Spectroscopic and DFT Characterization of a Highly Reactive Nonheme Fe-Oxo Intermediate.

The reaction of [(PyNMe)Fe(CFSO)], 1, with excess peracetic acid at -40 °C generates a highly reactive intermediate, 2b(PAA), that has the fastest rate to date for oxidizing cyclohexane by a nonheme iron species. It exhibits an intense 490 nm chromophore associated with an S = 1/2 EPR signal having g-values at 2.07, 2.

Oxoiron(IV) Tetramethylcyclam Complexes with Axial Carboxylate Ligands: Effect of Tethering the Carboxylate on Reactivity.

Oxoiron(IV) species are implicated as reactive intermediates in nonheme monoiron oxygenases, often acting as the agent for hydrogen-atom transfer from substrate. A histidine is the most likely ligand trans to the oxo unit in most enzymes characterized thus far but is replaced by a carboxylate in the case of isopenicillin N synthase. As the effect of a trans carboxylate ligand on the properties of the oxoiron(IV) unit has not been systematically studied, we have synthesized and characterized four oxoiron(IV) complexes supported by the tetramethylcyclam (TMC) macrocycle and having a carboxylate ligand trans to the oxo unit.

Small GSK-3 Inhibitor Shows Efficacy in a Motor Neuron Disease Murine Model Modulating Autophagy.

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron degenerative disease that has no effective treatment up to date. Drug discovery tasks have been hampered due to the lack of knowledge in its molecular etiology together with the limited animal models for research. Recently, a motor neuron disease animal model has been developed using β-N-methylamino-L-alanine (L-BMAA), a neurotoxic amino acid related to the appearing of ALS.

Enzyme Substrate Complex of the H200C Variant of Homoprotocatechuate 2,3-Dioxygenase: Mössbauer and Computational Studies.

The extradiol, aromatic ring-cleaving enzyme homoprotocatechuate 2,3-dioxygenase (HPCD) catalyzes a complex chain of reactions that involve second sphere residues of the active site. The importance of the second-sphere residue His200 was demonstrated in studies of HPCD variants, such as His200Cys (H200C), which revealed significant retardations of certain steps in the catalytic process as a result of the substitution, allowing novel reaction cycle intermediates to be trapped for spectroscopic characterization. As the H200C variant largely retains the wild-type active site structure and produces the correct ring-cleaved product, this variant presents a valuable target for mechanistic HPCD studies.

Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex.

It was shown previously (J. Am. Chem.

Upside Down! Crystallographic and Spectroscopic Characterization of an [Fe IV(O syn)(TMC)]2+ Complex.

Fe(II)(TMC)(OTf)2 reacts with 2-(t)BuSO2-C6H4IO to afford an oxoiron(IV) product, 2, distinct from the previously reported [Fe(IV)(Oanti)(TMC)(NCMe)](2+). In MeCN, 2 has a blue-shifted near-IR band, a higher ν(Fe═O), a larger Mössbauer quadrupole splitting, and quite a distinct (1)H NMR spectrum. Structural analysis of crystals grown from CH2Cl2 reveals a complex with the formulation of [Fe(IV)(Osyn)(TMC)(OTf)](OTf) and the shortest Fe(IV)═O bond [1.

Trapping a Highly Reactive Nonheme Iron Intermediate That Oxygenates Strong C-H Bonds with Stereoretention.

An unprecedentedly reactive iron species (2) has been generated by reaction of excess peracetic acid with a mononuclear iron complex [Fe(II)(CF3SO3)2(PyNMe3)] (1) at cryogenic temperatures, and characterized spectroscopically. Compound 2 is kinetically competent for breaking strong C-H bonds of alkanes (BDE ≈ 100 kcal·mol(-1)) through a hydrogen-atom transfer mechanism, and the transformations proceed with stereoretention and regioselectively, responding to bond strength, as well as to steric and polar effects. Bimolecular reaction rates are at least an order of magnitude faster than those of the most reactive synthetic high-valent nonheme oxoiron species described to date.

A Long-Lived Fe(III)-(Hydroperoxo) Intermediate in the Active H200C Variant of Homoprotocatechuate 2,3-Dioxygenase: Characterization by Mössbauer, Electron Paramagnetic Resonance, and Density Functional Theory Methods.

The extradiol-cleaving dioxygenase homoprotocatechuate 2,3-dioxygenase (HPCD) binds substrate homoprotocatechuate (HPCA) and O2 sequentially in adjacent ligand sites of the active site Fe(II). Kinetic and spectroscopic studies of HPCD have elucidated catalytic roles of several active site residues, including the crucial acid-base chemistry of His200. In the present study, reaction of the His200Cys (H200C) variant with native substrate HPCA resulted in a decrease in both kcat and the rate constants for the activation steps following O2 binding by >400 fold.

Oxoiron(IV) Complex of the Ethylene-Bridged Dialkylcyclam Ligand Me2EBC.

