Copper(I)-phenolate complexes as models of the reduced active site of galactose oxidase: synthesis, characterization, and O2 reactivity

Jazdzewski, Brian A.; Reynolds, Anne; Holland, Patrick L.; Young, Victor G.; Kaderli, Susan; Zuberbühler, Andreas D.; Tolman, William B.

doi:10.1007/s00775-002-0420-9

Cited by 54 publications

(50 citation statements)

References 68 publications

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“…Such species have been found in the reactions of O 2 with heme proteins and models (6,7) as well as with one copper enzyme (8) and several synthetic copper and nickel complexes (9)(10)(11)(12)(13)(14)(15)(16). Such species have also been invoked in the mechanisms for nonheme iron enzymes, but only indirect evidence has been obtained to date (39)(40)(41).…”

Section: Discussionmentioning

confidence: 98%

“…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.…”

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confidence: 99%

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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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Section: Discussionmentioning

confidence: 98%

mentioning

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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“…Our own interests in this area were piqued by recent work of Jazdzewski et al [30], who reported the synthesis of a 1:1 Cu-O 2 galactose oxidase model complex 6 supported by a ligand composed of a 2,4-di-tert-butylphenolate linked at N1 to a 4,7-diisopropyl-1,4,7-triazacyclononane. A crystal structure was not obtained for 6.…”

Section: Introductionmentioning

confidence: 99%

“…Optimization of the geometry of 6 was carried out at the DFT level for both the singlet and the triplet electronic states, although experiment is unambiguous in establishing the singlet as the ground state on the basis of the absence of an electron-spin-resonance spectrum [30]. The triplet state is found to have a single minimum-energy structure and that structure coordinates O 2 in an end-on fashion [ 3 6(g 1 ), Fig.…”

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confidence: 99%

“…Nevertheless, we consider the theoretical evidence in toto to provide strong support for a side-on oxygen coordination motif in 6. Jazdzewski et al [30] originally proposed a structure for 6 topologically equivalent to that of 1 6 r (g 2 ) in part on the basis of the failure to observe a mixed-isotopomer splitting in the RR spectrum and in part on the basis of the solid intuition inherent in the experimental group. While we have shown the former not to be diagnostic of side-on coordination, the latter should certainly never be discounted by theoreticians.…”

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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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Copper: Hemocyanin/Tyrosinase ModelsBased in part on the article Copper: Hemocyanin/Tyrosinase Models by Nobumasa Kitajima which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

Shearer

Karlin

2005

Encyclopedia of Inorganic Chemistry

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Coupled dinuclear copper(II) centers are found in metalloenzymes such as hemocyanin (Hc), tyrosinase (Tyr), and catechol oxidase (Co), and perform functions such as dioxygen transport, o ‐phenol aromatic hydroxylations, and dehydrogenation of o ‐catechols. These enzymes all contain two‐copper centers, each ligated by imidazole nitrogen ligands from histidine residues, and in their oxyforms are bridged by a μ‐η 2 :η 2 ‐peroxo moiety. Synthetic model compounds have proven useful in elucidating a number of different aspects of the protein chemistry, such as spectroscopic and structural properties. Also, new coordination chemistry has been developed, such as a new and possibly important equilibrium form of the μ‐η 2 :η 2 ‐peroxo‐ $\hbox{Cu}^{{\rm II}}_{2}$ species, namely, the $\hbox{Cu}^{{\rm III}}_{2}$ ‐bis‐μ‐oxo moiety. In conjunction with stopped‐flow kinetic studies, new fundamental reactions involving Cu I complexes and dioxygen have also been elucidated, such as the demonstration that an initial Cu II ‐superoxo species is formed prior to $\hbox{Cu}^{{\rm II}}_{2}$ ‐peroxo formation. Both species are enthalpically favored at low temperatures, but an unfavorable entropy term precludes the isolation of many of these complexes near room temperature. Considerable efforts are directed towards elucidation of detailed mechanistic pictures for substrate oxidations with copper–dioxygen adducts. Ortho ‐phenol hydroxylations proceed via an electrophilic aromatic substitution reaction. The mechanism of Co activity is still widely debated with evidence in model systems pointing towards both proton‐coupled electron transfer pathways, as well as direct hydrogen atom transfer reaction. Such mechanistic inquiries, and determining the differential reactivity of μ‐η 2 :η 2 ‐peroxo‐ $\hbox{Cu}^{{\rm II}}_{2}$ and $\hbox{Cu}^{{\rm III}}_{2}$ ‐bis‐μ‐oxo complexes, are of continuing and future interest.

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Copper(I)-phenolate complexes as models of the reduced active site of galactose oxidase: synthesis, characterization, and O2 reactivity

Cited by 54 publications

References 68 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

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

Copper: Hemocyanin/Tyrosinase ModelsBased in part on the article Copper: Hemocyanin/Tyrosinase Models by Nobumasa Kitajima which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

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