2025/04/02 更新

写真a

ヒガシ マサヒロ
東 雅大
HIGASHI Masahiro
所属
大学院情報学研究科 複雑系科学専攻 物質情報論 教授
大学院担当
大学院情報学研究科
学部担当
情報学部 自然情報学科
職名
教授
外部リンク

学位 2

  1. 博士(理学) ( 2007年3月   京都大学 ) 

  2. 修士(理学) ( 2002年3月   京都大学 ) 

研究キーワード 2

  1. Theoretical Chemistry

  2. 理論化学

研究分野 1

  1. ナノテク・材料 / 基礎物理化学  / 理論化学

経歴 6

  1. 名古屋大学   大学院情報学研究科 複雑系科学専攻   教授

    2023年9月

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  2. 京都大学   大学院工学研究科分子工学専攻   准教授

    2019年3月 - 2023年8月

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  3. 琉球大学 理学部 海洋自然科学科化学系 助教   理学部 海洋自然科学科化学系   助教

    2013年4月 - 2019年3月

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  4. 自然科学研究機構 分子科学研究所   理論・計算分子科学研究領域   日本学術振興会特別研究員(PD)

    2011年4月 - 2013年3月

  5. 自然科学研究機構 分子科学研究所   理論・計算分子科学研究領域   IMSフェロー

    2009年5月 - 2011年3月

  6. University of Minesota   Department of Chemistry   Postdoctoral Research Associate

    2007年5月 - 2009年4月

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    国名:アメリカ合衆国

▼全件表示

学歴 3

  1. 京都大学   大学院理学研究科   化学専攻 博士後期課程

    2002年4月 - 2007年3月

  2. 京都大学   大学院理学研究科   化学専攻 修士課程

    2000年4月 - 2002年3月

  3. 京都大学   理学部   理学科

    1997年4月 - 2000年3月

所属学協会 5

  1. The Electrochemical Society

    2021年5月 - 現在

  2. 理論化学会

    2019年6月 - 現在

  3. 日本生物物理学会

    2014年5月 - 現在

  4. 日本化学会

    2013年6月 - 現在

  5. 分子科学会

    2009年9月 - 現在

 

論文 69

  1. Effect of structural bending on the photophysical properties of perylene bisimide

    Hikaru Sotome, Masahiro Higashi, Yuki Tanaka, Hiroshi Shinokubo, Yasuhiro Kobori, Norihito Fukui

    The Journal of Chemical Physics   162 巻 ( 11 )   2025年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    The effect of nonplanarity on the electronic properties of π-systems has been difficult to study systematically because of the limited availability of suitable model compounds. Our group recently synthesized a series of end-to-end bent perylene bisimide (PBI) cyclophanes, whose degree of bending is adjustable by modifying the internal alkyl tethers. Herein, we subjected these bent PBI derivatives to theoretical calculations and time-resolved spectroscopy. The current study has offered rational explanations for several unique photophysical characteristics of bent PBIs: (1) the redshifts of the S0–S1 transitions, (2) the decrease in extinction coefficients, (3) the broadening of spectral shapes, and (4) the suppression of nonradiative decay processes. Furthermore, the investigation of the S1 states and radical anions has revealed that structural bending also substantially alters the energy levels of upper molecular orbitals such as LUMO+2.

    DOI: 10.1063/5.0255756

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  2. Theoretical Study on the Solvent-Dependent Optical Properties of 2-Aryl-3H-1,3-benzazaphosphole Oxide

    Sugiyama K., Nakagomi H., Matano Y., Kimura Y., Sato H., Higashi M.

    Journal of Physical Chemistry B   129 巻 ( 10 ) 頁: 2701 - 2707   2025年3月

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    出版者・発行元:Journal of Physical Chemistry B  

    Photoresponsive molecules that respond to the surrounding environment are expected to be utilized as optical functional materials, such as sensors. Recently reported 2-aryl-3H-1,3-benzazaphosphole oxide with a diphenylamino group (ABPO) is one such molecule having interesting solvent-dependent properties. The absorption spectra of ABPO in nonpolar and polar solvents are almost identical in shape and excitation energy, whereas the fluorescence spectrum is red-shifted as the solvent polarity increases. In addition, the fluorescence quantum yield drastically decreases in methanol and acetonitrile solvents. In this study, the solvent-dependent optical properties of ABPO were investigated using quantum chemical calculations with solvent models. To describe the solvation structures explicitly, the QM/MM reweighting free energy self-consistent field method was used. The calculated absorption and fluorescence energies qualitatively reproduced the experimental trends. The S1 excited state has charge-transfer (CT) character with a large dipole moment, which is responsible for the solvent dependency of fluorescence spectra. Furthermore, in addition to the CT state, the twisted intramolecular charge transfer (TICT) state plays an important role in the fluorescence quenching. It was indicated that the stabilization of the TICT state, which has a larger dipole moment than the CT state, affects the decrease in fluorescence quantum yield in polar solvents.

    DOI: 10.1021/acs.jpcb.4c05872

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  3. Ligand-enabled enantio- and site-selective remote C-H arylation of 2-(2-phenpropyl)pyridine derivatives

    Li D.Y., Li J.P., Yabu S., Wang L.S., Sato H., Higashi M., Kuninobu Y., Li H.L.

    Organic Chemistry Frontiers     2025年

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    出版者・発行元:Organic Chemistry Frontiers  

    The great potential of transition metal-catalyzed C-H functionalization lies in its ability to selectively target specific C-H bonds in complex molecules. Therefore, the development of enantio- and site-selective C-H functionalization is a long-term pursuit in this field. Herein, we disclose a ligand-enabled enantio- and site-selective remote C-H arylation of 2-(2-phenylpropyl)pyridine derivatives. The combination of an acetyl-protected aminoethyl phenyl thioether (MPA-thiol) with aryl iodides is found to enable γ-C(sp3)-H arylation, whereas l-pyroglutamic acid (l-pGlu) promotes δ-C(sp2)-H cross-coupling with various aryl-Bpin moieties. Notably, both C-H arylations proceed with high enantioselectivity and good yields. The results of DFT calculations support the enantioselectivity and site-selectivity of these two C-H arylations. Moreover the utility of this transformation was demonstrated by derivatization of a harmane alkaloid, a gram scale reaction and the successful removal of the pyridyl directing group.

    DOI: 10.1039/d4qo02236j

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  4. Development of Molecular Dynamics Parameters and Theoretical Analysis of Excitonic and Optical Properties in the Light-Harvesting Complex II Open Access

    Zhu, Z; Higashi, M; Saito, S

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   21 巻 ( 1 ) 頁: 413 - 427   2024年12月

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    出版者・発行元:Journal of Chemical Theory and Computation  

    The light-harvesting complex II (LHCII) in green plants exhibits highly efficient excitation energy transfer (EET). A comprehensive understanding of the EET mechanism in LHCII requires quantum chemical, molecular dynamics (MD), and statistical mechanics calculations that can adequately describe pigment molecules in heterogeneous environments. Herein, we develop MD simulation parameters that accurately reproduce the quantum mechanical/molecular mechanical energies of both the ground and excited states of all chlorophyll (Chl) molecules in membrane embedded LHCII. The present simulations reveal that Chl a molecules reside in more inhomogeneous environments than Chl b molecules. We also find a narrow gap between the exciton energy levels of Chl a and Chl b. In addition, we investigate the nature of the exciton states of Chl molecules, such as delocalization, and analyze the optical spectra of LHCII, which align with experimental results. Thus, the MD simulation parameters developed in this study successfully reproduce the excitonic and optical properties of the Chl molecules in LHCII, validating their effectiveness.

    DOI: 10.1021/acs.jctc.4c01214

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  5. Rational design of metal–organic cages to increase the number of components via dihedral angle control 査読有り 国際誌 Open Access

    Abe T., Takeuchi K., Higashi M., Sato H., Hiraoka S.

    Nature Communications   15 巻 ( 1 )   2024年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Nature Communications  

    The general principles of discrete, large self-assemblies composed of numerous components are not unveiled and the artificial formation of such entities is a challenging topic. In metal–organic cages, design strategies for tuning the coordination directions in multitopic ligands by the bend and twist angles were previously developed to solve this problem. In this study, the importance of remote geometric communications between components is emphasized, realizing several types of metal–organic assemblies based on dihedral angle control in multitopic ligands although they have the same coordination directions. Self-assembly of a tritopic ligand with dihedral angles θ = 36.5° and a cis-protected Pd(II) ion affords M9L6 and M12L8 cages as kinetic and thermodynamic products, respectively, whereas an M12L8 sheet is formed when θ = 90°. Geometric analyses of strains in the subcomponent rings reveals that remote geometric communications among neighboring multitopic ligands through coordination bonds are key for large assemblies.

    DOI: 10.1038/s41467-024-50972-z

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  6. Computational analysis of the thermodynamic stability and isomeric composition of cholestane 査読有り 国際誌

    Nukumi Y., Sato H., Saito R., Higashi M.

    Organic Geochemistry   195 巻   2024年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Organic Geochemistry  

    Cholestane is produced by diagenesis of cholesterol in the geosphere being known to have four main stereoisomers. The abundance ratios of these stereoisomers are important indicators of the geospheric thermal history. However, it has been unclear whether the isomeric ratios are caused by kinetic or thermodynamic dominance. In this study, we analyzed the isomeric ratios of cholestane under thermodynamic dominance using the density functional theory. The calculated isomeric ratios are in good agreement with the limit values in the geosphere, indicating that the isomeric ratios in the geosphere can be obtained under thermodynamic control. We also discussed the factors contributing to their stabilities.

    DOI: 10.1016/j.orggeochem.2024.104841

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  7. Nonfullerene Acceptors Bearing Spiro-Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy 査読有り 国際誌 Open Access

    Wang K., Jinnai S., Urakami T., Sato H., Higashi M., Tsujimura S., Kobori Y., Adachi R., Yamakata A., Ie Y.

    Angewandte Chemie - International Edition   63 巻 ( 47 ) 頁: e202412691   2024年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Angewandte Chemie - International Edition  

    The development of nonfullerene acceptors (NFAs), represented by ITIC, has contributed to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Although tuning the electronic structures to reduce the exciton binding energy (Eb) is considered to promote photocharge generation, a rational molecular design for NFAs has not been established. In this study, we designed and developed two ITIC-based NFAs bearing spiro-substituted bithiophene or biphenyl units (named SpiroT-DCI and SpiroF-DCI) to tune the frontier molecular orbital (FMO) distribution of NFAs. While the highest occupied molecular orbitals (HOMOs) of SpiroF-DCI and ITIC are delocalized in the main π-conjugated framework, the HOMO of SpiroT-DCI is distributed on the bithiophene unit. Reflecting this difference, SpiroT-DCI exhibits a smaller Eb than either SpiroF-DCI or ITIC, and exhibits greater external quantum efficiency in single-component OSCs. Furthermore, SpiroT-DCI shows improved PCEs for bulk-heterojunction OSCs with a donor of PBDB-T, compared with that of either SpiroT-DCI or ITIC. Time-resolved spectroscopy measurements show that the photo-induced intermolecular charge separation is effective even in pristine SpiroT-DCI films. This study highlights the introduction of spiro-substituted bithiophene units that are effective in tuning the FMOs of ITIC, which is desirable for reducing the Eb and improving the PCE in OSCs.

    DOI: 10.1002/anie.202412691

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  8. Synthesis of All-Peptide-Based Rotaxane from a Proline-Containing Cyclic Peptide 査読有り 国際誌

    Kurita T., Higashi M., Gimenez-Dejoz J., Fujita S., Uji H., Sato H., Numata K.

