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Química Nova, Volume: 37, Número: 9, Publicado: 2014
  • Particulate matter in the indoor environment of museums in the megacity of São Paulo

    Cavicchioli, Andrea; Morrone, Ericka Pardini; Fornaro, Adalgiza

    Resumo em Inglês:

    Atmospheric pollutants can have serious impacts on the preservation of São Paulo's tangible cultural heritage. The purpose of this paper is to report the results of a monitoring campaign focussed on particulate matter (PM) that was conducted in three of the most important museums of the São Paulo megacity (Brazil): the Museu de Arqueologia e Etnologia (MAE-USP), the Museu Paulista (MP-USP), and the Pinacoteca do Estado de São Paulo (PE). These museums exhibit indoor PM and black carbon (BC) concentrations consistent with their urban locations and their specific methods for managing the indoor environment.
  • Preconcentration of copper from natural water samples using ligand-less in situ surfactant-based solid phase extraction prior to FAAS determination

    Mohammadi, Sayed Zia; Afzali, Daryoush; Sabermahani, Fatemeh; Afshari, Samira

    Resumo em Inglês:

    In the present work, a simple and rapid ligand-less, in situ, surfactant-based solid phase extraction for the preconcentration of copper in water samples was developed. In this method, a cationic surfactant (n-dodecyltrimethylammonium bromide) was dissolved in an aqueous sample followed by the addition of an appropriate ion-pairing agent (ClO4-). Due to the interaction between the surfactant and ion-pairing agent, solid particles were formed and subsequently used for the adsorption of Cu(OH)2 and CuI. After centrifugation, the sediment was dissolved in 1.0 mL of 1 mol L-1 HNO3 in ethanol and aspirated directly into the flame atomic absorption spectrometer. In order to obtain the optimum conditions, several parameters affecting the performance of the LL-ISS-SPE, including the volumes of DTAB, KClO4, and KI, pH, and potentially interfering ions, were optimized. It was found that KI and phosphate buffer solution (pH = 9) could extract more than 95% of copper ions. The amount of copper ions in the water samples varied from 3.2 to 4.8 ng mL-1, with relative standard deviations of 98.5%-103%. The determination of copper in water samples was linear over a concentration range of 0.5-200.0 ng mL-1. The limit of detection (3Sb/m) was 0.1 ng mL-1 with an enrichment factor of 38.7. The accuracy of the developed method was verified by the determination of copper in two certified reference materials, producing satisfactory results.
  • Poliuretanos obtenidos a partir de aceite de higuerilla modificado y poli-isocianatos de lisina: síntesis, propiedades mecánicas y térmicas y degradación in vitro

    Valero, Manuel F.; Díaz, Luis E.

    Resumo em Inglês:

    Biodegradable polyurethanes (PUR) were prepared from polyols derived from castor oil by transesterification of pentaerythritol-modified castor oil and lysine polyisocyanates (LDI and LTI). The polyurethanes obtained were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA). The mechanical behavior of the polyurethanes was measured by Shore A hardness and tensile testing (stress-strain curves). The biodegradable nature of the material was determined by contact angle, water absorption tests, and in vitro degradation in PBS solution. This study aims to examine the effect of the structure and functionality of diisocyanate on the mechanical properties and in vitro degradation of the material. The results were compared with homologous materials obtained from isophorone diisocyanate (IPDI) used in previous works. The objective was to evaluate candidate materials that can be potentially used in tissue engineering.
  • Modulating the electronic structure of amino acids: interaction of model lewis acids with anthranilic acid

    Irshaidat, Tareq

    Resumo em Inglês:

