Multifrequency electron spin resonance of molybdenum(V) and tungsten(V) compounds

Hanson, Graeme R.; Wilson, G. L.; Bailey, Trevor D.; Pilbrow, John R.; Wedd, Anthony G.

doi:10.1021/ja00243a011

Cited by 53 publications

(42 citation statements)

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“…However, hyperfine coupling to the Mo nuclei with I=5/2 (~25% abundance) is clearly observable (A=34.110 ±4 cm ±1 ). The g value for 1 is similar to those found for other Mo(V) complexes [38], including oxo-thiolate complexes whose g av values range from 1.980 to 2.008 [56,59,68]. Most of the A av values for the Mo(V)-oxo-tetrathiolate complexes are comparable and are usually found between 30 and 3510 ±4 cm ±1 .…”

Section: Resultssupporting

confidence: 78%

A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

Conry

Tipton

2001

J. Biol. Inorg. Chem.

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The reaction of Mo(O)2(acac)2, H2L (2,2'-dimercaptobiphenyl), and NEt3 produced the mononuclear Mo(V) complex Et3NH[Mo(O)(L)2] (1). Molybdenum mono-oxo tetrathiolate complexes such as 1 are studied as potential structural or functional models for pyranopterin-containing molybdoenzymes. Complex 1 has been crystallographically characterized. The solid-state structure reveals that the molybdenum ion sits within a cleft formed by the biphenyl backbone of the ligands, providing some steric protection. In addition, there is a hydrogen bond between the amine hydrogen of [Et3NH]+ and one of the thiolate sulfur atoms. A difference in solution reactivity between 1 and a derivative without a hydrogen-bonding counterion suggests that hydrogen bonding occurs in solution also. There are two short S-S contacts and small S-Mo-S angles in the structure of 1 that may reflect a slight bonding interaction. Such short S-S distances and small angles have been found in a couple of other Mo-thiolate complexes and in many of the molybdoenzyme crystal structures. Further characterization of 1 by EPR, IR, and UV-vis spectroscopies, as well as by cyclic voltammetry, is discussed and compared to known Mo(V)-oxo-tetrathiolate complexes as well as to relevant molybdoenzyme data. Reactions to generate Mo(VI) complexes from 1 resulted in net oxidation at the ligand to form its disulfide derivative, which dissociated from the metal center. This result suggests that modifications to the ligand to prevent this process are needed.

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Section: Resultssupporting

confidence: 78%

A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

Conry

Tipton

2001

J. Biol. Inorg. Chem.

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“…Note that even in an axial position, an oxo ligand is expected to give a 17 O coupling that should be readily detectable by EPR or by ENDOR. Thus, for example, the complex [MoO(SPh)4]shows A( 17 O) 8.6, 8.6, 1.9 MHz (Hanson et al, 1987). Conversely, in the Alloxanthine species (taking structure Ab as the analogue of structure Vb), if the oxo group is exchangeable, it should also give detectable 17 O coupling, but no support for its presence has been found in the present ENDOR or in earlier EPR (Hawkes et al, 1984).…”

Section: Discussioncontrasting

confidence: 61%

Evidence Favoring Molybdenum−Carbon Bond Formation in Xanthine Oxidase Action: ¹⁷O- and ¹³C-ENDOR and Kinetic Studies

