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Bykov D.,University of Aarhus | Neese F.,Max Planck Institute For Chemische Energiekonversion
Inorganic Chemistry | Year: 2015

In this Forum Article, an extensive discussion of the mechanism of six-electron, seven-proton nitrite reduction by the cytochrome c nitrite reductase enzyme is presented. On the basis of previous studies, the entire mechanism is summarized and a unified picture of the most plausible sequence of elementary steps is presented. According to this scheme, the mechanism can be divided into five functional stages. The first phase of the reaction consists of substrate binding and N-O bond cleavage. Here His277 plays a crucial role as a proton donor. In this step, the N-O bond is cleaved heterolytically through double protonation of the substrate. The second phase of the mechanism consists of two proton-coupled electron-transfer events, leading to an HNO intermediate. The third phase involves the formation of hydroxylamine, where Arg114 provides the necessary proton for the reaction. The second N-O bond is cleaved in the fourth phase of the mechanism, again triggered by proton transfer from His277. The Tyr218 side chain governs the fifth and last phase of the mechanism. It consists of radical transfer and ammonia formation. Thus, this mechanism implies that all conserved active-site side chains work in a concerted way in order to achieve this complex chemical transformation from nitrite to ammonia. The Forum Article also provides a detailed discussion of the density functional theory based cluster model approach to bioinorganic reactivity. A variety of questions are considered: the resting state of enzyme and substrate binding modes, interaction with the metal site and with active-site side chains, electron- and proton-transfer events, substrate dissociation, etc. © 2015 American Chemical Society.

Plenk C.,Johannes Gutenberg University Mainz | Weyhermuller T.,Max Planck Institute For Chemische Energiekonversion | Rentschler E.,Johannes Gutenberg University Mainz
Chemical Communications | Year: 2014

Two novel record-sized heterometallic Cr12M12 (M = Co, Ni) chromium wheels with an unusual saddle-like architecture are created by reacting appropriate precursor complexes with the bridging ligand 2,2′-bipyrimidine. This journal is © the Partner Organisations 2014.

Meyer S.,University of Gottingen | Klawitter I.,University of Gottingen | Demeshko S.,University of Gottingen | Bill E.,Max Planck Institute For Chemische Energiekonversion | Meyer F.,University of Gottingen
Angewandte Chemie - International Edition | Year: 2013

Bioinspired organometallic chemistry: An oxoiron(IV) unit has been trapped within a macrocyclic tetracarbene ligand, merging a key bioinorganic intermediate with a popular organometallic scaffold (see picture). The stability of the new complex has allowed its characterization by a variety of methods, which show a strong σ-donating tetracarbene coordination leading to an S=1 ground state and unusual properties of the oxoiron(IV) species. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zadrozny J.M.,University of California at Berkeley | Xiao D.J.,University of California at Berkeley | Atanasov M.,Max Planck Institute For Chemische Energiekonversion | Atanasov M.,Bulgarian Academy of Science | And 4 more authors.
Nature Chemistry | Year: 2013

Single-molecule magnets that contain one spin centre may represent the smallest possible unit for spin-based computational devices. Such applications, however, require the realization of molecules with a substantial energy barrier for spin inversion, achieved through a large axial magnetic anisotropy. Recently, significant progress has been made in this regard by using lanthanide centres such as terbium(III) and dysprosium(III), whose anisotropy can lead to extremely high relaxation barriers. We contend that similar effects should be achievable with transition metals by maintaining a low coordination number to restrict the magnitude of the d-orbital ligand-field splitting energy (which tends to hinder the development of large anisotropies). Herein we report the first two-coordinate complex of iron(I), [Fe(C(SiMe3) 3)2]-, for which alternating current magnetic susceptibility measurements reveal slow magnetic relaxation below 29 K in a zero applied direct-current field. This S =complex exhibits an effective spin-reversal barrier of U eff = 226(4) cm-1, the largest yet observed for a single-molecule magnet based on a transition metal, and displays magnetic blocking below 4.5 K. © 2013 Macmillan Publishers Limited. All rights reserved.

Cox N.,Max Planck Institute For Chemische Energiekonversion | Messinger J.,Umea University
Biochimica et Biophysica Acta - Bioenergetics | Year: 2013

This brief article aims at presenting a concise summary of all experimental findings regarding substrate water-binding to the Mn4CaO5 cluster in photosystem II. Mass spectrometric and spectroscopic results are interpreted in light of recent structural information of the water oxidizing complex obtained by X-ray crystallography, spectroscopy and theoreticalmodeling. Within this framework current proposals for themechanismof photosyntheticwater-oxidation are evaluated. This article is part of a Special Issue entitled:Metals in Bioenergetics and Biomimetics Systems. © 2013 Elsevier B.V. All rights reserved.

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