Ana Cristina Figueiredo de Melo Costa

Helicobacter pylori induces gastric epithelial cell invasion in a c-Met and type IV secretion system-dependent manner

Helicobacter pylori interacts with gastric epithelial cells, activating signaling pathways important for carcinogenesis. In this study we examined the role of H. pylori on cell invasion and the molecular mechanisms underlying this process. The relevance of H. pylori cag pathogenicity island-encoded type IV secretion system (T4SS), CagA, and VacA for cell invasion was also investigated. We found that H. pylori induces AGS cell invasion in collagen type I and in Matrigel invasion assays. H. pylori-induced cell invasion requires the direct contact between bacteria and cancer cells. H. pylori-mediated cell invasion was dependent on the activation of the c-Met receptor and on increased MMP-2 and MMP-9 activity. The abrogation of the c-Met receptor using the specific NK4 inhibitor or the silencing of c-Met expression with small interference RNA suppressed both cell invasion and MMP activity. Studies with different H. pylori strains revealed that cell invasion, c-Met tyrosine phosphorylation, and increased MMP-2 and MMP-9 activity were all dependent on the presence of a functional bacterial T4SS, but not on VacA cytotoxicity. Our findings demonstrate that H. pylori strains with a functional T4SS stimulate gastric epithelial cell invasion through a c-Met-dependent signaling pathway that comprises an increase in MMP-2 and MMP-9 activity.

Pathogenesis ofHelicobacter pyloriInfection

Helicobacter pylori induces chronic inflammation of the gastric mucosa, but only a proportion of infected individuals develop peptic ulcer disease or gastric carcinoma. Reasons underlying these observations include differences in bacterial pathogenicity as well as in host susceptibility. Numerous studies published in the last year provided new insight into H. pylori virulence factors, their interaction with the host and consequences in pathogenesis. These include the role of bacterial genetic diversity in host colonization and persistence, outer membrane proteins and modulation of adhesin expression, new aspects of VacA functions, and CagA and its phosphorylation‐dependent and ‐independent cellular effects. This article will also review the recent novel findings on the interactions of H. pylori with diverse host epithelial signaling pathways and events involved in the initiation of carcinogenesis, including genetic instability and dysregulation of DNA repair.

Sintering of Ni-Zn ferrite nanopowders by the constant heating rate (CHR) method

The constant heating rate method employed in sintering studies offers several advantages over the isothermal method, particularly the fact that all the parameters that describe the sintering phenomena can be obtained from a single sample. The purpose of this work is to determine the parameters of sintering kinetics of nanosized Ni-Zn ferrite powders synthesized by combustion reaction. The nonisothermal sintering method was studied using a constant heating rate (CHR). The Ni-Zn ferrite powders, with average particle size varying from 18 nm to 29 nm, were uniaxially pressed and sintered in an horizontal dilatometer at a constant heating rate of 5.0 °C/min from 600 °C up to complete densification, which was reached at 1200 °C. The compacts were characterized by scanning electron microscopy (SEM). Experimental results revealed three different sintering stages, which were identified through the Bannister Theory. The shrinkage and the shrinkage rate analyzed showed a viscous contribution in the initial sintering stage, which was attributed to the mechanism of structural nanoparticle rearrangement.

Síntese e caracterização de nanopartículas de TiO2

Several methods of chemical synthesis have been developed and used to obtain powder for production of ceramic membranes. Amongst the alternative methods used in laboratory scale, the Pechini method has been used successfully for the preparation of several types of materials. The objective of this work is to synthesize and characterize TiO2 powders obtained by this method, aiming the preparation of ultra-filtration ceramic membranes. The powder has been characterized by gravimetric and differential thermal analysis, X-ray diffraction, infrared spectroscopy, nitrogen adsorption by BET, and scanning electron microscopy. The X-ray diffraction of the powders showed the presence of the anatase crystalline phase, with crystallite size 15 nm. The particle size calculated from the surface area was 19 nm and the powder morphology shows the presence of soft agglomerates. These results evidence that the Pechini method is interesting for the production of nanometric TiO2 appropriate for ceramic membranes preparation.

