Presence Of Iron Complexes Research Articles

RADICAL INITIATED COPOLYMERIZATION OF METHYL METHACRYLATE AND ACRYLONITRILE IN PRESENCE OF IRON COMPLEXES

This article represents data on the effect of organometallic iron complexes: ferrocene, dicarbonyl dimer of cyclopentadienyl iron and tricarbonyl cyclooctatetraene iron on the copolymerization of methyl methacrylate (MMA) and acrylonitrile (AN) initiated by benzoyl peroxide. It is shown that the introduction of metal complexes and their structure affect the initial rate of copolymerization, the form of the diagrams of the composition of the obtained copolymers, and the values of the effective constants of the relative activities of the comonomers in the copolymerization of methyl methacrylate and acrylonitrile (system metallocomplex of iron – peroxide benzoyl: ferrocene – peroxide benzoyl: rММА = 1.58; rАН= 0.08 in 60 °С; rММА = 1.30; rАН = 0.05 in 50 °С; dicarbonyl dimer cyclopentadienyl iron–peroxide benzoyl: rММА = 1.36; rАН = 0.06 in 60 °С; rММА = 1.09; rАН = 0.14 in 50 °С; tricarbonyl cyclooctatetraene iron -peroxide benzoyl: rММА = 1.08; rАН = 0.15 in 60 °С; rММА = 1.14; rАН = 0.05 in 50 °С; peroxide benzoyl: rММА = 1.11; rАН = 0.07 in 60 °С; rММА = 1.11; rАН = 0.07 in 50 °С). The proportions of triadic sequences of units in copolymers, experimentally determined from 1H NMR spectroscopy, are given, as well as the calculated proportions of dyads. The presence of iron metal complexes affects the distribution of the proportions of the triad and dyad sequences of units, as well as their microstructure in copolymers. These changes are explained by the formation of macromolecules, both with the participation of free radicals and the stereospecific coordination active centers of polymerization that are formed in the presence of iron complexes.

Contrasting the performance of photo-Fenton at neutral pH in the presence of different organic iron-complexes using hydrogen peroxide or persulfate as oxidants for naproxen degradation and removal of antimicrobial activity

This is the first study to compare the combination of different iron complexes (Fe3+-oxalate (FeOx), Fe3+-citrate (FeCit), Fe3+-nitrilotriacetic acid (FeNTA), Fe3+-ethylenediaminetetraacetic acid (FeEDTA) and Fe3+-ethylenediamine-N,N′-disuccinic acid (FeEDDS) with distinct oxidants (H2O2 and S2O82−) on the degradation of naproxen (NAP) via photo-Fenton. Experiments were performed in distilled water and in sewage treatment plant effluent and different Fe/organic ligand molar ratios, oxidant concentrations and radiation sources (black light and sunlight) were tested for each complex. Photo-Fenton at neutral pH was efficient for naproxen degradation in the presence of all iron complexes. Fe/ligand molar ratio was strongly affected by the ligand type, best results were obtained in the presence of Fe/EDDS (1:1) and Fe/NTA (1:1), Fe/EDTA (1:2), Fe/Cit (1:3) and Fe/Ox (1:12). Although NAP removal in distilled water was faster in the presence of H2O2 (max 20 kJ m−2 required) when compared to S2O82− (max 90 kJ m−2 required), better performance of S2O82− was observed in sewage treatment plant effluent. Antimicrobial activity was only observed in the presence of FeEDDS, yet it was eliminated after treatment in the presence of S2O82−. A critical comparison in terms of operational and electrical energy costs indicates that using FeCit complex with H2O2 is the most cost-effective alternative in both matrices.

Study on Chemical Modifications of Glutathione by Cold Atmospheric Pressure Plasma (Cap) Operated in Air in the Presence of Fe(II) and Fe(III) Complexes

