Search

This work was partly supported by a JSPS Grants-in-Aid for Scientific Research (JP19K15524) and a MEXT Grants-in-Aid for Scientific Research on Innovative Areas (JP21H00014, JP21H05419, and JP22H04800). Some of the computations were performed using computer facilities at the Research Institute for Information Technology, Kyushu University, and the Research Center for Computational Science, Okazaki, Japan (project:22-IMS-C122). We would like to thank Editage (www.editage.com) for English language editing.

Dimerization energies of amino acids in solution are investigated via first-principles calculations, and the results provide molecular insights into the enantioselectivity of their crystals.

New iron(ii) complex exhibiting the proton transfer coupled spin transition and easy single crystal formation was developed. The change of nuclear position with the spin transition was successfully detected by the neutron diffraction measurement.

We propose a new transmit diversity technique for frequency shift keying (FSK). The main idea behind our proposed scheme is to exploit the orthogonality between FSK carriers in order to render signals transmitted from different antennas orthogonal at the receiver, which results in full diversity. Since the proposed scheme achieves antenna orthogonality within one time unit while the well-known Alamouti space-time block code (STBC) needs two time units, it succeeds to be more robust against time-selectivity of the channels than the STBC without deteriorating peak-to-average power ratio (PAPR) of the signal. Simulation demonstrates that the proposed scheme has an error floor that is ten times lower than the STBC over time-selective channels.

The preferential synthesis or destruction of a single enantiomer by ultraviolet circularly polarized light (UV-CPL) has been proposed as a possible triggering mechanism for the extraterrestrial origin of homochirality. Herein, we investigate the photoabsorption property of propylene oxide (

Anhydrous organic crystalline materials incorporating imidazolium hydrogen succinate (Im-Suc), which exhibit high proton conduction even at temperatures above 100 °C, are attractive for elucidating proton conduction mechanisms toward the development of solid electrolytes for fuel cells. Herein, quantum chemical calculations were used to investigate the proton conduction mechanism in terms of hydrogen-bonding (H-bonding) changes and restricted molecular rotation in Im-Suc. The local H-bond structures for proton conduction were characterized by vibrational frequency analysis and compared with corresponding experimental data. The calculated potential energy surface involving proton transfer (PT) and imidazole (Im) rotational motion showed that PT between Im and succinic acid was a rate-limiting step for proton transport in Im-Suc and that proton conduction proceeded via the successive coupling of PT and Im rotational motion based on a Grotthuss-type mechanism. These findings provide molecular-level insights into proton conduction mechanisms for Im-based (or -incorporated) H-bonding organic proton conductors.

International audience; Enantiomeric excesses of l-amino acids have been detected in meteorites; however, their molecular mechanism and prebiotic syntheses are still a matter of debate. To elucidate the origin of homochirality, alanine and the chiral precursors formed in prebiotic processes were investigated with regard to their stabilities among their isomers by employing the minimum energy principle, namely, the abundancy of a molecule in the interstellar medium is directly correlated to the stability among isomers. To facilitate the search for possible isomers, we developed a new isomer search algorithm, the random connection method, and performed a thorough search for all the stable isomers within a given chemical formula. We found that alanine and most of its precursors are located at higher energy by more than 5.7 kcal mol−1, with respect to the most stable isomer that consists of a linear-chain structure, whereas only the 2-aminopropanenitrile is the most stable isomer among all others possible. The inherent stability of the α-amino nitrile suggests that the 2-aminopropanenitrile is the dominant contribution in the formation of the common enantiomeric excess over α-amino acids.

Poly(vinylphosphonic acid)-imidazole (PVPA-xIm) exhibits high proton conductivity above 100 °C. The high proton conductivity of PVPA-2Im depends on the molecular motions of Im. Molecular dynamics s...

A proton-electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi-step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric-like arrangement.

