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1. Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation

   https://doi.org/10.1002/anie.202310753  

   Bradley, Robert D.; McManus, Brennan D.; Yam, Jessalyn G.; Carta, Veronica; Bahamonde, Ana (September 2023, Angewandte Chemie International Edition)

   Abstract This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni‐photoredox amide arylation, which contrasts with other Ni‐photoredox C‐heteroatom couplings that operate via Ni(I/III) self‐sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)‐mediated oxidative addition into the aryl bromide. Using NiCl₂as the precatalyst resulted in an observable induction period, which was found to arise from a photochemical activation event to generate Ni(0) and to be prolonged by unproductive comproportionation between the Ni(II) precatalyst and the in situ generated Ni(0) active species. Ligand exchange after oxidative addition yields a Ni(II) aryl amido complex, which was identified as the catalyst resting state for the reaction. Stoichiometric experiments showed that oxidation of this Ni(II) aryl amido intermediate was required to yield functionalized amide products. The kinetic data presented supports a rate‐limiting photochemically‐mediated Ni(II/III) oxidation to enable C−N reductive elimination. An alternative Ni(I/III) self‐sustained manifold was discarded based on EPR and kinetic measurements. The mechanistic insights uncovered herein will inform the community on how subtle changes in Ni‐photoredox reaction conditions may impact the reaction pathway, and have enabled us to include aryl chlorides as coupling partners and to reduce the Ni loading by 20‐fold without any reactivity loss. 

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2. Elementary reaction-based kinetic model for the fate of N -nitrosodimethylamine under UV oxidation

   https://doi.org/10.1039/D1EW00262G  

   Barrios, Benjamin; Kamath, Divya; Coscarelli, Erica; Minakata, Daisuke (August 2021, Environmental Science: Water Research & Technology)

   null (Ed.)

   UV photolysis is an effective process to remove nitrosamines from contaminated water resources. Nitrosamines represent a class of compounds with high potential for carcinogenicity and, therefore, there are serious concerns regarding their threat to human health and their environmental toxicity. Although the photochemical parameters of parent nitrosamines and their initial reaction pathways are well understood, the fate of nitrogen-containing species and reactive nitrogen species generated from nitrosamine degradation has not yet been elucidated. In this study, we develop an elementary reaction-based kinetic model for the photolysis of N -nitrosodimethylamine (NDMA) and the photochemical transformation products. We use density functional theory quantum mechanical calculations to calculate the aqueous-phase free energies of activation and reaction to investigate the kinetics and thermodynamics properties of the elementary reactions. We generate ordinary differential equations for all species involved in the identified reactions and solve them to obtain the time-dependent concentration profiles of NDMA and the degradation products at pH 3 and pH 7. The profiles are compared to experimental results in the literature to validate our elementary reaction-based kinetic model. This is the first study to develop an elementary reaction-based kinetic model for the photochemical reaction of NDMA and reactive nitrogen species. The findings of this study have a significant impact on the active research area of nitrosative stress and advanced oxidation processes that utilize nitrogen-containing compounds such as UV/nitrate and UV/chloramine advanced oxidation processes. 

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3. Highly Active and Stable Single Atom Rh ₁ /CeO ₂ Catalyst for CO Oxidation during Redox Cycling

   https://doi.org/10.1002/cctc.202201210  

   García‐Vargas, Carlos E.; Pereira‐Hernández, Xavier Isidro; Jiang, Dong; Alcala, Ryan; DeLaRiva, Andrew T.; Datye, Abhaya; Wang, Yong (January 2023, ChemCatChem)

   Abstract We report a single atom Rh₁/CeO₂catalyst prepared by the high temperature (800 °C) atom trapping (AT) method which is stable under both oxidative and reductive conditions. Infrared spectroscopic and electron microscopy characterization revealed the presence of exclusively ionic Rh species. These ionic Rh species are stable even under reducing conditions (CO at 300 °C) due to the strong interaction between Rh and CeO₂achieved by the AT method, leading to high and reproducible CO oxidation activity regardless of whether the catalyst is reduced or oxidized. In contrast, ionic Rh species in catalysts synthesized by a conventional impregnation approach (e. g., calcined at 350 °C) can be readily reduced to form Rh nanoclusters/nanoparticles, which are easily oxidized under oxidative conditions, leading to loss of catalytic performance. The single atom Rh₁/CeO₂catalysts synthesized by the AT method do not exhibit changes during redox cycling hence are promising catalysts for emission control where redox cycling is encountered, and severe oxidation (fuel cut) leads to loss of performance. 

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4. Complete Charge Regulation by a Redox Enzyme Upon Single Electron Transfer

   https://doi.org/10.1002/anie.202001452  

   Zhang, Ao Yun; Koone, Jordan C.; Dashnaw, Chad M.; Zahler, Collin T.; Shaw, Bryan F. (April 2020, Angewandte Chemie International Edition)

   Abstract The degree by which metalloproteins partially regulate net charge (Z) upon electron transfer (ET) was recently measured for the first time using “protein charge ladders” of azurin, cytochrome c, and myoglobin [Angew. Chem. Int. Ed.2018,57(19), 5364–5368;Angew. Chem.2018,130, 5462–5466]. Here, we show that Cu, Zn superoxide dismutase (SOD1) is unique among proteins in its ability to resist changes in net charge upon single ET (e.g., ΔZ_ET(SOD1)=0.05±0.08 per electron, compared to ΔZ_ET(Cyt‐c)=1.19±0.02). This total regulation of net charge by SOD1 is attributed to the protonation of the bridging histidine upon copper reduction, yielding redox centers that are isoelectric at both copper oxidation states. Charge regulation by SOD1 would prevent long range coulombic perturbations to residue pK_a’s upon ET at copper, allowing SOD1’s “electrostatic loop” to attract superoxide with equal affinity (at both redox states of copper) during diffusion‐limited reduction and oxidation of superoxide. 

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5. Hydrogel Patterning with Catechol Enables Networked Electron Flow

   https://doi.org/10.1002/adfm.202007709  

   Wu, Si; Zhao, Zhiling; Rzasa, John_R; Kim, Eunkyoung; Li, Jinyang; VanArsdale, Eric; Bentley, William_E; Shi, Xiaowen; Payne, Gregory_F (January 2021, Advanced Functional Materials)

   Abstract Reduction–oxidation (redox) reactions provide a distinct modality for biological communication that is fundamentally different from the more‐familiar ion‐based electrical modality. Biology uses these two modalities for communication through different systems (immune versus nervous), and uses different mechanisms to control the flow of the charge carriers: the flow of soluble ions is controlled using structural barriers (i.e., membranes) and gates (e.g., membrane‐spanning protein channels), while the flow of insoluble electrons is controlled using redox‐reaction networks. Here, a simple electrochemical approach to pattern catechols onto a flexible polysaccharide hydrogel is reported and it is demonstrated that the patterned catechol regions serve as nodes for the mediated flow of electrons through redox reactions. Electron flow through this node involves the switching of binary redox states (oxidized and reduced) and this node's redox state can be detected (i.e., “read”) by passively observing its optical absorbance, or actively switching its redox‐state electrochemically. Further, this catechol node can be switched through biological mechanisms, and this enables the fabricated catechol node to be embedded within biochemical redox reaction networks to facilitate the spanning of bio‐electronic communication. Thus, it is envisioned that catechols can emerge as a molecular equivalent to a transistor for miniaturize‐able, deployable and sustainable redox‐linked bioelectronics. 

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