Energetic Comparison between Photoinduced Electron-Transfer Reactions from NADH Model Compounds to Organic and Inorganic Oxidants and Hydride-Transfer Reactions from NADH Model Compounds to p-Benzoquinone Derivatives

Shunichi Fukuzumi, Shintaro Koumitsu, Katsuhiko Hironaka, Toshio Tanaka

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Abstract

Kinetic studies on photoinduced electron-transfer reactions from dihydropyridine compounds (PyH2) as being NADH model compounds to organic and inorganic oxidants and hydride-transfer reactions from PyH2to p-benzoquinone derivatives in the absence and presence of Mg2+ion are reported by determining over 150 rate constants. These results, combined with the values of Gibbs energy change of the photoinduced electron-transfer reactions as well as those of each step of the hydride-transfer reactions as being the e“-H+-e” sequence, which are determined independently, revealed that the rate constants of the photoinduced electron-transfer reactions obey the Rehm-Weller-Gibbs energy relationship and that the activation barrier of the hydride-transfer reactions from PyH2to Q is dependent solely on the Gibbs energy changes of the initial electron transfer from PyH2to Q and the following proton transfer from PyH2'+to Q'~ and thus independent of the Gibbs energy change of the final electron transfer from PyHH to QH The retarding effect of Mg2+ion observed on the photoinduced electron transfer and hydride-transfer reactions of PyH2is ascribed to the positive shifts of the redox potentials of the ground and excited states of PyH2due to the complex formation with Mg2+ion.

Original languageEnglish
Pages (from-to)305-316
Number of pages12
JournalJournal of the American Chemical Society
Volume109
Issue number2
DOIs
StatePublished - 1 Jan 1987

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