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A One-Hole Cu₄S Cluster with N₂O Reductase Activity: A Structural and Functional Model for Cu_Z.

ABSTRACT: During bacterial denitrification, two-electron reduction of N₂O occurs at a [Cu₄(μ₄-S)] catalytic site (Cu_Z*) embedded within the nitrous oxide reductase (N₂OR) enzyme. In this Communication, an amidinate-supported [Cu₄(μ₄-S)] model cluster in its one-hole (S = ¹/₂) redox state is thoroughly characterized. Along with its two-hole redox partner and fully reduced clusters reported previously, the new species completes the two-electron redox series of [Cu₄(μ₄-S)] model complexes with catalytically relevant oxidation states for the first time. More importantly, N₂O is reduced by the one-hole cluster to produce N₂ and the two-hole cluster, thereby completing a closed cycle for N₂O reduction. Not only is the title complex thus the best structural model for Cu_Z* to date, but it also serves as a functional Cu_Z* mimic.

SUBMITTER: Johnson BJ

PROVIDER: S-EPMC5378702 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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A One-Hole Cu4S Cluster with N2O Reductase Activity: A Structural and Functional Model for CuZ.

Johnson Brittany J BJ Antholine William E WE Lindeman Sergey V SV Graham Michael J MJ Mankad Neal P NP

Journal of the American Chemical Society 20161003 40

During bacterial denitrification, two-electron reduction of N2O occurs at a [Cu4(μ4-S)] catalytic site (CuZ*) embedded within the nitrous oxide reductase (N2OR) enzyme. In this Communication, an amidinate-supported [Cu4(μ4-S)] model cluster in its one-hole (S = 1/2) redox state is thoroughly characterized. Along with its two-hole redox partner and fully reduced clusters reported previously, the new ...[more]

PMID: 27685680

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Cu4S Cluster in "0-Hole" and "1-Hole" States: Geometric and Electronic Structure Variations for the Active CuZ* Site of N2O Reductase.

Project description:The active site of nitrous oxide reductase (N2OR), a key enzyme in denitrification, features a unique μ4-sulfido-bridged tetranuclear Cu cluster (the so-called CuZ or CuZ* site). Details of the catalytic mechanism have remained under debate and, to date, synthetic model complexes of the CuZ*/CuZ sites are extremely rare due to the difficulty in building the unique {Cu4(μ4-S)} core structure. Herein, we report the synthesis and characterization of [Cu4(μ4-S)]n+ (n = 2, 2; n = 3, 3) clusters, supported by a macrocyclic {py2NHC4} ligand (py = pyridine, NHC = N-heterocyclic carbene), in both their 0-hole (2) and 1-hole (3) states, thus mimicking the two active states of the CuZ* site during enzymatic N2O reduction. Structural and electronic properties of these {Cu4(μ4-S)} clusters are elucidated by employing multiple methods, including X-ray diffraction (XRD), nuclear magnetic resonance (NMR), UV/vis, electron paramagnetic resonance (EPR), Cu/S K-edge X-ray emission spectroscopy (XES), and Cu K-edge X-ray absorption spectroscopy (XAS) in combination with time-dependent density functional theory (TD-DFT) calculations. A significant geometry change of the {Cu4(μ4-S)} core occurs upon oxidation from 2 (τ4(S) = 0.46, seesaw) to 3 (τ4(S) = 0.03, square planar), which has not been observed so far for the biological CuZ(*) site and is unprecedented for known model complexes. The single electron of the 1-hole species 3 is predominantly delocalized over two opposite Cu ions via the central S atom, mediated by a π/π superexchange pathway. Cu K-edge XAS and Cu/S K-edge XES corroborate a mixed Cu/S-based oxidation event in which the lowest unoccupied molecular orbital (LUMO) has a significant S-character. Furthermore, preliminary reactivity studies evidence a nucleophilic character of the central μ4-S in the fully reduced 0-hole state.

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