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Química Nova, Volume: 40, Número: 3, Publicado: 2017
  • Fabricação de filmes bionanocompósitos à base de pectina e polpa de cacau com potencial uso como embalagem para alimentos Artigo

    Melo, Pamela Thais S.; Aouada, Fauze A.; Moura, Marcia R. de

    Resumo em Inglês:

    The aim of this work was to produce biodegradable films based on the pectin and cocoa puree reinforced with chitosan nanoparticles. Nanoparticles were obtained by the ionotropic gelation. Films were produced according to the "casting" method, through a colloidal solution composed of water, cocoa puree, chitosan nanoparticles solution and different concentrations of pectin (2% and 3% w/w). Films were analyzed by thickness measurements, water vapor permeability, mechanical properties and scanning electron microscopy. Nanoparticles were characterized by zeta potential and showed spherical shape with a diameter of about 110 nm and zeta potential value of approximately +30 mV. Pectin 2% and 3% cocoa films exhibited tensile strength (mPa) of 15.1 ± 0.7 and 22.9 ± 1.6, respectively. After nanostructures addition, values increased to 25.2 ± 0.7 and 29.8 ± 1.3. Increasing concentration polymer and chitosan nanoparticles to improve tensile strength values. Films contained 3% of pectin exhibited more significant decrease in water vapor permeability values when chitosan nanoparticles were added, from 2.470 ± 0.101 to 1.904 ± 0.125 g mm / kPa h m2. Results of the analyzes demonstrated that nanocomposites produced with pectin of different concentration showed satisfactory properties for application as packaging for food.
  • Triterpenoides, fenólicos e efeito fitotóxico das folhas de Eugenia flavescens DC (Myrtaceae) Artigo

    Cantanhede, Antonio J.; Santos, Lourivaldo S.; Guilhon, Giselle M. S. P.; Zoghbi, Maria das Graças B.; Ports, Pollyane S.; Rodrigues, Iris C. S.

    Resumo em Inglês:

    This research deals with the chemical study and evaluation of the phytotoxic effects of the methanol extract of E. flavescens leaves. The compounds were isolated using classic chromatographic techniques and the identification of the phenolic profile was proposed from the HPLC/DAD/MS-MS data. Structure elucidation of the compounds was performed by 1H and 13C (1D e 2D) NMR techniques and HRMS. The chemical study led to the isolation of betulinic acid (1) and lupeol (2), identified in mixture quercitrin (3) and catechin (4) beyond myricetrin (5) in mixture with (3). In addition, several phenolic compounds were identified, among them, flavonoids and phenolic acids. For bioassays phytotoxic effect were used as test plants two invasive species, M. pudica and S. obtusifolia. The methanol extract showed significant seed germination inhibition. The triterpenoid 1 showed low inhibition effects on seed germination and moderate effects on radicle and hypocotyl growth. The mixture of flavonoids 3/4 showed effective phytotoxic effects, inhibiting 92,1% of the seed germination of M. pudica and 63,0% of S. obtusifolia. Inhibitions of 72,5% and 76,1% of M. pudica radicle and hypocotyl growths were observed, respectively, and 74,5% and 78,0% of S. obtusifolia for the same bioassays, respectively.
  • Celdas solares sensibilizadas con colorantes fotosensibles obtenidos de plantas de la región sur de ecuador Artigo

    Cabrera, Marcela; Figueroa, Jorge G.; Ramírez-Pérez, Javier C.; Solano-Cueva, Natalí

    Resumo em Inglês:

    Four vegetal species of the southern of Ecuador were used as sensitizers for making dye-sensitized solar cells (DSSCs). The effect of type and amount of material, type and time of maceration were tested in order to determine the best conditions of extraction. The extraction of the natural dye was made with acidified ethanol. The sensitizing agents were adsorbed on TiO2 nanoparticles in small solar cells. The DSSCs made with natural dyes from extracts of blackberry (Rubus glaucus B), mortiño (Solanum americanum Mill), escancel (Iresine herbstii Hook) and beet (Beta vulgaris L) developed an open-circuit tension (Voc) 0.65, 0.5, 0.45 and 0.19 V, respectively. The short-circuit currents (Isc) varies from 2.05 to 19.68 mA cm-2 and the fill factor ranging from 0.61 to 0.69. The DSSCs sensitized with the extract of Rubus glaucus B offered the highest maximum power of 8.83 mW. Thus, the natural dyes used showed great potential as sensitizers in DSSCs, besides being environmentally friendly and their low cost.
  • Study on the pozzolanic activity of sugar cane straw ash produced using different pretreatments Artigo

