In this frame, the assumption of classic protocols that the ionization correction factor q is independent on the composition of the mixture submitted to analysis is questionable. An alternative methodology is presented in this paper, which is aimed at circumventing the problem by excluding any chemical derivatization of the original raw mixture. It is based on the measurement of the actual distribution of ESI-formed proton-bound diastereomeric complexes from the enantiomeric mixture through a careful analysis of their reaction kinetics with a suitable reactant. [Figure not available: see fulltext.] © 2013 American Society for Mass Spectrometry.

DOI： 10.1007/s13361-012-0575-8

Synthetic macrocyclic receptors in chiral analysis and separation

Tadashi Ema

Journal of Inclusion Phenomena and Macrocyclic Chemistry 74 ( 1-4 ) 41 - 55 2012年12月

掲載種別：研究論文（学術雑誌）

Chiral synthetic macrocyclic receptors that can achieve chiral discrimination by NMR spectroscopy and/or chiral separation by HPLC are overviewed. Synthetic macrocycles introduced here include crown ethers, calixarenes/calixresorcinarenes/calixpyrroles, macrocyclic amides/amines, and porphyrins. These macrocyclic frameworks are advantageous because intermolecular interactions can take place effectively, such as the ion-dipole interactions in crown ethers, the CH/π and π-π interactions in calixarenes, hydrogen bonding and salt formation in macrocyclic amides and amines, and π-π stacking and metal coordination in porphyrins. Additional functional groups on the periphery of the macrocyclic platforms not only make the whole molecule chiral but also act as the interaction sites. Chiral macrocyclic receptors can show a high degree of chiral recognition/discrimination by using the peripheral functional groups as well as the macrocyclic skeletons (preorganization). Both hosts and guests are shown in the figures to quickly overview the molecular recognition scope of synthetic macrocyclic receptors in chiral analysis and separation. © 2012 Springer Science+Business Media B.V.

DOI： 10.1007/s10847-012-0136-6

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