    Biomacromolecules   25 巻 ( 6 ) 頁: 3661 - 3670   2024年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Biomacromolecules  

    Rotaxane cross-linkers enhance the toughness of the resulting rotaxane cross-linked polymers through a stress dispersion effect, which is attributed to the mobility of the interlocked structure. To date, the compositional diversity of rotaxane cross-linkers has been limited, and the poor compatibility of these cross-linkers with peptides and proteins has made their use in such materials challenging. The synthesis of a rotaxane composed of peptides may result in a biodegradable cross-linker that is compatible with peptides and proteins, allowing the fortification of polypeptides and proteins and ultimately leading to the development of innovative materials that possess excellent mechanical properties and biodegradability. However, the chemical synthesis of all-peptide-based rotaxanes has remained elusive because of the absence of strong binding motifs in peptides, which prevents an axial peptide from penetrating a cyclic peptide. Here, we synthesized all-peptide-based rotaxanes using an active template method for proline-containing cyclic peptides. The results of molecular dynamics simulations suggested that cyclic peptides with an expansive inner cavity and carbonyl oxygens oriented toward the center are favorable for rotaxane synthesis. This rotaxane synthesis method is expected to accelerate the synthesis of peptides and proteins with mechanically interlocked structures, potentially leading to the development of peptide- and protein-based materials with unprecedented functionalities.

    DOI: 10.1021/acs.biomac.4c00257

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  9. A coarse-grained analysis on coordination self-assembly of a caged dinuclear palladium complex 査読有り 国際誌

    Ichikawa, Y; Sugiyama, K; Higashi, M; Hiraoka, S; Sato, H

    CHEMISTRY LETTERS   53 巻 ( 6 )   2024年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemistry Letters  

    We propose a coarse-grained analysis to understand coordination self-assembly. The developed model reduced the system into the assembling components that interact mainly electrostatically. The modeled energies sufficiently reproduced the energy changes to produce a caged dinuclear palladium complex obtained by the density functional theory. The model made it possible to clarify the physicochemical background of the assembly process.

    DOI: 10.1093/chemle/upae099

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  10. The Effect of Torsional Motion on Multiexciton Formation through Intramolecular Singlet Fission in Ferrocene-Bridged Pentacene Dimers 査読有り 国際共著 国際誌 Open Access

    Hayasaka R., Sakai H., Fuki M., Okamoto T., Khan R., Higashi M., Tkachenko N.V., Kobori Y., Hasobe T.

    Angewandte Chemie - International Edition   63 巻 ( 8 ) 頁: e202315747   2024年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Angewandte Chemie - International Edition  

    A series of ferrocene(Fc)-bridged pentacene(Pc)-dimers [Fc−Ph(2,n)−(Pc)2: n=number of phenylene spacers] were synthesized to examine the tortional motion effect of Fc-terminated phenylene linkers on strongly coupled quintet multiexciton (5TT) formation through intramolecular singlet fission (ISF). Fc−Ph(2,4)−(Pc)2 has a relatively small electronic coupling and large conformational flexibility according to spectroscopic and theoretical analyses. Fc−Ph(2,4)−(Pc)2 exhibits a high-yield 5TT together with quantitative singlet TT (1TT) generation through ISF. This demonstrates a much more efficient ISF than those of other less flexible Pc dimers. The activation entropy in 1TT spin conversion of Fc−Ph(2,4)−(Pc)2 is larger than those of the other systems due to the larger conformational flexibility associated with the torsional motion of the linkers. The torsional motion of linkers in 1TT is attributable to weakened metal-ligand bonding in the Fc due to hybridization of the hole level of Pc to Fc in 1TT unpaired orbitals.

    DOI: 10.1002/anie.202315747

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  11. Boosting charge separation in organic photovoltaics: unveiling dipole moment variations in excited non-fullerene acceptor layers 査読有り 国際誌

    Yamakata A., Kato K., Urakami T., Tsujimura S., Murayama K., Higashi M., Sato H., Kobori Y., Umeyama T., Imahori H.

    Chemical Science   15 巻 ( 32 ) 頁: 12686 - 12694   2024年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Science  

    The power conversion efficiency (PCE) of organic photovoltaics (OPVs) has reached more than 19% due to the rapid development of non-fullerene acceptors (NFAs). To compete with the PCEs (26%) of commercialized silicon-based inorganic photovoltaics, the drawback of OPVs should be minimized. This drawback is the intrinsic large loss of open-circuit voltage; however, a general approach to this issue remains elusive. Here, we report a discovery regarding highly efficient NFAs, specifically ITIC. We found that charge-transfer (CT) and charge dissociation (CD) can occur even in a neat ITIC film without the donor layer. This is surprising, as these processes were previously believed to take place exclusively at donor/acceptor heterojunctions. Femtosecond time-resolved visible to mid-infrared measurements revealed that in the neat ITIC layers, the intermolecular CT immediately proceeds after photoirradiation (<0.1 ps) to form weakly-bound excitons with a binding energy of 0.3 eV, which are further dissociated into free electrons and holes with a time-constant of 56 ps. Theoretical calculations indicate that stacking faults in ITIC (i.e., V-type molecular stacking) induce instantaneous intermolecular CT and CD in the neat ITIC layer. In contrast, J-type stacking does not support such CT and CD. This previously unknown pathway is triggered by the larger dipole moment change on the excited state generated at the lower symmetric V-type molecular stacking of ITIC. This is in sharp contrast with the need of sufficient energy offset for CT and CD at the donor-acceptor heterojunction, leading to the significant voltage loss in conventional OPVs. These results demonstrate that the rational molecular design of NFAs can increase the local dipole moment change on the excited state within the NFA layer. This finding paves the way for a groundbreaking route toward the commercialization of OPVs.

    DOI: 10.1039/d4sc00917g

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  12. An emissive charge-transfer excited-state at the well-defined hetero-nanostructure interface of an organic conjugated molecule and two-dimensional inorganic nanosheet 査読有り 国際誌 Open Access

    Umeyama T., Mizutani D., Ikeda Y., Osterloh W.R., Yamamoto F., Kato K., Yamakata A., Higashi M., Urakami T., Sato H., Imahori H.

    Chemical Science   14 巻 ( 42 ) 頁: 11914 - 11923   2023年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Science  

    Precise engineering of excited-state interactions between an organic conjugated molecule and a two-dimensional semiconducting inorganic nanosheet, specifically the manipulation of charge-transfer excited (CTE) states, still remains a challenge for state-of-the-art photochemistry. Herein, we report a long-lived, highly emissive CTE state at structurally well-defined hetero-nanostructure interfaces of photoactive pyrene and two-dimensional MoS2 nanosheets via an N-benzylsuccinimide bridge (Py-Bn-MoS2). Spectroscopic measurements reveal that no charge-transfer state is formed in the ground state, but the locally-excited (LE) state of pyrene in Py-Bn-MoS2 efficiently generates an unusual emissive CTE state. Theoretical studies elucidate the interaction of MoS2 vacant orbitals with the pyrene LE state to form a CTE state that shows a distinct solvent dependence of the emission energy. This is the first example of organic-inorganic 2D hetero-nanostructures displaying mixed luminescence properties by an accurate design of the bridge structure, and therefore represents an important step in their applications for energy conversion and optoelectronic devices and sensors.

    DOI: 10.1039/d3sc03604a

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  13. Biomimetic design of an α-ketoacylphosphonium-based light-activated oxygenation auxiliary 国際誌 Open Access

    Oya R., Ota K., Fuki M., Kobori Y., Higashi M., Nagao K., Ohmiya H.

    Chemical Science   14 巻 ( 38 ) 頁: 10488 - 10493   2023年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Science  

    The biomimetic design of a transition metal complex based on the iron(iv)-oxo porphyrin π-cation radical species in cytochrome P450 enzymes has been studied extensively. Herein, we translate the functions of this iron(iv)-oxo porphyrin π-cation radical species to an α-ketoacyl phosphonium species comprised of non-metal atoms and utilize it as a light-activated oxygenation auxiliary for ortho-selective oxygenation of anilines. Visible light irradiation converts the α-ketoacyl phosphonium species to the excited state, which acts as a transiently generated oxidant. The intramolecular nature of the process ensures high regioselectivity and chemoselectivity. The auxiliary is easily removable. A one-pot protocol is also described.

    DOI: 10.1039/d3sc03572g

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  14. Probing exciton dynamics with spectral selectivity through the use of quantum entangled photons Open Access

    Fujihashi Y., Miwa K., Higashi M., Ishizaki A.

    Journal of Chemical Physics   159 巻 ( 11 )   2023年9月

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    出版者・発行元:Journal of Chemical Physics  

    Quantum light is increasingly recognized as a promising resource for developing optical measurement techniques. Particular attention has been paid to enhancing the precision of the measurements beyond classical techniques by using nonclassical correlations between quantum entangled photons. Recent advances in the quantum optics technology have made it possible to manipulate spectral and temporal properties of entangled photons, and photon correlations can facilitate the extraction of matter information with relatively simple optical systems compared to conventional schemes. In these respects, the applications of entangled photons to time-resolved spectroscopy can open new avenues for unambiguously extracting information on dynamical processes in complex molecular and materials systems. Here, we propose time-resolved spectroscopy in which specific signal contributions are selectively enhanced by harnessing nonclassical correlations of entangled photons. The entanglement time characterizes the mutual delay between an entangled twin and determines the spectral distribution of photon correlations. The entanglement time plays a dual role as the knob for controlling the accessible time region of dynamical processes and the degrees of spectral selectivity. In this sense, the role of the entanglement time is substantially equivalent to the temporal width of the classical laser pulse. The results demonstrate that the application of quantum entangled photons to time-resolved spectroscopy leads to monitoring dynamical processes in complex molecular and materials systems by selectively extracting desired signal contributions from congested spectra. We anticipate that more elaborately engineered photon states would broaden the availability of quantum light spectroscopy.

    DOI: 10.1063/5.0169768

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  15. Theoretical analysis of the coordination-state dependency of the excited-state properties and ultrafast relaxation dynamics of bacteriochlorophyll a

    Takabayashi Y., Sato H., Higashi M.

    Chemical Physics Letters   826 巻   2023年9月

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    出版者・発行元:Chemical Physics Letters  

    The coordination-state dependency of the excited-state properties and ultrafast relaxation dynamics from the S2 to the S1 state of bacteriochlorophyll a were analyzed using quantum chemical calculations and nonadiabatic molecular dynamics simulations. TDDFT calculations and orbital analysis clarified the molecular mechanism of the decrease in the excitation energy difference caused by ligand coordination. The results of dynamics simulations also showed that the ligand accelerated the relaxation, and the estimated time constant was in quantitative agreement with the experimental data. We demonstrated the importance of the environmental effects for the relaxation dynamics, which have not been investigated theoretically.

    DOI: 10.1016/j.cplett.2023.140669

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  16. Unique solvent effect of water in radical cyclization reaction

    Suzuki S., Govind S.A., Imamura K., Yorimitsu H., Shinokubo H., Higashi M., Sato H.

    Chemical Physics Letters   826 巻   2023年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Physics Letters  

    The radical cyclization reaction in the aqueous environment by Yorimitsu et al. is revisited using the RISM-SCF-cSED method, a hybrid of quantum chemistry and statistical mechanics theory for molecular liquids. The difference between the barrier height of the forward reaction from the intermediate E-rot, the cyclization step, and that of the backward reaction is crucial to the reaction yield. Considering the effect of hydrogen bonding through the RISM theory, we found that the barrier height for the forward reaction is lower, especially in water. In other words, considering microscopic solvation effects clearly shows the difference between water and DMSO solvents, explaining the remarkable acceleration of the reaction in the aqueous environment.