Cold atmospheric pressure plasma is an attractive new research area in clinical trials to treat skin diseases. However, the principles of plasma modification of biomolecules in aqueous solutions remain elusive. It is intriguing how reactive oxygen and nitrogen species (RONS) produced by plasma interact on a molecular level in a biological environment. Previously, we identified the chemical effects of dielectric barrier discharges (DBD) on the glutathione (GSH) and glutathione disulphide (GSSG) molecules as the most important redox pair in organisms responsible for detoxification of intracellular reactive species. However, in the human body there are also present redox-active metals such as iron, which is the most abundant transition metal in healthy humans. In the present study, the time-dependent chemical modifications on GSH and GSSG in the presence of iron(II) and iron(III) complexes caused by a dielectric barrier discharge (DBD) under ambient conditions were investigated by IR spectroscopy, mass spectrometry and High Performance Liquid Chromatography (HPLC). HPLC chromatograms revealed one clean peak after treatment of both GSH and GSSH with the dielectric barrier discharge (DBD) plasma, which corresponded to glutathione sulfonic acid GSO3H. The ESI-MS measurements confirmed the presence of glutathione sulfonic acid. In our experiments, involving either iron(II) or iron(III) complexes, glutathione sulfonic acid GSO3H appeared as the main oxidation product. This is in sharp contrast to GSH/GSSG treatment with DBD plasma in the absence of metal ions, which gave a wild mixture of products. Also interesting, no nitrosylation of GSH/GSSG was oberved in the presence of iron complexes, which seems to indicate a preferential oxygen activation chemistry by this transition metal ion.

Iron Complex Facilitated Copper Redox Cycling for Nitric Oxide Generation as Nontoxic Nitrifying Biofilm Inhibitor.

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.

Functionalization of Gold Nanoparticles by Iron(III) Complexes Derived from Schiff Base Ligands

AbstractA series of iron(III) complexes derived from a variety of pentadentate Schiff base ligands, namely salten [H2salten = bis(3‐salicylideneaminopropyl)amine] derivatives, have been synthesized and further used to stabilize and functionalize gold nanoparticles (Au‐NPs). The iron complexes have been specifically designed to interact with the Au‐NPs through an ambidentate thiocyanate ligand or through a pendant thiol group carried by the salten derivative ligand. The gold nanocomposites have been synthesized either by direct reduction of AuIII in the presence of iron complexes or by coordination chemistry on prefunctionalized gold nanoparticles; in the latter case Au‐NPs bearing pendant empty salten cages have been treated with FeIII to generate the iron complexes. Steric and electrostatic repulsions have been tuned to obtain stable colloidal solutions or to induce the precipitation of the gold nanocomposites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Effects of tetraalkylaluminoxane activators on ethylene polymerization catalyzed by iron-based complexes

Five different tetraalkylaluminoxanes, tetraisobutylaluminoxane ( A1), ethyltriisobutylaluminoxane ( A2), diethyldiisobutylaluminoxane ( A3), triethylisobutylaluminoxane ( A4) and tetraethylaluminoxane ( A5), were prepared to polymerize ethylene in the presence of iron complexes [((2,6-RPh)N C(Me)) 2C 5H 3N]FeCl 2 (R Me, M1; R iso-Pr, M2). Except M1/ A1 and M2/ A1, all other catalyst systems produced polyethylene with pronounced broad or bimodal molecular weight distribution (MWD). It was demonstrated that the low-MW fractions of these broad- or bimodal-MWD polyethylenes result from the chain transfer reaction to the alkylaluminium containing the Al–Et groups in the activator. As the Al/Fe ratio and the amount of the Al–Et groups in the activators increased in the order: A1 < A2 < A3 < A4 < A5, the polymerization activity and the low-MW fraction of broad- or bimodal-MWD polyethylene increased and the high-MW fraction correspondingly reduced.

Effect of alkylaluminum on ethylene polymerization catalyzed by 2,6-bis(imino)pyridyl complexes of Fe(II)

In the presence of tetraethylaluminoxane (TEAO), iron complexes were used to catalyze ethylene polymerizations with extremely high activities and generally produced polyethylene with a bimodal molecular weight distribution (MWD). This bimodal MWD of polyethylene was mainly derived from residual triethylaluminum in TEAO and was produced through a mechanism of chain transfer to aluminum. Ethylaluminoxane and tetraisobutylaluminoxane also were used to polymerize ethylene with high activities in the presence of iron complexes, and only polyethylene with a unimodal MWD was produced. The ratio of the rate constant of chain transfer to aluminum (k trA ) to the rate constant of chain propagation (k p ) was determined to be 0.12 for {[ArN=C(Me)] 2 C 5 H 3 N}FeCl 2 when Ar was 2,6-diisopropylphenyl (1) and 2.48 for {[ArN=C(Me)] 2 C 5 H 3 N}FeCl 2 when Ar was 2,6-dimethylphenyl (2); these values are far larger than those for metallocene-based catalysts. This explains why an iron complex usually produces polyethylene with a broader MWD than metallocene-based catalysts. Additionally, it can be concluded from the great difference between 1 and 2 with respect to k trA /k p that an iron complex with less congested aryl substituents is subjected to chain transfer to aluminum.

