Scielo RSS <![CDATA[Química Nova]]> vol. 39 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[ZNO and AG-ZNO crystals: synthesis, characterization, and application in heterogeneous photocatalysis]]> ZnO and Ag-ZnO were synthesized in a simple and efficient manner by thermal decomposition of zinc oxalate and silver/zinc mixed oxalate. The influence of the addition of metallic silver on ZnO particles and the effect of temperature in the thermal treatment were investigated. The samples were characterized by thermogravimetric analysis, Raman, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, specific surface area (Brunauer-Emmett-Teller) and diffuse reflectance spectroscopy. The photocatalytic activity of these materials in the decolorization of direct red 23 diazo dye was studied. The complete conversion into oxides from oxalates at lower temperatures was determinant in the photocatalytic efficiency of both the oxides. The presence of silver in zinc oxide, treated at 400 °C, more than doubled the rate constant of diazo dye decolorization (6.87×10-3 min-1) with respect to ZnO, treated at 600 °C, resulting in 3.07×10-3 min-1 under UV irradiation at 30 °C. <![CDATA[The novel mesoporous silica aerogel modified with protic ionic liquid for lipase immobilization]]> Mesoporous silica supports (aerogels) were used to immobilize Burkholderia cepacia lipase (BC) by encapsulation (EN or ENIL), physical adsorption (ADS or ADSIL) and covalent binding (CB or CBIL) into or onto the aerogel modified with protic ionic liquid (PIL). Yield immobilization (Ya) and operational stability were determined by the hydrolytic reaction of olive oil. Ya (37% to 83% by physical adsorption) and operational stability (2 to 23 batches by encapsulation) increased when the support was modified with PIL. For immobilized derivates observed by the BET method, in this case ADS and CB for ADSIL and CBIL, increased pores size was observed, possibly due to the higher amount of BC immobilized conferring Ya and operational stability. This effect was probably attributed to the entry of the enzyme into the pores of the silica aerogel structure. SEM images showed a change in the structure and properties of immobilized lipase derived with PIL. A characteristic FTIR band was obtained for the silanol groups and amides I, IV and V, demonstrating the efficiency of immobilization of BC. The most efficient biocatalysts were ADSIL with regard to yield immobilization and ENIL for operational stability. <![CDATA[INHIBITORY ACTION OF PAPAYA SEED EXTRACTS ON THE CORROSION OF CARBON STEEL IN 1 MOL L<sup>-1</sup> HCl SOLUTION.]]> The effect of two papaya seed extracts (infusion and acid extracts) on the corrosion of carbon steel in 1 mol L-1 HCl was examined. The efficiency for inhibiting the corrosion of C-steel in 1 mol L-1 HCl increased with the extract concentration and decreased slightly with the temperature. The inhibitory property of the extract is discussed in terms of the mechanism by which its components adsorb onto the C-steel surface decreasing the active surface area. This adsorption process obeyed a Langmuir adsorption isotherm. The infusion extract which presented more phenolic compounds than the acid extract showed higher inhibition efficiency. The apparent activation energy (Ea) for the dissolution of C-steel slightly increased when the infusion extract was used. <![CDATA[EFFECT OF CHEMICAL ACTIVATION ON SURFACE PROPERTIES OF OIL SHALE BY-PRODUCT]]> A pyrolyzed oil shale by-product known as retorted shale was functionalized with HCl, HNO3, H2SO4, H3PO4, HNO3/H2SO4 (3:1), Fenton's reagent, (NH4)2S2O7, NaOH, and KMnO4 using either ultrasound (Route 1) or reflux (Route 2). The products obtained were evaluated in terms of cation exchange capacity (CEC). Structural characterization was performed using X-ray diffraction, X-ray fluorescence, and infrared spectroscopy to identify the functional groups present. The best results were achieved using Route 2 with solutions of either H3PO4 or HNO3/H2SO4 (3:1), giving CEC values of 315 and 316 mmolc kg-1, respectively. The pyrolyzed oil shale functionalized using Route 2 (reflux) with NaOH as the activating agent showed the highest sorption of methylene blue (35.6 mg g-1). The main mechanisms observed for oil shale by-product functionalization were oxidation, nitration, and CaO leaching. <![CDATA[THEORETICAL STUDY OF THE BINUCLEAR COMPLEXES OF MANGANESE (II) WITH LIGAND 2-HYDROXYBENZYLGLYCINE, POSSIBLES MIMICS FOR CATECHOL OXIDASE]]> This work applies the Density Functional Theory (DFT) to study binuclear complexes of Mn2+ with the ligand 2-hydroxibenzilglycine and its substituted derivatives. The results showed the isomer 