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1. Synthesis, characterization, and electrocatalytic activity of bis(pyridylimino)isoindoline Cu( ii ) and Ni( ii ) complexes

   https://doi.org/10.1039/D0DT03030A  

   Saha, Soumen ; Sahil, Sha Tamanna ; Mazumder, Md. Motiur ; Stephens, Alexander M. ; Cronin, Bryan ; Duin, Evert C. ; Jurss, Jonah W. ; Farnum, Byron H. ( January 2021 , Dalton Transactions)

   null (Ed.)

   Two NNN pincer complexes of Cu( ii ) and Ni( ii ) with BPI Me − [BPI Me − = 1,3-bis((6-methylpyridin-2-yl)imino)isoindolin-2-ide] have been prepared and characterized structurally, spectroscopically, and electrochemically. The single crystal structures of the two complexes confirmed their distorted trigonal bipyramidal geometry attained by three equatorial N-atoms from the ligand and two axially positioned water molecules to give [Cu(BPI Me )(H 2 O) 2 ]ClO 4 and [Ni(BPI Me )(H 2 O) 2 ]ClO 4 . Electrochemical studies of Cu( ii ) and Ni( ii ) complexes have been performed in acetonitrile to identify metal-based and ligand-based redox activity. When subjected to a saturated CO 2 atmosphere, both complexes displayed catalytic activity for the reduction of CO 2 with the Cu( ii ) complex displaying higher activity than the Ni( ii ) analogue. However, both complexes were shown to decompose into catalytically active heterogeneous materials on the electrode surface over extended reductive electrolysis periods. Surface analysis of these materials using energy dispersive spectroscopy as well as their physical appearance suggests the reductive deposition of copper and nickel metal on the electrode surface. Electrocatalysis and decomposition are proposed to be triggered by ligand reduction, where complex stability is believed to be tied to fluxional ligand coordination in the reduced state. 

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2. Redox-switchable atom transfer radical polymerization

   https://doi.org/10.1039/c8cc09209e  

   Dadashi-Silab, Sajjad ; Lorandi, Francesca ; Fantin, Marco ; Matyjaszewski, Krzysztof ( January 2019 , Chemical Communications)

   Temporal control in atom transfer radical polymerization (ATRP) relies on modulating the oxidation state of a copper catalyst, as polymer chains are activated by L/Cu I and deactivated by L/Cu II . (Re)generation of L/Cu I activator has been achieved by applying a multitude of external stimuli. However, switching the Cu catalyst off by oxidizing to L/Cu II through external chemical stimuli has not yet been investigated. A redox switchable ATRP was developed in which an oxidizing agent was used to oxidize L/Cu I activator to L/Cu II , thus halting the polymerization. A ferrocenium salt or oxygen were used to switch off the Cu catalyst, whereas ascorbic acid was used to switch the catalyst on by (re)generating L/Cu I . The redox switches efficiently modulated the oxidation state of the catalyst without sacrificing control over polymerization. 

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3. Tuning Local Atomic Structures in MoS 2 Based Catalysts for Electrochemical Nitrate Reduction

   https://doi.org/10.1002/smll.202310562  

   Tian, Xiaoyin ; Zhang, Jing ; Rigby, Kali ; Rivera, Daniel J. ; Gao, Guanhui ; Liu, Yifeng ; Zhu, Yifan ; Zhai, Tianshu ; Stavitski, Eli ; Muhich, Christopher ; et al ( March 2024 , Small)

