Showing papers on "Ferric published in 2006"
TL;DR: It is shown that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp.
Abstract: The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.
391 citations
TL;DR: In this paper, the solubility data for amorphous ferric arsenate and scorodite have been reevaluated using the geochemical code PHREEQC with a modified thermodynamic database for the arsenic species.
348 citations
TL;DR: In this article, a phase-pure LiFePO 4 was synthesized by a hydrothermal process, and the critical synthesis parameters were determined and the electronic conductivity was enhanced by the deposition of carbon from the sugar, or by the addition of carbon nanotubes to the Hydrothermal reactor.
321 citations
TL;DR: An assessment of the mechanisms and kinetics of pyrite transformation in inert and oxygen-containing atmospheres at elevated temperatures has been performed based on a literature review in this paper.
261 citations
TL;DR: Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) under the following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L.
Abstract: X-ray diffraction and Raman spectroscopy were used in this study to characterize arsenate phases in the arsenate-ferrihydrite sorption system. Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) underthe following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L. Surface precipitation occurred under apparently undersaturated (in the bulk solution phase) conditions, and probably involved initial uptake of arsenate by surface complexation followed by transition to ferric arsenate formation on the surface as indicated by XRD analysis. At basic pH (i.e., pH 8), however, no ferric arsenate was observed in arsenate-ferrihydrite samples at a sorption density of As/Fe approximately 0.125-0.30 and an arsenic equilibrium concentration of 2.0-1100 mg/ L. At pH 8, arsenate is sorbed on ferrihydrite predominantly via surface adsorption, and the XRD patterns resemble basically that of ferrihydrite.
248 citations
TL;DR: The main objective of this study was to remove and recover metal ions from acid mine drainage by using lignite, a low cost sorbent, and recovery of the metal ions as well as regeneration of sorbent was achieved successfully.
205 citations
TL;DR: Water-based magnetic fluids containing iron oxide particles have been prepared by a co-precipitation method, using citric acid as stabilizer to assess the magnetic-particle size and various microstructural and rheological features.
Abstract: Water-based magnetic fluids, generally intended for biomedical applications, often have various coating molecules that make them stable and compatible with biological liquids. Magnetic fluids containing iron oxide particles have been prepared by a co-precipitation method, using citric acid as stabilizer. The magnetic particles of the magnetic fluids were obtained by chemical precipitation from ferric ( FeCl3) and ferrous salts ( FeSO4 or FeCl2) in alkali medium (ammonia hydroxide). Citric acid was used to stabilize the magnetic-particle suspension. Physical tests were performed in order to determine various microstructural and rheological features. Transmission electron microscopy was the main investigation method for assessing the magnetic-particle size. The dimensional distribution of the magnetic-particle physical diameter was analyzed using the box-plot statistical method while infrared absorption spectra were used to study the colloidal particle structure. The magnetic-fluid density (picnometric method), viscosity (capillary method) and surface tension (stalagmometric method) were measured using standard methods.
201 citations
TL;DR: The observed color of the solution is not a fortuitous result depending on trace components of low significance, but depends directly on the main reaction intermediates, so it is concluded that observed color depends on the level of oxidation reached.
Abstract: Fenton reaction is a highly effective treatment for degrading phenolic compounds in an aqueous solution. However, during phenol oxidation, the oxidized water takes on a dark brown color associated with increased toxicity. Then, although phenol can be completely removed, if the oxidation process is not carried out properly, the final wastewater will be brown in color and have higher toxicity, two parameters in which legislation imposes restrictions. This paper analyzes the development of the dark color observed in the solution under oxidation treatment and formulates a reaction mechanism to explain the color generation. The experiments were carried out following the batch-wise procedure, but with the solution pH being kept constant throughout the reaction at its optimum value for phenol removal, i.e., pH 3.0. It is checked experimentally that color is formed at the beginning of the reaction in less than five minutes, and follows the kinetic-path of a reaction intermediate. During the first steps of the reaction phenol is degraded to dihydroxylated rings (catechol, resorcinol, and hydroquinone). These aromatic intermediates generate higher colored compounds such as ortho- and parabenzoquinone. On the other hand the dihydroxylated rings can react with their own quinones to generate charge-transfer complexes (quinhydrone), compounds which take on a dark color at low concentrations. Moreover, when iron reacts with hydrogen peroxide, ferric ions are generated that can be coordinated to benzene rings to produce colored metal complexes. The observed color of the solution is not a fortuitous result depending on trace components of low significance, but depends directly on the main reaction intermediates, so it is concluded that observed color depends on the level of oxidation reached. The maximum color observable during oxidation treatment (A(o)) depends only on initial phenol concentration and not on oxidant or catalyst doses.
