Iron Aggregates Research Articles

Speciation of iron in river water using a specific catalytic determination and size fractionation.

A comprehensive speciation scheme was proposed for the speciation of iron in river water (0.45 microm filtrate). The speciation was based on the catalytic determination of reactive iron as Fe3+ and Fe(III)Li/(3 -in)+, where i = 1 or 2 for a unidentate and i = 1 for a bidentate ligand, Ln-. The scheme incudes size fractionation and acid decomposition of the sample and determination of the coexisting species. The proposed scheme was applied to natural and artificial samples and acidified preparations of these. Resulting fractionation patterns of reactive and unreactive iron and of coexisting humic acid were useful for the characterization of iron species in the natural samples. The reactive iron in the molecular weight (Mr) > or = 10(4) fraction was associated with humic iron aggregates and estimated as iron complexed with them. The unreactive iron in this fraction dissociated in 0.1 M HCI and was estimated as iron in the aggregates of iron(III) hydroxide (s) and humic iron. From the fractionation results of the artificial sample, the reactive and unreactive iron in the Mr < 10(3) fraction may be formed by complexing simple anions like F- and C2O4(2-) at their naturally-occurring concentration levels. The fractionation results also suggested that humic acid and Si contributed to the formation of reactive and unreactive iron in the Mr > or = 10(4) fraction.

Iron Cluster and Microstructure Formation in Metal-Centered Star Block Copolymers: Amphiphilic Iron Tris(bipyridine)-Centered Polyoxazolines

The microstructure of a metal-centered six-arm star block copolymer, amphiphilic iron tris(bipyridine)-centered poly(2-ethyl-2-oxazoline)-b-poly(2-undecyl-2-oxazoline), [Fe{bpy(PEOX−PUOX)2}3]2+, was investigated with small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Cylindrical PEOX microdomains were observed in a matrix of PUOX. A similar cylindrical morphology was noted for bpy(PEOX−PUOX)2, the metal-free macroligand subunit of which the Fe star is comprised. Thin films simple-cast from chloroform solution onto carbon substrates annealed at 160 °C for ≈2 days revealed in both TEM and AFM the formation of nanoscale iron clusters (≈20−40-nm diameter) distributed randomly across the surface of the film. No clusters were evident in “as-cast” films subjected to TEM analysis without the annealing step, suggesting the importance of thermal treatment for nanocrystal formation. For bulk films, larger micrometer-scale (1−2 μm) iron aggregates formed and segregated to the surface of the film after thermal treatment for ≈1 week. A liquid crystal-like mesophase due to undecyl alkyl side chain ordering was evidenced by SAXS and WAXS in the bulk sample.

Speciation of molybdenum in river water by size fractionation and catalytic determination.

A speciation scheme of trace molybdenum was proposed for river water based on size fractionation by filtration and ultrafiltration and the catalytic spectrophotometric determination of the reactive molybdenum concentration (CR). The total concentration (CT) of molybdenum was determined by the same method after acid decomposition to obtain the concentration (CT - CR) of unreactive molybdenum. Most molybdenum in natural river-water samples was found to be reactive species. A large part of the molybdenum was found in the fraction of molecular weight (MW) < 10(3), and was estimated to be MoO4(2-) from the chemical equilibria of molybdate ions. The residual part of molybdenum was found in the colloidal and particle fractions (MW > or = 10(4)), and was characterized as reactive molybdenum adsorbed or complexed on humic iron aggregates. The coexistence of silicate contributed to a decrease of the particle size of humic iron aggregates associated with molybdenum. The above-mentioned speciation results were confirmed by an analysis of artificial samples. The changes in the fractionation results by acidification (0.1 M HCl) were also used to characterize molybdenum in natural water.

Mutation in the gene encoding ferritin light polypeptide causes dominant adult-onset basal ganglia disease.

