The transcription factor FNR ( f umarate n itrate r eduction) requires the presence of an iron-sulfur (Fe-S) cluster for its function as a global regulator in Escherichia coli when oxygen becomes scarce. To define oxidation state and type Fe-S present active form FNR, we have studied anaerobically purified with Mössbauer spectroscopy. Our data showed that this contained [4Fe-4S] 2+ (δ = 0.45 mm/s; Δ E Q 1.22 mm/s) was rapidly destroyed on exposure to air. Under these conditions, yellow–green...

[Fe]-Hydrogenase II isolated from C. pasteurianum contains 14 Fe which are distributed among the so-called H cluster (the catalytic center) and two [4Fe-4S] clusters. Insights gained Mössbauer studies of M-[4Fe-4S]2+ assemblies (M is a paramagnetic in sulfite reductase carbon monoxide dehydrogenase have suggested that [4Fe-4S]2+ covalently linked to smaller Fe-containing cluster. Recent X-ray [Fe]-hydrogenases, combined with results FTIR studies, revealed novel binuclear cluster, [2Fe]H, by...

The compounds of this study have yielded to complementary structural, spectroscopic (Mössbauer, EPR/ENDOR, IR), and computational probes that illustrate the fine control electronic steric features are involved in two structural forms (μ-SRS)[Fe(CO)2PMe3]2(0,+) complexes. installation bridgehead bulk -SCH2CR2CH2S- dithiolate (R = Me, Et) model complexes produces 6-membered FeS2C3 cyclohexane-type rings produce substantial distortions Fe(I)Fe(I) precursors. Both innocent (Fc(+)) noninnocent or...

The geometric constraints imposed by a tetradentate P4N2 ligand play an essential role in stabilizing square planar Fe complexes with changes metal oxidation state. pyramidal Fe0(N2)(P4N2) complex catalyzes the conversion of N2 to N(SiR3)3 (R = Me, Et) at room temperature, representing highest turnover number any Fe-based silylation catalyst date (up 65 equiv N(SiMe3)3 per center). Elevated pressures (>1 atm) have dramatic effect on catalysis, increasing solubility and thermodynamic binding...

The characterization of high-valent iron centers in enzymes has been aided by synthetic model systems that mimic their reactivity or structural and spectral features. For example, the cleavage dioxygen often produces an iron(IV)-oxo characterized a number enzymatic systems. In non-heme 2-oxogluterate dependent (iron-2OG) enzymes, ferryl species abstracts H-atom from bound substrate to produce proposed iron(III)-hydroxo caged radical. Most iron-2OG perform radical rebound hydroxylation at...

The ferric uptake regulator (Fur) is a global transcription factor that regulates intracellular iron homeostasis in bacteria. current hypothesis states when the "free" concentration elevated, Fur binds ferrous iron, and iron-bound represses genes encoding for systems stimulates storage proteins. However, "iron-bound" has never been isolated from any Here we report Escherichia coli bright red color expressed E. mutant cells containing an elevated free content because of deletion iron–sulfur...

The global regulator FNR (for fumarate nitrate reduction) controls the transcription of >100 genes whose products facilitate adaptation Escherichia coli to growth under O 2 -limiting conditions. Previous Mössbauer studies have shown that anaerobically purified contains a [4Fe-4S] 2+ cluster that, on exposure oxygen, is converted into [2Fe-2S] cluster, process decreases DNA binding by FNR. Using 57 Fe spectroscopy E. cells containing overexpressed FNR, we show here same conversion also...

A series of mono- and disubstituted complexes, FeI2(CO)xL4−x, x = 2 or 3, is conveniently accessed from simple mixing N-heterocyclic carbenes, phosphines, aromatic amines with FeI2(CO)4, first reported by Hieber in 1928. The highly light sensitive complexes yield to crystallization X-ray diffraction studies for six showing them be rudimentary structural models the monoiron hydrogenase, [Fe]-H2ase Hmd, active site native (FeII(CO)2) CO-inhibited (FeII(CO)3) states. Diatomic ligand (ν(CO))...

