scholarly journals Mechanisms for Flavin Mediated Oxidation: Hydride or Hydrogen-Atom Transfer?

2020 ◽  
Author(s):  
Felipe Curtolo ◽  
Guilherme M. Arantes
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Broad Class ◽  
Hydrogen Atom Transfer ◽  
Cellular Respiration ◽  
Simple Analysis ◽  
Succinate Oxidation ◽  
Acceptor Group ◽  
Electron Transfers ◽  
Mediated Oxidation

Flavins are versatile biological cofactors which catalyze proton-coupled electron transfers (PCET) with varying number and coupling of electrons. Flavin mediated oxidation of nicotinamide adenine dinucleotide (NADH) and of succinate, initial redox reactions in cellular respiration, were examined here with multiconfigurational quantum chemical calculations and a simple analysis of the wave-function proposed to quantify electron transfer along the proton reaction coordinate. The mechanism of NADH oxidation is a prototypical hydride transfer, with two electrons moving concerted with the proton to the same acceptor group. However, succinate oxidation depends on the elimination step and can proceed through the transfer of hydride or hydrogen-atom, with proton and electrons moving to different groups in both cases. These results help to determine the mechanism of fundamental but still debated biochemical reactions, and illustrate a new diagnostic tool for electron transfer that can be useful to characterize a broad class of PCET processes. <br>

scholarly journals Mechanisms for Flavin Mediated Oxidation: Hydride or Hydrogen-Atom Transfer?

2020 ◽  
Author(s):  
Felipe Curtolo ◽  
Guilherme M. Arantes
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Broad Class ◽  
Hydrogen Atom Transfer ◽  
Cellular Respiration ◽  
Simple Analysis ◽  
Succinate Oxidation ◽  
Acceptor Group ◽  
Electron Transfers ◽  
Mediated Oxidation

Flavins are versatile biological cofactors which catalyze proton-coupled electron transfers (PCET) with varying number and coupling of electrons. Flavin mediated oxidation of nicotinamide adenine dinucleotide (NADH) and of succinate, initial redox reactions in cellular respiration, were examined here with multiconfigurational quantum chemical calculations and a simple analysis of the wave-function proposed to quantify electron transfer along the proton reaction coordinate. The mechanism of NADH oxidation is a prototypical hydride transfer, with two electrons moving concerted with the proton to the same acceptor group. However, succinate oxidation depends on the elimination step and can proceed through the transfer of hydride or hydrogen-atom, with proton and electrons moving to different groups in both cases. These results help to determine the mechanism of fundamental but still debated biochemical reactions, and illustrate a new diagnostic tool for electron transfer that can be useful to characterize a broad class of PCET processes. <br>

2-Aryl-1,3-dimethylbenzimidazolines as Effective Electron and Hydrogen Donors in Photoinduced Electron-Transfer Reactions

2015 ◽  
Vol 68 (11) ◽  
pp. 1640 ◽  
Author(s):  
Eietsu Hasegawa ◽  
Shin-ya Takizawa
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Photoinduced Electron Transfer ◽  
Hydrogen Atom Transfer ◽  
Transfer Reactions ◽  
Organic Substrates ◽  
Iridium Complexes ◽  
Effective Electron ◽  
Hydrogen Donors ◽  
Wavelength Light

2-Aryl-1,3-dimethylbenzimidazolines (DMBIHs) have been applied to photoinduced electron-transfer reductions of various organic substrates. Either direct or indirect electron transfer between the substrates and DMBIHs is utilized to promote the desired transformations. Photoexcitation of the substrates using light above 280 nm was carried out in the former protocol whereas a photosensitization method using materials such as substituted pyrenes, ruthenium and iridium complexes that absorb longer-wavelength light was employed in the latter. In these reactions, DMBIHs undergo initial electron transfer and subsequent proton or hydrogen atom transfer.

Atmospheric formation of the NO3 radical from gas-phase reaction of HNO3 acid with the NH2 radical: proton-coupled electron-transfer versus hydrogen atom transfer mechanisms

2014 ◽  
Vol 16 (36) ◽  
pp. 19437-19445 ◽  
Author(s):  
Josep M. Anglada ◽  
Santiago Olivella ◽  
Albert Solé
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Phase Reaction ◽  
Electron Transfer Mechanism ◽  
Proton Coupled Electron Transfer ◽  
No3 Radical ◽  
Transfer Mechanisms ◽  
Atmospheric Formation

The amidogen radical abstracts the hydrogen from nitric acid through a proton coupled electron transfer mechanism rather than by an hydrogen atom transfer process.

scholarly journals Light-driven deracemization enabled by excited-state electron transfer

Science ◽  
2019 ◽  
Vol 366 (6463) ◽  
pp. 364-369 ◽  
Author(s):  
Nick Y. Shin ◽  
Jonathan M. Ryss ◽  
Xin Zhang ◽  
Scott J. Miller ◽  
Robert R. Knowles
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Asymmetric Synthesis ◽  
Hydrogen Atom Transfer ◽  
Product Distributions ◽  
Reaction Proceeds ◽  
Molecular Catalysts ◽  
Distinct Approach

Deracemization is an attractive strategy for asymmetric synthesis, but intrinsic energetic challenges have limited its development. Here, we report a deracemization method in which amine derivatives undergo spontaneous optical enrichment upon exposure to visible light in the presence of three distinct molecular catalysts. Initiated by an excited-state iridium chromophore, this reaction proceeds through a sequence of favorable electron, proton, and hydrogen-atom transfer steps that serve to break and reform a stereogenic C–H bond. The enantioselectivity in these reactions is jointly determined by two independent stereoselective steps that occur in sequence within the catalytic cycle, giving rise to a composite selectivity that is higher than that of either step individually. These reactions represent a distinct approach to creating out-of-equilibrium product distributions between substrate enantiomers using excited-state redox events.

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