We describe here a previously unknown, dominantly inherited, late-onset basal ganglia disease, variably presenting with extrapyramidal features similar to those of Huntington's disease (HD) or parkinsonism. We mapped the disorder, by linkage analysis, to 19q13.3, which contains the gene for ferritin light polypeptide (FTL). We found an adenine insertion at position 460-461 that is predicted to alter carboxy-terminal residues of the gene product. Brain histochemistry disclosed abnormal aggregates of ferritin and iron. Low serum ferritin levels also characterized patients. Ferritin, the main iron storage protein, is composed of 24 subunits of two types (heavy, H and light, L) which form a soluble, hollow sphere. Brain iron deposition increases normally with age, especially in the basal ganglia, and is a suspected causative factor in several neurodegenerative diseases in which it correlates with visible pathology, possibly by its involvement in toxic free-radical reactions. We found the same mutation in five apparently unrelated subjects with similar extrapyramidal symptoms. An abnormality in ferritin strongly indicates a primary function for iron in the pathogenesis of this new disease, for which we propose the name 'neuroferritinopathy'.

Physicochemical speciation of molybdenum in rain water

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of molybdenum in natural and synthetic rain water samples. The concentration ( C L) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration ( C T) of molybdenum was determined after the acid decomposition of the sample to calculate the non-labile concentration ( C T− C L). From the speciation results, molybdenum species in the successive rainfall sample were found in a fraction with smaller molecular weights <10 3 Da and characterized as labile forms, i.e. simple molybdate ions. Non-labile molybdenum existed in particulate matter (≥0.45 μm in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the formation of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (≥0.45 μm). This type of molybdenum was associated with the formation of humic iron aggregates.

Speciation of Iron in Rain Water by Size Fractionation, Acid Decomposition, Acid Extraction and Catalytic Determination

For the speciation of trace iron in rain water, the concentration (CL) of labile iron was determined by a catalytic spectrophotometric method based on the oxidation of o-phenylenediamine with hydrogen peroxide. The total concentration (CT) of iron was determined by the same method after acid decomposition to obtain the concentration (CT-CL) of non-labile iron. For the particle fraction (particle size ≥0.45 µm), 0.1 M HCl-soluble iron was determined by atomic absorption spectrometry. Coexisting humic substances were spectrofluorometrically determined as humic acid. Labile iron was found in the fraction of molecular weight (MW) < 103 and estimated as FeOH2+ and Fe(OH)2+ from the chemical equilibria of hydroxo iron(III) ions. Non-labile iron was found in the particle fraction and characterized as acid-soluble iron hydroxide and humic iron aggregates as well as acid-insoluble compounds, like oxides and silicates. Labile iron was also found in the particle fraction of initial rainfall samples and characterized as iron complexed on humic iron aggregates. The above speciation results were confirmed by the analysis of synthetic samples.

Electrochemical and Column Investigation of Iron-Mediated Reductive Dechlorination of Trichloroethylene and Perchloroethylene

This research investigated the long-term performance of zero-valent iron aggregates for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE). The effects of elapsed time, mass transfer limitations, and influent halocarbon concentration on reductive dechlorination rates were investigated using groundwater obtained from a field site contaminated with chlorinated organic compounds. Over the first 300 days of operation, reaction rates for TCE and PCE gradually increased due to increasing porosity of the iron aggregates. Although there was microbial growth in the column, biological activity did not measurably contribute to reductive dechlorination. Dechlorination rates were pseudo-first-order in reactant concentration for submillimolar halocarbon concentrations. TCE concentrations near aqueous saturation resulted in passivation of the iron surfaces and deviation from first-order reaction kinetics. However, this passivation was slowly reversible upon lowering the influent TCE concentr...

Experiences from Operation and Regeneration of an Anionic Exchanger for Natural Organic Matter (NOM) Removal

Anionic exchange is an alternative to traditional drinking water purification processes when the main problem is a high concentration of natural organic matter (NOM) in the raw water. A few treatment plants employing anionic exchange have recently been installed in Norway. Some of these have after some time experienced increasing colour of the processed water. In the present study we show that the resin selectively adsorbs fulvic acid from the water while colloidal aggregates of humic substances and iron, which also contributes to the water colour, are nearly unaffected by the treatment. The treatment efficiency is successively reduced as the resin becomes fouled with iron from the raw water. Resin cleaning with hydrochloric acid had little effect, while treatment with a sodium dithionite solution resulted in full recovery of the treatment efficiency.

