Scielo RSS <![CDATA[Química Nova]]> vol. 41 num. 10 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[DETERMINAÇÃO DE POTÁSSIO EM ROCHAS SILICÁTICAS POR ESPECTROMETRIA DE EMISSÃO ATÔMICA COM CHAMA APÓS DISSOLUÇÃO ASSISTIDA POR ULTRASSOM]]> This work presents the development of an analytical method for sample preparation aiming at the K determination in silicate rocks (basalt, monzogranite and shale fines) following ultrasound dissolution and analysis by F AES. Sample preparation method was optimized by using fractional factorial designs. The following optimal conditions were obtained for each silicate rock: 0.1 g of sample mass for any of the three samples, and volumes of HNO3, HCl and HF, respectively, of 2.5, 0.8 and 2.5 mL for basalt; 3.5, 0.8 and 2.5 mL for monzogranite, and 2.5, 1.0 and 2.0 mL for shale fines. Sample dissolution was achieved by using the ultrasound bath at room temperature (25 °C) for 1 hour. The accuracy was evaluated through the analysis of two certified reference materials, for which there was no statistical difference between the certified and the found K concentration values (95% confidence level). The K concentrations determined were: 1.45 ± 0.01 for basalt; 4.19 ± 0.03 for monzogranite and 1.60 ± 0.02 for shale fines. The developed method presented accurate and reliable results for K amounts in silicate rocks and is simple and safe, which are important features for the implementation of a methodology as a routine analysis. <![CDATA[SÍNTESE DE Nb<sub>2</sub>O<sub>5</sub>, Al<sub>2</sub>O<sub>3</sub> E Nb<sub>2</sub>O<sub>5</sub>/Al<sub>2</sub>O<sub>3</sub> VIA MÉTODO DE PECHINI COMO PRÉ-TRATAMENTO ALTERNATIVO PARA ESQUEMAS DE PINTURA DO AÇO CARBONO AISI 1005]]> The use of industrial painting is one of the methods for corrosion protection of metals and requires a suitable surface treatment on the metallic substrate for better adhesion between metal and paint film. In cases where the substrate presents low thickness (less than 2 mm), the phosphating pretreatment is widely used, despite of such process generates harmful residues to environment and human health. In this context, the sol-gel method has been highlighted as an easy and a cheap process, and less harmful to the environment. This work shows the development of carbon steel AISI 1005 pre-treatment by sol-gel method using niobium and/or aluminium-containing-resins, synthetized by Pechini method. Electrochemical and performance analysis were carried out in samples coated by the resins, which showed analogous behavior to phosphated systems. The proposed pre-treatment has potential for phosphating process replacement, because the morphology of the deposited layers enhanced the metallic contact surface with the organic coating, increasing its mechanical and polar adhesion. Such observation can justify its better anticorrosive performance, comparing to the untreated substrate. <![CDATA[INFLUENCE OF LOW AND HIGH GLYCEROL CONCENTRATIONS ON WETTABILITY AND FLEXIBILITY OF CHITOSAN BIOFILMS]]> The use of chitosan biofilm in biomedical fields has a vast therapeutic potential due to useful properties such as biodegradability and antimicrobial activity, however, to achieve successful application some physicochemical properties need to be improved. In this context, the addition of glycerol to this biofilm is an alternative to improve its wettability and flexibility. Thus, low and high concentrations of plasticizer were added to this biomaterial for later characterization regarding its wettability, microstructure, mechanical and chemical properties. Glycerol addition to chitosan resulted in biofilms with more homogeneous surfaces, increased wettability, and increased flexibility, without significant changes in its chemical structure. <![CDATA[PLACAS CERÂMICAS CONTENDO LODO DE ETA E CINZA DE CASCA DE ARROZ: CORRELAÇÃO DE SUAS PROPRIEDADES FÍSICO-QUÍMICAS COM SUA MICROESTRUTURA]]> Pressed ceramic plates were made from mixtures with different proportions containing kaolinite clay, silica extracted from the rice husk ash after controlled burning at controlled temperature and sludge from a water treatment plant. Physical properties such as density, water absorption and porosity, mechanical properties such as compressive strength, and thermal characteristics such as thermal conductivity of the ceramic plates after burning (DIN