Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220160010&lang=es vol. 39 num. 10 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[A NEW RHODAMINE B DERIVATIVE RBMAB AS A HIGHLY SELECTIVE AND SENSITIVE CHEMOSENSOR FOR Fe<sup>3+</sup> WITH LOW DETECTION LIMIT]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001151&lng=es&nrm=iso&tlng=es A new Rhodamine B derivative RBMAB, namely 3-amino-N-(2-(3',6'-bis (diethylamino)-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)ethyl)benzamide, was designed, synthesized and structurally characterized to develop a chemosensor. The studies show that RBMAB exhibits high selectivity toward Fe3+ among many other metal cations in an ethanol-H2O (3:2, v/v, PBS buffer, 1.2 mmol L-1, pH 7.2) solution. It has a low detection limit of 0.021µm. Fluorescence microscopy experiments further demonstrate that RBMAB can be used as a fluorescent probe to detect Fe3+ in living cells. <![CDATA[Manufacture of nanosized apatite coatings on titanium with different surface treatments using a supersaturated calcification solution]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001159&lng=es&nrm=iso&tlng=es The biomimetic method is used for the deposition of calcium phosphate coatings (Ca - P) on the surface of different biomaterials. However, the application of this method requires long exposure times in order to obtain a suitable layer thickness for its use in medical devices. In this paper, we present a fast approach to obtain apatite coatings on titanium, using a combination of supersaturated calcification solution (SCS) with chemical modification of the titanium surface. Also, it was evaluated the effect of four different surface treatments on the apatite deposition rate. Commercially pure titanium plates were activated by chemical or thermochemical treatments. Then, the activated samples were immersed in a solution with high content of calcium and phosphate ions at 37 ºC for 24 h, mimicking the physiological conditions. The coatings were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The use of SCS solutions allowed the formation of crystalline hydroxyapatite coatings within a period of 24 h with a thickness between 1 and 5.3 µm. Besides, precipitates of hydroxyapatite nanoparticles with a globular configuration, forming aggregates with submicrometer size, were found in SCS solutions. <![CDATA[Photocatalytic degradation of tartrazine with immobilized TiO<sub>2</sub> in alginate beads]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001165&lng=es&nrm=iso&tlng=es The potential of heterogeneous photocatalysis using TiO2 immobilized in alginate beads was evaluated for the degradation of tartrazine yellow azo dye. The treatment was performed under the action of a high-pressure mercury vapor lamp of 125 W and the degradation performance was investigated with the absorbance supplied by a photocolorimeter. Alginate beads with TiO2 were prepared and the catalyst was quantified by thermogravimetric analysis (TG) and characterized by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and specific area analysis (BET). The immobilization was performed as a very simple and reproductible technique. The bead diameter was approximately 1 mm and its surface presented a homogeneous dispersion of catalytic sites containing about 1-2% (w/w) of TiO2. The TiO2/alginate beads presented low density and can be easier separated than the TiO2 dispersed from the reacting medium, remaining available to be reused in another batch. The dye degradation reached 30% after 120 minutes of irradiation, for the following conditions: alcaline pH (pH=9.0), 3 g of TiO2/alginate beads and 20 mol L-1 dye concentration. <![CDATA[Elemental composition of PM<sub>10</sub> and PM<sub>2.5</sub> for a savanna (Cerrado) region of southern Amazonia]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001170&lng=es&nrm=iso&tlng=es Brazil plays an important role with regard to the emission of aerosols into the atmosphere. Ecosystems such as the Amazonian tropical forest and Brazilian Cerrado are undergoing sweeping changes. These human activities promote an increase in the levels of gases and particles emitted into the atmosphere. To determine how these activities have affected the emission of coarse and fine particulate matter (PM10 and PM2.5), atmospheric aerosol samples were collected continuously from June 2004 to April 2005 in the Cuiaba Basin of south-central Mato Grosso, Brazil. Aerosols were sampled using stacked filter units. Filters were analysed for particulate mass, black carbon and for concentrations of seventeen elements by Particle Induced X-Ray Emission. The results revealed that Mg, Al, Si, S, K, Ca, Ti and Fe were the major components detected in PM2.5 and PM10. The high enrichment factors observed in PM2.5 and PM10 suggest that anthropogenic activities were the predominant source for elements such as Cu, Zn and Pb. These data indicate that most of the aerosols measured in the