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Abstract Herein, aqueous nitrate (NO3−) reduction is used to explore composition‐selectivity relationships of randomly alloyed ruthenium‐palladium nanoparticle catalysts to provide insights into the factors affecting selectivity during this and other industrially relevant catalytic reactions. NO3−reduction proceeds through nitrite (NO2−) and then nitric oxide (NO), before diverging to form either dinitrogen (N2) or ammonium (NH4+) as final products, with N2preferred in potable water treatment but NH4+preferred for nitrogen recovery. It is shown that the NO3−and NO starting feedstocks favor NH4+formation using Ru‐rich catalysts, while Pd‐rich catalysts favor N2formation. Conversely, a NO2−starting feedstock favors NH4+at ≈50 atomic‐% Ru and selectivity decreases with higher Ru content. Mechanistic differences have been probed using density functional theory (DFT). Results show that, for NO3−and NO feedstocks, the thermodynamics of the competing pathways for N–H and N–N formation lead to preferential NH4+ or N2production, respectively, while Ru‐rich surfaces are susceptible to poisoning by NO2−feedstock, which displaces H atoms. This leads to a decrease in overall reduction activity and an increase in selectivity toward N2production. Together, these results demonstrate the importance of tailoring both the reaction pathway thermodynamics and initial reactant binding energies to control overall reaction selectivity.
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A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species
Abstract The cytochrome P450 homolog, TxtE, efficiently catalyzes the direct and regioselective aromatic nitration of the indolyl moiety of L‐tryptophan to 4‐nitro‐L‐tryptophan, using nitric oxide (NO) and dioxygen (O2) as co‐substrates. Pathways for such direct and selective nitration of heteroaromatic motifs present platforms for engineering new nitration biocatalysts for pharmacologically beneficial targets, among a medley of other pivotal industrial applications. Precise mechanistic details concerning this pathway are only weakly understood, albeit a heme iron(III)‐peroxynitrite active species has been postulated. To shed light on this unique reaction landscape, we investigated the indole nitration pathway of a series of biomimetic ferric heme superoxide mimics, [(Por)FeIII(O2−⋅)], in the presence of NO. Therein, our model systems gave rise to three distinct nitroindole products, including 4‐nitroindole, the product analogous to that obtained with TxtE. Moreover,15N and18O isotope labeling studies, along with meticulously designed control experiments lend credence to a heme peroxynitrite active nitrating agent, drawing close similarities to the tryptophan nitration mechanism of TxtE. All organic and inorganic reaction components have been fully characterized using spectroscopic methods. Theoretical investigation into several mechanistic possibilities deem a unique indolyl radical based reaction pathway as the most energetically favorable, products of which, are in excellent agreement with experimental findings.
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- PAR ID:
- 10586053
- Publisher / Repository:
- John Wiley & Sons, Inc
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 49
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/anie.202409430
