Purification, crystallization and preliminary X-ray diffraction analysis of a class P-III metalloproteinase (BmMP-III) from the venom of Bothrops moojeni

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for heavy lepton partners of neutrinos in proton-proton collisions in the context of the type III seesaw mechanism

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Photo-Fenton degradation of the herbicide tebuthiuron under solar irradiation: Iron complexation and initial intermediates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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.

Structure of magnetic poly(oxyethylene)-siloxane nanohybrids doped with Fe-II and Fe-III

Hybrid organic - inorganic nanocomposites doped with Fe-II and Fe-III ions and exhibiting interesting magnetic properties have been obtained by the sol - gel process. The hybrid matrix of these ormosils ( organically modified silicates), classed as di-ureasils and termed U( 2000), is composed of poly( oxyethylene) chains of variable length grafted to siloxane groups by means of urea crosslinkages. Iron perchlorate and iron nitrate were incorporated in the diureasil matrices, leading to compositions within the range 80 greater than or equal to n greater than or equal to 10, n being the molar ratio of ether-type O atoms per cation. The structure of the doped diureasils was investigated by small-angle X-ray scattering (SAXS). For Fe-II-doped samples, SAXS results suggest the existence of a two-level hierarchical structure. The primary level is composed of spatially correlated siloxane clusters embedded in the polymeric matrix and the secondary, coarser level consists of domains where the siloxane clusters are segregated. The structure of Fe-III-doped hybrids is different, revealing the existence of iron oxide based nanoclusters, identified as ferrihydrite by wide-angle X-ray diffraction, dispersed in the hybrid matrix. The magnetic susceptibility of these materials was determined by zero-field-cooling and field-cooling procedures as functions of both temperature and field. The different magnetic features between Fe-II- and Fe-III-doped samples are consistent with the structural differences revealed by SAXS. While Fe-II-doped composites exhibit a paramagnetic Curie-type behaviour, hybrids containing Fe-III ions show thermal and field irreversibilities.

THERMAL ANALYSES OF COORDINATION-COMPOUNDS .2. THERMAL-DECOMPOSITION OF PALLADIUM COMPLEXES WITH TRIPHENYLPHOSPHINE, TRIPHENYLARSINE AND TRIPHENYLSTIBINE

The compounds [PdCl(2)L(2)] and [PdL(4)] (L=PPh(3), AsPh(3), SbPh(3)) were studied by thermogravimetric and differential thermal analyses in air. The residues of thermal decomposition consist of metallic palladium, except in the case of the complexes containing SbPh(3), when the residues are palladium and antimony mixtures in appropriate proportions with respect to the stoichiometry of the related complexes.

Organic complexation and translocation of ferric iron in podzols of the Negro River watershed. Separation of secondary Fe species from Al species

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrochemistry of organometallic compounds. Part IV. Oxidations of benzylic derivatives and p-substituted benzylic derivatives of bis(dimethylglyoximato) and bis(salicylaldehyde)o-phenylenediimine cobalt(III) in dimethylformamide

The electrochemical oxidation of some p-substituted benzylic derivatives of Co(III) dimethylglyoximato and Co(III)bis(salicylaldehydc)o-phenylenediimine in dimethylformamide. 0.2 M in tetraethyammonium perchlorate, on a platinum electrode, at several temperatures, is described as an ECE type, the first electrochemical step being a quasi-reversible one-electron charge transfer at room temperature. At temperatures around -20°C, or lower, the influence of the irreversible chemical decomposition of the oxidized species, via a solvent or other nucleophilic-assisted reaction, is negligible. It is suggested that at low temperatures the oxidation to the formally CoIV-R species is followed by an isomerization reaction in which this complex is partially transformed in a CoIII-(R) species or a s π-complex which undergoes an electroreduction at less positive potentials than those corresponding to the reduction of the CoIV-R species. © 1982.

Absorption and emission spectroscopic parameters of Nd3+ and Eu3+ ions in their hexamethylphosphoramide complexes

Syntheses of the following complexes are reported: LnX3·6L, LnX′3·4L, LnX″3·3L and Eu(NCS)3·3L, where Ln = Nd3+, Eu3+; L = hexamethylphosphoramide (hmpa); X = ClO4 -, PF6 -; X′ = NCS-, NO3 -, Br-, ClO4 -; X″=Cl-. Spectra of the complexes of Nd3+ (absorption) and Eu3+ (emission) in dichloromethane solutions were measured. The oscillator strengths of the Nd3+ f-f absorption bands within the 11 000-30 000 cm-1 region were determined and the τλ intensity parameters were obtained according to the Judd-Ofelt formalism. Covalency parameters were also determined for the Nd3+ complexes. The intensities relationship η21 of the 5D0→7F2 and 5D0→7F1 transitions of the Eu3+ was calculated. A good correlation between τ2 and the oscillator strength of the hypersensitive band of Nd3+ was found, as well as a correlation between τ2 and η21. There are only qualitative relations between τ2 and the covalency parameter. © 1991.