Pentacoordinate iron dicarbonyls, (NS)Fe(CO)(2)P (NS=2-amidothiophenylate, P=PCy(3) (4), PPh(3), (5), and P(OEt)(3) (6)) were prepared as potential biomimetics of the active site mono-iron hydrogenase, [Fe]-H(2)ase. Full characterization including X-ray diffraction, density functional theory (DFT) computations, Mössbauer studies for complexes 5 6 find that, despite similar infrared v(CO) pattern absorption frequencies [Fe]-H(2)ase, geometrical distortions towards trigonal bipyramidal,...

The benzoate 1,2-dioxygenase system (BZDOS) from Pseudomonas putida mt-2 catalyzes the NADH-dependent oxidation of to 1-carboxy-1,2-cis-dihydroxycyclohexa-3,5-diene. Both oxygenase (BZDO) and reductase (BZDR) components BZDOS have been purified characterized kinetically by optical, EPR, Mössbauer spectroscopies. BZDO has an (αβ)3 subunit structure in which each α contains a Rieske [2Fe-2S] cluster mononuclear iron site. Two different purification protocols were developed for allowing be...

To understand the role of [4Fe-4S]²⁺ cluster in controlling activity <i>Escherichia coli</i> transcription factor FNR (fumarate nitrate reduction) during changes O₂ availability, we have characterized a mutant protein containing substitution Leu-28 with His (FNR-L28H) which, unlike its wild type (WT) counterpart, is functional under aerobic growth conditions. The His-28 appears to stabilize FNR-L28H presence because air-exposed did not undergo rapid...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTChemistry of Iron Thiolate Complexes with CN- and CO. Models for the [Fe(CO)(CN)2] Structural Unit in Ni−Fe Hydrogenase EnzymesHua-Fen Hsu, Stephen A. Koch, Codrina V. Popescu, Eckard MünckView Author Information Department Chemistry State University New York at Stony Brook Brook, 11794-3400 Chemistry, Carnegie Mellon Pittsburgh, Pennsylvania 15213 Cite this: J. Am. Chem. Soc. 1997, 119, 35, 8371–8372Publication Date (Web):September 3,...

The A-center of carbon monoxide dehydrogenase (CODH) resides in the enzyme's α-subunit and is responsible for acetyl-CoA synthase activity. center comprises a Ni site an iron−sulfur cluster. We have isolated using both continuous discontinuous electrophoresis methods. When incubated with CO, samples prepared gels attain Ared-CO state that exhibits S = 1/2 EPR feature (g 2.048, 2.046, 2.021) similar to so-called NiFeC signal native CODH. Both signals consistently quantify <0.4 spin/α. In...

A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment have been prepared. Reduction ferrous {[PhTttBu]FeCl}2 [1; PhTttBu = phenyltris((tert-butylthio)methyl)borate] with KC8 the presence PR3 (R Me or Et) yields high-spin, monovalent phosphine [PhTttBu]Fe(PR3) (2). These provide entry into other low-valent derivatives via substitution. Carbonylation led to smooth formation low-spin dicarbonyl [PhTttBu]Fe(CO)2 (3). Alternatively, replacement...

To explore the effect of delocalization in Fe(NO)2 unit on possible linkage isomerism ambidentate ECN– ligands, E = S and O, anionic DNICs, dinitrosyl iron complexes, (SCN)2Fe(NO)2– (1) (OCN)2Fe(NO)2– (2) were synthesized by reaction situ-generated [Fe(CO)2(NO)2]+ PPN+ECN–. Other {Fe(NO)2}9 (Enemark–Feltham notation) (N3)2Fe(NO)2– (PhS)2Fe(NO)2–, prepared for comparison. The X-ray diffraction analysis 1 2 yielded typical tetrahedral structures DNICs with two slightly bent Fe–N–O oriented...