    DOI: 10.1016/j.cplett.2023.140641

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  17. Theoretical study on counter anion- and solvent-dependent fluorescence quenching mechanism of 2-phenylbenzo[b]phospholium salts

    Suzuki, S; Imamura, K; Fujii, K; Kimura, Y; Matano, Y; Higashi, M; Sato, H

    JOURNAL OF MOLECULAR LIQUIDS   382 巻   2023年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Molecular Liquids  

    Recently reported highly fluorescent 2-phenylbenzo[b]phospholium salt shows an interesting photochemical property. While the counter anion and solvent dependency indicate that the salt is mainly responsible for the absorption and fluorescence spectra, the fluorescence decay clearly depends on the counter anion. In the present study, the detailed mechanism is elucidated using quantum chemical computation and its hybrid with statistical mechanics called 3D-RISM-SCF. Based on the careful exploration of plausible structures of the ion pairs in the methanol and dichloromethane solution, we identify the structure of the charge transfer state, the key on the photoprocess.

    DOI: 10.1016/j.molliq.2023.121934

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  18. Raman Spectroscopic and DFT Study of COA-Cl and Its Analogues

    Umakoshi T., Urakami T., Kidoguchi H., Yang K., Verma P., Sato H., Higashi M., Tsukamoto I.

    Journal of Physical Chemistry A   127 巻 ( 8 ) 頁: 1849 - 1856   2023年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Physical Chemistry A  

    COA-Cl is a newly synthesized adenosine analogue that exhibits various physiological activities. Its angiogenic, neurotropic, and neuroprotective potencies make it promising for the development of medicines. In this study, we show Raman spectroscopic study of COA-Cl to elucidate molecular vibrations and related chemical properties. Density functional theory calculations were combined with the Raman spectroscopic data to understand the details of each vibrational mode. Comparative analysis with adenine, adenosine, and other nucleic acid analogues enabled identification of unique Raman peaks originating from the cyclobutane moiety and chloro group of COA-Cl. This study provides fundamental knowledge and crucial insights for further development of COA-Cl and related chemical species.

    DOI: 10.1021/acs.jpca.2c08382

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  19. Reference interaction site model self-consistent field with constrained spatial electron density approach for nuclear magnetic shielding in solution 国際誌 Open Access

    Imamura K., Yokogawa D., Higashi M., Sato H.

    Journal of Chemical Physics   157 巻 ( 20 ) 頁: 204105 - 204105   2022年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Chemical Physics  

    We propose a new hybrid approach combining quantum chemistry and statistical mechanics of liquids for calculating the nuclear magnetic resonance (NMR) chemical shifts of solvated molecules. Based on the reference interaction site model self-consistent field with constrained spatial electron density distribution (RISM-SCF-cSED) method, the electronic structure of molecules in solution is obtained, and the expression for the nuclear magnetic shielding tensor is derived as the second-order derivative of the Helmholtz energy of the solution system. We implemented a method for calculating chemical shifts and applied it to an adenine molecule in water, where hydrogen bonding plays a crucial role in electronic and solvation structures. We also performed the calculations of 17O chemical shifts, which showed remarkable solvent dependence. While converged results could not be sometimes obtained using the conventional method, in the present framework with RISM-SCF-cSED, an adequate representation of electron density is guaranteed, making it possible to obtain an NMR shielding constant stably. This introduction of cSED is key to extending the method's applicability to obtain the chemical shift of various chemical species. The present demonstration illustrates our approach's superiority in terms of numerical robustness and accuracy.

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  20. Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor

    Sugiyama M., Akiyama M., Yonezawa Y., Komaguchi K., Higashi M., Nozaki K., Okazoe T.

    Science   377 巻 ( 6607 ) 頁: 756 - 759   2022年8月

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    出版者・発行元:Science  

    Fluorinated analogs of polyhedral hydrocarbons have been predicted to localize an electron within their cages upon reduction. Here, we report the synthesis and characterization of perfluorocubane, a stable polyhedral fluorocarbon. The key to the successful synthesis was the efficient introduction of multiple fluorine atoms to cubane by liquid-phase reaction with fluorine gas. The solid-state structure of perfluorocubane was confirmed using x-ray crystallography, and its electron-accepting character was corroborated electrochemically and spectroscopically. The radical anion of perfluorocubane was examined by matrix-isolation electron spin resonance spectroscopy, which revealed that the unpaired electron accepted by perfluorocubane is located predominantly inside the cage.

    DOI: 10.1126/science.abq0516

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  21. Free Energy and Solvation Structure Analysis for Adsorption of Aromatic Molecules at Pt(111)/Water Interface by 3D-RISM Theory 査読有り Open Access

    Akihiko Takamatsu, Masahiro Higashi, Hirofumi Sato

    Chemistry Letters   51 巻 ( 7 ) 頁: 791 - 795   2022年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemistry Letters  

    The free energy change of aromatic molecules adsorbed at a Pt(111)/water interface was analyzed using the three-dimensional reference interaction site model (3D-RISM) theory with density functional theory (DFT), compared with the reported experimental data. The changes in the solvation structure induced by molecular adsorption were discussed.

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  22. Extraction of local spin-coupled states by second quantized operators 査読有り Open Access

    Kaho Nakatani, Masahiro Higashi, Hirofumi Sato

    The Journal of Chemical Physics   157 巻 ( 1 ) 頁: 014112   2022年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Chemical Physics  

    We present a methodology for analyzing chemical bonds embedded in the electronic wave function of molecules, especially in terms of spin correlations or so-called "local spin."In this paper, based on biorthogonal second quantization, the spin correlation functions of molecules are naturally introduced, which enables us to extract local singlet and local triplet elements from the wave function. We also clarify the relationship between these spin correlations and traditional chemical concepts, i.e., resonance structures. Several chemical reactions, including the intramolecular radical cyclization and the formation of preoxetane, are demonstrated to verify the analysis method numerically.

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  23. A Catalytic Alkylation of Ketones via sp<sup>3</sup> C-H Bond Activation 国際誌

    Peng X., Hirao Y., Yabu S., Sato H., Higashi M., Akai T., Masaoka S., Mitsunuma H., Kanai M.

    Journal of Organic Chemistry   88 巻 ( 10 ) 頁: 6333 - 6346   2022年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Organic Chemistry  

    We identified a ternary hybrid catalyst system composed of an acridinium photoredox catalyst, a thiophosphoric imide (TPI) catalyst, and a titanium complex catalyst that promoted an intermolecular addition reaction of organic molecules with various ketones through sp3 C-H bond activation. The thiyl radical generated via single-electron oxidation of TPI by the excited photoredox catalyst abstracted a hydrogen atom from organic molecules such as toluene, benzyl alcohol, alkenes, aldehydes, and THF. The thus-generated carbon-centered radical species underwent addition to ketones and aldehydes. This intrinsically unfavorable step was promoted by single-electron reduction of the intermediate alkoxy radical by catalytically generated titanium(III) species. This reaction provided an efficient and straightforward route to a broad range of tertiary alcohols and was successfully applied to late-stage functionalization of drugs or their derivatives. The proposed mechanism was supported by both experimental and theoretical studies.

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  24. Identification of a Self-Photosensitizing Hydrogen Atom Transfer Organocatalyst System 国際誌

    Fuse H., Irie Y., Fuki M., Kobori Y., Kato K., Yamakata A., Higashi M., Mitsunuma H., Kanai M.

    Journal of the American Chemical Society   144 巻 ( 14 ) 頁: 6566 - 6574   2022年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of the American Chemical Society  

    We developed organocatalyst systems to promote the cleavage of stable C-H bonds, such as formyl, α-hydroxy, and benzylic C-H bonds, through a hydrogen atom transfer (HAT) process without the use of exogenous photosensitizers. An electronically tuned thiophosphoric acid, 7,7'-OMe-TPA, was assembled with substrate or co-catalyst N-heteroaromatics through hydrogen bonding and π-πinteractions to form electron donor-acceptor (EDA) complexes. Photoirradiation of the EDA complex induced stepwise, sequential single-electron transfer (SET) processes to generate a HAT-active thiyl radical. The first SET was from the electron-rich naphthyl group of 7,7'-OMe-TPA to the protonated N-heteroaromatics and the second proton-coupled SET (PCET) from the thiophosphoric acid moiety of 7,7'-OMe-TPA to the resulting naphthyl radical cation. Spectroscopic studies and theoretical calculations characterized the stepwise SET process mediated by short-lived intermediates. This organocatalytic HAT system was applied to four different carbon-hydrogen (C-H) functionalization reactions, hydroxyalkylation and alkylation of N-heteroaromatics, acceptorless dehydrogenation of alcohols, and benzylation of imines, with high functional group tolerance.

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  25. Chemical Shift of Solvated Hydride Ion: Comparative Study with Solvated Fluoride Ion 査読有り Open Access

    Kosuke Imamura, Masahiro Higashi, Yoji Kobayashi, Hiroshi Kageyama, Hirofumi Sato

    The Journal of Physical Chemistry B   126 巻 ( 16 ) 頁: acs.jpcb.2c00326 - 3098   2022年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Physical Chemistry B  

    The NMR chemical shifts of hydride and fluoride ions in the solution phase are evaluated from the first principle. The cluster structure in the first solvation shell is calculated by density functional theory and MP2 theory, and the solvent effect around the cluster is considered by PCM and RISM-SCF-SEDD methods. The obtained shifts are analyzed in terms of electronic structure and solvent effects and are compared with available experimental data. The fluoride ion is deshielded in the presence of solvent molecules compared to the isolated state due to a larger paramagnetic contribution from the 2p orbital. On the other hand, there is no such change for the hydride ion. The paramagnetic and diamagnetic contributions are slightly changed due to the solvation, but they are canceled out. As a result, the chemical shift of the hydride ion is less affected by the solvent than that of the fluoride ion. The increased diamagnetic contribution of hydride ion dissolved in the solvent is attributed to the change in electron density coupled with microscopic solvation.

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  26. Excited states of chlorophyll a and b in solution by time-dependent density functional theory

    Zhu Z., Higashi M., Saito S.

    Journal of Chemical Physics   156 巻 ( 12 ) 頁: 124111 - 124111   2022年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Chemical Physics  

    The ground state and excited state electronic properties of chlorophyll (Chl) a and Chl b in diethyl ether, acetone, and ethanol solutions are investigated using quantum mechanical and molecular mechanical calculations with density functional theory (DFT) and time-dependent DFT (TDDFT). Although the DFT/TDDFT methods are widely used, the electronic structures of molecules, especially large molecules, calculated with these methods are known to be strongly dependent on the functionals and the parameters used in the functionals. Here, we optimize the range-separated parameter, μ, of the CAM-B3LYP functional of Chl a and Chl b to reproduce the experimental excitation energy differences of these Chl molecules in solution. The optimal values of μ for Chl a and Chl b are smaller than the default value of μ and that for bacteriochlorophyll a, indicating the change in the electronic distribution, i.e., an increase in electron delocalization, within the molecule. We find that the electronic distribution of Chl b with an extra formyl group is different from that of Chl a. We also find that the polarity of the solution and hydrogen bond cause the decrease in the excitation energies and the increase in the widths of excitation energy distributions of Chl a and Chl b. The present results are expected to be useful for understanding the electronic properties of each pigment molecule in a local heterogeneous environment, which will play an important role in the excitation energy transfer in light-harvesting complex II.

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  27. Solvation in nitration of benzene and the valence electronic structure of the Wheland intermediate Open Access

    Nakatani K., Teshigawara S., Tanahashi Y., Kasahara K., Higashi M., Sato H.

