Showing papers on "Ferric published in 2011"

Polymorphous Transformations of Nanometric Iron(III) Oxide: A Review

Abstract: There is great interest in iron oxides, especially in nanosized form, for both fundamental and practical reasons. Because of its polymorphism, iron(III) oxide (ferric oxide, Fe2O3) is one of the most interesting and potentially useful phases of the iron oxides. Each of the four different known crystalline Fe2O3 polymorphs (alpha-, beta-, gamma-, and epsilon-Fe2O3) has unique biochemical, magnetic, catalytic, and other properties that make it suitable for specific technical and biomedical applications. High temperature treatment is a key step in most syntheses of iron(III) oxides but often triggers polymorphous transformations that result in the formation of undesired mixtures of Fe2O3 polymorphs. It is therefore important to control the parameters that induce polymorphous transformations when seeking to prepare a given Fe2O3 polymorph as a single phase; identifying and understanding these parameters is a major challenge in the study of the polymorphism of solid compounds. This review discusses the depende...

Strong enhancement on fenton oxidation by addition of hydroxylamine to accelerate the ferric and ferrous iron cycles.

Abstract: The Fenton system generates reactive species with high oxidation potential such as hydroxyl radicals (HO•) or ferryl via the reaction between Fe (II) and H2O2. However, a number of drawbacks limit its widespread application including the accumulation of Fe (III) and the narrow pH range limits, etc. The aim of this study is to propose a much more efficient Fenton-HA system which is characterized by combining Fenton system with hydroxylamine (NH2OH), a common reducing agent, to relieve the aforementioned drawbacks, with benzoic acid (BA) as the probe reagent. The presence of NH2OH in Fenton’s reagent accelerated the Fe (III)/Fe (II) redox cycles, leading to relatively steady Fe (II) recovery, thus, increased the pseudo first-order reaction rates and expanded the effective pH range up to 5.7. The HO• mechanism was confirmed to be dominating in the Fenton-HA system, and the generation of HO• was much faster and the amount of HO• formed was higher than that in the classical Fenton system. Furthermore, the majo...

Magnetic Iron Oxide Nanoparticles in 10−40 nm Range: Composition in Terms of Magnetite/Maghemite Ratio and Effect on the Magnetic Properties

Abstract: Magnetic iron oxide nanoparticles in the 10−40 nm size range and with a reduced distribution in size have been synthesized under argon by using ammonium bases R4NOH (R = CH3, C2H5, C3H7) and a hydrothermal treatment. The size is tuned owing to the base to iron ratio and to the length of the alkyl chain R. We precipitate first ferric hydroxides at pH 1.5−2, then ferrous hydroxide at pH 5.5−6. The rapid increase of pH up to basic pH leads to the formation of magnetic iron oxide particles of 12 nm. For [base] to [Fe] ratio above 3.5, a homogeneous growth occurs during further hydrothermal treatment at 250 °C. The higher the quantity of base added and the longer the alkyl chain used, the smaller the particle size produced. For sizes above 20 nm, the Verwey transition at 120 K, characteristic of magnetite, is observed on the field cooling−zero field cooling magnetization curve. The nanoparticles can be described by a core−shell model, that is, a magnetite core surrounded by an oxidized layer close to maghemite...

The Pharmacokinetics and Pharmacodynamics of Iron Preparations

Abstract: Standard approaches are not appropriate when assessing pharmacokinetics of iron supplements due to the ubiquity of endogenous iron, its compartmentalized sites of action, and the complexity of the iron metabolism. The primary site of action of iron is the erythrocyte, and, in contrast to conventional drugs, no drug-receptor interaction takes place. Notably, the process of erythropoiesis, i.e., formation of new erythrocytes, takes 3−4 weeks. Accordingly, serum iron concentration and area under the curve (AUC) are clinically irrelevant for assessing iron utilization. Iron can be administered intravenously in the form of polynuclear iron(III)-hydroxide complexes with carbohydrate ligands or orally as iron(II) (ferrous) salts or iron(III) (ferric) complexes. Several approaches have been employed to study the pharmacodynamics of iron after oral administration. Quantification of iron uptake from radiolabeled preparations by the whole body or the erythrocytes is optimal, but alternatively total iron transfer can be calculated based on known elimination rates and the intrinsic reactivity of individual preparations. Degradation kinetics, and thus the safety, of parenteral iron preparations are directly related to the molecular weight and the stability of the complex. High oral iron doses or rapid release of iron from intravenous iron preparations can saturate the iron transport system, resulting in oxidative stress with adverse clinical and subclinical consequences. Appropriate pharmacokinetics and pharmacodynamics analyses will greatly assist our understanding of the likely contribution of novel preparations to the management of anemia.

