Study of soils by thermal analysis

The study of soils is very important in the geological and geological engineering researches. A study of ten samples of soils was carried out by thermal analysis, and X-Ray Fluorescence Spectrometry to understand soil evolution in Angra dos Reis region, Rio de Janeiro State, Brazil. The sample collection sites were chosen based on geological characteristics, the soil layer thickness, the soil composition pattern, and whether or not it was moved either by erosion or by gravitational shifts. Because of the humid tropical climatic condition, natural soils tend to show great thickness of weathered mantles with formation of saprolites and saprolite soils. Kaolinite is an important secondary mineral which can be formed from many different minerals, like k-mica and k-feldspar and can be weathered to gibbsite. The results from TG/DTG and DTA indicated which soils had more weathering, and the same results were obtained by XRF, when silica/aluminum ratios from samples are compared with thermal analysis results.

Quorum sensing detected by atomic force microscopy imaging of corrals surrounding multicellular arrangement of bacteria

Connectivity of the glycocalyx covering of small communities of Acidithiobacillus ferrooxidans bacteria deposited on hydrophilic mica plates was imaged by atomic force microscopy. When part of the coverage was removed by water rinsing, an insoluble structure formed by corrals surrounding each individual bacterium was observed. A collective ring structure with clustered bacteria (>= 3) was observed, which indicates that the bacteria perceived the neighborhood in order to grow a protective structure that results in smaller production of exopolysaccharides material. The most surprising aspect of these collective corral structures was that they occur at a low bacterial cell density. The deposited layers were also analyzed by confocal Raman microscopy and shown to contain polysaccharides, protein, and glucoronic acid.

Effect of a highly concentrated lipopeptide extract of Bacillus subtilis on fungal and bacterial cells

Lipopeptides produced by Bacillus subtilis are known for their high antifungal activity. The aim of this paper is to show that at high concentration they can damage the surface ultra-structure of bacterial cells. A lipopeptide extract containing iturin and surfactin (5 mg mL-1) was prepared after isolation from B. subtilis (strain OG) by solid phase extraction. Analysis by atomic force microscope (AFM) showed that upon evaporation, lipopeptides form large aggregates (0.1-0.2 mu m2) on the substrates silicon and mica. When the same solution is incubated with fungi and bacteria and the system is allowed to evaporate, dramatic changes are observed on the cells. AFM micrographs show disintegration of the hyphae of Phomopsis phaseoli and the cell walls of Xanthomonas campestris and X. axonopodis. Collapses to fungal and bacterial cells may be a result of formation of pores triggered by micelles and lamellar structures, which are formed above the critical micelar concentration of lipopeptides. As observed for P. phaseoli, the process involves binding, solubilization, and formation of novel structures in which cell wall components are solubilized within lipopeptide vesicles. This is the first report presenting evidences that vesicles of uncharged and negatively charged lipopeptides can alter the morphology of gram-negative bacteria.

Dibucaine effects on structural and elastic properties of lipid bilayers

In this work we report the interaction effects of the local anesthetic dibucaine (DBC) with lipid patches in model membranes by Atomic Force Microscopy (AFM). Supported lipid bilayers (egg phosphatidylcholine, EPC and dimyristoylphosphatidylcholine, DMPQ were prepared by fusion of unilamellar vesicles on mica and imaged in aqueous media. The AFM images show irregularly distributed and sized EPC patches on mica. On the other hand DMPC formation presents extensive bilayer regions on top of which multibilayer patches are formed. In the presence of DBC we observed a progressive disruption of these patches, but for DMPC bilayers this process occurred more slowly than for EPC. In both cases, phase images show the formation of small structures on the bilayer surface suggesting an effect on the elastic properties of the bilayers when DBC is present. Dynamic surface tension and dilatational surface elasticity measurements of EPC and DMPC monolayers in the presence of DBC by the pendant drop technique were also performed, in order to elucidate these results. The curve of lipid monolayer elasticity versus DBC concentration, for both EPC and DMPC cases, shows a maximum for the surface elasticity modulus at the same concentration where we observed the disruption of the bilayer by AFM. Our results suggest that changes in the local curvature of the bilayer induced by DBC could explain the anesthetic action in membranes. (C) 2008 Elsevier B.V. All rights reserved.

Neoformation of micas in soils surrounding an alkaline-saline lake of Pantanal wetland, Brazil

The mineralogy and origin of micas were investigated in incipient soils surrounding a modem alkaline-saline lake of Nhecolandia, a sub-region of Pantanal wetland. Soils were sampled along a toposequence and analyzed by XRD, TEM-EDS, and ICP-MS. The studied micas, mainly concentrated in a green horizon, are dioctahedral, strongly associated with Fe(3+) and Al, and interstratified with smectite layers. Classification of individual crystals shows that glauconite and Fe-illite are the dominant micas, but one crystal of illite was recognized. Si-rich amorphous materials are associated with small crystallites in the mica-enriched horizon. A recent study shows that water samples from the studied lake and the surrounding water table have high pH, negative Eh, temperatures up to 40 C. high concentration of K. and low concentration of Si(OH)(4). Experimental studies of micas synthesis reported in the literature show that similar water conditions allow for dioctahedral mica crystallization from initial precipitation of amorphous hydroxides. Therefore, water characteristics combined with presence of Si-rich amorphous materials in the mica-enriched horizon suggest that the micas of the study area are neoformed. The alternated origin of illite, glauconite, and Fe-illite mixed-layer minerals probably occurs due to seasonal variations of pH. temperature, and chemical composition of waters in microenvironments, since the changes at this scale are possibly faster and more extreme. (C) 2010 Elsevier B.V. All rights reserved.