    Physical Chemistry Chemical Physics   24 巻 ( 27 ) 頁: 16453 - 16461   2022年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Chemistry Chemical Physics  

    Nitration of benzene is a representative aromatic substitution reaction related to the σ-complex (arenium ion or “Wheland” intermediate) concept. This reaction is typically carried out in a mixed acid solution to generate nitronium ions, and how solvent molecules play roles in the reaction has been of great interest. Here we will shed new light on the reaction, namely the electronic structure and the microscopic insights of the solvation, which have been rarely discussed so far. We studied this process using the reference interaction site model-self consistent field with constrained spatial electron density distribution (RISM-SCF-cSED) method, considering sulfuric acid or water molecules as a solvent. In this method, the electronic structure of the solute and the solvation structure are self-consistently determined based on quantum chemistry and statistical mechanics of molecular liquids. The solvation free energy surfaces in solution and solvation structures were verified. In the bond formation process of benzene and nitronium ions, the solvation structure by sulfuric acid molecules drastically changes and the solvation effect on the free energy is quite large. We revealed largely contributing resonance structures in the π-electron system of the σ-complex in gas and solution phases by analysing the valence electronic structures.

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  28. Theoretical study of the mechanism of the solvent dependency of ESIPT in HBT 査読有り Open Access

    Keiji Naka, Hirofumi Sato, Masahiro Higashi

    Physical Chemistry Chemical Physics   23 巻 ( 36 ) 頁: 20080 - 20085   2021年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Chemistry Chemical Physics  

    2-(2′-Hydroxyphenyl)-benzothiazole (HBT) has been widely studied for use as a system for excited-state intramolecular proton transfer. However, the mechanism underlying the solvent dependency of HBT fluorescence spectra remains unclear. In this study, the HBT photochemical process in the S1state was analysed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The excited-state intramolecular proton transfer in the enol form of HBT was found to depend on the hydrogen-bond acceptability of the solvent. The twisting of the keto form of HBT is determined by whether HBT acts as a hydrogen-bond acceptor or donor. A specific stacking structure of the enol form of HBT was found to decrease the S1→ S0transition energy, which corresponds to the experimental fluorescence spectra in a DMSO/H2O solution mixture.

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  29. An analysis of valence electronic structure from a viewpoint of resonance theory: Tautomerization of formamide and diazadiboretidine Open Access

    Nakatani K., Higashi M., Fukuda R., Sato H.

    Journal of Computational Chemistry   42 巻 ( 23 ) 頁: 1662 - 1669   2021年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Computational Chemistry  

    The resonance theory is still very useful in understanding the valence electron structure. However, such a viewpoint is not usually obtained by general-purpose quantum chemical calculations, instead requires rather special treatment such as valence bond methods. In this study, we propose a method based on second quantization to analyze the results obtained by general-purpose quantum chemical calculations from the local point of view of electronic structure and analyze diazadiboretidine and the tautomerization of formamide. This method requires only the “PS”-matrix, consisting of the density matrix (P-matrix) and overlap matrix, and can be computed with a comparable load to that of Mulliken population analysis. A key feature of the method is that, unlike other methods proposed so far, it makes direct use of the results of general-purpose quantum chemical calculations.

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jcc.26703

  30. Theoretical study on isomerization of α-acids: A DFT calculation Open Access

    Kimura M., Ito T., Sato H., Higashi M.

    Food Chemistry   364 巻   頁: 130418 - 130418   2021年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Food Chemistry  

    The α-acids contained in hops are one of the ingredients of beer. The isomerization of α-acids produces iso-α-acids, the main source of bitterness in beer. In this study, the isomerization mechanism of the α-acid, cohumulone, was elucidated by using density functional theory in conjunction with the polarizable continuum model or 3D-RISM integral equation theory of liquids. The calculated reaction diagram is consistent with experimental results; the activation free energy difference between the cis and trans isomers is in good agreement with the experimental estimate. The activation energy difference results from solvation energy. Additionally, a calculation of NMR chemical shifts showed that the proton position of isocohumulone is different from that proposed previously. The effect of Mg2+ cation on the isomerization was also investigated. Both the activation and reaction free energy are stabilized by the presence of Mg2+, which is consistent with experimental results. Water solvation reduces the activation free energy.

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  31. A theoretical study of product selectivity in rhodium-catalyzed oxidative coupling reaction caused by the solvation effect Open Access

    Higashi M., Shibata N., Takeno S., Satoh T., Miura M., Sato H.

    Heterocycles   103 巻 ( 2 ) 頁: 952 - 952   2021年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Heterocycles  

    Solvation effects in the direct oxidative coupling of 1-phenylpyrazole with alkynes in the presence of rhodium catalyst was theoretically studied by means of the reference interaction site model self-consistent field with spatial electron density distribution (RISM-SCF-SEDD) method, which provides both of quantum chemical and statistical mechanical information on the solvation system. This reaction gives naphthalene and quinoline derivatives whose yields depend on the solvent environment. The computational results showed that the path for the naphthalene derivative is exothermic independently of solvent environment. On the other hand, the reaction energy of the reductive elimination for the quinoline derivative is considerably affected by solvation and endothermic in N,Ndimethylformamide (DMF) solution, indicating that the reaction is not preferable in DMF solution. The detailed analysis of solvation free energy and solvation structure are also reported.

    DOI: 10.3987/com-20-s(k)64

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  32. Uniform potential difference scheme to evaluate effective electronic couplings for superexchange electron transfer in donor-bridge-acceptor systems

    Nakano, H; Higashi, M; Sato, H

    JOURNAL OF CHEMICAL PHYSICS   152 巻 ( 22 ) 頁: 224103 - 224103   2020年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:The Journal of chemical physics  

    This article proposes an ab initio quantum chemical method to evaluate the effective electronic coupling that determines the rate of superexchange electron transfer in donor-bridge-acceptor (D-B-A) systems. The method utilizes the fragment charge difference to define electronic diabatic states and to apply an electrostatic potential in a form of a uniform potential difference that mimics solvation effects on the relative energies of the electronic states. The two-state generalized Mulliken-Hush method is used to obtain the effective electronic coupling as the nondiagonal element of the effective Hamiltonian that is derived based on the Green's function approach and the quasi-degenerate perturbation theory. A theoretical basis is provided for the dependence of the calculated effective electronic coupling on the applied potential and for how to find the optimal potential to give the desired effective electronic coupling that coincides with the result of the minimum energy splitting method. The method is applied to typical D-B-A molecules and gives the effective electronic couplings in reasonable agreement with the experimental estimates.

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  33. Nuclear magnetic shielding of molecule in solution based on reference interaction site model self-consistent field with spatial electron density distribution Open Access

    Imamura, K; Yamazaki, T; Yokogawa, D; Higashi, M; Sato, H

    JOURNAL OF CHEMICAL PHYSICS   152 巻 ( 19 ) 頁: 194102 - 194102   2020年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Chemical Physics  

    A new method for calculating nuclear magnetic shielding in solutions is developed based on the reference interaction site model self-consistent field (RISM-SCF) with spatial electron density distribution (SEDD). In RISM-SCF-SEDD, the electrostatic interaction between the solute and the solvent is described by considering the spread of electron to obtain more realistic electronic structure in solutions. It is thus expected to allow us to predict more quantitative chemical shifts of a wide variety of chemical species in solutions. In this study, the method is applied to a water molecule in water and is validated by examining the dependence of the solvent temperature and density on chemical shifts. The dependence of solvent species is also investigated, and more accurate results are obtained for polar solvents compared to the previous RISM-SCF study. Another application example of this method is the 15N chemical shifts of two azines in water, which is difficult to predict with the polarizable continuum model (PCM). Our results are in good agreement with the previous quantum mechanical/molecular mechanics study and experimental results. It is also shown that our method gives more realistic results for methanol and acetone than the PCM.

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  34. Site-Dependent Fluctuations Optimize Electronic Energy Transfer in the Fenna-Matthews-Olson Protein (vol 123, pg 9762, 2019)

    Saito, S; Higashi, M; Fleming, GR

    JOURNAL OF PHYSICAL CHEMISTRY B   123 巻 ( 51 ) 頁: 11055 - 11055   2019年12月

  35. Site-Dependent Fluctuations Optimize Electronic Energy Transfer in the Fenna-Matthews-Olson Protein Open Access

    Saito, S; Higashi, M; Fleming, GR

    JOURNAL OF PHYSICAL CHEMISTRY B   123 巻 ( 46 ) 頁: 9762 - 9772   2019年11月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Physical Chemistry B  

    Light absorbed by light-harvesting antennae is transferred to the reaction center (RC). The excitation energy transfer (EET) to the RC is known to proceed with nearly perfect quantum yield. However, understanding of EET is still limited at the molecular level. Here, we examine the dynamics in the Fenna-Matthews-Olson (FMO) protein by developing an efficient molecular dynamics simulation that can properly describe the electronic properties of bacteriochlorophylls. We find that the FMO protein consists of sites with heterogeneous fluctuations extending from fast to slow modulation. We also find that efficient EETs are facilitated by site-dependent fluctuations that enhance the resonance condition between neighboring sites with large site energy differences and circumvent exciton trapping on the pathway to the RC. Knowledge of site-dependent fluctuations is an important component of understanding optimization of EET in photosynthetic systems.

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  36. Effects of Water Addition on a Catalytic Fluorination of Dienamine 国際誌 Open Access

    Daiki Kuraoku, Tsunaki Yonamine, Genta Koja, Norio Yoshida, Satoru Arimitsu, Masahiro Higashi

    Molecules   24 巻 ( 19 ) 頁: 3428   2019年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Molecules  

    We investigate the effects of water addition on a highly stereocontrolled fluorination of dienamine generated by α-branched enals and 60-hydroxy-9-amino-9-deoxy-epi-quinidine with N-fluorobenzenesulfonimide (NFSI) in the presence of Brønsted acid both experimentally and theoretically. It is experimentally found that water addition to organic solvent significantly shortens the reaction time whereas excessive water addition decreases the enantiomeric excess. The results calculated with three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) method are in good agreement with the experimental ones. It is revealed that the shortness of reaction time is caused by the reactant destabilization and that the decrease in enantiomeric excess is due to the difference of hydration free energy between two transition states.

    DOI: 10.3390/molecules24193428

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  37. Kabirimine, a New Cyclic Imine from an Okinawan Dinoflagellate. 査読有り 国際誌 Open Access

    Hermawan I, Higa M, Hutabarat PUB, Fujiwara T, Akiyama K, Kanamoto A, Haruyama T, Kobayashi N, Higashi M, Suda S, Tanaka J

    Marine drugs   17 巻 ( 6 ) 頁: 353/1 - 9   2019年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Marine Drugs  

    On our quest for new bioactive molecules from marine sources, two cyclic imines (1, 2) were isolated from a dinoflagellate extract, inhibiting the growth of the respiratory syncytial virus (RSV). Compound 1 was identified as a known molecule portimine, while 2 was elucidated to be a new cyclic imine, named kabirimine. The absolute stereochemistry of 1 was determined by crystallographic work and chiral derivatization, whereas the structure of 2 was elucidated by means of spectroscopic analysis and computational study on all the possible isomers. Compound 1 showed potent cytotoxicity (CC50 < 0.097 µM) against HEp2 cells, while 2 exhibited moderate antiviral activity against RSV with IC50 = 4.20 µM (95% CI 3.31–5.33).

