Four-electron Reduction of Dioxygen by a Multicopper Oxidase, CueO, and Roles of Asp112and Glu506Located Adjacent to the Trinuclear Copper Center

Geometric and electronic structure changes in the copper (Cu) centers in bilirubin oxidase (BOD) upon a four-electron reduction were investigated by quantum mechanics/molecular mechanics (QM/MM) calculations. For the QM region, the unrestricted density functional theory (UDFT) method was adopted for the open-shell system. We found new candidates of the native intermediate (NI, intermediate II) and the resting oxidized (RO) states, i.e., NIH+ and RO0. Elongations of the Cu-Cu atomic distances for the trinuclear Cu center (TNC) and very small structural changes around the type I Cu (T1Cu) were calculated as the results of a four-electron reduction. The QM/MM optimized structures are in good agreement with recent high-resolution X-ray structures. As the structural change in the TNC upon reduction was revealed to be the change in the size of the triangle spanned by the three Cu atoms of TNC, we introduced a new index (l) to characterize the specific structural change. Not only the wild-type, but also the M467Q, which mutates the amino acid residue coordinating T1Cu, were precisely analyzed in terms of their molecular orbital levels, and the optimized redox potential of T1Cu was theoretically reconfirmed.

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Room Temperature Alkali Metal Reduction of Carbon Dioxide

10.26434/chemrxiv.12665336 ◽

2020 ◽

Author(s):

Lucas A. Freeman ◽

Akachukwu D. Obi ◽

Haleigh R. Machost ◽

Andrew Molino ◽

Asa W. Nichols ◽

...

Keyword(s):

Alkali Metal ◽

Alkali Metals ◽

Room Temperature ◽

Chemical Reduction ◽

Bond Cleavage ◽

Open Shell ◽

Metal Reduction ◽

One Pot ◽

Earth Abundant ◽

Electron Reduction

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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Tris(pyrazolyl)borate Copper Hydroxide Complexes Featuring Tunable Intramolecular H-bonding

10.26434/chemrxiv.7878065.v1 ◽

2019 ◽

Author(s):

Evan Gardner ◽

Caitlyn Cobb ◽

Jeffery A. Bertke ◽

Timothy H. Warren

Keyword(s):

Single Crystal ◽

Copper Hydroxide ◽

X Ray ◽

Modular Synthesis ◽

Pendant Arm ◽

Copper Center ◽

Vibrational Studies

A modular synthesis provides access to a series of new tris(pyrazolyl)borate ligands XpyMeTpK that possess a single functionalized pendant pyridyl (py) or pyrimidyl (pyd) arm designed to engage in tunable intramolecular H-bonding to metal–bound functionalities. To illustrate such H-bonding interactions, a series of [XpyMeTpCu]2(𝜇–OH)2(6a–6e) complexes were synthesized from the corresponding XpyMeTpCu–OAc (5a–5e) complexes. Single crystal X-ray structures of three new dinuclear [XpyMeTpCu]2(𝜇–OH)2complexes reveal H-bonding between the pendant heterocycle and bridging hydroxide ligands while the donor arm engages the copper center in an unusual monomeric DMAPMeTpCu–OH complex. Vibrational studies (IR) of each bridging hydroxide complex reveal reduced 𝜈OH frequencies that tracks with the H-bond accepting ability of the pendant arm.

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Tris(pyrazolyl)borate Copper Hydroxide Complexes Featuring Tunable Intramolecular H-bonding

10.26434/chemrxiv.7878065 ◽

2019 ◽

Author(s):

Evan Gardner ◽

Caitlyn Cobb ◽

Jeffery A. Bertke ◽

Timothy H. Warren

Keyword(s):

Single Crystal ◽

Copper Hydroxide ◽

X Ray ◽

Modular Synthesis ◽

Pendant Arm ◽

Copper Center ◽

Vibrational Studies

A modular synthesis provides access to a series of new tris(pyrazolyl)borate ligands XpyMeTpK that possess a single functionalized pendant pyridyl (py) or pyrimidyl (pyd) arm designed to engage in tunable intramolecular H-bonding to metal–bound functionalities. To illustrate such H-bonding interactions, a series of [XpyMeTpCu]2(𝜇–OH)2(6a–6e) complexes were synthesized from the corresponding XpyMeTpCu–OAc (5a–5e) complexes. Single crystal X-ray structures of three new dinuclear [XpyMeTpCu]2(𝜇–OH)2complexes reveal H-bonding between the pendant heterocycle and bridging hydroxide ligands while the donor arm engages the copper center in an unusual monomeric DMAPMeTpCu–OH complex. Vibrational studies (IR) of each bridging hydroxide complex reveal reduced 𝜈OH frequencies that tracks with the H-bond accepting ability of the pendant arm.

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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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