The FRD3 Citrate Effluxer Promotes Iron Nutrition between Symplastically Disconnected Tissues throughout Arabidopsis Development

Abstract: We present data supporting a general role for FERRIC REDICTASE DEFECTIVE3 (FRD3), an efflux transporter of the efficient iron chelator citrate, in maintaining iron homeostasis throughout plant development. In addition to its well-known expression in root, we show that FRD3 is strongly expressed in Arabidopsis thaliana seed and flower. Consistently, frd3 loss-of-function mutants are defective in early germination and are almost completely sterile, both defects being rescued by iron and/or citrate supply. The frd3 fertility defect is caused by pollen abortion and is associated with the male gametophytic expression of FRD3. Iron imaging shows the presence of important deposits of iron on the surface of aborted pollen grains. This points to a role for FRD3 and citrate in proper iron nutrition of embryo and pollen. Based on the findings that iron acquisition in embryo, leaf, and pollen depends on FRD3, we propose that FRD3 mediated-citrate release in the apoplastic space represents an important process by which efficient iron nutrition is achieved between adjacent tissues lacking symplastic connections. These results reveal a physiological role for citrate in the apoplastic transport of iron throughout development, and provide a general model for multicellular organisms in the cell-to-cell transport of iron involving extracellular circulation.

Synthesis, characterization and role of zero-valent iron nanoparticle in removal of hexavalent chromium from chromium-spiked soil

Abstract: Chromium is an important industrial metal used in various products/processes. Remediation of Cr contaminated sites present both technological and economic challenges, as conventional methods are often too expensive and difficult to operate. In the present investigation, Zero-valent iron (Fe0) nanoparticles were synthesized, characterized, and were tested for removal of Cr(VI) from the soil spiked with Cr(VI). Fe0 nanoparticles were synthesized by the reduction of ferric chloride with sodium borohydride and were characterized by UV–Vis (Ultra violet–Visible) and FTIR (Fourier transform infrared) spectroscopy. The UV–Vis spectrum of Fe0 nanoparticles suspended in 0.8% Carboxymethyl cellulose showed its absorption maxima at 235 nm. The presence of one band at 3,421 cm−1 ascribed to OH stretching vibration and the second at 1,641 cm−1 to OH bending vibration of surface-adsorbed water indicates the formation of ferrioxyhydroxide (FeOOH) layer on Fe0 nanoparticles. The mean crystalline dimension of Fe0 nanoparticles calculated by XRD (X-ray diffraction) using Scherer equation was 15.9 nm. Average size of Fe0 nanoparticles calculated from TEM (Transmission electron microscopy) images was found around 26 nm. Dynamic Light Scattering (DLS) also showed approximately the same size. Batch experiments were performed using various concentration of Fe0 nanoparticles for reduction of soil spiked with 100 mg kg−1 Cr(VI). The reduction potential of Fe0 nanoparticles at a concentration of 0.27 g L−1 was found to be 100% in 3 h. Reaction kinetics revealed a pseudo-first order kinetics. Factors like pH, contact time, stabilizer, and humic acid facilitates the reduction of Cr(VI).

