Luminescence quenching by iron in barium aluminoborate glasses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ashcroft model potential study of lattice dynamics of α-iron and barium

Ashcroft model potential has been used to compute phonon dispersion relations along the three principal symmetry directions, i.e. [k00], [kk0] and [kkk] for alpha-iron and barium. The computed phonons gave a reasonable agreement with the experimental ones in all the three principal summetry directions expect for the T-2 branch in [KK0] direction where the present study failed to reproduce the experimental findings.

Electroactive layer-by-layer films of iron tetrasulfonated phthalocyanine

Electroactive films of iron tetrasulfonated phthalocyanine (FeTsPc) were assembled via the electrostatic layer-by-layer technique (LBL), in which FeTsPc layers were alternated with the polycationic poly(allylamine hydrochloride) (PAN). The multilayer formation was monitored via UV-Vis spectroscopy by measuring the increase in the Q Band of FeTsPc at 676 nm. Film thickness was estimated by profilometry as ca. 10 Angstrom per bilayer. Fourier transform infrared and UV-Vis absorption spectroscopy suggested specific interactions between FeTsPc and PAR Cyclic voltammograms showed reproducible pairs of oxidation-reduction peaks at 0.92 mV and 0.70 mV, respectively, for a 50-bilayer PAH/FeTsPc film at 50 mV/s (vs Ag/AgNO3).

Magnetic properties of acicular ultrafine iron particles

Magnetic properties of acicular (similar to60 and similar to200 nm) iron particles, obtained by reduction of alumina-coated goethite particles, are reported. X-ray diffraction and Mossbauer spectroscopy showed that the particles consist of a alpha-Fe core and a thin surface layer of maghemite. Magnetization data indicated an improvement of similar to28% in the saturation magnetization, coercive field, and squareness for particles with similar to60 nm. This magnetic property enhancement of the present particles, whose size is 40% smaller than those commercially available, could result in a similar decrease of the bit-size for higher density of magnetic media.

THE ELECTROCHEMICAL OXIDATION OF (BENZYLIDENEACETONE)DICARBONYL(PHOSPHINE)IRON(0) AND (BENZYLIDENEACETONE)DICARBONYL(PHOSPHITE)IRON(0) COMPLEXES IN DIMETHYL FORMAMIDE

The electrochemical oxidation of (benzylideneacetone)dicarbonyl(phosphine)iron(0) and benzylideneacetone)dicarbonyl(phosphite)iron(0) complexes was studied by cyclic voltammetry and controlled potential electrolysis in 0.5 M NaClO4 (dimethyl formamide). The results suggest that the electrode process involves a complicated mechanism, the species formed in the first oxidation step being highly unstable and its decomposition producing free benzylideneacetone, free phosphine or phosphite, solvated iron(II) species and carbon monoxide which adsorbs on the platinum electrode. A linear relationship between E(p/2)ox and the ligand parameter P(L) was obtained with E(s) = 0.41 V and beta = 0.964, where E(s) and beta-denote electron-richness and polarizability of the metal centre, respectively.

Photo luminescence: A probe for short, medium and long-range self-organization order in ZrTiO4 oxide

Photoluminescent disordered ZrTiO4 powders were obtained by the polymeric precursor soft-chemical method. This oxide system (ordered and disordered) was characterized by photoluminescence, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and UV vis absorption experiments. The UV absorption tail formation in the disordered oxides was related to the diminution of optical band gap. In the disordered phase, this oxide displayed broad band photoluminescence caused by change in coordination number of titanium and zirconium with oxygen atoms. The gap decreased from 3.09 eV in crystalline oxide to 2.16 eV in disordered oxide. The crystalline oxide presented an orthorhombic alpha-PbO2-type structure in which Zr4+ and Ti4+ were randomly distributed in octahedral coordination polyhedra with oxygen atoms. The amorphous-crystalline transition occurred at almost 700 degrees C, at which point the photoluminescence vanished. The Raman peak at close to 80-200 cm(-1) indicated the presence of locally ordered Ti-O-n and Zr-O-n polyhedra in disordered photoluminescent oxides. (c) 2006 Elsevier B.V. All rights reserved.