Experiences from operation and regeneration of an anionic exchanger for natural organic matter (NOM) removal

Anionic exchange is an alternative to traditional drinking water purification processes when the main problem is a high concentration of natural organic matter (NOM) in the raw water. A few treatment plants employing anionic exchange have recently been installed in Norway. Some of these have after some time experienced increasing colour of the processed water. In the present study we show that the resin selectively adsorbs fulvic acid from the water while colloidal aggregates of humic substances and iron, which also contributes to the water colour, are nearly unaffected by the treatment. The treatment efficiency is successively reduced as the resin becomes fouled with iron from the raw water. Resin cleaning with hydrochloric acid had little effect, while treatment with a sodium dithionite solution resulted in full recovery of the treatment efficiency.

Colocalization of iron and ceroid in human atherosclerotic lesions.

The presence of ceroid, a complex of protein associated with oxidized lipids, is commonly observed in human atherosclerotic lesions. When the human aortic walls were examined by Perls' staining, it was found that the iron deposits were evident in aortas with atherosclerosis. The extent of iron deposition was associated with the severity of the lesion. Furthermore, the iron deposits appeared to be colocalized with ceroids either extracellularly or intracellularly in foam cell-like macrophages or smooth muscle cells. Electron microscopy and X-ray microanalysis revealed that some of the extracellular iron aggregates were present within the ceroids. Likewise, some of the subcellular iron aggregates were found to be located near the lipid droplets or within the ceroids of foam cells. Collectively, these observations support the theory that the lipid oxidation occurring in lipid-laden cells of aortic lesions is facilitated by iron-overload in these cells.

Origin and composition of settling iron aggregates in oligotrophic Sombre Lake, Signy Island, Antarctica

Sediment traps were deployed in an oligotrophic, seasonally anoxic maritime Antarctic lake for 15 months. Immediately after the onset of the inflow in spring many iron oxyhydroxide aggregates were collected in the traps. Image analysis, scanning electron microscopy and energy dispersive X-ray analysis were used to examine the aggregates. The aggregates consisted of primary particles that persisted in the aggregates. The mean diameter of the aggregates was constant with depth. The aggregates consisted predominantly of iron, phosphorus and oxygen but calcium was also an important constituent. Significant concentrations of manganese and sodium were also detected. The molar ratio Fe:P remained constant at 4:1 as did the ratio Fe:Ca at 52:1. The concentration of iron, phosphorus and calcium in the aggregates increased with depth, whilst the concentration of manganese decreased with depth in parallel with a gradient of increasing anoxia. The stable water column formed under ice cover and the temporal and spatial data provide evidence that the Fe:P and Fe:Ca ratios are constant and characteristic of the aggregates, whilst the overall composition of the aggregates is more dynamic and dependant on redox conditions and water chemistry.

Aggregation and Sedimentation of Iron, Phosphorus and Organic Carbon in Experimental Mixtures of Freshwater and Estuarine Water

The importance of salinity and suspended minerogenic particles on the aggregation and sedimentation processes of iron, phosphorus and organic carbon was studied in experimental procedures with waters from the River Öre and from the Öre Estuary, northern Sweden. The aggregation of dissolved iron and phosphorus reached at least 40–90% and 30–60%, respectively, at salinities between 4 and 6. Only a few percent, less than 10%, of the dissolved organic carbon aggregated. Rapid and nearly complete sedimentation of iron and phosphorus aggregates was found at high salinities (4–5) and in the presence of clay particles. Mineral particles increase sedimentation by sorption of formed iron and phosphorus aggregates. Only a small amount of the organic carbon sedimented.