Synthesis and characterization of ruthenium complexes immobilized on poly(4-vinylpyridine)

The [Ru(NH3)5(H2O)]2+ and trans-[Ru(NH3)4SO2(H2O)]2+ complexes ions were immobilized on poly(4-vinylpyridine) (4-PVP) through reactions in aqueous solutions. The stability of the imobilized complexes was checked in aqueous solution in the pH 2.0-8.0 range. The number of pyridinic nitrogens in the polymer 4-PVP is 2.80±0.05 mmol/g according to nitrogen elemental analysis. Potentiometric titration experiments showed that the accessible nitrogen, in aqueous medium, was 0.94±0.02 mmol/g with a p Ka value of 7.4±0.2. In addition, ruthenium and sulfate analysis has demonstrated that about 15% of the accessible nitrogen sites are able to coordinate to the metal centers. The characterization of the immobilized complexes was made through diffuse electronic and infrared spectroscopies and differential pulse and cyclic voltammetries. © 1993 Plenum Publishing Corporation.

Luminescence and non-radiative processes in lanthanide squarate hydrates

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O) x; x = 8 or 13;Ln3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2K. The luminescence of the squarate group is observed for the Gd3+ and La3+ compounds at low temperatures (below 150K). The Pr3+ compound does not show any emission at all, not even at 4.2K. This is ascribed to the quenching of the Pr3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu3+ and of the 5D4 emission of Tb3+ in these squarate complexes are strikingly different. Whereas the Tb3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2K upon ligand excitation. This quenching is ascribed to the low energy position of the charge-transfer state of Eu3+ in these compounds.

Study of Hybrid Silica-Polyethyleneglycol Xerogels by Eu3+ Luminescence Spectroscopy

Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.

Room-temperature photoluminescence in amorphous SrTiO3-The influence of acceptor-type dopants

Room-temperature photoluminescence (PL) was observed in undoped and 2 mol% Cr-, Al- and Y-doped amorphous SrTiO3 thin films. Doping increased the PL, and in the case of Cr significantly reduced the associated PL wavelength. The optical bandgaps, calculated by means of UV-vis absorption spectra, increased with crystallinity and decreased with the doping level. It was considered that yttrium and aluminum substituted Sr2+, whereas chromium replaced Ti4+. It is believed that luminescence centers are oxygen-deficient BO6 complexes, or the same centers with some other defects, such as oxygen or strontium vacancies, or BO6 complexes with some other defects placed in their neighborhood. The character of excitation and the competition for negatively charged non-bridging oxygen (NBO) among numerous types of BO6 defect complexes in doped SrTiO3 results in various broadband luminescence peak positions. The results herein reported are an indicative that amorphous titanates are sensitive to doping, which is important for the control of the electro-optic properties of these materials. The probable incorporation of Cr into the Ti site suggests that the existence of a double network former can lead to materials displaying a more intense photoluminescence.

Thermal study of nickel(II) pyrazolyl complexes

The thermal behavior of the pyrazolyl complexes [NiCl2(HPz) 4] (1), [Ni(NCS)2(HPz)4] (2), [NiCl 2(HdmPz)4]·2H2O (3) and [Ni(NCS) 2(HdmPz)4]·2H2O (4) (HPz=pyrazole, HdmPz=3,5-dimethylpyrazole) has been studied by thermogravimetry (TG) and differential thermal analysis (DTA). The TG data indicated that the thermal stability of [NiX2(HL)4] (X=Cl, NCS) compounds varies depending on the pyrazolyl ligand in the following order HL=HPz>HdmPz. From the thermal decomposition of 3 and 4 it was possible to isolate the intermediate compounds [Ni(μ-Cl)2(HdmPz)2] (3a) and [Ni(μ-1,3-NCS) 2(HdmPz)2] (4a), respectively. The final products of the thermal decompositions of 1-4 were identified as NiO by X-ray powder diffraction. © 2005 Akadémiai Kiadó, Budapest.

Study of a series of cobalt(II) sulfonamide complexes: Synthesis, spectroscopic characterization, and microbiological evaluation against M. tuberculosis. Crystal structure of [Co(sulfamethoxazole)2(H 2O)2]·H2O

Nowadays, the research for new and better antimicrobial compounds is an important field due to the increase of immunocompromised patients, the use of invasive medical procedures and extensive surgeries, among others, that can affect the incidence of infections. Another big problem associated is the occurrence of drug-resistant microbial strains that impels a ceaseless search for new antimicrobial agents. In this context, a series of heterocyclic- sulfonamide complexes with Co(II) was synthesized and characterized with the aim of obtaining new antimicrobial compounds. The structural characterization was performed using different spectroscopic methods (UV-Vis, IR, and EPR). In spite of the fact that the general stoichiometry for all the complexes was Co(sulfonamide)2·nH2O, the coordination atoms were different depending on the coordinated sulfonamide. The crystal structure of [Co(sulfamethoxazole)2(H2O)2]·H 2O was obtained by X-ray diffraction showing that Co(II) is in a slightly tetragonal distorted octahedron where sulfamethoxazole molecules act as a head-to-tail bridges between two cobalt atoms, forming polymeric chains. Besides, the activity against Mycobacterium tuberculosis, one of the responsible for tuberculosis, and the cytotoxicity on J774A.1 macrophage cells were evaluated. © 2012 Elsevier B.V. All rights reserved.