Iron(II) djenkolate: synthesis and properties

Djenkolate complex of iron, [Fe(C(7)H(12)N(2)O(4)S(2))]. H(2)O, has been synthesized by the reaction of potassium djenkolate with Fe(SO(4)). 7H(2)O under nitrogen atmosphere. X-Ray diffraction pattern has been indexed in orthorhombic system with lattice parameters: a=11.24 Angstrom, b=7.50 Angstrom and c=6.96 Angstrom. According to IR spectroscopy, coordination is performed through COO(-) and NH(2) groups. An octahedral geometry for Fe ion is suggested by UV-Vis and Mossbauer spectroscopies. Thermal decomposition leads to the formation of Fe(2)O(3) (hematite). The compound shows poor solubility in water and in common organic solvents. (C) 2000 Elsevier B.V. S.A. All rights reserved.

From Plinthic Acrisols to Plinthosols and Gleysols: iron and groundwater dynamics in the tertiary sediments of the upper Amazon basin

Topography has been reported to be the major factor ruling the spatial distribution of Acrisols, Plinthosols and Gleysols on the seasonally flooded, low elevation plateaux of the upper Amazon basin occupied by Tertiary (Ica & Solimoes) sediments. In this study, detailed morphological and mineralogical investigations conducted in a representative 25-ha site were combined with hydro-geochemical data to relate the vertical and lateral soil differentiations observed to the hydro-geological history of that part of the basin. As a result of the uplift of the Andes, several cuts in the extensive Tertiary marshlands have formed, at first, slightly incised plateaux of low elevation. There, weathering under hot and humid climates would have generated a reddish, freely drained and bioturbated topsoil layer and the vertical differentiation in subsoil sediments of a plinthite over an iron-depleted mottled clay. The second episode of soil differentiation is linked to the replacement of the forest by a savannah under the drier climates of the late Pleistocene, which favours surface runoff and the infill of the incisions by fine particles. This infill, combined with the return to the present humid climate, has then enabled the local groundwater to rise on the plateaux and to generate episaturation at the topsoil/subsoil transition close to the depressions. Nowadays, ferrous iron is released from the partly iron-depleted topsoil weathering front at high water levels during the rainy seasons. It moves from footslope to low-lying positions and from top to bottom in the soil profile according to the groundwater dynamics. The present general trend is thus to the lateral export of iron at high water levels due to subsurface and overland flows, its vertical transfer during the recession of the groundwater and accumulation in a nodular plinthite. In the latter, ferrous iron is adsorbed onto its softest iron masses where it feeds the neoformation of ferrihydrite that rapidly dehydrates into haematite.

Serum iron and plasma fibrinogen concentrations as indicators of systemic inflammatory diseases in horses

Background: Detection of systemic inflammation, which is important for proper diagnosis and prompt treatment, can be challenging.Hypothesis: Measurement of plasma iron concentration is a sensitive method for detecting systemic inflammation in horses compared with measurements of plasma Fibrinogen concentration, a traditional marker for inflammation in the horse.Animals: Ninety-seven horses hospitalized with diseases causing systemic inflammation, 22 horses with localized inflammation, and 12 clinically normal horses were included in this study.Methods: A retrospective study was made on hospitalized horses that had both plasma iron and fibrinogen concentrations measured on hospital admission.Results: Plasma iron concentration was lower in horses with systemic inflammation (64 +/- 45 mu g/dL) than the reference interval minimum (105 mu g/dL) and were significantly lower (P = .001) than the value in a group of horses with local inflammation (123 +/- 45 mu g/dL) and in healthy transported horses (143 +/- 29 mu g/dL). Low plasma iron and high fibrinogen concentrations were both sensitive indicators of systemic inflammation in horses with sensitivity of 90 and 82%, respectively. There was a similar correlation between either continued decreases in iron concentration (R-sp of 0.239) or increases in fibrinogen concentration (R-sp of 0.280) during hospitalization and a worse prognosis.Conclusions and Clinical Importance: Measurement of plasma iron concentration better reflected acute inflammation than did fibrinogen concentration.

