Contribuição ao estudo de uma metodologia alternativa para obtenção de dioxissulfeto de terras raras

In the last decade, many method has been developed to obtain oxysufides. However, theses materials were obtained by reaction involved gaseous toxics, CO, CS2, H2S and S. In the present work, the synthesis of lanthanum oxysufides actived by europium (III) through an alternative method has been made. This method involve the rare earth sulfate reduction under an atmosphere of argon contained 10% hydrogen using the thermogravimetric technique. The results showed the formation of the phase TR2O2S (TR = La and Eu) at temperatures which depend upon the heating rate, respectively 650 - 830ºC at 5ºC min-1 and 680 - 800ºC at 10ºC min-1. The oxysufides obtained are characterized by infrared spectroscopy. The method developed is more economic than the usual industrial methods and the environmental problems during the synthesis are also better controled.

Spectrophotometric study of iron oxidation in the iron(II)/thiocyanate/acetone system and some analytical applications

The possibility of using thiocyanate to determine iron(II) and/or iron(III) in water-acetone mixture has been re-examined as part of a systematic and comparative study involving metallic complexes of pseudohalide ligands. Some parameters that affect the complete oxidation of the ferrous cations, their subsequent complexation and the system stability have been studied to optimize the experimental conditions. Our results show the viability and potentiality of this simply methodology as an alternative analytical procedure to determine iron cations with high sensitivity, precision and accuracy. Studies on the calibration, stability, precision, and effect of various different ions have been carried out by using absorbance values measured at 480 nm. The analytical curve for the total iron determination obeys Beer's law (r = 0.9993), showing a higher sensitivity (molar absorptivity of 2.10x10(4) L cm-1 mol-1) when compared with other traditional systems (ligands) or even with the "similar" azide ion [1.53x10(4) L cm-1 mol-1, for iron-III/azide complexes, in 70% (v/v) tetrahydrofuran/water, at 396 nm]. Under such optimized experimental conditions, it is possible to determine iron in the concentration range from 0.5 to 2 ppm (15-65% T for older equipments, quartz cells of 1.00 cm). Analytical applications have been tested for some different materials (iron ores), also including pharmaceutical products for anemia, and results were compared with atomic absorption determinations. Very good agreement was obtained with these two different techniques, showing the potential of the present experimental conditions for the total iron spectrophotometric determinations (errors < 5%). The possibility of iron speciation was made evident by using another specific and auxiliary method for iron(II) or (III).

An investigation into the oxidation of organic sulphides, organic selenides and simple hydrocarbons by Mortierella isabellina NRRL 1757

The work presented in this thesis is divided into three separate sections 4!> Each' 'section is involved wi th a different problem, however all three are involved with a microbial oxidation of a substrate~ A series of 'aryl substituted phenyl a.nd be,nzyl methyl sulphides were oxidized to the corre~pondi~g sulphoxides by 'Mo:rtierellai's'a'b'e'llina NRR.L17'S7 @ For this enzymic Qxidation, based on 180 labeled experiments, the oxygen atom is derived fr'orn the atmosphere and not from water. By way of an u~.traviolet analysis, the rates of oxidation, in terms of sulphox~ de appearance, were obtained and correlated with the Hatnmett p s~grna constants for the phenyl methyl sulphide series. A value of -0.67 was obtained and, is interpreted in terms of a mechanism of oxidation that involves an electrophilic attack on the sulphide sulphur by an enzymic ironoxygen activated complex and the conversion of the resulti!lg sulphur cation to sulphoxide. A series of alkyl phenyl selen~des have been incubated with the fu~gi, Aspergillus niger ATCC9l42, Aspergillus fO'etidus NRRL 337, MIIJisabellina NF.RLl757 and'He'lminth'osparium sp'ecies NRRL 4671 @l These fu?gi have been reported to be capable of carrying out the efficient oxidation of sulphide to sulphoxide, but in no case was there any evidence to supp'ort the occurrence of a microbialox,idation. A more extensive inves·t~gation was carried out with'M,e 'i's'a'b'e'l'l'i'na, this fu~gus was capable of oxidizing the correspondi~g sulphides to sulphoxi.de·s·$ Usi:ng a 1abel.edsubstra.te, [Methyl-l4c]-methyl phenyl selenide, the fate of this compound was invest~gated followi!lg an i'ncubation wi th Me isabellina .. BeSUldes th. e l4C-ana1YS1Q S-,'. a quant"ltta"lve selen'lum ana1Y"S1S was carried out with phenyl methyl selenide. These techniques indicate that thesel'enium was capable of enteri!1g thefu!1gal cell ef'ficiently but that s'ome metabolic cleav~ge of the seleni'um-carbon bond' may take plac'e Ie The l3c NMR shifts were assigned to the synthesized alkyl phenyl sulphides and selenides@ The final section involved the incubation ofethylben~ zene and p-e:rtr.hyltoluene wi th'M ~ 'isab'e'llina NRRL 17574b Followi~ g this incubation an hydroxylated product was isolated from the medium. The lH NMR and mass spectral data identify the products as I-phenylethanol and p-methyl-l-phenylethanol. Employi!lg a ch'iral shift re~gent,tri~ (3-heptafluorobutyl-dcamphorato)'- europium III, the enantiomeric puri ty of these products was invest~gated. An optical rotation measurement of I-phenylethanol was in ~greement with the results obtained with the chiral shift re~gen,te 'M.isabe'l'lina is capable of carryi~g out an hydroxylation of ethylbenzene and p-ethyltoluene at the ~ position.