Iron and CYP2E1-dependent oxidative stress and toxicity

Iron plays a critical role in catalyzing the formation of potent oxidants. Increases in iron content enhance oxidative stress, whereas removal of iron deceases such stress. An association between iron and alcoholic liver injury has been proposed. The ability of iron to modulate the biochemical and toxicologic actions of cytochrome P450 2E1 (CYP2E1) has been evaluated by using isolated microsomes and intact liver cells. The ability of different iron complexes to stimulate microsomal lipid peroxidation and hydroxyl radical production during reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)– and reduced form of nicotinamide adenine dinucleotide (NADH)–dependent electron transfer has been characterized. Certain iron complexes have been shown to be effective in promoting lipid peroxidation; others are better catalysts of hydroxyl radical production as a complex pattern has been found. Reactive oxygen production, lipid peroxidation, and interaction with iron chelates have been shown to be enhanced with microsomes isolated from ethanol-treated rats with elevated levels of CYP2E1. This increase was prevented by anti-CYP2E1 immunoglobulin (Ig)G or chemical inhibitors of CYP2E1. Thus, in the presence of iron complexes, microsomes enriched in CYP2E1 are especially reactive in generation of reactive oxygen species. To assess the toxicologic significance of this iron–CYP2E1 interaction, iron (ferric-nitrilotriacetate) was added to HepG2 cells, which were engineered to express the human CYP2E1. Ferric-nitrilotriacetate produced a greater toxicity in the CYP2E1-expressing HepG2 cells than that in control HepG2 cells. This enhanced, synergistic toxicity was blocked by antioxidants and inhibitors of CYP2E1. Mitochondrial membrane potential and ATP levels were decreased, and damage to the mitochondria played a critical role in the CYP2E1-plus-iron–dependent toxicity. These results support the suggestion that low concentrations of iron and polyunsaturated fatty acids can act as priming or sensitizing factors for CYP2E1-induced injury in HepG2 cells and hepatocytes. Such interactions may play a role in alcohol-induced liver injury.

The photoinitiation of MMA polymerization in the presence of iron complexes

The photoinitiated polymerization of methyl methacrylate (MMA) by Fe(III) complexes was studied in aqueous and organic solvents. Although [Fe(bpy)3]3+ and [Fe(DMSO)6]3+ initiate the polymerization in the presence and absence of co-initiators, polymerization was also observed just dissolving FeCl3 in the solvents. The complexes [Fe(CH3OH)6]3+ and [Fe(MMA)6]3+ initiated the polymerization when irradiated in the visible LMCT band. The photoinitiation by both complexes proceeds by different mechanisms due to the different binding of MMA and methanol to the central atom in the complex. It was found that the methanol complex is more effective in producing initiating radicals than the MMA complex. A good agreement is observed between the experimental reaction rates and those calculated assuming different effectiveness for both complexes.

FeIII(PMA)]2+: A Mononuclear Non-Heme Iron Complex That Catalyzes Alkane Oxidation

