Spectroscopic and theoretical studies of an end-on peroxide-bridged coupled binuclear copper(II) model complex of relevance to the active sites in hemocyanin and tyrosinase

Baldwin, Michael J.; Ross, Paul K.; Pate, James E.; Tyeklár, Zoltán; Karlin, Kenneth D.; Solomon, Edward I.

doi:10.1021/ja00023a014

Cited by 150 publications

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“…The symmetric ( s ) and antisymmetric ( as ) stretch energies correlate with ЄCuOCu, and by fitting the four observables ( s and as with 16 O 2 and 18 O 2 ) to NCA calculations, the observed stretches are consistent with a ЄCuOCu of 140° (Table S1). We further used these NCA calculations to evaluate the dependence of s and as of a Cu 2 O site on ЄCuOCu.…”

Section: Geometric and Electronic Structure Of The Cu2o Core In Cu-zsmentioning

confidence: 79%

“…The weak 870 cm Ϫ1 vibration is then assigned as an antisymmetric metal-oxo stretch ( as ), which should not be enhanced in the rR spectrum, while its second quantum (2 as ) is symmetric and consequently would have higher rR intensity than the fundamental, as observed for the 1,725 cm Ϫ1 vibration. † The energy of the second quantum of the as for 16 O 2 -activated Cu-ZSM-5 is expected to be at twice the energy of the fundamental (1,740 cm Ϫ1 ) but is instead observed at 1,725 cm Ϫ1 . Further, both the energy splitting and the intensity of the 1,725 cm Ϫ1 peak relative to the nearby 1,852 cm Ϫ1 peak change upon 18 O 2 -isotopic labeling.…”

Section: Resultsmentioning

confidence: 95%

“…Fig. 1 B Inset (green) shows the rR spectrum of the active species prepared with '' 16,18 O 2 ,'' which overlays a 1:1 normalized sum of the pure 16 O 2 (red) and 18 O 2 (blue) spectra (black in Fig. 1, Inset B).…”

Section: Resultsmentioning

confidence: 99%

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A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

Woertink

Smeets

Groothaert

et al. 2009

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

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Driven by the depletion of crude oil, the direct oxidation of methane to methanol has been of considerable interest. Promising low-temperature activity of an oxygen-activated zeolite, Cu-ZSM-5, has recently been reported in this selective oxidation and the active site in this reaction correlates with an absorption feature at 22,700 cm ؊1 . In the present study, this absorption band is used to selectively resonance enhance Raman vibrations of this active site. 18 O2 labeling experiments allow definitive assignment of the observed vibrations and exclude all previously characterized copper-oxygen species for the active site. In combination with DFT and normal coordinate analysis calculations, the oxygen activated Cu core is uniquely defined as a bent mono-( -oxo)dicupric site. Spectroscopically validated electronic structure calculations show polarization of the low-lying singly-occupied molecular orbital of the [Cu 2O] 2؉ core, which is directed into the zeolite channel, upon approach of CH 4. This induces significant oxyl character into the bridging O atom leading to a low transition state energy consistent with experiment and explains why the bent mono-( -oxo)dicupric core is highly activated for H atom abstraction from CH 4. The oxygen intermediate of Cu-ZSM-5 is now the most well defined species active in the methane monooxygenase reaction. density functional theory ͉ dicopper(II)-oxo ͉ oxygen activation ͉ resonance Raman spectroscopy ͉ zeolite

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Section: Geometric and Electronic Structure Of The Cu2o Core In Cu-zsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 95%

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A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

