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Title: Spectroscopic studies of molybdenum complexes as models for nitrogenase

Abstract

Because biological nitrogen fixation requires Mo, there is an interest in inorganic Mo complexes which mimic the reactions of nitrogen-fixing enzymes. Two such complexes are the dimer Mo/sub 2/O/sub 4/ (cysteine)/sub 2//sup 2 -/ and trans-Mo(N/sub 2/)/sub 2/(dppe)/sub 2/ (dppe = 1,2-bis(diphenylphosphino)ethane). The H/sup 1/ and C/sup 13/ NMR of solutions of Mo/sub 2/O/sub 4/(cys)/sub 2//sup 2 -/ are described. It is shown that in aqueous solution the cysteine ligands assume at least three distinct configurations. A step-wise dissociation of the cysteine ligand is proposed to explain the data. The Extended X-ray Absorption Fine Structure (EXAFS) of trans-Mo(N/sub 2/)/sub 2/(dppe)/sub 2/ is described and compared to the EXAFS of MoH/sub 4/(dppe)/sub 2/. The spectra are fitted to amplitude and phase parameters developed at Bell Laboratories. On the basis of this analysis, one can determine (1) that the dinitrogen complex contains nitrogen and the hydride complex does not and (2) the correct Mo-N distance. This is significant because the Mo inn both complexes is coordinated by four P atoms which dominate the EXAFS. A similar sort of interference is present in nitrogenase due to S coordination of the Mo in the enzyme. This model experiment indicates that, given adequate signal tomore » noise ratios, the presence or absence of dinitrogen coordination to Mo in the enzyme may be determined by EXAFS using existing data analysis techniques. A new reaction between Mo/sub 2/O/sub 4/(cys)/sub 2//sup 2 -/ and acetylene is described to the extent it is presently understood. A strong EPR signal is observed, suggesting the production of stable Mo(V) monomers. EXAFS studies support this suggestion. The Mo K-edge is described. The edge data suggests Mo(VI) is also produced in the reaction. Ultraviolet spectra suggest that cysteine is released in the course of the reaction.« less

Authors:
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
OSTI Identifier:
6428156
Report Number(s):
LBL-12823
ON: DE81023019; TRN: 81-011402
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: Thesis
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; ACETYLENE; CHEMICAL REACTIONS; MOLYBDENUM COMPLEXES; NMR SPECTRA; STRUCTURAL CHEMICAL ANALYSIS; X-RAY SPECTROSCOPY; CYSTEINE; ELECTRON SPIN RESONANCE; LIGANDS; NITROGENASE; ORGANIC NITROGEN COMPOUNDS; ORGANIC PHOSPHORUS COMPOUNDS; ULTRAVIOLET SPECTRA; ALKYNES; AMINO ACIDS; CARBOXYLIC ACIDS; COMPLEXES; ENZYMES; HYDROCARBONS; MAGNETIC RESONANCE; NITRO-GROUP DEHYDROGENASES; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC SULFUR COMPOUNDS; OXIDOREDUCTASES; RESONANCE; SPECTRA; SPECTROSCOPY; THIOLS; TRANSITION ELEMENT COMPLEXES; 400201* - Chemical & Physicochemical Properties; 400301 - Organic Chemistry- Chemical & Physicochemical Properties- (-1987); 550200 - Biochemistry

Citation Formats

Walker, T P. Spectroscopic studies of molybdenum complexes as models for nitrogenase. United States: N. p., 1981. Web. doi:10.2172/6428156.
Walker, T P. Spectroscopic studies of molybdenum complexes as models for nitrogenase. United States. https://doi.org/10.2172/6428156
Walker, T P. 1981. "Spectroscopic studies of molybdenum complexes as models for nitrogenase". United States. https://doi.org/10.2172/6428156. https://www.osti.gov/servlets/purl/6428156.
@article{osti_6428156,
title = {Spectroscopic studies of molybdenum complexes as models for nitrogenase},
author = {Walker, T P},
abstractNote = {Because biological nitrogen fixation requires Mo, there is an interest in inorganic Mo complexes which mimic the reactions of nitrogen-fixing enzymes. Two such complexes are the dimer Mo/sub 2/O/sub 4/ (cysteine)/sub 2//sup 2 -/ and trans-Mo(N/sub 2/)/sub 2/(dppe)/sub 2/ (dppe = 1,2-bis(diphenylphosphino)ethane). The H/sup 1/ and C/sup 13/ NMR of solutions of Mo/sub 2/O/sub 4/(cys)/sub 2//sup 2 -/ are described. It is shown that in aqueous solution the cysteine ligands assume at least three distinct configurations. A step-wise dissociation of the cysteine ligand is proposed to explain the data. The Extended X-ray Absorption Fine Structure (EXAFS) of trans-Mo(N/sub 2/)/sub 2/(dppe)/sub 2/ is described and compared to the EXAFS of MoH/sub 4/(dppe)/sub 2/. The spectra are fitted to amplitude and phase parameters developed at Bell Laboratories. On the basis of this analysis, one can determine (1) that the dinitrogen complex contains nitrogen and the hydride complex does not and (2) the correct Mo-N distance. This is significant because the Mo inn both complexes is coordinated by four P atoms which dominate the EXAFS. A similar sort of interference is present in nitrogenase due to S coordination of the Mo in the enzyme. This model experiment indicates that, given adequate signal to noise ratios, the presence or absence of dinitrogen coordination to Mo in the enzyme may be determined by EXAFS using existing data analysis techniques. A new reaction between Mo/sub 2/O/sub 4/(cys)/sub 2//sup 2 -/ and acetylene is described to the extent it is presently understood. A strong EPR signal is observed, suggesting the production of stable Mo(V) monomers. EXAFS studies support this suggestion. The Mo K-edge is described. The edge data suggests Mo(VI) is also produced in the reaction. Ultraviolet spectra suggest that cysteine is released in the course of the reaction.},
doi = {10.2172/6428156},
url = {https://www.osti.gov/biblio/6428156}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1981},
month = {Fri May 01 00:00:00 EDT 1981}
}