The iron(III) complex [FeIII(PMA)](ClO4)2 (3) of a designed ligand PMAH (1; H is a dissociable amide H), which mimics the metal-binding domain of the antitumor antibiotic bleomycin, promotes alkane oxidation in conjunction with TBHP or H2O2. In anhydrous acetonitrile, reaction of 3 + TBHP with cyclohexane affords high yields of cyclohexanol and cyclohexanone (1:1 ratio, 1700% yield on the basis of catalyst concentration) along with the mixed peroxide tBu−OO−Cy. The presence of water lowers the yields of oxidized products. Product ratios obtained in oxidations of adamantane and 3-methylpentane with 3 + TBHP confirm that reaction occurs at more-substituted carbon centers. No oxidation of an aromatic C−H bond is observed with 3 + TBHP. EPR spectra at low temperatures indicate that the low-spin Fe(III)−peroxo intermediate [(PMA)FeIII−O−OR]+ (R = H, tBu) is formed in the reaction mixture. Since the PMA- ligand framework is incapable of stabilizing the high-valent iron center and oxidation of both cyclohexene and norbornene with 3 + TBHP yields only the allylic oxidation products and the exo-epoxide, respectively, involvement of a perferryl [(PMA)FeVO]2+ intermediate in the oxidation reactions appears unlikely. Product distributions of the oxidation reactions strongly suggest that homolysis of the O−O bond in [(PMA)FeIII−O−OtBu]+ occurs in the reaction mixtures. Abstraction of an H atom from cyclohexane by tBuO•, a product of the homolytic cleavage of the O−O bond in [(PMA)FeIII−O−OtBu]+, results in the production of the cyclohexyl radical. A kH/kD value of 6.5 ± 0.5 for the cyclohexane oxidation by the 3 + TBHP system indicates that C−H bond cleavage is an important step in the overall oxidation mechanism. Reaction of the cyclohexyl radical with O2 (generated in reactions of tBuO• and tBuOO•) produces CyOO• in the reaction mixture, which undergoes a Russell-type termination to afford cyclohexanol and cyclohexanone in a 1:1 ratio. Combination of tBuOO• and the cyclohexyl radical results in the formation of the mixed peroxide tBu−OO−Cy. The second product from the homolytic cleavage of the O−O bond in [(PMA)FeIII−O−OtBu]+, namely [(PMA)FeIII−O•]+, also takes part in the catalytic process by abstracting an H atom from TBHP and generating tBuOO•, a species that provides both O2 and tBuO• in the reaction mixture. Since catalysis is noted only in the presence of iron complexes that give rise to the [(ligand)nFeIII−O−OR]+ intermediates (EPR results) and the yields of the oxidation products vary depending on the nature of the ligands in the starting iron complexes, it is evident that the iron complexes do take part in the oxidation reactions. Results of the present work also suggest that low-spin Fe(III) peroxides are viable intermediates in peroxide-mediated alkane oxidations by certain non-heme iron complexes.

Antioxidant mechanism of Mn(II) in phospholipid peroxidation

Antioxidant action of Mn 2+ on radical-mediated lipid peroxidation without added iron in microsomal lipid liposomes and on iron-supported lipid peroxidation in phospholipid liposomers or in microsomes was investigated. High concentrations of Mn 2+ above 50 μM inhiibited 2,2′-azobis (2-amidinopropane) (ABAP)-supported lipid peroxidation without added iron at the early stage, while upon prolonged incubation, malondialdehyde production was rather enhanced as compared with the control in the absence of Mn 2+. However, in a lipid-soluble radical initiator, 2,2′-azobis, (2,4-dimethyl-valeronitrile) (AMVN)- supported lipid peroxidation of methyl linoleate in methanol Mn 2+ apparently did not scavenge lipid radicals and lipid peroxyl radicals, contrary to a previous report. At concentrations lower than 5 μM, Mn 2+ competitively inhibited Fe 2+-pyrophosphate-supported lipid peroxidation in liposomes consisting of phosphatidylcholine with arachidonic acid at the β-position and phosphatidylserine dipalmitoyl, and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-supported lipid peroxidation in the presence of iron complex in microsomes. Iron reduction responsible for lipid peroxidation in microsomes was not influenced by Mn 2+.

Electrochemical conversion of nitrous oxide into ammonia in the presence of iron complexes

Download options Please wait... Article information DOI https://doi.org/10.1039/F19848002243 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 1, 1984,80, 2243-2253 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Electrochemical conversion of nitrous oxide into ammonia in the presence of iron complexes K. Ogura and H. Ishikawa, J. Chem. Soc., Faraday Trans. 1, 1984, 80, 2243 DOI: 10.1039/F19848002243 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Kotaro Ogura Hiroshi Ishikawa

Reaction of 1,3-butadiene with CCl4, catalyzed by complexes of iron of mixed (II, III) oxidation state

1. The catalytic reaction of 1,3-butadiene and CCl4 was carried out in the presence of iron complexes of mixed (II, III) oxidation state, in DMFA or DMSO medium. 2. In DMSO tetrachlorooligobutadiene, and in DMFA its dehydrochlorination product were obtained with 90% selectivity and characterized. 3. The binuclear bridge-type heterovalent iron compounds L3Fe2Cl5 (where L is DMFA or DMSO) that are responsible for the catalysis were isolated and characterized by physical and chemical methods.