Kinetics of the interconversion of sulfido- and oxomolybdate(VI) species MoOxS4-x2- in aqueous solutions

Harmer, Mark A.; Sykes, A. Geoffrey

doi:10.1021/ic50212a006

Cited by 64 publications

(43 citation statements)

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“…These conclusions are strongly supported by reports of both the aquation of [MoS412-and the reaction of H2S with [MoOS3I2- [27]. Both reactions are extremely slow in water at pH 9, conditions not too dissimilar from those used herein, due to steric crowding by the sulfides at Mo coupled with an associative-type mechanism.…”

Section: Decomposition Of Synthetic Fe-mo-s Complexessupporting

confidence: 89%

Elicitation of thiomolybdates from the iron‐molybdenum cofactor of nitrogenase

Newton

Gheller

Hedman

et al. 1986

European Journal of Biochemistry

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Aerial oxidation of the iron-molybdenum cofactor (FeMoco) of Azotobacter vinelandii nitrogenase has been shown to yield either the tetrathiomolybdate ion ([MoS4I2-) or the oxotrithiomolybdate ion ([MoOS3l2-), depending on the reaction conditions. Thus, when N-methylformamide (NMF) solutions of FeMoco either were titrated with measured aliquots of air or were diluted with air-saturated NMF, [MoOS3I2-was found to be the predominant product while dilution of NMF solutions of FeMoco with air-saturated methanol produced [MoS4I2-almost exclusively. Similar aerial oxidation of solutions of chemically synthesized Fe-Mo-S clusters showed that significant information about the molybdenum environment in these species could be deduced from the nature of the elicited thiomolybdates. The differences in decomposition products as a function of solvent are postulated to be due to the loss through precipitation of the reducing agent sodium dithionite on addition of methanol but not NMF. These overall decomposition results are discussed in the context of recent X-ray absorption spectroscopic data which suggest the presence of an 'MoS3' core in FeMoco. A possible mechanism whereby [MoS4I2-might be rapidly formed from this core is presented.The iron-molybdenum cofactor (FeMoco) is the extruded, putative Nz-reducing site of nitrogenase [I], obtained by acid treatment of the molybdenum-iron protein of that enzyme followed by extraction with the organic solvent N-methylformamide (NMF) [2, 31. Nitrogenase contains two such cofactors, each of which accounts for one Mo and 6 -8 atoms of Fe and probably 8 -9 atoms of sulfur arranged in a cluster [2-41 so far unrecognized elsewhere in biology [3-91. Although numerous attempts have been made to simulate the structure and/or chemical properties of FeMoco via synthesis and study of Mo-Fe-S cluster compounds, a close chemical model of the site has remained elusive [lo-131. The most incisive structural information on FeMoco has come from Xray absorption spectroscopy (XAS), both near edge spectra (XANES) and fine structure analysis (EXAFS), with the recent data [14, 151 suggesting a molybdenum environment which is comprised of three 0 (or N) and three S atoms from anionic ligands. However, although EXAFS is very precise in identifying the type of donor atom and its distance from the absorber (Mo), it is very much less precise in defining the number of such atoms. Thus, in order to obtain independent, complementary insight into the nature of the molybdenum environment in FeMoco, especially with respect to the number of S donor atoms, we have carried out oxidative decomposition studies of this entity and herein report our results, which Correspondence to W. E.

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Section: Decomposition Of Synthetic Fe-mo-s Complexessupporting

confidence: 89%

Elicitation of thiomolybdates from the iron‐molybdenum cofactor of nitrogenase

Newton

Gheller

Hedman

et al. 1986

European Journal of Biochemistry

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“…It has been proposed that local concentrations of sulphide in rumen contents may be sufficient to generate TTM (El Gallad el al. 1983) and it is known that an equilibrium is established between AM, H,S, and the mono-, di-, tri-and tetrathiomolybdate species in aqueous solutions (Weber et al 1979;Harmer & Sykes, 1980). Although only a low concentration of TTM is formed at equilibrium in pure aqueous solutions, we suggest that the continual removal of TTM via binding with proteins and other macromolecules in rumen contents could alter the position of equilibrium and result in the formation of more TTM than would be expected from solution chemistry.…”

Section: Discussionmentioning

confidence: 99%

Involvement of the solid phase of rumen digesta in the interaction between copper, molybdenum and sulphur in sheep

