Resumo em Inglês:

In the present work was performed a quantitative structure-activity relationship (QSAR) for a set of derivatives of 1,4-quinoxaline N-oxides with antichagasic activity based on reactivity descriptors from the frame conceptual DFT. QSAR models showed a good statistical quality and capacity internal prediction with R2 > 0.6 and Q2> 0.5 respectively. QSAR model suggest that antichagasic activity of the studied compounds depends largely from the reactive behavior of N-oxide group (N-O). Also, reactivity descriptors showed that the N-oxide group is a reactive site in theses derivatives with nucleophilic characteristics. The results QSAR shed light on the understanding of the mechanism of action and design of new drugs based on derivatives of 1,4-di-N-oxides quinoxaline.

Resumo em Inglês:

The reduction of zeolite particle is one of the main features currently searched; it is due to the catalytic gains that these materials come in some reactions. In this work two faujasite zeolites of type X were evaluated, a micrometer and nanometric. Zeolites in sodium form were exchanged ionically with methylammonium cations. These materials were evaluated as catalysts in the Knoevenagel condensation reaction. Steric impediments restricted the ion exchange in the micrometer zeolite and have become more predominant due to the increase in the volume of cations. In nanometric sample such impediments were less evident due to the reduction of the particles provide greater accessibility to exchangers cations to inaccessible sodium in micrometer zeolite. The best catalytic performances were achieved with zeolites containing the monomethylammonium cation. The increased of the accessibility and diffusion of the reactants and products through the pores of the nanometric zeolite provided the best butyraldehyde conversions independent the exchanger cation

Resumo em Inglês:

This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 ºC for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 ºC. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.

Resumo em Inglês:

Ni-BTC (BTC = 1,3,5-benzene tricarboxylate) metal organic framework (MOF) was synthesized using different solvent conditions. Solvent mixtures of water/N,N-dimethylformamide (DMF), water/ethanol, and water/ethanol/DMF were used for the reactions with or without a variety of bases at 160 ºC for 48 hours. Even with same green crystals, prepared MOFs show all different BET surface areas and different XRD patterns. The highest BET surface area of the crystals was 850 m2/g obtained from water/DMF solvent with NH4OH as a base. The measured surface areas of the crystals follows the order of Ni-BTC(water/DMF-NH4OH) > Ni-BTC(water/DMF-TMA) > Ni-BTC(water/DMF) > Ni-BTC(water/DMF-Pyridine)> Ni-BTC(water/ethanol)> Ni-BTC(water/DMF-aniline)> Ni-BTC(water/DMF-NaOH).

Resumo em Inglês:

The nature of the metal-ligand interactions, in the [Ti(CO)6]2-, [V(CO)6]-, [Cr(CO)6], [Mn(CO)6]+, [Fe(CO)6]2+ and [Co(CO)6]3+ complexes has been studied by means of topological analyses of the electron charge density, using the Quantum Theory of Atoms in Molecules (QTAIM) and Electron Function Localization (ELF). The calculations were made using B3LYP method with the 6-311++G(2d,2p) basis set. The results show that the charge transferences (both σ-donation and π-backbonding) and the electrostatic interaction between the lone pair of C atom of the CO molecule and nucleus of the metal species play a key role in stabilizing of these metal complexes. Finally, we have found QTAIM parameters that explaining the nature of the Mδ+•••δ+C-Oδ- interactions in metal carbonyls.

Resumo em Inglês:

In this work the sol-gel method was used to synthesize a nanocomposite containing TiO2 and graphene oxide (GO). The photocatalytic activity of the TiO2/GO nanocomposite was evaluated regarding the degradation of a reactive dye (reactive black 5) in aqueous solution using processes assisted by UV-A radiation. Under these conditions the nanocomposite showed higher degradation efficiency than the reference photocatalyst (Degussa P25 TiO2), mainly due to the high degradation capacity of the synthesized TiO2 nanoparticles. Although contradictory to several reports in the specialized literature, no synergistic effect was observed between the nanocomposite components.

