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Title: Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase

Abstract

Fungal denitrification plays a crucial role in the nitrogen cycle and contributes to the total N 2O emission from agricultural soils. Here, cytochrome P450 NO reductase (P450nor) reduces two NO to N 2O using a single heme site. Despite much research, the exact nature of the critical "Intermediate I" responsible for the key N-N coupling step in P450nor is unknown. This species likely corresponds to a Fe-NHOH-type intermediate with an unknown electronic structure. Here we report a new strategy to generate a model system for this intermediate, starting from the iron(III) methylhydroxylamide complex [Fe(3,5-Me-BAFP)(NHOMe)] (1), which was fully characterized by 1H NMR, UV-vis, electron paramagnetic resonance, and vibrational spectroscopy (rRaman and NRVS). Our data show that 1 is a high-spin ferric complex with an N-bound hydroxylamide ligand that is strongly coordinated (Fe–N distance, 1.918 Å; Fe-NHOMe stretch, 558 cm –1). Simple one-electron oxidation of 1 at –80 °C then cleanly generates the first model system for Intermediate I, [Fe(3,5-Me-BAFP)(NHOMe)] + (1 +). UV–vis, resonance Raman, and Mössbauer spectroscopies, in comparison to the chloro analogue [Fe(3,5-Me-BAFP)(Cl)] +, demonstrate that 1 + is best described as an Fe III-(NHOMe)• complex with a bound NHOMe radical. Further reactivity studies show that 1 +more » is highly reactive toward NO, a reaction that likely proceeds via N–N bond formation, following a radical–radical-type coupling mechanism. Here our results therefore provide experimental evidence, for the first time, that an Fe III-(NHOMe)• electronic structure is indeed a reasonable electronic description for Intermediate I and that this electronic structure is advantageous for P450nor catalysis because it can greatly facilitate N–N bond formation and, ultimately, N 2O generation.« less

Authors:
 [1];  [2];  [1];  [3];  [3];  [3]; ORCiD logo [2]; ORCiD logo [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. The Pennsylvania State Univ., University Park, PA (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1509892
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 58; Journal Issue: 2; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

McQuarters, Ashley B., Blaesi, Elizabeth J., Kampf, Jeff W., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael, Krebs, Carsten, and Lehnert, Nicolai. Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase. United States: N. p., 2019. Web. doi:10.1021/acs.inorgchem.8b02947.
McQuarters, Ashley B., Blaesi, Elizabeth J., Kampf, Jeff W., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael, Krebs, Carsten, & Lehnert, Nicolai. Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase. United States. doi:10.1021/acs.inorgchem.8b02947.
McQuarters, Ashley B., Blaesi, Elizabeth J., Kampf, Jeff W., Alp, E. Ercan, Zhao, Jiyong, Hu, Michael, Krebs, Carsten, and Lehnert, Nicolai. Wed . "Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase". United States. doi:10.1021/acs.inorgchem.8b02947.
@article{osti_1509892,
title = {Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase},
author = {McQuarters, Ashley B. and Blaesi, Elizabeth J. and Kampf, Jeff W. and Alp, E. Ercan and Zhao, Jiyong and Hu, Michael and Krebs, Carsten and Lehnert, Nicolai},
abstractNote = {Fungal denitrification plays a crucial role in the nitrogen cycle and contributes to the total N2O emission from agricultural soils. Here, cytochrome P450 NO reductase (P450nor) reduces two NO to N2O using a single heme site. Despite much research, the exact nature of the critical "Intermediate I" responsible for the key N-N coupling step in P450nor is unknown. This species likely corresponds to a Fe-NHOH-type intermediate with an unknown electronic structure. Here we report a new strategy to generate a model system for this intermediate, starting from the iron(III) methylhydroxylamide complex [Fe(3,5-Me-BAFP)(NHOMe)] (1), which was fully characterized by 1H NMR, UV-vis, electron paramagnetic resonance, and vibrational spectroscopy (rRaman and NRVS). Our data show that 1 is a high-spin ferric complex with an N-bound hydroxylamide ligand that is strongly coordinated (Fe–N distance, 1.918 Å; Fe-NHOMe stretch, 558 cm–1). Simple one-electron oxidation of 1 at –80 °C then cleanly generates the first model system for Intermediate I, [Fe(3,5-Me-BAFP)(NHOMe)]+ (1+). UV–vis, resonance Raman, and Mössbauer spectroscopies, in comparison to the chloro analogue [Fe(3,5-Me-BAFP)(Cl)]+, demonstrate that 1+ is best described as an FeIII-(NHOMe)• complex with a bound NHOMe radical. Further reactivity studies show that 1+ is highly reactive toward NO, a reaction that likely proceeds via N–N bond formation, following a radical–radical-type coupling mechanism. Here our results therefore provide experimental evidence, for the first time, that an FeIII-(NHOMe)• electronic structure is indeed a reasonable electronic description for Intermediate I and that this electronic structure is advantageous for P450nor catalysis because it can greatly facilitate N–N bond formation and, ultimately, N2O generation.},
doi = {10.1021/acs.inorgchem.8b02947},
journal = {Inorganic Chemistry},
number = 2,
volume = 58,
place = {United States},
year = {2019},
month = {1}
}

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