EN12667) were evaluated. The silica when inserted in the kaolinite clay can have a gradual increase of its performance, be reduced in the porous phase, with reduction of the thermal conductivity and increase of the mechanical resistance. The use of the sludge from a water treatment plant when incorporated to the ceramic mass is a great number of peaks of charge and of crystallization, expressive increase of porosity and decrease of the thermal and mechanical resistances. As ceramic plates with a trace 72% kaolinite clay, 18% rice husk and 10% sludge from a water treatment plant show lower thermal conductivity 0.2574 W m-1K-1, and a higher compressive strength of 172.12 MPa when compared to the other plates tested where the substitutions for sludge from a water treatment plant occurred. <![CDATA[HIDRÓLISE ENZIMÁTICA, FERMENTAÇÃO E PRODUÇÃO DE BIOCOMBUSTÍVEIS ATRAVÉS DA COROA DE <em>Ananas comosus</em>]]> Problems related to the use of fossil fuels and greenhouse gas emissions have become global concerns. To address this issue, the strategy adopted in the present study was to use Ananas comosus residues as a source of fermentable carbohydrates to produce second generation ethanol and briquettes. The demand for biofuel is addressed in the present study by the integrated processing of several stages of treatment of the lignocellulosic substrate: chemical characterization, pretreatment, enzymatic hydrolysis and fermentation. It was verified under the conditions used that the enzymatic hydrolysis liberated after 72 hours 58.44 and 21.91 g L-1 of glucose and xylose, respectively. Conversion of the sugars in the fermentation step resulted in 18.80 g L-1 ethanol in 24 hours. The briquettes produced from the remaining solid fraction of the enzymatic hydrolysis presented a calorific value of 18.41 kJ kg -1. <![CDATA[ESTUDO TEÓRICO DE POTENCIAIS AGENTES PARA O TRATAMENTO DA DOENÇA DE ALZHEIMER DERIVADOS DA 8-HIDROXIQUINOLINA COM SUBSTITUINTES DO TIPO <em>N</em>-ACIL-HIDRAZONA]]> In this work, Density Functional Theory was used in the theoretical study of the coordination of three ligands derived from 8-hydroxyquinoline (8-HQ) with N-acylhydrazone: 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INHHQ), 2-[(8-hydroxyquinolinyl)methylene] acetohydrazide (8-H2QH) and 2-[(8-hydroxyquinolinyl)methylene] hydrazinecarboxamide (8-H2QS); with the Zn2+ion. These complexes prevent interactions of the metal ions present in the brain, with the β-amyloid peptide (Aβ), avoiding the formation of aggregates that are responsible for the development of the Alzheimer's disease. The results show that the three ligands coordinate the Zn2+ion in a tridentate form through the O and N atoms of the 8-hydroxyquinoline center and the N of the hydrazonic group, completing the coordination sphere with two chloride ions, creating a bipyramidal structure trigonal, different from the structures of the complexes reported in the literature. <![CDATA[POLYPHENOL AND TRITERPENOID CONSTITUENTS OF <em>Eugenia florida</em> DC. (MYRTACEAE) LEAVES AND THEIR ANTIOXIDANT AND CYTOTOXIC POTENTIAL]]> Leaves of Eugenia florida DC. have been used in folk medicine as hypotensive, hypoglycemic, antipyretic and for gastrointestinal disorders, among others. In this study dried leaves were extracted with ethanol and the extract was partitioned with hexane, CHCl3, EtOAc, BuOH and water to afford triterpenoid- and polyphenol-rich fractions which were analyzed by GC-MS and UFLC-DAD-ESI-Ion Trap-MSn. All fractions were tested against the proliferation of leukemic K562 and human melanoma SK-Mel-28 cell lines and for their ability to scavenge DPPH radical. Twenty-nine compounds were fully identified (among triterpenic and phenolic acids, flavonol- and dihydroflavonol-monoglyclosides) based on mass fragmentation patterns and comparison to standards and/or literature data. The ability to scavenge DPPH radical resulted in the following order: BuOH ≈ EtOAc &gt; crude extract ≈ Water &gt;&gt; CHCl3 &gt;&gt; hexane; with the two most active reaching half of the TBHQ control potency (EC50 6.59 ± 0.03 µg mL-1). On testing against the proliferation of K562 and SK-Mel-28 cell lines, the most significant inhibitions were achieved on the former by the crude extract (IC50 12 µg mL-1) and the hexane and EtOAc fractions at 15 µg mL-1. <![CDATA[SÍNTESE, CARACTERIZAÇÃO E AVALIAÇÃO DA