Howes¹,

Bray²,

Richards³

et al. 1996

Biochemistry

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The reaction mechanism of the molybdoenzyme xanthine oxidase has been further investigated by 13 C and 17 O ENDOR of molybdenum(V) species and by kinetic studies of exchange of oxygen isotopes. Three EPR signalgiving species were studied: (i) Very Rapid, a transient intermediate in substrate turnover, (ii) Inhibited, the product of an inhibitory side reaction with aldehyde substrates, and (iii) Alloxanthine, a species formed by reaction of reduced enzyme with the inhibitor, alloxanthine. The Very Rapid signal was developed either with [8-13 C]xanthine or with 2-oxo-6-methylpurine using enzyme equilibrated with [ 17 O]H2O. The Inhibited signal was developed with 2 H 13 C 2 HO and the Alloxanthine signal by using [ 17 O]H2O. Estimates of Mo−C distances were made, from the anisotropic components of the 13 C-couplings, by corrected dipolar coupling calculations and by back-calculation from assumed possible structures. Estimated distances in the Inhibited and Very Rapid species were about 1.9 and less than 2.4 Å, respectively. A Mo−C bond in the Inhibited species is very strongly suggested, presumably associated with side-on bonding to molybdenum of the carbonyl of the aldehyde substrate. For the Very Rapid species, a Mo−C bond is highly likely. Coupling from a strongly coupled 17 O, not in the form of an oxo group, and no coupling from other oxygens was detected in the Very Rapid species. No coupled oxygens were detected in the Alloxanthine species. That the coupled oxygen of the Very Rapid species is the one that appears in the product uric acid molecule was confirmed by new kinetic data. It is concluded that this oxygen of the Very Rapid species does not, as frequently assumed, originate from the oxo group of the oxidized enzyme. A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al. [

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“…It is interesting to note that the hfi of the oxo ligand in the Mo(V) complexes is noticeably weaker than in the oxovanadium aquo complex ( a iso = 8.4 MHz, T ⊥ = 7.6 MHz (54), although the orientation dependence of the hfi parameters (52, 54) and the characteristic property of very slow exchange rate of this oxygen with the buffer (30, 51) are common for both species.…”

Section: Resultsmentioning

confidence: 99%

Structural Studies of the Molybdenum Center of Mitochondrial Amidoxime Reducing Component (mARC) by Pulsed EPR Spectroscopy and ¹⁷O-Labeling

et al. 2011

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Mitochondrial amidoxime reducing components (mARC-1 and mARC-2) represent a novel group of Mo containing enzymes in eukaryotes. These proteins form the catalytic part of a three-component enzyme complex known to be responsible for the reductive activation of several N-hydroxylated prodrugs. No X-ray crystal structures are available for these enzymes as yet. Previous biochemical investigation by B. Wahl et al. (J. Biol. Chem. 285 (2010) 37847–37859) has revealed that two of the Mo coordination positions are occupied by sulfur atoms from a pyranopterindithiolate (molybdopterin, MPT) cofactor. In this work, we have used continuous wave and pulsed electron paramagnetic resonance (EPR) and density functional theoretical (DFT) calculations to determine the nature of remaining ligands in the Mo(V) state of the active site of mARC-2. The experiments with samples in D2O have identified the exchangeable equatorial ligand as a hydroxyl group. The experiments on samples in H217O-enriched buffer have shown the presence of a slowly exchangeable axial oxo ligand. The comparison of the experimental 1H and 17O hyperfine interactions with those calculated using DFT has shown that the remaining non-exchangeable equatorial ligand is, most likely, protein-derived, and that the possibility of an equatorial oxo ligand can be excluded.

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Multifrequency electron spin resonance of molybdenum(V) and tungsten(V) compounds

Cited by 53 publications

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A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

Evidence Favoring Molybdenum−Carbon Bond Formation in Xanthine Oxidase Action: ¹⁷O- and ¹³C-ENDOR and Kinetic Studies

Structural Studies of the Molybdenum Center of Mitochondrial Amidoxime Reducing Component (mARC) by Pulsed EPR Spectroscopy and ¹⁷O-Labeling

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Multifrequency electron spin resonance of molybdenum(V) and tungsten(V) compounds

Cited by 53 publications

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A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

A mononuclear molybdenum(V) mono-oxo biphenyl-2,2′-dithiolate complex in which the metal resides within a cleft formed by the ligands and that exhibits N-H...S hydrogen bonding in the solid state

Evidence Favoring Molybdenum−Carbon Bond Formation in Xanthine Oxidase Action: 17O- and 13C-ENDOR and Kinetic Studies

Structural Studies of the Molybdenum Center of Mitochondrial Amidoxime Reducing Component (mARC) by Pulsed EPR Spectroscopy and 17O-Labeling

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Evidence Favoring Molybdenum−Carbon Bond Formation in Xanthine Oxidase Action: ¹⁷O- and ¹³C-ENDOR and Kinetic Studies

Structural Studies of the Molybdenum Center of Mitochondrial Amidoxime Reducing Component (mARC) by Pulsed EPR Spectroscopy and ¹⁷O-Labeling