6 research outputs found

    Spectroscopic Study of Firefly Oxyluciferin in an Enzymatic Environment on the Basis of Stability Monitoring

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    To understand the influence of the enzyme microenvironment on the properties of the emitter oxyluciferin (OL) in firefly bioluminescence, we investigated the spectroscopic characteristics of OL in a complex with the enzyme luciferase formed in a consumed reaction mixture. By monitoring the in situ absorption spectra, we analyzed the enzymatic synthesis and the stability of OL in luciferase environment. The absorption spectra of OL in <i>Photinus pyralis</i> luciferase showed that the dominant form was neutral OL, probably the enol form, which emitted blue fluorescence (∌450 nm). A monoanionic OL emitting green fluorescence (∌560 nm) exhibited a weak pH-dependent equilibrium with the neutral enol-OL. The red-emitting form of OL was almost completely absent from the consumed reaction mixture. The peak wavelengths of the green and red emissions of the fluorescence and bioluminescence were similar, but the peak intensities, and hence the spectral shapes, differed greatly. The above characteristics were also found in the absorption and fluorescence spectra of OL in a complex with the H433Y mutant of <i>Luciola cruciata</i> luciferase, which catalyzes pH-independent red bioluminescence. Optical excitation could not reproduce the excited states of bioluminescence that was generated from the chemical reaction. The probable reason is that the chemical excited states formed from a keto-like transition state after decomposition of a dioxetanone intermediate, whereas the optical excited states were generated by exciting the neutral enol-OL. Different luciferases only influenced the chemical transition state during the bioluminescence reaction; they did not influence the ground states or optical excited states after the reaction

    Reverse Stability of Oxyluciferin Isomers in Aqueous Solutions

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    We investigated the stability of oxyluciferin anions (keto, enol, and enolate isomers) in aqueous solution at room temperature by performing a nanosecond time scale first-principles molecular dynamics simulation. In contrast to all previous quantum chemistry calculations, which suggested the keto-type to be the most stable, we show that the enol-type is slightly more stable than the keto-type, in agreement with some recent experimental studies. The simulation highlights the remarkable hydrophobicity of the keto-type by the cavity formed at the oxyluciferin–water interface as well as a reduction in hydrophobicity with the number of hydrating water molecules. It is therefore predicted that the isomeric form in a hydrated cluster is size-dependent

    Reverse Stability of Oxyluciferin Isomers in Aqueous Solutions

    No full text
    We investigated the stability of oxyluciferin anions (keto, enol, and enolate isomers) in aqueous solution at room temperature by performing a nanosecond time scale first-principles molecular dynamics simulation. In contrast to all previous quantum chemistry calculations, which suggested the keto-type to be the most stable, we show that the enol-type is slightly more stable than the keto-type, in agreement with some recent experimental studies. The simulation highlights the remarkable hydrophobicity of the keto-type by the cavity formed at the oxyluciferin–water interface as well as a reduction in hydrophobicity with the number of hydrating water molecules. It is therefore predicted that the isomeric form in a hydrated cluster is size-dependent

    First-Principles Investigation of Strong Excitonic Effects in Oxygen 1s X‑ray Absorption Spectra

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    We calculated the oxygen 1s X-ray absorption spectra (XAS) of acetone and acetic acid molecules in vacuum by utilizing the first-principles <i>GW</i>+Bethe–Salpeter method with an all-electron mixed basis. The calculated excitation energies show good agreement with the available experimental data without an artificial shift. The remaining error, which is less than 1% or 2–5 eV, is a significant improvement from those of time-dependent (TD) density functional methods (5% error or 27–29 eV for TD-LDA and 2.4–2.8% error or 13–15 eV for TD-B3LYP). Our method reproduces the first and second isolated peaks and broad peaks at higher photon energies, corresponding to Rydberg excitations. We observed a failure of the one-particle picture (or independent particle approximation) from our assignment of the five lowest exciton peaks and significant excitonic or state-hybridization effects inherent in the core electron excitations

    “Visible” 5d Orbital States in a Pleochroic Oxychloride

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    Transition metal compounds sometimes exhibit attractive colors. Here, we report a new oxychloride, Ca<sub>3</sub>ReO<sub>5</sub>Cl<sub>2</sub>, that shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. This pleochroism is a consequence of the coincidental complex crystal field splitting of the 5d orbitals of the Re<sup>6+</sup> ion in a square-pyramidal coordination of low symmetry in the energy range of the visible spectrum. Since the relevant d–d transitions show characteristic polarization dependence according to the optical selection rule, the orbital states are “visible” in Ca<sub>3</sub>ReO<sub>5</sub>Cl<sub>2</sub>

    Atomically Engineered Metal–Insulator Transition at the TiO<sub>2</sub>/LaAlO<sub>3</sub> Heterointerface

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    We demonstrate that the atomic boundary conditions of simple binary oxides can be used to impart dramatic changes of state. By changing the substrate surface termination of LaAlO<sub>3</sub> (001) from AlO<sub>2</sub> to LaO, the room-temperature sheet conductance of anatase TiO<sub>2</sub> films are increased by over 3 orders of magnitude, transforming the intrinsic insulating state to a high mobility metallic state, while maintaining excellent optical transparency
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