    On the basis of theoretical B3LYP calculations, Yáñez and co-workers (J. Chem. Theory Comput. 2012, 8, 2293) illustrated that beryllium ions are capable of significantly modulating (changing) the electronic structures of imidazole. In this computational organic chemistry study, the interaction of this β-amino acid and five model Lewis acids (BeF1+, Be2+, AlF2(1+), AlF2+, and Al3+) were investigated. Several aspects were addressed: natural bond orbitals, including second order perturbation analysis of intra-molecular charge delocalization and the natural population analysis atomic charges; molecular geometries; selected infrared stretching frequencies (C-N, C-O, and N-H), and selected ¹H-NMR chemical shifts. The data illustrate that this interaction can weaken the H-O bond and goes beyond strengthening the intra-molecular hydrogen bond (N...H-O) to cause a spontaneous transfer of the proton to the nitrogen atom in five cases generating zwitterion structures. Many new features are observed. Most importantly, the zwitterion structures include a stabilizing hydrogen bond (N-H...O) that varies in relative strength according to the Lewis acid. These findings explain the experimental observations of α-amino acids (for example: J. Am. Chem. Soc. 2001, 123, 3577) and are the first reported fundamental electronic structure characterization of β-amino acids in zwitterion form.
  • Alcaloides isoquinolínicos e investigação das atividades antiplasmódica e antibacteriana de Guatteria citriodora (Annonaceae) Artigo

    Rabelo, Diego de M.; Pinheiro, Maria L. Belém; Barison, Andersson; Salomé, Kahlil S.; Costa, Emmanoel V.; Silva, Felipe M. Araujo da; Chaves, Yury O.; Bastos, Ivanildes dos S.

    Resumo em Inglês:

    Phytochemical investigations of the stem bark, leaves and twigs of Guatteria citriodora resulted in the isolation of eight alkaloids: liriodenine, lysicamine, O-methylmoschatoline, 3-methoxyoxoputerine, palmatine, 3-methoxyguadiscidine, guattescidine and oxoputerine. The structures of the isolated substances were established by extensive spectroscopic techniques (1D and 2D NMR) and mass spectrometry (MS), as well as by comparison with data reported in the literature. The in vitro antimalarial activity of the alkaloidal fractions of the leaves and twigs against Plasmodium falciparum FCR3 showed significant results, with IC50 = 1.07 and 0.33 mg mL-1, respectively. The alkaloidal fraction of the leaves showed moderate activity against Enterococcus faecalis, with IC50 = 125.0 mg mL-1. Antiplasmodial and antibacterial activities are attributed to alkaloidal constituents.
  • Modificação do polímero condutor polianilina para uso como trocador catiônico Artigo

    Zornitta, Rafael L.; Pincelli, Guilherme; Ruotolo, Luís A. M.

    Resumo em Inglês:

    This article reports the use of polyaniline (PAni), chemically and electrochemically synthesized, for copper removal from aqueous solutions. PAni films were electrodeposited on reticulated vitreous carbon (RVC). In all cases, p-toluenesulfonate anion (PTS-) was used as the dopant to obtain cation exchange properties. RVC/PAni showed no expressive copper removal due to the small amount of polymer in the film. Chemically synthesized PAni-PTS- was obtained in its reduced form (leucoesmeraldine). PAni degraded at neutral pH but remained stable at low pH, showing a very high ion-exchange capacity, which is superior to those observed for commercial resins.
  • Separation and purification of three stilbenes from the radix of Polygonum cillinerve (Nakai) Ohwl by macroporous resin column chromatography combined with high-speed counter-current chromatography

    Chi, Xiaofeng; Xing, Yuxiu; Xiao, Yuancan; Dong, Qi; Hu, Fengzu

    Resumo em Inglês:

    An effective method for the rapid separation and purification of three stilbenes from the radix of Polygonum cillinerve (Nakai) Ohwl by macroporous resin column chromatography combined with high-speed counter-current chromatography (HSCCC) was successfully established. In the present study, a two-phase solvent system composed of chloroform-n-butanol-methanol-water (4:1:4:2, v/v/v/v) was used for HSCCC separation. A one-step separation in 4 h from 150 mg of crude extract produced 26.3 mg of trans-resveratrol-3-O-glucoside, 42.0 mg of pieceid-2"-O-gallate, and 17.9 mg of trans-resveratrol with purities of 99.1%, 97.8%, and 99.4%, respectively, as determined by high-performance liquid chromatography (HPLC). The chemical structures of these compounds were identified by nuclear magnetic resonance (NMR) spectroscopy.
  • Comportamento eletroquímico e avaliação da difusão in vitro do α-tocoferol associado à iontoforese Artigo