The synthesis and characterization of an Fe(III) catecholate-nitronylnitroxide (CAT-NN) complex (1-NN) that undergoes spin-crossover is described. Our aim to determine whether the intraligand exchange coupling semiquinone-nitronylnitroxide Fe(II)(SQ-NN) excited state resulting from irradiation CAT → LMCT band would affect either intrinsic photophysics or iron event when compared lacking nitronylnitroxide radical (1). X-ray crystallographic analysis provides bond lengths consistent with a...

O2 activation at nonheme iron centers is a common motif in biological systems. While synthetic models have provided numerous insights into the reactivity of high-valent iron–oxo complexes related to processes, majority these are synthesized using alternative oxidants. This report describes by an iron(II)–triflate complex imino-functionalized tris(pyrrol-2-ylmethyl)amine ligand framework, H3[N(piCy)3]. Initial reaction conditions result formation mixture oxidation products including terminal...

This study describes the O2 reactivity of a series high-spin mononuclear Fe(II) complexes each containing facially coordinating tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (Ph2TIP) ligand and one following bidentate, redox-active ligands: 4-tert-butylcatecholate (tBuCatH–), 4,6-di-tert-butyl-2-aminophenolate (tBu2APH–), or 4-tert-butyl-1,2-phenylenediamine (tBuPDA). The preparation X-ray structural characterization [Fe2+(Ph2TIP)(tBuCatH)]OTf, [3]OTf [Fe2+(Ph2TIP)(tBuPDA)](OTf)2,...

Abstract The oxidative CC bond cleavage of o ‐aminophenols by nonheme Fe dioxygenases is a critical step in both human metabolism (the kynurenine pathway) and the microbial degradation nitroaromatic pollutants. catalytic cycle ‐aminophenol (APDOs) has been proposed to involve formation an II /O 2 /iminobenzosemiquinone complex, although presence substrate radical called into question studies related ring‐cleaving dioxygenases. Recently, we reported first synthesis iron(II) complex...

The synthesis and structure of the pseudotetrahedral, sulfur-rich, high-spin organoiron(II) [phenyltris((tert-butylthio)methyl)borate]Fe(Me), [PhTttBu]Fe(Me), 1, are reported. Low-temperature Mössbauer spectroscopic studies reveal an isomer shift δ = 0.60(3) mm/s ΔEQ 0.00(1) S 2 ground multiplet with a negative zero-field splitting, D −33(3) cm−1, E/D ≈ 0.01. small separation doublet, Δ 0.01 allows for observation X-band EPR signals at geff 10 (gz 2.6, gx,y 2.00). relatively large splitting...

The dinuclear iron cluster of the oxidized hydroxylase component methane monooxygenase (MMOH) contains two antiferromagnetically coupled high-spin ferric ions (ℋ = JSA·SB, SA SB 5/2, J 15 cm-1). Previous Mössbauer studies revealed that electronic ground state a paramagnetic admixture; this is manifested in magnetic hyperfine splittings are larger by about 10% than those attributable to applied field. This observation cannot be explained anisotropic Zeeman interactions, zero-field splittings,...

The interaction of the soluble methane monooxygenase regulatory component (MMOB) and active site-bearing hydroxylase (MMOH) is investigated using spin fluorescent probes. MMOB from Methylosinus trichosporium OB3b devoid cysteine. Consequently, site-directed mutagenesis was used to incorporate single cysteine residues, allowing specific placement probe molecules. Sixteen Cys mutants were prepared labeled with EPR 4-maleimido-2,2,6,6-tetramethyl-1-piperidinyloxy (MSL). Spectral evaluation...

Incorporating radical ligands into metal complexes is one of the emerging trends in design single-molecule magnets (SMMs). While significant effort has been expended to generate multinuclear transition metal-based SMMs with bridging ligands, less attention paid mononuclear metal–radical SMMs. Herein, we describe first α-diiminato radical-containing SMM, namely, [κ2-PhTttBu]Fe(AdNCHCHNAd) (1), and its analogue [κ2-PhTttBu]Fe(CyNCHCHNCy) (2) (PhTttBu = phenyltris(tert-butylthiomethyl)borate,...