Scielo RSS <![CDATA[Química Nova]]> vol. 40 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[SYNTHESIS, THERMAL STUDIES AND CONVERSION DEGREE OF DIMETHACRYLATE POLYMERS USING NEW NON-TOXIC COINITIATORS]]> The aim of this paper is to replace toxic coinitiators (tertiary amines) by non-toxic compounds such as glycerol and inositol (polyalcohol) in dimethacrylate resins. For this purpose, mid infrared spectroscopy (MIR) was used to calculate the monomers' degree of conversion (%DC); as well as simultaneous Thermogravimetric Analysis – Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC) were conducted to evaluate thermal stability, degradation steps, and thermal events. The use of different initiator systems did not modify the thermal events or the thermal stability of each of the dimethacrylate resins. Results show a substitution of system 2 (toxicity) by system 3 (low toxicity), which had a good conversion velocity and total conversion in some monomers, is plausible. <![CDATA[SELECTIVE HYDROGENOLYSIS OF GLYCEROL TO PROPYLENE GLYCOL IN A CONTINUOUS FLOW TRICKLE BED REACTOR USING COPPER CHROMITE AND Cu/Al<sub>2</sub>O<sub>3</sub> CATALYSTS]]> The glycerol hydrogenolysis reaction was performed in a continuous flow trickle bed reactor using a water glycerol feed and both copper chromite and Cu/Al2O3 catalysts. The commercial copper chromite had a higher activity than the laboratory prepared Cu/Al2O3 and was used for most of the tests. Propylene glycol was the main product with both catalysts, acetol being the main by-product. It was found that temperature is the main variable influencing the conversion of glycerol. When the state of the glycerol-water reactant mixture was completely liquid, at temperatures lower than 190 ºC, conversion was low and deactivation was observed. At reaction temperatures of 210-230 ºC the conversion of glycerol was complete and the selectivity to propylene glycol was stable at about 60-80% all throughout the reaction time span of 10 h, regardless of the hydrogen pressure level (1 to 20 atm). These optimal values could not be improved significantly by using other different reaction conditions or increasing the catalyst acidity. At higher temperatures (245-250 ºC) the conversion was also 100%. Under reaction conditions at which copper chromite suffered deactivation, light by-products and surface deposits were formed. The deposits could be completely burned at 250 ºC and the catalyst activity fully recovered. <![CDATA[USE POTENTIAL OF BIOGLYCERIN AS A BASIS FOR AQUEOUS DRILLING FLUIDS FORMULATION OF OIL AND GAS WELLS]]> The growing global concern about the environment associated with academic and government efforts are enabling a number of alternatives for sustainable development. Within this perspective one can include the search for value-added products using waste from renewable energy sources, such as those from the production of biodiesel. The rapid development of biodiesel production in Brazil directly affected the supply of glycerin and therefore the sector is seeking a market that can absorb this waste. Thus, with the increasing search for environmentally friendly products, formulation of a drilling fluid using a co-product of biodiesel production to replace the n-paraffin is of great importance to the oil industry for meeting the requirement of environmental regulation and, in addition, considerably reducing the cost of raw materials. In this context, the aim of this study was to characterize different glycerins to evaluate their potential as basis for drilling fluids for oil wells and gas. The glycerins were stable under the conditions evaluated without phase separation and precipitation of solids, exhibited good rheological profile and low value of interface tension. The results indicate a strong possibility of use of these glycerins as basis for drilling fluids and applicability by the oil industry. <![CDATA[THERMAL DECOMPOSITION REACTION IN ETHANOL SOLUTION OF DEUTERATED ACETONE CYCLIC DIPEROXIDE AND ACETONE DIPEROXIDE. SECONDARY INVERSE ISOTOPIC EFFECT]]> The characterization by mass spectrometry and the kinetic study of the thermal decomposition reaction of deuterated acetone diperoxide (dACDP) was studied in ethanol in the 140-165 ºC temperature range. The comparison with the non deuterated species (ACDP) was also made. The kinetic behavior observed for both compounds follows a pseudo first order kinetic law up to at least 86 % peroxide conversions. It could be observed that under the established experimental conditions, the dACDP decomposes ca. 1.2 times faster than the ACDP. The activation parameters were calculated for both peroxides and allowed to postulate a single process initial step, the unimolecular thermal decomposition through the O-O bond cleavage to form an intermediate biradical. The products of the acetone derived peroxides thermal decomposition support a radical-based decomposition mechanism. The changes in kinetic parameters