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1. Redox‐Neutral S ‐nitrosation Mediated by a Dicopper Center

   https://doi.org/10.1002/anie.202102589  

   Tao, Wenjie ; Moore, Curtis E. ; Zhang, Shiyu ( June 2021 , Angewandte Chemie International Edition)

   A redox‐neutralS‐nitrosation of thiol has been achieved at a dicopper(I,I) center. Treatment of dicopper (I,I) complex with excess NO^.and thiol generates a dicopper (I,I) di‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)₂]²⁺or dicopper (I,I) mono‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)]²⁺, which readily release RSNO in 88–94 % yield. TheS‐nitrosation proceeds by a mixed‐valence [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺species, which deprotonates RS‐H at the basic μ‐O site and nitrosates RS⁻at the μ‐NO site. The [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺complex is also competent forO‐nitrosation of MeOH. A rare [Cu^IICu^II(μ‐NO)(OMe)]²⁺intermediate was isolated and fully characterized, suggesting theS‐nitrosation may proceed through the intermediary of analogous [Cu^IICu^II(μ‐NO)(SR)]²⁺species. This redox‐ and proton‐neutralS‐nitrosation process is the first functional model of ceruloplasmin in mediatingS‐nitrosation of external thiols, with implications for biological copper sites in the interconversion of NO^./RSNO.

    

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2. Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

   https://doi.org/10.1002/ange.202105421  

   Vargo, Natasha P. ; Harland, Jill B. ; Musselman, Bradley W. ; Lehnert, Nicolai ; Ertem, Mehmed Z. ; Robinson, Jerome R. ( July 2021 , Angewandte Chemie)

   Coupled dinuclear copper oxygen cores (Cu₂O₂) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O₂transport and substrate oxidation in many organisms.μ‐1,2‐cisperoxido dicopper cores (^CP) have been proposed as key structures in the early stages of O₂binding in these proteins; their reversible isomerization to other Cu₂O₂cores are directly relevant to enzyme function. Despite the relevance of such species to type III copper proteins and the broader interest in the properties and reactivity of bimetallic^CPcores in biological and synthetic systems, the properties and reactivity of^CPCu₂O₂species remain largely unexplored. Herein, we report the reversible interconversion ofμ‐1,2‐transperoxido (^TP) and^CPdicopper cores. Ca^IImediates this process by reversible binding at the Cu₂O₂core, highlighting the unique capability for metal‐ion binding events to stabilize novel reactive fragments and control O₂activation in biomimetic systems.

    

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3. Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

   https://doi.org/10.1002/anie.202105421  

   Vargo, Natasha P. ; Harland, Jill B. ; Musselman, Bradley W. ; Lehnert, Nicolai ; Ertem, Mehmed Z. ; Robinson, Jerome R. ( July 2021 , Angewandte Chemie International Edition)

   Coupled dinuclear copper oxygen cores (Cu₂O₂) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O₂transport and substrate oxidation in many organisms.μ‐1,2‐cisperoxido dicopper cores (^CP) have been proposed as key structures in the early stages of O₂binding in these proteins; their reversible isomerization to other Cu₂O₂cores are directly relevant to enzyme function. Despite the relevance of such species to type III copper proteins and the broader interest in the properties and reactivity of bimetallic^CPcores in biological and synthetic systems, the properties and reactivity of^CPCu₂O₂species remain largely unexplored. Herein, we report the reversible interconversion ofμ‐1,2‐transperoxido (^TP) and^CPdicopper cores. Ca^IImediates this process by reversible binding at the Cu₂O₂core, highlighting the unique capability for metal‐ion binding events to stabilize novel reactive fragments and control O₂activation in biomimetic systems.

    

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4. DFT Analysis of Methane C−H Activation and Over‐Oxidation by [Cu 2 O] 2+ and [Cu 2 O 2 ] 2+ Sites in Zeolite Mordenite: Intra‐ versus Inter‐site Over‐Oxidation

   https://doi.org/10.1002/cphc.202100580  

   Panthi, Dipak ; Adeyiga, Olajumoke ; Odoh, Samuel O. ( October 2021 , ChemPhysChem)

   Methane over‐oxidation by copper‐exchanged zeolites prevents realization of high‐yield catalytic conversion. However, there has been little description of the mechanism for methane over‐oxidation at the copper active sites of these zeolites. Using density functional theory (DFT) computations, we reported that tricopper [Cu₃O₃]²⁺active sites can over‐oxidize methane. However, the role of [Cu₃O₃]²⁺sites in methane‐to‐methanol conversion remains under debate. Here, we examine methane over‐oxidation by dicopper [Cu₂O]²⁺and [Cu₂O₂]²⁺sites using DFT in zeolite mordenite (MOR). For [Cu₂O₂]²⁺, we considered the μ‐(η²:η²) peroxo‐, and bis(μ‐oxo) motifs. These sites were considered in the eight‐membered (8MR) ring of MOR. μ‐(η²:η²) peroxo sites are unstable relative to the bis(μ‐oxo) motif with a small interconversion barrier. Unlike [Cu₂O]²⁺which is active for methane C−H activation, [Cu₂O₂]²⁺has a very large methane C−H activation barrier in the 8MR. Stabilization of methanol and methyl at unreacted dicopper sites however leads to over‐oxidation via sequential hydrogen atom abstraction steps. For methanol, these are initiated by abstraction of the CH₃group, followed by OH and can proceed near 200 °C. Thus, for [Cu₂O]²⁺and [Cu₂O₂]²⁺species, over‐oxidation is an inter‐site process. We discuss the implications of these findings for methanol selectivity, especially in comparison to the intra‐site process for [Cu₃O₃]²⁺sites and the role of Brønsted acid sites.

    

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5. Ascorbate oxidation by iron, copper and reactive oxygen species: review, model development, and derivation of key rate constants

   https://doi.org/10.1038/s41598-021-86477-8  

   Shen, Jiaqi ; Griffiths, Paul T. ; Campbell, Steven J. ; Utinger, Battist ; Kalberer, Markus ; Paulson, Suzanne E. ( April 2021 , Scientific Reports)

   Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biological response. Because ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical organic molecule, reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chemistry, but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chemical kinetics model, and use seven sets of laboratory measurements to constrain mechanisms for the iron and copper reactions and derive key rate constants. We find that micromolar concentrations of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH₂and AH⁻) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II) + AH₂/AH⁻ + O₂→ Fe(III)/Cu(II) + H₂O₂ + products. Rate constants are 5.7 × 10⁴and 4.7 × 10⁴ M⁻² s⁻¹for Fe(III) + AH₂/AH⁻and 7.7 × 10⁴and 2.8 × 10⁶ M⁻² s⁻¹for Cu(II) + AH₂/AH⁻, respectively.

    

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