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CO2 Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

Journal Article · · Journal of the American Chemical Society
 [1];  [2];  [3];  [4];  [5];  [1]
  1. Utah State University
  2. Virginia Tech
  3. Intel Corp
  4. Northwestern University
  5. BATTELLE (PACIFIC NW LAB)

The reduction of N2 to NH3 by Mo-dependent nitrogenase at its active-site metal cluster FeMo-cofactor utilizes reductive elimination (re) of Fe-bound hydrides with obligatory loss of H2 to activate the enzyme for binding/reduction of N2. Earlier work showed that wild type nitrogenase and a nitrogenase with amino acid substitutions in the MoFe protein near FeMo-cofactor can catalytically reduce CO2 by 2 or 8 electrons/protons to carbon monoxide (CO) and methane (CH4) at low rates. Here, it is demonstrated that nitrogenase preferentially reduces CO2 by 2 electrons/protons to formate (HCOO-) at rates >10 times higher than rates of CO2 reduction to CO and CH4. The failure of H2 to inhibit CO2 reduction rules out a re mechanism in this case. Quantum mechanical (QM) calculations on the activated FeMo-cofactor with a bound hydride (E2(2H) state) favor a direct reaction of CO2 with the hydride (‘direct hydride transfer’ reaction pathway), with facile hydride transfer to CO2 yielding formate. In contrast, a significant barrier is observed for reaction of Fe-bound CO2 with the hydride (‘associative’ reaction pathway), which leads to CO and CH4. Remarkably, in the direct hydride transfer pathway, the Fe-H behaves as a hydridic hydrogen, whereas in the associative pathway it acts as a protic hydrogen. MoFe proteins with amino acid substitutions near FeMo-cofactor (a-70Val?Ala, a -195His?Gln) are found to significantly alter the distribution of products between formate and CO/CH4. This work is based upon work supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (LCS and DRD), the Division of Chemical Sciences, Geosciences, and Bio-Sciences (SR) and the NIH (GM 111097; BMH).

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
1706087
Report Number(s):
PNNL-SA-114863
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 17 Vol. 55
Country of Publication:
United States
Language:
English

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Cited By (10)

Selective electroreduction of CO 2 to formate on 3D [100] Pb dendrites with nanometer-sized needle-like tips journal January 2017
Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies: Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies journal February 2019
Computational Investigations of the Chemical Mechanism of the Enzyme Nitrogenase journal January 2020
Biofunctionalized conductive polymers enable efficient CO 2 electroreduction journal August 2017
Interfacing nature’s catalytic machinery with synthetic materials for semi-artificial photosynthesis journal October 2018
Influence of Energy and Electron Availability on In Vivo Methane and Hydrogen Production by a Variant Molybdenum Nitrogenase journal March 2019
Chicken fat for catalysis: a scaffold is as important for molecular complexes for energy transformations as it is for enzymes in catalytic function journal January 2019
Exploring the alternatives of biological nitrogen fixation journal January 2018
Interfacing nature's catalytic machinery with synthetic materials for semi-artificial photosynthesis. text January 2018
Critical computational analysis illuminates the reductive-elimination mechanism that activates nitrogenase for N 2 reduction journal October 2018

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