Ab initio study of SO2 molecules interacting with pristine and transition metal covered fullerenes as a possible route for nanofilters

In this work, a systematic study of SO2 molecules interacting with pristine and transition metal (TM) covered C-60 is presented by means of first principles calculations. It is observed that the SO2 molecule interacts weakly with the pristine C-60 fullerene, although the resulting interaction is largely increased when the C-60 structure is covered with Fe, Mn, or Ti atoms and the SO2 Molecules are bounded through the TM atoms. The number of bounded SO2 molecules per TM atoms, in addition to the elevated binding energies per molecules, allows us to conclude that such composites can be used as a template for efficient devices to remove SO2 molecules or, alternatively, as SO2 gas sensor.

Cross-situational learning of object-word mapping using Neural Modeling Fields

The issue of how children learn the meaning of words is fundamental to developmental psychology. The recent attempts to develop or evolve efficient communication protocols among interacting robots or Virtual agents have brought that issue to a central place in more applied research fields, such as computational linguistics and neural networks, as well. An attractive approach to learning an object-word mapping is the so-called cross-situational learning. This learning scenario is based on the intuitive notion that a learner can determine the meaning of a word by finding something in common across all observed uses of that word. Here we show how the deterministic Neural Modeling Fields (NMF) categorization mechanism can be used by the learner as an efficient algorithm to infer the correct object-word mapping. To achieve that we first reduce the original on-line learning problem to a batch learning problem where the inputs to the NMF mechanism are all possible object-word associations that Could be inferred from the cross-situational learning scenario. Since many of those associations are incorrect, they are considered as clutter or noise and discarded automatically by a clutter detector model included in our NMF implementation. With these two key ingredients - batch learning and clutter detection - the NMF mechanism was capable to infer perfectly the correct object-word mapping. (C) 2009 Elsevier Ltd. All rights reserved.

Constraining the age of the iporanga formation with SHRIMP U-Pb zircon: Implications for possible ediacaran glaciation in the Ribeira Belt, SE Brazil

The Ribeira belt in SE Brazil is a Neoproterozoic to Early Palaeozoic orogen, whose architecture and history is not yet fully understood. The depositional age of many of the sedimentary sequences in the Ribeira Belt remains unconstrained, and with debate concerning their depositional environment and tectonic setting. In this paper we present SHRIMP zircon U/Pb age constraints for one such problematic unit in the Ribeira Belt the lporanga Formation - and discuss the significance of this age with regards to the timing of Neoproterozoic glacial events in southeast Brazil. Using a felsic volcanic unit immediately under the lporanga Formation and granite cobbles from breccias in its basal parts a reconnaissance SHRIMP U/Pb zircon maximum depositional age of 580 Ma is assigned for the base of this unit. This age is marginally younger than the 625605 Ma ages for intrusions into the Lajeado and Ribeira subgroups, with which the lporanga Formation is in tectonic contact. This indicates that the Lajeado and Ribeira subgroups are not stratigraphically equivalent to the lporanga Formation, as thought previously by some workers. The maximum depositional age of 580 Ma also places a maximum time constraint on the tectonic juxtaposition of the lporanga Formation with other supracrustal units, and on the greenschist facies metamorphism and isoclinal folding that affected it. The potential glacial origin for the lporanga Formation, if correct, would place it in the late Ediacaran - provisionally equivalent to the Gaskiers glaciation. (c) 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Geology and geochronology of the Betara region in south-southeastern Brazil: Evidence for possible Statherian (1.80-1.75 Ga) and Calymmian (1.50-1.45 Ga) extension events

The results of geological mapping, chemical analysis and radiometric dating of metabasic rocks of Betara Formation, and mapping and dating of those present in the Betara basement nucleus together with mylonitic granodiorite and syenogranite are reported here. U-Pb analysis of bulk zircon fractions from the metabasic rocks of the basement nucleus yielded a Statherian age of 1790 +/- 22 Ma, while the metabasic rocks from the upper part of the Betara Formation yielded a Calymmian age between 1500 and 1450 Ma. This age is a minimum for the deposition of the Betara Formation. The older metabasic rocks are associated with post-tectonic, possibly anorogenic syenogranite, while the younger ones are gabbro or very porphyritic ankaramite whose REE patterns are consistent with crystallization from an N-MORB parent magma. The observations and data point to the probable events associated with extensional processes of the end of Paleoproterozoic and early Mesoproterozoic. Similar registers of Statherian (1.80-1.75 Ga) and Calymmian (1.50-1.45 Ga) extensional events are recorded in other parts of the South American and African continents. The Neoproterozoic witnessed the formation and junction of the tectonic slices which formed the Apiai domain during the assemblage of western Gondwana. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

INSECT CHYMOTRYPSINS: CHLOROMETHYL KETONE INACTIVATION AND SUBSTRATE SPECIFICITY RELATIVE TO POSSIBLE COEVOLUTIONAL ADAPTATION OF INSECTS AND PLANTS

