Density Functional Theory Calculations and Exploration of a Possible Mechanism of N<sub>2</sub> Reduction by Nitrogenase

Huniar, Uwe; Ahlrichs, Reinhart; Coucouvanis, D.

doi:10.1021/ja030541z

Cited by 98 publications

(86 citation statements)

References 79 publications

(104 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Several density functional theory (DFT) studies on FeMoco were published thus far. [3][4][5][6][7] Although they do not agree in essential steps of the biological mechanism, they all suggest that the reduction reaction starts at the iron centers of FeMoco. Recently, the first nitrogen reducing complex that works catalytically at the ambient conditions of nitrogenase was synthesized.…”

Section: Introductionmentioning

confidence: 95%

“…[9] This model was substantiated by some of the above-mentioned DFT calculations only recently. [6,7] A main goal of Sellmann and co-workers was the synthesis of a sulfur-based dinitrogen-reducing ruthenium or iron complex with the properties of working i) catalytically, ii) at ambient conditions and iii) by using only moderately strong reductants. [10,11] To date, [m-N 2 {Ru(PiPr 3 )("N 2 Me 2 S 2 ")} 2 ]["N 2 Me 2 S 2 " 2À = 1,2-ethanediamine-N,N'-dimethyl-N,N'-bis(2-benzenethiolate)(2À)], represents the only known example of a stable dinuclear metalsulfur N 2 complex.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Kirchner

Reiher

Hille

et al. 2004

Chemistry A European J

View full text Add to dashboard Cite

Car-Parrinello molecular dynamics study of the initial dinitrogen reduction step in Sellmann-type nitrogenase model complexes AbstractWe have studied reduction reactions for nitrogen fixation at Sellmann-type model complexes with Car-Parrinello simulation techniques. These dinuclear complexes are especially designed to emulate the so-called open-side FeMoco model. The main result of this work shows that in order to obtain the reduced species several side reactions have to be suppressed. These involve partial dissociation of the chelate ligands and hydrogen atom transfer to the metal center. Working at low temperature turns out to be one necessary pre-requisite in carrying out successful events. The successful events cannot be described by simple reaction coordinates. Complicated processes are involved during the initiation of the reaction. Our theoretical study emphasizes two experimental strategies which are likely to inhibit the side reactions. Clamping of the two metal fragments by a chelating phosphane ligand should prevent dissociation of the complex. Furthermore, introduction of tert-butyl substituents could improve the solubility and should thus allow usage of a wider range of (mild) acids, reductants, and reaction conditions.

show abstract

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Kirchner

Reiher

Hille

et al. 2004

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…This exclusion was made on the basis of electronic energy differences of minimum structures, which turned out to be as small as 26 kJ mol À1 in isolated FeMoco model systems. [19] In reference [22] molybdenum is considered as the N 2 coordinating center. Furthermore, all DFT studies on FeMoco rely on pure density functionals like (R)PBE [23,24] and BP86, [25,26] while it is well known that the energetical ordering of different spin states can hardly be reproduced without inclusion of exact exchange in critical cases.…”

Section: Introductionmentioning

confidence: 99%

Nitrogen Fixation under Mild Ambient Conditions: Part I—The Initial Dissociation/Association Step at Molybdenum Triamidoamine Complexes

Guennic

Kirchner

Reiher

2005

Chemistry A European J

View full text Add to dashboard Cite

In several recent studies Schrock and collaborators demonstrated for the first time how molecular dinitrogen can be catalytically transformed under mild and ambient conditions to ammonia by a molybdenum triamidoamine complex. In this work, we investigate the geometrical and electronic structures involved in this process of dinitrogen activation with quantum chemical methods. Density functional theory (DFT) has been employed to calculate the coordination energies of ammonia and dinitrogen relevant for the dissociation/association step in which ammonia is substituted by dinitrogen. In the DFT calculations the triamidoamine chelate ligand has been modeled by a systematic hierarchy of increasingly complex substituents at the amide nitrogen atoms. The most complex ligand considered is an experimentally known ligand with an HMT = 3,5-(2,4,6-Me3C6H2)2C6H3 substituent. Several assumptions by Schrock and collaborators on key reaction steps are confirmed by our calculations. Additional information is provided on many species not yet observed experimentally. Particular attention is paid to the role of the charge of the complexes. The investigation demonstrates that dinitrogen coordination is enhanced for the negatively charged metal fragment, that is, coordination is more favorable for the anionic metal fragment than for the neutral species. Coordination of N2 is least favorable for the cationic metal fragment. Furthermore, ammonia abstraction from the cationic complex is energetically unfavorable, while NH3 abstraction is less difficult from the neutral and easily feasible from the anionic low-spin complex.