    Cordeiro, Guilherme Chagas; Vieira, Amanda Pereira; Lopes, Érica da Silva

    Resumo em Inglês:

    This work systematically describes a laboratory study on different pretreatments of sugar cane straw to produce pozzolanic ash. Two procedures were used to accelerate the hydrolysis of celluloses and hemicelluloses and remove metallic impurities present in significant levels in sugar cane straw: hot water washing and acid leaching. Proximate analysis by thermogravimetry was carried out to cover volatile matter, fixed carbon, and ash content of the different straws. Detailed measurements of X-ray diffraction, oxide percentages, loss on ignition, and BET specific surface area were performed to compare hot water washed, acid leached, and non-pretreated ashes, after controlled processes of burning and grinding. The pozzolanic activity of the ashes was evaluated from the modified Chapelle and electrical conductivity methods. The results revealed that ashes with a high content of amorphous silica were produced, in spite of the straw pretreatments. However, both straw pretreatments induced a significant increase in pozzolanic activity, mainly associated with the removal of impurities, especially CaO, SO3, K2O, and carbon compounds. The effect of the hot water washing treatment was relatively small in relation to the acid leaching, but the hot washed ash was significantly more pozzolanic than non-treated ash.
  • Detecção de inibidores de proteases em sementes de Punica granatum Artigo

    Colares, Lara Franca; Santos, Antero Ricardo; Cordeiro, Isac Henrique; Castro, Sandra Bertelli Ribeiro de; Verly, Rodrigo Moreira; Alves, Caio Cesar de Souza; Carli, Alessandra de Paula

    Resumo em Inglês:

    The use of plants as a way to prevent and treat disease comes from ancient times. With the increasing return on consumption of plants for medicinal purposes, the plant-based medicines have gained greater appreciation. Protease inhibitors are compounds that can decrease activity of an enzyme. They are found in plants, especially in Fabaceae, Poaceae, and Solanaceae families, and show satisfactory use to treat diseases due to their regulatory activities and selective proteolytic degradation of target substrates. This study aimed to obtain protease inhibitors in the seeds of Punica granatum, due its use in traditional medicine. The alcohol-acid solution was used to extract and isolate the protease inhibitors in P. granatum seeds and Glycine max grains. The extract of P. granatum seeds showed similar concentration of protease inhibitors when compared to G. max. A 14 kDa band was detected by electrophoresis on polyacrylamide gel, which was characterized by high-performance liquid chromatography as protease inhibitors. The extract of P. granatum seeds showed a potent trypsin inhibitor activity (EC50 18.2 ng mL-1). This study showed for the first time the extraction, purification, and identification of protease inhibitors in Punica granatum seeds.
  • Novos surfactantes alquil poliglicosídicos à base de amilose extraída da batata inglesa (Solanum tuberosum L.) Artigo

    França, Francisco C. F. de; Moreira, Denise R.; Almeida, Raimundo R. de; Rodrigues, Francisco H. A.; Ribeiro, Maria E. N. P.; Ricardo, Nágila M. P. S.

    Resumo em Inglês:

    Alkyl polyglycosides (APGs) are new biodegradable surfactants, non-toxic, synthesized from abundant renewable sources, potentially more appropriate than anionic surfactants. A range of glycosides denoted APG-Cy was synthesized by the Köenig-Knorr reaction using C10, C16 and C18 alcohols and derived from the degradation of amylose from English potato. The molecular structures of the glycosides were characterized by Nuclear Magnetic Resonance (1H and 13C NMR) together with Infrared Spectroscopy (FTIR) and Gel Permeation Chromatography (GPC). The study by NMR allowed the junctions between hydrophilic head groups and hydrophobic tail-groups to be characterized in detail. Conformation of the glycosidic units is 4C1 type with a b anomeric configuration. The formation of glycosides with five glucose rings linked to the alkyl chain was confirmed by 1H NMR and GPC. Liquid crystals identified by the presence of double melting points were observed by Differential Scanning Calorimetry (DSC) showing thermotropic properties. The surface tension (γ) and critical micelle concentration (cmc) were determined by du Noüy method, noting that increasing the length of alkyl chain led to the expected reduction in the cmc. The energies of adsorption and micellization processes calculated from isotherms γ versus ln c (g.dm-3) indicate cooperativeness of hydrophilic and hydrophobic groups.
  • Thermogravimetric and spectroscopic study (TG–DTA/FT–IR) of activated carbon from the renewable biomass source babassu Artigo