Cartographie du réseau d'interactions protéiques de la machinerie de transcription dans les cellules humaines

Les protéines sont les macromolécules les plus polyvalentes de la cellule. Elles jouent un rôle fondamental dans la majorité des processus biologiques à travers la formation de complexes multi-protéiques. Durant la transcription, une multitude de facteurs sont impliquées dans le contrôle de l’activité des complexes ARN polymérases. Notre laboratoire s’est intéressé au réseau d’interaction de la machinerie de transcription des ARN polymérases nucléaires, dans le but de mieux comprendre leurs mécanismes de régulation. Pour ce faire, une procédure protéomique comprenant la purification de complexes protéiques par affinité couplée à la spectrométrie de masse et à l’analyse bioinformatique a été développée. La méthode de purification TAP (Tandem Affinity Purification) a été adaptée pour permettre la purification de complexes protéiques solubles assemblés in vivo à partir de cellules humaines. L’objectif de mon projet de maîtrise était de purifier le complexe de l’ARN Pol I ainsi que de poursuivre l’expansion du réseau d’interactions protéine-protéine de la machinerie de transcription de l’ARN Pol II humaine. À l’aide des protéines POLR1E, TWISTNB, POLR2E, PFDN4, MBD2, XPA, CAND1 et PDCD5 étiquetées (TAP-tag) exprimées dans des lignées cellulaires ECR-293, plusieurs complexes protéiques solubles ont été purifiés et analysés par spectrométrie de masse. Les interactions protéiques ont été triées et validées bioinformatiquement pour donner en final une liste d’interactions ayant un haut degré de confiance à partir de laquelle des réseaux d’interactions protéine-protéine ont été créés. Le réseau créé au cours de ce projet connecte plusieurs composantes de la machinerie transcriptionnelle tels que les ARN Pol I, II et III, les complexes RPAP3/R2TP/prefoldin-like, TRiC/CCT, Mi-2/NuRD et des facteurs de transcription et de réparation de l’ADN. Ce type d’analyse nous a permis d’identifier et de caractériser de nouveaux régulateurs de la machinerie de transcription de l’ARN Pol I et II et de mieux comprendre son fonctionnement.

QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes

Quantitative structure activity relationships (QSARs) have been developed to optimise the choice of nitrogen heterocyclic molecules that can be used to separate the minor actinides such as americium(III) from europium(III) in the aqueous PUREX raffinate of nuclear waste. Experimental data on distribution coefficients and separation factors (SFs) for 47 such ligands have been obtained and show SF values ranging from 0.61 to 100. The ligands were divided into a training set of 36 molecules to develop the QSAR and a test set of 11 molecules to validate the QSAR. Over 1500 molecular descriptors were calculated for each heterocycle and the Genetic Algorithm was used to select the most appropriate for use in multiple regression equations. Equations were developed fitting the separation factors to 6-8 molecular descriptors which gave r(2) values of >0.8 for the training set and values of >0.7 for the test set, thus showing good predictive quality. The descriptors used in the equations were primarily electronic and steric. These equations can be used to predict the separation factors of nitrogen heterocycles not yet synthesised and/or tested and hence obtain the most efficient ligands for lanthanide and actinide separation. (C) 2003 Elsevier B.V. All rights reserved.

