慶應義塾研究者情報データベース

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• Fe–O bond character of a µ-oxo-bridged iron phthalocyanine dimer investigated by O K-edge X-ray absorption spectroscopy

  Yamada Y., Kumaki F., Sugihara K., Ito N., Adachi J.i., Nagasaka M., Phung Q.M., Tanaka K.

  Physical Chemistry Chemical Physics 28 （ 31 ） 19283 - 19289 2026年08月

  ISSN  14639076

  　概要を見る

  A µ-oxo-bridged iron phthalocyanine dimer with eight peripheral tert-butyl substituents was investigated using soft X-ray absorption spectroscopy in its solid state. The O K-edge spectrum of the dimer showed a peak at 529.1 eV, corresponding to that of the Fe–µO–Fe core. The peak position is apparently at a lower energy than that of single-bonded oxygens, such as the oxygen of H<inf>2</inf>O (>535 eV), and is almost comparable to the peak of oxytitanium phthalocyanine, whose oxygen atom has a double-bond character (530.6 eV), despite the fact that the µO–Fe bonds of the µ-oxo-bridged dimer have a single-bond character. DFT calculations clarified that the peak of the µ-oxo dimer at 529.1 eV is assignable to the excitation to the antibonding orbital localized in the µO–Fe unit.

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• Simultaneous measurements of solid–liquid interfaces and bulk liquids using soft X-ray absorption spectroscopy

  Kumaki F., Nagasaka M.

  Journal of Synchrotron Radiation 33   1055 - 1062 2026年07月

  ISSN  09090495

  　概要を見る

  Simultaneous measurement methods for soft X-ray absorption spectroscopy (XAS) of solid–liquid interfaces and bulk liquids have been developed. The O K-edge XAS spectra of H<inf>2</inf>O/Au interfaces and bulk H<inf>2</inf>O were measured using a transmission-type liquid cell, in which the liquid layer was sandwiched between Au/Cr/Si<inf>3</inf>N<inf>4</inf> and Si<inf>3</inf>N<inf>4</inf> membranes. The XAS spectrum of bulk H<inf>2</inf>O was obtained using the transmission method by controlling the thickness of the liquid layer, whereas the XAS spectrum of the H<inf>2</inf>O/Au interface was obtained using the electron-yield method by measuring the drain currents from the Au surface after soft X-ray absorption. The XAS spectra of bulk H<inf>2</inf>O and the H<inf>2</inf>O/Au interfaces were differentiated to determine the appropriate measurement conditions for the solid–liquid interfaces interfaces.

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• Double-Bond Character of Phosphates in Solid and Liquid Phases Probed by Oxygen K-Edge X-ray Absorption Spectroscopy

  Nagasaka M., Kumaki F., Adachi J.i.

  Journal of Physical Chemistry Letters 17 （ 23 ） 6432 - 6437 2026年06月

  ISSN  1948-7185

  　概要を見る

  Double-bond character of phosphate groups has important roles for biological reactions and was investigated using the P═O π* peaks in the oxygen K-edge X-ray absorption spectroscopy (XAS). The O K-edge XAS spectra of phosphates in the solid phase found that the double-bond character of phosphates is enhanced as the negative charge increases, where the weak P═O π* peak was observed in NaH<inf>2</inf>PO<inf>4</inf>, but distinct P═O π* peaks were obtained in Na<inf>2</inf>HPO<inf>4</inf> and Na<inf>3</inf>PO<inf>4</inf>. Conversely, the P═O π* peaks were not observed in the XAS spectra of any phosphates in the liquid phase, indicating a substantial reduction in the double-bond character of the phosphate groups owing to the interaction of Na⁺ ions and the formation of hydration structures. The XAS spectra of diphosphates validated that change in the double-bond character of the phosphate groups is a general phenomenon also observed in high-energy phosphate compounds, which is closely related to the reactivity of adenosine triphosphate hydrolysis.

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• Probing electronic structures of metal complexes from the ligand side using soft x-ray absorption spectroscopy

  Kumaki F., Nagasaka M.

  Journal of Physics Condensed Matter 38 （ 19 ）  2026年05月

  ISSN  09538984

  　概要を見る

  Metal–ligand delocalization in metal complexes participating in various chemical processes was probed from the ligand side using nitrogen K-edge x-ray absorption spectroscopy (XAS). The electronic structures, spin multiplicities, and hydration structures of metal complexes in solutions with different metal ion centers, such as iron and cobalt protoporphyrin IX complexes, were investigated by N K-edge XAS. The influence of a phytol chain in chlorophyll a in the solid phase was studied by the XAS measurements with a radiation-induced effect which may cleave the phytol chain. Time-resolved N K-edge XAS measurements at the 100 ps timescale were used to examine the photorelaxation process of iron phenanthroline complexes in aqueous solution. Future directions of studies of various chemical and biological processes that involve metal complexes using N K-edge XAS measurements of ligands are discussed.

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• N K-edge XAS measurements for ionic liquids and N-heterocycle molecules in liquid phase analyzed by simulations with explicit inclusion of solvent molecules

  Xu H., Kumaki F., Nagasaka M., Sasaki T.

  Journal of Chemical Physics 164 （ 10 ）  2026年03月

  ISSN  00219606

  　概要を見る

  We present a framework for interpreting nitrogen K-edge x-ray absorption of ionic liquids and imidazole derivatives in water on a single absolute energy scale. Liquid transmission measurements provide reproducible spectra that can be compared across solutes without ad hoc shifting. Experimental line shapes fall into three patterns defined by the availability of low-lying π acceptors. Pyrrolidinium and ammonium-like centers show no discrete pre-edge. Imidazolium cations show a single pre-edge. Imidazole derivatives show a robust doublet. Real-space calculations with explicit inclusion of water molecules test how hydration controls these patterns. A radius scan in simulation identifies a practical cluster size that captures the first hydration shell while avoiding spurious long-range structure. Direct summation of simulated spectra based on 100 molecular dynamics snapshots on a common energy scale converts discrete transitions into a continuous liquid-phase profile. It merges the two ring nitrogen atoms of imidazolium into one pre-edge and preserves the imidazole doublet with improved intensity ratios. A minimal protocol that combines absorber-centered p DOS with targeted COOP maps separates σ and π channels and locates hydration-sensitive π windows without broader projections. Hydration increases low-energy π overlap while leaving the σ onset comparatively stable. The result is a transferable set of rules for assignment and for choosing simulation settings that match spectra for liquid phases.

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