A Raman Study of Iron–Phosphate Crystalline Compounds and Glasses

Abstract: Ferrous and ferric phosphate crystalline compounds and glasses were studied using Raman spectroscopy. A comparison of the spectra from crystalline and glassy ortho-, pyro-, and metaphosphates indicates that similar phosphate anions constitute the structures of the respective materials, and some information about the compositional dependence of the phosphate-site distributions in the glasses can be gleaned from relative peak intensities. A correlation exists between the average P–O bond distance and the Raman peak frequencies in the crystalline compounds, and this correlation is used to provide information about the structures of the iron phosphate glasses. For example, the average P–O bond distance is estimated to decrease from about 1.57 A for iron metaphosphate glasses (O/P∼3.0) to 1.54 A for iron orthophosphate glasses (O/P∼4.0). These bond distances are in good agreement with those reported from diffraction studies of similar glasses.

Stable iron isotope fractionation between aqueous Fe(II) and hydrous ferric oxide.

Abstract: Despite the ubiquity of poorly crystalline ferric hydrous oxides (HFO, or ferrihydrite) in natural environments, stable Fe isotopic fractionation between HFO and other Fe phases remains unclear. In particular, it has been difficult to determine equilibrium Fe isotope fractionation between aqueous Fe(II) and HFO due to fast transformation of the latter to more stable minerals. Here we used HFO stabilized by the presence of dissolved silica (2.14 mM), or a Si−HFO coprecipitate, to determine an equilibrium Fe(II)−HFO fractionation factor using a three-isotope method. Iron isotope exchange between Fe(II) and HFO was rapid and near complete with the Si−HFO coprecipitate, and rapid but incomplete for HFO in the presence of dissolved silica, the latter case likely reflecting blockage of oxide surface sites by sorbed silica. Equilibrium Fe(II)−HFO 56Fe/54Fe fractionation factors of −3.17 ± 0.08 (2σ)‰ and −2.58 ± 0.14 (2σ)‰ were obtained for HFO plus silica and the Si−HFO coprecipitate, respectively. Structural si...

Plant species traits regulate methane production in freshwater wetland soils

Abstract: Ecosystem and biogeochemical responses to anthropogenic stressors are the result of complex interactions between plants and microbes. A mechanistic understanding of how plant traits influence microbial processes is needed in order to predict the ecosystem-level effects of natural or anthropogenic change. This is particularly true in wetland ecosystems, where plants alter the availability of both electron donors (e.g., organic carbon) and electron acceptors (e.g., oxygen and ferric iron), thereby regulating the total amount of anaerobic respiration and the production of methane, a highly potent greenhouse gas. In this study, we examined how plant traits associated with plant inputs of carbon (photosynthesis and biomass) and oxygen (root porosity and ferric iron on roots) to mineral soils relate to microbial competition for organic carbon and, ultimately, methane production. Plant productivity was positively correlated with microbial respiration and negatively correlated to methane production. Root porosity was relatively constant across plant species, but belowground biomass, total biomass, and the concentration of oxidized (ferric) iron on roots varied significantly between species. As a result the size of the total root oxidized iron pool varied considerably across plant species, scaling with plant productivity. Large pools of oxidized iron were related to high CO2:CH4 ratios during microbial respiration, indicating that as plant productivity and biomass increased, microbes used non-methanogenic respiration pathways, most likely including the reduction of iron oxides. Taken together these results suggest that increased oxygen input from plants with greater biomass can offset any potential stimulation of methanogenic microbes from additional carbon inputs. Because the species composition of plant communities influences both electron donor and acceptor availability in wetland soils, changes in plant species as a consequence of anthropogenic disturbance have the potential to trigger profound effects on microbial processes, including changes in anaerobic decomposition rates and the proportion of mineralized carbon emitted as the greenhouse gas methane.

Mechanism of Autoxidation of Polyphenols and Participation of Sulfite in Wine: Key Role of Iron

