Control of the Evolution of Iron Peroxide Intermediate in Superoxide Reductase from Desulfoarculus baarsii. Involvement of Lysine 48 in Protonation

International audienceSuperoxide reductase is a nonheme iron metalloenzyme that detoxifies superoxide anion radicals O(2)(•-) in some microorganisms. Its catalytic mechanism was previously proposed to involve a single ferric iron (hydro)peroxo intermediate, which is protonated to form the reaction product H(2)O(2). Here, we show by pulse radiolysis that the mutation of the well-conserved lysine 48 into isoleucine in the SOR from Desulfoarculus baarsii dramatically affects its reaction with O(2)(•-). Although the first reaction intermediate and its decay are not affected by the mutation, H(2)O(2) is no longer the reaction product. In addition, in contrast to the wild-type SOR, the lysine mutant catalyzes a two-electron oxidation of an olefin into epoxide in the presence of H(2)O(2), suggesting the formation of iron-oxo intermediate species in this mutant. In agreement with the recent X-ray structures of the peroxide intermediates trapped in a SOR crystal, these data support the involvement of lysine 48 in the specific protonation of the proximal oxygen of the peroxide intermediate to generate H(2)O(2), thus avoiding formation of iron-oxo species, as is observed in cytochrome P450. In addition, we proposed that the first reaction intermediate observed by pulse radiolysis is a ferrous-iron superoxo species, in agreement with TD-DFT calculations of the absorption spectrum of this intermediate. A new reaction scheme for the catalytical mechanism of SOR with O(2)(•-) is presented in which ferrous iron-superoxo and ferric hydroperoxide species are reaction intermediates, and the lysine 48 plays a key role in the control of the evolution of iron peroxide intermediate to form H(2)O(2)

Artificial Enzymes Crystals: New heterogeneous Catalysts for a sustainable oxidation

Keynote lectureInternational audienc

Artificial Enzymes Crystals: New heterogeneous Catalysts for a sustainable oxidation

Keynote SpeakerInternational audienc

Artificial Enzymes Crystals: New heterogeneous Catalysts for a sustainable oxidation

Keynote SpeakerInternational audienc

Artificial Enzymes Crystals : New heterogeneous Catalysts for a sustainable oxidation

International audienc

Influence of the copper coordination spheres on the N2Or activity of a mixed-valent copper complex containing a {Cu2S} core

International audienceA new mixed-valent dicopper complex [5] was generated from ligand exchange by dissolving a bis(CH3CN) precursor [3] in acetone. Introduction of a water molecule in place of an acetonitrile ligand was evidenced by base titration and the presence of a remaining coordinated CH3CN by IR, 19F NMR, and theoretical methods. The proposed structure (CH3CN–Cu–(SR)–Cu–OH2) was successfully DFT-optimized and the calculated parameters are in agreement with the experimental data. [5] has a unique temperature-dependence EPR behavior, with a localized valence from 10 to 120 K that undergoes delocalized at room temperature. The electrochemical signatures are in the line of the other aquo parent [2] and sensibly different from the rest of the series. Similar to the case of [2], [5] was finally capable of single turnover N2O reduction at room temperature. N2 was detected by GC-MS, and the redox character was confirmed by EPR and ESI-MS. Kinetic data indicate a reaction rate order close to 1 and a rate 10 times faster compared to [2]. [5] is thus the second example of that kind and highlights not only the main role of the Cu–OH2 motif, but also that the adjacent Cu-X partner (X = OTf– in [2] and CH3CN in [5]) is a new actor in the casting to establish structure/activity correlations

Small Molecule Activation by Organo-iron Complexes

International audienceThis chapter describes the main advances in the field of small molecule activation with organo-iron complexes. It focuses on four reactivities that have experienced the greatest growth in recent years, N2 activation and reduction, H2 production and oxidation and O2 activation for oxidation reactions. A brief description of the structural and spectroscopic properties of the complexes of interest will be provided, followed by their potential reactivity under stoichiometric and catalytic conditions