    Oliveira, Giulyane Felix de; Andrade, Robson Carlos de; Trindade, Magno Aparecido Gonçalves; Andrade, Heloysa Martins Carvalho; Carvalho, Cláudio Teodoro de

    Resumo em Inglês:

    Activated carbons (ACs) with well–developed microstructure and high microporosity were obtained from biomass by potassium hydroxide activation. The preparation process consisted in producing carbon materials in the ratios of activating agent to raw material 70:30, 50:50, 30:70 and 25:75 (w/w) characterized by thermal analysis coupled to spectroscopy (TG–DTA / FT–IR), scanning electron microscopy (SEM), N2 adsorption isotherms at –196 ºC and activation isotherm at 500 and 600 ºC for 3.0 h. Specific surface areas (SBET) within 728 and 1712 m2 g-1 and (Smic) within 1054 and 1923 m2 g-1 were obtained, while the micropores surface area was calculated using the Dubinin-Astakhov (DA) equation and the pore size distribution calculated from density functional theory (DFT) was found to be in the range 1.09 – 1.77 nm. Adsorption isotherms were fitted using Langmuir and Freundlich non–linear models and the adsorption capacity determined for methylene blue dye was between 27.13 and 459.20 mg g-1.
  • Immobilization of lipase on mesoporous molecular sieve MCM-48 obtained using ionic solid as a structure director and esterification reaction on solvent-free Artigo

    Battiston, Catia S. Z.; Ficanha, Aline M. M.; Levandoski, Katarine L. D.; Silva, Bernardo A. da; Battiston, Suellen; Dallago, Rogério M.; Mignoni, Marcelo L.

    Resumo em Inglês:

    Candida antarctica lipase B (CALB) is an enzyme able to catalyze chemical reaction, however when it is used as a free enzyme, it cannot be recovered from reaction medium. One of the alternatives is to immobilize the enzymes on a support which allows the maintenance of their catalytic activities. The purpose of this paper was to immobilize the CALB on MCM-48 using the ionic solid [C16MI]Cl as structure director. 22 CCRD (Central Composite Rotational Design) was proposed to analyze the influence of the variables like enzyme mass (0.059 to 0.341 g) and ionic solid concentration (0.59 to 3.41%) in the enzyme immobilization process to obtain the maximum esterification activity in order to optimize the process. After immobilization, the study results showed that the enzymes exhibited improvement of thermal (40, 60 and 80 ºC) and storage stability (90 days), besides the possibility to reuse of the enzyme up to 10 times, showing residual activity of 50%.
  • Estudio teorico de las interacciones de dos modelos de ácidos húmicos con los cationes Al3+, Ca2+, Mg2+, Zn2+, K+ y NH4+ a un nivel de calculo DFT y un modelo de solvatación PCM Artigo

    Espinosa-Fuentes, Eduardo; Castillo, Fredy Colpas; Fuentes, Edgardo Meza

    Resumo em Inglês:

    In this paper, two models of humic acids, the Temple-Northeastern-Birmingham (TNB) and Kolla models, were studied. Also, the complexation reaction of the structures formed by the interaction of the TNB and Kolla models with Al3+, Ca2+, Mg2+, Zn2+, K+ and NH4+ cations, common in agricultural soils, was studied. These calculations were made for the complexes, at PM6 and DFT / LANL2DZ level of theory, both in vacuum and in aqueous medium. We found a strong affinity between Kolla and TNB models, and Al3+, Ca2+, Mg2+, Zn2+, K+ and NH4+ cations, influenced by the solvent that affected the interaction sites; the solvent increased the rate of reactivity and affinity for the cations in nucleophilic regions and decreased it in electrophilic regions of the structures. Calculations of molecular electronic potential, MEP and atomic charges, the local smoothness, Fukui functions and the HSAB principle adequately described the HA/cations interactions which were affected by the number of hydrogen bonds. The most reactive sites were the hydroxyl, phenolic, carbonyls oxygens and nitrogens at both vacuum and aqueous medium, especially carbonyl oxygens. These results are consistent with the properties of HA that make them attractive as components of agricultural soils.
  • Binary systems of Brij® surfactants with Pluronic® F127 as griseofulvin carrier Artigo