Abstract: The involvement of iron (Fe) in the reaction of wine with oxygen was deduced at least 80 years ago. It was observed that when wine was exposed to air, some O2 reacted rapidly, in part to oxidize the Fe to the ferric state and in part to generate what were thought to be unstable peroxides. It was proposed that it was these intermediate oxidants that oxidized wine polyphenols. In this present work the oxidation of (+)-catechin was reexamined in model wine to determine if different phases of oxidation could be observed. In the absence of sulfite, after an initial uptake of O2 very little further reaction occurred. This initial O2 uptake increased with increasing concentrations of Fe(II) and Cu(II), indicating that Fe was the initial reactant and furthermore was absent when Fe was added as Fe(III). In contrast, in the presence of sulfite, the oxidation of (+)-catechin was markedly accelerated and, again, an initial more rapid phase of oxidation, presumably due to the metals, was discernable. With (+)-catechin, insufficient O2 to oxidize all the Fe was initially taken up and formation of other oxidants such as peroxides was unlikely. Further evidence is presented that nucleophiles such as sulfite accelerate oxidation by reacting with quinones. The rate of oxidation in the presence of sulfite was found to increase in the order (+)-catechin< caffeic acid< (−)-epicatechin < gallic. It is proposed that the rate of oxidation is determined by the relative reactivity of their respective quinones. In the absence of sulfite, these additional phenols were also oxidized extremely slowly. The initial faster phase of oxidation was also observed in a white wine.

High-temperature stable, iron-based core-shell catalysts for ammonia decomposition.

Abstract: High-temperature, stable core-shell catalysts for ammonia de- composition have been synthesized. The highly active catalysts, which were found to be also excellent model sys- tems for fundamental studies, are based on a-Fe2O3 nanoparticles coated by porous silica shells. In a bottom-up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, l-lysine, and water with adjustable average sizes of 35, 47, and 75 nm. Secondly, parti- cles of each size could be coated by a porous silica shell by means of the base-catalyzed hydrolysis of tetraethyl- A (TEOS) with cetyltetra- methylammonium bromide (CTABr) as porogen. After calcination, TEM, high-resolution scanning electron mi- croscopy (HR-SEM), energy-dispersive X-ray (EDX), XRD, and nitrogen sorption studies confirmed the success- ful encapsulation of hematite nanopar- ticles inside porous silica shells with a thickness of 20 nm, thereby leading to composites with surface areas of ap- proximately 380 m 2 g 1 and iron con- tents between 10.5 and 12.2 wt %. The obtained catalysts were tested in am- monia decomposition. The influence of temperature, iron oxide core size, pos- sible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 7508C with a space velocity of 120 000 cm 3 gcat 1 h 1 and maintained conversions of around 80 % for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 8008C, the system was investigated by in situ XRD, in which body-centered iron was determined, in addition to FeNx, as the crystalline phase under reaction condi- tions above 6508C.

Pentachlorophenol reduction by Pd/Fe bimetallic nanoparticles: Effects of copper, nickel, and ferric cations

Abstract: Bimetallic nanoparticles have been used for effective reduction of chlorinated compounds; however, the study of cation effect on degradation is limited. This study examined the effect of three selected cations normally co-present in soil and groundwater contamination sites on the degradation kinetics and removal efficiency of pentachlorophenol (PCP) by Pd/Fe nanoparticles. Degradation of PCP by Pd/Fe nanoparticles was carried out in aqueous solutions containing different cations in sulfate form, Na2SO4, CuSO4, NiSO4, and Fe2(SO4)3, respectively. The observed inhibitory effect of Na2SO4 on degradation of PCP was contributed to the existence of SO42− ions. Overcoming the inhibitory effect of SO42− ions, Cu2+, Ni2+, and Fe3+ could facilitate the degradation kinetics and efficiencies of PCP by Pd/Fe nanoparticles. XANES absorption spectra were performed to characterize their valences. The enhancement effect of Cu2+ and Ni2+ ions result from the presence of reduced forms of copper and nickel on Pd/Fe surfaces. The presence of reduced forms of copper and nickel on Pd/Fe nanoparticles were confirmed by ICP–MS analysis. The addition of Fe3+ ions caused a decrease in pH and can reasonably account for the enhancement seen in the PCP degradation process. These observations lead to a better understanding of PCP degradation with Pd/Fe nanoparticles and can facilitate the remediation design and prediction of treatment efficiency of PCP at remediation sites.

