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We have calculated redox potentials of the two metal clusters in Mo-nitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron–sulfur clusters with 1–4 Fe ions, involving QM-cluster calculations in continuum solvent and large QM systems (400–500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the P-cluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P1+/PN redox potential is nearly the same independently of whether P1+ is protonated or deprotonated, explaining why redox titrations do not show any pH dependence. For the FeMo cluster, the calculations clearly show that the formal oxidation state of the cluster in the resting E0 state is , in agreement with previous experimental studies and QM calculations. Moreover, the redox potentials of the first five E0–E4 states are nearly constant, as is expected if the electrons are delivered by the same site (the P-cluster). However, the redox potentials are insensitive to the formal oxidation states of the Fe ion (i.e., whether the added protons bind to sulfide or Fe ions). Finally, we show that the later (E4–E8) states of the reaction mechanism have redox potential that are more positive (i.e., more exothermic) than that of the E0/E1 couple. 相似文献
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Prof. Dr. Jörg Grunenberg 《Angewandte Chemie (International ed. in English)》2017,56(25):7288-7291
The first quantum-mechanical calculations of all relevant potential constants in both the iron-molybdenum cofactor and the iron-vanadium cofactor of nitrogenase suggest that the carbide is bound to the center of the enzyme much more strongly than hitherto assumed. Previous studies seemed to indicate a dummy function of the interstitial carbon, with a weak force constant (ca. 0.32 N cm−1). Our new investigations confirm a different picture: the central carbon atom binds the iron-sulfur cluster through six covalent C−Fe bonds. With a potential constant of more than 1.3 N cm−1, the interstitial carbon also appears to be dynamically persistent. According to our investigations, the values for the elasticity within the iron-sulfur cluster have to be corrected too. These new details on the mechano-chemical properties of the FeMo cofactor will be important for elucidating the catalytic cycle of nitrogen fixation. By implementing our new algorithm in the freely available COMPLIANCE program, the dependence on the coordinates during the calculation of Hesse matrices is eliminated completely. 相似文献
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Man‐Rong Li David Walker Maria Retuerto Tapati Sarkar Joke Hadermann Peter W. Stephens Mark Croft Alexander Ignatov Christoph P. Grams Joachim Hemberger Israel Nowik P. Shiv Halasyamani T. Thao Tran Swarnakamal Mukherjee Tanusri Saha Dasgupta Martha Greenblatt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(32):8564-8568
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Reduced and oxidized forms of the FeMo- cofactor of Azotobacter vinelandii nitrogenase are examined theoretically within the intermediate neglect of differential overlap model. The results obtained
favor one of the experimentally suggested modes of contraction of the metal system which results in an expansion of the central
cavity of the cofactor. The bond index analysis indicates marked changes in the Mo coordination upon electron addition which
may contribute to an opening of the Mo atom as a possible binding site at the advanced stages of the reduction process. In
this work we also compare the 39- and 41-electron [MoFe7] core as possible native resting states, both compatible with known spin and M?ssbauer spectroscopies.
Received: 19 March 1997 / Accepted: 8 May 1997 相似文献
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Zexing Cao Zhaohui Zhou Huilin Wan Qianer Zhang 《International journal of quantum chemistry》2005,103(3):344-353
We used density functional calculations to model dinitrogen reduction by a FeMo cofactor containing a central nitrogen atom and by a Mo‐based catalyst. Plausible intermediates, reaction pathways, and relative energetics in the enzymatic and catalytic reduction of N2 to ammonia at a single Mo center are explored. Calculations indicate that the binding of N2 to the Mo atom and the subsequent multiple proton–electron transfer to dinitrogen and its protonated species involved in the conversion of N2 are feasible energetically. In the reduction of N2 the Mo atom experiences a cycled oxidation state from Mo(IV) to Mo(VI) by nitrogenase and from Mo(III) to Mo(VI) by the molybdenum catalyst, respectively, tuning the gradual reduction of N2. Such a wide range of oxidation states exhibited by the Mo center is crucial for the gradual reduction process via successive proton–electron transfer. Present results suggest that the Mo atom in the N‐centered FeMo cofactor is a likely alternative active site for dinitrogen binding and reduction under mild conditions once there is an empty site available at the Mo site. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
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Dr. Man‐Rong Li Dr. David Walker Maria Retuerto Tapati Sarkar Dr. Joke Hadermann Dr. Peter W. Stephens Dr. Mark Croft Alexander Ignatov Dr. Christoph P. Grams Joachim Hemberger Dr. Israel Nowik Dr. P. Shiv Halasyamani T. Thao Tran Dr. Swarnakamal Mukherjee Dr. Tanusri Saha Dasgupta Martha Greenblatt 《Angewandte Chemie (International ed. in English)》2013,52(32):8406-8410
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Thomas Spatzal Oliver Einsle Susana L. A. Andrade 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(38):10303-10306