    Coelho, Ethanielda de L.; Moura, Carolina L. de; Maia, Deyse de S.; Araújo, Tamara G. de; França, Francisco C. F. de; Ricardo, Nadja M. P. S.; Ribeiro, Maria Elenir N. P.; Ricardo, Nágila M. P. S.

    Resumo em Inglês:

    The binary mixtures of Brij® surfactant and Pluronic® F127 were studied as carriers of griseofulvin. The F127 systems and Brij® 78 (C18H37E20), Brij® 98 (C18H35E20) and Brij® 700 (C18H37E100) were prepared in the proportions 10/90, 30/70, 50/50 and 70/30, respectively. The characterizations were carried out by tube inversion, rheology, particle size, and theoretical cmcs. The griseofulvin solubilization tests were performed at 25 and 37 ºC in micellar solutions of 1 wt. % and quantified by UV/Vis. According to the rheological data, the presence of F127 make the F127/Brij 78 70/30 and F127/Brij 98 70/30 mixtures thermoresponsive at concentrations of 30 and 35 wt.%, with transition fluid/gel in the range of 28-30 ºC, ideal for topical use. All of the F127 / Brij 700 mixtures showed moderate distribution polydisperse (PDI < 0.4), as well as mixtures of F127 / Brij 98, with the exception of the mixture with ratio 30/70. Mixtures of F127 / Brij 78 had wide polydisperse distribution (PDI > 0.4). The optimal mixing for oral application would be of F127/Brij 78 because it exhibits greater solubilizing capacity (Scp) of griseofulvin at temperatures of 25 to 37 ºC when compared to F127 alone.
  • Decomposição ácida assistida por ultrassom para a determinação de Cu, Fe, Mg e Zn por F AAS em cerâmicas de uso doméstico Artigo

    Oreste, Eliézer Quadro; Souza, Alexander Ossanes de; Pereira, Camila Corrêa; Vieira, Mariana Antunes; Ribeiro, Anderson Schwingel

    Resumo em Inglês:

    This paper describes a sample preparation method for domestic ceramics, based on the acid decomposition assisted by ultrasound for further determination of Cu, Fe, Mg and Zn by Flame Atomic Absorption Spectrometry technique. The main optimized conditions were: particle size (25 µm); sample mass (25 mg) and the acid volume (0.5 mL of HNO3 and 0.5 mL of HF). The samples were placed in an ultrasonic bath for 2 hours at 40 ºC. The method was employed for eight commercial samples of domestic ceramic, which showed different concentrations for all analytes investigated, showing the existing variety of raw materials. The method showed good accuracy and precision, attested by the addition and recovery test, with values of 87 to 112% for all analytes and relative standard deviation lower than 3.0%.
  • Retardantes de chama bromados: uma revisão Revisão

    Pieroni, Michelle C.; Leonel, Juliana; Fillmann, Gilberto

    Resumo em Inglês:

    Polybrominated diphenyl ethers (PBDEs), Polybrominated biphenyls (PBBs), Hexabromocyclododecane (HBCD) and Tetrabromobisphenol A (TBBP-A) are flame retardant widely used in plastics, textiles, furniture, consumer electronics, automobiles, among others.They are important components added to retard the spread of flame and, thus,mitigate deaths and destruction caused by fires. However, environmental studies conducted in several places show that these compounds exhibit toxic effects. In addition, some are resistant to degradation, persistant in the environment, bioaccumulate and biomagnify in biota, which have worried the scientific community and government agencies. Therefore, production and use of some brominated flame retardants is being restricted and / or prohibited in many countries and some have recently been listed in the Annexs of Stockholm Convention as Persistent Organic Pollutants (POPs). Thus, a review of their use, production, legislation and environmental occurrence is presented, as well as a brief introduction to the new generation of flame retardants.
  • Remediação de solos contaminados por processos fenton: uma revisão crítica Revisão