Extended X‐ray Absorption Fine Structure (EXAFS) Studies of Hydroxo(oxo)iron Aggregates and Minerals, and a Critique of their Use as Models for Ferritin

AbstractStructural models for the hydroxo(oxo)iron core of ferritin include extended mineral structures and cluster systems such as [Fe11O6(OH)6(O2CPh)15] ( = Fe11) and two clusters that crystallise in the same lattice (compound 1), namely, [Fe17(μ3‐O)4(μ3‐OH) 6(μ2‐OH)10(heidi)8(H2O)12]3+and[Fe19(μ3‐O)6(μ3‐OH)6(μ2‐OH)8(heidi)10(H2O)12]1+. The suitability of these systems as models for the structure of the core of ferritin has been tested by comparing their Fe K‐edge EXAFS and X‐ray crystallographic results with the Fe K‐edge EXAFS data on horse spleen ferritin. The interpretative procedure for the EXAFS analysis was optimised by using the X‐ray crystallographic data for compound 1 as a basis. This protocol was then used to interpret the Fe K‐edge EXAFS spectra of α‐ and γ‐Fe(O)OH and to reinterpret that previously recorded for horse spleen ferritin. The published Fe K‐edge EXAFS data on Fe11 were also considered. The Fe ⃛Fe distances provide a clear indication of the nature of the hydroxo(oxo)iron assembly. It was found that the iron–iron interactions are the most reliable guide. Clusters are shown to be more appropriate than infinite lattices as structural models for the core of ferritin.

Isolation of the four forms of transferrin with respect to iron by high-performance liquid chromatography: comparison of three mammalian species

A method, based on anion exchange combined with high-performance liquid chromatography, is presented for the separation of the four different forms of transferrin with respect to iron, i.e. diferric, monoferric with Fe in the C-terminal lobe, monoferric with Fe in the N-terminal lobe, and apo (iron-free). Depending on the size of column applied, these forms can be obtained on a preparative scale amounting to milligrams. The procedure was also found to free transferrin from loosely bound iron and protein aggregates. Comparative studies with human, murine and rat transferrins showed that optimal resolution of these proteins depended on establishing a distinct elution programme for each species. The order in which the four forms referred to above were displaced from the exchanger differed from species to species.

Polyiron(III) Oxyhydroxide Clusters: The Role of Iron(III) Hydrolysis and Mineralization in Nature

Abstract The compounds which form in aqueous solutions containing iron(III) and chelating ligands are considered and the control of iron(III) hydrolysis as a synthetic strategy for the preparation of iron(III) species of different nuclearities is explained. The relevance of such complexes to naturally occurring iron species is discussed. Hydroxide, oxide, carboxylate and alkoxide bridged iron(III) aggregates are compared to iron(III) clusters in Nature with particular attention paid to the way in which their formation can aid in understanding the biomineralization of iron. The structures of trapped mineralized iron(III) oxyhydroxide clusters are proposed as good models for the iron storage protein ferritin, which itself is best regarded as a cluster species. Synthetic strategies for producing clusters of different shapes and sizes are suggested.

Nanostructural Studies by MÖssbauer Spectroscopy

ABSTRACTApplication of 57Fe MÖssbauer spectroscopy to the determination of magnetic structural parameters relevant to nanostructural studies is discussed. Variable temperature and applied magnetic field strength investigations are considered in order to illustrate the power of the technique in rendering a microscopic picture of the internal spin structure and dynamical spin relaxation phenomena associated with nanoscale systems. Examples from biology and chemistry, where iron aggregates of nanometer dimensions are encountered, are presented.

Study of Fe: Al 2O 3 ion beam sputtered thin films with various iron contents

Iron and Al 2O 3 were simultaneously ion beam sputtered on polycrystalline alumina substrate at room temperature. The atomic iron concentration was varied in the range 5–60 at.%. Thicknesses of the films (≈450 nm) and iron concentrations were controlled using Rutherford backscattering spectrometry (RBS). Iron charge states and phases were deduced from conversion electron Mössbauer spectroscopy (CEMS) and grazing-angle X-ray diffraction (GXRD) measurements. At low iron concentrations, CEMS shows that iron is mainly dispersed in Al 2O 3 together with the presence of small iron precipitates appear, whereas for 50 at.% magnetic of the FeAlO 3 phase and iron aggregates. Around 40 at.% of iron bigger precipitates appear, whereas for 50 at.% magnetic aggregates with different sizes are formed. For the highest concentration only magnetically ordered metallic particles are detected.

