Synthesis, Characterization, and Biomimetic Chemistry of <i>cis</i>-Oxosulfidomolybdenum(VI) Complexes Stabilized by an Intramolecular Mo(O)S···S Interaction

Laughlin, Les J.; Eagle, Aston A.; George, Graham N.; Tiekink, Edward R. T.; Young, Charles G.

doi:10.1021/ic061213d

Cited by 29 publications

(28 citation statements)

References 63 publications

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“…The MoO 2 (S-N(RR 0 )) 2 complexes present a triatomic motif which supports the metal and sulfur oxidation interplay according to the resonance structures in Scheme 1. Other examples of complexes with Mo-S and S-S distances similar to our results include cis-oxosulfido Mo(VI) complexes [35]. Two recent reviews (and references therein) provide further examples and address the relevance of redox interplay and molybdenum/sulfur in enzymes in greater detail [36,37].…”

Section: Mechanistic Implications Of a Sulfido Ligand And A Partial Ssupporting

confidence: 71%

“…2 Gallery of the molybdenum active sites for four of the structures analyzed. a SAD, b NITRATE, c PERCHLORATE, and d CYANIDE, The2mFo-DFc electron density maps contoured at 1r (blue) and the mFo-DFc electron density maps contoured at 3r (red) calculated in the absence of a sixth ligand (left) and calculated in the presence of the sulfur atom in the final refinement (right) g n * 0.5 for 35,37 Cl and I = 1/2, g n = 2.26 for 31 P) and hence superhyperfine structure from these nuclei might be observed in the EPR spectra associated with Mo(V) species. Hyperfine couplings associated with chloride nuclei in equatorial positions have been reported in model complexes of Mo(V) ions in nearly octahedral or squarepyramidal coordination [24] and in the molybdenum enzyme sulfite oxidase [25].…”

Section: Analysis Of the Structures Around The Molybdenum Active Sitementioning

confidence: 99%

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Periplasmic nitrate reductase revisited: a sulfur atom completes the sixth coordination of the catalytic molybdenum

et al. 2008

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Nitrate reductase from Desulfovibrio desulfuricans ATCC 27774 (DdNapA) is a monomeric protein of 80 kDa harboring a bis(molybdopterin guanine dinucleotide) active site and a [4Fe-4S] cluster. Previous electron paramagnetic resonance (EPR) studies in both catalytic and inhibiting conditions showed that the molybdenum center has high coordination flexibility when reacted with reducing agents, substrates or inhibitors. As-prepared DdNapA samples, as well as those reacted with substrates and inhibitors, were crystallized and the corresponding structures were solved at resolutions ranging from 1.99 to 2.45 Å . The good quality of the diffraction data allowed us to perform a detailed structural study of the active site and, on that basis, the sixth molybdenum ligand, originally proposed to be an OH/OH 2 ligand, was assigned as a sulfur atom after refinement and analysis of the B factors of all the structures. This unexpected result was confirmed by a single-wavelength anomalous diffraction experiment below the iron edge (k = 1.77 Å ) of the as-purified enzyme. Furthermore, for six of the seven datasets, the S-S distance between the sulfur ligand and the Sc atom of the molybdenum ligand Cys A140 was substantially shorter than the van der Waals contact distance and varies between 2.2 and 2.85 Å , indicating a partial disulfide bond. Preliminary EPR studies under catalytic conditions showed an EPR signal designated as a turnover signal (g values 1.999, 1.990, 1.982) showing hyperfine structure originating from a nucleus of unknown nature. Spectropotentiometric studies show that reduced methyl viologen, the electron donor used in the catalytic reaction, does not interact directly with the redox cofactors. The turnover signal can be obtained only in the presence of the reaction substrates. With use of the optimized conditions determined by spectropotentiometric titration, the turnover signal was developed with 15 N-labeled nitrate and in D 2 O-exchanged DdNapA samples. These studies indicate that this signal is not associated with a Mo(V)-nitrate adduct and that the hyperfine structure originates from two equivalent solvent-exchangeable protons. The new coordination sphere of molybdenum proposed on the basis of our studies led us to revise the currently accepted reaction mechanism for periplasmic nitrate reductases. Proposals for a new mechanism are discussed taking into account a molybdenum and ligandbased redox chemistry, rather than the currently accepted redox chemistry based solely on the molybdenum atom.