Cuiaba Basin originate from land conversion and biomass burning. These patterns are similar to those observed in other Cerrado and Amazonian forest areas that are undergoing rapid and spatially extensive land-cover change. <![CDATA[Tropospheric ozone and volatile organic compounds on a region impacted by the sugarcane industry]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001177&lng=es&nrm=iso&tlng=es The purpose of this study was to evaluate the concentrations of tropospheric ozone and VOCs under the sugarcane agro-industry emissions in urban and rural areas of Araraquara, SP. The sampling was performed using active and passive air samplers during the sugarcane harvest and in the period between harvests in 2011 and 2012. Also, canisters were undertaken in 3 situations: during and after the burning of the cane plantations and in an urban area. Instrumental analysis was carried out using gas and ion chromatography. The highest VOC concentrations were found for toluene and d-limonene at the urban area and for ethene during the burning of sugarcane. Although sugarcane industry is an important emission source of ozone precursors, in this study the tropospheric ozone levels do not increased significantly under sugarcane agro-industry emissions. <![CDATA[Enzyme kinetic modelling and analytical solution of nonlinear rate equation in the transformation of D-methionine into L-methionine in batch reactor using the new homotopy perturbation method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001184&lng=es&nrm=iso&tlng=es A mathematical model of biotransformation of D-methionine into L-methionine in the cascade of the enzymes such as, D-amino acid oxidase (D-AAO), L-phenylalanine dehydrogenase (L-PheDH) and formate dehydrogenase (FDH) is discussed. The model is based on a system of coupled nonlinear reaction equations under non steady-state conditions for biochemical reactions occurring in the batch reactor that describes the substrate and product concentration within the catalyst. Simple analytical expressions for the concentration of substrate and product have been derived for all values of reaction parameters using the new homotopy perturbation method (NHPM). Enzyme reaction rate in terms of concentration and kinetic parameters are also reported. The analytical results are also compared with experimental and numerical ones and a good agreement is obtained. The graphical procedure for estimating the kinetic parameters is also reported. <![CDATA[Comparison between chemical composition and antioxidant activity of different extracts of green propolis]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001192&lng=es&nrm=iso&tlng=es In this work were determined the total phenolic contents, antioxidant activity and chemical composition of twelve samples of green propolis acquired from beekeepers and other twelve commercial extracts samples from different regions of Southeast Brazil. The phenolic contents and the antioxidant activity were evaluated by the Folin-Ciocalteau and DPPH, ABTS and FRAP methods, respectively. Both types of propolis showed significant radical scavenging properties. HPLC-PDA was applied for quantification of chlorogenic acid, caffeic acid, ferulic acid, para-coumaric acid, rosmarinic acid, vanillin, hesperidin, naringenin, pinobanksin, kaempferol, Artepillin-C (4-hydroxy-3,5-diprenyl cinnamic acid), kampheride and pinostrobin. Despite the chemical composition of both in natura and commercial propolis extracts were similar the multivariate analysis allowed the discrimination between them. <![CDATA[Application of electrodialysis to the treatment of effluent from the agate dyeing industry with nitrate and chromium ions]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001200&lng=es&nrm=iso&tlng=es The dyeing agate employs large quantities of potentially harmful wastewater to the environment, such as, effluent with chromium and nitrate ions. The aim of the present study was investigate the electrodialysis technique efficiency in the removal of contaminant ions present in wastewater generated by the agate dyeing industry and evaluate the toxicity of the effluent studied. The electrodialysis experiments were performed in acrylic cell 5 compartments separated by ion selective membranes and fitted with a 70TiO2/30RuO2 DSA® anode and a titanium plate as cathode. After application of the electrodialysis treatment, toxicity of the effluent was evaluated in two different trophic levels, Artemia salina and Lactuca sativa. The results indicated the removal of 233.3 mg L-1 of nitrate and 223.6 mg L-1 of chromium was extracted, in flow mode. The toxicity tests showed a tendency to decrease the percentage of mortality of organisms after application of the electrodialysis technique. Thus, it concludes that the electrodialysis is an effective method for treating effluents containing metal ions, and is possible reuse the recovered solutions in the dyeing process. <![CDATA[COMPARISONS BETWEEN REAL-TIME <em>p</em>CO<sub>2</sub> MEASUREMENTS WITH INDIRECT ESTIMATES IN TWO CONTRASTING BRAZILIAN ESTUARIES: THE EUTROPHIC GUANABARA BAY (RJ) AND THE OLIGOTROPHIC SÃO FRANCISCO RIVER ESTUARY (AL).]