Soil mineral genesis and distribution in a saline lake landscape of the Pantanal Wetland, Brazil

The origin of the saline lakes in the Pantanal wetland has been classically attributed to processes occurring in past periods. However, recent studies have suggested that saline water is currently forming from evaporative concentration of fresh water, which is provided annually by seasonal floods. Major elements (Ca, Mg, K) and alkalinity appear to be geochemically controlled during the concentration of waters and may be involved in the formation of carbonates and clay minerals around the saline lakes. The mineralogy of soils associated with a representative saline lake was investigated using XRD, TEM-EDS, and ICP-MS in order to identify the composition and genesis of the secondary minerals suspected to be involved in the control of major elements. The results showed that Ca, Mg, and K effectively undergo oversaturation and precipitation as the waters become more saline. These elements are incorporated in the authigenically formed carbonates, smectites, and micas surrounding the saline lake. The control of Ca occurs by precipitation of calcite and dolomite in nodules while Mg and K are mainly involved in the neoformation of Mg-smectites (stevensitic and saponitic minerals) and, probably, iron-enriched micas (ferric-illite) in surface and subsurface horizons. Therefore, our study confirms that the salinity of Pantanal, historically attributed to inheritance from former regimes, has a contribution of current processes. (C) 2009 Elsevier B.V. All rights reserved.

MINERALOGY AND GENESIS OF SMECTITES IN AN ALKALINE-SALINE ENVIRONMENT OF PANTANAL WETLAND, BRAZIL

Smectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolandia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation. Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA. The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REE contents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.

Antibody-mediated rejection (AMR) after pancreas and pancreas-kidney transplantation

P>Antibody-mediated rejection (AMR) requires specific diagnostic tools and treatment and is associated with lower graft survival. We prospectively screened C4d in pancreas (n = 35, in 27 patients) and kidney (n = 33, in 21 patients) for cause biopsies. Serum amylase and lipase, amylasuria, fasting blood glucose (FBG) and 2-h capillary glucose (CG) were also analysed. We found that 27.3% of kidney biopsies and 43% of pancreatic biopsies showed C4d staining (66.7% and 53.3% diffuse in peritubular and interacinar capillaries respectively). Isolated exocrine dysfunction was the main indication for pancreas biopsy (54.3%) and was followed by both exocrine and endocrine dysfunctions (37.1%) and isolated endocrine dysfunction (8.6%). Laboratorial parameters were comparable between T-cell mediated rejection and AMR: amylase 151.5 vs. 149 U/l (P = 0.075), lipase 1120 vs. 1288.5 U/l (P = 0.83), amylasuria variation 46.5 vs. 61% (P = 0.97), FBG 69 vs. 97 mg/dl (P = 0.20) and 2-h CG maximum 149.5 vs. 197.5 mg/dl (P = 0.49) respectively. Amylasuria values after treatment correlated with pancreas allograft loss (P = 0.015). These data suggest that C4d staining should be routinely investigated when pancreas allograft dysfunction is present because of its high detection rate in cases of rejection.

Anisotropic Reversible Aggregation of Latex Nanoparticles Suspended in a Lyotropic Nematic Liquid Crystal: Effect of Gradients of Biaxial Order

We studied the anisotropic aggregation of spherical latex particles dispersed in a lyotropic liquid crystal presenting three nematic phases; calamitic, biaxial, and discotic. We observed that in the nematic calamitic phase aggregates of latex particles are formed, which become larger and anisotropic in the vicinity of the transition to the discotic phase, due to a coalescence process. Such aggregates are weakly anisotropic and up to 50 mu m long and tend to align parallel to the director field. At the transition to the discotic phase, the aggregates dissociated and re-formed when the system was brought back to the calamitic phase. This shows that the aggregation is due to attractive and repulsive forces generated by the particular structure of the nematic phase. The surface-induced positional order was investigated by surface force apparatus experiments with the lyotropic system confined between mica surfaces, revealing the existence of a presmectic wetting layer around the surfaces and oscillating forces of increasing amplitude as the confinement thickness was decreased. We discuss the possible mechanisms responsible for the reversible aggregation of latex particles, and we propose that capillary condensation of the N(C) phase, induced by the confinement between the particles, could reduce or remove the gradient of order parameter, driving the transition of aggregates from solidlike to liquidlike and gaslike.