The composite materials of acidic polymers and imidazole (Im) exhibit good high-proton conduction, making them potentially useful in proton-exchange membrane fuel cells. The proton conduction mechanism must be clearly elucidated for the design of future high proton-conduction materials. This study examines the local hydrogen-bonding structures and dynamics of Im for proton-conducting poly(vinylphosphonic acid)-Im (PVPA-xIm) composites by using molecular dynamics simulations. Radial distribution functions (RDFs) characterize the hydrogen bonds between Im or imidazolium cation (ImH+) and phosphonic acid (PA) group and among Im molecules. RDFs and diffusion coefficients suggest that the intercalation of Im to PVPA reduces Im mobility because of the interaction between Im and PA groups. However, similar to pure Im, the amount of Im with fast rotational motions increases as the amount of Im increases. Our study leads us to conclude that long-range proton transport occurs through the hydrogen-bonding network of...

The selective oxidation of CH4 using O2 is one of the most attractive subjects as an elusive target reaction. Ohkubo and Hirose recently reported that chlorine dioxide radical (ClO2•), which is gen...

Indium-doped zinc oxide (IZO) is an n-type semiconductor and an alternative to indium tin oxide, which is widely used in transparent electrodes. In order to design and prepare optical and electrical functional materials with IZO, it is important to understand the effects of indium (In) doping on zinc oxide (ZnO). In this study, the local structures and electronic properties of IZO were investigated by first-principle calculations. The formation energies of IZO with the substitution of an In atom in the place of a Zn atom were determined to be less than those of IZO with the intercalation of In atoms into interstitial sites in ZnO regardless of the amount of In atoms. From analyzing calculated band structures for the substitution and intercalation models, the relationship between the effect of In dopant and the conductivity of IZO is discussed.

Formation of an active oxygen species at the dicopper site of pMMO is studied by using density functional theory (DFT) calculations. The role of the amino acid residues of tyrosine (Tyr374) and glutamate (Glu35) located in the second coordination sphere of the dicopper site is discussed in detail. The phenolic proton of the tyrosine residue is transferred to the Cu2O2 core in a two-step manner via the glutamate residue, and an electron is directly transferred to the Cu2O2 core. These proton- and electron-transfer processes induce the O-O bond cleavage of the μ-η2:η2-peroxodicopper(II) species to form the (μ-oxo)(μ-hydroxo)CuIICuIII species, which is able to play a key role of methane hydroxylation at the dicopper site of pMMO ( Inorg. Chem. 2013 , 52 , 7907 ). This proton-coupled electron-transfer mechanism is a little different from that in tyrosinase in that the proton of substrate tyrosine is directly transferred to the dicopper site ( J. Am. Chem. Soc. 2006 , 128 , 9873 ) because there is no proton acceptor in the vicinity of the dicopper site of tyrosinase. The rate-determining step for the formation of the (μ-oxo)(μ-hydroxo)CuIICuIII species is determined to be the O-O bond cleavage. These results shed new light on the interpretation of the role of the tyrosine and glutamate residues located in the second coordination sphere of the dicopper site of pMMO.

An important technique to realize novel electron- and/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex-a phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

While hydrogenase and photosystem II enzymes are known to oxidize H2 and H2O, respectively, a recently reported iridium aqua complex [IrIII(η5-C5Me5){bpy(COOH)2}(H2O)]2+ is able to oxidize both of ...

Much recent attention has been focused on the structure and reactivity of transition-metal superoxide complexes, among which mononuclear copper(II)-superoxide complexes are recognized as key reactive intermediates in many biological and abiological dioxygen-activation processes. So far, several types of copper(II)-superoxide complexes have been developed and their electrophilic reactivity has been explored in C–H and O–H bond activation reactions. Here we demonstrate that a mononuclear copper(II)-(end-on)superoxide complex supported by a N-[(2-pyridyl)methyl]-1,5-diazacyclooctane tridentate ligand can induce catalytic C–C bond formation reaction between carbonyl compounds (substrate) and the solvent molecule (acetone), giving β-hydroxy-ketones (aldol). Kinetic and spectroscopic studies at low temperature as well as DFT calculation studies support a nucleophilic reactivity of the superoxide species toward the carbonyl compounds, providing new insights into the reactivity of transition-metal superoxide species not only in biological oxidation reactions but also in synthetic organic chemistry. Copper(II)-superoxide complexes are known to behave as electrophiles but there are few examples of nucleophilic reactivity by such species. Here a mononuclear copper(II)-superoxide species is shown to promote simple aldol reactions, and this reactivity is found to be sensitive to minor changes to the ligand structure.

