The “Promoting”-Mode Phonon-Induced Electron Tunneling Through Bridging Chains. The H2O/D2O Isotope Effect in Cytochrome Oxidation/Reduction Reactions.

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概要

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• A new mechanism of electron-tunneling through a "quasi-one dimensional" electron-transfer ("ET") pathway in biological systems is presented in place of the conventional electron-tunneling mechanism. It arises from the long-range electrostatic coupling between the electron and "promoting" modes ("P-modes") of molecular vibration. It is shown that when the ET pathway involves at least one intermolecular hydrogen (H-) bond, the out-of-plane torsional motion of the H-bond can predominantly promote ET because of the significantly enhanced coupling due to the quasi-one dimensionality of the ET pathway. In this mechanism, electronic wave functions for reactant and product states depend upon nuclear coordinates of "accepting" modes ("A-modes") of molecular vibration mainly through each binding energy along the ET pathway. It is shown that this dependence can be neglected in the normal region of rate constant (k_<RP>) vs energy gap (ΔE) relation far from the activationless case, but can not otherwise. Especially, around the energy region of ΔE as large as the reorganization energy (λ), this dependence could lead to an appreciable negative activation type behavior of k_<RP> vs temperature (T). It is shown that this mechanism with predicted ET pathway quantitatively interprets known results on the cytochrome oxidation reaction in photosynthetic bacteria, including the H_2O/D_2O isotope effect of √<2> for the ratio of the ET rates observed by Kihara and McCray (Biochim. Biophys. Acta 292, 297 (1973)). Such a deuterium effect requires that the pendulum frequency of the H-bond is sufficiently low.

• 明治大学の論文

著者

• 楠 正美

  Department Of Physics School Of Science And Technology Meiji University

関連論文

• Resonance Neutron Scattering by Crystal Lattice
• High-Resolution XANES Study of Molecular Structure of the Manganese Clusters in S_1 and S_2 States in Photosynthetic O_2-Evolving Complex
• The “Promoting”-Mode Phonon-Induced Electron Tunneling Through Bridging Chains. The H2O/D2O Isotope Effect in Cytochrome Oxidation/Reduction Reactions.
• 光合成の初期過程における理論的諸問題
• The Quantum Theory of Transient Resonance Raman Scattering including Light Source and Observation Process
• Transient Resonance Raman Scattering in Strongly Coupled Localized Electron-Phonon System
• 共鳴光パルス散乱における不確定性関係

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