Accumulation of Non-Transferrin-Bound Iron by Neurons, Astrocytes, and Microglia

Abstract: Neurodegenerative conditions such as Alzheimer’s disease, Parkinson’s disease, and hemorrhagic stroke are associated with increased levels of non-transferrin-bound iron (NTBI) in the brain, which can promote Fenton chemistry. While all types of brain cells can take up NTBI, their efficiency of accumulation and capacity to withstand iron-mediated toxicity has not been directly compared. The present study assessed NTBI accumulation in cultures enriched in neurons, astrocytes, or microglia after exposure to ferric ammonium citrate (FAC). Microglia were found to be the most efficient in accumulating iron, followed by astrocytes, and then neurons. Exposure to 100 μM FAC for 24 h increased the specific iron content of cultured neurons, astrocytes, and microglial cells by 30-, 80-, and 100-fold, respectively. All cell types accumulated iron against the concentration gradient, resulting in intracellular iron concentrations that were several orders of magnitude higher than the extracellular iron concentrations. Accumulation of these large amounts of iron did not affect the viability of the cell cultures, indicating a high resistance to iron-mediated toxicity. These findings show that neurons, astrocytes and microglia cultured from neonatal mice all have the capacity to accumulate and safely store large quantities of iron, but that glial cells do this more efficiently than neurons. It is concluded that neurodegenerative conditions involving iron-mediated toxicity may be due to a failure of iron transport or storage mechanisms, rather than to the presence of high levels of NTBI.

Prediction of high-valent iron K-edge absorption spectra by time-dependent Density Functional Theory

Abstract: In recent years, a number of high-valent iron intermediates have been identified as reactive species in iron-containing metalloproteins. Inspired by the interest in these highly reactive species, chemists have synthesized Fe(IV) and Fe(V) model complexes with terminal oxo or nitrido groups, as well as a rare example of an Fe(VI)-nitrido species. In all these cases, X-ray absorption spectroscopy has played a key role in the identification and characterization of these species, with both the energy and intensity of the pre-edge features providing spectroscopic signatures for both the oxidation state and the local site geometry. Here we build on a time-dependent DFT methodology for the prediction of Fe K- pre-edge features, previously applied to ferrous and ferric complexes, and extend it to a range of Fe(IV), Fe(V) and Fe(VI) complexes. The contributions of oxidation state, coordination environment and spin state to the spectral features are discussed. These methods are then extended to calculate the spectra of the heme active site of P450 Compound II and the non-heme active site of TauD. The potential for using these methods in a predictive manner is highlighted.

Catalytic wet hydrogen peroxide oxidation of para-chlorophenol over Al/Fe pillared clays (AlFePILCs) prepared from different host clays

Abstract: In this work, three AlFePILCs prepared from different host clays were synthesized, characterized and tested in the catalytic wet hydrogen peroxide oxidation of 4-chlorophenol. Two reference clays, with widely different cation exchange capacities (1.2 meq/g for SAz-1 and 0.87 meq/g for SWy-2), and a Romanian montmorillonite (Mt) were used for the preparation of the catalysts, their structural and textural properties being determined by X-ray diffraction and nitrogen adsorption-desorption isotherms. The catalyst based on SAz-1 has a more ordered structure and a higher surface area than the other two catalysts, prepared from SWy-2 and Mt, and this was attributed to its higher layer charge. The 4-chlorophenol oxidation proceeds with the formation of 4-chlorocatechol (main reaction intermediate) and hydroquinone. Other chlorinated benzenediols and triols as well as dimerization products have been also identified by derivatization and GC–MS analysis. All the catalysts allowed the total elimination of 4-chlorophenol and significant removal efficiencies for the total organic carbon, of 60, 52 and 45%, for Mt, SWy-2 and SAz-1 based catalysts, respectively. The iron leaching was very low, but the most active catalyst produced the higher amount of dissolved iron (1 ppm), as compared with AlFePILCs based on SWy-2 and SAz-1 (0.5 ppm). To explain the differences in the catalytic properties, Mossbauer and diffuse-reflectance UV–vis spectroscopies were used to investigate the nature of the active sites. Both methods suggested the presence of two iron species: low-nuclearity ferric oxides and well-ordered hematite-like nanoparticles. The low-nuclearity ferric oxides seem to be responsible for the iron leaching and for the differences in the catalytic activity.

