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Abstract: Treatment of [Fe3(CO)12] with tri(2-furyl)phosphine (PFu3) or tri(2-thienyl)phosphine (PTh3) in dichloromethane at 40°C leads to facile phosphorus–carbon bond scission affording di-iron furyl- and thienyl-bridged complexes [Fe2(CO)6(μ-η1,η2-C4H3E){μ-P(C4H3E)2}] (1 E =O, Fu; 3 E =S, Th) in good yields, together with smaller amounts of the phosphine-substituted [Fe2(CO)5(μ-η1,η2-C4H3E){μ-P(C4H3E)2}{P(C4H3E)3}] (2 E =O, 4 E =S). When the same reactions were carried out at room temperature, small amounts of the tri-iron clusters [Fe3(CO)11{P(C4H3E)3}] (5 E =O, 6 E =S) were isolated in which the coordinated phosphine(s) remain intact. Thermolysis of [Fe3(CO)11{P(C4H3E)3}] at 40°C in dichloromethane gave [Fe2(CO)6(μ-η1,η2-C4H3E){μ-P(C4H3E)2}], which also undergo phosphine substitution under similar conditions. However, both of these processes are too slow to account for the reaction product ratios and yields observed in the room temperature reactions. In contrast, addition of catalytic amounts of Na+[Ph2CO]old>5 resulted in the rapid formation of 1. We therefore propose that these reactions may occur via a radical-initiated mechanism proceeding through the initial formation of the 49-electron radical anions [Fe3(CO)11{P(C4H3E)3}]stal structures of [Fe2(CO)6(μ-η1,η2-Fu)(μ-PFu2)] (1), [Fe2(CO)5(μ-η1,η2-Fu)(μ-PFu2)(PFu3)] (2), [Fe2(CO)6(μ-η1,η2-Th)(μ-PTh2)] (3) and [Fe3(CO)11(PFu3)] (5) have been determined. The di-iron complexes all show the expected cis arrangement of three-electron donor ligands, short iron–iron distances consistent with a 34-valence electron count, and, in 2, the phosphine is coordinated to the π-bound iron atom and lies trans to the metal–metal bond. Close inspection of the bonding parameters within the Fe2C2E core reveals that these alkenyl species are quite different to those without electron-withdrawing substituents. The tri-iron cluster 5 has two independent molecules in the asymmetric unit. Each contains two bridging carbonyls and the molecules differ in the relative positions of these carbonyls and the coordinated phosphine ligand, the latter lying in the equatorial plane in both molecules. [Copyright &y& Elsevier]

The nonheme di-iron oxygenase, AurF, converts p-aminobenzoate (Ar-NH2, where Ar = 4-carboxyphenyl) to p-nitrobenzoate (Ar-NO2) in the biosynthesis of the antibiotic, aureothin, by Streptomyces thioluteus. It has been reported that this net six-electron oxidation proceeds in three consecutive, two-electron steps, through p-hydroxylaminobenzoate (Ar-NHOH) and p-nitrosobenzoate (Ar-NO) intermediates, with each step requiring one equivalent of O2 and two exogenous reducing equivalents. We recently demonstrated that a peroxodiiron(III/III) complex (peroxo-Fe2III/III-AurF) formed by addition of O2 to the diuron(II/II) enzyme (Fe2II/II-AurF) effects the initial oxidation of Ar-NH2, generating a μ-(oxo)diiron (III/III) form of the enzyme (μ-oxo-Fe2III/III-AurF) and (presumably) Ar-NHOH. Here we show that peroxo-Fe2III/III-AurF also oxidizes Ar-NHOH. Unexpectedly, this reaction proceeds through to the Ar-NO2 final product, a four-electron oxidation, and produces Fe2II/II-AurF, with which O2 can combine to regenerate peroxo- Fe2III/III-AurF. Thus, conversion of Ar-NHOH to Ar-NO2 requires only a single equivalent of O2 and (starting from Fe2II/II-AurF or peroxo- Fe2III/III-AurF) is fully catalytic in the absence of exogenous reducing equivalents, by contrast to the published stoichiometry. This novel type of four-electron N-oxidation is likely also to occur in the reaction sequences of nitro-installing di-iron amine oxygenases in the biosyntheses of other natural products. [ABSTRACT FROM AUTHOR]