Resumo em Inglês:

Polymeric precursor method and wet impregnation route were applied to synthesize copper and aluminium-based catalysts in order to obtain a material with interesting properties in catalytic reactions. The changes in the structural, morphological and textural properties due to the choice of preparation method were characterized by different techniques, such as XRD, N2 physisorption isotherms and SEM. The XRD results of the solids present the formation of γ-Al2O3 or CuO and β-Al(OH)3, depending on the preparation method. The average crystallite diameters of the alumina were estimated by the Scherrer's formula with a particle size of 5.2 nm. N2 physisorption isotherms analysis shows that the alumina is a mesoporous material with a high specific surface area. An excessive increase in surface area was observed after Cu2+ insertion by wet impregnation from β-Al(OH)3 support, which is explained by the redissolution and recrystallization of bayerite to γ-Al2O3 during the impregnation of Cu2+ and recalcination process, respectively. The SEM images confirmed this phenomenon. Catalytic tests explain that the combination of the two methods improves the activity, selectivity and the stability in the conversion of glycerol to acetol. The results indicate that the way of catalyst preparation affects its structural, textural and morphological properties and consequently the catalytic performance

Resumo em Inglês:

An analytical method to determine tin concentrations in natural samples, by coupling atomic fluorescence spectrometry, hydride generation and flow injection system was developed. The sample digestion procedure and the conditions of hydride generation were fully optimized. The best conditions for the generation of SnH4 were obtained with NaBH4 4% (m v-1) and HCl 0.6 mol L-1. The optimized flow rates were 1.2 mL min-1 for sample, 1.2 mL min-1 for HCl and 1.6 mL min-1 for NaBH4 solution. The sample volume was 500 µL. The best acid volume for digestion of solid samples was stablished to be 3 mL HNO3 + 1 mL HCl. The accuracy of the method was established by the analysis of certified reference materials and by comparative determinations, using inductively coupled optical emission spectrometry. The approach developed was shown to offer a robust method with excellent accuracy and precision for the determination of Sn in environmental samples. Finally, the method was applied to analyse the soil, sediment and water samples, collected in area under anthropogenic activities: processing area of cassiterite in Corumbataí/SP. The obtained data indicated that there was alteration in the natural quality of the environment as a result of the activities developed in that site

Resumo em Inglês:

Organic/inorganic membranes based on sulfonated poly(vinyl alcohol) (SPVA) and in situ prepared TiO2 nanoparticles nanocomposite membranes with various compositions were prepared to use as proton exchange membranes in direct membrane fuel cells. Poly(vinyl alcohol) (PVA) was sulfonated and cross-linked separately by 4-formylbenzene-1,3-disulfonic acid disodium salt hydrate and glutaraldehyde. The ion exchange capacity and proton conductivity of the membranes increased with increasing amount of TiO2 nanoparticles. The composite membranes with 15 wt% TiO2 exhibited excellent proton conductivity of 0.0822 S cm-1, as well as remarkably low methanol permeability of 1.11×10-9 cm2 s-1. The thermal stability and durability were also superior and performance in methanol fuel cell was also reasonably good

Resumo em Inglês:

The aim of this study was to compare the usefulness of three extraction methods: solid-phase microextraction (SPME) with four different coating (PDMS, PDMS/DVB, DVB/CAR/PDMS and PA), supercritical fluid extraction with carbon dioxide (SCF) and simultaneous distillation and extraction (SDE) for isolation of flavor compounds from roasted ground coffee (Coffea arabica L. var. Typica) of Vilcabamba (Ecuador). Identification and characterization of volatile compounds were achieved using gas chromatography / mass spectrometry (GC-MS). Analysis of variance and principal components analysis was done. For the SPME method the coating material affect the amount and concentration of compounds extracted, the DVB/CAR/PDMS coating provided the most representative aroma extract (44 compounds were identified). The SCF method allowed extracting a higher amount of compounds and also their identification by GC-MS (72) that SDE (64) and SPME (57), in addition provide higher extractions. The acetic acid, caffeine, furfuryl alcohol, furfural, 5-methylfurfural, butylated hydroxytoluene and maltol were the compounds with higher concentrations found with SPME and SDE, with SCF were found higher concentration to compounds with high molecular weights (> 194 g mol-1). Preferably SPME-DVB/CAR/PDMS method should be used for a characterization of coffee aroma compounds.

Resumo em Inglês:

The isolation and identification of bioactive metabolites from complex extracts obtained from microbial growth media is a time consuming, costly, and labor-intensive task. A strategy to rapidly identify secondary metabolites isolated from extracts obtained from the culture media of marine-derived and endophytic fungal strains is described. Identification was achieved by HPLC-UV-MS and 1H NMR analyses in combination with data obtained from the Dictionary of Natural Products. Among the compounds identified, (-)-naphthoquinoneimine, citreorosein, emodin, pyrenocine A and harzianopyridone displayed moderate to potent antiviral activity. (-)-Naphthoquinoneimine was isolated as the enantiomer of its previously reported dextrorotatory congener, while 6,7-dihydroxy-2,2-dimethyl-4-chromanone is herein reported for the first time as a natural product.