2 with multiplicity 11-ete as the most stable between all the structures and multiplicities obtained. Then, the most stable complex with the -OCH3, -Br, -Cl and -NO2 substituents were analyzed. Finally, the absolute hardness and the percentage of LUMO orbital participation for the substituted complexes were evaluated. Among them, the complexes with -NO2, -H, -Br groups were more likely to play the catalytic activity, respectively. <![CDATA[DETERMINATION OF METALS IN WATER AND LEAF OF <em>Aechmea blanchetiana</em> (Baker) L.B]]> The aim of this research was to determine the concentrations of calcium, iron, manganese, zinc, potassium and sodium in the water and leaves of Aechmea blanchetiana (Baker) L.B species collected between the cities of Ilhéus and Itacaré, Bahia, Brazil and verify if the metals found in the water can be absorbed by the leaves. Flame atomic absorption spectrometry (F AAS) and flame photometry were used for the determination of metals. pH measurements, dissolved oxygen and water temperature were also made. The results obtained were used in an exploratory analysis. Principal component analysis (PCA) showed clearly the distinct formation of two clusters and the correlation analysis indicated that the leaves of A. blanchetiana seem to absorb iron, calcium, manganese and zinc from the water tank. <![CDATA[PREPARATION AND CHARACTERIZATION OF PHOSPHORYLATED STARCH BLENDS WITH CHITOSAN AND POLYVINYL ALCOHOL]]> The aims of this study were to produce films from phosphorylated starch/chitosan/PVA blends and evaluate their physicochemical properties. The film properties were dependent on the starch percentage in the blend. The infrared spectra of the blends showed the appearance of bands at 1716 and 1733 cm-1 (stretching C = O of PVA acetate residues) and 1556 cm-1 (amide II deformation of the chitosan) indicating the incorporation of these components into the blends. The films with high phosphorylated starch content showed low thermal and mechanical strength and high water absorption capacity while blends with higher content of chitosan and PVA showed good mechanical properties and low water vapor permeability. Films containing 40% and 20% starch showed excellent properties such as high water absorption capacity and biodegradability for use as bandages and agricultural films and also as a source of organic matter in soil. <![CDATA[Actividad antioxidante de los polifenoles de <em>HYPOGYMNIA TAVARESII</em> D. HAWKSW. & P. JAMES]]> Lichen substances have more than one phenolic hydroxyl group attached to one or more benzene rings, thus qualifying them as polyphenols. The secondary metabolites isolated from the lichen H. tavaresii have been studied in a bid to find compounds protective against oxidative stress and free radical-induced damage. The compounds were identified based on their MS and 1H-NMR spectra as well as retention factors of TLC analysis. In addition to the previously described metabolites (atranorin, chloroatranorin, physodic and physodalic acids) of H. tavaresii, a further three were identified in its thalli: 2´-O-methylphysodone, isophysodic and ursolic acids. The newly identified compounds of H. tavaresii thalli may be useful in the chemotaxonomic classification of this species. Antioxidant effectiveness of the acetone extract's fractions was measured. The compounds of the active fractions were purified and exhibited 180-800 fold less radical scavenging activity than the reference substance α-(+)-tocopherol in a DPPH• model expressed by IC50 values. <![CDATA[3D nanocomposite chitosan/bioactive glass scaffolds obtained using two different routes: an evaluation of the porous structure and mechanical properties]]> Porous synthetic substrates are developed through tissue engineering technologies to grow new tissue, restoring the function of tissue or an organ. For bone regeneration, these scaffolds must support the dynamic load exerted on this tissue, achieved primarily by increasing their compression strength, as established in the literature. The aim of this paper was to incorporate an inorganic composite bioactive glass (60%SiO2 - 36%CaO - 4%P2O5) as a reinforcing agent in mechanical 3D scaffolds that must remain porous. Two strategies were adopted: a co-precipitation method to obtain a nanoparticulate dispersion of bioactive glass (BGNP) and a sol-gel method to combine a bioactive glass solution (BG) with a previously prepared chitosan polymer solution. Moreover, a lyophilization process was also used, generating highly porous scaffolds. Various aspects of the scaffold were evaluated, including the morphology, orientation and size of the pores, and mechanical strength, as obtained using the