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Bazhenova, T. A.; Bazhenova, M. A.; Петрова, Г. Н.; Mironova, S. A.

doi:10.1023/a:1016005801442

Cited by 5 publications

(9 citation statements)

References 19 publications

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“…Since the rate of the reduction reaction depends considerably on the sur face area of the amalgam [15], it is obvious that adding a compound that has both proton donating and sur face active properties is favorable for the system to stay in the finely dispersed state. These requirements are met by stearic acid.…”

Section: Resultsmentioning

confidence: 99%

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Effect of the acidity and chemical nature of the protonating agent on the rate of acetylene reduction catalyzed by the nitrogenase active site isolated from the enzyme

2012

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The effect of the acidity (pK a ) of the source of protons on the rate and selectivity of acetylene reduction has been investigated in order to elucidate the mechanism of protonation of substrate molecules coordinated to the reduced FeMoco cluster. A number of compounds whose pK a in DMF varies between 6 and 20 have been examined as protonating agents. The rate of the reaction is almost independent of the acid ity of the proton donor in a wide pK a range. This can be explained in terms of the specific features of substrate protonation catalyzed by iron-sulfur clusters. Active protonating agents in the system are those which react with the catalyst to form hydrogen bonded association species or those which are ligands reversibly binding to the cluster and are capable of donating protons, likely with simultaneous electron transfer.

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Section: Resultsmentioning

confidence: 99%

“…The iron-molybdenum cofactor was isolated from the MoFe protein of Azotobacter vinelandii nitroge nase using earlier described procedures [15,16]. According to the analysis of FeMoco for molybdenum and iron (see below), the FeMoco yield was 70-85%.…”

Section: Chemicals and Preparationsmentioning

confidence: 99%

Effect of the acidity and chemical nature of the protonating agent on the rate of acetylene reduction catalyzed by the nitrogenase active site isolated from the enzyme

2012

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“…It is exactly what we observe as a dependence of C 2 H 2 reduction on FeMoco concentration in solution for europium amalgam electrode in the presence of PhSH. 9 The rate of C 2 H 6 formation which accumulates in parallel to C 2 H 4 , also depends on the specified cathode potential as an exponential function. This implies that for both products the reaction rate is limited by electron trans fer from an external reducing agent to the catalyst.…”

Section: Resultsmentioning

confidence: 99%

“…This implies that, as for enzymatic catalysis, N 2 and С 2 Н 2 as ligands compete for binding at the same coordination site on the FeMoco cluster re duced by amalgam, with quantitative parameters charac teristic of nitrogenase enzyme in vitro, both wild type 12, 13 and mutant. 13, 14 Our data [8][9][10][11] show that in many aspects FeMoco iso lated from the enzyme catalyzes C 2 H 2 reduction quite similarly to M center of nitrogenase. Therefore, it can be concluded that the FeMoco cluster is an obligatory and, to some extent, sufficient active center of the enzyme: it is responsible for the formation of a substrate-enzyme complex and specificity of the nitrogenase action as a catalyst.…”

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confidence: 84%

“…8, 9 The reaction proceeds in aprotic sol vents (DMF, N methylformamide, THF) where FeMoco is stable in the absence of oxygen for a long time, in the presence of electron donors, for instance, zinc amalgam (Zn/Hg; Е 0 = -0.84 V against the standard hydrogen electrode (SHE)) or europium amalgam (Eu/Hg; Е 0 = -1.4 V against SHE) 8 and proton donors, e.g., thiophenol.…”

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Effect of the potential of an external electron donor on C2H2 reduction catalyzed by the nitrogenase active center (FeMoco) isolated from the enzyme

et al. 2004

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The effect of potential value and chemical properties of an external electron donor on C 2 H 2 reduction catalyzed by nitrogenase active center (cluster [(µ 6 N)Fe 7 MoS 9 •homocitrate] FeMoco isolated from the enzyme) has been investigated in the presence of proton donors of different acidity. The temperature-reaction rate dependences of these reactions have been studied. It has been shown that the rate limiting steps of the reactions differ depending on the proton donor used. When thiophenol or water are used as proton donors, and electrochemical step -the electron transfer from cathode to adsorbed catalytic cluster -has been found to be a rate limiting one. The effective activation energy of ethane formation as a product of four electron C 2 H 2 reduction is found to be 1.5 times lower than that of ethylene, namely, 13 kcal mol -1 . When stronger acid, pentafluorothiophenol, is used as a proton donor, the chemical step of intramolecular rearrangement of the catalyst-substrate complex taking place in solution becomes a rate limiting one. The effective activation energies of both ethylene and ethane become equal to 32 kcal mol -1 .The main function of the enzyme nitrogenase is the catalysis of the mild reduction of atmospheric nitrogen to ammonia which is the first step in the global "nitrogen" cycle. The enzyme has already been studied for a long time, and the last decade was the most productive in terms of obtaining information on the enzyme structure. The three dimensional X ray crystal structures of both protein components of nitrogenase, Fe protein and MoFe protein, were determined for several nitrogenases from different bacteria. 1-3 The structures of the metal clusters included in the protein components of nitrogenases were established. The Fe protein contains a [4Fe-4S] cluster, while the MoFe protein contains two types of metal clus ters unique in composition and structure: the so called P cluster [8Fe-7S], 2 and M center: iron molybdenum cofactor [(µ 6 N)Fe 7 MoS 9 •homocitrate] or FeMoco. 2,3 Generally, the functions of both protein components of the enzyme and all three types of metal clusters are clear. From the experimental data available up to date, it is commonly accepted that FeMoco acts as catalytic center of enzyme. 4 Although the composition and molecular structure of the cluster are known, the detailed mecha nism of catalysis of N 2 reduction involving FeMoco is to be elucidated. Where and how a substrate binds to the reduced cofactor? What is the mechanism of nitrogen protonation to form ammonia? What intermediate states are formed during this process?Unlike for P cluster, it is possible to probe the reactiv ity of FeMoco not only as a part of enzyme but also as an isolated cluster. 5 FeMoco as the M center of the MoFe protein and the cofactor isolated from the protein are not identical species but very similar. 6,7 We study the reactiv ity of FeMoco extracted from the protein as a catalyst of reactions of nitrogenase substrate reduction when elec trons, protons, and the substrate are provi...

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Chemical Models, Theoretical Calculations, and the Reactivity of Isolated Iron-Molybdenum Cofactor

Barrière

Durrant

Pickett

2004

Catalysts for Nitrogen Fixation

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Cited by 5 publications

References 19 publications

Effect of the acidity and chemical nature of the protonating agent on the rate of acetylene reduction catalyzed by the nitrogenase active site isolated from the enzyme

Effect of the acidity and chemical nature of the protonating agent on the rate of acetylene reduction catalyzed by the nitrogenase active site isolated from the enzyme

Effect of the potential of an external electron donor on C2H2 reduction catalyzed by the nitrogenase active center (FeMoco) isolated from the enzyme

Chemical Models, Theoretical Calculations, and the Reactivity of Isolated Iron-Molybdenum Cofactor

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