[Me<sub>4</sub>N](Ni<sup>II</sup>(BEAAM)):  A Synthetic Model for Nickel Superoxide Dismutase That Contains Ni in a Mixed Amine/Amide Coordination Environment

Shearer, Jason; Zhao, Ningfeng

doi:10.1021/ic061604s

Cited by 57 publications

(84 citation statements)

References 18 publications

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“…12,21,34,40,42,54−56 The Grapperhaus research group and our research group have suggested this is due (in part) to the electronic consequences of the mixed amine/amidate ligand set. 21,40,42,54 Harrop and Grapperhaus have also suggested that hydrogen bonds to the cysteinate sulfurs will protect the cysteinates from oxidative damage induced by ROSs. 34,54 This study shows that {Ni II (SOD m1 )} contains both a Ni II -S(H + )-Cys(6) moiety and water cysteinate hydrogen bonds, which likely enhance its observed robustness against oxidative damage in addition to the electronic finetuning of the Ni−S bond imparted by the primary coordination environment.…”

Section: ■ Discussionmentioning

confidence: 99%

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

et al. 2014

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Nickel-containing superoxide dismutase (NiSOD) is a mononuclear cysteinate-ligated nickel metalloenzyme that catalyzes the disproportionation of superoxide into dioxygen and hydrogen peroxide by cycling between Ni(II) and Ni(III) oxidation states. All of the ligating residues to nickel are found within the first six residues from the N-terminus, which has prompted several research groups to generate NiSOD metallopeptide-based mimics derived from the first several residues of the NiSOD sequence. To assess the viability of using these metallopeptide-based mimics (NiSOD maquettes) to probe the mechanism of SOD catalysis facilitated by NiSOD, we computationally explored the initial step of the O2(-) reduction mechanism catalyzed by the NiSOD maquette {Ni(II)(SOD(m1))} (SOD(m1) = HCDLP CGVYD PA). Herein we use spectroscopic (S K-edge X-ray absorption spectroscopy, electronic absorption spectroscopy, and circular dichroism spectroscopy) and computational techniques to derive the detailed active-site structure of {Ni(II)(SOD(m1))}. These studies suggest that the {Ni(II)(SOD(m1))} active-site possesses a Ni(II)-S(H(+))-Cys(6) moiety and at least one associated water molecule contained in a hydrogen-bonding interaction to the coordinated Cys(2) and Cys(6) sulfur atoms. A computationally derived mechanism for O2(-) reduction using the formulated active-site structure of {Ni(II)(SOD(m1))} suggests that O2(-) reduction takes place through an apparent initial outersphere hydrogen atom transfer (HAT) from the Ni(II)-S(H(+))-Cys(6) moiety to the O2(-) molecule. It is proposed that the water molecule aids in driving the reaction forward by lowering the Ni(II)-S(H(+))-Cys(6) pK(a). Such a mechanism is not possible in NiSOD itself for structural reasons. These results therefore strongly suggest that maquettes derived from the primary sequence of NiSOD are mechanistically distinct from NiSOD itself despite the similarities in the structure and physical properties of the metalloenzyme vs the NiSOD metallopeptide-based models.

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Section: ■ Discussionmentioning

confidence: 99%

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

et al. 2014

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“…[20] It has been argued that the mixed amine/amide coordination at the active site of NiSOD plays a crucial role in tuning the redox chemistry and reactivity of the active site. [13,14] Thus, filled-filled interactions between the p-donating amide ligand and the Ni-p orbitals destabilize metal-based orbitals, thereby facilitating electron transfer from Ni II to O 2 C À to generate a Ni III center, rather than Sbased radicals, in the catalytic cycle.…”

Section: N]a C H T U N G T R E N N U N G [Ni Ii a C H T U N G T R E Nmentioning

confidence: 99%

“…[20] The addition of pyridine to solutions of 1 at 293 and 253 K does not change the profile of the UV/Vis spectrum of 1, suggesting that pyridine does not bind to 1 over this temperature range. The oxidation of 1 and 2 to 1 + and 2 + , respectively, was monitored spectroelectrochemically using an optically transparent electrode cell (Figure 8).…”