Woertink

Smeets

Groothaert

et al. 2009

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

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“…Peroxide has a doubly degenerate highest occupied molecular orbital (HOMO) set which will split in energy upon binding to Cu(II), the π* σ being stabilized to deeper binding energy due to σ bonding to the half occupied d orbital and the π* v (vertical) not being very affected by bonding as it is perpendicular to the Cu(II) Figure 3B) which is characteristic of peroxide bridging in a "normal" binuclear Cu(II) complex. 3 We now consider the unique geometric and electronic structure of oxy-Hc/Oxy-Ty. Again, we take the symmetric and antisymmetric combination of the d x 2 − y 2 half occupied valence orbitals of the two coppers (here the ligand field of each Cu is square pyramidal) and allow for their bonding interactions with the peroxide π* valence orbitals, but in the side-on peroxide bridged structure of the oxy-Hc site ( Figure 2C).…”

Section: Unique Spectroscopic Features → Novel Electronic Structurementioning

confidence: 99%

O₂ and N₂O Activation by Bi-, Tri-, and Tetranuclear Cu Clusters in Biology

et al. 2007

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Copper cluster sites in biology exhibit unique spectroscopic features reflecting exchange coupling between oxidized Cu's and e − delocalization in mixed valent sites. These novel electronic structures play critical roles in O 2 binding and activation for electrophilic aromatic attack and H atom abstraction, the 4e − /4H + reduction of O 2 to H 2 O, and in the 2e − /2H + reduction of N 2 O. These electronic structure/reactivity correlations are summarized below.Cu proteins play central roles in Fe, Cu, and O 2 metabolism, are related to a range of genetic diseases and are important in biotechnology, detoxification, and the elimination of greenhouse gases. Understanding Cu biochemistry on a molecular level provides mechanisms to improve or inhibit these processes and enhance drug design. The Cu proteins involved in O 2 binding, activation, reduction to H 2 O and the reduction of N 2 O to water and dinitrogen are summarized in Figure 1. The term "coupled" is used here to refer to the antiferromagnetic (AF) "coupling" between paramagnetic metal centers that can lead to a diamagnetic S tot =0 ground state. If two Cu(II)'s, S=1/2, directly overlap they will spin pair. If, however, they are far enough apart so that their d orbitals do not directly overlap but have a bridging ligand this can provide a superexchange pathway (i.e. a delocalized molecular orbital) between the two paramagnetic Cu(II)'s that results in their spin pairing, indirectly through overlap with the bridge. This is described by the exchange Hamiltonian H =−2JS A ·S B which spin couples the two S=1/2's on Cu A and Cu B to form total spins S tot =1 and 0 where for AF coupling the S tot =0 is lower in energy by 2J (J<0).In this paper we will: 1) consider the unique spectral features of the coupled binuclear Cu proteins, hemocyanin (Hc), catechol oxidase, and tyrosinase (Ty), that reflect a novel electronic structure that allows their reversible binding of O 2 (a spin forbidden process) and its activation for electrophilic attack on an aromatic substrate by Ty; 2) contrast this electronic structure to that of the non-coupled binuclear Cu enzymes (i.e. no magnetic interaction between the two Cu(II)'s S=1/2) to evaluate the contribution of these differences in AF exchange coupling to the reaction mechanisms, where the non-coupled binuclear Cu sites in dopamine α-monooxygenase (DβM) and peptidylglycine α-hydroxylating monooxygenase (PHM) activate O 2 for H-atom abstraction; 3) Extend these studies to the trinuclear Cu cluster site in the multicopper oxidases, where the exchange coupling among the three coppers plays a central role in the 4e − /4H + reduction of O 2 to H 2 O; and 4) Consider how the interactions among the coppers in the μ 4 sulfide bridged tetranuclear Cu z cluster promote the 2e − /2H + cleavage of the N-O bond by N 2 O reductase. for trigonal bipyramidal geometries. Peroxide has a doubly degenerate highest occupied molecular orbital (HOMO) set which will split in energy upon binding to Cu(II), the π* σ being stabilized to deeper bi...