two synthetic methods. The data for compressive strength revealed increased strength after the incorporation of bioactive glass, which was more pronounced when utilizing the nanoscale bioactive glass. <![CDATA[Computational study on structure and properties of new energetic material 3,7-bis(dinitromethylene)-2,4,6,8-tetranitro-2,4,6,8-tetraaza-bicyclo[3.3.0]octane]]> The IR spectrum, crystal structure, electronic structure, thermodynamic properties, heat of formation and detonation properties of a new polynitro heterocyclic energetic material 3,7-bis(dinitromethylene)-2,4,6,8-tetranitro-2,4,6,8-tetraazabicyclo[3.3.0]octane were investigated theoretically. The calculated results show that this compound has a centrosymmetric structure and the molecular packing prediction indicates that the crystalline packing of the title compound is P212121 and the corresponding cell parameters are as follows: Z=4, a= 22.03 Å, b=8.73 Å, c=8.42 Å, Ꮁ=90°, β=90° and γ=90°. Based on the high positive heat of formation (HOF, 740.4 kJ mol-1), excellent detonation properties (detonation velocity D, 9.77 km s−1; detonation pressure P, 45.9 GPa), energy gap (ΔELUMO-HOMO) 4.19 eV and the molecular electrostatic potentials (MEP), it is predicted that 3,7-bis(dinitromethylene)-2,4,6,8-tetranitro-2,4,6,8-tetraazabicyclo[3.3.0] octane could be may be a superior high-energy density compound (HEDC) to RDX and HMX. <![CDATA[TURING PATTERNS IN CHEMICAL SYSTEMS]]> Spontaneous pattern formation in reaction-diffusion systems was theoretically proposed by Alan M. Turing in 1952. His breakthrough conceptions of chemical self-organization were able to explain how patterns emerge in nature and the symmetry breaking, which are of utmost importance, for instance, in the context of origin of life. Along with the experimental observations in the Belousov-Zhabotinsky reaction and the development of the nonequilibrium thermodynamics by Prigogine and co-workers, Turing predictions are considered the foundation of the field of Nonlinear Chemical Dynamics. This review aims to describe the basis of Turing structures with their consequent scientific achievements and to provide future directions in the development of this field. <![CDATA[SOURCES, FORMATION, REACTIVITY AND DETERMINATION OF QUINONES IN THE ATMOSPHERE]]> Quinones are a group of semi-volatile organic substances, ubiquitous in nature, belonging to the class of oxygenated polycyclic aromatic hydrocarbons (Oxygenated PAH). These compounds are formed in biogenic processes, through the oxidative metabolism of endogenous compounds, such as catecholamines, estrogen hormones and xenobiotics, as well as directly emitted to the atmosphere, through the incomplete combustion of organic matter, especially the fossil fuels. Additionally, the quinones are formed in the atmosphere by photooxidation of Polycyclic Aromatic Hydrocarbons (PAH). Their reduction products (semiquinones and hydroquinones) are of toxicological interest, due to their ability in generate reactive oxygen species, which may cause damage to membranes, proteins and DNA and, among others damages, may lead to carcinogenesis and induce apoptosis. The most frequently used analytical methods for quantification of quinones in the atmosphere, either in its original form or as derivatized compounds, are high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS) and gas chromatography coupled to mass spectrometry (GC-MS). This review aims to highlight the chemical properties of 1,2-naphthoquinone, 1,4-naphthoquinone, 1,4-benzoquinone, 9,10-phenanthraquinone and 9,10-anthraquinone, the more volatile, reactive and abundant quinones in the atmosphere, as well as the methods usually employed for their determination. <![CDATA[Evaluation of cryolite from pitinga (Amazonas-Brazil) as a source of hydrogen fluoride]]> This paper reports the use of cryolite from the Pitinga Mine (Amazonas state, Brazil) as raw material in hydrogen fluoride production. Samples were initially characterized by chemical and mineralogical analyses. They presented low silica content (&lt; 4 wt.%). After milling, cryolite samples were digested with concentrated sulfuric acid under stirring (200 rpm) and variable temperature, time and liquid to solid ratio conditions. Under the best experimental conditions (140 °C, 3-5 h), 96 wt.