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confidence: 94%

Molecular and Electronic Structures of One‐Electron Oxidized Ni^II–(Dithiosalicylidenediamine) Complexes: Ni^III–Thiolate versus Ni^II–Thiyl Radical States

Stenson

Board

Marín-Becerra

et al. 2008

Chemistry A European J

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The dithiosalicylidenediamine Ni II complexes [Ni(L)] (R=tBu, R'=CH2C(CH3)2CH2 1, R'=C6H4 2; R=H, R'=CH2C(CH3)2CH2 3, R'=C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R'=CH2C(CH3)2CH2 7, R'=C6H4 8; R=H, R'=CH2C(CH3)2CH2 9, R'=C6H4 10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H2N-R'-NH2 in the presence of Zn II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N2S2 coordination environment and have been characterized by 1H- and 13C NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for complexes 3 and 4 are not reversible. The one-electron oxidized species, 1+ and 2+, can be generated quantitatively either electrochemically or chemically with 70 % HClO4. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1+ and 2+ possess thiyl radical character, whereas those of 1(py)2 + and 2(py)2 + possess formal Ni III centers. Species 2+ dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)2](ClO4)2.2 CH2Cl2 confirms that this dimerization involves the formation of a S-S bond (S...S=2.202(5) A).

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“…[11,20,21] The UV region in Figure 2 shows only one broad band centered around 38 167 cm À1 (262 nm; e = 10 787 m À1 cm…”

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New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

Tietze

Breitzke

Imhof³

et al. 2008

Chemistry A European J

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For the first time, the existence of a substrate adduct of a nickel superoxide dismutase (NiSOD) model, based on the first nine residues from the N terminus of the active form of Streptomyces coelicolor NiSOD, has been proven and the adduct has been isolated. This adduct is based on the cyanide anion (CN(-)), as a substrate analogue of the superoxide anion (O(2)(*-)), and the nickel metallopeptide H-HCDLPCGVY-NH(2)-Ni. Spectroscopic studies, including IR, UV/Vis, and liquid- and solid-state NMR spectroscopy, show a single nickel-bound cyanide anion, which is embedded in the metallopeptide structure. This complex sheds new light on the question of whether the mode of action of the NiSOD enzyme is an inner- or outer-sphere mechanism. Whereas discussion was previously biased in favor of an outer-sphere electron-transfer mechanism due to the fact that binding of cyanide or azide moieties to the nickel active site had never been observed, our results are a clear indication in favor of the inner-sphere electron-transfer mechanism for the disproportionation of the O(2)(*-) ion, whereby the substrate is attached to the Ni atom in the active site of the NiSOD.

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[Me₄N](Ni^II(BEAAM)): A Synthetic Model for Nickel Superoxide Dismutase That Contains Ni in a Mixed Amine/Amide Coordination Environment

Cited by 57 publications

References 18 publications

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

Molecular and Electronic Structures of One‐Electron Oxidized Ni^II–(Dithiosalicylidenediamine) Complexes: Ni^III–Thiolate versus Ni^II–Thiyl Radical States

New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

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[Me4N](NiII(BEAAM)): A Synthetic Model for Nickel Superoxide Dismutase That Contains Ni in a Mixed Amine/Amide Coordination Environment

Cited by 57 publications

References 18 publications

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

Cysteinate Protonation and Water Hydrogen Bonding at the Active-Site of a Nickel Superoxide Dismutase Metallopeptide-Based Mimic: Implications for the Mechanism of Superoxide Reduction

Molecular and Electronic Structures of One‐Electron Oxidized NiII–(Dithiosalicylidenediamine) Complexes: NiIII–Thiolate versus NiII–Thiyl Radical States

New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

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[Me₄N](Ni^II(BEAAM)): A Synthetic Model for Nickel Superoxide Dismutase That Contains Ni in a Mixed Amine/Amide Coordination Environment

Molecular and Electronic Structures of One‐Electron Oxidized Ni^II–(Dithiosalicylidenediamine) Complexes: Ni^III–Thiolate versus Ni^II–Thiyl Radical States