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Correlation of the electronic and geometric structures in mononuclear copper(II) superoxide complexes.

ABSTRACT: The geometry of mononuclear copper(II) superoxide complexes has been shown to determine their ground state where side-on bonding leads to a singlet ground state and end-on complexes have triplet ground states. In an apparent contrast to this trend, the recently synthesized (HIPT3tren)Cu(II)O2(•-) (1) was proposed to have an end-on geometry and a singlet ground state. However, reexamination of 1 with resonance Raman, magnetic circular dichroism, and (2)H NMR spectroscopies indicate that 1 is, in fact, an end-on superoxide species with a triplet ground state that results from the single Cu(II)O2(•-) bonding interaction being weaker than the spin-pairing energy.

SUBMITTER: Ginsbach JW

PROVIDER: S-EPMC3882273 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Correlation of the electronic and geometric structures in mononuclear copper(II) superoxide complexes.

Ginsbach Jake W JW Peterson Ryan L RL Cowley Ryan E RE Karlin Kenneth D KD Solomon Edward I EI

Inorganic chemistry 20131028 22

The geometry of mononuclear copper(II) superoxide complexes has been shown to determine their ground state where side-on bonding leads to a singlet ground state and end-on complexes have triplet ground states. In an apparent contrast to this trend, the recently synthesized (HIPT3tren)Cu(II)O2(•-) (1) was proposed to have an end-on geometry and a singlet ground state. However, reexamination of 1 with resonance Raman, magnetic circular dichroism, and (2)H NMR spectroscopies indicate that 1 is, in ...[more]

PMID: 24164429

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Project description:The active-site structures of the oxidized and reduced forms of manganese-substituted iron superoxide dismutase (Mn(Fe)SOD) are examined, for the first time, using a combination of spectroscopic and computational methods. On the basis of electronic absorption, circular dichroism (CD), magnetic CD (MCD), and variable-temperature variable-field MCD data obtained for oxidized Mn(Fe)SOD, we propose that the active site of this species is virtually identical to that of wild-type manganese SOD (MnSOD), with both containing a metal ion that resides in a trigonal bipyramidal ligand environment. This proposal is corroborated by quantum mechanical/molecular mechanical (QM/MM) computations performed on complete protein models of Mn(Fe)SOD in both its oxidized and reduced states and, for comparison, wild-type (WT) MnSOD. The major differences between the QM/MM optimized active sites of WT MnSOD and Mn(Fe)SOD are a smaller (His)N-Mn-N(His) equatorial angle and a longer (Gln146(69))NH···O(sol) H-bond distance in the metal-substituted protein. Importantly, these modest geometric differences are consistent with our spectroscopic data obtained for the oxidized proteins and high-field electron paramagnetic resonance spectra reported previously for reduced Mn(Fe)SOD and MnSOD. As Mn(Fe)SOD exhibits a reduction midpoint potential (E(m)) almost 700 mV higher than that of MnSOD, which has been shown to be sufficient for explaining the lack of SOD activity displayed by the metal-subtituted species (Vance, C. K.; Miller, A. F. Biochemistry 2001, 40, 13079-13087), E(m)'s were computed for our experimentally validated QM/MM optimized models of Mn(Fe)SOD and MnSOD. These computations properly reproduce the experimental trend and reveal that the drastically elevated E(m) of the metal substituted protein stems from a larger separation between the second-sphere Gln residue and the coordinated solvent in Mn(Fe)SOD relative to MnSOD, which causes a weakening of the corresponding H-bond interaction in the oxidized state and alleviates steric crowding in the reduced state.

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Correlation of the electronic and geometric structures in mononuclear copper(II) superoxide complexes.

Publications

Correlation of the electronic and geometric structures in mononuclear copper(II) superoxide complexes.

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