Formation of an End-On Ferric Peroxo Intermediate upon One-Electron Reduction of a Ferric Superoxo Heme

The reduction of the relatively inert carbon–oxygen bonds of CO2 to access useful CO2-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO2 and the MGE. Herein we report the first successful chemical reduction of CO2 at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO2 adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO2)]n(M = Li, Na, K, 2-4) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M2(CAAC–CO2)]n (5-8). It is notable that these crystalline clusters of reduced CO2 may also be isolated via the “one-pot” reaction of free CO2 with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products 2-8 were investigated using a combination of experimental and theoretical methods.

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A Comparative Study of Isocyanates and Isothiocyanates via One Electron Reduction

10.30707/etd2016.servos.m ◽

2016 ◽

Author(s):

Mark Alan Servos

Keyword(s):

Comparative Study ◽

Electron Reduction

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Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

Nature Communications ◽

10.1038/s41467-020-20769-x ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yanming Cai ◽

Jiaju Fu ◽

Yang Zhou ◽

Yu-Chung Chang ◽

Qianhao Min ◽

...

Keyword(s):

Energy Barrier ◽

Active Sites ◽

Theoretical Calculations ◽

High Energy ◽

Single Atom ◽

Faradaic Efficiency ◽

High Energy Barrier ◽

Catalytic Sites ◽

Electron Reduction ◽

First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

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One- and Two-Electron Reduction of Triarylborane-Based Helical Donor-Acceptor Compounds

Chemical Science ◽

10.1039/d1sc02409d ◽

2021 ◽

Author(s):

Xiangqing Jia ◽

Jörn Nitsch ◽

Zhu Wu ◽

Alexandra Friedrich ◽

Johannes Krebs ◽

...

Keyword(s):

Chemical Reduction ◽

Helix 12 ◽

Donor Acceptor ◽

Electron Reduction

One-electron chemical reduction of 10-(dimesitylboryl)-N,N-di-p-tolylbenzo[c]phenanthrene-4-amine (3-B(Mes)2-[4]helix-9-N(p-Tol)2) 1 and 13-(dimesitylboryl)-N,N-di-p-tolyldibenzo[c,g]phenanthrene-8-amine (3-B(Mes)2-[5]helix-12-N(p-Tol)2) 2 gives rise to monoanions with extensive delocalization over the annulated helicene rings and the boron pz orbital. Two-electron chemical...

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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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A QM/MM Evaluation of the Missing Step in the Reduction Mechanism of HMG-CoA by Human HMG-CoA Reductase

Processes ◽

10.3390/pr9071085 ◽

2021 ◽

Vol 9 (7) ◽

pp. 1085

Author(s):

Paula Mihaljević-Jurič ◽

Sérgio F. Sousa

Keyword(s):

Mevalonate Pathway ◽

Atomic Level ◽

Amino Acid Residues ◽

Protonation State ◽

Primary Target ◽

Cholesterol Levels ◽

The Subject ◽

Electron Reduction ◽

Dynamics Simulations ◽

Coa Reductase

Statins are important drugs in the regulation of cholesterol levels in the human body that have as a primary target the enzyme β-hydroxy-β-methylglutaryl-CoA reductase (HMGR). This enzyme plays a crucial role in the mevalonate pathway, catalyzing the four-electron reduction of HMG-CoA to mevalonate. A second reduction step of this reaction mechanism has been the subject of much speculation in the literature, with different conflicting theories persisting to the present day. In this study, the different mechanistic hypotheses were evaluated with atomic-level detail through a combination of molecular dynamics simulations (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations. The obtained Gibbs free activation and Gibbs free reaction energy (15 kcal mol−1 and −40 kcal mol−1) show that this hydride step takes place with the involvement of a cationic His405 and Lys639, and a neutral Glu98, while Asp715 remains in an anionic state. The results provide an atomic-level portrait of this step, clearly demonstrating the nature and protonation state of the amino acid residues involved, the energetics associated, and the structure and charge of the key participating atoms in the several intermediate states, finally elucidating this missing step.

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