Scielo RSS <![CDATA[Química Nova]]> vol. 40 num. 8 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[PREPARATION AND VISIBLE LIGHT RESPONSIVE PHOTOCATALYTIC ACTIVITY OF Fe<sub>3</sub>O<sub>4</sub>/Ni-Al-Ce LDH/Bi<sub>2</sub>WO<sub>6</sub> COMPOSITES]]> Novel Fe3O4/Ni-Al-Ce LDH/Bi2WO6 composites were prepared through a hydrothermal method and co-precipitation method. The morphologies and structures of the photocatalysts were characterized by XRD, Raman, TEM, UV-vis-DRS, BET surface area and VSM techniques. The photocatalytic performances of the photocatalysts were investigated by the decolorization of methyl orange (MO) under visible-light irradiation. The results showed that the Fe3O4/Ni-Al-Ce LDH/Bi2WO6 composites exhibited greater photocatalytic activities compared to pure Bi2WO6 and the Ni-Al-Ce LDH; the decolorization rate of MO was 87% within 60 min under visible-light irradiation. The decolorization efficiency of the composite material remained at 71% after 4 recycling runs, showing improved stability. Furthermore, the experimental results also showed that the photocatalytic reactions for the composites followed first-order reaction kinetics. Therefore, the Fe3O4/Ni-Al-Ce LDH/Bi2WO6 composites were photocatalysts with high efficiencies and stabilities for a photocatalytic reaction of an organic pollutant, and this study provides a new, effective method for the development of wastewater treatment. <![CDATA[PHYSICOCHEMICAL PROPERTIES OF ENCENILLO MONOFLORAL HONEY FROM HIGHLANDS ANDEAN ZONES IN BOYACÁ, COLOMBIA]]> Honey is the natural product with sweetening properties more widely known, is produced by bees from the nectar of flowers and secretions from the plants. Its physicochemical properties depend on the season of harvest, environmental factors prevailing in the harvest period and the biogeographic zones. The aim of this work was focused in honeys produced by Weinmannia tomentosa from highlands andean of Colombia, that were characterized on melissopalynology, sensory attributes, composition, physicochemical properties and volatile compounds. Pollen grains at the samples were greater than 45%, conferring a quality of monofloral. Color pfund 69.0 ± 1.00, pH and total acidity 3.87 ± 0.04; 31.8 ± 1.40 meq kg-1, still within the standard limits, electrical conductivity 0.525 ± 0.004 mS cm-1, moisture 20.1 ± 0.43 g 100 g-1, ash 0.198 ± 0.002%, reducing sugars 69.7 ± 0.17 g 100g-1, total phenols 1570 ± 14 mg kg-1 A. Ga, flavonoids 129.4 ± 1.20 mg kg-1. Tabouret's index 3.75 ± 0.06 based on 1.35 ± 0.03 relationship fructose/glucose and 0.604 ± 0.050 water activity. Honey show a Newtonian's behavior. GC/MS analysis permitted to identify 25 volatile compounds, between alcohols, aldehydes, ketones, esters, hydrocarbons, furans, nitriles, sulfide and terpenes. The study is related as a model for characterization of types of honey and consolidated as the first research on unifloral honey in Colombia. <![CDATA[INFLUÊNCIA DO ENVELHECIMENTO ACELERADO EM <em>FLARES</em> MAGNÉSIO/PTFE/FPM]]> Magnesium/PTFE/FPM decoy flares, also named conventional flares, were designed in order to protect combat aircraft from the threat caused by infrared-guided missiles. Adverse storage or transport conditions may cause reactions that deteriorates chemical properties of the conventional flares, causing the aging and compromising its performance. The aim of this article was to characterize the influence of accelerated aging on conventional flares. The study was performed with the latest lot of conventional flares from Brazilian Air Force, subjected to 50 days exposure in a climatic chamber at 76 °C and 62% RH. Upon completion of the accelerated aging process, samples of aged conventional flares were compared with unaged material. Qualitative determination of chemical species present was carried out using the techniques FT-IR and SEM/EDS. Magnesium hydroxide, the main product of aging process and primary aging indicator on conventional flares performance, was determined using thermogravimetric analysis and the amount was correlated with results of the experimental techniques Density Determination, Calorimetry and Vacuum Stability Test. Formation of additional magnesium hydroxide mass, that increased 100% during the aging process, caused the passivation of magnesium, compromising the combustion process and making the composition less energy efficient, as verified in the results of the calorimetric tests. <![CDATA[GEOCHEMISTRY OF SUSPENDED PARTICULATE MATTER IN A TROPICAL ESTUARINE SYSTEM, SOUTHEASTERN BRAZIL]]> The aim of this study is to assess the variation of the geochemistry of suspended particulate matter (SPM) in the tropical estuarine system composed of the adjacent Piraquê-Açu and