between dACDP and ACDP were justified attending to differences in ring substituents sizes. A secondary inverse kinetic isotope effect is observed (kH/kD &lt;1). <![CDATA[COMPARATIVE STUDY OF THE INHIBITIVE ACTION BETWEEN THE BITTER ORANGE LEAF EXTRACT AND ITS CHEMICAL CONSTITUENT LINALOOL ON THE MILD STEEL CORROSION IN HCL SOLUTION]]> Bitter orange, Citrus Aurantium (CA), extract and one of its chemical constituents, Linalool, have been evaluated as a corrosion inhibitor for mild steel in 0.5 mol L-1 hydrochloric acid (HCl) solution using potentiodynamic polarization, electrochemical impedance, Fourier transform infrared spectroscopy (FTIR), and atomic force spectroscopy (AFM) techniques. Functional groups of CA and Linalool were identified by FTIR spectroscopy. The Potentiodynamic polarization and electrochemical impedance studies showed that CA and Linalool act as mixed type inhibitors. The activation parameters showed that the corrosion inhibition takes place by spontaneous physical adsorption on the mild steel surface. Thermodynamic-kinetic model and Flory-Huggins isotherms were used to investigate the adsorption characteristics of CA and Linalool. The surface morphologies of mild steel specimens were studied using AFM, in which the surface roughness of the metal specimens on a micro scale was characterized. <![CDATA[A CONCEPTUAL DFT STUDY OF THE CHEMICAL REACTIVITY OF MAGNESIUM OCTAETHYLPORPHYRIN (MgOEP) AS PREDICTED BY THE MINNESOTA FAMILY OF DENSITY FUNCTIONALS]]> The Minnesota family of density functionals has been assessed for the calculation of the molecular structure and electronic properties of a Mg(II)-porphyrin, namely Magnesium Octaethylporphyrin (MgOEP). Several global descriptors arising from Conceptual DFT have been calculated through a ΔSCF procedure, and by means of the HOMO and LUMO frontier orbitals. On the basis of the obtained Conceptual DFT indices, a series of descriptors have been devised in order to verify the fulfillment of the "Koopmans' theorem in DFT" procedure. It is shown that the density functionals that verify this approximation with a certain degree of accuracy are only those denoted as range-separated hybrids (RSH), while the usual GGA-hybrids and the local density functionals fail completely. <![CDATA[QUANTIFICATION OF SOIL CO<sub>2</sub> EMISSIONS IN TWO FORESTED AREAS UNDER DIFERENT REGENERATION STAGES IN ATLANTIC FOREST]]> In order to quantify emission rates of CO2 through the soil from the Atlantic forest under different regeneration stages, two areas located in Rio Claro(SP) were studied. In the first area the forest is regenerated (Plot 23) and the average CO2 emission is 1.91 mmol m-2s-1, while in the recently planted area (Plot 15), the average emission is 1.38 mmol m-2s-1. The CO2 emissions are fairly correlated to soil moisture (r=0.53, P=&lt;0.0001), C/N ratio (r=0.27, p&lt;0.05) and time of measurement (r=0.33, p&lt;0.05). Multiple linear regression models developed are better to reproduce CO2 soil emissions in recently planted area. <![CDATA[COMPUTATIONAL STUDY OF THE INTERACTION BETWEEN INDENE PYRAZOLE AND CYCLIN DEPENDENT KINASE 2]]> Proteins have been traditionally out of reach of electronic structure methods. But with technological advances in the development of powerful computers and the need to extend the methods of computational chemistry to problems of biological interest, such as the rational design of drugs, new technologies in silico have been developed that allow to study condensed systems of phase, which consist of thousands of atoms. Here, there are some techniques that combine two or more methods of calculating in a calculation that allows precise chemical exploration of very large systems. The aim of this work is to find the binding affinity of CDK2 inhibitors calculating their electronic densities and then comparing the similarities of these with the biological activity of ligands developing a QSAR in order to establish correlations between quantum similarity, which is a physical-chemical property and biological activity of said set of molecules that change their properties by varying any of their substituents. <![CDATA[EVALUATION OF A NIR HANDHELD DEVICE AND PLS-DA FOR DISCRIMINATION OF SIX SIMILAR AMAZONIAN WOOD SPECIES]]> Supervising wood exploitation can be very challenging due to the existence of many similar species and the reduced number of wood identification experts to meet the demand. There is evidence that valuable endangered wood species are being smuggled disguised as other species. Near infrared spectroscopy (NIRS) and chemometrics has been successfully used to discriminate between Amazonian wood species using high resolution instruments. In this study, a handheld spectrometer was evaluated for the discrimination of six visually similar tropical wood species using PLS-DA. Woods of mahogany (Swietenia macrophylla) and cedar (Cedrela odorata), both high value tropical timber species included in