189 citations
TL;DR: In this article, the authors present a conceptual model of iron formation that offers insight into the deposition of silica, based on the proclivity of dissolved silica to adsorb onto the hydrous surfaces of ferric oxides.
Abstract: Iron formations are typically thinly bedded or laminated sedimentary rocks containing 15% or more of iron and a large proportion of silica (commonly > 40%). In the ca. 2590-2460 Ma Campbellrand-Kuruman Complex, Transvaal Supergroup, South Africa, iron formation occurs as a sediment-starved deepwater facies distal to carbonates and shales. Iron minerals, primarily siderite, define the lamination. The silica primarily occurs as thin beds and nodules of diagenetic chert (now microcrystalline quartz), filling pore space and replacing iron formation minerals and co-occurring deepwater lithologies. Mechanisms proposed to explain precipitation of the iron component of iron formation include photosynthetic oxygen production, anoxygenic photosynthesis, abiotic photochemistry, and chemoautotrophy using Fe(II) as an electron donor. The origin and mechanism of silica precipitation in these deposits have received less attention. Here we present a conceptual model of iron formation that offers insight into the deposition of silica. The model hinges on the proclivity of dissolved silica to adsorb onto the hydrous surfaces of ferric oxides. Soluble ferrous iron is oxidized in the surface ocean to form ferric hydroxides, which precipitate. Fe(OH)_3 binds silica and sinks from the surface ocean along with organic matter, shuttling silica to basinal waters and sediments. Fe(III) respiration in the sediments returns the majority of iron to the water column but also generates considerable alkalinity in pore waters, driving precipitation of siderite from Fe2+ and respiration-influenced CO2. Silica liberated during iron reduction becomes concentrated in pore fluids and is ultimately precipitated as diagenetic mineral phases. This model explains many of the mineralogical, textural, and environmental features of Late Archean and earliest Paleo-proterozoic iron formation.
180 citations
TL;DR: This part, besides well known reactions of Fenton and photo-Fenton chemistry, involves additional reactions which describe removal of iron from catalytic cycle through formation of ferric complexes and its regeneration induced by UV radiation.
177 citations
TL;DR: It is concluded that by coagulation it is not possible to entirely remove pharmaceuticals from water, and a high amount of high-molecular-weight dissolved organic matter enhanced the removal of ionisable pharmaceuticals.
Abstract: The removal of selected pharmaceuticals (diclofenac, ibuprofen, bezafibrate, carbamazepine and sulfamethoxazole) by chemical coagulation was studied. Jar test experiments were done in MilliQ water, in lake water and in commercial humic acid solutions using aluminium (pH 6) and ferric sulphate (pH 4.5). The concentrations of the pharmaceuticals in the studied water samples were determined by HPLC analysis and UV detection. In MilliQ water coagulation, the pharmaceuticals were poorly removed (< 10%) with the exception of diclofenac, which was removed up to 66% with ferric sulphate. This compound was also the only pharmaceutical removed (30%) during the lake water coagulation with ferric sulphate. In the presence of dissolved humic matter, diclofenac as well as ibuprofen and bezafibrate could be removed by ferric sulphate coagulation. The removal of diclofenac reached a maximum of 77%, while 50% of ibuprofen and 36% of bezafibrate were removed. Hence, a high amount of high-molecular-weight dissolved organic ...
TL;DR: The results obtained suggest that ethylene participates in the regulation of ferric reductase, the iron transporter, and H(+)-ATPase gene expression by affecting the FER (or FER-like) levels.
Abstract: In previous works, it has been shown, by using ethylene inhibitors and precursors, that ethylene could participate in the regulation of the enhanced ferric reductase activity of Fe-deficient Strategy I plants. However, it was not known whether ethylene regulates the ferric reductase gene expression or other aspects related to this activity. This paper is a study of the effects of ethylene inhibitors and precursors on the expression of the genes encoding the ferric reductases and iron transporters of Arabidopsis thaliana (FRO2 and IRT1) and Lycopersicon esculentum (=Solanum lycopersicum )( FRO1 and IRT1) plants. The effects of ethylene inhibitors and precursors on the activity of the iron reductase and the iron transporter have been examined in parallel. Also studied were the effects of ethylene inhibitors and precursors on the expression of the H + -ATPase genes of cucumber (CsHA1 and CsHA2) and the transcription factor genes of tomato (LeFER) and Arabidopsis (AtFRU or AtFIT1 ,a nLeFER homologue) that regulate ferric reductase, iron transporter, and H + -ATPse activity. The results obtained suggest that ethylene participates in the regulation of ferric reductase, the iron transporter, and H + -ATPase gene expression by affecting the FER (or FER-like) levels.
