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The active E4 structure of nitrogenase studied with different DFT functionals.

Wen-Jie Wei1, Per E M Siegbahn2

  • 1Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, China.

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This study re-evaluates DFT functionals for nitrogenase (N2-fixing enzyme) E4 state energetics. Calculations suggest TPSS and TPSSh functionals do not align with experimental EPR findings for nitrogen fixation.

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Area of Science:

  • Biochemistry
  • Computational Chemistry
  • Enzyme Mechanisms

Background:

  • Nitrogenase is crucial for biological nitrogen fixation (N2 to ammonia).
  • The E4 state of nitrogenase is proposed to be key for N2 activation.
  • EPR experiments suggest a specific structure for the E4 state involving hydrides and sulfides in the FeMo-cofactor.

Purpose of the Study:

  • To critically assess the accuracy of recent DFT studies on the nitrogenase E4 state.
  • To investigate the energetics of the E4 state using TPSS and TPSSh functionals.
  • To determine if these DFT functionals agree with experimental EPR data.

Main Methods:

  • Density Functional Theory (DFT) calculations.
  • Evaluation of TPSS and TPSSh functionals.
  • Calculation of critical energetic values implied by EPR experiments.

Main Results:

  • Previous DFT studies claimed agreement with experimental suggestions for the E4 state structure.
  • This study's calculations indicate that TPSS and TPSSh functionals do not support the experimentally suggested E4 structure.
  • Energetic values calculated contradict the conclusions of recent DFT studies.

Conclusions:

  • The TPSS and TPSSh DFT functionals may not accurately represent the energetics of the nitrogenase E4 state.
  • Further investigation is needed to reconcile DFT calculations with experimental EPR data for nitrogenase.
  • The precise structure and energetics of the E4 state remain a critical area for computational and experimental research.