    Paludo, Elisa; Bresciani, Laís; Hilgemann, Maurício; Tassinary, João Alberto; Stülp, Simone

    Resumo em Inglês:

    Iontophoresis is a method of administering substances through the skin, which uses electrical current or potential to promote transdermal delivery. We focused on α-tocopherol (vitamin E), a natural antioxidant able to reduce or block the oxidation reactions induced by free radicals in biological membranes. The aim of this study was to perform electrochemical evaluation and analysis of vertical diffusion of gel + α-tocopherol undergoing iontophoresis. The results showed a reduction in peak current at 0.78 V of α-tocopherol molecules when subjected to iontophoresis, increasing the diffusion and degradation of the system.
  • Phytochemical study, antioxidant and antibacterial activities of Stemodia maritima

    Silva, Francisca R. L. da; Rodrigues, Francisco E. A.; Gomes, Aldenia R. S.; Arriaga, Angela M. C.; Mafezoli, Jair; Lemos, Telma L. G.; Almeida, Macia C. S. de; Santiago, Gilvandete M. P.; Braz-Filho, Raimundo; Costa, José G. M. da; Rodrigues, Fabiola F. G.; Coutinho, Henrique D. M.

    Resumo em Inglês:

    Stemodinol, a new natural compound, together with known compounds including jaceidin, stemodin, stemodinoside B, isocrenatoside, verbascoside, crenatoside, and isoverbascoside, were isolated from Stemodia maritima Linn. The antioxidant (DPPH method) and antimicrobial activities of stemodin, stemodinoside B, and crenatoside were investigated. Among the components tested, only crenatoside isolated from the roots showed a high antioxidant power. Stemodin and stemodinoside B exhibited antibacterial activities.
  • Avaliação da labilidade de alumínio em infusões de erva-mate empregando voltametria adsortiva de redissolução catódica Artigo

    Campos, Bruna Kauely de; Prazeres, Jéssica Pacheco dos; Torres, Yohandra Reyes; Anjos, Vanessa Egéa dos; Quináia, Sueli Pércio

    Resumo em Inglês:

    Infusions of yerba mate obtained at different stages of industrialization were evaluated to determine the bioavailable fraction of Al. Adsorptive Cathodic Stripping Voltammetry using DASA (complexing agent) was applied to determine the labile fraction of Al at pH 5.0 and pH 8.0 for the total fraction of dissolved Al. The results indicate that on average 60% of Al is complexed with organic compounds, minimizing their bioavailability; however, the labile fraction exceeds by up to 4 times the maximum weekly intake recommended by the World Health Organization.
  • Estudo químico das folhas de Trichilia silvatica (Meliaceae) Artigo

    Soares, Aloízio de Oliveira; Ferreira, Adrienn Gianny Leguizamon; Soares, Luzinátia Ramos; Corsino, Joaquim; Garcez, Fernanda Rodrigues; Garcez, Walmir Silva

    Resumo em Inglês:

    From the leaves of a specimen of Trichilia silvatica Meliaceae, eight known compounds were isolated, namely, two pregnanes, 2α,3β,4β-trihydroxypregnan-16-one (1) and 2β,3β,4β-trihydroxypregnan-16-one (2), three diterpenes, cneorubine X (3), kolavelool (4) and kolavenol (5), in addition to γ-tocopherol, 3-O-β-D-glucopyranosyl-β-sitosterol and 3-O-β-D-glucopyranosyl-stigmasterol. This is the first reported occurrence of pregnane 1, diterpenes 3-5 and µ-tocopherol in the genus Trichilia. The structures of the isolated compounds were determined on the basis of their spectral data.
  • Phytochemical investigation of Wissadula periplocifolia (L.) C. Presl and evaluation of its antibacterial activity

    Teles, Yanna C. F.; Gomes, Roosevelt A.; Oliveira, Micaelly da S.; Lucena, Kaio L. de; Nascimento, José S. do; Agra, Maria de Fátima; Igoli, John O.; Gray, Alexander I.; Souza, Maria de Fátima V. de

