Histological aspects and structural characteristics of the testes of Dendropsophus minutus (Anura, Hylidae)

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

Characterization and oxygen binding properties of des-Arg human hemoglobin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Intermolecular interactions and characterization of the novel factor Xa exosite involved in macromolecular recognition and inhibition: Crystal structure of human Gla-domainless factor Xa complexed with the anticoagulant protein NAPc2 from the hematophagous nematode Ancylostoma caninum

NAPc2, an anticoagulant protein from the hematophagous nematode Ancylostoma caninum evaluated in phase-II/IIa clinical trials, inhibits the extrinsic blood coagulation pathway by a two step mechanism, initially interacting with the hitherto uncharacterized factor Xa exosite involved in macromolecular recognition and subsequently inhibiting factor VIIa (K-i = 8.4 pM) of the factor VIIa/tissue factor complex. NAPc2 is highly flexible, becoming partially ordered and undergoing significant structural changes in the C terminus upon binding to the factor Xa exosite. In the crystal structure of the ternary factor Xa/NAPc2/selectide complex, the binding interface consists of an intermolecular antiparallel beta-sheet formed by the segment of the polypeptide chain consisting of residues 74-80 of NAPc2 with the residues 86-93 of factor Xa that is additional maintained by contacts between the short helical segment (residues 67-73) and a turn (residues 26-29) of NAPc2 with the short C-terminal helix of factor Xa (residues 233-243). This exosite is physiologically highly relevant for the recognition and inhibition of factor X/Xa by macromolecular substrates and provides a structural motif for the development of a new class of inhibitors for the treatment of deep vein thrombosis and angioplasty. (c) 2006 Elsevier Ltd. All rights reserved.

Crystallographic and spectroscopic characterization of a molecular hinge: Conformational changes in bothropstoxin I, a dimeric Lys49 phospholipase A2 homologue

Bothropstoxin I(BthTX-I) from the venom of Bothrops jararacussu is a myotoxic phospholipase A2 (PLA2) homologue which, although catalytically inactive due to an Asp49-->Lys substitution, disrupts the integrity of lipid membranes by a Ca2+-independent mechanism, the crystal structures of two dimeric farms of BthLTX-I which diffract X-rays eo resolutions of 3.1 and 2.1 Angstrom have been determined, the monomers in both structures are related by an almost perfect twofold axis of rotation and the dimer interfaces are defined by contacts between the N-terminal alpha-helical regions and the tips of the beta-wings of partner monomers. Significant differences in the relative orientation of the monomers in the two crystal forms results in open and closed dimer conformations, Spectroscopic Investigations of BthTX-I in solution have correlated these conformational differences with changes in the intrinsic fluorescence emission of the single tryptophan residues located at the dimer interface, the possible relevance of this structural transition in the Ca2+-independent membrane damaging activity is discussed. (C) 1998 Wiley-Liss, Inc.

NiTiO3 powders obtained by polymeric precursor method: Synthesis and characterization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparation and characterization of new glassy system As2P2S8-Ga2S3

Glasses having the composition (100 - x)As2P2S8-xGa(2)S(3) with x ranging from 0 to 50% were investigated to determine the compositional effect on properties and local structure. The glass transition temperature (T-g) and the stability parameter against crystallization (T-x - T-g) increased with the addition of Ga2S3. The structure of these glasses was probed by Raman scattering, Fourier transform infrared (FT-IR) and P-31 nuclear magnetic resonance. on the basis of the observed vibrations and the strength of the P-31-P-31 homonuclear magnetic dipolar coupling, two scenarios can be proposed for the structural evolution induced by the addition of Ga2S3. For x <= 20% we may have the formation of GaS4E- groups (E = nonbonding electron), and for x >= 30% we have depolymerization of the As2P2S8 units and the formation of a network of GaPS4 units with each PS4/2 unit (Q(4)) species carrying a single positive formal charge.

Synthesis, characterization and photophysical properties of Eu3+ doped in BaMoO4

In this work Ba0.99Eu0.01MoO4 (BEMO) powders were prepared by the first time by the Complex Polymerization Method. The structural and optical properties of the BEMO powders were characterized by Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Raman Spectra, High-Resolution Scanning Electron Microscopy (HR-SEM) and Photoluminescent Measurements. XRD show a crystalline scheelite-type phase after the heat treatment at temperatures greater than 400 degrees C. The ionic radius of Eu3+ (0.109 nm) is lower than the Ba2+ (0.149 nm) one. This difference is responsible for the decrease in the lattice parameters of the BEMO compared to the pure BaMoO4 matrix. This little difference in the lattice parameters show that Eu3+ is expected to occupy the Ba2+ site at different temperatures, stayed the tetragonal (S-4) symmetry characteristic of scheelite-type crystalline structures of BaMoO4. The emission spectra of the samples, when excited at 394 nm, presented the D-5(1)-> F-7(0, 1 and 2) and D-5(0)-> F-7(0, 1, 2, 3 and 4) Eu3+ transitions at 523, 533, 554, 578, 589, 614, 652 and 699 nm, respectively. The emission spectra of the powders heat-treated at 800 and 900 degrees C showed a marked increase in its intensities compared to the materials heat-treated from 400 to 700 C. The decay times for the sample were evaluated and all of them presented the average value of 0.61 ms. Eu3+ luminescence decay time follows one exponential curve indicating the presence of only one type of Eu3+ symmetry site.