Piraquê-Mirim (ES) rivers using SPM sampled with sediment traps (45 µm mesh) installed in the drainage channels. We collected SPM during different tidal stages and seasonal periods and analysed the metals using inductively coupled plasma mass spectrometry according to EPA 3051A, the mineralogy using X-ray diffraction, the particle size using laser ray diffraction, and organic matter (OM) using calcination. The traps collected enough SPM to perform analyses for each sampling period. The SPM consists of silt size particles, and the percentage of OM is between 20 and 40%. The particles are dominated by kaolinite and quartz, and gibbsite, haematite, goethite, and pyrite are also present. These materials are found in the Barreiras Formation, through which the drainage system cuts. The metal concentrations were higher in the summer: Al (3208.32 g kg-1), Pb (28.05 mg kg-1), Mn (676.35 mg kg-1), Cr (136.12 mg kg-1), and Cu (13.76 mg kg-1). The Piraquê-Açu River had higher metal concentrations than the Piraquê-Mirim River, and the geochemical indices of both rivers indicate that they naturally contribute to the estuarine system of the Piraquê-Açu and Piraquê-Mirim rivers (SEPAPM). However, anthropic interferences influence these indices at the confluence of the two channels. <![CDATA[MATHEMATICAL MODEL OF CATALYTIC PROCESSES AT MODIFIED ELECTRODES]]> A mathematical modeling of electrocatalytic processes taking place at modified electrodes is discussed. In this paper we obtained the approximate analytical solutions for the nonlinear equations under non steady state conditions using homotopy perturbation method. Simple and approximate polynomial expressions for the concentration of reactant, product and charge carrier were obtained in terms of diffusion coefficient and rate constant. In this work the numerical simulation of the problem is reported using Scilab program. In this manuscript analytical results are compared with simulation results and satisfactory agreement is noted. <![CDATA[FUNGAL BIODEGRADATION OF RIGID POLYURETHANE]]> Polyurethane (PU) is one of the most widely used polymer materials. This generates a serious environmental problem because of its poor biodegradability since most of the native microorganisms cannot use it as a source of nutrients. Several techniques involving mechanical and chemical processes have been used for its recovery and reuse; however, the problem of contamination has not been solved, and recently research has focused on developing strategies that use different microorganisms for the biodegradation of PU. In this work, the biodegradation and enzymatic capacity of three fungal strains were evaluated. Thermogravimetric and infrared spectrophotometry analyzes were used to evaluate the ability of the three fungal strains to biodegrade PU and also their enzymatic activities were studied. It was found that a strain of Trichoderma was able to modify the PU structure enough that the changes were detected by both TGA and FTIR. These changes can be caused by urease activity that breaks down carbon-nitrogen bonds in the structure because the signals suggesting the formation of carboxylic acids and decreasing corresponding to carbon-nitrogen bonds of the urethane bond are increased. <![CDATA[PERFIL DOS COMPONENTES VOLÁTEIS PRODUZIDOS PELO FUNGO FITOPATÓGENO <em>Albonectria rigidiuscula</em> EM DIFERENTES CONDIÇÕES DE CULTIVO]]> The VOCs produced by the Albonectria rigidiuscula fungus in different conditions were obtained by headspace-solid phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). Fourty-four VOCs were identified in different culture media and incubation periods. The highest production of VOCs occurred in solid rice medium and 14 days of incubation. The compounds 3-methylbutan-1-ol, 2-methylbutan-1-ol, γ-muurolene and nerolidol acetate were produced by A. rigidiuscula in all culture conditions. γ-Muurolene was identified as the major compound (40.78%, 26.24% and 27.04%) in PD medium and it was suggested as a chemical marker for this fungus. The use of multivariate data analysis (PCA) and (HCA) allowed the discrimination of the volatile chemical profiles according to the culture medium. <![CDATA[AVALIAÇÃO DE FRAGMENTOS DE LENHOS CARBONIZADOS DE ARAUCARIACEAE POR MEIO DE TERMOGRAVIMETRIA E INFRAVERMELHO ASSOCIADAS À ANÁLISE MULTIVARIADA]]> The aim of the study is to evaluate the physical and chemical changes that occur on wood fragments submitted to different temperatures, verifying their influence on significant chemical characteristics in the forming process. Carbonization process in muffle associated to the techniques of Thermogravimetry, Fourier Transform Infrared Spectroscopy (FTIR) and multivariate analysis. The analyses were