% of fluorine was recovered as hydrogen fluoride. The application of a 23 full factorial design showed that temperature and reaction time were relevant parameters during leaching, whereas liquid to solid ratio was not statistically significant. <![CDATA[UNDERSTANDING THE CHEMICAL PROCESS RELATED TO THE BIOACTIVATION OF SIMVASTATIN THROUGH EXPERIMENTAL AND <em>IN SILICO</em> METHODS: A PRACTICAL CLASS]]> Cholesterol is a lipid which in high concentration can be an important risk factor for coronary diseases and atherosclerotic lesions. This lipid presents an endogenous biosynthesis that involves several steps; one of them is modulated by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase). HMG-CoA reductase is inhibited by statins, such as simvastatin, in order to reduce seric become active. The structure of simvastatin has a lactone ring that undergoes enzymatic hydrolysis giving the 3,5-dihydroxy-heptanoate metabolite. This group is essential for simvastatin antilipemic activity, but significantly increases their water solubility. Make students understand the influence of chemical groups and organic functions on physicochemical properties and pharmacokinetic profiles of drugs, as simvastatin, is not an easy task. In this context, combine practical strategies and theoretical presentations of the concepts involved on drug biotransformation certainly could improve the teaching learning process. This manuscript correlates organic strategies and in silico techniques throught simvastatin hydrolysis followed by comparative ClogP measurement. This approach intends to allow students to have contact with a cross-platform and multidisciplinary learning, making it ludic, easier and more interesting than theoretical classes. <![CDATA[DEVELOPING A PROFESSIONAL PROFILE FOR A SUCCESSFUL CAREER IN THE INDUSTRY]]> In this work, chemists with experience in different areas of industry and academy raised some important issues in career planning to help undergraduate chemistry students to get prepared for the future professional life. <![CDATA[PRE-SERVICE CHEMISTRY TEACHERS AND SCIENTIFIC ARGUMENTATION: TRENDS IN DISCURSIVE ACTIONS IN CLASSROOM]]> School science teaching has traditionally been focused on the content of science. However, recent debates about science education emphasize the importance of the nature of science and the process of argument. In order to change the emphasis in teaching science to incorporate argumentation, teachers need to adopt more dialogic approaches that involve students in discussion, and to consider how they themselves interact with students to foster argumentation skills. In this paper we examine the pre-service chemistry teachers' ability to incorporate and use argumentation in their teaching. The chemistry lessons conducted by four pre-service teachers were audiotaped and transcribed in full and the transcript sections were coded using a framework for argumentation processes. An analysis of the audiotaped lessons transcripts suggested that three factors that promoted argumentation in pre-service teachers' classrooms emerged from the data. These factors included: the role of pre-service teachers in encouraging students to share their ideas and comments, providing evidence that support students ideas, and implementing instructional strategies that give students an opportunity to articulate and support an explanation in an argument. <![CDATA[STUDENTS' PROFILE AND EXPECTATIONS OF COURSE DEGREE IN CHEMISTRY UEPG]]> This paper presents and discusses socioeconomic aspects and expectations of chemistry students at the State University of Ponta Grossa. Six classes, in the period from 2011 to 2013, were consulted during the first academic week through questionnaires. It was possible to verify that a significant part of students has the expectation to become teachers and pursue studies in postgraduate courses. <![CDATA[Unremitting problems with chlorogenic acid Nomenclature: A review]]> This paper summarizes a problematic nomenclature of isomers belonging to chlorogenic acid family since its first occurrence until present. During decades, there have been a high number of articles dealing with the family. Unfortunately, researchers who want to get knowledge about this topic may be strongly confused after reading a few articles. Due to gradual discoveries and isolations of the individual isomers from plenty of matrices and because of the changing system of terminology after these discoveries, discrepancies among articles are common. The cause of this confusion is that the main compound of the family, 5-caffeoylquinic acid (also well-known as chlorogenic acid), was truly called as 3-caffeoylquinic acid before 1976, when new rules for nomenclature were published. Many researchers and also chemicals suppliers, however, keep using the "pre-IUPAC" nomenclature and wrongly call 3-caffeoylquinic acid as chlorogenic acid, the main substituent of the family. Despite there have been some works struggling with this issue, the problem is still appearing. Therefore, the present work was written.