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Ground-state electronic and magnetic properties of a mu3-oxo-bridged trinuclear Cu(II) complex: correlation to the native intermediate of the multicopper oxidases.

ABSTRACT: The ground-state electronic and magnetic properties of one of the possible structures of the trinuclear Cu(II) site in the native intermediate (NI) of the multicopper oxidases, the mu(3)-oxo-bridged structure, are evaluated using the C(3)-symmetric Cu(3)(II) complex, mu(3)O. mu(3)O is unique in that no ligand, other than the oxo, contributes to the exchange coupling. However, mu(3)O has a ferromagnetic ground state, inconsistent with that of NI. Therefore, two perturbations have been considered: protonation of the mu(3)-oxo ligand and relaxation of the mu(3)-oxo ligand into the Cu(3) plane. Notably, when the oxo ligand is sufficiently close to the Cu(3) plane (<0.3 Angstroms), the ground state of mu(3)O becomes antiferromagnetic and can be correlated to that of NI. In addition, the ferromagnetic (4)A ground state of mu(3)O is found from variable-temperature EPR to undergo a zero-field splitting (ZFS) of 2D = -5.0 cm(-1), which derives from the second-order anisotropic exchange. This allows evaluation of the sigma-to-pi excited-state exchange pathways and provides experimental evidence that the orbitally degenerate (2)E ground state of the antiferromagnetic mu(3)O would also undergo a ZFS by the first-order antisymmetric exchange that has the same physical origin as the anisotropic exchange. The important contribution of the mu(3)-oxo bridge to the ground-to-ground and ground-to-excited-state superexchange pathways that are responsible for the isotropic, antisymmetric, and anisotropic exchanges are discussed.

SUBMITTER: Yoon J

PROVIDER: S-EPMC2630029 | biostudies-literature | 2005 Oct

REPOSITORIES: biostudies-literature

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Ground-state electronic and magnetic properties of a mu3-oxo-bridged trinuclear Cu(II) complex: correlation to the native intermediate of the multicopper oxidases.

Yoon Jungjoo J Solomon Edward I EI

Inorganic chemistry 20051001 22

The ground-state electronic and magnetic properties of one of the possible structures of the trinuclear Cu(II) site in the native intermediate (NI) of the multicopper oxidases, the mu(3)-oxo-bridged structure, are evaluated using the C(3)-symmetric Cu(3)(II) complex, mu(3)O. mu(3)O is unique in that no ligand, other than the oxo, contributes to the exchange coupling. However, mu(3)O has a ferromagnetic ground state, inconsistent with that of NI. Therefore, two perturbations have been considered: ...[more]

PMID: 16241158

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Project description:The multicopper oxidases (MCOs) utilize a blue type 1 (T1) copper site and a trinuclear Cu cluster composed of a type 2 (T2) and a binuclear type 3 (T3) site that together catalyze the four-electron reduction of O2 to H2O. Reaction of the fully reduced enzyme with O2 proceeds via two sequential two-electron steps generating the peroxy intermediate (PI) and the native intermediate (NI). While a detailed description of the geometric and electronic structure of NI has been developed, this has been more elusive for PI largely due to the diamagnetic nature of its ground state. Density functional theory (DFT) calculations have been used to correlate to spectroscopic data to generate a description of the geometric and electronic structure of PI. A highly conserved carboxylate residue near the T2 site is found to play a critical role in stabilizing the PI structure, which induces oxidation of the T2 and one T3 Cu center and strong superexchange stabilization via the peroxide bridge, allowing irreversible binding of O2 at the trinuclear Cu site. Correlation of PI to NI is achieved using a two-dimensional potential energy surface generated to describe the catalytic two-electron reduction of the peroxide O-O bond by the MCOs. It is found that the reaction is thermodynamically driven by the relative stability of NI and the involvement of the simultaneous two-electron-transfer process. A low activation barrier (calculated approximately 5-6 kcal/mol and experimental approximately 3-5 kcal/mol) is produced by the triangular topology of the trinuclear Cu cluster site, as this symmetry provides good donor-acceptor frontier molecular orbital (FMO) overlap. Finally, the O-O bond cleavage in the trinuclear Cu cluster can be achieved via either a proton-assisted or a proton-unassisted process, allowing the MCOs to function over a wide range of pH. It is found that while the proton helps to stabilize the acceptor O22- sigma* orbital in the proton-assisted process for better donor-acceptor FMO overlap, the third oxidized Cu center in the trinuclear site assumes the role as a Lewis acid in the proton-unassisted process for similarly efficient O-O bond cleavage.

Dataset Information

Ground-state electronic and magnetic properties of a mu3-oxo-bridged trinuclear Cu(II) complex: correlation to the native intermediate of the multicopper oxidases.

Publications

Ground-state electronic and magnetic properties of a mu3-oxo-bridged trinuclear Cu(II) complex: correlation to the native intermediate of the multicopper oxidases.

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