    Resumo em Inglês:

    A phytochemical study on the aerial parts of Wissadula periplocifolia using chromatographic techniques has led to the isolation of sitosterol (1a), stigmasterol (1b), sitosterol 3-O-β-D-glucopyranoside (2a), stigmasterol 3-O-β-D-glucopyranoside (2b), phaeophytin A (3), 13²-hydroxy-(13²-S)-phaeophytin A (4), phaeophytin B (5), 17³-ethoxyphaeophorbide (6), 3,4-seco-urs-4(23),20(30)-dien-3-oic acid (7), 3-oxo-21β-H-hop-22(29)-ene (8), dammaradienone (9a), and taraxastenone (9b). The isolated compounds were characterised by spectroscopic analysis. A preliminary assay to evaluate the antibacterial activity of W. periplocifolia extracts and fractions showed that the dichloromethane, ethyl acetate, and n-butanol fractions were active against Enterococcus faecalis.
  • Determinação voltamétrica de amitriptilina em formulações farmacêuticas com eletrodo de diamante dopado com boro explorando medidas em meio ácido Artigo

    Duarte, Eduardo Henrique; Gorla, Felipe Augusto; Sartori, Elen Romão; Tarley, César Ricardo Teixeira

    Resumo em Inglês:

    A simple and reliable voltammetric method is presented for the determination of amitriptyline using a boron-doped diamond electrode in 0.1 mol L-1 sulfuric acid solution as the support electrolyte. Under optimized differential pulse voltammetry conditions (modulation time 5 ms, scan rate 70 mV s-1, and pulse amplitude 120 mV), the electrode provides linear responses to amitriptyline in the concentration range 1.05 to 92.60 µmol L-1 and at a detection limit of 0.52 µmol L-1. The proposed method was successfully applied in pharmaceutical formulations, with results similar to those obtained using UV-vis spectrophotometric method as reference (at 95% confidence level), as recommended by the Brazilian Pharmacopoeia.
  • Interactions of chitosan/genipin hydrogels during drug delivery: a QSPR approach

    Delgadillo-Armendariz, Nancy L.; Rangel-Vazquez, Norma A.; Marquez-Brazon, Edgar A.; Rojas-De Gascue, Blanca

    Resumo em Inglês:

    A hydrogel comprised of chitosan crosslinked using the low-toxicity crosslinker genipin was prepared, and the absorption of glibenclamide by the hydrogel was investigated. Optimized structures and their molecular electrostatic potentials were calculated using the AM1 method, and the results were used to evaluate the molecular interactions between the three compounds. The quantitative structure-property relationship model was also used to estimate the activity of the chemicals on the basis their molecular structures. In addition, theoretical Fourier transform infrared spectra were calculated to analyze the intermolecular interactions in the proposed system. Finally, the hydrophilicity of the hydrogel and its influence on the absorption process were also estimated.
  • Simultaneous determination of four phenolic compounds in extracts of aerial parts of Ipomoea pes-caprae (L.) R. Br. (Convolvulaceae) by HPLC-UV

    Dutra, Daniela Maes; Barth, Cristiane da Silva; Block, Luciana Catia; Quintão, Nara Lins Meira; Couto, Angélica Garcia; Cechinel Filho, Valdir; Bresolin, Tania Mari Bellé

    Resumo em Inglês:

    Among other applications, Ipomoea pes-caprae is popularly used to treat jellyfish stings, supporting the development of a product for dermatological use. Hydroethanolic spray-dried extract was chosen for the further development of phytomedicines, and a stability-indicative HPLC-UV method was developed and validated for the determination of isoquercitrin and isochlorogenic acids A, B and C. The method was developed using a C18 column (250 x 4.6 mm, 5 µm) with an acetonitrile:water mobile phase at pH 3.0 in a gradient run. The four constituents and other unidentified components of the extract were appropriately resolved without interference of degradation products after stress tests (acid, alkali, neutral, oxidant, photolysis). The method showed linearity in the isoquercitrin concentration range from 5.0-50.0 µg mL-1, with adequate precision (RSD% < 2.5% for the intra- and inter-day studies), accuracy (recovery of 100.0 ± 2.0%), and robustness. Both the herbal drug and spray-dried extract of I. pes-caprae were subjected to stability studies in accelerated and long-term conditions over four months. The samples maintained their characteristics and marker contents (< 10% of variation).
  • Cristalização convencional de zeólitas e induzida por sementes Revisão