Our previous analysis of the transcriptome of Escherichia coli under nitrosative stress showed that the ytfE gene was one of the highest induced genes. Furthermore, the E. coli strain mutated on the ytfE gene was found to be more sensitive to nitric oxide than the wild-type strain. In the present work, we show that the mutation of the ytfE gene in E. coli yielded a strain that grows poorly under anaerobic respiratory conditions and that has an increased sensitivity to iron starvation. Furthermore, all examined iron–sulphur proteins have decreased activity levels in the strain lacking ytfE. Altogether, the results suggest a role for ytfE in iron–sulphur cluster biogenesis. YtfE was overexpressed in E. coli and it is shown to contain a di-iron centre of the histidine-carboxylate family. [ABSTRACT FROM AUTHOR]

The Keggin-type di-iron-substituted silicotungstate, γ-SiW10{Fe(OH2)}2O38 6− ( I), was synthesized by the reaction of the lacunary [γ-SiW10O36]8− with Fe(NO3 in an acidic aqueous solution and isolated as the tetra- n-butylammonium salt (TBA- I). It was characterized by various analyses and the structure with the oxo-bridged di-iron site was clarified. TBA- I was stable and catalyzed selective oxidation of various alkanes and alkenes with hydrogen peroxide: cyclohexane, adamantane, n-hexane, and n-pentane were catalytically oxidized. Even lower alkanes such as methane, ethane, propane, and n-butane were catalytically oxidized. It was remarkable that the efficiency of hydrogen peroxide utilization to oxygenated products reached up to ca. 100% for the oxidation of cyclohexane and adamantane. Alkenes were mainly epoxidized with hydrogen peroxide. It was demonstrated that the TBA- I showed high turnover number of 135–147 for the oxidation of cyclohexane with 1 atm oxygen. [ABSTRACT FROM AUTHOR]3 in an acidic aqueous solution and isolated as the tetra- n-butylammonium salt (TBA- I). It was characterized by various analyses and the structure with the oxo-bridged di-iron site was clarified. TBA- I was stable and catalyzed selective oxidation of various alkanes and alkenes with hydrogen peroxide: cyclohexane, adamantane, n-hexane, and n-pentane were catalytically oxidized. Even lower alkanes such as methane, ethane, propane, and n-butane were catalytically oxidized. It was remarkable that the efficiency of hydrogen peroxide utilization to oxygenated products reached up to ca. 100% for the oxidation of cyclohexane and adamantane. Alkenes were mainly epoxidized with hydrogen peroxide. It was demonstrated that the TBA- I showed high turnover number of 135–147 for the oxidation of cyclohexane with 1 atm oxygen. [ABSTRACT FROM AUTHOR]

The RIC (repair of iron clusters) protein of Escherichia coli is a di-iron hemerythrin-like protein that has a proposed function in repairing stress-damaged iron-sulfur clusters. In this work, we performed a bacterial two-hybrid screening to search for RIC-protein interaction partners in E. coli As a result, the D NA-binding p rotein from s tarved cells (Dps) was identified, and its potential interaction with RIC was tested by bacterial adenylate cyclase-based two-hybrid (BACTH) system, bimolecular fluorescence complementation, and pulldown assays. Using the activity of two Fe-S-containing enzymes as indicators of cellular Fe-S cluster damage, we observed that strains with single deletions of ric or dps have significantly lower aconitase and fumarase activities. In contrast, the ric dps double mutant strain displayed no loss of aconitase and fumarase activity with respect to that of the wild type. Additionally, while complementation of the ric dps double mutant with ric led to a severe loss of aconitase activity, this effect was no longer observed when a gene encoding a di-iron site variant of the RIC protein was employed. The dps mutant exhibited a large increase in reactive oxygen species (ROS) levels, but this increase was eliminated when ric was also inactivated. Absence of other iron storage proteins, or of peroxidase and catalases, had no impact on RIC-mediated redox stress induction. Hence, we show that RIC interacts with Dps in a manner that serves to protect E. coli from RIC protein-induced ROS. IMPORTANCE The mammalian immune system produces reactive oxygen and nitrogen species that kill bacterial pathogens by damaging key cellular components, such as lipids, DNA, and proteins. However, bacteria possess detoxifying and repair systems that mitigate these deleterious effects. The Escherichia coli RIC (repair of iron clusters) protein is a di-iron hemerythrin-like protein that repairs stress-damaged iron-sulfur clusters. E. coli Dps is an iron storage protein of the ferritin superfamily with DNA-binding capacity that protects cells from oxidative stress. This work shows that the E. coli RIC and Dps proteins interact in a fashion that counters RIC protein-induced reactive oxygen species (ROS). Altogether, we provide evidence for the formation of a new bacterial protein complex and reveal a novel contribution for Dps in bacterial redox stress protection., (Copyright © 2018 American Society for Microbiology.)