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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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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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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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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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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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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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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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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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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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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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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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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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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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.

DOI： 10.1063/5.0122326

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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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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.

DOI： 10.1246/cl.220215

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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.

DOI： 10.1063/5.0092834

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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.

DOI： 10.1021/acs.joc.2c00603

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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.

DOI： 10.1021/jacs.2c01705

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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.

DOI： 10.1021/acs.jpcb.2c00326

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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.

DOI： 10.1063/5.0083395

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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.

DOI： 10.1039/d2cp01699k

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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.

DOI： 10.1039/d0cp06604d

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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.

DOI： 10.1002/jcc.26703

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

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.

DOI： 10.1016/j.foodchem.2021.130418

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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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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.

DOI： 10.1063/5.0010943

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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.

DOI： 10.1063/5.0008903

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DOI： 10.1021/acs.jpcb.9b11080

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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.

DOI： 10.1021/acs.jpcb.9b07456

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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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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).

DOI： 10.3390/md17060353

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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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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.

DOI： 10.1007/978-981-13-9753-0_12

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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.jpcb.8b07967

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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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出版者・発行元：Elsevier {BV}  

DOI： 10.1016/j.chemphys.2018.03.012

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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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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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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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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.

DOI： 10.1074/jbc.RA118.001817

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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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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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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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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.

DOI： 10.1016/j.cplett.2017.04.082

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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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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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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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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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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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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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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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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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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.

DOI： 10.1021/jp507259g

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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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/jp310621p

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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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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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ct8000816

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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/ct800004y

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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.

DOI： 10.1016/j.cplett.2007.02.044

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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.

DOI： 10.1063/1.2715941

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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/jp0581429

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