    Vieira, Luiz H.; Rodrigues, Mariana V.; Martins, Leandro

    Resumo em Inglês:

    Seed-assisted synthesis of zeolites diminishes crystallization time and enables the industrial use of certain zeolites, which was conventionally unfeasible due to the complexity of synthesis and the cost of organic structure-directing agents. This study reports the primary results of zeolite crystallization in the presence of seeds, which are used as a substitute for organic compounds.
  • Resolução multivariada de curvas com mínimos quadrados alternantes: descrição, funcionamento e aplicações Revisão

    Março, Paulo Henrique; Valderrama, Patrícia; Alexandrino, Guilherme Lionello; Poppi, Ronei Jesus; Tauler, Romà

    Resumo em Inglês:

    Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) is a resolution method that has been efficiently applied in many different fields, such as process analysis, environmental data and, more recently, hyperspectral image analysis. When applied to second order data (or to three-way data) arrays, recovery of the underlying basis vectors in both measurement orders (i.e. signal and concentration orders) from the data matrix can be achieved without ambiguities if the trilinear model constraint is considered during the ALS optimization. This work summarizes different protocols of MCR-ALS application, presenting a case study: near-infrared image spectroscopy.
  • Efeitos da rugosidade superficial nas propriedades de passivação de monocamadas orgânicas automontadas Nota Técnica

    Benites, Tiago A.; Ribeiro, Willian C.; Góes, Márcio S.; Ferreira, Antonio A. P.; Bueno, Paulo R.

    Resumo em Inglês:

    Precise surface area is needed for accurate characterization of self-assembled monolayers (SAMs) on metallic surfaces. The aim of this manuscript was to emphasize that miscalculation of surface area is the major source of errors in SAM electrochemical characterization. Limitations are discussed and recommendations given for beginners in analyses of SAM functionalized electrodes. The electrochemical measurements and examples were based on bare gold electrode immobilized with dodecanethiol. The degree of compression of the monolayer properties of formation and reproducibility of the electrochemical response depends on roughness factor, with values closer to the unit being better.
  • Estudo do teste de Scott via técnicas espectroscópicas: um método alternativo para diferenciar cloridrato de cocaína e seus adulterantes Nota Técnica

    Conceição, Vitor N.; Souza, Lindamara M.; Merlo, Bianca B.; Filgueiras, Paulo R.; Poppi, Ronei J.; Romão, Wanderson

    Resumo em Inglês:

    Cocaine is usually seized mixed with a wide variety of adulterants such as benzocaine, lidocaine, caffeine, and procaine. The forensic identification of cocaine in these street drug mixtures is normally performed using colorimetric testing kits, but these tests may suffer from interferences, producing false-positive results. Here, we describe the use of analytical techniques including attenuated total reflection Fourier transform infrared (ATR-FTIR) and ultraviolet-visible (UV-VIS) spectroscopies to distinguish between cocaine and other adulterants (lidocaine, promethazine, powdered milk and yeast) that yield positive results on the Scott test using the thiocyanate cobalt reagent. A further 13 substances were also analyzed using the Scott test.
  • Experimento utilizando grãos para explorar a calibração em análises químicas Educação

    Silvestre, Daniel Menezes; Naozuka, Juliana; Correia, Paulo Rogério Miranda; Nomura, Cassiana Seimi

    Resumo em Inglês:

    The conventional curriculum of Analytical Chemistry undergraduate courses emphasizes the introduction of techniques, methods and procedures used for instrumental analysis. All these concepts must be integrated into a sound conceptual framework to allow students to make appropriate decisions. Method calibration is one of the most critical parameters that has to be grasped since most analytical techniques depend on it for quantitative analysis. The conceptual understanding of calibration is not trivial for undergraduate students. External calibration is widely discussed during instrumental analysis courses. However, the understanding of the limitations of external calibration to correct some systematic errors is not directly derived from laboratory examples. The conceptual understanding of other calibration methods (standard addition, matrix matching, and internal standard) is imperative. The aim of this work is to present a simple experiment using grains (beans, corn and chickpeas) to explore different types of calibration methods.
  • Automatic evaluation and data generation for analytical chemistry instrumental analysis exercises