We report herein the first example of an oxoiron(IV) complex of an ethylene-bridged dialkylcyclam ligand, [Fe(IV)(O)(Me2EBC)(NCMe)](2+) (2; Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane).

Morphometric and neurochemical alterations found in l-BMAA treated rats.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive muscle paralysis that reflects the motoneurons' degeneration. Several studies support the relationship between β-N-methylamino-l-alanine (l-BMAA), a neurotoxic amino acid produced by cyanobacteria and diatoms, and the sporadic occurrence of ALS and other neurodegenerative diseases. Therefore, the study of its neurotoxicity mechanisms has assumed great relevance in recent years.

Spectroscopic identification of an Fe(III) center, not Fe(IV), in the crystalline Sc-O-Fe adduct derived from [Fe(IV)(O)(TMC)]²⁺.

The apparent Sc(3+) adduct of [Fe(IV)(O)(TMC)](2+) (1, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) has been synthesized in amounts sufficient to allow its characterization by various spectroscopic techniques. Contrary to the earlier assignment of a +4 oxidation state for the iron center of 1, we establish that 1 has a high-spin iron(III) center based on its Mössbauer and EPR spectra and its quantitative reduction by 1 equiv of ferrocene to [Fe(II)(TMC)](2+). Thus, 1 is best described as a Sc(III)-O-Fe(III) complex, in agreement with previous DFT calculations (Swart, M.

Modeling TauD-J: a high-spin nonheme oxoiron(IV) complex with high reactivity toward C-H bonds.

High-spin oxoiron(IV) species are often implicated in the mechanisms of nonheme iron oxygenases, their C-H bond cleaving properties being attributed to the quintet spin state. However, the few available synthetic S = 2 Fe(IV)═O complexes supported by polydentate ligands do not cleave strong C-H bonds. Herein we report the characterization of a highly reactive S = 2 complex, [Fe(IV)(O)(TQA)(NCMe)](2+) (2) (TQA = tris(2-quinolylmethyl)amine), which oxidizes both C-H and C═C bonds at -40 °C.

An unusual peroxo intermediate of the arylamine oxygenase of the chloramphenicol biosynthetic pathway.

Streptomyces venezuelae CmlI catalyzes the six-electron oxygenation of the arylamine precursor of chloramphenicol in a nonribosomal peptide synthetase (NRPS)-based pathway to yield the nitroaryl group of the antibiotic. Optical, EPR, and Mössbauer studies show that the enzyme contains a nonheme dinuclear iron cluster. Addition of O(2) to the diferrous state of the cluster results in an exceptionally long-lived intermediate (t(1/2) = 3 h at 4 °C) that is assigned as a peroxodiferric species (CmlI-peroxo) based upon the observation of an (18)O(2)-sensitive resonance Raman (rR) vibration.

Redesigning the blue copper azurin into a redox-active mononuclear nonheme iron protein: preparation and study of Fe(II)-M121E azurin.

Much progress has been made in designing heme and dinuclear nonheme iron enzymes. In contrast, engineering mononuclear nonheme iron enzymes is lagging, even though these enzymes belong to a large class that catalyzes quite diverse reactions. Herein we report spectroscopic and X-ray crystallographic studies of Fe(II)-M121E azurin (Az), by replacing the axial Met121 and Cu(II) in wild-type azurin (wtAz) with Glu and Fe(II), respectively.

Characterization of a paramagnetic mononuclear nonheme iron-superoxo complex.

O2 bubbling into a THF solution of Fe(II)(BDPP) (1) at -80 °C generates a reversible bright yellow adduct 2. Characterization by resonance Raman and Mössbauer spectroscopy provides complementary insights into the nature of 2. The former shows a resonance-enhanced vibration at 1125 cm(-1), which can be assigned to the ν(O-O) of a bound superoxide, while the latter reveals the presence of a high-spin iron(III) center that is exchange-coupled to the superoxo ligand, like the Fe(III)-O2(-) pair found for the O2 adduct of 4-nitrocatechol-bound homoprotocatechuate 2,3-dioxygenase.

An Ultra-Stable Oxoiron(IV) Complex and Its Blue Conjugate Base.

Treatment of [Fe()](OTf) (), (where = 1,4,8-Mecyclam-11-CHC(O)NMe) with iodosylbenzene yielded the corresponding = 1 oxoiron(IV) complex [Fe(O()](OTf) () in nearly quantitative yield. The remarkably high stability of ( ≈ 5 days at 25 °C) facilitated its characterization by X-ray crystallography and a raft of spectroscopic techniques. Treatment of with strong base was found to generate a distinct, significantly less stable = 1 oxoiron(IV) complex, ( ~ 1.

Cyanobacterial aldehyde deformylase oxygenation of aldehydes yields n-1 aldehydes and alcohols in addition to alkanes.

Aldehyde-deformylating oxygenase (ADO) catalyzes O-dependent release of the terminal carbon of a biological substrate, octadecanal, to yield formate and heptadecane in a reaction that requires external reducing equivalents. We show here that ADO also catalyzes incorporation of an oxygen atom from O into the alkane product to yield alcohol and aldehyde products. Oxygenation of the alkane product is much more pronounced with C aldehyde substrates, so that use of nonanal as the substrate yields similar amounts of octane, octanal, and octanol products.

