Binuclear oxygen carriers: hemerythrin

Klotz, Irving M.; Kurtz, Donald M.

doi:10.1021/ar00097a003

Cited by 113 publications

(69 citation statements)

References 43 publications

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“…5a can thus be fit with four equally intense bands of comparable linewidth at 1,239, 1,262, 1,282, and 1,310 cm Ϫ1 , which are assigned to the various isotopomers of an end-on bound iron-superoxo unit. Such a well resolved isotopic pattern has not yet been reported for a metal-superoxo complex but is similar to those previously observed for the end-on bound hydroperoxo ligands in oxyhemerythrin (37) ϩ (38) and the peroxo intermediates of nonheme diiron enzymes such as the D84E R2 protein of E. coli ribonucleotide reductase (17), fatty acid desaturase (18), and ferritin (19). Unfortunately, no insight into the dioxygen binding mode in 3 could be obtained from a similar analysis of its (O-O) features, because of spectral interference from 4 and solvent bands.…”

supporting

confidence: 89%

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Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Shan

Que

2005

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

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The reaction of [Fe2(-OH)2(6-Me3-TPA)2] 2؉ (1) [6-Me3-TPA, Tris(6-methyl-2-pyridylmethyl)amine] with O2 in CH2Cl2 at ؊80°C gives rise to two new intermediates, 2 and 3, before the formation of previously characterized [Fe2(O)(O2)(6-Me3-TPA)2] 2؉ (4) that allow the oxygenation reaction to be monitored one electron-transfer step at a time. Raman evidence assigns 2 and 3 as a diiron-superoxo species and a diiron-peroxo species, respectively. Intermediate 2 exhibits its (O-O) at 1,310 cm ؊1 with a ؊71-cm ؊1 18 O isotope shift. A doublet peak pattern for the 16 O 18 O isotopomer of 2 in mixedisotope Raman experiments strongly suggests that the superoxide ligand of 2 is bound end-on. This first example of a nonheme iron-superoxo intermediate exhibits the highest frequency (O-O) yet observed for a biomimetic metal-dioxygen adduct. The bound superoxide of 2, unlike the bound peroxide of 4, is readily reduced by 2,4-di-tert-butylphenol via a proton-coupled electron-transfer mechanism, emphasizing that metal-superoxo species may serve as oxidants in oxygen activation mechanisms of metalloenzymes. The discovery of intermediates 2 and 3 allows us to dissect the initial steps of dioxygen binding at a diiron center leading to its activation for substrate oxidation.nonheme diiron enzymes ͉ oxygen activation ͉ superoxo intermediate T he first step in the oxygen activation mechanisms of metalloenzymes is typically the binding of dioxygen, resulting in electron transfer from metal to O 2 to form a metal-superoxo species (1-5). This conversion is best exemplified by heme proteins and synthetic iron porphyrin complexes where there is strong crystallographic and spectroscopic evidence for an Fe III -( 1 -O 2•Ϫ ) formulation (6, 7). Crystallographic evidence for an analogous formulation has also recently been reported for a copper enzyme peptidylglycine ␣-hydroxylating monooxygenase (PHM) (8). Furthermore, synthetic copper(I) and nickel(I) complexes react with O 2 to give rise to copper and nickel superoxo species (9)(10)(11)(12)(13)(14)(15)(16) 2 was prepared by using the same procedure in the presence of 10 eq of D 2 O. All manipulations with complex 1 and solutions thereof were carried out under inert atmosphere by using a glovebox filled with nitrogen. Dichloromethane was distilled from CaH 2 under nitrogen. 2,4-di-tert-butylphenol (DTBP) was purchased from Aldrich and used as received. Saturated solutions of O 2 in CH 2 Cl 2 for the kinetic studies were prepared by bubbling the dried O 2 gas through the solvent for 10 min at room temperature. The concentration of O 2 in this saturated solution was accepted to be as reported in the literature (25) Sample Preparation. For UV-visible experiments, an anaerobic solution of 1⅐(OTf) 2 (3.3 mg) in dry CH 2 Cl 2 (3 ml) was introduced into a 1-cm-path-length cuvette and then cooled to 193 K in a Unisoku cryogenic cell holder attached to a HewlettPackard 8453A diode array spectrophotometer. O 2 gas was bubbled through the solution for 5 min, and the formation of 2 was complete within 1 h....