A 4.2 kDa synthetic peptide as a potential probe to evaluate the antibacterial activity of coumarin drugs

The coumarin antibiotics are potent inhibitors of DNA replication whose target is the enzyme DNA gyrase, an ATP-dependent bacterial type II topoisomerase. The coumarin drugs inhibit gyrase action by competitive binding to the ATP-binding site of DNA gyrase B protein. The production of new biologically active products has stimulated additional studies on coumarin-gyrase interactions. In this regard, a 4.2 kDa peptide mimic of DNA gyrase B protein from Escherichia coli has been designed and synthesized. The peptide sequence includes the natural fragment 131-146 (coumarin resistance-determining region) and a segment containing the gyrase-DNA interaction region (positions 753-770). The peptide mimic binds to novobiocin (K-a = 1.4 +/- 0.3 x 10(5) m(-1)), plasmid (K-a = 1.6 +/- 0.5 x 10(6) m(-1)) and ATP (K-a = 1.9 f 0.4 x 10(3) m(-1)), results previously found with the intact B protein. on the other hand, the binding to novobiocin was reduced when a mutation of Arg-136 to Leu-136 was introduced, a change previously found in the DNA gyrase B protein from several coumarin-resistant clinical isolates of Escherichia coLi. In contrast, the binding to plasmid and to ATP was not altered. These results suggest that synthetic peptides designed in a similar way to that described here could be used as mimics of DNA gyrase in studies which seek a better understanding of the ATP, as well as coumarin, binding to the gyrase and also the mechanism of action of this class of antibacterial drugs. Copyright (C) 2004 European Peptide Society and John Wiley Sons, Ltd.

Effect of iron on inhibition of acid demineralisation of bovine dental enamel in vitro

Objectives: Iron ions (Fe2+) have been shown to be cariostatic in many studies particularly by their ability to reduce bacterial metabolism. Nevertheless, the role of iron ions on dissolution of enamel is unexplored. The aim of the present study was therefore to investigate the protective effect of increasing concentrations (0-120 mmol/L) of Fe2+ on the dissolution of enamel.Design: Enamel powder was subjected to acetic acid made with increasing concentrations with respect to FeSO4 center dot 7H(2)O. In order to determine the amount of enamel dissolved, the phosphate released in the medium was analysed spectrophotometrically using the Fiske-Subarrow method. Data were tested using Kruskall-Wall and Dunn's tests (p < 0.05). The degree of protection was found to approach maximum at about 15 mmol/L Fe2+. Higher concentrations of Fe2+ did not have an extra effect on inhibition of dissolution of enamel powder. In the next step, the protective effect of 15 mmol/L Fe2+ against mineral dissolution of the bovine enamel was evaluated using a simple abiotic model system. Enamel blocks were exposed to a sequence of seven plastic vials, each containing 1 mL of 10 mmol/L acetic acid. The acid in vial 4 was made 15 mmol/L with respect to FeSO4 center dot 7H(2)O. The mineral dissolved during each challenge was thus determined by phosphate released as described above. Data were tested using two-way ANOVA (p < 0.05). Results: Lower demineralisation (around 45%) was found in vial 4 (with Fe) that continued stable until vial 7.Conclusions: Thus, our data suggest that Fe2+, can be effective on inhibition of dissolution of enamel and that this effect may be durable. (c) 2006 Elsevier Ltd. All rights reserved.

Eu3+ as a spectroscopic probe in phosphors based on spherical fine particle gadolinium compounds

This work reports on the luminescence spectroscopy sensitivity in the determination of the phase purity in gadolinium compounds using Eu3+ as a probe. Cubic Gd2O3 and hexagonal Gd2O2S doped with Eu3+ spherical fine particles were obtained from doped gadolinium basic carbonates with morphological control and were also characterized by IR and XRD. Doped samples present Eu3+ characteristic transitions, with specific energy positions related to each phase. Emission and excitation spectra patterns were established for oxide and oxysulfide compounds, then oxysulfate and oxide impurities generated during oxysulfide preparation were monitored. From emission spectra some experimental intensity parameters were also calculated. All spectroscopic results reflect the presence or not of impurities in all compounds. (C) 2001 Elsevier B.V. Ltd. All rights reserved.