One-electron Oxidation Potentials of an NADH Model Compound and a Dimeric Rhodium(I) Complex in Irreversible Systems. A Convenient Determination from the Fluorescence Quenching by Electron Acceptors

Abstract

A new methodology for experimental determinations of redox potentials of oxidants or reductants in both reversible and irreversible systems is presented. The Rehm-Weller free energy relationship between the activation free energy ΔG− and the free energy change ΔG for the electron transfer quenching of the excited states of oxidants or reductants by a series of reductants or oxidants is converted to a linear correlation between ΔG\eweq−ΔG and (ΔG\eweq)−1, which can be utilized in convenient determinations of redox potentials of oxidants or reductants. This methodology is established in various reversible systems where the redox potentials of oxidants or reductants determined based on the Rehm-Weller free energy relationship agree well with those determined independently by electrochemical methods. By using this method, one-electron oxidation potentials of two quite different compounds, one is an NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), and the other [Rh2(dicp)4]2+ (dicp=1,3-diisocyanopropane), in MeCN have been determined as 0.60±0.10 and 0.38±0.10 V vs. SCE, respectively. The relation between the oxidation potential and the oxidation peak potential of BNAH measured by the cyclic voltammetry is discussed in the context of free energy relationships.

Photocatalytic Reduction of Carbon Dioxide to CO and HCO2H Using fac-Mn(CN)(bpy)(CO)3

“…In Scheme , we present a proposed mechanism for the photocatalytic reduction of CO 2 by 1 based on the photocatalytic results presented above and additional experiments detailed below. In the photosensitization step, the reduced [Ru­(dmb) 3 ] •+ ([Ru­(dmb) 3 ] 2+ / •+ = −1.85 V vs Fc/Fc+) transfers an electron to the ligand of Mn complex 1 , forming a [Mn­(CN)­(bpy)­(CO) 3 ] •– species, 2 [eq 1 in Scheme ; [Mn­(CN)­(bpy)­(CO) 3 ] 0 / •– = −1.91 V vs Fc/Fc + ] {[Ru­(dmb) 3 ] 2+* / + = 0.24 V; BNAH 0 / •+ = 0.20 V vs Fc/Fc + }. ,− The reduced photosensitizer [Ru­(dmb) 3 ] •+ is capable of driving catalysis at this potential, but at a diminished rate. Indeed, in comparison to MnBr­(bpy)­(CO) 3 much lower rates are observed .…”

The Electrochemical Approach towards Proton Coupled Electron Transfer Pathways for Oxidation of Thymine in Water

“…In the equation, ∆G is the free energy which is zero for a self exchange electron transfer reaction i.e., ‫ܩ∆‬ ‡ = ‫ܩ∆‬ ‡ (0) at ∆G = 0. This free energy relationship, if manipulate mathematically, offers us possibility of determining the reversible oxidation potential of irreversible systems from the cyclic voltammetric measurements (34,(36)(37)(38)(39)(40). The transformation of Rehm-Weller equation is shown below, see equation 1-3.…”

On the electron transfer and hydrogen atom abstraction mechanism for 1-benzyl-1,4-dihydronicotinamide reduction of benzoquinones

“…[13]. The hydrogen + atom abstraction mechanism had been discarded by Tanaka (1 1 To evaluate a and b in eq.…”

“…For BNAH, several values for the redox potentialin acetonitrile have been reported (13). 4 We have chosen +0.57 V vs. SCE (13) because the CV technique used in these studies was similar to those used to determine the L ?…”