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154 results on '"Nakamuro, Takayuki"'

1. Unveiling a crystal's entropy of disorder via electron diffraction. A statistical mechanics approach

Author

Liu, Dongxin, Elishav, Oren, Fu, Jiarui, Sakakibara, Masaya, Yamanouchi, Kaoru, Hirshberg, Barak, Nakamuro, Takayuki, and Nakamura, Eiichi

Subjects
Physics - Chemical Physics
Abstract

Upon melting, the molecules in the crystal explore numerous configurations, reflecting an increase in disorder. The molar entropy of disorder can be defined by Bolzmann's formula dSd = Rln(Wd) where Wd is the increase in the number of microscopic states, so far inaccessible experimentally. We found that the Arrhenius frequency factor A of the electron diffraction signal decay provides Wd via an experimental equation A = AINTWd where AINT is an inelastic scattering cross-section. The method connects Clausius and Boltzmann experimentally and supplements the Clausius approach, being applicable to a femtogram quantity of thermally unstable and biomolecular crystals. The data also showed that crystal disordering and crystallization of melt are reciprocal, both governed by the entropy change, but manifesting in opposite directions., Comment: 18 pages, 5 figures, 1 table

Published
2024

2. Ionization and electron excitation of fullerene molecules in a carbon nanotube. A variable temperature/voltage transmission electron microscopic study

Author

Liu, Dongxin, Kowashi, Satori, Nakamuro, Takayuki, Lungerich, Dominik, Yamanouchi, Kaoru, Harano, Koji, and Nakamura, Eiichi

Subjects
Physics - Chemical Physics, Condensed Matter - Materials Science
Abstract

There is increasing attention to chemical applications of transmission electron microscopy, which is often plagued by radiation damage. The damage in organic matter predominantly occurs via ionization (radiolysis). Although radiolysis is highly important, previous studies on radiolysis have largely been descriptive and qualitative, lacking in such fundamental information as the product structure, the influence of the energy of the electrons, and the reaction kinetics. We need a chemically well-defined system to obtain such data, and have chosen as a model a variable-temperature and variable-voltage (VT/VV) study of the dimerization of a van der Waals dimer [60]fullerene (C60) to C120 in a carbon nanotube (CNT) as studied for individual reaction events at atomic resolution. We report here the identification of five reaction pathways that serve as mechanistic models of radiolysis damage. Two of them occur via a radical cation of the specimen generated by specimen ionization, and three involve singlet or triplet excited states of the specimen, as initiated by electron excitation of the CNT followed by energy transfer to the specimen. The pathways were distinguished by the pre-exponential factor and the Arrhenius activation energy. The prototypal reaction path is the radical cation reaction that we saw at <200 K, but, at >350 K, the excited-state reactions dominate. The results illustrate the importance of VT/VV kinetic analysis in the studies of radiation damage, and show that chemical ionization and electron excitation are inseparable but different mechanisms of radiation damage, which has so far been classified loosely under the single term "ionization.", Comment: 23 pages, 9 figures

Published
2021
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3. Atomic-Number (Z)-Correlated Atomic Sizes for Deciphering Electron Microscopic Molecular Images

Author

Xing, Junfei, Takeuchi, Keishi, Kamei, Ko, Nakamuro, Takayuki, Harano, Koji, and Nakamura, Eiichi

Subjects
Condensed Matter - Materials Science
Abstract

With the advent of atomic-resolution transmission electron microscopy (AR-TEM) achieving sub-{\AA}ngstrom image resolution and submillisecond time resolution, an era of visual molecular science where chemists can visually study the time evolution of molecular motions and reactions at atomistic precision has arrived. However, the appearance of experimental TEM images often differs greatly from that of conventional molecular models, and the images are difficult to decipher unless we know in advance the structure of the specimen molecules. The difference arises from the fundamental design of the molecular models that represent atomic connectivity and/or the electronic properties of molecules rather than the nuclear charge of atoms and electrostatic potentials that are felt by the e-beam in TEM imaging. We found a good correlation between the atomic number (Z) and the atomic size seen in TEM images when we consider shot noise in digital images. We propose here Z-correlated (ZC) atomic radii for modeling AR-TEM images of single molecules and ultrathin crystals, with which we can develop a good estimate of the molecular structure from the TEM image much more easily than with conventional molecular models. Two parameter sets were developed for TEM images recorded under high-noise (ZCHN) and low-noise (ZCLN) conditions. The new molecular models will stimulate the imaginations of chemists planning to use AR-TEM for their research., Comment: 27 pages, 6 figures

