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Abstract Some pathogens use heme‐containing nitric oxide reductases (NORs) to reduce NO to N2O as their defense mechanism to detoxify NO and reduce nitrosative stress. This reduction is also significant in the global N cycle. Our previous experimental work showed that Fe and Co porphyrin NO complexes can couple with external NO to form N2O when activated by the Lewis acid BF3. A key difference from conventional two‐electron enzymatic reaction is that one electron is sufficient. However, a complete understanding of the entire reaction pathways and the more favorable reactivity for Fe remains unknown. Here, we present a quantum chemical study to provide such information. Our results confirmed Fe's higher experimental reactivity, showing advantages in all steps of the reaction pathway: easier metal oxidation for NO reduction and N−O cleavage as well as a larger size to expedite the N/O coordination mode transition. The Co system, with a similar product energy as the enzyme, shows potential for further development in catalytic NO coupling. This work also offers the first evidence that this new one‐electron NO reduction is both kinetically competitive and thermodynamically more favorable than the native pathway, supporting future initiatives in optimizing NO reduction agents in biology, environment, and industry.
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Not Limited to Iron: A Cobalt Heme–NO Model Facilitates N–N Coupling with External NO in the Presence of a Lewis Acid to Generate N 2 O
Abstract Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N2O. We previously reported that a heme Fe–NO model engages in this N−N bond‐forming reaction with NO. We now demonstrate that (OEP)CoII(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX3(X=F, C6F5) to generate N2O. DFT calculations support retention of the CoIIoxidation state for the experimentally observed adduct (OEP)CoII(NO⋅BF3), the presumed hyponitrite intermediate (P.+)CoII(ONNO⋅BF3), and the porphyrin π‐radical cation by‐product of this reaction, and that the π‐radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous‐to‐ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO‐to‐N2O conversion reaction.
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- PAR ID:
- 10122757
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 58
- Issue:
- 51
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 18598-18603
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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