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  38. CHAPTER 2: Importance of C-H hydrogen bonding in asymmetric catalysis

    Satoru Arimitsu, Masahiro Higashi

    RSC Catalysis Series   2019-January 巻 ( 37 ) 頁: 26 - 65   2019年

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    掲載種別:論文集(書籍)内論文  

    © 2019 The Royal Society of Chemistry. This chapter describes the important roles of nonclassical C-H hydrogen bonds in asymmetric catalysis. Recently, many asymmetric catalytic reactions have demonstrated that weak C-H hydrogen bond interactions play important roles in selectivity. This chapter introduces the historical background of C-H hydrogen bonds, describes computational analyses of C-H hydrogen bonds in asymmetric catalysis and presents notable examples of asymmetric catalytic reactions in which C-H hydrogen bonds play important roles in selectivity.

    DOI: 10.1039/9781788016490-00026

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  39. Importance of C-H Hydrogen Bonding in Asymmetric Catalysis

    Arimitsu, S; Higashi, M

    NONCOVALENT INTERACTIONS IN CATALYSIS   36 巻   頁: 26 - 65   2019年

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  40. Vibrational frequency fluctuations of ionic and non-ionic vibrational probe molecules in aqueous solutions

    Okuda M., Higashi M., Ohta K., Saito S., Tominaga K.

    Springer Series in Optical Sciences   226 巻   頁: 259 - 285   2019年

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    記述言語:英語   掲載種別:論文集(書籍)内論文   出版者・発行元:Springer Series in Optical Sciences  

    In this chapter we review our studies on vibrational frequency fluctuations in aqueous solutions. Experimentally, the frequency fluctuations were investigated by measuring frequency-frequency time-correlation function (FFTCF) by two-dimensional spectroscopy, and molecular dynamics simulations were carried to obtain molecular pictures for the frequency fluctuations in water. We here compare the two different types of vibrational probes; one is non-ionic, and the other is ionic. For the non-ionic probe, we chose 2-nitro-5-thiocyanate benzoic acid (NTBA), which possesses an electronically neutral vibrational probe (SCN group) and an aromatic ring. For the ionic probe, three atomic ions, SCN− and N3−, were used. Although the charge distributions of the solutes and, consequently, hydration structures around the solutes are different for the ionic and non-ionic vibrational probes, both the ionic and non-ionic probes show similar decay time constants for FFTCF of about 1 ps. It is found that the frequency fluctuation for three atomic ions is almost determined by the electrostatic interaction from the water molecules in the first hydration shell. The collective dynamics of the water molecules in the first-hydration shell are found to be similar to those of bulk water, though the hydrogen bond between the ion and water molecule is very strong. In contrast to the hydration structure and water dynamics in these small ionic solutions, the hydration structure and water dynamics in the vicinity of the vibrational probe of NTBA are found to be similar to those in bulk. We consider that the electrostatic interactions with “bulk-like” water molecules around NTBA induce the slow decay component, i.e., 1-ps decay component, of the FFTCF of NTBA in H2O.

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  41. Vibrational and Molecular Properties of Mg2+ Binding and Ion Selectivity in the Magnesium Channel MgtE 査読有り 国際誌

    Kimura Tetsunari, Lorenz-Fonfria Victor A, Douki Shintaro, Motoki Hideyoshi, Ishitani Ryuichiro, Nureki Osamu, Higashi Masahiro, Furutani Yuji

    JOURNAL OF PHYSICAL CHEMISTRY B   122 巻 ( 42 ) 頁: 9681 - 9696   2018年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  42. Intramolecular Vibrations Complement the Robustness of Primary Charge Separation in a Dimer Model of the Photosystem II Reaction Center 査読有り

    Fujihashi, Y; Higashi, M; Ishizaki, A

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   9 巻 ( 17 ) 頁: 4921 - 4929   2018年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.jpclett.8b02119

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  43. Theoretical investigation on vibrational frequency fluctuations of SCN-derivatized vibrational probe molecule in water 査読有り

    Masaki Okuda, Masahiro Higashi, Kaoru Ohta, Shinji Saito, Keisuke Tominaga

    Chemical Physics   512 巻   頁: 82 - 87   2018年8月

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    出版者・発行元:Elsevier {BV}  

    DOI: 10.1016/j.chemphys.2018.03.012

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  44. Analysis of Gas Phase Reaction Pathways for InN Metal Organic Vapor Phase Epitaxy 査読有り

    Sone Junji, Uematsu Kouta, Matsufuji Yuuki, Oshima Masato, Yamada Katsumi, Higashi Masahiro

    JOURNAL OF CHEMICAL ENGINEERING OF JAPAN   51 巻 ( 7 ) 頁: 605 - 608   2018年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1252/jcej.17we288

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  45. Theoretical approaches for dynamical ordering of biomolecular systems 査読有り

    Okumura, H; Higashi, M; Yoshida, Y; Sato, H; Akiyama, R

    BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS   1862 巻 ( 2 ) 頁: 212 - 228   2018年2月

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    記述言語:英語   出版者・発行元:Biochimica et Biophysica Acta - General Subjects  

    Background Living systems are characterized by the dynamic assembly and disassembly of biomolecules. The dynamical ordering mechanism of these biomolecules has been investigated both experimentally and theoretically. The main theoretical approaches include quantum mechanical (QM) calculation, all-atom (AA) modeling, and coarse-grained (CG) modeling. The selected approach depends on the size of the target system (which differs among electrons, atoms, molecules, and molecular assemblies). These hierarchal approaches can be combined with molecular dynamics (MD) simulation and/or integral equation theories for liquids, which cover all size hierarchies. Scope of review We review the framework of quantum mechanical/molecular mechanical (QM/MM) calculations, AA MD simulations, CG modeling, and integral equation theories. Applications of these methods to the dynamical ordering of biomolecular systems are also exemplified. Major conclusions The QM/MM calculation enables the study of chemical reactions. The AA MD simulation, which omits the QM calculation, can follow longer time-scale phenomena. By reducing the number of degrees of freedom and the computational cost, CG modeling can follow much longer time-scale phenomena than AA modeling. Integral equation theories for liquids elucidate the liquid structure, for example, whether the liquid follows a radial distribution function. General significance These theoretical approaches can analyze the dynamic behaviors of biomolecular systems. They also provide useful tools for exploring the dynamic ordering systems of biomolecules, such as self-assembly. This article is part of a Special Issue entitled “Biophysical Exploration of Dynamical Ordering of Biomolecular Systems” edited by Dr. Koichi Kato.

    DOI: 10.1016/j.bbagen.2017.10.001

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  46. Theoretical analysis of the domain-swapped dimerization of cytochrome c: An MD and 3D-RISM approach 査読有り

    Yoshida, N; Higashi, M; Motoki, H; Hirota, S

    JOURNAL OF CHEMICAL PHYSICS   148 巻 ( 2 ) 頁: 025102/1 - 7   2018年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1063/1.5009785

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  47. Theoretical Study on Oligomerization of Cytochrome c 査読有り

    Motoki Hideyoshi, Yoshida Norio, Hirota Shun, Higashi Masahiro

    JOURNAL OF COMPUTER CHEMISTRY-JAPAN   17 巻 ( 1 ) 頁: 8 - 13   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.2477/jccj.2018-0006

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  48. Structural properties determining low K<SUP>+</SUP> affinity of the selectivity filter in the TWIK1 K<SUP>+</SUP> channel 査読有り Open Access

    Tsukamoto, H; Higashi, M; Motoki, H; Watanabe, H; Ganser, C; Nakajo, K; Kubo, Y; Uchihashi, T; Furutani, Y

    JOURNAL OF BIOLOGICAL CHEMISTRY   293 巻 ( 18 ) 頁: 6969 - 6984   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Biological Chemistry  

    Canonical K channels are tetrameric and highly K-selective, whereas two-pore– domain K (K2P) channels form dimers, but with a similar pore architecture. A two-pore– domain potassium channel TWIK1 (KCNK1 or K2P1) allows permeation of Na and other monovalent ions, resulting mainly from the presence of Thr-118 in the P1 domain. However, the mechanistic basis for this reduced selectivity is unclear. Using ion-exchange–induced difference IR spectroscopy, we analyzed WT TWIK1 and T118I (highly K-selective) and L228F (substitution in the P2 domain) TWIK1 variants and found that in the presence of K ions, WT and both variants exhibit an amide-I band at 1680 cm1. This band corresponds to interactions of the backbone carbonyls in the selectivity filter with K, a feature very similar to that of the canonical K channel KcsA. Computational analysis indicated that the relatively high frequency for the amide-I band is well explained by impairment of hydrogen bond formation with water molecules. Moreover, concentration-dependent spectral changes indicated that the K affinity of the WT selectivity filter was much lower than those of the variants. Furthermore, only the variants displayed a higher frequency shift of the 1680-cm1 band upon changes from K to Rb or Cs conditions. High-speed atomic force microscopy disclosed that TWIK1’s surface morphology largely does not change in K and Na solutions. Our results reveal the local conformational changes of the TWIK1 selectivity filter and suggest that the amide-I bands may be useful “molecular fingerprints” for assessing the properties of other K channels.

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  49. Vibrational frequency fluctuations of ionic vibrational probe in water: Theoretical study with molecular dynamics simulation 査読有り

    Okuda, M; Higashi, M; Ohta, K; Saito, S; Tominaga, K

    CHEMICAL PHYSICS LETTERS   683 巻   頁: 547 - 552   2017年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.cplett.2017.03.008

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  50. Two Furanosesterterpenoids from the Sponge <i>Luffariella variabilis</i> 査読有り

    Ahmadi, P; Higashi, M; de Voogd, NJ; Tanaka, J

    MARINE DRUGS   15 巻 ( 8 ) 頁: 249/1 - 8   2017年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.3390/md15080249

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  51. Theoretical study on photoexcitation dynamics of a bis-diimine Cu(I) complex in solutions 査読有り

    Agena, A; Iuchi, S; Higashi, M

    CHEMICAL PHYSICS LETTERS   679 巻   頁: 60 - 65   2017年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Physics Letters  

    We investigate the photoexcitation dynamics of [Cu(phen)2] + (phen = 1,10-phenanthroline) in solutions by using the molecular mechanics with Shepard interpolation method, which enables us to generate potential energy surfaces of the Cu complex efficiently. The calculated flattening rates and coherent vibration motions are in good agreement with the experimental results. We find that the photoexcitation dynamics in the gas phase is much different from those in solutions, which indicates the importance of the solvent effects on the photoexcitation dynamics.

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  52. Cinchona-Based Primary Amine Catalyzed a Proximal Functionalization of Dienamines: Asymmetric α-Fluorination of α-Branched Enals 査読有り

    Arimitsu, S; Yonamine, T; Higashi, M

    ACS CATALYSIS   7 巻 ( 7 ) 頁: 4736 - 4740   2017年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acscatal.7b01178

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  53. Four Aromatic Sulfates with an Inhibitory Effect against HCV NS3 Helicase from the Crinoid <i>Alloeocomatella polycladia</i> 査読有り

    Hermawan, I; Furuta, A; Higashi, M; Fujita, Y; Akimitsu, N; Yamashita, A; Moriishi, K; Tsuneda, S; Tani, H; Nakakoshi, M; Tsubuki, M; Sekiguchi, Y; Noda, N; Tanaka, J

    MARINE DRUGS   15 巻 ( 4 ) 頁: 117/1 - 10   2017年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.3390/md15040117

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  54. QM/MM Geometry Optimization on Extensive Free-Energy Surfaces for Examination of Enzymatic Reactions and Design of Novel Functional Properties of Proteins 査読有り

    Hayashi, S; Uchida, Y; Hasegawa, T; Higashi, M; Kosugi, T; Kamiya, M

    ANNUAL REVIEW OF PHYSICAL CHEMISTRY, VOL 68   68 巻   頁: 135 - 154   2017年

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    記述言語:英語   掲載種別:論文集(書籍)内論文   出版者・発行元:Annual Review of Physical Chemistry  

    Many remarkable molecular functions of proteins use their characteristic global and slow conformational dynamics through coupling of local chemical states in reaction centers with global conformational changes of proteins. To theoretically examine the functional processes of proteins in atomic detail, a methodology of quantum mechanicalmolecular mechanical (QMMM) free-energy geometry optimization is introduced. In the methodology, a geometry optimization of a local reaction center is performed with a quantum mechanical calculation on a free-energy surface constructed with conformational samples of the surrounding protein environment obtained by a molecular dynamics simulation with a molecular mechanics force field. Geometry optimizations on extensive free-energy surfaces by a QMMM reweighting free-energy self-consistent field method designed to be variationally consistent and computationally efficient have enabled examinations of the multiscale molecular coupling of local chemical states with global protein conformational changes in functional processes and analysis and design of protein mutants with novel functional properties.