Published
2021
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13. Bottom-up design of peptide nanoshapes in water using oligomers of N-methyl-L/D-alanine

Author

Morimoto, Jumpei, primary, Shiratori, Yota, additional, Yokomine, Marin, additional, Ueda, Takumi, additional, Nakamuro, Takayuki, additional, Takaba, Kiyofumi, additional, Maki-Yonekura, Saori, additional, Umezawa, Koji, additional, Miyanishi, Koichiro, additional, Fukuda, Yasuhiro, additional, Watanabe, Takumu, additional, Mizukami, Wataru, additional, Takeuchi, Koh, additional, Yonekura, Koji, additional, Nakamura, Eiichi, additional, and Sando, Shinsuke, additional

Published
2023
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16. Ligand‐Controlled Regiodivergence in Nickel‐Catalyzed Vinylcyclopropane Rearrangement.

Author

Irifune, Keiichi, Yamazaki, Ken, Nakamuro, Takayuki, Murakami, Masahiro, and Miura, Tomoya

Subjects
DENSITY functional theory, VINYLCYCLOPROPANES, CYCLOPENTENES
Abstract

A ligand‐controlled regiodivergence in Ni‐catalyzed rearrangement of vinylcyclopropanes to 1,4‐ or 1,5‐disubstituted cyclopentenes is reported. The 1,4‐ or 1,5‐disubstituted cyclopentene is selectively obtained depending on the choice of ligands. Detailed kinetic studies and density functional theory calculations on the catalytic cycle revealed that the product selectivity is determined at the reductive elimination step from the six‐membered η1‐allyl intermediate. [ABSTRACT FROM AUTHOR]

Published
2023
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21. Alternating Heterochiral Supramolecular Copolymerization

Author

Ueda, Michihisa, primary, Aoki, Tsubasa, additional, Akiyama, Takayoshi, additional, Nakamuro, Takayuki, additional, Yamashita, Keitaro, additional, Yanagisawa, Haruaki, additional, Nureki, Osamu, additional, Kikkawa, Masahide, additional, Nakamura, Eiichi, additional, Aida, Takuzo, additional, and Itoh, Yoshimitsu, additional

Published
2021
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34. High-speed imaging and quantitative analysis of nonequilibrium stochastic processes using atomic resolution electron microscopy

Author

Nakamuro, Takayuki

Abstract

Chemical phenomena are inherently complex and stochastic, making them difficult to fully understand using conventional ensemble-averaged analytical methods. These methods primarily capture long-lived species and common structural features, limiting the study of transient intermediates and minute structural characteristics. In contrast, single-molecule time-resolved analysis using advanced microscopy techniques, particularly transmission electron microscopy, offers high spatial and temporal resolution to observe the nonequilibrium dynamics of molecules and their assemblies. This account discusses the authors’ research on developing transmission electron microscopy techniques to visualize intricate and transient interactions within molecular systems, enhancing the understanding of chemical phenomena at atomic and molecular levels.Graphical AbstractChemical phenomena are complex and stochastic, challenging traditional ensemble-averaged methods like nuclear magnetic resonance and X-ray diffraction. These techniques focus on long-lived species, missing transient intermediates. Single-molecule analysis, particularly via advanced TEM, offers high spatial and temporal resolution to observe nonequilibrium molecular dynamics. This account reviews the authors’ TEM techniques for visualizing transient molecular interactions and advancing chemical understanding.

Published
2024
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35. Chiral Macrocycles Having C3 Symmetry Resulting from Orientation of Thiophene Rings.