Use of Ni-Zn ferrites doped with Cu as catalyst in the transesterification of soybean oil to methyl esters

The purpose of this work is to evaluate the performance of Ni0.5Zn0.5Fe2O4 ferrite doped with 0.1 and 0.4 mol of Cu as a catalyst for the transesterification of soybean oil to biodiesel, using methanol. The samples were characterized by X-ray diffraction, nitrogen adsorption and scanning electron microscopy. The reaction was performed for 2 hours at a temperature of 160 °C, using 10 g of soybean oil, a molar ratio of oil: alcohol of 1:20, and 4% (w/w) of catalyst. The product of the reaction was characterized by gas chromatography, which confirmed conversion to methyl esters. The diffraction patterns showed the presence only of Ni0.5Zn0.5Fe2O4 ferrite phase with a crystallite size of 29 nm. The samples doped with 0.1 and 0.4 mol of Cu showed a surface area and particle size of 22.17 m2g - 1 and 50.47 nm; and 23.49 m2g - 1 and 47.64 nm, respectively. The morphology of both samples consisted of brittle block-shaped agglomerates with a wide particle size distribution. A comparative analysis of the two catalysts indicated that the catalyst doped with 0.4 mol of Cu showed the better performance, with a conversion rate of 50.25%, while the catalyst doped with 0.1 mol of Cu showed 42.71% conversion.

Preparation and Characterization of Spinel MCr2O4 (M = Zn, Co, Cu and Ni) by Combustion Reaction

The ceramic industry applies many natural and synthetic pigments as coloring agents in glasses, enamels and unglazed bodies. The purpose of the present work was to prepare a series of chromium spinels MCr2O4 (M = Zn, Co, Cu and Ni) by combustion reaction, using urea as fuel and characterizing the resulting powders. The compositions were prepared by a single step solution combustion reaction using nitrates and urea as fuel. The fired pigments and enameled samples were characterized by X-ray diffraction, BET, scanning electron microscopy (SEM), UV-VIS-NIR spectroscopy, and CIE-L*a*b* color-measurements. The results demonstrated that synthesis by the combustion reaction was very fast and safe, resulting in crystalline spinel with nanoparticles in all the compositions under study. The pigments obtained by combustion reaction displayed better solubility in the molten glazes than pigments obtained by mechanical mixture of oxide precursors. The results demonstrate the viability of using the powders obtained as ceramic pigments. Introduction Pigments are defined as particulate solids, which may be organic or inorganic, white, black, colored or fluorescent, that are insoluble in the substrate in which they become incorporated and that do not react chemically or physically with this substrate [1, 2]. Pigments should present well defined optical and physical properties. These properties, in turn, depend directly on the pigment’s crystalline structure, on its physical (particle shape, distribution, and degree of agglomeration) and chemical characteristics (purity and stability of the composition). The most important characteristic to be considered in a pigment is its capacity to develop color (its pigmentary capacity) [3]. The control of these properties is closely dependent on obtaining nanometric scale particle sizes, i.e., obtaining molecular structures at the atomic level. The most common form of obtaining pigments is the conventional one of mixing oxides, although several other chemical methods allow one to obtain nanometric material with highly controlled purity and chemical homogeneity. Some of the most wellknown methods are sol-gel [4], micro-emulsion [5], co-precipitation [6], supersonic radiation [7], Pechini’s method [8], hydrothermal synthesis [9], freeze-drying [10], and combustion synthesis [1113]. Among the aforementioned methods of chemical synthesis, combustion reaction synthesis stands out as an alternative and promising method for obtaining after-ceramics on a nanometric scale. This synthesization method, also known as auto-propagating synthesis, allows for particles to be obtained (without pre-sintering) in sizes in the order of 30nm [14]. Compared to other synthesization methods, the combustion reaction process offers the advantages of being simple, fast, without requiring subsequent intermediary calcination stages, and consuming less energy during the synthesis [11]. Moreover, using the non-conventional method of combustion reaction results in the synthesis of highly pure, chemically homogeneous powders, which usually generate products with the desired structures and composition due to the high homogeneity aided by the solubility of the salts in water, allowing Journal of Metastable and Nanocrystalline Materials Vols. 20-21 (2004) pp 325-332 online at http://www.scientific.net