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Section: Mechanistic Implications Of a Sulfido Ligand And A Partial Ssupporting

confidence: 71%

Section: Analysis Of the Structures Around The Molybdenum Active Sitementioning

confidence: 99%

Periplasmic nitrate reductase revisited: a sulfur atom completes the sixth coordination of the catalytic molybdenum

et al. 2008

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“…4b contribute to the bonding. The well-developed SÁ Á ÁS interaction persists in solution, according to S K-edge X-ray absorption spectroscopy [39]. However, the interaction does not lead to a marked reduction at the Mo center nor does it mask the intrinsic chemical reactivity of the sulfido group.…”

Section: Sulfido Ligand Complexesmentioning

confidence: 99%

“…Thus, the reactions of green Tp * MoO(S 2 PR 2 ) (R = Pr i , Ph) with the sulfur atom donor propylene sulfide produce red Tp * MoOS(S 2 PR 2 ), possessing distorted octahedral structures (see Fig. 4a) [38,39]. These complexes are also stabilized by a weak SÁ Á ÁS interaction (SÁ Á ÁS $ 2.4 Å ), this time between the Mo@S unit (Mo@S $ 2.21 Å ) and the uncoordinated sulfur atom of the monodentate dithiophosphinate ligand.…”

Section: Sulfido Ligand Complexesmentioning

confidence: 99%

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

Young

2007

Journal of Inorganic Biochemistry

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“…Comparison of their reactivity towards OAT would allow the elucidation of the influence of the spectator oxo effect. However, the preparation of two such comparable compounds is challenging, because the substitution of the spectator oxo ligand in complexes with a [MoO 2 ] 2 + core by another doubly bonded group is either difficult to achieve (substitution by sulfido) [35] or also changes the sterical situation (substitution by imido), [27,36] preventing comparison on electronic grounds. For this reason we envisioned the development of two ligand systems that exhibit very similar sterical constraints but allow the preparation of molybdenum dioxo compounds with asymmetric surroundings, and thus not identical molybdenum oxo bonds (with two different trans ligands), as well as symmetric surroundings with identical Mo À O bonds.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Insight into the Reactivity of Oxotransferases by Novel Asymmetric Dioxomolybdenum(VI) Model Complexes

Mayilmurugan

Harum

Volpe

et al. 2010

Chemistry A European J

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The asymmetric molybdenum(VI) dioxo complexes of the bis(phenolate) ligands 1,4-bis(2-hydroxybenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-4-methylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-4-flurobenzyl)-1,4-diazepane, and 1,4-bis(2-hydroxy-4-chlorobenzyl)-1,4-diazepane (H(2)(L1)-H(2)(L6), respectively) have been isolated and studied as functional models for molybdenum oxotransferase enzymes. These complexes have been characterized as asymmetric complexes of type [MoO(2)(L)] 1-6 by using NMR spectroscopy, mass spectrometry, elemental analysis, and electrochemical methods. The molecular structures of [MoO(2)(L)] 1-4 have been successfully determined by single-crystal X-ray diffraction analyses, which show them to exhibit a distorted octahedral coordination geometry around molybdenum(VI) in an asymmetrical cis-β configuration. The Mo-O(oxo) bond lengths differ only by ≈0.01 Å. Complexes 1, 2, 5, and 6 exhibit two successive Mo(VI)/Mo(V) (E(1/2), -1.141 to -1.848 V) and Mo(V)/Mo(IV) (E(1/2), -1.531 to -2.114 V) redox processes. However, only the Mo(VI)/Mo(V) redox couple was observed for 3 and 4, suggesting that the subsequent reduction of the molybdenum(V) species is difficult. Complexes 1, 2, 5, and 6 elicit efficient catalytic oxygen-atom transfer (OAT) from dimethylsulfoxide (DMSO) to PMe(3) at 65 °C at a significantly faster rate than the symmetric molybdenum(VI) complexes of the analogous linear bis(phenolate) ligands known so far to exhibit OAT reactions at a higher temperature (130 °C). However, complexes 3 and 4 fail to perform the OAT reaction from DMSO to PMe(3) at 65 °C. DFT/B3LYP calculations on the OAT mechanism reveal a strong trans effect.

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Synthesis, Characterization, and Biomimetic Chemistry of cis-Oxosulfidomolybdenum(VI) Complexes Stabilized by an Intramolecular Mo(O)S···S Interaction

Cited by 29 publications

References 63 publications

Periplasmic nitrate reductase revisited: a sulfur atom completes the sixth coordination of the catalytic molybdenum

Periplasmic nitrate reductase revisited: a sulfur atom completes the sixth coordination of the catalytic molybdenum

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

Mechanistic Insight into the Reactivity of Oxotransferases by Novel Asymmetric Dioxomolybdenum(VI) Model Complexes

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