performed on 3 replicates for each burn temperature. The temperature of the thermal muffle process was in every 50 °C, from 200 °C to 600 °C. TGA were performed under nitrogen atmosphere, using a heating ramp from 25 °C min-1 to 995 °C. A range between 1900 to 650 cm-1 was used, with a resolution of 4 cm-1 and 64 scans. The PCA showed that it is possible to describe 95.73% of the data, grouping the samples into three main clusters. These clusters were used to build a SIMCA (Soft Independent Modeling of Class Analogy) model, enabling to predict with 100%. Results showed that technical associations, such as TGA, FTIR and multivariate analysis may help to characterize the natural carbonization process and, in future works, contribute to significant (paleo)environmental inferences. <![CDATA[FACILE SYNTHESIS, CHARACTERIZATION AND DFT CALCULATIONS OF 2-ACETYL PYRIDINE DERIVATIVES]]> Deprotonation of 2-acetylpyridine was carried out in the presence of NaH as a phase transfer catalyst instead of NaOH to minimize side products formation. The products were then treated with two equivalents of alkyl/aryl halide to synthesize a variety of acetyl pyridine derivatives. The compounds were structurally characterized by 1H- and 13C-NMR spectroscopy in solution state. Structure of compound 2 was also confirmed in solid state by X-ray diffraction. Electronic properties such as Mulliken charges, frontier molecular orbitals (HOMO-LUMO), ionization energy (IE), electron affinity (EA), global hardness (η), Chemical Potential (µ) and Global electrophilicity (ω) of some compounds were investigated by the same theory using B3LYP-6-311G basis set. <![CDATA[PEROXIDASE FROM SOYBEAN MEAL: OBTENTION, PURIFICATION AND APPLICATION IN REDUCTION OF DEOXYNIVALENOL LEVELS]]> This study established the conditions for the extraction of the enzyme peroxidase (PO) from soybean meal (SBM). An experimental design methodology was carried out in order to evaluate the effects of stirring rate time, pH and extracting solvent volume on the enzyme extraction. By using 5 g SBM and 50 mL phosphate buffer 10 mmol L-1 pH 4.7, 60 min stirring rate at 100 rpm, an enzyme with specific activity of 100 U mg-1 for SBM was obtained. Two techniques of purification were tested and compared for purification of peroxidase from soybean meal: triphasic partition (TPP) and molecular exclusion chromatography. TPP showcased a greater efficiency with 50% recuperation and a purification factor of 13.6. Peroxidase in crude and pure forms was characterized for kinetics, thermodynamics and biochemistry. The parameter of thermal inactivation indicates high stability to exposure time and temperature increase, showing that enzyme activity is not altered by the presence of constituents of the reaction medium. Peroxidase in crude form represented a greater upkeep in activity, keeping 50% activity for 114 days at 0 °C. Peroxidase in pure form had greater affinity for substrate and reduced Deoxynivalenol levels by 80%, 20% more than the crude form. <![CDATA[THE FUNGAL ABILITY FOR BIOBLEACHING/BIOPULPING/BIOREMEDIATION OF LIGNIN-LIKE COMPOUNDS OF AGRO-INDUSTRIAL RAW MATERIAL]]> Lignin is present in plant cell secondary wall, associated to carbohydrates preventing their efficient hydrolysis, and cellulose pulp manufacture basically consists in breaking down the middle lamella of plant cells, individualizing fibers such as cellulose from the other biopolymers. Different levels of lignocellulose are found in plant residues and they can be decomposed by extracellular fungal lignin modifying enzymes, used as a tool to reduce waste materials in contaminated soils and effluents. In the paper mill industries, for instance, they are a suitable or complementary alternative to the traditional methods of pulping/bleaching, contributing to improve paper strength as well as to reduce the pitch content, the quantity of chemicals and the consume of electrical energy. The aim of this review was to describe the fungal degradation of lignocellulosic like-material, the non-specific enzymatic aspects of the attack of wood and agricultural wastes, the fungal ability for biosorption and bioconversion, and its applications in the pulp/paper industry and bioremediation. <![CDATA[AVANÇOS RECENTES NA HIDROAMINAÇÃO DE COMPOSTOS INSATURADOS]]> This review presents thermodynamics and kinetics aspects of the hydroamination reaction, recent advancements on this field for non-activated alkenes, alkynes and allenes, employing transition metal catalysis or organocatalysis, including activation by hydrogen bonding or Brønsted acids. Selected syntheses that contain a strategic hydroamination step will be discussed, and advancements on the asymmetric version will also be highlighted. The