Appendixes II and III of the CITES, respectively; crabwood (Carapa guianensis); cedrinho (Erisma uncinatum); curupixá (Micropholis melinoniana); and jatobá (Hymenea coubaril). The data for model development and validation take into account both laboratory and field measurements. Outlier exclusion was performed based on Hotelling T2, residuals Q and errors in the estimated class values. The efficiency rates were higher than 90% for all species, showing that the handheld NIR combined with PLS-DA succeeded in discriminate between these species. These results stimulate the application of handheld NIR spectrometers in the supervision of wood exploitation, which can contribute to the species preservation. <![CDATA[SCREENING OF SPECIES FROM THE GENUS Penicillium PRODUCING CELL BOUND LIPASES TO BE APPLIED IN THE VEGETABLE OIL HYDROLYSIS]]> Ten species of Penicillium genus isolated from different habitats were evaluated as mycelium bound lipase producers to be used in the hydrolysis of vegetable oils. Using olive oil as an inducer three species (P. italicum AT4421, P. janthinellum CCT3162 and P. purpurogenum AT2008) were able to produce lipases having high mycelium bound activities (&gt;150 U g-1) and were further characterized in relation to their biochemical and kinetic properties and specificity using vegetable oils having majority fatty acids composition in C12:0 (coconut); C16:0 (palm); C18:1 (canola) and C18:1 (soybean). All the three lipases could enrich the medium with fatty acids according to their respective selectivity and the reaction hydrolysis was found to enhance at least three folds under ultrasonic irradiations. For P. purpurogenum lipase the highest hydrolysis degree (66.8 ± 0.2%) was attained with coconut oil. Both P. italicum and P. janthinellum lipases showed high selectivity for canola oil, resulting in hydrolysis degrees of 79.9 ± 0.5% and 63.5 ± 0.6%, respectively. Analysis of the hydrolysates confirmed that the majority of the fatty acids released by P. italicum and P. janthinellum lipases was composed by oleic acid, and P. purpurogenum lipase the hydrolysate contained approximately 50% of lauric acid. <![CDATA[QUANTUM DOT-SENSITIZED SOLAR CELLS]]> Quantum dot solar cells (QDSC) have been subject of extensive research in recent years. QDSC, as a promising alternative to existing solar cells, are among the candidates for next-generation photovoltaic devices that require low cost, high efficiency, so that quantum dots stand out for their unique features and versatile desirable on photovoltaic systems. The rapid development of QDSC provided a significant increase in energy conversion efficiency, which was certified for the first time in 2010 as 2% then being currently as 11.3%, according to the National Renewable Energy Laboratory (NREL). This paper presents a review of the quantum dot-sensitized solar cells and the major advances reported concerning these cells, besides other types of cell architectures involving quantum dots. <![CDATA[VALIDATION OF THE ELECTROCOAGULATION PROCESS AND EVALUATION OF THE ELECTRO-DISSOLUTION OF ELECTRODES IN THE TREATMENT OF POULTRY SLAUGHTERHOUSE WASTEWATER]]> The electrocoagulation have been considered a promising technology for wastewater food treatment. This paper evaluates the application of electrocoagulation for the treatment of poultry slaughterhouse wastewater using two types of electrode, iron and aluminum. The initial pH, the electrolysis time and the electrical current density were used as the operating variables. The optimal operating conditions for each electrode were validated by applying the Response Surface Methodology (RSM). It was observed that the best conditions for Chemical Oxygen Demand (COD) reduction were the use of aluminum electrodes with electrolysis time of 40 minutes, initial pH of 4,0 and electrical current density of 30 A·m-2. These conditions resulted in a COD removal of 86% with a final pH of 7,5. In the validation it was found a little over-prediction and a good fit for the total removal of COD with a bias and accuracy factor of 1,04 and 1,16 respectively. The developed models aim to facilitate the values prediction of process variables that should be favored when using the electrolytic method on a larger scale or in additional tests for poultry slaughterhouse wastewater treatment. <![CDATA[FACULTY AND STUDENT GOALS FOR UNDERGRADUATE LABORATORY]]> Laboratory is a part of most undergraduate chemistry curricula, however the goals that faculty and students hold have received scant attention. Our research has revealed two broad goals for laboratory learning held by faculty. Students however, hold entirely different goals that may pose obstacles for faculty achieving the goals they have set out. Herein we describe our research and propose methods of bringing these goals into better alignment. <![CDATA[HOW WE HAVE USED ITEM RESPONSE THEORY AND CLASSROOM MANAGEMENT TO IMPROVE STUDENT SUCCESS RATES IN LARGE GENERAL