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“…In the UV/Vis spectrum, compound 3 is characterized by l max = 465 nm (inset Figure 2; À1 band are consistent with assignment of this band as an intraperoxide stretch. [11][12][13] The lower frequency mode is ascribed to the ñ(NiÀO) mode associated with this peroxo intermediate, (ñ(NiÀ 16 O)/ñ(NiÀ 18 O) = 1.050; calcd 1.048). The rR excitation profile of the 778 cm À1 mode closely parallels the dominant absorption band, which leads to the assignment of this absorption band as a peroxo!Ni 2+ charge transfer (CT) transition.…”

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confidence: 99%

Spectroscopic Elucidation of a Peroxo Ni₂(μ‐O₂) Intermediate Derived from a Nickel(I) Complex and Dioxygen

et al. 2004

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The preparative chemistry and reactivity of NiÀO x intermediates has advanced significantly in the past few years with the identification of a number of new structure types. The most common synthetic approach, reaction of a nickel(ii) precursor with H 2 O 2 , has yielded bis-m-oxo [1][2][3][4] and bis-msuperoxo complexes.[4] An attractive alternate route utilizes the reaction of nickel(i) complexes with O 2 . This strategy relies on, and is limited by, the ability to prepare suitable nickel(i) species. We have utilized this latter approach to[5] (PhTt tBu = phenyltris((tertbutylthio)methyl)borate) and the related side-on bound superoxo complex, [{PhTt Ad }Ni(O 2 )] (PhTt Ad = phenyltris((1-adamantylthio)methyl)borate).[6] During the course of these studies, we considered whether a m-peroxo Ni 2 species was a possible intermediate along the reaction trajectory leading to the bis-m-oxo dimer. Lacking experimental evidence, a m-h 2 ,h 2 -peroxo bridged Ni 2 dimer supported by the tris(thioether) borato ligand was evaluated by density functional methods. [7] This hypothetical species was deemed to be of high energy, significantly destabilized (DH8 = 32 kcalmol À1 ) relative to the bis-m-oxo dimer and, therefore, an unlikely intermediate. Consequently, we turned our attention to macrocyclic tetradentate ligands that coordinate in a planar array, reasoning that such an attribute would render access to the m-h 2 ,h 2 -peroxo coordination more difficult. Herein, we report on the successful pursuit of this strategy, which led to the discovery of a Ni 2 (m-O 2 ) complex in which the peroxo moiety spans the metals in the m-1,2 mode.Addition of dry O 2 to [Ni(tmc)]OTf [8,9] (1; tmc = 1, 4,8,4,8, OTf = [CF 3 SO 3 ] À ) in THF or acetonitrile at room temperature resulted in a color change from pale blue to clover green. The FT-IR spectrum of the paramagnetic product (m eff = 2.7(1) m B ) included a prominent new feature at 3628 cm À1 assigned to the ñ(OÀH) mode

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Spectroscopic and theoretical studies of an end-on peroxide-bridged coupled binuclear copper(II) model complex of relevance to the active sites in hemocyanin and tyrosinase

Cited by 150 publications

References 0 publications

A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

O₂ and N₂O Activation by Bi-, Tri-, and Tetranuclear Cu Clusters in Biology

Spectroscopic Elucidation of a Peroxo Ni₂(μ‐O₂) Intermediate Derived from a Nickel(I) Complex and Dioxygen

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Spectroscopic and theoretical studies of an end-on peroxide-bridged coupled binuclear copper(II) model complex of relevance to the active sites in hemocyanin and tyrosinase

Cited by 150 publications

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A [Cu 2 O] 2+ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

A [Cu 2 O] 2+ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

O2 and N2O Activation by Bi-, Tri-, and Tetranuclear Cu Clusters in Biology

Spectroscopic Elucidation of a Peroxo Ni2(μ‐O2) Intermediate Derived from a Nickel(I) Complex and Dioxygen

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A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

A [Cu ₂ O] ²⁺ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

O₂ and N₂O Activation by Bi-, Tri-, and Tetranuclear Cu Clusters in Biology

Spectroscopic Elucidation of a Peroxo Ni₂(μ‐O₂) Intermediate Derived from a Nickel(I) Complex and Dioxygen