full coverage of scientific activity about hydroamination is beyond this review, therefore the examples presented are from the last ten years, except when there are historical reasons for the discussion of previous works. <![CDATA[PAPEL INDICADOR COLORIMÉTRICO PARA DETECÇÃO DE FORMOL EM PRODUTOS LÁCTEOS E PRODUTOS DE HIGIENE PESSOAL]]> Due to its low cost, formaldehyde was commonly used as conservative in hygienic and cosmetic products. However, formaldehyde is strongly reactive and toxic, so its use has been forbidden in several products. Recently, it was reported by different media that formaldehyde has been added illegally in milk, causing innumerous health problems. In this work we developed a colorimetric indicator paper based on Schiff 's reagent, which can be associated with a smartphone application. It was observed that the paper stabilizes the Schiff 's reagent, avoiding its decomposition during short periods. It was also possible to successfully detect the presence of formaldehyde in commercial products, such as: detergents, shampoos and conditioners. Regarding milk based products, the indicator paper is very sensitive to detect formaldehyde, having a sensibility of 0.01% (v/v). The developed indicator paper has low cost and can help the supervision of milk products, as a trial test. Also it is possible to commercialize this product to common consumer, due to its simplicity. <![CDATA[DETERMINAÇÃO CONDUTOMÉTRICA DE CLORIDRATO DE TETRACICLINA EM FORMULAÇÕES FARMACÊUTICAS]]> In the present article it is described, a simple, precise, rapid and low-cost conductometric titration of tetracycline hydrochloride in pharmaceutical formulations using silver nitrate as titrant. The method is based on the precipitation of chloride ions derived from tetracycline hydrochloride with silver ions, yielding silver chloride precipitate and the conductance of the solution is measured as a function of the volume of titrant. The coefficient of variation for six successive measurements was 0.64% and no interferences were observed in the presence of common components of the pharmaceutical formulations. Recovery values from two samples, ranging from 99.0 to 105%, were obtained. The method was applied for tetracycline hydrochloride determination in two pharmaceuticals formulations and these results are in good accordance with the declared values of manufacturer and an official method of the Brazilian Pharmacopoeia, based on spectrophotometric analysis, at a 95% confidence level. <![CDATA[OPERAÇÃO CAFÉ PASSADO: UMA PERSPECTIVA DIDÁTICO-PEDAGÓGICA PARA O ENSINO EM ENGENHARIA QUÍMICA]]> In the present work, the application of a didactic activity proposed for the teaching-learning of mass transfer initial concepts unit operations for students of Introduction to Chemical Engineering course of a public institution was evaluated. For this, the class was separated in four moments: brief introduction to the subject, pre-test application, experimental activity and post-test application. Also, a survey of students' satisfaction about the activity was conducted by e-mail and on a voluntary basis. The results obtained from the pre- and post-test were analyzed using Wilcoxon's nonparametric statistical test. This way, it could be verified that the proposed didactic methodology contributed positively in the teaching-learning process of these students. <![CDATA[ESTRUTURAS DE FULERENOS: ESTABELECENDO INTERFACES NO ENSINO DE MATEMÁTICA E QUÍMICA EM NÍVEL SUPERIOR]]> The objective of this paper is to study fullerene geometry properties and attempt to stablish a dialogue between the teaching of mathematics and chemistry concepts using hands-on cardboard geometric models, in classroom, in order to facilitate the understanding of fullerene structures. This approach to the study of such molecules represents a unique opportunity to explore a complex and rich array of concepts that are essential to the teaching of chemistry at university level and have to be applied by the students along their course. At the same time the study of fullerenes can also profit from a mathematics approach to it, especially from a geometry perspective as argued here. In our research, the use of paper-made geometric models has proven to help the students to visualize and understand such molecular structures, their chemical bonds and their physical-chemical properties. These models have also contributed to overcome representational constraints of such tiny structures, which often come close to a "quasi-abstract' dimension, in a scale that can be manually handled by the students and at the same time played into multiple possible variations that allow them to test concepts and compare different molecular structures and arrangements.