   In recent years, there has been a substantial surge in the investigation of transition‐metal dichalcogenides such as MoS₂as a promising electrochemical catalyst. Inspired by denitrification enzymes such as nitrate reductase and nitrite reductase, the electrochemical nitrate reduction catalyzed by MoS₂with varying local atomic structures is reported. It is demonstrated that the hydrothermally synthesized MoS₂containing sulfur vacancies behaves as promising catalysts for electrochemical denitrification. With copper doping at less than 9% atomic ratio, the selectivity of denitrification to dinitrogen in the products can be effectively improved. X‐ray absorption characterizations suggest that two sulfur vacancies are associated with one copper dopant in the MoS₂skeleton. DFT calculation confirms that copper dopants replace three adjacent Mo atoms to form a trigonal defect‐enriched region, introducing an exposed Mo reaction center that coordinates with Cu atom to increase N₂selectivity. Apart from the higher activity and selectivity, the Cu‐doped MoS₂also demonstrates remarkably improved tolerance toward oxygen poisoning at high oxygen concentration. Finally, Cu‐doped MoS₂based catalysts exhibit very low specific energy consumption during the electrochemical denitrification process, paving the way for potential scale‐up operations.

    

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4. Copper( ii ) ketimides in sp 3 C–H amination

   https://doi.org/10.1039/D1SC01990B  

   Jayasooriya, Isuri U. ; Bakhoda, Abolghasem ; Palmer, Rachel ; Ng, Kristi ; Khachemoune, Nour L. ; Bertke, Jeffery A. ; Warren, Timothy H. ( December 2021 , Chemical Science)

   Commercially available benzophenone imine (HNCPh 2 ) reacts with β-diketiminato copper( ii ) tert -butoxide complexes [Cu II ]–O t Bu to form isolable copper( ii ) ketimides [Cu II ]–NCPh 2 . Structural characterization of the three coordinate copper( ii ) ketimide [Me 3 NN]Cu–NCPh 2 reveals a short Cu-N ketimide distance (1.700(2) Å) with a nearly linear Cu–N–C linkage (178.9(2)°). Copper( ii ) ketimides [Cu II ]–NCPh 2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R–NCPh 2 products in a process that competes with N–N coupling of copper( ii ) ketimides [Cu II ]–NCPh 2 to form the azine Ph 2 CN–NCPh 2 . Copper( ii ) ketimides [Cu II ]–NCAr 2 serve as intermediates in catalytic sp 3 C–H amination of substrates R–H with ketimines HNCAr 2 and t BuOO t Bu as oxidant to form N -alkyl ketimines R–NCAr 2 . This protocol enables the use of unactivated sp 3 C–H bonds to give R–NCAr 2 products easily converted to primary amines R–NH 2 via simple acidic deprotection. 

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5. Are granulins copper sequestering proteins?

   https://doi.org/10.1002/prot.26031  

   Bhopatkar, Anukool A. ; Rangachari, Vijayaraghavan ( December 2020 , Proteins: Structure, Function, and Bioinformatics)

   Granulins (GRN 1‐7) are short (~6 kDa), cysteine‐rich proteins that are generated upon the proteolytic processing of progranulin (PGRN). These peptides, along with their precursor, have been implicated in multiple pathophysiological roles, especially in neurodegenerative diseases. Previously we showed that GRN‐3 and GRN‐5 are fully disordered in the reduced form implicating redox sensitive attributes to the proteins. Redox‐based modulations are often carried out by metalloproteins in mitigating oxidative stress and maintaining metal‐homeostasis within cells. To probe whether GRNs play a role in metal sequestration, we tested the metal binding propensity of the reduced forms of GRNs −3 and − 5 under neutral and acidic pH mimicking cytosolic and lysosomal conditions, respectively. We found, at neutral pH, both GRNs selectively bind Cu and no other divalent metal cations, with a greater specificity for Cu(I). Binding of Cu did not result in a disorder‐to‐order structural transition but partly triggered the multimerization of GRNs via uncoordinated cystines at both pH conditions. Overall, the results indicate that GRNs −3 and − 5 have surprisingly strong affinity for Cu in the pM range, comparable to other known copper sequestering proteins. The results also hint at a potential of GRNs to reduce Cu(II) to Cu(I), a process that has significance in mitigating Cu‐induced ROS cytotoxicity in cells. Together, this report uncovers metal‐coordinating property of GRNs for the first time, which may have profound significance in their structure and pathophysiological functions.

    

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