Synthesis, structure, and electronic characterization of reactive diiron(II) 1,2-bis(2-hydroxybenzamido)benzene complexes as models for methane monooxygenase

Stassinopoulos, Adonis; Schulte, Gayle K.; Papaefthymiou, Georgia C.; Caradonna, John P.

doi:10.1021/ja00023a016

Cited by 65 publications

(68 citation statements)

References 3 publications

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“…Given that the two ferric sites of the dinuclear cluster have different ligand environments as indicated by their distinct ⌬E Q values, a ͉⌬j͞J͉ Յ 0.001 is rather improbable. Finally, we note that the reaction catalyzed by AlkB requires oxygen activation chemistry of the type catalyzed by both diiron enzymes (11) and synthetic dinuclear iron complexes (33,34).…”

Section: Discussionmentioning

confidence: 97%

Mössbauer studies of alkane ω-hydroxylase: Evidence for a diiron cluster in an integral-membrane enzyme

Shanklin

Achim

Schmidt

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

203

160

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The gene encoding the alkane -hydroxylase (AlkB; EC 1.14.15.3) from Pseudomonas oleovorans was expressed in Escherichia coli. The integral-membrane protein was purified as nearly homogeneous protein vesicles by differential ultracentrifugation and HPLC cation exchange chromatography without the detergent solubilization normally required for membrane proteins. Purified AlkB had specific activity of up to 5 units͞mg for octane-dependent NADPH consumption. Mössbauer studies of AlkB showed that it contains an exchange-coupled dinuclear iron cluster of the type found in soluble diiron proteins such as hemerythrin, ribonucleotide reductase, methane monooxygenase, stearoyl-acyl carrier protein (ACP) ⌬ 9 desaturase, rubrerythrin, and purple acid phosphatase. In the as-isolated enzyme, the cluster contains an antiferromagnetically coupled pair of high-spin Fe(III) sites, with an occupancy of up to 0.9 cluster per AlkB. The diferric cluster could be reduced by sodium dithionite, and the diferrous state was found to be stable in air. When both O 2 and substrate (octane) were added, however, the diferrous cluster was quantitatively reoxidized, proving that the diiron cluster occupies the active site. Mössbauer data on reduced AlkB are consistent with a cluster coordination rich in nitrogen-containing ligands. New sequence analyses indicate that at least 11 nonheme integral-membrane enzymes, including AlkB, contain the 8-histidine motif required for catalytic activity in stearoyl-CoA desaturase. Based on our Mössbauer studies of AlkB, we propose that the integral-membrane enzymes in this family contain diiron clusters. Because these enzymes catalyze a diverse range of oxygenation reactions, this proposal suggests a greatly expanded role for diiron clusters in O 2 -activation biochemistry.

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Section: Discussionmentioning

confidence: 97%

Mössbauer studies of alkane ω-hydroxylase: Evidence for a diiron cluster in an integral-membrane enzyme

Shanklin

Achim

Schmidt

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

203

160

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“…We have previously described the structural, spectroscopic and reactivity properties of a binuclear ferrous analog reaction system, [Fe? + (H,Hbab),(NMe1m)J (5), that is a reasonable approximation to the electronic environment of the reduced binuclear active site of methane monooxygenase as judged by Mossbauer, EPR and magnetic susceptibility data comparisons [8,9]. Of equivalent interest is the ability of 5 to heterolytically cleave the percarboxylic 0-0 bond of phenylperacetic acid and catalyze the OIPh oxidation of a variety of simple organic substrates yielding both 'oxenoid'-like and radical-like products in a manner analogous to that reported for cytochrome P-450 and MMO [8].…”

Section: Ja9709482mentioning

confidence: 69%

“…These data were consistent with two limiting mechanisms involving either coordination of hypervalent iodine(II1) of OIPh to the Fe2+ center leading to oxygen activation (Lewis acid catalyzed oxygen atom transfer) or the formal formation of a high valent Fe-oxenoid species [SI. Despite the mechanistic insights gained from examining the influence of d-electron count on the reactivity properties of heme complexes, the comparison of isostructural binuclear metal complexes capable of catalyzing oxygen atom transfer reactions remains relatively unexplored [7]. Herein, we extend our studies from the binuclear d6 Fez+ system, 5, to an isostructural d7 Co2 + system, [Co,'+ (H,Hbab) (H,Hbab),(N-MeIm), (5) [8,9], were synthesized by literature procedures.…”

Section: Ja9709482mentioning

confidence: 99%

“…We have found that 1 is a facile synthon for the introduction of a Co2+(N-MeIm) moiety into a complex with the added features that it is easy to prepare, is air stable, and it exhibits high solubility in a variety of organic solvents. The synthesis of [Co,, + (H,Hbab),(N-MeIm),] uses methods analogous to those previously reported for the synthesis of the binuclear ferrous complex, [Fe,, + (H,Hbab),(NMeIm),] (5) [8,9]. The solubility properties of 2 and 5 are similar with both being practically insoluble in most common organic solvents, but fairly soluble in DMF and DMSO (40 mM).…”