TL;DR: Sediment redox potential is an important parameter affecting metal and nutrient solubility and mobility in Louisiana coastal freshwater lake sediment and reduction or aeration status of sediment should be considered in predicting the release of these elements into the aquatic environment.
TL;DR: In this article, the authors examined the efficacy of various washing techniques, the mechanisms effecting FeOx dissolution, and the methods for controlling contamination from the wash solutions, and showed that a wash solution containing two types of chelating agents, oxalate and EDTA, is effective for dissolving fresh precipitates via a ligand-promoted process.
TL;DR: The solution-phase arsenate-Fe(Ill)-NOM associations are at least partially colloidal in nature, and may include larger NOM species that are coagulated by the presence of chelated Fe(lll) and/or NOM-stabilized ferric (oxy)hydroxide colloids.
Abstract: Dialysis experiments with arsenate and three different NOM samples amended with Fe(III) showed evidence confirming the formation of aquatic arsenate−Fe(III)−NOM associations. A linear relationship was observed between the amount of complexed arsenate and the Fe(III) content of the NOM. The dialysis results were consistent with complex formation through ferric iron cations acting as bridges between the negatively charged arsenate and NOM functional groups and/or a more colloidal association, in which the arsenate is bound by suspended Fe(III)−NOM colloids. Sequential filtration experiments confirmed that a significant proportion of the iron present at all Fe/C ratios used in the dialysis experiments was colloidal in nature. These colloids may include larger NOM species that are coagulated by the presence of chelated Fe(III) and/or NOM-stabilized ferric (oxy)hydroxide colloids, and thus, the solution-phase arsenate−Fe(III)−NOM associations are at least partially colloidal in nature.
TL;DR: In this paper, nanoscaled polyaniline (PANI) fibers with 17-30 nm in diameter were successfully prepared by oxidation polymerization using ferric hydrochloride (FeCl 3 · 6H 2 O) as an oxidant in the presence of p-TSA, β-naphthalenesulfonic acid (β-NSA), and camphorsulfonic acids (CSA) as the dopants.
Abstract: Nanoscaled polyaniline (PANI) fibers with 17-30 nm in diameter were successfully prepared by oxidation polymerization using ferric hydrochloride (FeCl 3 · 6H 2 O) as an oxidant in the presence of p-toluenesulfonic acid (p-TSA), β-naphthalenesulfonic acid (β-NSA), and camphorsulfonic acid (CSA) as the dopants. The resulting nanofibers show smaller diameter, higher crystallinity and conductivity (10 -1 S·cm -1 ) compared with the nanofibers oxidized by ammonium persulfate (APS), which may be due to the lower oxidation/reduction potential of FeCl 3 .
TL;DR: The main objective of this study was to remove metal ions [Fe(II, Fe(III), Mn(II), Zn(II)] from AMD using lignite, a low-cost adsorbent, and sorption capacities were compared in single, binary, ternary, and multicomponent systems.
TL;DR: It is shown that iron accumulation, which is reflected in increased ferritin expression, occurs mainly in astrocytes by 24 months in Cp−/− mice and is accompanied by a significant loss of these cells, suggesting that astroCytes play a central role in the acquisition of iron from the circulation.
Abstract: Iron is essential for a variety of cellular functions, but its levels and bioavailability must be tightly regulated because of its toxic redox activity. A number of transporters, binding proteins, reductases, and ferroxidases help maintain iron homeostasis to prevent cell damage. The multi-copper ferroxidase ceruloplasmin (Cp) converts toxic ferrous iron to its nontoxic ferric form and is required for iron efflux from cells. Absence of this enzyme in humans leads to iron accumulation and neurodegeneration in the CNS. Here we report on the changes that occur in the cerebellum of Cp null (Cp-/-) mice with aging. We show that iron accumulation, which is reflected in increased ferritin expression, occurs mainly in astrocytes by 24 months in Cp-/- mice and is accompanied by a significant loss of these cells. In contrast, Purkinje neurons and the large neurons in the deep nuclei of Cp-/- mice do not accumulate iron but express high levels of the iron importer divalent metal transporter 1, suggesting that these cells may be iron deprived. This is also accompanied by a significant reduction in the number of Purkinje neurons. These data suggest that astrocytes play a central role in the acquisition of iron from the circulation and that two different mechanisms underlie the loss of astrocytes and neurons in Cp-/- mice. These findings provide a better understanding of the degenerative changes seen in humans with aceruloplasminemia and have implications for normal aging and neurodegenerative diseases in which iron accumulation occurs.