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001206&lng=es&nrm=iso&tlng=es Carbon dioxide (CO2) fluxes from aquatic systems are generally derived from the gradient in the partial pressure of CO2 (pCO2) between air and surface waters. In this study, we compare real-time measurements of water pCO2 using an equilibrator and non-dispersive infrared gas detector, with calculations based on pH and total alkalinity (TA) in two contrasting Brazilian estuaries: Guanabara Bay (Rio de Janeiro) and the São Francisco River Estuary (Alagoas). In Guanabara Bay, the measured and calculated values showed an excellent agreement (R2 = 0.95, p &lt; 0.0001), without significant statistical differences between the two methods. In the São Francisco River Estuary, where the entire gradient from freshwaters to seawater could be sampled, important overestimates were found for the calculated pCO2. The overestimation was on average 71%, and reached up to 737%. This large bias in pCO2 calculation was verified at low pH and TA concentrations in freshwaters (pH &lt; 7.5; TA &lt; 700 µmol kg-1) possibly due to the contribution of organic alkalinity, lowering the buffer capacity of the carbonate system. As such, direct measurements of pCO2 should be considered as a priority for CO2 studies conducted in estuarine systems, particularly tropical systems where physical and biological processes are prone to significant spatial and temporal variability. <![CDATA[CHITOSAN-CLAY HYBRID FOR ENCAPSULATION OF FERTILIZERS AND RELEASE SUSTAINED OF POTASSIUM NITRATE FERTILIZER]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001215&lng=es&nrm=iso&tlng=es The use of controlled release fertilizers is a trend for improving productivity, reducing costs and environmental pollution. Such materials release gradually the nutrients to the plant in order to supply its requirement and are an alternative to improve fertilization. The preparation of a microsphere from natural materials (chitosan and montmorilonite clay) added with nutrients, according to the needs of plants nutritional, is one of the main motivations of this work. The addition of lamellar silicates as natural clays is a promising alternative to increase water and chemical compounds sorption capacity. In the present chitosan/montmorilonite clay composites were prepared via inversion phase and thermal, structural and morphologically studies were performed. The release of the KNO3 was realized in water using conductimetry and time domain reflectometry technique was used to monitor the in situ release in soil. Double coated microspheres provide the better nutrient encapsulation and a swelling of 200% was observed. The release was influenced by pH and fast release was observed for pH 4 and 5.5. According to the soil tests a slow release was observed since the KNO3 delivery was accompanied during 60 days showing higher values in the first ten days and a constant value until 60 days. <![CDATA[ONE STRAIN-MANY COMPOUNDS (OSMAC) METHOD FOR PRODUCTION OF PHENOLIC COMPOUNDS USING <em>Camarops sp.</em>, AN ENDOPHYTIC FUNGUS FROM <em>Alibertia macrophylla</em> (Rubiaceae)]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001221&lng=es&nrm=iso&tlng=es Seven phenolic derivatives including p-hydroxyphenyllactic acid (1), p-hydroxybenzoic acid (2), p-hydroxybenzaldehyde (3), phenyllactic acid (4), n-butyl-3,4-dihydroxybenzoate (5), n-hexyl-3,4-dihydroxybenzoate (6) and n-octyl-3,4-dihydroxybenzoate (7) were produced using Camarops sp. via the one strain-many compounds (OSMAC) approach. Their structures were determined using 2D NMR and ESI-MS spectra and were compared with works reported in the literature. This paper deals with the first report of these compounds in Camarops sp. <![CDATA[APPLICATION OF AMIDOXIMES AS CATALYSTS FOR THE ALLYLATION REACTION BY POTASSIUM ALLYLTRIFLUOROBORATE IN ORGANIC BIPHASIC]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001225&lng=es&nrm=iso&tlng=es We describe the application of an amidoxime as catalyst in the synthesis of homoallylic alcohols from the allylation reaction of aldehydes with different features using potassium allyltrifluoroborate. The reaction was conducted with a catalytic amount of the appropriate amidoxime in a biphasic system (water:dichloromethane), open atmosphere and ambient temperature. The products were obtained in yields ranging from moderate to excellent in short reaction times without the need for further purifications for almost all examples. Additionally, the reaction has proved chemo- and regioselective. <![CDATA[STUDYING THE INTERACTIONS BETWEEN NANOPARTICLES AND BIOLOGICAL SYSTEMS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001236&lng=es&nrm=iso&tlng=es Although in recent years there has been an increasing amount