Emplacement mechanism of the main granite pluton of the Lavras do Sul intrusive complex, South Brazil, determined by magnetic anisotropies

Magnetic fabric and rock magnetism studies were performed on apparently isotropic granite facies from the main intrusion of the Lavras do Sul Intrusive Complex pluton (LSIC, Rio Grande do Sul, South Brazil). This intrusion is roughly circular (similar to 12 x 13.5 km), composed of alkali-calcic and alkaline granitoids, with the latter occupying the margin of the pluton. Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The two fabrics are coaxial. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect on the AMS fabric of the granites. Several rock-magnetism experiments performed in one specimen from each sampled site show that for all sites the magnetic susceptibility is dominantly carried by ferromagnetic minerals, while mainly magnetite carries the magnetic fabrics. Lineations and foliations in the granite facies were successful determined by applying magnetic methods. Magnetic lineations are gently plunging and roughly parallel to the boundaries of the pluton facies, except at the few sites in the central facies which have a radial orientation pattern. In contrast, the magnetic foliations tend to follow the contacts between the different granite facies. They are gently outerward-dipping inside the pluton, and become either steeply southwesterly dipping or vertical towards its margin. The lack of solid-state and subsolidus deformations at outcrop scale and in thin sections precludes deformation after full crystallization of the pluton. This evidence allows us to interpret the observed magnetic fabrics as primary in origin (magmatic) acquired when the rocks were solidified as a result of processes reflecting magma flow. The foliation pattern displays a dome-shaped form for the main LSIC-pluton. However, the alkaline granites which outcrop in the southern part of the studied area have an inward-dipping foliation, and the steeply plunging magnetic lineation suggests that this area could be part of a feeder zone. The magma ascent probably occurred due to ring-diking. (C) 2008 Elsevier B.V. All rights reserved.

The role in the substrate specificity and catalysis of residues forming the substrate aglycone-binding site of a beta-glycosidase

The relative contributions to the specificity and catalysis of aglycone, of residues E190, E194, K201 and M453 that form the aglycone-binding site of a beta-glycosidase from Spodoptera frugiperda (EC 3.2.1.21), were investigated through site-directed mutagenesis and enzyme kinetic experiments. The results showed that E190 favors the binding of the initial portion of alkyl-type aglycones (up to the sixth methylene group) and also the first glucose unit of oligosaccharidic aglycones, whereas a balance between interactions with E194 and K201 determines the preference for glucose units versus alkyl moieties. E194 favors the binding of alkyl moieties, whereas K201 is more relevant for the binding of glucose units, in spite of its favorable interaction with alkyl moieties. The three residues E190, E194 and K201 reduce the affinity for phenyl moieties. In addition, M453 favors the binding of the second glucose unit of oligosaccharidic aglycones and also of the initial portion of alkyl-type aglycones. None of the residues investigated interacted with the terminal portion of alkyl-type aglycones. It was also demonstrated that E190, E194, K201 and M453 similarly contribute to stabilize ES double dagger. Their interactions with aglycone are individually weaker than those formed by residues interacting with glycone, but their joint catalytic effects are similar. Finally, these interactions with aglycone do not influence glycone binding.

La(2-x)Ce(x)Cu(1-y)Zn(y)O(4) perovskites for high temperature water-gas shift reaction

The performance of La(2-x)Ce(x)Cu(1-y)Zn(y)O(4) perovskites as catalysts for the high temperature water-gas shift reaction (H T-W G S R) was investigated. The catalysts were characterized by EDS, XRD, BET surface area, TPR, and XANES. The results showed that all the perovskites exhibited the La(2)CuO(4) orthorhombic structure, so the Pechini method is suitable for the preparation of pure perovskite. However, the La(1.90)Ce(0.10)CuO(4) perovskite alone, when calcined at 350/700 degrees C, also showed a (La(0.935)Ce(0.065))(2)CuO(4) perovskite with tetragonal structure, which produced a surface area higher than the other perovskites. The perovskites that exhibited the best catalytic performance were those calcined at 350/700 degrees C and, among these, La(1.90)Ce(0.10)CuO(4) was outstanding, probably because of the high surface area associated with the presence of the (La(0.935)Ce(0.065))(2)CuO(4) perovskite with tetragonal structure and orthorhombic La(2)CuO(4) phase.

CO preferential oxidation (CO-PROx) on La(1-x)Ce(x)NiO(3) perovskites

La(1-x)Ce(x)NiO(3) perovskites have been prepared, characterized by XRD. TPR and surface area and tested as catalysts for CO-PROx, with a feed of 2.5% CO, 5% O(2), 33% H(2) and N(2) to 100%. The samples exhibited an XRD pattern typical of the perovskite, with traces of NiO in the LaNiO(3) and La(0.95)Ce(0.05)NiO(3) samples, with some La(2)NiO(4) in the La(0.90)Ce(0.10)NiO(3) sample. All samples were active, but the perovskites with cerium showed good catalytic activity, demonstrating the promoter effect of cerium. The highest conversion of CO and H(2) was obtained with La(0.95)Ce(0.05)NiO(3), probably due to a synergy between Ni and Ce that enhanced O(2) mobility. (c) 2010 Elsevier B.V. All rights reserved.

Study of Water-Gas-Shift Reaction over La((1-y))Sr(y)Ni(x)Co((1-x))O(3) Perovskite as Precursors

The performance of La((1-y))Sr(y)Ni(x)Co((1-x))O(3) perovskites for the water gas shift reaction (WGSR) was investigated. The samples were prepared by the co- precipitation method and were performed by the BET method, XRD, TPR, and XPS. The catalytic tests were performed at 300 and 400 A degrees C and H(2)O(v)/CO = 2.3/1 (molar ratio). The sample with the highest surface area is La(0.70)Sr(0.30)NiO(3). The XRD results showed the formation of perovskite structure for all samples, and the La(0.70)Sr(0.30)NiO(3) sample also presented peaks corresponding to La(2)NiO(4) and NiO, indicating that the solubility limit of Sr in the perovskite lattice was surpassed. The replacement of Co by Ni favored the reduction of the species at lower temperatures, and the sample containing Sr presented the highest amount of reducible species, as identified by TPR results. All samples were active, the Sr containing perovskite appearing the most active due to the highest surface area, presence of the La(2)NiO(4) phase, and higher content of Cu in the surface, as detected by XPS. Among the samples containing Co, the most active one was that with x = 0.70 (60% of CO conversion).