CHEMISTRY CLASSES]]> Since 2012 we have tracked general chemistry student success rates at the University of Utah. In efforts to improve those rates we have implemented math prerequisites, changed our discussion session format, installed some metacognitive exercises aimed at the lowest quartile of students and instituted a flipped classroom model. Furthermore, using Item Response Theory we have identified what topics each individual student struggles with on practice tests. These steps have increased our success rates to ~76%. As well, student performance on nationally normed American Chemical Society final exams has improved to a median of 86 percentile. Our lowest quartile of students in spring 2016 scored at the 51 st percentile, above the national median. <![CDATA[AN INQUIRY-BASED FRESHMAN BIOCHEMISTRY LAB SET TO ENHANCE STUDENTS' AUTONOMY]]> Inquiry-based laboratory sessions are recognized for contributing to enhancing students' autonomy and they were used in the reorganization of the Biochemistry laboratory offered to freshman Biology students in this university. Students were previously asked to follow rigid laboratory protocols attempting to achieve the correct results of their experiments. The inquiry-based activities were designed to develop students autonomy to plan and to perform experiments, as well as communicating and discussing their results. The inquiry-based and autonomy approach followed is classified in the literature as Organizational, Procedural, and Cognitive. The levels of autonomy required from students were increased sequentially. The first activity was the least demanding, since the students received detailed instructions from the worksheet. The activities became gradually more complex, transferring to students most decisions on setting up and performing the experiments. Student skill improvement was obtained, as verified by excerpts from student reports, by data obtained from content analysis of the exams, and scientific report scores indicate that this approach may have stimulated the improvement of several skills related to different autonomy aspects. Most important, students showed increased ownership of the laboratory materials, reagents, laboratory environment and especially of learning, showing a sense of active participation in the experimental activities. <![CDATA[STUDYING STUDENT BEHAVIOR AND CHEMISTRY SKILL USING BROWSER-BASED TOOLS AND EYE-TRACKING HARDWARE]]> Browser-based tools were created to collect quantitative data about university student problem-solving skills. Three of these tools have been described: a word question tool that creates ideal gas law and stoichiometry questions using a set of complexity factors; a Lewis structure drawing tool that enables the user to draw a solution to an ion or molecule assigned to them; and a "spheres" tool that uses spheres to represent atoms and molecules to denote the particulate nature of matter. Results from these studies show that relatively simple questions can be made very complex by the addition of many complexity factors that challenge the cognitive skills. The drawing tools can be used for instruction or to collect data about student understanding; the outcomes suggest that students with more instruction in chemistry are more successful but even the performance of students after four semesters is somewhat disappointing. Eye-tracking hardware enabled the study of the student use of the visual interface of the other tools and to study molecular representation or interpret spectral data. <![CDATA[EXPLORING THE DESIGN AND USE OF MOLECULAR ANIMATIONS THAT CONFLICT FOR UNDERSTANDING CHEMICAL REACTIONS]]> Understanding chemical reactions conceptually involves recognizing characteristics of observable phenomena and envisioning how atoms, ions and molecules move and interact to cause the macroscopic changes. Our research focuses on the development of effective strategies for designing and presenting visualizations (videos and animations) to assist students with making connections between macroscopic and molecular level behaviors of chemical reactions. Specifically, we study how students, who view videos of a redox reaction that exhibits obvious signs of macroscopic chemical change, can determine which molecular animation of a set of contrasting animations is best supported by its fit with experimental evidence. Herein we describe how we develop our videos and animations, and how students are learning from this animation task. Students who select inaccurate animation models are often enticed by a model that is easier to explain and fits with their understanding of reaction equations. We note that even though students indicate a preference for one animation over another, they often revise their drawn representations to fit with features from multiple animations. With the assistance of eye tracking research, we are gaining a better understanding of what students view and how they make sense of it.