In the past decades, quantum chemical calculations such as density functional theory (DFT) have played important roles in catalytic reactions, which provide important guidelines and practical strategies for rational catalytic design. Because direct conversion of methane to methanol is a major challenge in catalysis, theoretical approach requires for the catalyst design in methane hydroxylation. In the present review, examples are given of applications of DFT to the reaction mechanisms and successful predictions of methane hydroxylation catalyzed by homogeneous catalysts and developed by the interplay with theory and experiment. Platinum complexes as organometallic catalysts and diiron, dicopper, and tricopper complexes as biomimetic catalysts are introduced.

We propose extending Bohmian mechanics (BM) with the moving particle semi-implicit method, a particle method for uncompressed fluids. The application of this method prevents the node of the Bohm quantum potential from breaking numerical calculations while maintaining a low calculation cost. We validated our extended method by comparing our results with those from the conventional method for a one-dimensional harmonic oscillator, Gaussian barrier and rectangular barrier. The proposed method was found to simulate the temporal changes in the probability density for a rectangular barrier. In addition, the relational equation obtained by this method reveals an interesting correspondence between the pressure of a classical fluid and the Bohm quantum potential.

Stable square planar organocopper(III) complexes (CuNCC2, CuNCC4, and CuBN) supported by carbacorrole-based tetradentate macrocyclic ligands with NNNC coordination cores were synthesized, and their structures were elucidated by spectroscopic means including X-ray crystallographic analysis. On the basis of their distinct planar structures, X-ray absorption/photoelectron spectroscopic features, and temperature-independent diamagnetic nature, these organocopper complexes can be preferably considered as novel organocopper(III) species. The remarkable stability of the high-valent Cu(III) states of the complexes stems from the closed-shell electronic structure derived from the peculiar NNNC coordination of the corrole-modified frameworks, which contrasts with the redox-noninnocent radical nature of regular corrole copper(II) complexes with an NNNN core. The proposed structure was supported by DFT (B3LYP) calculations. Furthermore, a π-laminated dimer architecture linked through the inner carbons was obtained from the one-electron oxidation of CuNCC4. We envisage that the precise manipulation of the molecular orbital energies and redox profiles of these organometallic corrole complexes could eventually lead to the isolation of yet unexplored high-valent metal species and the development of their organometallic reactions.

This paper proposes a new physical layer architecture based on orthogonal frequency-division multiplexing (OFDM) for uplink multiple access. It aims at high reliability with fixed decoder latency targeting emergent low-latency wireless applications, such as transmission of control information in machine-to-machine (M2M) and device-to-device (D2D) communications. Our proposed system is based on the judicious combination of subcarrier hopping and super-orthogonal convolutional codes for achieving high coding gain and frequency diversity, together with Golay complementary sequences for low peak-to-average power ratio (PAPR) signaling. The low PAPR nature improves the power efficiency at a power amplifier (PA) and thus contributes to the transmission range enhancement. Furthermore, by introducing non-orthogonality among users through the assignment of the same set of subcarriers to multiple users, the overall spectral efficiency can be improved. In order to suppress multiple access interference caused by the non-orthogonal overlap of users, multiuser detection (MUD) is employed. Theoretical expressions of approximate bit error rate for the proposed system with MUD are also developed. Numerical results reveal that our proposed system achieves higher reliability and higher spectral efficiency than the conventional orthogonal frequency-division multiple access (OFDMA)-based system.