    Santos, Alecsandra dos; Costa, Graziela da Silva; Peralta-Zamora, Patricio

    Resumo em Inglês:

    The remediation of contaminated soils is probably one of the biggest environmental challenges, mainly due to the complex dynamics of the pollutants in this medium. Among a variety of treatment alternatives proposed for the in-situ remediation of contaminated soils, Fenton processes appear as the most cost-effective, particularly when catalyzed by native iron oxides. However, both the efficiency of the Fenton process and its effect on the treated soil, are largely dependent of the treatment conditions and the main characteristics of the soil, which implies the nonexistence of universal procedures. In this work, the use of Fenton processes in soil remediation routines is critically evaluated, emphasizing aspects related to the degradation efficiency, the influence of the soil properties, the degradation mechanisms and the impacts on the treated soil.
  • Quantificação de alquilbenzeno linear sulfonato em estação de tratamento de efluentes e rios por cromatografia líquida de alta eficiência e extração em fase sólida Nota Técnica

    Silva, Luiz G.; Gavazza, Sávia; Florencio, Lourdinha; Kato, Mario T.

    Resumo em Inglês:

    The procedures to implement a chromatographic method for the quantification of linear alkyl benzene sulfonate (LAS) in the influent, effluent and sludge of a wastewater treatment plant (WWTP), and in river water and sediment, are described and evaluated. The columns octylsilane (C8) and octadecylsilane (C18) for high performance liquid chromatography were evaluated for separation of LAS homologues. The results showed that both columns separated the four homologues, but C18 was better for separation of the isomers of each homologue. This enabled to qualitatively evaluate the degradation of homologues in the WWTP, according to their respective isomers. Samples pre-treatment by solid phase extraction (SPE) columns, strong anionic exchange (SAX) and C18, was also evaluated. SPE was necessary for water river samples, either to concentrate LAS or to remove interference in the matrix; however, for WWTP samples, SPE showed unnecessary. The recovery of LAS homologues, after the procedures for sample preparation, was 90 to 110% with an accuracy of 1 to 5%. The WWTP was efficient in LAS removal from domestic sewage; however, the concentrations in water and sediments of the receiving body were higher than the limits established by legislation due to illegal discharges of untreated sewage.
  • Modelos estereoquímicos de adição à carbonila Educação

    Martins, Bruna S.; Lüdtke, Diogo S.; Moro, Angélica Venturini

    Resumo em Inglês:

    The stereochemical control in the generation of new stereogenic centers is of paramount importance in organic chemistry. In this context, diastereoselective additions to carbonyl compounds bearing a stereogenic center at the α-position are of particular importance, since an increase in molecular complexity can be achieved by constructing a new bond, together with the introduction of a new stereocenter. Despite the relevance of the topic, it is discussed only briefly in several of the most popular organic chemistry textbooks, or not discussed at all. The present article intends to discuss the evolution of stereochemical models for 1,2-induction and present to students a tool to understand and predict the stereochemical outcome of addition of nucleophiles to aldehydes and ketones bearing a stereogenic center at the α-position.
  • Pictogramas do GHS e sua aplicação como ferramenta de comunicação de perigos para estudantes de graduação Assuntos Gerais

    Uema, Leila K.; Ribeiro, Marcela G.

    Resumo em Inglês:

    Regularly, teaching laboratories use chemicals hazardous to health. Students must be aware of such hazards, to safely perform didactic experiments. The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is a hazard communication tool designed to harmonize the classification with a standardized labeling system worldwide. This work aimed at investigating whether undergraduate students correctly identify the hazards associated with a series of chemicals handled during practical laboratory classes. A questionnaire was administered to the students using the hazard classification established by the GHS as reference. They had to match each chemical with one or more pictograms and hazard classes. Statistical tests were performed to correlate the association between right answers and background items, such as having contact with chemicals during earlier classes, having contact with chemical labels at work or having received training courses in hazard communication. The overall assessment showed that students do not recognize GHS pictograms, especially those representing health hazards and thus, they were not aware of the hazards they were exposed to. Many are the reasons for that. At last, strategies to embed health and safety practices into formal education are needed to strengthen the prevention culture in such a learning environment.
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