ATIVIDADE CITOTÓXICA DE COMPOSTOS CICLOPALADADOS CONTENDO COMO LIGANTES BENZALDEIDOXIMA ORTOMETALADA E ETILENOTIOURÉIA]]> The halide-bridge cleavage reaction of the [Pd(C2 ,N-bzox)(µ-Cl)]2 compound (bzox = benzaldehydeoxime) with ethylenethiourea (L) in the 1:2 molar ratio at room temperature yielded the cyclopalladated compound [Pd(C2 ,N-bzox)(Cl)(L)] (1) whose replacement of the halide group by the addition of suitable salts afforded compounds of general formulae [Pd(C2 ,N-bzox)(X)(L)] {X = Br- (2), I- (3)}. All compounds were characterized by melting point, elemental analyses, infrared and 1H- and 13C{1H}-NMR spectroscopies revealing the complexes formation with the oxime coordinated to Pd(II) as C,N-chelating and the ethylenethiourea as a monodentate ligand via the sulfur atom. The cytotoxicity of cyclopalladated compounds has been evaluated in vitro against murine mammary tumor cell (LM3) showing cytotoxic activity similar to cisplatin. <![CDATA[EFFECT OF CALCINATION TEMPERATURE ON THE STRUCTURE AND CATALYTIC PERFORMANCE OF THE CU-MCM-41 CATALYSTS FOR THE SYNTHESIS OF DIMETHYL CARBONATE]]> A series of Cu-MCM-41 catalysts were synthesized through in-situ hydrothermal preparation method, calcinated at different temperatures and characterized by thermogravimetric and differential scanning calorimetry (TG-DSC), N2 adsorption-desorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FI-IR), transmission electron microscopy (TEM) and hydrogen temperature-programmed (H2-TPR). The effect of calcination temperature on the structural properties and selective oxidation of dimethoxymethane (DMM) to dimethyl carbonate (DMC) were discussed in detail. The results showed that the calcination temperature played important role on the microstructure and catalytic activity of the Cu-MCM-41 catalysts. At the calcination temperature 550 °C, the Cu-MCM-41 catalyst possessed higher surface area, smaller pore diameter, stronger metal-support interaction, and better CuO dispersion compared the other catalysts, and the corresponding catalyst exhibited excellent activity and stability for the DMC synthesis. Under the reaction conditions at 2.0 MPa and 130 °C, the highest DMM conversion was 99.47% with the best DMC selectivity of 85.01%. In addition, the catalyst was reused four times without significant loss of performance. <![CDATA[PRODUÇÃO DE MATERIAL DE REFERÊNCIA CERTIFICADO DE ÓXIDO DE HÓLMIO(III) EM AMPOLAS]]> This work reports the development of a certified reference material (CRM) of holmium(III) oxide Ho2O3 in acidic solution for the wavelength scale calibration of UV-Vis spectrophotometers. A 4.0% Ho2O3 solution was gravimetrically prepared in 10% perchloric acid and bottled in 5.0 mL glass ampoules. Homogeneity, stability and characterization were assessed according to ISO 17034 and ISO Guide 35. The material certification was undertaken by two laboratories by using UV-Vis spectrophotometry for characterization of the 14 peaks of minimum transmittance of Ho2O3, using a spectral bandwidth of 1.00 nm and a scanning speed of 30.0 nm min‒1. The material property values in wavelength (nm) were obtained for these 14 peaks, together with the expanded uncertainty (U) of 0.12 nm, for a coverage factor (k = 2.00) corresponding to a probability of approximately 95%, which took into account the standard uncertainties obtained in each study performed for the certification of the produced reference material. <![CDATA[AVANÇOS QUÍMICOS NO PLANEJAMENTO E DESENVOLVIMENTO DE DERIVADOS DO PARACETAMOL]]> Acetaminophen or paracetamol is a widely used analgesic and antipyretic drug and appears to be safe if used at normal therapeutic doses, but in large doses produce liver and / or kidney damage in humans and experimental animals. Prostaglandin endoperoxide synthase (PGES) and cytochrome P-450 are the key enzymes in humans as they are responsible for the analgesic and toxicity effects of paracetamol, respectively. At present, the development of new derivatives still has few impacts on clinical applications of safe compounds. Thus, in this work are discussed, a series of approaches on the design and development of acetaminophen derivatives. Some efforts were realized in our own research group. <![CDATA[MOFs (METAL-ORGANIC FRAMEWORKS): UMA FASCINANTE CLASSE DE MATERIAIS INORGÂNICOS POROSOS]]> Metal-Organic Frameworks (MOFs) are, according