Anhydrous organic proton conductors have attracted considerable attention as potential candidates for next-generation solid electrolytes in fuel cells. For further material development, a clear understanding of the conduction mechanism is essential, which can be accessed using crystalline materials as model systems. Recently, it has been reported that single-crystalline imidazolium hydrogen succinate (Im-Suc) exhibits a structural transition with the orientational disordering of imidazolium, which promotes proton conduction. In this study, we investigated the effects of mechanical grinding on the phase behavior and anhydrous proton conductivity of Im-Suc by comparing single-crystalline and mechanically crushed powder samples to understand the connection between ideal single crystals and highly disordered polymer systems. Thermal and structural analyses showed that grinding suppressed the structural transition through the introduction of structural disorder and mechanical stress. Moreover, the anhydrous proton conductivity was drastically enhanced with a significant decrease in activation energy in the low-temperature regime. Infrared spectroscopy indicated that the imidazolium dynamics was modulated by mechanical grinding. These findings reveal the possibility of improving the performance of anhydrous organic proton conductors and modulating their molecular dynamics properties and conduction mechanisms by simple mechanical grinding.

A cost-free modification of second-order electron propagator theory (ex-SCS-EP2) to improve the description of ionization energies based on spin-component-scaled approximation is proposed. The relaxation part (PRX) and correlation part (PRM) in second-order self-energy are partitioned into parallel- and anti-parallel-spin component then scaled separately. The scaling factors are optimized with 23 valence orbital energies and results shown that ex-SCS-EP2 performs significantly better than regular EP2, SCS-EP2 and OVGF with 0.22 eV of mean absolute error (MAE) and 0.11 eV of mean absolute deviation (MAD). The effects of SCS parameters on self-energy are also examined to ensure better description in total correlation energy.

To improve the unrestricted second-order Moller-Plesset (UMP2) method, we propose a method in which spin contamination is eliminated due to spin adaptation of the double excitation space based on the unitary group approach (UGA), because the UMP2 calculations intrinsically involve spin contamination from the double excitation space. Numerical results for the activation energies of several radical reactions show that this UGA-UMP2 method offers substantial improvement over the UMP2 method. Furthermore, the UGA-SUMP2 method, which completely eliminates the spin contamination from both the reference and excitation space present in UMP2 calculations, is also formulated.

Formic acid (HCOOH) is a suitable hydrogen storage material because of its high gravimetric and volumetric H2 capacities. Although H2 is produced by the thermal decomposition of HCOOH (HCOOH → H2 + CO2, dehydrogenation), the production of water and carbon monoxide (HCOOH → H2O + CO, dehydration) is the major pathway in HCOOH decomposition despite the thermodynamic favorability of the dehydrogenation process over the dehydration process. A large number of experimental and theoretical studies have suggested that both processes are competitive or that the dehydrogenation process has a lower activation energy in HCOOH decomposition. In the present work, we revisit the factors hindering the progress of the dehydrogenation process, using a whole chemical reaction network based on the graph theory. The calculated chemical reaction network shows that the factor controlling the dehydrogenation and dehydration processes is simple and fundamental and can be explained by the oxidation number of carbon and the betweenness centrality. Based on this understanding of the factors hindering the progress of dehydrogenation, the advantage of the dehydration process in HCOOH decomposition is discussed.

While hydrogenase and photosystem II enzymes are known to oxidize H

金沢大学ナノマテリアル研究所 / 金沢大学理工研究域数物科学系, In order to simulate Auger electron spectra (AES), we propose the use of the two-electron Dyson propagator with the shifted denominator approximation (SD2). The double ionization potentials (DIPs) of molecules calculated using the SD2 method have shown good agreement with experimental data. This method can be used to calculate each DIP separately, and reducing the matrix dimensionality into that of only a two-hole configurations. We carried out AES simulations of water (H2O), ethylene (C2H4), and formaldehyde (H2CO) molecules and compared with the observed spectra. Furthermore Auger line shapes of glycine and hydrated glycine molecules were simulated, it found out that the peaks of nitrogen K-LL Auger were broadened due to hydration. From these results, we conclude that the SD2 method is very useful for the calculation of DIPs to investigate the properties of a double ionized molecule. © 2016 Elsevier B.V. All rights reserved., Embargo Period 24 months

Bit-interleaved coded modulation (BICM), together with orthogonal frequency-division multiplexing (OFDM) signaling, has found its application in many recent wireless standards. BICM–OFDM systems are able to simplify the design of coding and modulation with various information rates for link adaptation. Furthermore, they provide robustness against frequency-selective fading channels. The combination of BICM–OFDM and convolutional code turns out to be attractive as it allows for low complexity and low latency decoding architecture at the receiver. It has been known that the performance of convolutionally coded BICM–OFDM systems depends on the bit interleaver structure, but little attention has been paid for its theoretical performance analysis. In this paper, we develop a novel theoretical expression for approximate BER of convolutionally coded BICM–OFDM that can be used for evaluating the performance of a given bit interleaver structure, and propose a design guideline for its optimization. Numerical comparisons between the optimized interleaver that satisfies our guideline and other random and structured interleavers demonstrate the validity of our design criterion.

