Binuclear Iron Complexes Research Articles

Sandwich complexes of iron and ruthenium with the semiconducting aromatic hydrocarbon picene

Pentacyclic aromatic hydrocarbon picene C22H14 was synthesized by the improved two-step procedure from 1-naphthaldehyde in ca. 50% total yield. Reaction of picene with ferrocene in the presence of AlCl3 produced the binuclear iron complex [(CpFe)2(C22H14)](PF6)2. Reactions of picene with [Cp*Ru(MeCN)3]PF6 produced mono- or binuclear complexes depending on the concentration and ratio of reactants. The structures of the binuclear iron complex and the mononuclear ruthenium complex were established by X-ray diffraction analysis. Irradiation of the iron complex regenerated free picene; this method is proposed for purification and deposition of insoluble aromatic hydrocarbons.

Magnetic shielding of quantum entanglement states

The measure of quantum entanglement is determined for any dimer, either ferromagnetic or antiferromagnetic, spin-1/2 Heisenberg systems in the presence of external magnetic field. The physical quantity proposed as a measure of thermal quantum entanglement is the distance between states defined through the Hilbert-Schmidt norm. It has been shown that for ferromagnetic systems there is no entanglement at all. However, although under applied magnetic field, antiferromagnetic spin-1/2 dimers exhibit entanglement for temperatures below the decoherence temperature -- the one above which the entanglement vanishes. In addition to that, the decoherence temperature shows to be proportional to the exchange coupling constant and independent on the applied magnetic field, consequently, the entanglement may not be destroyed by external magnetic fields -- the phenomenon of {\it magnetic shielding effect of quantum entanglement states}. This effect is discussed for the binuclear nitrosyl iron complex [Fe$_2$(SC$_3$H$_5$N$_2$)$_2$(NO)$_4$] and it is foreseen that the quantum entanglement survives even under high magnetic fields of Tesla orders of magnitude.

Theoretical investigations on the structural products of the amphiphilic copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate and the μ-S–C–N type binuclear tetranitrosyl iron complex interaction

The amphiphilic copolymer of N-vinylpyrrolidone forms in isopropyl alcohol the copolymer particles with a core composed of low polar fragments of triethylene glycol dimethacrylate. In this work, quantum chemical modelling of various variants of the structural products of this copolymer and the μ-S–C–N type tetranitrosyl iron complex with a benzothiazole ligand was carried out. The theoretical IR spectra of these possible structural products are calculated and compared with experiments. Based on the results, it is assumed that the C=O bond of the copolymer’s methacrylate units is coordinated by the mononuclear iron complex, which is formed upon dissociation of the initial binuclear nitrosyl complex via the Fe–N bond of the heterocyclic ligand.

Fe(III), Cu(II) and U(VI) binuclear complexes with a new isothiosemicarbazone ligand: Syntheses, characterization, crystal structures, thermal behavior and theoretical investigations

A new Schiff base ligand, salicylaldehyde S-benzylisothiosemicarbazone.hydrochloride (H2L∙HCl), and three new binuclear complexes of iron(III), copper(II) and uranium(VI) of this ligand with general formulas [μ2-O-(FeLSal)2] (1), [μ2-O-(CuLSCN)2].2H2O (2) and TEAH[(UO2(LSal))2-μ2-OAc] (3), (Sal: salicylaldehyde, SCN: thiocyanate, OAc: acetate, TEAH: triethylammonium) were synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy; and TGA technique. The solid-state structures of the complexes were also determined by single crystal X-ray diffraction. The metal atoms in complexes 1, 2 and 3 adopt distorted square pyramidal, square pyramidal and pentagonal bipyramidal geometries respectively. The strength of the bonding in these complexes and the formation of pure metal oxide residues by thermal degradation of the complexes were investigated and confirmed by thermogravimetric studies. Furthermore, computational studies of the new complexes were performed by DFT methods. Geometry optimization and natural bond orbital analysis of the complexes are discussed.

Fe2(µ-SR)2(NO)4]0 complexes with R being phenolyl with different substituents in the meta-position: Synthesis, structure, and NO release

Single crystals of new binuclear tetranitrosyl iron complexes ([Fe2(SR)2(NO)4]) have been synthesized, with R being m-aminophenyl (1) and m-hydroxyphenyl (2). The structure, physical–chemical properties, and NO release of new complexes in comparison with the formerly studied isostructural analog, the complex with R being m-nitrophenyl ligand, were studied by experimental (X-ray, IR, Mössbauer spectroscopy and amperometry) and theoretical (quantum chemical modeling (DFT)) methods.

Hemodynamic Effects of Glutathione-Liganded Binuclear Dinitrosyl Iron Complex: Evidence for Nitroxyl Generation and Modulation by Plasma Albumin.