15 Jun 2006
TL;DR: The reactivity toward selenite is similar, contrary to acid-base properties which depend on the nature of the oxide and its level of purity, to that of other ferric oxides.
Abstract: The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2–12), ionic strength (0.01–0.1 M), and concentration of selenium ( 10 −7 – 10 −2 M ). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [ Se ] = 4 × 10 −4 M (surface coverage > ca. 2 at nm−2). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeO Se(O)O− or >FeO Se(O)OH and bidentate (>FeO)2SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area ( K D in L m−2), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid–base properties which depend on the nature of the oxide and its level of purity.
TL;DR: Hydrolysis of acyloxy nitroso compounds produces nitrous oxide, the dimerization and dehydration product of HNO, and provides evidence for the intermediacy of H NO, andKinetic analysis shows that the rate of hydrolysis depends on pH and the structure of the acyl group of theAcyloxy Nitroso compound relax pre-constricted rat aortic rings similar to known HNO donors.
Abstract: Nitroxyl (HNO/NO-), the reduced form of nitric oxide, has gained attention based on its separate chemistry and biology from nitric oxide. The inherent reactivity of HNO requires new and mechanistically unique donors for the detailed study of HNO chemistry and biology. Oxidation of cyclohexanone oxime with lead tetraacetate yields 1-nitrosocyclohexyl acetate, whereas oxidation of oximes in the presence of excess carboxylic acid gives various acyloxy nitroso compounds. These bright blue compounds exist as monomers as indicated by their infrared, proton, and carbon NMR spectra, and X-ray crystallographic analysis reveals the nitroso groups possess a “nitroxyl-like” bent configuration. Hydrolysis of these compounds produces nitrous oxide, the dimerization and dehydration product of HNO, and provides evidence for the intermediacy of HNO. Both thiols and oxidative metal complexes inhibit nitrous oxide formation. Hydrolysis of these compounds in the presence of ferric heme complexes forms ferrous nitrosyl comple...
TL;DR: A review of both applications and fundamental research is made, including a review of the recent results from laboratory studies at the University of Utah as discussed by the authors, showing that thiourea decomposition is quite slow in the presence of ferric sulfate for simple solutions.
Abstract: Since the initial report of thiourea as a complexing reagent for gold leaching, considerable research has been directed toward the use of thiourea as an alternative to cyanide for gold extraction from different auriferous mineral resources. At the same time, some fundamental investigations of the system have been reported. In this article, a review of both applications and fundamental research is made, including a review of the recent results from laboratory studies at the University of Utah. Recent research results demonstrate that thiourea decomposition is quite slow in the presence of ferric sulfate for simple solutions. Ferric sulfate and formamidine disulfide (FDS) are effective oxidants with fast kinetics. No passivation of the gold surface is observed in simple acidic solutions. However, in actual leaching systems, some sulfide minerals significantly catalyze the redox reaction between thiourea and ferric ion, causing high thiourea consumption if ferric ion is present in excess. The presence of cop...
TL;DR: In this paper, the authors reported results of UV-Vis spectrophotometric and synchrotron XAFS experiments of ferric chloride complexes in chloride concentrations up to 15 m and at temperatures of 25-90 °C.
TL;DR: The hexadentate triscatecholamide bacillibactin delivers iron to Bacillus subtilis and is structurally similar to enterobactin, although in a more oblate conformation.
Abstract: The hexadentate triscatecholamide bacillibactin delivers iron to Bacillus subtilis and is structurally similar to enterobactin, although in a more oblate conformation. B. subtilis uses two partially overlapping permeases (1 and 2) to acquire iron from its endogenous siderophores (bacillibactin and itoic acid). Enterobactin and bacillibactin have opposite metal chiralities, different affinity for ferric ion, and dissimilar iron transport behaviors. The solution thermodynamic stability of ferric bacillibactin has been investigated through potentiometric and spectrophotometric titrations. The addition of a glycine to the catechol chelating arms causes a destabilization of the ferric complex of bacillibactin compared to ferric enterobactin. B. subtilis appears to express a separate receptor for enterobactin (permease 3), although enterobactin can also be transported through the permease for bacillibactin (permease 2).