Effect of heat treatment on the generation of structural defects in LaTaO4 ceramics and their correlation with photoluminescent properties

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

Karyotypic characterization of Prochilodus mariae, Semaprochilodus kneri and S. laticeps(Teleostei: Prochilodontidae) from Caicara del Orinoco, Venezuela

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

Characterization of ndh gene of isoniazid resistant and susceptible Mycobacterium tuberculosis isolates from Brazil

Resistance in Mycobacterium tuberculosis to isoniazid (INH) is caused by mutations in the catalase-peroxidase gene (katG) , and within the inhA promoter and/or in structural gene. A small percentage (~ 10%) of INH-resistant strains do not present mutations in both of these loci. Other genes have been associated with INH resistance including the gene encoding for NADH dehydrogenase (ndh) . Here we report the detection of two ndh locus mutations (CGT to TGT change in codon 13 and GTG to GCG change in codon 18) by analyzing 23 INH-resistant and in none of 13 susceptible isolates from Brazilian tuberculosis patients. We also detected two isolates without a mutation in ndh, or any of the other INH resistance-associated loci examined, suggesting the existence of additional, as yet to be described, INH resistance mechanisms.

Preparation and characterization of nanocrystalline h-BN films prepared by PECVD method

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

Surface morphology and optical characterization of OC1 OC6-PPV films

We report optical and morphological properties of poly(2-methoxy-5-hexyloxy-p-phenylenevinylene) (OC1OC6-PPV) films processed by casting, spin-coating (SC) and Langmuir-Blodgett (LB) techniques. The absorption spectra are practically the same, with an absorption maximum at approximately at 500 nm. For the photoluminescence (PL) spectra at low temperature (T=10K), a small but significant difference was noted in the cast film, in comparison with the LB and SC films. The zero-phonon transition shifted from 609 nm for the LB film to 615 and 621 nm for the SC and cast films, respectively. At room temperature, the PL spectra are similar for all films, and blue shifted by ca. 25 nm in comparison with the spectra at low temperature due to thermal disorder. Using atomic force microscopy (AFM) we inferred that the distinctive behavior of the cast film, probably associated with structural defects, is related to the large thickness of this film. The surface roughness, which was surprisingly higher for the LB film, apparently played no role in the emission properties of OC1OC6-PPV films.

Purification, partial characterization and preliminary X-ray diffraction analysis of a mannose-specific lectin from Cymbosema roseum seeds

A lectin from Cymbosema roseum seeds (CRL) was purified, characterized and crystallized. The best crystals grew in a month and were obtained by the vapour-diffusion method using a precipitant solution consisting of 0.1 M Tris-HCl pH 7.8, 8% (w/v) PEG 3350 and 0.2 M proline at a constant temperature of 293 K. A data set was collected to 1.77 angstrom resolution at a synchrotron-radiation source. CRL crystals are orthorhombic, belonging to space group P2(1)2(1)2(1). Crystallographic refinement and full amino-acid sequence determination are in progress.

Structural and electrical properties of ZnO varistors containing different spinel phases

Structural and electrical properties of ZnO varistors were investigated as a function of spinel composition. Six varistor mixtures differing only in chemical composition of spinel, were prepared by mixing separately synthesized constituent phases (DSCP method). Compositions of constituent phases in sintered samples were investigated by changes of lattice parameters of the phases, as well as by EDS analysis of the constituent phases. It was found that compositions of ZnO, intergranular and spinel phases were partially changed during sintering due to redistribution of additives, that was controlled by starting spinel composition and its stability. Electrical characterization showed significant difference in electrical properties of investigated varistors: nonlinearity coefficients ranging from 22 to 55 and leakage currents differing by the order of magnitude. Activation energies of conduction were obtained from ac impedance spectroscopy measurements. Calculated values of activation energies were in the range 0.61-1.0 eV confirming difference in defect structure of ZnO grain boundaries in varistors containing different spinel phases. (C) 2001 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Optical characterization of cubic AlGaN/GaN quantum wells

Cubic phase group III-nitrides were grown using RF plasma assisted Molecular Beam Epitaxy on GaAs (001) substrates. High-resolution X-ray diffraction, photoluminescence, cathodoluminescence and photoreflectance measurements were employed to characterize the structural and optical properties of GaN/AlxGa1-xN Multi Quantum Well (MQW) structures, in which both Aluminum content and well widths were varied. The observed quantized states are in agreement with first-principles based theoretical calculations.