    Muñoz de la Peña, Arsenio; Muñoz de la Peña, David; Godoy-Caballero, María P.; González-Gómez, David; Gómez-Estern, Fabio; Sánchez, Carlos

    Resumo em Inglês:

    In general, laboratory activities are costly in terms of time, space, and money. As such, the ability to provide realistically simulated laboratory data that enables students to practice data analysis techniques as a complementary activity would be expected to reduce these costs while opening up very interesting possibilities. In the present work, a novel methodology is presented for design of analytical chemistry instrumental analysis exercises that can be automatically personalized for each student and the results evaluated immediately. The proposed system provides each student with a different set of experimental data generated randomly while satisfying a set of constraints, rather than using data obtained from actual laboratory work. This allows the instructor to provide students with a set of practical problems to complement their regular laboratory work along with the corresponding feedback provided by the system's automatic evaluation process. To this end, the Goodle Grading Management System (GMS), an innovative web-based educational tool for automating the collection and assessment of practical exercises for engineering and scientific courses, was developed. The proposed methodology takes full advantage of the Goodle GMS fusion code architecture. The design of a particular exercise is provided ad hoc by the instructor and requires basic Matlab knowledge. The system has been employed with satisfactory results in several university courses. To demonstrate the automatic evaluation process, three exercises are presented in detail. The first exercise involves a linear regression analysis of data and the calculation of the quality parameters of an instrumental analysis method. The second and third exercises address two different comparison tests, a comparison test of the mean and a t-paired test.
  • Textos científicos de autoria de graduandos em química: análise dos professores Educação

    Oliveira, Jane Raquel Silva de; Queiroz, Salete Linhares

    Resumo em Inglês:

    This study aimed to analyze the aspects of scientific language considered by chemistry professors in the evaluation of scientific texts authored by undergraduate chemistry students. Interviews were conducted with four professors who had evaluated reports and scientific articles written by students enrolled in undergraduate chemistry courses. The professors highlighted aspects pertaining to the structure and general organization of scientific texts typically adopted by the scientific community, and mentioned the importance of certain rhetoric elements in scientific language. This study can be an impetus for further investigation into the importance of language in chemistry education.
  • Desenvolvimento de um sistema de análise por injeção em fluxo utilizando materiais alternativos de baixo custo para fins didáticos Educação

    Moreira, Bruna C. S.; Takeuchi, Regina M.; Richter, Eduardo M.; Santos, André L.

    Resumo em Inglês:

    This work describes a simple and inexpensive flow injection analysis system in which gravity force provides fluid propulsion while needles for insulin administration or metallic wires act as electrodes for amperometric detection. The proposed system was able to demonstrate the influence of several operational parameters on the transient signals. Moreover, this system was successfully used to evaluate both the stoichiometry of Cu2+-EDTA complex and the effect of pH on the kinetics of the reaction between ferricyanide and ascorbic acid. Therefore, the proposed system can be regarded as an efficient and accessible didactic tool for the teaching of FIA principles.
  • Dinâmicas de inquiry no estudo de perturbações a um estado de equilíbrio químico Educação

    Vieira, Hugo; Morais, Carla; Paiva, João

    Resumo em Inglês:

    Educational institutions are not being effective, because they do not give individuals what they need to integrate into postmodern society, nor produce citizens that postmodern society needs. Shortcomings include the scientific literacy and cognitive domain levels attained, with an aggravating waning interest in science among pre-university students. We present an inquiry module, an inquiry dynamic, as an education resource for the study of perturbations of a chemical equilibrium state by pre-university or university students of basic chemistry, to contribute to the relevance and popularity of science, potentiation of science literacy and development of cognition. Here we describe an investigation with pre-university students.
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