Studies on the parallel synthesis and evaluation of new heterocyclic extractants for the partitioning of minor actinides

Multiple parallel synthesis and evaluation have been combined in order to identify new nitrogen heterocycles for the partitioning of minor actinides(III) such as americium(III) from lanthanides such as europium(Ill). An array of triazine-containing molecules was made using multiple parallel syntheses from diketones and amide hydrazides. An excess of each of the resulting purified reagents was dissolved in 1,1,2,2-tetrachloroethane containing 2-bromodecanoic acid, and equilibrated with an aqueous solution containing the radiotracers Eu-152 and Am-241 in nitric acid ([Eu] + [Am] < 400 nanomol dm(-3)). Gamma counting of the organic and aqueous phases led to the identification of several new reagents for the selective extraction of americium(III). In particular, 6-(2-pyridyl)-2-(5,6-dialkyl-1,2,4-triazaphenyl)pyridines were found to be effective reagents for the separation of americium(III) from europium(III), (SFAm/Eu was ca. 30 in [HNO3] = 0.013 mol/L).

Ligand-rare-earth ion energy transfer in coordination compounds. A theoretical approach

A theoretical approach to the energy transfer process that occurs between a ligand and a rare-earth ion in luminescent complexes is presented. A discussion on the energy transfer mechanisms involved and on the associated selection rules is made. Numerical estimates are also presented.

Degradation of the herbicide tebuthiuron using solar photo-Fenton process and ferric citrate complex at circumneutral pH

The influence of pH on the degradation of the herbicide tebuthiuron (TBH) was investigated using in situ generated Fe(III)-citrate complexes (Fe:cit) submitted to the photo-Fenton process under solar irradiation. Using Fe:cit in a wide pH range (2.5-7.5), 100-78% TBH oxidation was achieved respectively from a UV dose of 2.0 J cm(-2) (15 min). Moreover, the oxidation of TBH obtained in the presence of Fe:cit at pH 6.0 was higher than that obtained using Fe(NO3)3 at pH 2.5. A similar behavior is observed for the removal of total organic carbon (TOC) in TBH solutions. In the presence of Fe:cit, 20% and 85% of TOC was removed at pH 7.5 and 2.5, respectively, after 7.5 J cm-2 irradiation, while no mineralization was observed employing Fe(NO3)(3) for the same UV dose. Using Fe(NO3)(3), mineralization was observed only after 11 J cm-2 (8%). A higher mineralization rate was obtained with Fe(NO3)(3) only when a concentration three times higher was employed at pH 2.5. Besides the high efficiency of TBH degradation observed using the ferric citrate complex in the solar photo-Fenton process, it also offers the advantage of application at a pH of up to 7.5. (c) 2007 Elsevier B.V. All rights reserved.

Microwave synthesis of YAG : Eu by sol-gel methodology

Yttrium-aluminum oxides are interesting compounds and they have been extensively used as host for lasers and phosphors, due to their stable physical and chemical properties. The fabrication of yttrium-aluminum garnet (YAG) has been investigated thoroughly. Single-crystal YAG is expensive and to produce it a new way has been investigated. This process consists of modifying the methodology of reagents mixture and the process of heating them. The microwave irradiation is used to heat-treat the oxide mixture. The traditional synthesis of YAG powders occurs through the reaction of aluminum and yttrium powders at high temperatures. With this work we investigated the preparation of YAG by non-hydrolytic sol-gel route as an alternative methodology to obtain yttrium-aluminum matrix from inorganic precursors (yttrium and aluminum chloride). The preparation of the gel was carried out in an oven-dried glassware. The AlCl3, YCl3 and ethanol were reacted in reflux under argon atmosphere. Europium III chloride was added as a structural probe. The powder was dried and heat-treated in modified microwaves. The samples were pre-treated at 50 and 800 C during I h and then heated in microwaves for 30 s, 2 and 4 min. The formation process and structure of the powders were studied by means of X-ray diffraction (XRD), photoluminescence (PL) and transmission electronic microscopy (TEM). XRD presents only picks corresponding to the YAG phase and confirmed by TEM. PL date showed that the YAG phase was formed in 2 min with the samples pre-treated at 50 C. For the samples pretreated at 800 degrees C, the YAG phase appears in 30s. The excitation spectra present a maximum of 394 nm corresponding to the L-5(6) level and emission spectra of Eu III ion present bands characteristic transitions arising from the D-5(0) -> F-7(J) (J= 1, 2, 3, 4) monifolds excited at their maximum. The magnetic dipole D-5(0) -> F-7(1) transition presents more intensity than the electric dipole D-5(0) -> F-7(2) transition. This methodology showed efficiency in obtaining YAG phase. (c) 2006 Elsevier B.V. All rights reserved.