    DOI: 10.1146/annurev-physchem-052516-050827

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  55. The ion dependence of carbohydrate binding of CBM36: an MD and 3D-RISM study 査読有り

    Tanimoto, S; Higashi, M; Yoshida, N; Nakano, H

    JOURNAL OF PHYSICS-CONDENSED MATTER   28 巻 ( 34 ) 頁: 344005/1 - 8   2016年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/0953-8984/28/34/344005

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  56. One-pot synthesis and theoretical calculation for trifluoromethylated pyrrolizidines by 1,3-dipolar cycloaddition with azomethine ylides and β-trifluoromethyl acrylamides 査読有り

    Toma, Y; Kunigami, M; Watanabe, KJ; Higashi, M; Arimitsu, S

    JOURNAL OF FLUORINE CHEMISTRY   189 巻   頁: 22 - 32   2016年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.jfluchem.2016.07.013

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  57. Spin-Blocking Effect in CO and H<sub>2</sub> Binding Reactions to Molybdenocene and Tungstenocene: A Theoretical Study on the Reaction Mechanism via the Minimum Energy Intersystem Crossing Point 査読有り

    Watanabe, K; Nakatani, N; Nakayama, A; Higashi, M; Hasegawa, J

    INORGANIC CHEMISTRY   55 巻 ( 16 ) 頁: 8082 - 8090   2016年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.inorgchem.6b01187

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  58. Quantitative Evaluation of Site Energies and Their Fluctuations of Pigments in the Fenna-Matthews-Olson Complex with an Efficient Method for Generating a Potential Energy Surface 査読有り

    Higashi, M; Saito, S

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   12 巻 ( 8 ) 頁: 4128 - 4137   2016年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/acs.jctc.6b00516

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  59. A New Trinor-guaiane Sesquiterpene from an Indonesian Soft Coral <i>Anthelia</i> sp. 査読有り

    Hanif, N; Murni, A; Yamauchi, M; Higashi, M; Tanaka, J

    NATURAL PRODUCT COMMUNICATIONS   10 巻 ( 11 ) 頁: 1907 - 1910   2015年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1177/1934578x1501001124

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  60. Theoretical Study on Excited States of Bacteriochlorophyll <i>a</i> in Solutions with Density Functional Assessment 査読有り

    Higashi, M; Kosugi, T; Hayashi, S; Saito, S

    JOURNAL OF PHYSICAL CHEMISTRY B   118 巻 ( 37 ) 頁: 10906 - 10918   2014年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Physical Chemistry B  

    The excited-state properties of bacteriochlorophyll (BChl) a in triethylamine, 1-propanol, and methanol are investigated with the time-dependent density functional theory by using the quantum mechanical and molecular mechanical reweighting free energy self-consistant field method. It is found that no prevalent density functionals can reproduce the experimental excited-state properties, i.e., the absorption and reorganization energies, of BChl a in the solutions. The parameter μ in the range-separated hybrid functional is therefore optimized to reproduce the differences of the absorption energies in the solutions. We examine the origin of the differences of the absorption energies in the solutions and find that sensitive balance between contributions of structural changes and solute-solvent interactions determines the differences. The accurate description of the excitation with the density functional with the adjusted parameter is therefore essential to the understanding of the excited-state properties of BChl a in proteins and also the mechanism of the photosynthetic systems.

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  61. Concerted Hydrogen Atom and Electron Transfer Mechanism for Catalysis by Lysine-Specific Demethylase 査読有り

    Yu, T; Higashi, M; Cembran, A; Gao, JL; Truhlar, DG

    JOURNAL OF PHYSICAL CHEMISTRY B   117 巻 ( 28 ) 頁: 8422 - 8429   2013年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jp404292t

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  62. Theoretical and Experimental Studies on Vibrational Energy Relaxation of the CO Stretching Mode of Acetone in Alcohol Solutions 査読有り

    Higashi, M; Hirai, S; Banno, M; Ohta, K; Saito, S; Tominaga, K

    JOURNAL OF PHYSICAL CHEMISTRY B   117 巻 ( 16 ) 頁: 4723 - 4731   2013年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  63. Direct Simulation of Excited-State Intramolecular Proton Transfer and Vibrational Coherence of 10-Hydroxybenzo[h]quinoline in Solution 査読有り

    Higashi, M; Saito, S

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   2 巻 ( 18 ) 頁: 2366 - 2371   2011年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/jz201042u

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  64. Efficient Approach to Reactive Molecular Dynamics with Accurate Forces 査読有り

    Higashi, M; Truhlar, DG

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   5 巻 ( 11 ) 頁: 2925 - 2929   2009年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1021/ct900301d

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  65. Combined electrostatically embedded multiconfiguration molecular mechanics and molecular mechanical method: Application to molecular dynamics simulation of a chemical reaction in aqueous solution with hybrid density functional theory 査読有り

    Higashi, M; Truhlar, DG

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   4 巻 ( 7 ) 頁: 1032 - 1039   2008年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  66. Electrostatically embedded multiconfiguration molecular mechanics based on the combined density functional and molecular mechanical method 査読有り

    Higashi, M; Truhlar, DG

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   4 巻 ( 5 ) 頁: 790 - 803   2008年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  67. Transition state determination of enzyme reaction on free energy surface: Application to chorismate mutase 査読有り

    Higashi, M; Hayashi, S; Kato, S

    CHEMICAL PHYSICS LETTERS   437 巻 ( 4-6 ) 頁: 293 - 297   2007年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Physics Letters  

    The transition state on the free energy surface for Claisen rearrangement of chorismate in Bacillus subtilis chorismate mutase is calculated with a method based on a linear response theory. The calculated activation free energy is 16.9 kcal/mol, which is in good agreement with the experimental one. The catalytic ability of the enzyme is examined by comparing the activation barrier with that in aqueous solution and found to be mainly attributed to the conformational restriction of the substrate. We also calculate the kinetic isotope effects, which are in accord with the experimental estimates. © 2007 Elsevier B.V. All rights reserved.

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  68. Geometry optimization based on linear response free energy with quantum mechanical/molecular mechanical method: Applications to Menshutkin-type and Claisen rearrangement reactions in aqueous solution 査読有り

    Higashi, M; Hayashi, S; Kato, S

    JOURNAL OF CHEMICAL PHYSICS   126 巻 ( 14 ) 頁: 144503/1 - 10   2007年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Chemical Physics  

    The authors present a method based on a linear response theory that allows one to optimize the geometries of quantum mechanical/molecular mechanical (QM/MM) systems on the free energy surfaces. Two different forms of linear response free energy functional are introduced, and electronic wave functions of the QM region, as well as the responses of electrostatic and Lennard-Jones potentials between QM and MM regions, are self-consistently determined. The covariant matrix relating the QM charge distribution to the MM response is evaluated by molecular dynamics (MD) simulation of the MM system. The free energy gradients with respect to the QM atomic coordinates are also calculated using the MD trajectory results. They apply the present method to calculate the free energy profiles of Menshutkin-type reaction of NH3 with CH 3Cl and Claisen rearrangement of allyl vinyl ether in aqueous solution. For the Menshutkin reaction, the free energy profile calculated with the modified linear response free energy functional is in good agreement with that by the free energy perturbation calculations. They examine the nonequilibrium solvation effect on the transmission coefficient and the kinetic isotope effect for the Claisen rearrangement. © 2007 American Institute of Physics.

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  69. Theoretical study on electronic and spin structures of [Fe2S2](2+,+) cluster: reference interaction site model self-consistent field (RISM-SCF) and multireference second-order Møller-Plesset perturbation theory (MRMP) approach. 査読有り

    Higashi M, Kato S

    The journal of physical chemistry. A   109 巻 ( 43 ) 頁: 9867 - 9874   2005年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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▼全件表示

書籍等出版物 1

  1. Vibrational frequency fluctuations of ionic and non-ionic vibrational probe molecules in aqueous solutions

    Okuda M., Higashi M., Ohta K., Saito S., Tominaga K.

    Springer Series in Optical Sciences  2019年 

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    In this chapter we review our studies on vibrational frequency fluctuations in aqueous solutions. Experimentally, the frequency fluctuations were investigated by measuring frequency-frequency time-correlation function (FFTCF) by two-dimensional spectroscopy, and molecular dynamics simulations were carried to obtain molecular pictures for the frequency fluctuations in water. We here compare the two different types of vibrational probes; one is non-ionic, and the other is ionic. For the non-ionic probe, we chose 2-nitro-5-thiocyanate benzoic acid (NTBA), which possesses an electronically neutral vibrational probe (SCN group) and an aromatic ring. For the ionic probe, three atomic ions, SCN− and N3−, were used. Although the charge distributions of the solutes and, consequently, hydration structures around the solutes are different for the ionic and non-ionic vibrational probes, both the ionic and non-ionic probes show similar decay time constants for FFTCF of about 1 ps. It is found that the frequency fluctuation for three atomic ions is almost determined by the electrostatic interaction from the water molecules in the first hydration shell. The collective dynamics of the water molecules in the first-hydration shell are found to be similar to those of bulk water, though the hydrogen bond between the ion and water molecule is very strong. In contrast to the hydration structure and water dynamics in these small ionic solutions, the hydration structure and water dynamics in the vicinity of the vibrational probe of NTBA are found to be similar to those in bulk. We consider that the electrostatic interactions with “bulk-like” water molecules around NTBA induce the slow decay component, i.e., 1-ps decay component, of the FFTCF of NTBA in H2O.

