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Shafaat H.S.,Max Planck Institute fu R Chemische Energiekonversion | Shafaat H.S.,Ohio State University | Griese J.J.,University of Stockholm | Pantazis D.A.,Max Planck Institute fu R Chemische Energiekonversion | And 10 more authors.
Journal of the American Chemical Society | Year: 2014

The electronic structure of the Mn/Fe cofactor identified in a new class of oxidases (R2lox) described by Andersson and Hö gbom [Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 5633] is reported. The R2lox protein is homologous to the small subunit of class Ic ribonucleotide reductase (R2c) but has a completely different in vivo function. Using multifrequency EPR and related pulse techniques, it is shown that the cofactor of R2lox represents an antiferromagnetically coupled MnIII/ FeIII dimer linked by a μ-hydroxo/bis-μ-carboxylato bridging network. The MnIII ion is coordinated by a single water ligand. The R2lox cofactor is photoactive, converting into a second form ( R2lox Photo) upon visible illumination at cryogenic temperatures (77 K) that completely decays upon warming. This second, unstable form of the cofactor more closely resembles the MnIII/FeIII cofactor seen in R2c. It is shown that the two forms of the R2lox cofactor differ primarily in terms of the local site geometry and electronic state of the MnIII ion, as best evidenced by a reorientation of its unique 55Mn hyperfine axis. Analysis of the metal hyperfine tensors in combination with density functional theory (DFT) calculations suggests that this change is triggered by deprotonation of the μ-hydroxo bridge. These results have important consequences for the mixed-metal R2c cofactor and the divergent chemistry R2lox and R2c perform. © 2014 American Chemical Society.

Atanasov M.,Max Planck Institute fu r Chemische Energiekonversion | Atanasov M.,Bulgarian Academy of Science | Aravena D.,Max Planck Institute fu r Chemische Energiekonversion | Suturina E.,Max Planck Institute fu r Chemische Energiekonversion | And 4 more authors.
Coordination Chemistry Reviews | Year: 2014

In this review, a self-contained (although brief) introduction to electronic structure calculations for single molecule magnet (SMM) properties is provided in conjunction with several contemporary case studies on diverse mononuclear 3d-transition metal complexes. The adequacy of density functional and wavefunction based theories for the prediction and interpretation of magnetic properties is addressed. Furthermore, the connection between calculations and experimental properties is discussed in some detail, in particular with respect to the derivation of spin-Hamiltonian parameters. In addition, we present an outline of the most important features of the most commonly employed quasi-classical spin relaxation model. The presented case studies include Fe, Co and Ni complexes with orbitally degenerate and non-degenerate ground states. The focus is on establishing magneto-structural correlations on both, a qualitative and quantitative level. © 2014 Elsevier B.V.

Kindermann N.,Georg August University Go ttingen | Bill E.,Max Planck Institute fu r chemische Energiekonversion | Dechert S.,Georg August University Go ttingen | Demeshko S.,Georg August University Go ttingen | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2014

Copper enzymes play important roles in the binding and activation of dioxygen in biological systems. Key copper/dioxygen intermediates have been identified and studied in synthetic analogues of the metalloprotein active sites, including the μ-η2:η2-peroxodicopper(II) motif relevant to type III dicopper proteins. Herein, we report the synthesis and characterization of a bioinspired dicopper system that forms a stable μ-η1:η1-peroxo complex whose Cu-O-O-Cu torsion is constrained to around 90° by ligand design. This results in sizeable ferromagnetic coupling between the copper(II) ions, which is detected by magnetic measurements and HF-EPR spectroscopy. The new dicopper peroxo system is the first with a triplet ground state, and it represents a snapshot of the initial stages of O2 binding at type III dicopper sites. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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