Titania-based organic-inorganic hybrid planar waveguides

Eu3+ -doped titania-silica planar waveguides were prepared from tetraethylorthotitanate (TEOT) and modified silane 3-amino-propyltriethoxysilane (APTS). Films were deposited on borosilicate glass substrates by a dip-coating technique. The refractive index, the thickness and the total attenuation coefficient of the waveguides were measured at 632.8 and 1550 nm by prism coupling technique. Starting from pure titania films, the addition of modified silane leads to a decrease in the refractive index and an increase in thickness. Squared electric field simulation has shown that the light confinement in the waveguide increases with the silane content of the so]. Emission spectra present a broad emission band due to the modified silane and EU emission transitions arising mainly from the D-5(0) level to the F-7(J) (J = 0-4) manifolds. The dependence of transition intensities and excited state lifetimes on the initial composition and also on the heat treatment performed was interpreted in terms of structural changes occurring during the preparation process. (C) 2002 Elsevier B.V. B.V. All rights reserved.

A new beta-diketone complex with high color purity

In this work a new europium (III) complex with the following formula NH(4) [Eu(bmdm)(4)] was synthesized and characterized. The bmdm (butyl methoxy-dibenzoyl-methane) is a P-diketone molecule used as UV radiation absorber in sunscreen formulations. Coordination of this ligand to the Eu(3+) ion was confinned by FT-IR, while the Raman spectrum suggests the presence of NH(4)(+) ions. The photoluminescence spectra present narrow lines arising from f-f intra-configurational transitions (5)D(0-)(7)F(0,1,2,3,4), dominated by the hypersensitive (5)D(0)-(7)F(2) transition. In the spectrum recorded at 77 K, all transitions split into 2J + 1 lines suggesting that there is just one symmetry site around Eu(3+) ion. This symmetry is not centrosymmetric. The calculated intensity parameters are ohm(2) = 30.5 x 10(-20) cm(2) and ohm(4) = 5.91 x 10(-20) cm(2) for this complex. The CIE chromaticity coordinates (x = 0.67 and y = 0.32) show a dominant wavelength of 615 nm. The color gamut achieved by this complex is a 100% in the CIE color space. (c) 2005 Elsevier B.V. All rights reserved.

Determination of the local site occupancy of Eu3+ ions in ZnAl2O4 nanocrystalline powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural and optical properties of Eu3+ and Mg2+ doped LiTaO3 obtained via the polymeric precursor method

This work reports on the pure lithium tantalate (LiTaO3), europium (III)-doped LiTaO3 and magnesium (II)-europium (III)-doped LiTaO3 preparared by the polymeric precursor method, using four different powered samples of Eu3+ ion concentrations 0.1 to 1at %. Structural and optical properties of powders have been studied. The different possible sites occupied by the rare earth were examined. The phase contents and lattice parameters were studied by the Rietveld method and the structural disorder in the LiTaO3 host caused by Eu3+ ions was analyzed. Results indicated LiTaO3 free of secondary phases at 650°C and the photoluminescence (PL) emission spectra showed the characteristic sharp emission bands given by Eu3+ ions when they are excited at a wavelength of 399 nm. An increase of dopants contents caused a non-homogeneous broadening and showed a slightly larger one when Mg was added. A displacement of the transition 5D0-7F0 to shorter wavelengths as function of Eu3+ concentration was also noticed.

Síntese e caracterização de híbridos orgânico-inorgânicos luminescentes para aplicação em ensaios biológicos

Pós-graduação em Química - IBILCE

Aplicação do '[RuCl IND. 3(DPPB)H IND.2 O] na obtenção do complexos mono e binucleares

Pós-graduação em Química - IQ