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supporting

confidence: 89%

“…Intermediates 2 and 3 are formulated to be diiron(II,III)-superoxo and diiron(III)-hydroperoxo species, reminiscent of the chemistry of oxyhemerythrin (37). These results afford an unprecedented opportunity to dissect this transformation one electron-transfer step at a time.…”

Section: Discussionmentioning

confidence: 99%

Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Shan

Que

2005

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

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“…Similarly, in complexes of the type Pt(L),O, (L = phosphine or CH,=CH,), IR spectra also exhibit absorptions in the 8 14-828 cm-' range associated with v(0,) (23). In biologically related Fe dimers bridged by 0, (in a Fe-(pl-0,)-Fe fashion), v(0,) and v(Fe0) are observed at 844 and 504 cm-', respectively (24). The IR spectra of the bisdioxygen product ( (25,26), indicating that n back-bonding is (as expected) greater in the ~d ,~+ cluster with respect to the electron poorer Pd" centers.…”

Section: Photoadditionsupporting

confidence: 57%

Photoinduced addition of dioxygen molecules in the unsaturated sites of the Pd₃(dppm)₃CO²⁺ catalyst

Harvey¹,

Crozet²,

Aye³

1995

Can. J. Chem.

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The photoinduced addition of 0, onto the unsaturated cluster Pd,(dppm),C~~+ (as a CF,CO,-salt) in acetonitrile is reported. The final product ~d , ( d~~m ) , ( O , )~ (~( 0 , ) = 838 and 866 cm-') is formed in a multistep fashion in which two photochemical intermediates are observed (presumably ~d,(dppm),(0,)(~0)~+ and ~d , ( d~~m ) , ( 0 , )~+ ) .No X-ray structure could be obtained, but numerous spectroscopic findings demonstrate that 0, binds the Pd, center as a peroxo-02, and acts as a two-electron donor that triply bridges the metal atoms (forming a 44-electron cluster). The very small excited state lifetimes (between 25 and 35 ? 10 ps) obtained by picosecond flash photolysis indicate that the primary photoreaction is unimolecular, and demonstrate that the first photochemically added 0, molecule must be preassembled in the excited state prior to any photoinduced transformation. This ~d , ( d~~m ) , C 0~+ . . . 0 , ground state complex is responsible for the photoinduced production of the bisdioxygen compound and can be observed by UV-visible spectroscopy. The low efficiency of the photoreaction (quantum yield (0) = 0.033 ? 0.004) is explained by the very short excited state lifetime at 298 K, and the competition of 0, with solvent molecules to occupy the unsaturated site of the empty cavity in ~d , ( d~~m ) ,~0~+ (i.e., ground state guest-host chemistry). The binding constant for 0, with ~d , ( d~~m ) ,~0~+ is roughly estimated to range between 1 and 730 M-I in the ground state and is considered to be weak.

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“…While this idea is clear in principle, its utility in practice has been limited: isotopomer peak splitting has only rarely been reported with certainty. The ''classic'' example is oxyhemerythrin, where mixed-isotope peaks were not resolved, but deconvolution of a flattened, broadened absorption band led to an assignment of isotopomeric absorptions separated by 5 cm À1 and having widths at half height of 5.5 cm À1 [20,21] (the O 2 fragment in this case is protonated, i.e., it is a hydroperoxo ligand [22], although this was not known at the time of the original experiment). In other examples, cobalt(tetramesitylporphine)superoxide 3 has been assigned [23] to exhibit a separation between isotopomers of about 11 cm À1 in m(O-O) (the splitting is approximate since both O-O stretching bands are observed as shoulders on a porphyrin absorption) and a broad mixed-isotope band for Pd(O 2 )(t-BuNC) 2 in an oxygen matrix has been resolved into two peaks separated by 4-5 cm À1 [24].…”

Section: Introductionmentioning

confidence: 99%

How useful are vibrational frequencies of isotopomeric O2 fragments for assessing local symmetry? Some simple systems and the vexing case of a galactose oxidase model

et al. 2005

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Binuclear oxygen carriers: hemerythrin

Cited by 113 publications

References 43 publications

Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Photoinduced addition of dioxygen molecules in the unsaturated sites of the Pd₃(dppm)₃CO²⁺ catalyst

How useful are vibrational frequencies of isotopomeric O2 fragments for assessing local symmetry? Some simple systems and the vexing case of a galactose oxidase model

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Binuclear oxygen carriers: hemerythrin

Cited by 113 publications

References 43 publications

Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Photoinduced addition of dioxygen molecules in the unsaturated sites of the Pd3(dppm)3CO2+ catalyst

How useful are vibrational frequencies of isotopomeric O2 fragments for assessing local symmetry? Some simple systems and the vexing case of a galactose oxidase model

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Photoinduced addition of dioxygen molecules in the unsaturated sites of the Pd₃(dppm)₃CO²⁺ catalyst