Author

Miura, Tomoya, Nakamuro, Takayuki, Ishihara, Yumi, Nagata, Yuuya, and Murakami, Masahiro

Subjects
*ELECTRONIC spectra, *SYMMETRY, *CHIRALITY, *MONOMERS, *ASYMMETRIC synthesis
Abstract

An chiral RhII‐catalyzed cyclooligomerization reaction of thiophenes having triazolyl and vinyl substituents at the 2‐ and 4‐positions was studied. Structurally interesting cyclic trimers, having chirality that is ascribed only to the orientation of the 2,4‐disubstituted thiophene rings, are obtained. The 2,4‐disubstitution of the starting thiophene monomer allows production of each of the enantiomers. The observed electronic circular‐dichroism spectra are in accord with those simulated by density‐functional theory calculations. [ABSTRACT FROM AUTHOR]

Published
2020
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38. Deep‐red Emitting Copper(I) Indenediyltrisphosphine Complexes with Minimized Skeletal Vibrations and Configurational Disorder.

Author

Fukuma, Shota, Fu, Jiarui, Nakamuro, Takayuki, Shang, Rui, and Nakamura, Eiichi

Abstract

The full width at half maximum (FWHM) of emission spectra, which plays an important role in determining color purity, may not always receive sufficient attention in the design of emissive materials. Particularly for the red emitter, the traditional focus has been on emission maxima, yet broad FWHM values can significantly change the perceived color. For example, the red color (λem=616–677 nm) emitted from reported Cu(I) complexes is perceived as orange to yellow if FWHM is large. To reduce FWHM, we incorporated a strained and rigid metalaphosphadicyclopenta[a,f]pentalene motif into Cu(I) complexes using trisphosphine ligands featuring a 1H‐indene‐2,3‐diyl backbone (ITP). Herein, we present the synthesis, structure, and emission properties of ITP‐MX and the congeners, showcasing genuinely deep‐red emission with narrow FWHM values of 56 nm. These materials exhibit color coordinates close to pure red on the CIE diagram, unlike reported broader‐emitting counterparts. Measurement of the entropy of disorder of the emissive crystal by a recently reported statistical mechanical method revealed a quantitative correlation between FWHM and the increase in the number of microstates (the degree of freedom) of the crystals and suggested that mechanical stress can increase the entropy of the crystal, which results in emission broadening. [ABSTRACT FROM AUTHOR]

Published
2024
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40. Spiro-Conjugated Carbon/Heteroatom-Bridged p-Phenylenevinylenes: Synthesis, Properties, and Microcrystal Electron Crystallographic Analysis of Racemic Solid Solutions

Author

Hamada, Hiroyoshi, Nakamuro, Takayuki, Yamashita, Keitaro, Yanagisawa, Haruaki, Nureki, Osamu, Kikkawa, Masahide, Harano, Koji, Shang, Rui, and Nakamura, Eiichi

Abstract

Two planar conjugated systems perpendicularly connected via a quaternary sp3carbon center interact with each other through the spiro linkage. Such spiro-conjugated p-systems show useful optoelectronic properties. Herein, we present a unified modular synthetic strategy for a series of chiral spiro-conjugated carbocycles utilizing a C–H activation reaction as a key step. The chiral spiro-conjugated carbon/heteroatom-bridged p-phenylenevinylenes (spiro-Xcompounds) possessing C, O, N, S, and SO2as bridging groups are thermally stable, and exhibit circular dichroism and circularly polarized luminescence (CPL). Spiro-SO2undergoes intramolecular charge transfer. It exhibits CPL with a large |glum| of 2.1 × 10-3and shows rarely reported solvatofluorochromism for CPL luminophores. The racemic spiro-Ocompound solidifies as a racemic solid solution (or pseudoracemate). It did not form X-ray-quality crystals. This therefore provided us with a unique opportunity to examine the potential of the microcrystal electron crystallography popularized recently. The diffraction data sets, merged over many micrometer-sized solid particles, afforded the 3D molecular structure and the crystal packing of the spiro compound.Spiro-conjugated carbon/heteroatom-bridged p-phenylenevinylenes were synthesized via a modular synthetic route, utilizing C–H activation as a key step. They exhibited circularly polarized luminescence, and formed racemic solid solutions (or pseudoracemates) as elucidated by microcrystal electron crystallography.

Published
2020
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