Insect digestive chymotrypsins are present in a large variety of insect orders but their substrate specificity still remains unclear. Ewer insect chymotrypsins from 3 different insect orders (Dictyoptera, Coleoptera and two Lepidoptera) were isolated using affinity chromatography. Enzymes presented molecular masses in the range of 20 to 31 kDa and pH optima in the range of 7.5 to 10.0. Kinetic characterization. using different, colorimetric and fluorescent substrates indicated that insect chymotrypsins differ from, bovine chymotrypsin in their primary specificity toward small substrates (like N-benzoyl-L-Tyr p-nitroanilide) rather than on their preference for large substrates (exemplified by Succynil-Ala-Ala-Pro-Phe P-nitroanilide). Chloromethyl ketones (TPCK, N-alpha-tosyl-L-Phe chloromethyl ketone and Z-GGF-CK, N-carbobenzoxy-Gly-Gly-phe-CK) inactivated all chymotrypsins legated. Inactivation rates follow apparent first-order kinetics with variable second order rates (TPCK, 42 to 130 M(-1)s(-1); Z-GGF-CK, 150 to 450 M(-1)s(-1) that may be remarkably low for S. frugiperda chymotrypsin (TPCK, 6 M(-1)s(-1); Z-GGF-CK, 6.1 M(-1) s(-1)). Homology modelling and sequence alignment showed that. in lepidopteran chymotrypsins, differences in the amino acid residues in the neighborhood of the catalytic His 57 may affect its pKa, value. This is Proposed as the cause of the decrease in His 57 reactivity toward chloromethyl ketones. Such amino acid replacement in the active site is proposed. to be an adaptation to the presence of dietary ketones. (C) 2009 Wiley Periodicals, Inc.

Stimulation of Acidic Reduction of Nitrite to Nitric Oxide by Soybean Phenolics: Possible Relevance to Gastrointestinal Host Defense

This study aimed to evaluate the potential of soybean-promoted acidic nitrite reduction and to correlate this activity with the content of phenolics and with the bactericidal activity against Escherichia coli O157:H7. Extracts of embrionary axes and cotyledons enriched in phenolics increased (center dot)NO formation at acidic pH at values that were 7.1 and 4.5 times higher, respectively, when compared to the reduction of the nonenriched extracts. Among the various phenolics accumulated in the soybean extracts, five stimulated nitrite reduction in the following decreasing order of potency: epicatechin gallate, chlorogenic acid, caffeic acid, galic acid and p-coumaric acid. Extracts of embrionary axes presented higher contents of epicatechin gallate and caffeic acid, compared to that of cotyledons, indicating a positive correlation between activity of the extracts and content of phenolics with regard to nitrite reducing activity. Soybean extracts enriched in phenolics interacted synergistically with acidified nitrite to prevent E. coli O157:H7 growth. The results suggest that soybean phenolics may interfere with the metabolism of (center dot)NO in an acidic environment by accelerating the reduction of nitrite, with a potential antimicrobial effect in the stomach.

Acetyl Radical Production by the Methylglyoxal-Peroxynitrite System: A Possible Route for L-Lysine Acetylation

Methylglyoxal is an a-oxoaldehyde putatively produced in excess from triose phosphates, aminoacetone, and acetone in some disorders, particularly in diabetes. Here, we investigate the nucleophilic addition of ONOO(-), known as a potent oxidant and nucleophile, to methylglyoxal, yielding an acetyl radical intermediate and ultimately formate and acetate ions. The rate of ONOO(-) decay in the presence of methylglyoxal [k(2,app) = (1.0 +/- 0.1) x 10(3) M(-1) s(-1); k(2) approximate to 1.0 x 10(5) M(-1) s(-1)] at pH 7.2 and 25 degrees C was found to be faster than that reported with monocarbonyl substrates (k(2) < 10(3) M(-1) diacetyl (k(2) = 1.0 x 10(4) M(-1) s(-1)), or CO(2) (k(2) = 3-6 x 10(4) M(-1) s(-1)). The pH profile of the methylglyoxal peroxynitrite reaction describes an ascendant curve with an inflection around pH 7.2, which roughly coincides with the pK(a) values of both ONOOH and H(2)PO(4)(-) ion. Electron paramagnetic resonance spin trapping experiments with 2-methyl-2-nitrosopropane revealed concentration-dependent formation of an adduct that can be attributed to 2-methyl-2-nitrosopropane-CH(3)CO(center dot) (a(N) = 0.83 mT). Spin trapping with 3,5-dibromo-4-nitrosobenzene sulfonate gave a signal that could be assigned to a methyl radical adduct [a(N) = 1.41 mT; a(H) = 1.35 mT; a(H(m)) = 0.08 mT]. The 2-methyl-2-nitrosopropane-CH(3)CO(center dot) adduct could also be observed by replacement of ONOO(-) with H(2)O(2), although at much lower yields. Acetyl radicals could be also trapped by added L-lysine as indicated by the presence of W-acetyl-L-lysine in the spent reaction mixture. This raises the hypothesis that ONOO(-)/H(2)O(2) in the presence of methylglyoxal is endowed with the potential to acetylate proteins in post-translational processes.