金沢大学ナノマテリアル研究所 / 金沢大学理工研究域数物科学系, This work examined the hydride transfer processes during the reduction of formaldehyde by LiAlH4 or LiBH4, including investigations of the geometries, solvent effects and charge transfer processes along the reaction coordinate, using density functional theory (DFT). The energy and geometry results demonstrate that the transition state (TS) structure for the LiAlH4-formaldehyde complex is reactant-like, while the structure generated by LiBH4 has a product-like geometry, consistent with the Hammond postulate. From a charge density analysis, we also found that both complexes undergo the same essential hydride transfer mechanism, which consists of: (1) single electron transfer to the carbonyl carbon, (2) formation of a bridge bond (X-H-C; X=Al or B) and (3) hydrogen transfer driven by electron transfer. Subsequently, in a fourth step, a single electron flows through the X-H-C bond during transfer of the hydrogen, such that hydrogen atom or proton-coupled electron transfer occurs. In both systems, the presence of tetrahydrofuran as a solvent affects the structure and energy values during the reaction, but not the charge transfer characteristics. We propose that the rate-determining steps during hydride transfer when employing LiAlH4 and LiBH4 are one electron transfer to the carbonyl carbon and B-H bond dissociation, respectively. © 2015 Elsevier B.V., Embargo Period 24 months

The dihydrogenated porphycene cobalt(II) complex was synthesized and electrochemical experiments were carried out. The one-electron reduction of the complex proceeded at the central metal to afford the Co(I) species; in contrast, for the non-hydrogenated porphycene cobalt(II) complex, the one-electron reduction gave the ligand reduced radical anion species. The reactivity of the one-electron reduced species with alkyl halides showed clear differences between the complexes. Hydrogenation of the β-position of the porphycene makes it possible to generate a central cobalt reduced species possessing a higher reactivity than the ligand reduced radical anion species.

Composite materials of acidic polymers and basic molecules have high proton-conductivity. Understanding the proton conduction mechanism of the composite materials, which depends on hydrogen bond characteristics, is an important task for developing materials with high proton-conductivity. This work is focused on poly(vinylphosphonic acid)-imidazole and alginic acid-imidazole as examples of composite materials of acidic polymers and basic molecules and examines the local structure and hydrogen bond characteristics of imidazole (Im) molecules in composite materials using density functional theory. The results show that Im molecules interact strongly with polymeric acids in these composite materials and that the interaction energy increases with the increase in the number of Im molecules. The rotational motion of Im molecules occurs in the segment where only Im molecules without excess protons are hydrogen-bonded to each other. The calculation results for the various segments, which depend on the hydrogen bonding environment, show that the proton conduction process in composite materials consists of the following steps: proton transfer in the segment where Im molecules interact with polymeric acids, proton transfer in the segment where Im molecules are affected by excess protons, and Grotthuss diffusion with reorientation of Im molecules in the segment where only Im molecules without excess protons are bonded to each other.

We propose a simple construction method of the potential energy surface based on diabatic model for proton transfer in molecular pairs. Assuming two-state valence bond electronic wave functions as a diabatic basis, the diagonal and non-diagonal matrix elements in diabatic potential of water, ammonia, and imidazole pairs were obtained. The validity of the construction procedure was confirmed by comparing two adiabatic potentials: one was transformed from the obtained diabatic potential and another was calculated by DFT calculation. Diabatic potentials were also obtained using fewer reference points than conventional methods at various intermolecular distances. Finally, we discuss the resulting diabatic potential and non-diagonal elements in detail.