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Química Nova, Volume: 41, Número: 7, Publicado: 2018
  • ETHYLENE POLYMERIZATION WITH NICKEL DIIMINE COMPLEXES CONTAINING PSEUDOHALIDES Artigo

    Dias, Marcos L.; Silva, Luciana P.; Crossetti, Geraldo L.; Filgueiras, Carlos A. L.

    Resumo em Inglês:

    Nickel-diimine complexes DADNiX2 (DAD= 2,6-iPr2-C6H3-N=C(Me)-C(Me)=N-2,6-iPr2-C6H3) containing the non-chelating pseudo-halide ligands isothyocyanate and isoseleniumcyanate (X= NCS 1 and NCSe 2) were synthesized and used in ethylene polymerization activated by methyaluminoxane (MAO) at temperatures from 0 to 50°C. Polymerizations with these complexes were compared with the analogous Ni-diimines halide (X= Br 3) as non-chelating ligand. All systems were very active in this polymerization. The increase of reaction temperature favored the increase in catalytic activity. The catalyst system 1/MAO was more stable than the others, showing the best catalytic activity at the molar ratio Al/Ni between 200 and 300. System 2/MAO showed to be the less stable and less active, particularly at 50°C. Polyethylenes obtained with systems 1, 2 and 3 show high molecular weights, are branched polymers, and predominately amorphous, but the majority still present DSC endothermal events related to melting of small crystals. When halide (Br) are compared with these pseudo-halides, different activities, polymerization kinetics and characteristics of the final polymer indicated modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content was not significantly influenced by the non-chelating ligand, being much more dependent on the MAO/Ni molar ratio and polymerization temperature.
  • IMOBILIZAÇÃO DE COMPLEXO DE RUTÊNIO CONTENDO BASE DE SCHIFF NA UNIDADE METALOORGÂNICA UiO-67 Artigo

    Jorge, Herculys B.; Silva, Cleiser T. P. da; Nakatani, Helena S.; Rinaldi, Andrelson W.; Souza, Vagner R. De

    Resumo em Inglês:

    Zirconium-based metal-organic framework, UiO-67, was synthesized and used as support for the immobilization of the [RuCl2(ENAPY)] (ENAPY = N,N'-bis(7-metyl-2-pyridylmethylene)-1,2-diiminoethane)). The immobilized system exhibited violet-blue color. The {UiO-67/[RuCl2(ENAPY)]} was characterized by cyclic voltammetry, X-ray diffraction, UV-Vis, FTIR and X-ray photoelectron spectroscopy. The electrochemistry of the immobilized system is characterized by a reversible pair of waves at +0.40 V (vs NHE), ascribed to the Ru3+/2+ redox process. The electronic spectrum of the immobilized system is characterized by bands at 520 and 380 nm ascribed to a ligand-to-metal charge-transfer transitions {Ru2+(dπ) → ENAPY(pπ*)}. The IR bands of immobilized complex {1630 cm-1 (νasC=C), 1590 cm-1 (νasC=N), 1450 cm-1 (νsC=C), 1340 cm-1 (νsC=C)} are weak in comparison with the neat complex due to their low concentration in MOF cages. X-ray diffractogram of the immobilized system indicated that the crystallinity and morphology of UiO-67 was preserved during inclusion of ruthenium complex. The XPS spectra of UiO-67 and UiO-67/ruthenium complex shows a signal at 462 eV that can be ascribed to Ru 3p3/2 and at 400 eV ascribed to N 1s core level of the ruthenium Schiff base complex immobilized into MOF.
  • VALIDATION OF COMPUTATIONAL METHODS APPLIED IN MOLECULAR MODELING OF CAFFEINE WITH EPITHELIAL ANTICANCER ACTIVITY: THEORETICAL STUDY OF GEOMETRIC, THERMOCHEMICAL AND SPECTROMETRIC DATA Artigo

    Costa, Josivan da Silva; Santos, Cleydson Breno Rodrigues dos; Costa, Karina da Silva Lopes; Ramos, Ryan da Silva; Silva, Carlos Henrique Tomich de Paula da; Macêdo, Williams Jorge da Cruz

    Resumo em Inglês:

    Models validation in QSAR, pharmacophore, docking, and others, can ensure the accuracy and reliability of future predictions in design and selection of molecules with biological activity. In these study, the caffeine molecule was optimized using Hartree-Fock (HF) and Density Functional Theory (DFT/B3LYP) methods, with seven basis sets. Linear correlation data, errors and RMSD values between theoretical and experimental data allowed us to classify the methods and basis sets for evaluating their correspondence with experimental data (geometric parameters, heat capacity, as well as Infrared, Raman and NMR spectra). The HF method has shown the highest correspondence with the experimental data, occupying the top-five rank of the general classification. The HF/6-31G** method was the best one classified and it can be used to model the biological activity of the caffeine molecule.
  • INFLUÊNCIA DO MÉTODO EXTRATIVO NO TEOR DE FLAVONOIDES DE Cnidoscolus quercifolius POHL (EUPHORBIACEAE) E ATIVIDADE ANTIOXIDANTE Artigo

    Torres, Daniel da S.; Pereira, Emanuella C. V.; Sampaio, Pedrita A.; Souza, Nathália A. C. de; Ferraz, Christiane A. A.; Oliveira, Ana P. de; Moura, Celuane A.; Almeida, Jackson R. G. S.; Rolim-Neto, Pedro J.; de Oliveira-Júnior, Raimundo G.; Rolim, Larissa A.

    Resumo em Inglês:

    Cnidoscolus quercifolius Pohl is a Brazilian medicinal plant from Caatinga biome and possesses several pharmacological properties. Phytochemical investigations have attributed some of these properties to the presence of flavonoids. In this paper, we report the influence of the extraction process on the flavonoid content obtained from leaves of C. quercifolius and its antioxidant activity. A factorial design 22 was performed, using temperature and agitation as independent variables. Qualitative and quantitative analyzes of the extracts were performed by HPLC-DAD. Rutin and apigenin were identified in the extracts and chosen as analytical markers. Pareto chart and Surface response plots suggested that rutin content was increased up to 3.93 times when temperature was employed during the extraction process. However, apigenin content was significantly reduced in the method whose temperature or agitation were used (p<0.05). A higher antioxidant activity was observed in extracts whose rutin extraction was favored, suggesting that this flavonoid contributes at least in part to the antioxidant potential of the species.
  • AVALIAÇÃO DO PAPEL DO ÓXIDO DE GRAFENO (GO) NA GERAÇÃO FOTOCATALÍTICA DE HIDROGÊNIO EM SISTEMAS BINÁRIOS (GO-CdS) E TERNÁRIOS (Pt-GO-CdS) Artigo

    Almeida, Cristiane Gomes; Trindade, Tuany Nascimento dos Santos; Silva, Marcus Vinicius Santos da; Silva, Luciana Almeida

    Resumo em Inglês:

    Water splitting is a promising process to produce hydrogen from friendly feedstock and solar energy. In this work we have evaluated binary (GO-CdS) and ternary (Pt-GO-CdS) hybrid photocatalysts for hydrogen production assisted by visible light irradiation. Cadmium sulfide and composites with GO were prepared by sonochemical and thermal methods. GO addition took place by different strategies: during the synthesis or by mechanical mixture. A variety of configurations was tested and the best performance in hydrogen production among all materials was the ternary photocatalyst named Pt(GO/CdSTT), whose hydrogen production rate was 651 µmol gcat-1 h-1. Such material was obtained by thermal method with GO addition during the synthesis. Additionally, the XRD and Raman analyses have confirmed the GO photoreduction during photocatalytic hydrogen evolution.
  • PREPARATION AND CHARACTERIZATION OF NANOEMULSION CONTAINING A NATURAL NAPHTHOQUINONE Artigo

    Rodrigues, Fernando V. S.; Diniz, Laerte S.; Sousa, Rosa M. G.; Honorato, Thalita D.; Simão, Daniele O.; Araújo, Cleônia R. M.; Gonçalves, Talita M.; Rolim, Larissa A.; Goto, Patrícia L.; Tedesco, Antonio C.; Siqueira-Moura, Marigilson P.

    Resumo em Inglês:

    Natural naphthoquinones such as lapachol (Lp) have demonstrated promising biological activities. However, these quinones present low systemic biodisponibility due to its poor aqueous solubility. To overcome this problem, nanoemulsions (NE) formed by oily core are able to incorporate hydrophobic molecules thus enabling them to be dispersed into an aqueous phase. The present study reports the development, characterization, and physical stability of NE containing lapachol. NE formulations (F1, F2, F3, F4, and F2-Lp) were prepared using emulsion phase inversion (EPI) method and characterized in relation to droplet size, size distribution (PDI), zeta potential, and physical stability. The formulation chosen to incorporate lapachol (F2-Lp) showed droplet size in nanometric scale with homogeneous size distribution (PDI < 0.2) and negative zeta potential (about −30 mV). In addition, good physical stability of F2 and F2-Lp was demonstrated using analytical centrifugation with photometric detection where the light transmission profiles did not change throughout the dispersions. Nanoemulsion containing lapachol presented a strong reddish aspect; however, the incorporation of this naphthoquinone did not alter the main physicochemical parameters of NE formulation. The in vitro release study demonstrated a sustained release profile from NE with about 60% of lapachol released within 54 h.
  • PRODUCTION, CHARACTERIZATION AND USAGE OF A NOVEL DISULFONIC ACID-FUNCTIONALIZED IONIC LIQUID AS A HIGHLY EFFICIENT AND DUAL-FUNCTIONAL CATALYST FOR THE SYNTHESIS OF 1,8-DIOXO-9,10-DIARYL-DECAHYDROACRIDINES Artigo

    Karami, Mostafa; Zare, Abdolkarim

    Resumo em Inglês:

    We have produced a novel ionic liquid {N,N,N',N'-tetramethylethylene-diaminium-N,N'-disulfonic acid trifluoroacetate ([TMEDSA][TFA]2)}, and identified it by analysis of 1H NMR, 13C NMR, 19F NMR, mass, TG (thermogravimetry) and DSC (differential scanning calorimetry) data. Then, we have applied [TMEDSA][TFA]2 as a dual-functional catalyst for the production of 1,8-dioxo-9,10-diaryl-decahydroacridines by the multi-component reaction of dimedone with arylaldehydes and primary amines. Furthermore, we have proposed a plausible and attractive mechanism based on dual-functionality of the catalyst. Due to dual-functionality of [TMEDSA][TFA]2 (possessing acidic and basic sites), and also possessing two sites of each, it was highly effective and general, and produced the products in high yields.
  • SEPARATION OF ZINC FROM MANGANESE BY SOLVENT EXTRACTION FROM ACIDIC LEACHATES OF SPENT ZINC-MnO2 DRY CELLS USING NEUTRAL ORGANOPHOSPHORUS EXTRACTANTS Artigo

    Ibiapina, Vinício Francisco; Afonso, Júlio Carlos; Silva, Rubens Souza da; Vianna, Cláudio Augusto; Mantovano, José Luiz

    Resumo em Inglês:

    This paper describes a route for recovering manganese and zinc from spent zinc-MnO2 dry cells via acid leaching using sulfuric or hydrochloric acids as leachants. Hydrogen peroxide was added as reductant. Experiments were run at 25-40 °C for 1-3 h. Under the best optimal conditions, over 97.5 wt.% of zinc and manganese were leached by both acids. Zn(II) was best extracted at high free acidity (≥ 1 mol L-1) with tributylphosphate (TBP) or trialkylphosphine oxides (Cyanex 923) diluted in n-heptane. Cyanex 923 was a better extractant than TBP, and the extraction was better performed in hydrochloric leachates. Mn(II) was more co-extracted from hydrochloric leachates and when Cyanex 923 was the extractant, but was easily scrubbed with dilute leachant (~1-2 mol L-1). Zn(II) striping was possible using 5 mol L-1 HCl or H2SO4. Manganese was precipitated as oxalate (MnC2O4.2H2O), free of leached contaminants. High-purity sodium salts of the anions of the leachants were recovered after slow evaporation of the final solution.
  • ISOLATION OF CYTOTOXIC NEOLIGNANS FROM Saururus cernuus L. (SAURURACEAE) USING IONIC LIQUID IN THE MICROWAVE ASSISTED EXTRACTION (MAE) Artigo

    Brito, Juliana R.; Camilo, Fernanda F.; Figueiredo, Carlos R.; Azevedo, Ricardo A.; Romoff, Paulete; Buturi, Fátima O. S.; Fávero, Oriana A.; Lago, João Henrique G.; Ferreira, Edgard A.

    Resumo em Inglês:

    In the present work, dried leaves of Saururus cernuus (Saururaceae) were subjected to extraction using an ionic liquid (1-butyl-3-methylimidazolium bromide - BMImBr) in the microwave assisted extraction (MAE). The obtained extract was partitioned using n-hexane and cytotoxicity activity of this organic phase against murine melanoma cell line (B16F10-Nex2) was evaluated in vitro. Since this extract displayed activity (100% of cell death at 200 µg mL-1) it was subjected to a bioactivity-guided fractionation to afford four related neolignans: threo-austrobailignan-5 (1), threo-austrobailignan-6 (2), threo-dihydroguaiaretic acid (3) and saucernetin (4). Their chemical structures were established based on NMR and MS spectral analysis. Among the isolated neolignans, compound 2 exhibited the highest cytotoxic activity against HeLa (human cervical melanoma) cells with IC50 of 28.3 ± 3.9 µg mL-1 (86 ± 12 µmol L-1). Furthermore, compounds 2 and 3 exhibited the highest cytotoxic activity against A2058 (human melanoma) cells with IC50 of 44.3 ± 4.2 µg mL-1 (135 ± 13 µmol L-1) and 41.5 ± 7.5 µg mL-1 (126 ± 23 µmol L-1), respectively, similar to positive control cisplatin (IC50 = 43.2 ± 3.2 µg mL-1 or 144 ± 11 µmol L-1). Otherwise, compound 4 was inactive (IC50 > 100 µg mL-1 or > 300 µmol L-1). The obtained results provide important data for the selection of bioactive neolignans with promising cytotoxic potential using a simple and fast method employing a green solvent as 1-butyl-3-methylimidazolium bromide (BMImBr).
  • ÉTERES DIFENÍLICOS POLIBROMADOS (PBDE) COMO CONTAMINANTES PERSISTENTES: OCORRÊNCIA, COMPORTAMENTO NO AMBIENTE E ESTRATÉGIAS ANALÍTICAS Revisão

    Annunciação, Daniel L. R.; Almeida, Fernanda V.; Hara, Emerson L. Y.; Grassi, Marco T.; Sodré, Fernando F.

    Resumo em Inglês:

    Flame retardants are substances mixed with numerous materials to inhibit the combustion process, reducing risks and damages caused by fires. Among these substances, polybrominated diphenyl ethers (PBDEs) have been widely used for decades due to their low cost and high efficiency. However, since they are mixed and not chemically bonded to the materials, PBDEs can be released over time being transported through numerous pathways until they reach soils and aquatic systems, where they can accumulate in sediments and biota. Due to their high chemical stability, an essential feature for flame retardants, they are considered persistent contaminants. Several studies report the presence of PBDEs in atmospheric and aquatic particulate matter, sediments, soils and biological matrices such as marine animals, tissues and human fluids. In Brazil, little is known about the use and commercialization of PBDEs, as well as their levels in different environmental compartments. Thus, this review provides an overview of the origin of PBDEs in the environment as well as information inherent to the understanding of the behavior and presence of this contaminants of recent interest in different environmental compartments. Finally, the manuscript also brings state-of-the-art analytical approaches used for environmental sampling, preservation, preparation and sample analysis.
  • ESPECIAÇÃO DINÂMICA DE METAIS TRAÇO EM AMBIENTE AQUÁTICO USANDO CRONOPOTENCIOMETRIA DE REDISSOLUÇÃO ANÓDICA Revisão

    Monteiro, Adnívia Santos Costa; Goveia, Danielle; Rotureau, Elise; Rosa, André Henrique; Masini, Jorge Cesar; Pinheiro, José Paulo

    Resumo em Inglês:

    The contamination of natural environments by trace metals has several adverse effects on human health, which is mainly due to the high toxicity, persistence and reactivity of these species in the environment. To understand the bioavailability of trace metals, it is necessary to know the speciation in equilibrium and the dynamic behavior of the system. In this context, the present work aims to present a bibliographic review about the potentialities of the Stripping Chronopotentiometry (SCP) and Stripping Chronopotentiometry at Scanned Deposition Potential (SSCP) in the study of dynamic trace metal speciation. These techniques have low detection limits and do not suffer interference due to the adsorption of organic matter on the surface of the working electrode. Coupling these techniques with the Absence of Gradients and Nernstian Equilibrium Stripping (AGNES) enables simultaneous determination of free ions, complexation equilibrium constants and diffusion coefficients of the complexes, thus providing information on the dynamic and heterogeneity of the metal complexes in the presence of macromolecules or particles. In this paper we will present the theory of dynamic speciation of trace metals, a detailed description of how to use the techniques to obtain this information, and examples of application in model systems and natural samples.
  • CORK MEMBRANE FOR EFFICIENT OIL AND WATER SEPARATION Nota Técnica

    Zhou, Yanbiao; Liao, Binghua; Qu, Kaige; Zhang, Lihui; Ye, Luyang

    Resumo em Inglês:

    Cork is a renewable, biocompatible, environmentally friendly and abundant biological material with microscale cellular structure. Fabrication of filtration membranes for the separation of oil and water by utilizing such natural materials to replace nonnatural membranes is a green method. A cork membrane with a water contact angle greater than 150° and an oil contact angle close to 0° was fabricated by chemically modifying cork membranes with 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane. The special wettability was achieved owing to the cellular structure and the surface composition of the cork membrane. Just like nonnatural filtration membranes, natural cork membranes exhibited excellent permeability for oils. After at least 40 cycles of oil-removal processes, the separation efficiency of the membrane was still above 99.1%. Under harsh conditions such as strong acid/alkali, high humidity, and high temperature environments, the wettability and separation efficiency exhibited excellent stability and durability. This method offers an opportunity to the practical applications of the superhydrophobic cork membrane.
  • MEASURING THE CONDUCTIVITY OF VERY DILUTE ELECTROLYTE SOLUTIONS, DROP BY DROP Educação

    Martínez, Leandro

    Resumo em Inglês:

    Undergraduate experiments on ionic conductivity are common practice in general chemistry and advanced physical chemistry laboratories. Often, the conductivities are measured for solutions prepared for various salts, in a range of concentrations, and the relationship between solution conductivity and concentration is interpreted in terms of the Kohlrausch law. Contaminations can dominate the conductivity of the solutions such that students might obtain unsatisfactory results for analysis. Here, the experience of using a simple experimental procedure to obtain the concentration dependence of ionic conductivities for very dilute (sub-millimolar) electrolyte solutions in undergraduate laboratories is described. The experiment consists of measuring the conductivity of solutions of increasing concentration prepared by dropping the electrolyte solution into an initial vessel of deionized water. The range of concentrations achieved is one in which the conductivities vary linearly with the concentrations, such that the molar conductivities can be obtained directly without the use of the Kohlrausch equation. The simplicity of the experimental procedure leads the students to obtain good quality results using minimal amounts of materials. Examples are presented for the conductivities of strong electrolytes, and for the weak acetic acid electrolyte, for which the conductivity is dependent on the degree of dissociation also for dilute solutions.
  • REVISITING IDEAL GASES AND PROPOSAL OF A SIMPLE EXPERIMENT FOR DETERMINING ATMOSPHERIC PRESSURE IN THE LABORATORY Educação

    Silva, Leonardo M. Da; Castro, Arthur H. de

    Resumo em Inglês:

    Relevant historical aspects concerning ideal gases were briefly reviewed to provide a condensed resource for the undergraduate student of chemistry. The importance of the barometer and the concept of atmospheric pressure were reviewed and discussed. A combination of Boyle's law with the well-known equation for determining the pressure produced by a column of stationary fluid was used to obtain a graphical method for determining atmospheric pressure under isothermal conditions in the laboratory. Important aspects related to the study of ideal gases were reviewed in light of the pressure-volume data that can be obtained by physical chemistry students using a simple apparatus composed of a commercial hypodermic syringe connected to a mercury manometer. Relevant concepts associated with the measurement of a physical quantity, the importance of linear regression, as well as the use of a graphical method to test the validity of a theory were reviewed from a pedagogical perspective through the experimental study of Boyle's law during regular experimental physical chemistry classes.
  • TOPOLOGIA DOS ORBITAIS MOLECULARES DE POLIENOS PARA DEDUZIR ENERGIAS RELATIVAS E AVALIAR AROMATICIDADE Educação

    Cunha, Silvio

    Resumo em Inglês:

    A didactic alternative approach is proposed for deducing the molecular orbital topology of acyclic and cyclic polyenes and then evaluating their bonding, antibonding, and nonbonding character. The relative energies of molecular orbitals of neutral molecules and ions were described, in addition to the orbital degeneracy to cyclic conjugated polyenes, and the method deduce correctly the relative stability of polyenes. This alternative method complements the lack of explanation of a substantial number of organic chemist undergraduate textbooks in relation to orbital degeneracy in benzene and is a pedagogical approach to teach aromaticity and antiaromaticity.
  • CONSIDERAÇÕES SOBRE TEXTOS QUE TRATAM DO DESENVOLVIMENTO DE METALOFÁRMACOS DE RUTÊNIO Assuntos Gerais

    Nikolaou, Sofia; Silva, Camila F. N. da

    Resumo em Inglês:

    It is relatively easy to verify that literature focused on the planning and investigation of ruthenium complexes biological properties (and their possible application as metallodrugs) has assumed certain generalizations that have been systematically repeated, mainly with respect to parallelisms and antagonisms with the chemistry of iron and platinum. This work proposes a discussion on the construction of the texts that deal with the theme, aiming to criticize the misuse of such generalizations.
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