    DOI: 10.1007/978-981-13-9753-0_12

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科研費 13

  1. 光合成超分子複合体における光エネルギー伝達ダイナミクスの理論的解明

    研究課題/研究課題番号:22K05022  2022年4月 - 2026年3月

    日本学術振興会  科学研究費助成事業  基盤研究(C)

    東 雅大

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    担当区分:研究代表者 

    配分額:4160000円 ( 直接経費:3200000円 、 間接経費:960000円 )

    光合成系における最初のステップは、光捕集アンテナと呼ばれるタンパク質による光エネルギーの吸収および反応中心への伝達である。光捕集アンテナは、内部に含まれる色素の励起エネルギーの大きさと揺らぎを適切に制御することで、高効率なエネルギー移動を達成しているが、その詳細はよく分かっていない。これまで我々は独自の高精度理論解析手法を用いて、光捕集アンテナ内のエネルギー移動の解析を行ってきた。本研究課題では、その研究を発展させ、光捕集アンテナから反応中心への高効率な光エネルギー伝達機構を分子論的に明らかにする。
    光合成系における最初のステップは、光捕集アンテナと呼ばれるタンパク質による光エネルギーの吸収および反応中心への伝達である。光捕集アンテナは、内部に含まれる色素の励起エネルギーの大きさと揺らぎを適切に制御することで、高効率なエネルギー移動を達成しているが、その詳細はよく分かっていない。本研究課題では、光捕集アンテナから反応中心への高効率な光エネルギー伝達機構を分子論的に明らかにすることを目的とする。本年度は、昨年度に引き続き、主に紅色細菌の光捕集アンテナLH2の吸収スペクトルの解析を行った。LH2はB800とB850と呼ばれる吸収エネルギーの異なる2つの色素リングを内包するが、色素が重なったB850の吸収エネルギーを分子シミュレーションにより再現するのは困難だった。本年度は分子シミュレーションの結果を丁寧に解析し、色素バクテリオクロロフィルのアセチル基のねじれ角の制御が重要であり、タンパク質環境を適切に再現することが重要であることが明らかになった。現在、テスト計算では良好な結果を得ており、引き続き解析を進める予定である。また、LH2の集合体を解析するための粗視化モデルの開発も進めている。さらに、これまで研究を進めてきた色素バクテリオクロロフィルのS2状態からS1状態への超高速緩和ダイナミクスの解析も論文としてまとめた。分子軌道の解析や非断熱分子動力学シミュレーションにより配位子が緩和ダイナミクスを高速化することを明らかにした。
    本年度は光捕集アンテナLH2の吸収スペクトルの解析を進め、また色素の励起状態緩和ダイナミクスの解析も進めた。研究はおおむね順調に進行していると考えている。
    今後も引き続き、光捕集アンテナの吸収スペクトルの解析を進める。その後、光エネルギー伝達の機構解析に進み、光捕集アンテナ集合体の解析にも展開する予定である。

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  2. 動的エキシトンの理論

    研究課題/研究課題番号:20H05839  2020年11月 - 2025年3月

    日本学術振興会  科学研究費助成事業  学術変革領域研究(A)

    東 雅大, 杉山 佳奈美

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    担当区分:研究代表者 

    配分額:58890000円 ( 直接経費:45300000円 、 間接経費:13590000円 )

    本研究では、独自の高精度理論解析手法を発展させて動的エキシトンの理論を確立することを目的とする。本年度は、昨年度に引き続きA01今堀やA02小堀により系統的に合成および物性測定されたポルフィリン連結フラーレン化合物の電子励起状態や電荷分離状態の解析を行った。これまでの我々の研究で、電子励起状態や電荷分離状態を適切に記述するためには、化合物の構造緩和や溶媒分子の応答を分子レベルで露わに取り扱う必要があることが明らかになった。そこで、それらを効率的に記述可能なQM/MM RWFE-SCF法を用いてモデル分子を解析したところ、概ね実験結果と良い一致を示した。特に、電荷分離状態は溶媒により大きく安定化していることが明らかになった。さらに、QM/MM RWFE-SCF法の計算を高速化するプログラムの改良も行った。また、A01今堀らにより合成された非フラーレン型アクセプター分子TACICの励起状態や薄膜状態の構造の解析を行った。TACICの薄膜状態での励起状態の寿命は、溶液中の寿命と比較して大幅に長くなる。これは構造やバンド構造が似たITICと全く逆の挙動であるが、その理由は不明である。まず、量子化学計算により、TACICとITIC単量体の励起状態のポテンシャル面はよく似ていることが分かった。これは溶液中での寿命が同程度であることに対応する。一方、分子動力学シミュレーションを用いて薄膜状態の構造を解析したところ、ITICでは主に端同士がスタックしているのに対して、TACICでは端と中央がスタックした構造も同程度存在していた。この薄膜状態での構造の違いが、励起状態の寿命の違いと関連していると考えられる。また、A03三ツ沼が開発したドナーアクセプター相互作用を利用した水素引き抜き触媒の生成機構をA02小堀やA02山方と共同で解析し、ラジカルが2段階で生成していることを明らかにした。

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  3. 動的エキシトンの学理構築と機能開拓

    研究課題/研究課題番号:20H05831  2020年11月 - 2025年3月

    日本学術振興会  科学研究費助成事業  学術変革領域研究(A)

    今堀 博, 小堀 康博, 佐伯 昭紀, 山田 容子, 東 雅大, 三ツ沼 治信, 梶 弘典, 山方 啓, 家 裕隆, 作田 絵里, 村上 達也, 鈴木 克明, 小堀 康博, 佐伯 昭紀, 山田 容子, 東 雅大, 三ツ沼 治信, 梶 弘典, 山方 啓, 家 裕隆, 作田 絵里, 村上 達也, 鈴木 克明

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    担当区分:研究分担者 

    本学術変革領域では、従来の光化学における「静的エキシトン」の概念を打ち破る学術領域「動的エキシトン学」の構築にむけ、分野融合・統合的研究を推進する。そのために総括班では、本領域全体での「学問分野の枠を超えた有機的連携の堅持」を最重要課題と位置づけ、期間内に全ての計画班員12名が役割分担して領域の推進に貢献する。特に、班長及び研究課題代表者による共同研究支援に加えて、若手研究者育成支援、女性研究者育成支援、国際活動支援、産学連携支援の五つの支援を柱に、様々な具体的施策により、領域の目標と方針を計画班員に周知徹底し、目標の達成に向け先導的な役割を達成を目指す。
    研究領域全体の研究方針の作成は領域代表者の今堀と各班長、研究課題代表1-4を中心に行った。拡大運営委員会、領域会議等で計画班、公募班員全員が集まる機会を複数回設け、領域目標の周知・確認を繰り返し行った。また、広報活動の一環として、また領域目標の共有に向けて、領域ホームページ、プレスリリース、学会発表、アウトリーチ等も積極的に活用した。これらの機会を利用して、計画班員全員が互いの動的エキシトン研究の進捗を密に共有した。計画、公募班員は二ヶ月に一回程度、メールやZoomなどのインターネット会議で研究の進捗を各班長、研究課題代表に報告し 、各班長、研究課題代表は班長会議、研究課題会議、サイトビジットにより、計画、公募班全体の研究の進捗を把握した。これにより、必要に応じて適切なタイミングで、機動的な共同研究の提案、開始、とりまとめを行えた。

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  4. 天然および人工光捕集アンテナ系における光エネルギー伝達機構の理論的解明

    研究課題/研究課題番号:20H05099  2020年4月 - 2022年3月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    東 雅大

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    担当区分:研究代表者 

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    光合成における最初のステップは、光捕集アンテナと呼ばれるタンパク質による光エネルギーの吸収および反応中心への伝達である。このエネルギー伝達効率は非常に高いことが知られており、その構造を模した人工の光捕集アンテナが作られてきた。しかし、天然と人工光捕集アンテナ系で何が同じで何が違うのか未だよく分かっていない。本研究課題の目的は、我々が独自に開発してきた量子化学計算と分子動力学シミュレーションを効率的に結びつける手法を活用し、天然及び人工光捕集アンテナ系の光エネルギー伝達機構を分子論的に明らかにすることである。
    本年度は、まず、天然及び人工のクロロゾームに含まれる色素であるバクテリオクロロフィル (BChl) c,d,e,fや亜鉛BChl誘導体の励起状態の解析を行った。概ね実験結果と定性的に一致する結果が得られたが、過去のBChl aの研究と同様に、再配向エネルギーの値は量子化学計算手法により大きく依存することが明らかになった。今後、天然及び人工クロロゾームの解析には用いる量子化学計算を注意深く検討する予定である。
    また分子動力学シミュレーションを用いて、天然及び人工のクロロゾームの構造の作成を行った。これまでの研究に基づいてBChl同士が水素結合したチューブ状の構造を作り上げ、分子動力学シミュレーションにより、その構造が安定であることを確認した。現在、量子化学計算の情報を基に、BChlの基底状態と励起状態のポテンシャル関数を作成中であり、それを用いてBChlの励起エネルギーの大きさと揺らぎを解析する予定である。

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  5. 反応環境に着目したハイブリッド触媒反応の分子論的機構解明

    研究課題/研究課題番号:20H04813  2020年4月 - 2022年3月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    東 雅大

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    担当区分:研究代表者 

    配分額:5200000円 ( 直接経費:4000000円 、 間接経費:1200000円 )

    本研究の目的は、量子化学計算などの理論計算手法を用いて、反応環境により反応性が大きく変化するハイブリッド触媒反応の分子論的機構を明らかにすることである。
    今年度は、金井 求 教授(東京大)のグループが開発したハイブリッド触媒反応の解析を行った。この反応は、光触媒と不斉クロム触媒の存在下に可視光を照射することにより、単純アルケンとアルデヒドを反応させ、キラルアルコールへと変換する。この反応は、添加剤の影響を大きく受け、Mg(ClO4)2 の存在下では収率と鏡像体過剰率が大幅に向上するが、その詳細は不明である。この反応を量子化学計算により解析したところ、立体選択性を決定する2つの遷移状態の自由エネルギーが非常に近接していることが明らかになった。また、もともとの不斉クロム触媒に配位していたCl-イオンがMg(ClO4)2 の存在下ではClO4-イオンと入れ替わることも示唆された。しかし、得られた計算結果が用いる汎関数や溶媒モデルなどの計算手法に依存して安定な遷移状態が入れ替わるため、引き続き詳細な解析を進める予定である。
    また、林雄二郎教授(東北大)と山中正浩教授(立教大)と共同で、水の添加量により立体選択性が反転する不斉マイケル反応の解析も引き続き行った。反応物から生成物まで一連の反応経路を求め、溶媒の極性によって律速段階となる遷移状態が変化することが明らかになった。実験結果と対応する計算結果が得られており、引き続き詳細な解析を進める予定である。

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  6. 混合溶媒中におけるハイブリッド触媒反応の分子論的機構解明

    研究課題/研究課題番号:18H04657  2018年4月 - 2020年3月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    東 雅大

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    担当区分:研究代表者 

    配分額:8190000円 ( 直接経費:6300000円 、 間接経費:1890000円 )

    本研究の目的は、水を添加すると大幅に反応性が向上するハイブリッド触媒反応の分子論的機構を理論計算により明らかにすることである。
    本年度は、有光暁助教(琉球大)らにより開発されたハイブリッド触媒反応における水の影響を解析した。この反応は、アミン触媒と酸触媒により従来はγ-位に付加しやすいα,β-不飽和アルデヒドのα-位を立体選択的にフッ素化するが、水を少量添加すると反応性が向上する。しかし一方、水を過剰に添加すると鏡像体過剰率が低下する。この反応の分子レベルでのメカニズムを解明するために、量子化学計算と分子性液体の統計力学理論のハイブリッド計算手法である3D-RISM-SCF法を用いて、有機溶媒と水の様々な混合比での遷移状態の活性化エネルギーを計算した。
    得られた計算結果から、水の混合比が増えると、活性化エネルギーが減少することや、主生成物と副生成物の活性化エネルギーの差が小さくなることが明らかになった。これらの計算結果は、実験結果とよく一致する。また詳細な解析の結果、水が増加するにつれて活性化エネルギーが減少するのは、水が相対的に反応物を不安定化させるためと分かった。さらに、水の増加により主生成物と副生成物の活性化エネルギーの差が小さくなるのは、副生成物の遷移状態の方が酸触媒と水が強く相互作用するためと明らかになった。現在、論文を投稿する準備を進めている。
    また、林雄二郎教授(東北大)と山中正浩教授(立教大)と共同で、水の添加量により立体選択性が反転する不斉マイケル反応の解析も進めている。

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  7. 光合成反応中心における初期電荷分離過程の分子論的機構解明