to IUPAC, coordination polymers with an open framework containing potential voids, which can be accessible after activation processes. These materials have aroused interest in the academic environment – and more recently in industry - because their properties such as high crystallinity, permanent microporosity, high surface areas, and the possibility of functionalization. This has enabled applications in different areas, such as gas adsorption, catalysis, drug delivery, photonics and others. Depending on the judicious choice of the metals and the organic linkers, MOFs with different topologies and functions can be created. Synthetic routes for the preparation of these materials will be discussed, highlighting those in consonance with the Green Inorganic Chemistry. Strategies for controlling the size and morphology of the crystals will also be presented, as well the most recent methodologies for the large-scale production. This review will also discuss the use of MOFs in the context of energy and environment, particularly referring to the adsorption and/or transformation of CO2, storage of H2 and CH4 as well potable water capture. <![CDATA[STRAIGHTFORWARD, ECONOMICAL PROCEDURES FOR MICROSCALE ELLMAN'S TEST FOR CHOLINESTERASE INHIBITION AND REACTIVATION]]> Straightforward, microscale, Ellman's cholinesterase test procedures are presented, useful for screening of novel compounds aiming at neurodegenerative diseases and antidotes towards nerve agents and pesticides. Herein, we detail the different procedure features and set forth guidelines on experimental choices researchers may make. The detailed procedure lowers the costs for Ellman´s test, what is highly desirable for low-budget groups in science-lagging and developing countries. <![CDATA[CONSTRUÇÃO DE UMA BOMBA PERISTÁLTICA E DE UM SISTEMA DE DETECÇÃO UTILIZANDO UM HARDWARE DE CÓDIGO FONTE ABERTO “ARDUINO” PARA ANÁLISE EM FLUXO]]> This work describes the development of a peristaltic pump and a photometric detector, using “Arduino” and alternative and low-cost materials for flow analysis system. The analytical calibration curve of the acid-red-283 using the proposed system presents 0.9984 and 3.9% as the coefficients of determination and variation, and 1.1 and 3.8 mg L-1 as limits of detection and quantification, respectively. Three prepared samples of the acid-red-283 (25, 30 and 35 mg L-1) showed recovery between 99 to 104%. For construction of the peristaltic pump and the photometer using Light Emitting Diodes (LED), light-dependent resistor (LDR) were spent less than 10% of the cost was spent on a commercial system employing a peristaltic pump and a spectrophotometer. Furthermore, the peristaltic pump and the photometer developed in this work allow the implementation of practical disciplines, such as molecular absorption spectrophotometry and flow analysis system in undergraduate courses, making these instruments more accessible, especially for the chemistry students. <![CDATA[BIOFUELS FROM COCONUT FAT AND SOYBEAN OIL: MICROWAVE-ASSISTED SYNTHESIS AND GAS CHROMATOGRAPHY/MASS SPECTROMETRY ANALYSIS]]> We developed a project during an undergraduate course (advanced experimental chemistry) on the microwave-assisted synthesis of biodiesel (BD), via base-catalyzed transesterification of coconut fat (CF) and soybean oil (SO) by ethanol, followed by product analysis by gas chromatography/mass spectrometry. Our goals were to introduce a problem with relevant socio-economic impact (production of BD); to discuss and compare methods for biofuel analysis, and to gain insight into transesterification mechanism as an important example of acyl-transfer reactions. Comparison of both BFs showed clear difference in fatty acid composition; that from CF contains shorter, saturated chains (mainly ethyl dodecanoate- and tetradecanoate), whereas biodiesel from SO is essentially composed of longer unsaturated chains (e.g., ethyl oleate and linoleate). The project takes eight hours to complete, is conceptually simple, being suitable for inclusion in the undergraduate science curriculum. <![CDATA[MICROWAVE-ASSISTED SYNTHESIS AND PKA DETERMINATION OF UMBELLIFERONE: AN EXPERIMENT FOR THE UNDERGRADUATE ORGANIC CHEMISTRY LABORATORY]]> A synthetic procedure for obtaining the fluorescent coumarin umbelliferone (7-hydroxycoumarin) and its spectral parameters were fully