Glutathione-liganded binuclear dinitrosyl iron complex (glut-BDNIC) has been proposed to be a donor of nitric oxide (NO). This study was undertaken to investigate the mechanisms of vasoactivity, systemic hemodynamic effects, and pharmacokinetics of glut-BDNIC. To test the hypothesis that glut-BDNICs vasodilate by releasing NO in its reduced [nitroxyl (HNO)] state, a bioassay method of isolated, preconstricted ovine mesenteric arterial rings was used in the presence of selective scavengers of HNO or NO free radical (NO•); the vasodilatory effects of glut-BDNIC were found to have characteristics similar to those of an HNO donor and markedly different than an NO• donor. In addition, products of the reaction of glut-BDNIC with CPTIO [2-(4-carboxyphenyl)-4,4,5-tetramethyl imidazoline-1-oxyl-3-oxide] were found to have electron paramagnetic characteristics similar to those of an HNO donor compared with an NO• donor. In contrast to S-nitroso-glutathione, which was vasodilative both in vitro and in vivo, the potency of glut-BDNIC-mediated vasodilation was markedly diminished in both rats and sheep. Wire myography showed that plasma albumin contributed to this loss of hypotensive effects, an effect abolished by modification of the cysteine-thiol residue of albumin. High doses of glut-BDNIC caused long-lasting hypotension in rats that can be at least partially attributed to its long circulating half-life of ∼44 minutes. This study suggests that glut-BDNIC is an HNO donor, and that its vasoactive effects are modulated by binding to the cysteine residue of plasma proteins, such as albumin.

Synthesis and characterization of a novel oxo-bridged binuclear iron(iii) complex: its catalytic application in the synthesis of benzoxazoles using benzyl alcohol in water

A novel oxo-bridged binuclear iron(iii) complex was found to be an efficient catalyst in the synthesis of benzoxazoles from benzyl alcohols.

New nitric oxide-carrier systems based on an amphiphilic copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate

The polymer nanoparticles based on an amphiphilic copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate downloaded by antitumor agents (binuclear nitrosyl complexes of iron) were produced.

Bis(4-nitrobenzenethiolato)tetranitrosyldiiron: synthesis, structure, and pharmacological activity of a new nitric oxide (NO) donor

A preparative procedure was developed for the synthesis of new binuclear tetranitrosyl iron complex of the “μ-S” structural type, [Fe2(SC6H4NO2)2(NO)4] (1), comprising the replacement of the thiosulfate ligands in Na2[Fe2(S2O3)2(NO)4]•4H2O by anions of the 4-nitrobenzenethiolate hydrazinium salt. The salt was obtained by the reduction of bis(4-nitrophenyl) disulfide with hydrazine hydrate in ethanol. The physicochemical properties of the complex in the solid state were studied by IR and Mossbauer spectroscopy. According to amperometric measurements in aqueous solutions, the complex generates NO in a protic medium without additional photo, thermal, or redox activation, providing prolonged release of NO, since the para-positioned nitro group in the aromatic ligand functions as an additional NO source. A study of the pharmacological activity by the MTT assay showed that the complex possesses a high cytotoxic activity against the MCF7 human breast cancer cells (IC50 = 47 μmol L–1) and an antibacterial activity against gram-negative (E. coli, BB strain) and gram-positive (M. luteus, 21/26 strain) microorganisms.

NO-donating and hemolytic activity of tetranitrosyl iron complexes with ligands of the 2-mercaptopyridine series

The NO-donating and hemolytic activity of the binuclear tetranitrosyl iron complexes (TNIC) with thiolate ligands of the composition [Fe2(SR)2(NO)4], where R is pyridin-2-yl and 5-nitropyridin-2-yl, was studied. The NO-donating and hemolytic activities of the com- plex with the nitrosubstituted ligand are approximately two and three times higher than the corresponding characteristics of the complex with unsubstituted 2-mercaptopyridine, respectively. Symbate changes in these parameters confirm the conclusion made earlier on the peroxynitrite-dependent mechanism of erythrocyte hemolysis under the action of TNIC. The NO-donating activity of TNIC with ligands of the 2-mercaptopyridine series, unlike the previously studied complexes containing thioderivatives of other nitrogenous heterocycles as S-ligands, did not decrease with an increase in the concentration of erythrocytes. This allows one to consider them as promising NO-donating substances for the preparation of pharma- cological remedies.