show abstract

“…It is generally accepted that the sequential addition of electrons and protons to the N 2 bound on FeMo-cofactor results in a series of semi-reduced and semiprotonated intermediates (11)(12)(13)(14)(15)(16)(17)(18)(19), ultimately yielding two ammonia molecules. In contrast to this situation, much more is known about how N 2 is activated and reduced by metal complexes (20).…”

mentioning

confidence: 99%

Diazene (HNNH) Is a Substrate for Nitrogenase: Insights into the Pathway of N₂ Reduction

et al. 2007

View full text Add to dashboard Cite

Nitrogenase catalyzes the sequential addition of six electrons and six protons to a N 2 that is bound to the active site metal cluster FeMo-cofactor, yielding two ammonia molecules. The nature of the intermediates bound to FeMo-cofactor along this reduction pathway remains unknown, although it has been suggested that there are intermediates at the level of reduction of diazene (HN=NH, also called diimide) and hydrazine (H 2 N-NH 2 ). Through in situ generation of diazene during nitrogenase turnover, we show that diazene is a substrate for the wild-type nitrogenase and is reduced to NH 3 . Diazene reduction, like N 2 reduction, is inhibited by H 2 . This contrasts with the lack of H 2 inhibition when nitrogenase reduces hydrazine. These results support the existence of an intermediate early in the N 2 reduction pathway at the level of reduction of diazene. Freeze-quenching a MoFe protein variant with α-195 His substituted by Gln and α-70 Val substituted by Ala during steady-state turnover with diazene resulted in conversion of the S = 3/2 resting state FeMo-cofactor to a novel S = 1/2 state with g 1 = 2.09, g 2 = 2.01, and g 3 ~ 1.98. 15 N-and 1 H-ENDOR establish that this state consists of a diazene-derived [-NH x ] moiety bound to FeMo-cofactor. This moiety is indistinguishable from the hydrazine-derived [-NH x ] moiety bound to FeMo-cofactor when the same MoFe protein is trapped during turnover with hydrazine. These observations suggest that diazene joins the normal N 2 -reduction pathway, and that the diazene-and hydrazine-trapped turnover states represent the same intermediate in the normal reduction of N 2 by nitrogenase. The implications of these findings for the mechanism of N 2 reduction by nitrogenase are discussed. KeywordsFeMo-cofactor; EPR; ENDOR; Active Site; Substrate Nitrogenase is the enzyme responsible for catalyzing biological reduction of N 2 to two NH 3 , an essential reaction in the global biogeochemical nitrogen cycle (1-3). The minimum stoichiometry for the nitrogenase catalyzed reduction of N 2 involves delivery of 8e − and 8H + (eqn 1). † This work was supported by grants from the National Institutes of Health (R01-GM59087 to LCS and DRD; HL13531 to BMH), the National Science Foundation (MCB-0316038 to BMH) and the United States Department of Agriculture Postdoctoral Fellowship program (2004-35318-14905 to BMB).*Address correspondence to these authors: LCS, phone (435) 797-3964, fax (435) email seefeldt@cc.usu.edu; DRD, phone (540) 231-5895, fax (540) email deandr@vt.edu; BMH, phone (847) (Figure 1).Relatively little is known at a molecular level about the nitrogenase N 2 -reduction mechanism beyond the fact that N 2 binds to and is reduced at one or more of the metal atoms of FeMocofactor ( Figure 1) Both the Chatt and Schrock cycles belong to one fundamental class of potential nitrogenase mechanismsin which the first three 'H-atoms' (e − /H + ) are sequentially added to a single N atom, in those instances the distal N of an end-on bound N 2 , followed by cleava...

show abstract

Density Functional Theory Calculations and Exploration of a Possible Mechanism of N₂ Reduction by Nitrogenase

Cited by 98 publications

References 79 publications

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Nitrogen Fixation under Mild Ambient Conditions: Part I—The Initial Dissociation/Association Step at Molybdenum Triamidoamine Complexes

Diazene (HNNH) Is a Substrate for Nitrogenase: Insights into the Pathway of N₂ Reduction

Contact Info

Product

Resources

About

Density Functional Theory Calculations and Exploration of a Possible Mechanism of N2 Reduction by Nitrogenase

Cited by 98 publications

References 79 publications

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Car–Parrinello Molecular Dynamics Study of the Initial Dinitrogen Reduction Step in Sellmann‐Type Nitrogenase Model Complexes

Nitrogen Fixation under Mild Ambient Conditions: Part I—The Initial Dissociation/Association Step at Molybdenum Triamidoamine Complexes

Diazene (HNNH) Is a Substrate for Nitrogenase: Insights into the Pathway of N2 Reduction

Contact Info

Product

Resources

About

Density Functional Theory Calculations and Exploration of a Possible Mechanism of N₂ Reduction by Nitrogenase

Diazene (HNNH) Is a Substrate for Nitrogenase: Insights into the Pathway of N₂ Reduction