    2018年 - 2021年

    科学技術振興機構  戦略的な研究開発の推進 戦略的創造研究推進事業 さきがけ 

    東 雅大

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    担当区分:研究代表者 

    光合成の最初のステップは、初期電荷分離と呼ばれる電子移動反応です。植物は進化の過程で、この反応が起こりやすいようにタンパク質の構造を変遷させてきたと考えられていますが、その詳細は不明です。また近年、この反応でコヒーレンスと呼ばれる現象が観測されていますが、その現象が起きる理由や果たす役割もよく分かっていません。本研究では私が開発してきた独自の理論計算手法を用いてこれらを解明します。

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  8. 光合成系における光エネルギー伝達機構の理論的解明

    研究課題/研究課題番号:17K05757  2017年4月 - 2021年3月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    東 雅大

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    担当区分:研究代表者 

    配分額:4810000円 ( 直接経費:3700000円 、 間接経費:1110000円 )

    本年度は、光捕集アンテナFMOタンパクの吸収スペクトルおよび励起エネルギー移動ダイナミクスの解析を行った。
    まず、これまで開発してきた色素の励起エネルギーや色素間の励起子相互作用の大きさや揺らぎを効率的に解析可能な手法を用いて、FMOタンパク中の色素全てを量子化学的に取り扱った分子動力学シミュレーションを行った。低温(77K)と常温(300K)の分子動力学シミュレーションから得られた吸収スペクトルは、実験とよく一致した。この結果は、計算で得られた色素の励起エネルギーや色素間の励起子相互作用の大きさや揺らぎが適切に記述できていることを意味している。
    また、階層方程式を用いて、励起エネルギー移動ダイナミクスの解析を行った。色素の揺らぎを一定にした場合と、色素ごとに分子動力学シミュレーションで得られた揺らぎを用いた場合では、後者の方がエネルギー移動が加速されることが明らかになった。タンパク質がそれぞれの色素の揺らぎを制御することで、効率的に光エネルギーを伝達していると考えられる。さらに、色素の揺らぎをパラメータとして変化させて励起エネルギー移動ダイナミクスの計算を行ったところ、低温ではよりエネルギー移動が高速になるパラメータが存在したが、常温ではシミュレーションで得られた揺らぎがほぼ最適であった。この結果は、温度によって最適値が異なり、タンパク質は生存する常温付近で揺らぎをより最適化していると考えられる。
    現在、これらの研究成果を論文に投稿する準備を行っているところである。

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  9. 銅錯体における光励起ダイナミクスの反応機構及び制御法の解明

    研究課題/研究課題番号:16KT0165  2016年7月 - 2020年3月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    東 雅大

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    担当区分:研究代表者 

    配分額:4810000円 ( 直接経費:3700000円 、 間接経費:1110000円 )

    本年度は、ビスジイミン銅(I)錯体と類似の光励起ダイナミクスとして、水溶液中の金(I)三量体錯体の光励起ダイナミクスの解析を行った。
    金(I)三量体錯体は、基底状態は一重項で金イオン3つが折れ曲がり緩く結合した状態であるが、光励起すると系間交差が起きて三重項励起状態となり、3つの金イオンが直線状になり強く結合することが知られている。この光励起ダイナミクスについて、時間分解分光実験により解析が行われてきたが、主張が異なり議論が分かれている状況である。
    そこで、本研究では理論計算により一重項基底状態と三重項励起状態の金(I)三量体錯体の構造を解析した。特に、周囲の水溶媒の影響に着目し、どの溶媒モデルでX線溶液散乱実験で得られた構造を再現可能か調べた。その結果、単純な分極連続体モデルや分子性液体の積分方程式で溶媒の平均的な描像を記述するモデルでは、一重項基底状態で緩く非対称に結合している実験構造を再現できないことが明らかになった。一方、溶質と溶媒の熱揺らぎの効果や溶媒の量子性を取り込んだ第一原理分子動力学シミュレーションでは、定性的に実験の傾向を再現した。また、一重項基底状態の金イオン間の結合長は、量子化学計算手法によっても大きく異なり、定量的な記述には分散力補正が必要であることも明らかになった。したがって、この金(I)三量体錯体の光励起による結合生成ダイナミクスを解析するためには、溶質と溶媒の両方の適切な記述が必要であると考えられる。
    今後、より定量的に金(I)三量体錯体の構造を記述するために、さらに計算手法に対する依存性を詳細に調べる予定である。また、中間状態である一重項励起状態の解析も行う予定である。

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  10. 光捕集複合体における自己組織化過程と機能発現の理論的究明

    研究課題/研究課題番号:16H00778  2016年4月 - 2018年3月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    東 雅大

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    担当区分:研究代表者 

    配分額:6240000円 ( 直接経費:4800000円 、 間接経費:1440000円 )

    本年度は昨年度に引き続き、分子動力学シミュレーションを用いて、紅色光合成細菌の光捕集複合体のサブユニットB820の物性や自己組織化過程の解析を行った。昨年度に開発した、静電相互作用を減衰させた仮想的な状態を導入して結合自由エネルギーを計算する手法を様々な菌種由来のサブユニットB820に適用し、ポリペプチドの構造を壊すことなく結合自由エネルギーを計算することができた。現在、手法に由来する統計誤差の評価を行っている。また、自己組織化の過程についても引き続き解析を進めている。
    また、本年度はシトクロムcのドメインスワッピング機構の解析も行った。シトクロムcは、ミトコンドリア内の呼吸に関わる反応において電子を伝達する役割を担うヘムタンパク質である。シトクロムcは、互いのC末端ヘリックスを交換するドメインスワッピングにより多量体を形成し、電子伝達の機能を失うことが知られているが、多量体形成のメカニズムは未だはっきりしていない。この多量体形成メカニズムの解明を目指して、分子動力学シミュレーションと液体の積分方程式理論を用いてシトクロムcの単量体と二量体の熱力学安定性の解析を行った。得られた計算結果は、実験とよく一致し、タンパク質の構造変化が二量体の不安定化に、また水和が二量体の安定化に寄与することを明らかにした。また、単量体と二量体の自由エネルギーの差を各残基ごとの寄与に分解にすることにより、正の電荷と負の電荷を持つ残基が、それぞれ二量体の安定化と不安定化に寄与することを明らかにした。さらに、2つのユニットをつなぐヒンジループも二量体の安定化に寄与することも明らかにしている。

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  11. 分子シミュレーションによる生体分子系における励起エネルギー移動の理論的解明

    研究課題/研究課題番号:26810008  2014年4月 - 2018年3月

    日本学術振興会  科学研究費助成事業 若手研究(B)  若手研究(B)

    東 雅大, 斉藤 真司, 斉藤 真司

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    担当区分:研究代表者 

    配分額:4160000円 ( 直接経費:3200000円 、 間接経費:960000円 )

    本研究では、量子化学計算と分子動力学シミュレーションを効率良く結びつける手法を開発し、光捕集アンテナの高効率な光エネルギー伝達機能におけるタンパク質の構造および揺らぎの役割を解明することを目的とする。これまで光捕集アンテナ中の色素の励起エネルギーの大きさと揺らぎを解析可能な手法を開発し、光捕集アンテナFMOタンパク中の7つの色素の励起エネルギーの大きさと揺らぎを、世界で初めて定量的に再現することに成功した。また、色素間の励起子相互作用の大きさと揺らぎを解析可能な手法の開発も行った。

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  12. 光捕集アンテナにおける励起エネルギー移動の分子論的機構の理論的解明

    研究課題/研究課題番号:25888020  2013年8月 - 2015年3月

    日本学術振興会  科学研究費助成事業 研究活動スタート支援  研究活動スタート支援

    東 雅大

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    担当区分:研究代表者 

    配分額:2470000円 ( 直接経費:1900000円 、 間接経費:570000円 )

    光合成反応で重要な光捕集アンテナと呼ばれるタンパク質は、内部に含まれる色素で吸収した光エネルギーを励起エネルギー移動(EET)の形で高速・高効率に活性中心に伝達することが知られている。EETの反応速度は励起エネルギーの揺らぎが小さ過ぎても大き過ぎても低下するが、光捕集アンテナではEETの反応速度が最大になるように励起エネルギーの揺らぎが最適化されている。しかし、生体分子の微細な構造や揺らぎがどのように高速・高効率なEETを制御しているか全く明らかになっていない。
    そこで本研究では、分子レベルで励起エネルギーの揺らぎを解析するために、色素の励起エネルギーを高精度・低コストに計算可能な手法(MMSIC法)を開発した。MMSIC法では、分子力場と修正Shepard内挿法を組み合わせることで、色素の基底状態と励起状態を表すポテンシャル関数を高精度・低コストに生成する。修正Shepard内挿法を色素の構造だけでなく、色素にかかる静電ポテンシャルにも適用することで、周囲の生体分子の揺らぎの影響も取り込む。MMSIC法により必要な量子化学計算の計算コストを大幅に削減し、様々な構造で励起エネルギーを効率的に計算可能となる。
    このMMSIC法を光捕集アンテナの1つであるFenna-Matthews-Olsonタンパク中の色素バクテリオクロロフィル aに適用した。MMSIC法により励起状態のポテンシャルエネルギーの計算を精度を保ったまま約100万倍加速することに成功しただけでなく、シミュレーションにより得られた励起エネルギーの揺らぎを表すSpectral Densityは実験から得られたものとよく一致した。また、EETダイナミクスに重要なSpectral Densityの低振動数部分がほぼ色素の分子内振動によるものと明らかにした。

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  13. タンパク質内における励起状態反応ダイナミクスの理論的解明

    研究課題/研究課題番号:11J00238  2011年 - 2012年

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    東 雅大

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    近年、光収穫アンテナにおける励起エネルギー移動ダイナミクスは注目を集めており、実験的にも理論的にも非常によく研究されている。この励起エネルギー移動ダイナミクスを分子レベルで理論的に取り扱うためには、光収穫アンテナに含まれる発色団の電子励起状態を正確に取り扱わなければならない。昨年度の研究結果から代表的な発色団の1つであるバクテリオクロロフィルa(BChl a)の電子励起状態は、用いる電子状態計算手法に大きく依存することが判明した。そこで、適切な電子状態計算手法を見つけるために、溶液中のBChl aの電子励起状態について、電子状態計算と分子動力学シミュレーションを組み合わせて研究を行った。
    BChl aの第一電子励起状態は、様々な溶媒中で吸収エネルギーがほとんど変化しないが、アルコール溶液中では、アルコールのアルキル基が大きくになるにつれて僅かに吸収エネルギーが減少することが知られている。しかし、何故そうなるのかはよく分かっていない。そこで、電子状態計算と分子動力学シミューレションを効率良く結びつけ、揺らぐ溶媒の平均場の元で溶質の構造を最適化出来るQM/MM-RWFE-SCF法を用いて、トリエチルアミン、メタノール、1-プロパノール中で吸収エネルギーの計算を行った。その結果、B3LYPやCAM-B3LYPなどの既存の電子状態計算手法では、基底状態と励起状態の双極子モーメントの差を過少あるいは過大評価してしまうため、実験の傾向を再現出来ないことが分かった。そこで、CAM-B3LYPに含まれるパラメータを最適化し、実験結果を再現することに成功した。また、BChl aの吸収エネルギーについて溶媒依存性がほとんど見られないのは、基底状態から第一励起状態に遷移した時の双極子モーメントの減少による不安定化と負電荷がカルボニル基に飛ぶことによる溶媒との水素結合の安定化が打ち消し合うことによって、溶質-溶媒間の相互作用が基底状態と励起状態でほぼ一定に保たれるためであることが分かった。

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