of literature on nanotechnology and their clinical applications, it is still scarce a deep understanding of the interactions at the molecular levels between nanoparticles and cells. Studies demonstrating the underlying mechanisms of nanoparticles endocytosis, intracellular trafficking, and cellular processing are imperative to understand better how cells interact with those materials and their possible undesired effects, e.g. nanotoxicity. The rising awareness concerning nanoparticles applications and its interactions with the cellular environment is part of the new research field called Nanotoxicology. The cumulative knowledge in nanotoxicology will allow us to foresee toxic effects, establish regulations and limits for nanoparticles applications. In this work, we discuss the theoretical concepts about studying endocytosis and intracellular trafficking of nanoparticles. The nanoparticles-cell interactions are a multi-step process, which can be divided into nanoparticles' internalization, intracellular processing and triggering effects of nanomaterials on eukaryotic cells. Finally, we discuss the main techniques used to study this process: flow cytometry, use of endocytosis inhibitors and confocal microscopy. <![CDATA[EVALUATION OF TO-15 METHOD EFICIENCY TO DETERMINE VOLATILE ORGANIC COMPOUNDS IN TYPICAL URBAN CONDITIONS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001245&lng=es&nrm=iso&tlng=es The efficiency of U.S.EPA TO-15 Method was evaluated under typical conditions of an urban environment with natural and anthropic emission sources. The performance criteria which should be met for a system to qualify, were fulfilled: a detection limit of ≤0.2 ng for all target compounds, replicate precision for a calibration standard and ambient samples within 20%. The stability of the target compounds during storage of sampled air in canisters was also evaluated at atmospheric pressure and relative humidity of 50%. Results show that, in the sampling conditions, compounds are not stable for more than a week. For validation experiments, samples were collected at the entrance of Tijuca National Park, located at the city of Rio de Janeiro. Isoprene was selected as a marker of biogenic emissions, and aromatic compounds were selected as markers of anthropogenic emissions, primarily vehicular emissions. Then, samples were collected in Saens Peña Square, a central area in the Tijuca District, in the northern part of the city, approximately 10 km from the entrance of Tijuca National Park. Volatile organic compounds were determined and the results were compared with previous data obtained in the same local using other methods. <![CDATA[INFLUENCE OF TASKS’ FEATURES AND OF ARTICULATION OF TASKS IN THE QUALITY OF CHEMISTRY LEARNING IN HIGHER EDUCATION]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001254&lng=es&nrm=iso&tlng=es The lack of empirical findings, particularly about how to make and how to handle, intentionally, certain features of tasks, to improve the quality of learning, justifies the research questions: How to combine the features of a task to potentially improve the quality of the student learning? How to articulate different tasks over time, so as to promote good learning results? Was used an action-research study (completed in two stages) with a teacher of introductory chemistry in higher education and her students. Were analyzed data related to teaching (teacher logbook, practical worksheets, laboratory work guides) and data related to learning (students' worksheets, competences test, laboratory work observation grids). The results obtained were: (1) The open or closed typology of the task becomes less important when the contextualization in real situations is integrated, which acquired a decisive importance. That is, some features are more important than others. (2) The relevance of the tasks' features in learning is not independent of the moment when the features are integrated into the tasks. The most important factor is the articulation of tasks with specific features which results in a certain sequence of tasks over time. <![CDATA[GILBERT LEWIS AND THE CENTENNIAL OF THE ELECTRON PAIR THEORY OF CHEMICAL BONDING]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016001001262&lng=es&nrm=iso&tlng=es The year 2016 marks the centennial of the first approach to describe all types of chemical bonds by means of a unified theory, that of the electron pair, as proposed by the American chemist Gilbert Newton Lewis (1875-1946). Lewis probably became the best known chemist of the twentieth century. Any highschool student anywhere has heard of him and uses concepts such as Lewis acids and bases. His seminal ideas, albeit modified with time, remain a source of inspiration as the basis of much that came later. Lewis established his theory in a series of articles, the most important dating from 1916. His life and achievements are the stuff of much study and debate, as this essay aims to show.