Resumo em Inglês:

The phosphorus used as fertilizer in agriculture is extracted from phosphate rocks, which after extraction reacts with sulfuric acid, releasing phosphoric acid, a raw material for the fertilizer industry. Studies point to a possible depletion of world reserves of phosphate rock in the next 50-100 years. A phosphorus scarcity is closely linked to global food security, given the dependence of soil fertilization to maintaining agricultural productivity within the current patterns of agribusiness. The application of fertilizers in soil and the sanitary sewers have been historically responsible for the larger eutrophication of water environments. In recent years, phosphorus has been seen as a finite resource and extremely important for the maintenance of the agricultural productivity. Therewith it is necessary investments to improve of fertilizers practices soils, safe technologies of organic waste reuse such as animal waste and phosphorus recovery, both released into water resource. Taking into account the depletion scenario of phosphorus deposits and eutrophication of water bodies, the water and phosphorus scarcity are among the most urgent environmental issues of the XXI century. Economic development, protection of public health, and maintenance of aquatic life are dependent of water availability and quality.

Resumo em Inglês:

During heat treatment milk suffers changes among which whey proteins insolubility and Maillard reaction can be monitored using spectrophotometric methods by determining the whey protein nitrogen (WPNI) and 5-hydroxymethylfurfural (HMF). The aim of this work was the evaluation of heat treatment in commercial UHT milk samples through HMF and WPNI determination by spectrophotometric methods in visible region, using chemometric tools in data analysis. The regression models were fitted and statistical assumptions were tested. The WPNI confidence interval (CI) was (0.91; 3.73) mg mL-1 showing the heat treatment severity and classifying the samples as "medium heat treatment" according to American Dairy Products Association. For free HMF index, the CI were: (2.39; 3.27) and (6.01; 6.89) µmol L-1 for regular and low lactose content samples, respectively; while these two samples group presented CI of (11.67; 12.39) and (132.28; 143.22) µmol L-1 for total HMF index, respectively; showing the influence of lactose content in total HMF index. Descriptive statistical analysis associated with principal component analysis demonstrated a lack of standardization in the current Brazilian UHT process. The spectrophotometric methods allowed obtaining further inferences about the product quality associated to its heat treatment.

Resumo em Inglês:

This study aimed to investigate environmental education (EE) in the initial training of teachers of chemistry. The data were based on documentary analysis of the political pedagogical project of the Chemical Education course, the syllabus of school subjects, questionnaires and interviews with students. The resulting diagnosis explicitly shows little evidence of concern over inclusion of EE in teacher training. Beginner students showed representations centered on recycling and awareness. More advanced students had representations on sustainability and awareness, while the graduating students showed representations centered on pollution and awareness. In general, the representations involved awareness for environmental preservation.

Resumo em Inglês:

The aim of this study was a didactic presentation of the Shannon entropy in the quantum theory context, followed by application to the case of a one-dimensional harmonic oscillator in its ground state, both in the free case and confined case. The study of these systems allows us to highlight notions such as location or delocation of a particle, a possible interpretation that the Shannon entropy can adopt. The Shannon entropy in position (Sx) and momentum (Sp) spaces were calculated for both systems, beyond the entropic sum (St = Sx + Sp). With this procedure it was possible to identify trends in the behavior of the Shannon entropy (Sx and Sp) and test the compliance of the entropic uncertainty relation (St = Sx + Sp ≥ n(1 + ln(π))).

Resumo em Inglês:

Hydrogen sulfide is presented in textbooks as toxic, environmentally unacceptable species, however some positive effects in human metabolism were discovered in the last decades. It is important to offer students also some new information about this compound. As didactic tool in this case may serve serial precipitation of Cd2+, Cu2+, Zn2+, Mn2+ and Pb2+ ions forming various colored sulfides in bubblers with chemically generated hydrogen sulfide stream. This experiment has strong and diverse color effect for enhancing the visual perception to motivate students to understand more abstract and complex information about hydrogen sulfide. It also may be helpful in analytical chemistry courses for conditional precipitation equilibrium teaching and calculations.