Microestrutura e propriedades magnéticas de ferritas Ni-Zn-Sm

Nanosize powders of Ni-Zn-Sm ferrites were synthesized by combustion reaction using urea as fuel. The influence of the additio n of the rare-earth ion samarium on the, microstructure, relative density and magnetic properties of the Ni 0.5Zn0.5Fe2-xSmxO4 ferrite with x = 0.0; 0.05; 0.075 and 0.1% mol of Sm 3+ was studied. The samples were uniaxially compacted by dry pressing and sintered at 1200 oC for 2 h with heating rate of 5 oC/min. Apparent density, relative density, XRD, SEM and magnetic hysteresis loop tracer were used for analyzing the samples. The addition of Sm 3+ altered the characteristics of the powders in an advantageous way and increased the relative density and decrease grain size of the of the samples after sintering at 1200 oC/2h. It was found that the samples have sintered density to about 95.4 – 100% of the corresponding theoretical density, microstructure with grain size to

Evaluation of the Cu Doping Effects in CeO2 Catalytic Supports Obtained by Combustion Reaction

This work has for aim to synthesize CeO2 catalytic supports doped with Cu2+ by combustion reaction method. Thus were obtained catalytic supports with the composition Ce1-xCuxO2 and the effect caused by doped element in the structure of the CeO2 was evaluated. The concentration value (x) of the Cu doped took over the values of 0.0; 0.3 and 0.5 mol. The catalytic supports developed were submitted to the structural characterization by X-ray diffraction, morphologic analysis by SEM and textural analysis by means of adsorption-dessorption of N2 by BET method. The results showed that the doped element (Cu) was not completely incorporated in the CeO2 structure and was evidenced that how much larger the quantity of Cu larger maid the disorder of the atomic structure of the obtained material. The analyzed supports present mesoporous nature structure.

Influence of Fuel in the Synthesis of ZnAl2O4 Catalytic Supports by Combustion Reaction

The aim of this work is to evaluate the influence of fuel in the synthesis of ZnAl2O4 catalytic supports by combustion reaction. For this, it was used the fuels: urea, carbohidrazide, glycine and aniline. The total amount of reagents was calculated according to the theory of propellants and explosive using urea in the stoichiometric proportion (Φe = 1). The structural and morphological characteristics of the powders were evaluated by XRD, FTIR, TEM, SEM and particle size distribution. The results from XRD showed the formation of the normal cubic spinel structure. The powders presented nanosized particles with narrow agglomerates size distribution. The powders prepared with urea showed better value of surface area and smaller crystallite size.

Evaluation of Catalyst Ni0.4Cu0.1Zn0.5Fe2O4 on Methyl Esterification of Free Fatty Acid Present in Cottonseed Oil

This study aimed to assess the performance of the solid catalyst Ni0.4Cu0.1Zn0.5Fe2O4, synthesized by combustion reaction, over the methyl esterification reaction of the fatty acids present in cottonseed oil. The catalyst was characterized by XRD, FTIR pyridine absorption, Raman spectroscopy, and SEM. The reactions were conducted at 140 and 180°C with molar ratios of 1:3, 1:6 and 1:9, with 2% of catalyst and reaction time of 2 h. The XRD results showed that the single phase ferrite was obtained with surface area of 87 m2/g and with mesoporous characteristic. It was observed from the FTIR pyridine absorption only the presence of Lewis acid sites. The Raman spectra confirm the presence of the inverse spinel phase. The results indicated that at 180°C and molar ratio of 1:9, the conversion of free fatty acids was about 87%.