First stage of precipitation in iron-carbon-nitrogen martensites; diffraction analysis using synchrotron radiation

A considerable amount of research has been done on the aging and tempering behavior of iron-carbon and iron-nitrogen martensites. These martensites can be described on the basis of an overall body-centered tetragonal (b.c.t.) lattice of iron atoms containing interstitial atoms which are randomly distributed over the c-type octahedral interstices. The interstitial martensites seem to be similar in many respects; they have, for instance, comparable lattice parameters and M{sub s} temperatures (the M{sub s} temperature is the temperature at which the martensite formation starts on quenching from the austenite-phase field). However, some distinct differences occur between the decomposition behavior of both martensites. On aging at room temperature for example, local enrichments of interstitials develop in both nitrogen and carbon martensites. In FeN martensites these enrichments are considered to possess a fully ordered arrangement of the nitrogen interstitials in c-type octahedral interstices according to the {alpha}{double prime}-Fe{sub 16}N{sub 2} structure. However, in FeC martensites no indications for such an ordering have been observed (yet) and the enrichments are denoted as clusters which are conceived as aggregates of iron and carbon atoms, containing different amounts of carbon interstitials distributed randomly over the c-type octahedral interstices. This paper reports that because of the abovemore » mentioned apparent difference between the aging of FeN and FeC martensites, it is interesting to study the (pre)precipitation behavior of iron-carbon-nitrogen martensitic alloys with different ratios of the amounts of carbon and nitrogen atoms. Only a few results on the tempering of FeCN have been reported until now. In these studies alloys were used which were very rich in nitrogen.« less

Annealing behaviour of iron implanted zirconia

A zirconia film was implanted at room temperature with 100 keV57Fe+ to a fluence of 8×1016 ions/cm2. The analysis of the Conversion Electron Mossbauer spectra shows that iron is distributed among different charge states: Fe0 (in a form of small and large metallic iron aggregates) Fe2+ and Fe4+. The evolution of the iron depth profile deduced from Rutherford backscattering measurements as well as the change in the charge states of iron as a function of annealing under argon atmosphere are presented.

Effect of Eight Individual Rare-earth Elements on the Graphite Nodule Count of a Thin-section of Spheroidal-graphite Cast Iron

Eight rare-earth elements, Y, La, Ce, Pr, Nd, Sm, Dy, and Yb, were added individually to two irons, one containing 0.02% S and the other 0.08% S. After nodularisation, the metal was poured into CO2 Process sand moulds to produce stepped test-specimens with thicknesses of 3,6 and 9 mm and into shell moulds to provide ‘break-off’ type specimens with a dia of 30 mm. The effect of each of these rare earth elements on the nodule number, and chill formation was investigated and the mechanism of the nodule number increase studied.The increase in the nodule number differed significantly with each kind of rare-earth element added to the molten iron. The largest rise in the nodule number was with Ce followed in turn by La, Pr, Nd, Sm, Yb and Y. It was seen that the increase in nodule number was more pronounced when the elements were added to the iron with the higher sulphur content. To maximise the increase in nodule number, it was found that the optimum added quantity of these rare-earth elements was almost stoichiometric with the sulphur content of the iron.X-ray microanalysis of the prepared specimens containing these rare-earth elements confirmed that only sulphides formed in the melts treated with Ce, La, Pr, Nd, or Yb, whilst both sulphides and phosphides formed when additions were made of Dy, Sm or Y. The specimens poured into a metal mould during the eutectic solidification stage, and subsequently quenched showed that graphite had formed on the rare-earth sulphide substrates, but not on the phosphide. It was concluded that the latter cannot act as substrates for the formation of graphite.Measurement of the average diameters of the rare-earth sulphides (Ce, La, Pr, and Nd) showed that the largest effects upon nodule numbers were associated with elements producing sulphides of smaller diameter. This phenomena may reasonably be explained. A rare-earth sulphide exists as a liquid phase in an iron melt and aggregates until it solidifies, increasing its diameter. The degree of aggregation differs amongst the different rare-earth sulphides, resulting in a different number of substrates for each graphite formation.