Identification of a low-spin acylperoxoiron(III) intermediate in bio-inspired non-heme iron-catalysed oxidations.

Synthetically useful hydrocarbon oxidations are catalysed by bio-inspired non-heme iron complexes using hydrogen peroxide as oxidant, and carboxylic acid addition enhances their selectivity and catalytic efficiency. Talsi has identified a low-intensity g=2.7 electron paramagnetic resonance signal in such catalytic systems and attributed it to an oxoiron(V)-carboxylate oxidant.

Spectroscopic and theoretical investigation of a complex with an [O═Fe(IV)-O-Fe(IV)═O] core related to methane monooxygenase intermediate Q.

Previous efforts to model the diiron(IV) intermediate Q of soluble methane monooxygenase have led to the synthesis of a diiron(IV) TPA complex, 2, with an O=Fe(IV)-O-Fe(IV)-OH core that has two ferromagnetically coupled Sloc = 1 sites. Addition of base to 2 at -85 °C elicits its conjugate base 6 with a novel O═Fe(IV)-O-Fe(IV)═O core. In frozen solution, 6 exists in two forms, 6a and 6b, that we have characterized extensively using Mössbauer and parallel mode EPR spectroscopy.

In utero hepatocellular transplantation in rats.

This work represents a step forward in the experimental design of an in utero hepatocellular transplantation model in rats. We focused on the enrichment optimization of isolated fetal hepatocytes suspension, arranging the surgery methodology of in utero transplantation, monitoring the biodistribution of the transplanted hepatocytes, and assessing the success of the transplants. Rat fetuses have been transplanted at the 17th embryonic day (ED17) with fetal hepatocytes isolated from rats at the end of pregnancy (ED21).

Sc3+-triggered oxoiron(IV) formation from O2 and its non-heme iron(II) precursor via a Sc3+-peroxo-Fe3+ intermediate.

We report that redox-inactive Sc(3+) can trigger O2 activation by the Fe(II)(TMC) center (TMC = tetramethylcyclam) to generate the corresponding oxoiron(IV) complex in the presence of BPh4(-) as an electron donor. To model a possible intermediate in the above reaction, we generated an unprecedented Sc(3+) adduct of [Fe(III)(η(2)-O2)(TMC)](+) by an alternative route, which was found to have an Fe(3+)-(μ-η(2):η(2)-peroxo)-Sc(3+) core and to convert to the oxoiron(IV) complex. These results have important implications for the role a Lewis acid can play in facilitating O-O bond cleavage during the course of O2 activation at non-heme iron centers.

Intermediate P* from soluble methane monooxygenase contains a diferrous cluster.

During a single turnover of the hydroxylase component (MMOH) of soluble methane monooxygenase from Methylosinus trichosporium OB3b, several discrete intermediates are formed. The diiron cluster of MMOH is first reduced to the Fe(II)Fe(II) state (H(red)). O₂ binds rapidly at a site away from the cluster to form the Fe(II)Fe(II) intermediate O, which converts to an Fe(III)Fe(III)-peroxo intermediate P and finally to the Fe(IV)Fe(IV) intermediate Q.

β-N-methylamino-l-alanine causes neurological and pathological phenotypes mimicking Amyotrophic Lateral Sclerosis (ALS): the first step towards an experimental model for sporadic ALS.

β-N-methylamino-l-alanine (L-BMAA) is a neurotoxic amino acid that has been related to various neurodegenerative diseases. The aim of this work was to analyze the biotoxicity produced by L-BMAA in vivo in rats, trying to elucidate its physiopathological mechanisms and to search for analogies between the found effects and pathologies like Amyotrophic Lateral Sclerosis (ALS). Our data demonstrated that the neurotoxic effects in vivo were dosage-dependent.

β-N-methylamino-L-alanine induces changes in both GSK3 and TDP-43 in human neuroblastoma.

β-N-methylamino-L-alanine (L-BMAA) is a neurotoxic amino acid produced by most cyanobacteria, which are extensively distributed in different environments all over the world. L-BMAA has been linked to a variety of neurodegenerative diseases. This work aims to analyze the toxicological action of L-BMAA related to alterations observed in different neurodegenerative illness as Alzheimer disease and amyotrophic lateral sclerosis.

Effect of β-N-methylamino-L-alanine on oxidative stress of liver and kidney in rat.

β-N-methylamino-(L)-alanine (L)-BMAA) is a neurotoxic amino acid, found in the majority of cyanbacterial genera tested. Evidence for implication of (L)-BMAA in neurodegenerative disorders, like amyotrophic lateral sclerosis (ALS), relies on bioaccumulation and biomagnification from symbiotic cyanobacteria. The involvement of (L)-BMAA in oxidative stress was demonstrated in several studies in the central nervous system.