Allen

Gawthorne

1987

Br J Nutr

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1. Merino sheep fed on a diet of chopped wheaten hay, chopped lucerne (Medicago saliva) hay and oat grain were the source of rumen contents for the study. The diet contained (mg/kg dry weight) 3.3 copper, 024 molybdenum and 2-8 sulphur. The effects of adding between 5 and 25 mg Mo/kg as ammonium molybdate (AM) or tetrathiomolybdate (TTM) on the distribution and forms of Cu and Mo in rumen contents were investigated in vivo and in vitro. 2.Approximately 88 YO of the Cu and 94% of the Mo in rumen contents were associated with the solid phase.When AM or TTM was added to rumen contents in vivo or in vitro the proportion of these elements in the solid phase was increased at the expense of the fluid phase.3. The addition of AM and TTM to rumen contents also decreased the proportion of Cu that was soluble in trichloroacetic acid (50 g/l ; TCA) and increased the proportion of Cu that was not extractable by sequential treatment with TCA and neutral detergent.4. Column chromatography of neutral-detergent extracts of rumen contents revealed that TTM treatment caused Cu to be strongly bound to proteins of high molecular weight.5. Addition of sulphide to rumen contents did not result in significant changes in the distribution of Cu between the fluid and solid phases, or in the solubility of Cu in TCA.6. It is postulated that constant removal of TTM from the fluid phase via reaction with proteins and other macromolecules in the solid phase results in greater formation of TTM in vivo than would be expected from solution chemistry. The molybdo-proteins so formed are strong chelators of Cu and may be the agents responsible for the decrease in Cu absorption in animals that consume diets containing high concentrations of Mo.When relatively high concentrations of molybdenum and sulphur are simultaneously present in the diet of ruminants the availability of copper to the animal is seriously compromised (Dick, 1956). The production of thiomolybdates in the rumen, and the subsequent decrease in the availability of Cu due to the formation of insoluble Cu thiomolybdates has been suggested as a hypothesis for the interaction (Dick et al. 1975). Confirmation of the hypothesis via spectrophotometric evidence of the presence of these compounds in rumen contents has been hampered by interference from other compounds, and by the low concentrations of Mo normally present. However, at moderately high molybdate concentrations, absorption spectra typical of thiomolybdates have been found in washed suspensions of rumen micro-organisms (Dick et al. 1975;El Gallad et al. 1983), in an artificial rumen apparatus (Bray et al. 1982), and in whole rumen contents (El Gallad et al. 1983), thereby indicating that the potential for thiomolybdate formation does exist .Interest has also centred on the particular species of thiomolybdates that may occur in vivo. Based on observations of solution chemistry, Clarke 8z Laurie (1980) concluded that tetrathiomolybdate (TTM) would not form unless the sulphide : Mo ratio was very high, and that at the lower ratios mor...

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“…As shown in Table 3, the experimental band maxima of the ν(Rh→Mo) transitions for the complexes with π-acid ligands (2-8) were observed at higher energies, as compared with the maxima of the complexes with σ-only electron donor ligands (9)(10)(11). (Arbitary absorbance scale).…”

Section: Complexmentioning

confidence: 92%

“…This is due to the fact that the salts of WS 4 2are more resistant to hydrolysis (conversion to oxo-species) than the corresponding MoS 4 2compounds. 9 Structurally characterized dinuclear complexes L n M'(MoS 4 ) have been reported for M'=Mo 0 , Fe II , Pd II , Cu I and Ag I . 10 Many tetrathiometallato complexes have been described as having unusual electronic properties on the ground of spectroscopic (UV-Vis, IR, Raman, NMR) and electrochemical (CV) measurements, chemical reactivity and X-ray solid state structures.…”

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confidence: 99%

Tetrathiomolybdate Complexes of Rhodium(I) with Molybdenum–Rhodium Interactions

et al. 2016

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The synthesis and characterization of the tetrathiomolybdatorhodium(I) monoanionic complexes [L2Rh(μ-S)2MoS2](-) (L = CO (3), P(OPh)3 (4), P(O-o-Tol)3 (P(o-CH3C6H4)3; 5), P(OMe)3 (6), P(OEt)3 (7), P(O-i-Pr)3 (8); L2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCH═CHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb (Ph2P(CH2)4PPh2; 11)) is presented. The complex 2 (NEt4(+) salt) was characterized by X-ray diffraction analysis. A detailed DFT study of the electronic structures of 2-4 and 6-8 has revealed the existence of extended electron delocalization over the four-membered Rh(μ-S)2Mo ring and hence the possibility of electronic communication between the metal centers. The electronic spectra were studied with TDDFT calculations, and the main absorption band in the visible region was assigned to ν(Rh→Mo) electron transfer transition, which is actually a HOMO-LUMO transition. The ν(Rh→Mo) transition was found to correlate linearly both with Tolman's electronic parameter of the phosphite ligands and the calculated HOMO-LUMO gap of the complexes, rendering it a well-defined ligand electronic parameter, which describes the net donating ability of monodentate and bidentate ligands (CO, COD, phosphites, diphosphines). The study of the variation of Δδ((31)P) and (1)J(Rh-P) of the phosphite complexes with respect to the QALE model electronic parameters χd, πp, and Ear has succeeded in the assessment of the σ and π effects on these NMR spectral parameters.

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Kinetics of the interconversion of sulfido- and oxomolybdate(VI) species MoOxS4-x2- in aqueous solutions

Cited by 64 publications

References 11 publications

Elicitation of thiomolybdates from the iron‐molybdenum cofactor of nitrogenase

Elicitation of thiomolybdates from the iron‐molybdenum cofactor of nitrogenase

Involvement of the solid phase of rumen digesta in the interaction between copper, molybdenum and sulphur in sheep

Tetrathiomolybdate Complexes of Rhodium(I) with Molybdenum–Rhodium Interactions

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