Features of the decomposition of the neutral nitrosyl iron complexes with aryl-containing thiolate ligands in various solvents. Reaction with glutathione

The decomposition of two neutral binuclear nitrosyl iron complexes (NICs) of the µ-S structural type and general composition [Fe2(SR)2(NO)4]0 was studied in comparison. The exchange reaction of the thiophenol or 2-aminothiophenol thiolate ligand by glutathione (GSH) in neutral NICs was studied. The reaction system was analyzed by spectrophotometry to prove the presence of a new NICs with the GS– ligand in it. It was found that, unlike the earlier studied binuclear cationic NICs of the µ-S type and general composition [Fe2(µ-SR)2(NO)4]2+SO4•nH2O with cysteamine and penicillamine ligands in which both thiolate ligands exchange by GS–, in these neutral complexes both thiolate ligands are de-tached by only one GSH ligand is attached. A water molecule is inserted into the second free site. It is assumed that the antitumor activity of the neutral NICs can be determined not only by their NO-donor activity but also by their ability to exchange the thiolate ligand by GS–, i.e., "to remove" GSH from the medium as in the case of cationic NICs. The discovered reaction can prevent, most likely, the S-glutathionylation of important metabolites in the presence of GSH and is very significant for metabolism of NICs.

The antitumor effect of dinitrosyl iron complexes with glutathione in a murine solid-tumor model

A significant antitumor activity of aqueous solutions of binuclear dinitrosyl iron complexes with glutathione was found when they were injected intravenously in a model of a solid malignant tumor, that is, Lewis carcinoma, in mice. Dinitrosyl iron complexes completely inhibited the tumor growth (by 100%) at doses of 20, 10, and 2 μmol/kg in the first 11 days after the beginning of experiment followed by tumor proliferation at a rate that was lowest for the lowest of the used doses. At day 16, the inhibition of tumor growth was 90% when a solution of dinitrosyl iron complexes was injected at a dose of 2 μmol/kg five times with an interval of 2 to 3 days between injections; whereas the inhibition of tumor growth did not exceed 70 and 30% at doses of 10 and 20 μmol/kg, respectively. Acceleration, rather than inhibition of carcinoma growth was observed at a dose of 100 μmol/kg. The tumor weight increased 1.5–2.0 times compared to the control values, depending on the time.

Dinitrosyl iron complexes with thiol-containing ligands in plant tissues

The formation of dinitrosyl iron complexes with thiol-containing ligands in plant tissues (parsley and apple leaves) in the presence of nitric monoxide was demonstrated using electron paramagnetic resonance. In two types of tissues dinitrosyl iron complexes are predominantly represented by the binuclear diamagnetic form. This diamagnetic form can be transformed in EPR-detectable mononitrosyl iron complexes with diethyldithiocarbamate due to the ability of diethyldithiocarbamate to accept the iron-mononitrosyl groups from iron-dinitrosyl fragments of binuclear complexes. A similar transformation was observed under the effect of diethyldithiocarbamate on a mononuclear paramagnetic form of dinitrosyl iron complexes. The significant amount of binuclear dinitrosyl iron complexes found in plant tissues suggests that these complexes can be considered as a “working form” of nitric monoxide, which is recognized now as a universal regulator of metabolic processes in plants as well as in other organisms.

Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor

In analogy to peroxide, disulfide is an oxidant as well as a reductant. Accordingly, as a ligand of a reducing metal center, low-energy MLCT transitions can occur, while with oxidizing metals low-energy LMCT transitions should be observed. Such MLCT and LMCT excitations are expected to induce redox reactions. The complexes [CpFe(II)(CO)2]2μ-S2 (CpC5H5) and {[Fe(III)(CN)5]2μ-S2}6− are suitable examples to explore this behavior.

Antiproliferative Activity of a New Nitrosyl Iron Complex with Cysteamine in Human Tumor Cells In Vitro.

We studied cytotoxic activity of a new NO-releasing tetranitrosyl binuclear iron complex with cysteamine (CysAm) for human tumor cells, the relationship between the expression of O6-methylguanine-DNA methyltransferase (MGMT) and cell sensitivity to CysAm, and apoptosis-inducing capacity of this preparation. It was found that histogenetically different cell lines are characterized by different sensitivity to CysAm, and this parameter correlated with the basal level of MGMT. CysAm induced apoptosis via activation of caspases 3 and 7. These data suggest that CysAm can be considered as a potential antitumor agent, but definitive conclusions can be made after preclinical trials.

The Effects of Preparation Methods on Iron Structures of Iron-Supported HZSM-5 and their Catalytic Performance for Methanol Dehydration

Iron-supported HZSM-5 catalysts were prepared by hydrothermal (Fe-HZSM-5_HYD) and impregnation methods (Fe/HZSM-5_IMP). The active species of binuclear-iron complex and iron-substituted zeolite framework, confirmed by EXAFS analysis, were observed on Fe/HZSM-5_IMP and Fe-HZSM-5_HYD, respectively. The catalysts were used for production of dimethyl ether (DME) by methanol dehydration at 200-350 °C using fixed bed flow reactor. Fe/HZSM-5_IMP showed higher catalytic conversion than Fe-HZSM-5_HYD. However, the Fe/HZSM-5_IMP catalyst was less selective to DME product and strongly deactivated for 24h. The deactivation might due to transformation of binuclear-iron to the a-iron site which was strong acidic strengh. The iron-substituted zeolite framework of Fe-HZSM-5_HYD showed high stability toward methanol dehydration. Moreover, the catalyst showed advantages of good selective to DME and low carbon deposition on surface. These results suggested that the iron-substituted zeolite framework structure could improve catalytic performance for mrthanol dehydration.