On the Reactivity of Mononuclear Iron(V)oxo Complexes

Abstract: Ferric tetraamido macrocyclic ligand (TAML)-based catalysts [Fe{C6H4-1,2-(NCOCMe2NCO)2CR2}(OH2)]PPh4 [1; R = Me (a), Et (b)] are oxidized by m-chloroperoxybenzoic acid at −40 °C in acetonitrile containing trace water in two steps to form Fe(V)oxo complexes (2a,b). These uniquely authenticated FeV(O) species comproportionate with the FeIII starting materials 1a,b to give μ-oxo-(FeIV)2 dimers. The comproportionation of 1a–2a is faster and that of 1b–2b is slower than the oxidation by 2a,b of sulfides (p-XC6H4SMe) to sulfoxides, highlighting a remarkable steric control of the dynamics. Sulfide oxidation follows saturation kinetics in [p-XC6H4SMe] with electron-rich substrates (X = Me, H), but changes to linear kinetics with electron-poor substrates (X = Cl, CN) as the sulfide affinity for iron decreases. As the sulfide becomes less basic, the FeIV/FeIII ratio at the end of reaction for 2b suggests a decreasing contribution of concerted oxygen-atom transfer (FeV → FeIII) concomitant with increasing electron t...

The Siderophore-Interacting Protein YqjH Acts as a Ferric Reductase in Different Iron Assimilation Pathways of Escherichia coli

Abstract: Siderophore-interacting proteins (SIPs), such as YqjH from Escherichia coli, are widespread among bacteria and commonly associated with iron-dependent induction and siderophore utilization. In this study, we show by detailed biochemical and genetic analyses the reaction mechanism by which the YqjH protein is able to catalyze the release of iron from a variety of iron chelators, including ferric triscatecholates and ferric dicitrate, displaying the highest efficiency for the hydrolyzed ferric enterobactin complex ferric (2,3-dihydroxybenzoylserine)(3). Site-directed mutagenesis revealed that residues K55 and R130 of YqjH are crucial for both substrate binding and reductase activity. The NADPH-dependent iron reduction was found to proceed via single-electron transfer in a double-displacement-type reaction through formation of a transient flavosemiquinone. The capacity to reduce substrates with extremely negative redox potentials, though at low catalytic rates, was studied by displacing the native FAD cofactor with 5-deaza-5-carba-FAD, which is restricted to a two-electron transfer. In the presence of the reconstituted noncatalytic protein, the ferric enterobactin midpoint potential increased remarkably and partially overlapped with the effective E(1) redox range. Concurrently, the observed molar ratios of generated Fe(II) versus NADPH were found to be ~1.5-fold higher for hydrolyzed ferric triscatecholates and ferric dicitrate than for ferric enterobactin. Further, combination of a chromosomal yqjH deletion with entC single- and entC fes double-deletion backgrounds showed the impact of yqjH on growth during supplementation with ferric siderophore substrates. Thus, YqjH enhances siderophore utilization in different iron acquisition pathways, including assimilation of low-potential ferric substrates that are not reduced by common cellular cofactors.

Probing a complex of cytochrome c and cardiolipin by magnetic circular dichroism spectroscopy: implications for the initial events in apoptosis.

Abstract: Oxidation of cardiolipin (CL) by its complex with cytochrome c (cyt c) plays a crucial role in triggering apoptosis. Through a combination of magnetic circular dichroism spectroscopy and potentiometric titrations, we show that both the ferric and ferrous forms of the heme group of a CL:cyt c complex exist as multiple conformers at a physiologically relevant pH of 7.4. For the ferric state, these conformers are His/Lys- and His/OH–-ligated. The ferrous state is predominantly high-spin and, most likely, His/–. Interconversion of the ferric and ferrous conformers is described by a single midpoint potential of −80 ± 9 mV vs SHE. These results suggest that CL oxidation in mitochondria could occur by the reaction of molecular oxygen with the ferrous CL:cyt c complex in addition to the well-described reaction of peroxides with the ferric form.