Browsing by Author "Fujii, Asuka"

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An infrared spectroscopic study on proton transfer from CH bonds in ionized dimers of cyclic ethers
(2018-03-07)
Xie, Min
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Matsuda, Yoshiyuki
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Fujii, Asuka
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應用化學系
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應用化學系分子科學碩博班
Infrared (IR) spectroscopy of neutral and cationic dimers of tetrahydrofuran (THF) and tetrahydropyran (THP) is carried out to investigate isomerization reactions of these dimers following ionization. In the neutral state, both the THF and THP dimers tend to form the stacking structures bound essentially by dispersion. After ionization, both of these dimer cations form the proton transferred structures, in which the proton of the C alpha H bond is intermolecularly transferred and shared between the oxygen atoms. Along with the pseudorotation of the five-member ring, the barrierless proton transfer from CH occurs in the ionized THF dimer, and the dimer finally forms the proton transferred structure. In the case of the THP dimer cation, the barrierless intracluster proton transfer occurs with the conformational change of the proton donor site because the acidic CH site of the THP cation strongly depends on its conformation. These isomerization processes involving proton transfer from CH are discussed based on IR spectroscopy and theoretical reaction path searches. Published by AIP Publishing.
An integrated experimental and theoretical reaction path search: analyses of the multistage reaction of an ionized diethylether dimer involving isomerization, proton transfer, and dissociation
(2018-06-07)
Matsuda, Yoshiyuki
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Xie, Min
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Fujii, Asuka
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應用化學系
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應用化學系分子科學碩博班
An ionization-induced multistage reaction of an ionized diethylether (DEE) dimer involving isomerization, proton transfer, and dissociation is investigated by combining infrared (IR) spectroscopy, tandem mass spectrometry, and a theoretical reaction path search. The vertically-ionized DEE dimer isomerizes to a hydrogen-bonded cluster of protonated DEE and the [DEE-H] radical through barrierless intermolecular proton transfer from the CH bond of the ionized moiety. This isomerization process is confirmed by IR spectroscopy and the theoretical reaction path search. The multiple dissociation pathways following the isomerization are analyzed by tandem mass spectrometry. The isomerized cluster dissociates stepwise into a [protonated DEE-acetaldehyde (AA)] cluster, protonated DEE, and protonated AA. The structure of the fragment ion is also analyzed by IR spectroscopy. The reaction map of the multistage processes is revealed through a harmony of these experimental and theoretical methods.
Effects of solvent molecules on hemi-bonded (CH3SH)(2)(+): infrared absorption of [(CH3SH)(2)-X](+) with X = H2O, (CH3)(2)CO, or NH3 and (CH3SH)(n)(+) (n=3-6)
(2019-08-07)
Xie, Min
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Tsai, Huei-Ru
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Fujii, Asuka
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Lee, Yuan-Pern
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交大名義發表
Three-electron two-center (3e-2c) hemi-bonds play important roles in the oxidation and electron transport of proteins and are implicated to be involved in some neurodegenerative diseases. Our previous investigations on infrared (IR) spectra of (CH3SH)(2)(+) using vacuum-ultraviolet photoionization, infrared dissociation, and time-of-flight detection have shown that (CH3SH)(2)(+) is (3e-2c)-bonded. To investigate the influence of the solvent molecules on the (3e-2c)-bonded (CH3SH)(2)(+) in a supersonic jet, we added H2O or (CH3)(2)CO or NH3 or (CH3SH)(n) (n = 1-4) to (CH3SH)(2)(+) and investigated their IR action spectra. The (3e-2c)-bonded (CH3SH)(2)(+) ion core was maintained when a molecule of H2O or (CH3)(2)CO or CH3SH binds, indicating that the ion core is more stable than the hydrogen bond, whereas the (3e-2c)-bond became broken by a NH3 molecule because the proton transfer led to a more stable hydrogen-bonded structure. The spectral features of the SH-stretching modes of (CH3SH)(n)(+) (n = 3-6) indicate that the (3e-2c)-bonded (CH3SH)(2)(+) ion core is maintained and the first two additional CH3SH are H-bonded to the free SH groups of the ion core. For larger clusters with n = 5 and 6, the additional solvent molecules likely bind to the first solvation shell. These results show also that the (3e-2c)-bonded S therefore S structure is more stable than the S therefore O and S therefore N structures in [(CH3SH)(2)-X](+) with X = H2O or (CH3)(2)CO or CH3SH or NH3.
Infrared Spectroscopic Investigation of the Acidic CH Bonds in Cationic n-Alkanes: Pentane, Hexane, and Heptane
(2016-08-18)
Xie, Min
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Matsuda, Yoshiyuki
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Fujii, Asuka
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應用化學系
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應用化學系分子科學碩博班
Radical cations of n-alkanes (pentane, hexane, and heptane) in the gas phase are investigated by infrared predissociation spectroscopy with the argon Or nitrogen tagging. All-trans and gauche-involving conformers are identified for these cations by comparisons of observed infrared spectra and vibrational simulations. Intense CH stretch bands are observed in the frequency region lower than the normal alkyl CH stretch frequency. These low frequencies and high intensities of the CH stretch bands are caused by the CH bond weakening and the enhanced positive charge of the hydrogen atoms through the delocalization of the sigma electron in the CH bonds. These effects of the delocalization of the a electron result in the enhanced acidity of the CH bonds. The conformation as well as alkyl chain length dependence of the acidity of the CH bonds is demonstrated by the CH stretch frequency shift trend.
Spectral Characterization of Three-Electron Two-Center (3e-2c) Bonds of Gaseous CH3-S therefore S(H)CH3 and (CH3SH)(2)(+) and Enhancement of the 3e-2c Bond upon Protonation
(2018-07-05)
Xie, Min
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Shen, Zhitao
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Wang, Dandan
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Fujii, Asuka
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Lee, Yuan-Pern
The three-electron two-center (3e-2c) bond plays an important role in structures and electron communication in biological systems involving cationic sulfur compounds. Although the nature of 3e-2c bonds and their theoretical formalism have attracted great interest, direct spectral identifications of 3e-2c-bound molecules are scarce. We observed the infrared spectra of the weakly 3e-2c-bound CH3S:.S(H)CH3 and the strongly 3e-2c-bound (CH3SH)(2)(+) in a supersonic jet using infrared (IR) dissociation with vacuum-ultraviolet photoionization and time-of-flight detection. Protonation of CH3S:.S(H)CH3 to form [CH3(H)S therefore S(H)CH3](+) significantly enhances the 3e-2c bond, characterized by a large red shift of the SH-stretching band with enhanced IR intensity, shortening of the calculated S-S distance from 3.00 to 2.86 angstrom, and a dissociation energy increased from similar to 23 to 162 kJ mol(-1).