The binuclear form of dinitrosyl iron complexes with thiol-containing ligands in animal tissues

It has been established that treatment of mice with sodium nitrite, S-nitrosoglutathione and the water-soluble nitroglycerine derivative isosorbide dinitrate (ISDN) as NO donors initiates in vivo synthesis of significant amounts of EPR-silent binuclear dinitrosyl iron complexes (B-DNIC) with thiol-containing ligands in the liver and other tissues of experimental mice. This effect is especially apparent if NO donors are administered to mice simultaneously with the Fe2+-citrate complex. Similar results were obtained in experiments on isolated liver and other mouse tissues treated with gaseous NО in vitro and during stimulation of endogenous NO synthesis in the presence of inducible NO synthase. B-DNIC appeared in mouse tissues after in vitro treatment of tissue samples with an aqueous solution of diethyldithiocarbamate (DETC), which resulted in the transfer of iron-mononitrosyl fragments from B-DNIC to the thiocarbonyl group of DETC and the formation of EPR-detectable mononitrosyl iron complexes (MNIC) with DETC. EPR-Active MNIC with N-methyl-d-glucamine dithiocarbamate (MGD) were synthesized in a similar way. MNIC-MGD were also formed in the reaction of water-soluble MGD-Fe2+ complexes with sodium nitrite, S-nitrosoglutathione and ISDN.

Synthesis, crystal structure and magnetic property of a binuclear iron(III) complex with phenol–pyrazole based ligands

ABSTRACTThe compound [Fe2(Hmpp)4(OMe)2]⋅3MeOH (1) (Hmpp = 2-(4-methyl-1H-pyrazol-3-yl)phenol) was characterized by elementary analysis, IR, X-ray crystallography, and magnetic measurements. The X-ray crystallography results reveal that the molecule 1 consists of a binuclear iron(III) natural complex and three methanol molecules. In the complex, two Fe3+ ions are bridged by two μ2-OMe. Magnetic measurements indicate that the two Fe3+ ions are antiferromagnetically coupled.

Redox reactions of binuclear tetranitrosyl iron complexes with bridging N-C-S ligands

Reduction of neutral binuclear tetranitrosyl iron complexes of “μ-N-C-S” structural type of [Fe2(SR)2(NO)4] composition with R being functional azaheterocyclic thiolyls has been studied by cyclic voltammetry in aprotic solvents in a wide range of potential scan rates. Redox potentials of these reactions have been determined. The consecutive transfer of two electrons was shown to be typical for all the complexes. For some complexes the products of the first electron addition are unstable, while for the others the products of reduction by both the first and the second electrons are stable. The calculations of geometric and electronic structures of monoanions, dianions and intermediates forming upon the reduction of the complexes were performed by DFT methods. Using quantum-chemical modeling, electrochemical reduction of the complexes has been studied; their energy and theoretical redox potentials have been calculated.

Nitric oxide donation by the binuclear tetranitrosyl iron complexes in the presence of erythrocytes

The kinetic regularities of nitric oxide donation in the presence of erythrocytes by representatives of a new class of synthetic nitric oxide donors, binuclear tetranitrosyl iron complexes (B-TNIC) [Fe2(SR)2(NO)4] with thiol-containing ligands, where R is pyrimidin-2-yl, 1-methylimidazol-2-yl, benzothiazol-2-yl, and penicillamine residue, were established. The NO-donating ability of B-TNIC was estimated from the apparent rate constants of the first order for the formation of intraerythrocyte methemoglobin with the variation of the initial concentration of the complex. During the standard experimental time (15—17 min), three of the four complexes released in the solution no more than a quarter of available NO groups. Their NO-donating ability turned out to be variable increasing with an increase in the initial concentration of the complex. At the same time, the complex bearing penicillamine residues as ligands donated almost all NO groups within approximately 1 min. Features of NO donation by the B-TNIC in the presence of erythrocytes are related to the formation in the system of an additional equilibrium pool of the membrane-associated complex, which is characterized by a reduced rate of hydrolytic dissociation with NO releasing to the solution. The NO-donating ability of the B-TNIC in the presence of erythrocytes is determined by the ratio of volumes of the free and membrane-associated pools of the complex.