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

TLDR: In this paper, the rate constants of photo-induced electron transfer reactions obey the Rehm-Weller-Gibbs energy relationship and the activation barrier of hydride-transfer reactions from dihydropyridine compounds (PyH/sub 2/) to p-benzoquinone derivatives (Q) in the absence and presence of Mg/sup 2 +/ ion are reported by determining over 150 rate constants.

Abstract: Kinetic studies on photoinduced electron-transfer reactions from dihydropyridine compounds (PyH/sub 2/) as being NADH model compounds to organic and inorganic oxidants and hydride-transfer reactions from PyH/sub 2/ to p-benzoquinone derivatives (Q) in the absence and presence of Mg/sup 2 +/ 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/sup -/-H/sup +/-e/sup -/ 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 PyH/sub 2/ to Q is dependent solely on the Gibbs energy changes of the initial electron transfer from PyH/sub 2/ to Q and the following proton transfer from PyH/sub 2//sup .+/ to Q/sup .-/ and thus independent of the Gibbs energy change of the final electron transfer from PyH/sup ./ to QH/sup ./. The retarding effect of Mg/sup 2 +/ ion observed on the photoinduced electron transfer and hydride-transfer reactions of PyH/sub 2/ is ascribed to the positive shifts of the redox potentials of the ground and excitedmore » states of PyH/sub 2/ due to the complex formation with Mg/sup 2 +/ ion.« less