Section: Synthesismentioning

confidence: 99%

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Binuclear Non-heme Iron Catalysts

Caradonna¹

2004

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This project involved the investigation of the ability of non-heme iron metalloenzyme reactivity model complexes to catalyze the oxidation of alkane and arene molecules. The objectives were to synthesize a series of non-heme mononuclear and dinuclear iron complexes, characterize their electronic structure and reactivity properties, characterize intermediates formed during oxygen atom transfer chemistry, and elucidate the mechanisms and specificity of the reactions. These data also were to be compared to analogous heme-based chemistry.A series of diferrous, ferrous/ferric, and diferric complexes were synthesized from simple polyamide and polycarboxylate ligands and characterized by visible absorption, EPR and IR spectroscopy and by cyclic voltametry. The diferrous compounds, which are all powerful reductants, heterolytically decompose peracids and are capable of acting as oxygen atom transfer catalysts when reacted with oxygen atom donor compounds and simple olefins, yielding both allylic oxidation and epoxidation products. Lowtemperature optical spectroscopic studies provide evidence in support of an Fe(IV)=O intermediate, rather than an 0-donor adduct, as the reactive species. An isostructural dicobalt(I1) complex gives rise only to epoxidation products. These reactivity studies provide important new information of the chemistry of dinuclear nonheme iron systems.Publications resulting from this project:1. 2.3. 4."Fe2+-catalyzed heterolytic RO-OH bond cleavage and substrate oxidation: A fhctional synthetic non-heme iron monooxygenase system", Foster TL, Caradonna ' in anhydrous 1% methanol-acetonitrile under anaerobic conditions afforded @?e22+(Hzbamb)2(N-MeIm)2] (1)25a (60% yield). Isothermal distillation techniquesls indicate that 1 has a molecular weight of 4 100, consistent with its dimeric formulation. EPR spectra of 1 show a g H % 16 signal, suggesting a ferromagnetically coupled S = 4 core as previously reported for an analogous binuclear system.I9 Cyclic voltammetry experiments show two coupled le-oxidationheduction processes; a scanrate-dependent quasi-reversible process at -310 mV ("E) and an electrochemically reversible couple at -690 mV ("E), giving K , , = 2.7 x loa. Repetitive scans showed no significant decrease in either cathodic or anodic current; ligand centered redox behavior was observed outside this region of interest. The scan-rate dependence of AEp, attributed to kinetic effects, allowed the measurement of an intrinsic rate constant, k = 2 x assuming pseudo-first-order kinetics. This rate constant, thought to reflect a structural change, is independent of [I] interfaced to a "33% series U integrator. Mass spectral analyses were performed on a HP 5971 mass-selective detector attached to a HPS890 Series 2 GC. Authentic samples were used to verify all retention times. Expected reaction products were stable to GC conditions.(21) Studies using Fa12 and FeCla were performed and analyzed by GC and GUMS techniques using identical conditions as reported for 1-3 (Table 1) with catalyst:OIF'h:sub...

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“…= 496 nm (ε = 1100), which can be assigned to a charge-transfer transition [10]. The 1 H NMR spectrum of 2 in CD 2 Cl 2 /MeOH-d 4 (Fig.…”

Section: Resultsmentioning

confidence: 99%

Unexpected assembly of a novel triply bridged diiron(II) core by a bidentate Schiff base ligand

Smith

Day

Que

et al. 2007

Inorganica Chimica Acta

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The unusual dinucleating properties of a simple bidentate Schiff base (LH, 1) in the presence of weakly coordinating methanol solvent lead to the self-assembly of [Fe II 2 (2) (b and t refer to bridging and terminally bound ligands, respectively). Complex 2 is the first diiron (II) species in which the two metal centers are triply bridged by single atoms in an asymmetric fashion, involving both μ-O Ph and μ-OH Me bridges. This binding mode produces an Fe···Fe distance of 3.139 (1) Å. Dinucleation appears to be driven by a combination of ligand deficiency and solvent-mediated chemistry reminiscent of host-guest interactions. The presence of a μ-MeOH ligand is unprecedented in iron chemistry. Parallel-mode EPR spectra of complex 2 recorded at 4 K show an intense negative signal at g || ≈ 16, suggesting the dimeric form exists in solution.

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Synthesis, structure, and electronic characterization of reactive diiron(II) 1,2-bis(2-hydroxybenzamido)benzene complexes as models for methane monooxygenase

Cited by 65 publications

References 3 publications

Mössbauer studies of alkane ω-hydroxylase: Evidence for a diiron cluster in an integral-membrane enzyme

Mössbauer studies of alkane ω-hydroxylase: Evidence for a diiron cluster in an integral-membrane enzyme

Binuclear Non-heme Iron Catalysts

Unexpected assembly of a novel triply bridged diiron(II) core by a bidentate Schiff base ligand

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