One-Step versus Stepwise Mechanism in Protonated Amino Acid-Promoted Electron-Transfer Reduction of a Quinone by Electron Donors and Two-Electron Reduction by a Dihydronicotinamide Adenine Dinucleotide Analogue. Interplay between Electron Transfer and Hydrogen Bonding

AbstractAn asymmetric organocatalytic nucleophilic aromatic substitution reaction of azlactones with electron-deficient aryls was established. A variety of α-aryl α-alkyl α-amino acid esters and peptides were obtained in decent yields and stereoselectivities. A new bifunctional catalytic mode involving charge-transfer interaction and hydrogen bonding is proposed to explain the enantioselectivity.

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Autocatalytic photoredox Chan-Lam coupling of free diaryl sulfoximines with arylboronic acids

Nature Communications ◽

10.1038/s41467-021-21156-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Cong Wang ◽

Hui Zhang ◽

Lucille A. Wells ◽

Tian Liu ◽

Tingting Meng ◽

...

Keyword(s):

Electron Transfer ◽

Hydrogen Atom Abstraction ◽

Coupling Reactions ◽

Ambient Light ◽

Environmental Friendliness ◽

Copper Species ◽

Arylboronic Acids ◽

Ligand Free ◽

Byproduct Formation ◽

Electron Reduction

AbstractN-Arylation of NH-sulfoximines represents an appealing approach to access N-aryl sulfoximines, but has not been successfully applied to NH-diaryl sulfoximines. Herein, a copper-catalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids is described. This neutral and ligand-free coupling is initiated by ambient light-induced copper-catalyzed single-electron reduction of NH-sulfoximines. This electron transfer route circumvents the sacrificial oxidant employed in traditional Chan-Lam coupling reactions, increasing the environmental friendliness of this process. Instead, dihydrogen gas forms as a byproduct of this reaction. Mechanistic investigations also reveal a unique autocatalysis process. The C–N coupling products, N-arylated sulfoximines, serve as ligands along with NH-sulfoximine to bind to the copper species, generating the photocatalyst. DFT calculations reveal that both the NH-sulfoximine substrate and the N-aryl product can ligate the copper accounting for the observed autocatalysis. Two energetically viable stepwise pathways were located wherein the copper facilitates hydrogen atom abstraction from the NH-sulfoximine and the ethanol solvent to produce dihydrogen. The protocol described herein represents an appealing alternative strategy to the classic oxidative Chan-Lam reaction, allowing greater substrate generality as well as the elimination of byproduct formation from oxidants.

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Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair

Molecules ◽

10.3390/molecules26102911 ◽

2021 ◽

Vol 26 (10) ◽

pp. 2911

Author(s):

Miriam Navarrete-Miguel ◽

Antonio Francés-Monerris ◽

Miguel A. Miranda ◽

Virginie Lhiaubet-Vallet ◽

Daniel Roca-Sanjuán

Keyword(s):

Electron Transfer ◽

Energy Barrier ◽

Ring Opening ◽

Dna Lesions ◽

Barrier Heights ◽

Dna Lesion ◽

Electron Reduction ◽

The Stability ◽

Electron Transfer Processes

Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocycloaddition between 6-azauracil and cyclohexene. First, we analyze the efficiency of the electron-transfer processes by computing the redox properties of the azetidine isomers as well as those of a series of aromatic photosensitizers acting as photoreductants and photo-oxidants. We find certain stereodifferentiation favoring oxidation of the cis-isomer, in agreement with previous experimental data. Second, we determine the reaction profiles of the ring-opening mechanism of the cationic, neutral, and anionic systems and assess their feasibility based on their energy barrier heights and the stability of the reactants and products. Results show that oxidation largely decreases the ring-opening energy barrier for both stereoisomers, even though the process is forecast as too slow to be competitive. Conversely, one-electron reduction dramatically facilitates the ring opening of the azetidine heterocycle. Considering the overall quantum-chemistry findings, N,N-dimethylaniline is proposed as an efficient photosensitizer to trigger the photoinduced cycloreversion of the DNA lesion model.

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Lack of Electricity Production by Pelobacter carbinolicus Indicates that the Capacity for Fe(III) Oxide Reduction Does Not Necessarily Confer Electron Transfer Ability to Fuel Cell Anodes

Applied and Environmental Microbiology ◽

10.1128/aem.00804-07 ◽

2007 ◽

Vol 73 (16) ◽

pp. 5347-5353 ◽

Cited By ~ 93

Author(s):

Hanno Richter ◽

Martin Lanthier ◽

Kelly P. Nevin ◽

Derek R. Lovley

Keyword(s):

Electron Transfer ◽

Fuel Cells ◽

Fuel Cell ◽

Microbial Fuel Cell ◽

Microbial Fuel Cells ◽

Electron Donors ◽

Rrna Genes ◽

Anode Surface ◽

Oxide Reduction ◽

Fuel Cell Anodes

ABSTRACT The ability of Pelobacter carbinolicus to oxidize electron donors with electron transfer to the anodes of microbial fuel cells was evaluated because microorganisms closely related to Pelobacter species are generally abundant on the anodes of microbial fuel cells harvesting electricity from aquatic sediments. P. carbinolicus could not produce current in a microbial fuel cell with electron donors which support Fe(III) oxide reduction by this organism. Current was produced using a coculture of P. carbinolicus and Geobacter sulfurreducens with ethanol as the fuel. Ethanol consumption was associated with the transitory accumulation of acetate and hydrogen. G. sulfurreducens alone could not metabolize ethanol, suggesting that P. carbinolicus grew in the fuel cell by converting ethanol to hydrogen and acetate, which G. sulfurreducens oxidized with electron transfer to the anode. Up to 83% of the electrons available in ethanol were recovered as electricity and in the metabolic intermediate acetate. Hydrogen consumption by G. sulfurreducens was important for ethanol metabolism by P. carbinolicus. Confocal microscopy and analysis of 16S rRNA genes revealed that half of the cells growing on the anode surface were P. carbinolicus, but there was a nearly equal number of planktonic cells of P. carbinolicus. In contrast, G. sulfurreducens was primarily attached to the anode. P. carbinolicus represents the first Fe(III) oxide-reducing microorganism found to be unable to produce current in a microbial fuel cell, providing the first suggestion that the mechanisms for extracellular electron transfer to Fe(III) oxides and fuel cell anodes may be different.

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An electron transfer driven magnetic switch: ferromagnetic exchange and spin delocalization in iron verdazyl complexes

Dalton Transactions ◽

10.1039/c8dt00805a ◽

2018 ◽

Vol 47 (18) ◽

pp. 6351-6360 ◽

Cited By ~ 11

Author(s):

David J. R. Brook ◽

Connor Fleming ◽

Dorothy Chung ◽

Cardius Richardson ◽

Servando Ponce ◽

...

Keyword(s):

Electron Transfer ◽

Spin Crossover ◽

Large Change ◽

Single Electron ◽

Spin Multiplicity ◽

Magnetic Switch ◽

Ferromagnetic Exchange ◽

Spin Delocalization ◽

Electron Reduction

A single electron reduction of an iron bis(verdazyl) complex results in a large change in spin multiplicity resulting from a combination of spin crossover and exceptionally strong ferromagnetic exchange.

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