TL;DR: After 42 d of anoxic operation at 35 degrees C, nitrite ion was detected in a fixed-bed reactor effluent supplying ammonium and Fe(III) EDTA Na.
TL;DR: A comprehensive comparative study on horse heart Cyt c by subpicosecond time-resolved resonance Raman and femtosecond transient absorption spectroscopy found that in ferric Cyt C, the photodissociation of an internal ligand does not take place, and relaxation dynamics is dominated by vibrational cooling in the ground electronic state of the heme.
Abstract: Cytochrome c (Cyt c) is a heme protein involved in electron transfer and also in apoptosis. Its heme iron is bisaxially ligated to histidine and methionine side chains and both ferric and ferrous redox states are physiologically relevant, as well as a ligand exchange between internal residue and external diatomic molecule. The photodissociation of internal axial ligand was observed for several ferrous heme proteins including Cyt c, but no time-resolved studies have been reported on ferric Cyt c. To investigate how the oxidation state of the heme influences the primary photoprocesses, we performed a comprehensive comparative study on horse heart Cyt c by subpicosecond time-resolved resonance Raman and femtosecond transient absorption spectroscopy. We found that in ferric Cyt c, in contrast to ferrous Cyt c, the photodissociation of an internal ligand does not take place, and relaxation dynamics is dominated by vibrational cooling in the ground electronic state of the heme. The intermolecular vibrational en...
TL;DR: The growth of V. cholerae strains carrying mutations in one or more of the potential iron transport genes indicated that both Feo and Fbp contribute to iron acquisition, suggesting that at least one other iron transport system can be used in vivo.
Abstract: Vibrio cholerae has multiple iron acquisition systems, including TonB-dependent transport of heme and of the catechol siderophore vibriobactin. Strains defective in both of these systems grow well in laboratory media and in the infant mouse intestine, indicating the presence of additional iron acquisition systems. Previously uncharacterized potential iron transport systems, including a homologue of the ferrous transporter Feo and a periplasmic binding protein-dependent ATP binding cassette (ABC) transport system, termed Fbp, were identified in the V. cholerae genome sequence. Clones encoding either the Feo or the Fbp system exhibited characteristics of iron transporters: both repressed the expression of lacZ cloned under the control of a Fur-regulated promoter in Escherichia coli and also conferred growth on a Shigella flexneri mutant that has a severe defect in iron transport. Two other ABC transporters were also evaluated but were negative by these assays. Transport of radioactive iron by the Feo system into the S. flexneri iron transport mutant was stimulated by the reducing agent ascorbate, consistent with Feo functioning as a ferrous transporter. Conversely, ascorbate inhibited transport by the Fbp system, suggesting that it transports ferric iron. The growth of V. cholerae strains carrying mutations in one or more of the potential iron transport genes indicated that both Feo and Fbp contribute to iron acquisition. However, a mutant defective in the vibriobactin, Fbp, and Feo systems was not attenuated in a suckling mouse model, suggesting that at least one other iron transport system can be used in vivo.
TL;DR: In this paper, the authors reported the significant enhancement of hydrogen production during the gasification of Victorian brown coal with steam using iron as a catalyst and showed that the overall gasification rate of a char increases greatly in the presence of iron.
TL;DR: CD spectroscopy suggests that the chirality of the ferric complexes of aerobactin and its photoproduct are similar and promotes iron acquisition by the source bacterium, Vibrio sp.
Abstract: UV photolysis of the ferric aerobactin complex results in decarboxylation of the α-hydroxy carboxylic acid group of the central citrate moiety of aerobactin. The structure determination of the photooxidized ligand shows that decarboxylation occurs at the citrate moiety forming a 3-ketoglutarate moiety. Proton and carbon-13 NMR establish the presence of keto and enol tautomers of the apo-photoproduct, with the enol form prevailing in water. The photoproduct retains the ability to coordinate iron(III). The values of the ligand protonation constants, the pKa of the Fe(III)−ligand complex, and the Fe(III) stability constant of the photoproduct of aerobactin are all close to those of aerobactin. CD spectroscopy suggests that the chirality of the ferric complexes of aerobactin and its photoproduct are similar. Like aerobactin, the photoproduct promotes iron acquisition by the source bacterium, Vibrio sp. DS40M5.
TL;DR: In this article, a galvanostatic electrochemical reduction of graphite/ferric product composite electrodes was investigated at 25°C in mildly alkaline pH-buffered solutions containing chloride, sulphate or bicarbonate anions.