developed aiming at an undergraduate organic chemistry laboratory class. Umbelliferone is traditionally prepared via Pechmann condensation using malic acid, resorcinol and sulfuric acid as catalyst. The use of domestic microwave oven and the absence of solvent allow our methodology to be simple, fast and easy applied in obtaining umbelliferone at organic chemistry laboratory being greener than classical techniques of synthesis. In this class the student will learn how to measure the potency of a microwave oven, the applicability of this kind of irradiation in the organic synthesis of fluorescent compounds and how to determine the pKa of an organic compound through an UV/VIS spectrometric analysis. These experiments were designed to be suitable for a second and third year undergraduate curriculum. <![CDATA[O TEMA CARBOIDRATOS ATRAVÉS DA METODOLOGIA DE ESTUDOS DE CASO: DESENVOLVIMENTO DE CONTEÚDOS CONCEITUAIS, PROCEDIMENTAIS E ATITUDINAIS]]> This study aimed to analyze the contribution of the methodology of Case Studies to the development of conceptual, procedural and attitudinal contents inherent to the future professionals of Chemistry. In this sense, Cases on Carbohydrate Chemistry were elaborated to be solved by the students who studied the discipline of Organic Chemistry of Biomolecules of UFRGS. This research has a qualitative nature and it is a Case Study. For the data collection we used the Field Diary where the events were recorded along the activities developed through Participant Observation, audio recordings and the material produced by the participants as reports and presentations. In order to understand the students' perceptions about the activities, we used questionnaires with open questions and likert type. For the analysis of the data obtained were analyzed through coding categories, these elaborated using the guidelines of Bogdan and Biklen. According to the data analysis, the teaching methodology contributed to the development of knowledge related to the conceptual contents of carbohydrates, procedural contents such as oral and written argumentation, and attitudinal contents such as the investigative spirit. <![CDATA[DETERMINAÇÃO DE CÁDMIO EM BIJUTERIAS ORIUNDAS DA CHINA]]> This study aimed to determine cadmium in low-cost jewelry from China. In the qualitative test the sulfide was used as precipitating agent. Due to the strong interference of copper in qualitative analysis, this element was removed by chemical reaction or electrolysis. This removal was of paramount importance for the qualitative analysis of Cd2+. Quantification of Cd2+ was performed by means of atomic absorption spectrometry. The concentration of Cd was ~ 30% (w/w) in one of the pieces. It is noteworthy that in a small universe of low-cost jewelry analyzed (four samples), such a high cadmium content found in one of them leads us to think that jewelry containing Cd are widespread among citizens. This work can be useful to approach the case study method for teaching Analytical Chemistry at the undergraduate level. <![CDATA[EIXOS MOBILIZADORES EM QUÍMICA: UM BREVE OLHAR QUINZE ANOS DEPOIS]]> In 2002, the Brazilian Chemical Society have promoted several activities aiming to prepare a document to discuss the education in Chemistry in Brazil, the new model of research funding, the area situation and its perspectives. The document drew up diagnoses and brought up proposals that were organized into six mobilizing axes. Among its conclusions it was expected an alignment of scientific and technological research, considering the central role of Chemistry in solving problems and overcoming challenges affecting the education, full citizenship, climate changes, food production and quality, access to and quality of water, energy security, preservation of ecosystems and species, emerging diseases and quality of life. The current moment brings again challenges, imposed by a new technological generation, the transformations of the urban societies and by the commitment with a sustainable development. This article seeks to outline a panorama, using as background the Industry 4.0, the Society 5.0, the Sustainable Development Objectives, the creation of the EMBRAPII, the SENAI Institutes of Innovation and the role of the graduate programs in Chemistry, in order to construct a new agenda under the scope of the SBQ for the next 15 years.