DIFERENCIAÇÃO CATIÔNICA DE BENTONITAS POR INFRAVERMELHO: UM ESTUDO DOS EFEITOS DA HIDRATAÇÃO DOS CÁTIONS TROCÁVEIS

CATIONIC DIFFERENTIATION OF BENTONITES BY INFRARED: A STUDY OF THE HYDRATION EFFECTS OF EXCHANGEABLE CATIONS. In the bentonite industry, the most common procedure for quality control of the ore and the sodium activation process is the swelling method. However, this tool is restricted only to the differentiation of the sodium and non-sodium types, not considering the other cationic varieties. The objective of this study was to establish parameters for cationic differentiation of bentonites based on Near Infrared (NIR) and Medium (MIR) spectroscopy, which proved to be an effective technique in the cationic differentiation of bentonites using the characteristic bands “7072 cm-1” and “3620 and 3430 cm-1” under the condition of the dry-hydrated sample and not under the anhydrous condition. NIRS can be considered a measure of great scientific and technological contribution, as it allows the cationic differentiation of bentonites in a practical way and with low analytical cost.

APLICAÇÃO DE UMA HISTÓRIA EM QUADRINHOS, TRINITY, NA EDUCAÇÃO EM QUÍMICA

THE APPLICATION OF A COMIC STRIP, TRINITY, IN CHEMISTRY EDUCATION. Faced with obstacles encountered in lessons and the search for actions that meet current educational needs, some attention has been paid to the role of comics as instructional tool. This article focuses on the use of a comic strip, Trinity: A Graphic History of the First Atomic Bomb, to develop knowledge and promote science learning. Three case studies were extracted from the comic and implemented to a group of pre-service chemistry teachers. A questionnaire was utilized to assess their perceptions about the usefulness of comics for their learning. One hundred percent of students indicated that comics helped improve their understanding of the nature of science. On the basis of the data, comic strips may be utilized as an acceptable educational tool in science education.

RECENTES AVANÇOS NA FUNCIONALIZAÇÃO SELETIVA DE QUINOLINAS

RECENT ADVANCES IN SELECTIVE FUNCTIONALIZATION OF QUINOLINES. Heterocyclic compounds form an important and extensive group of organic substances. Among nitrogenous heterocyclic molecules, quinolines stand out for exhibiting attractive chemical and biological properties. These substances can be used as ligands, sensors, luminescent and agrochemical materials. In addition, quinoline-containing compounds can exhibit a wide spectrum of pharmacological properties, allowing their use in several approved drugs nowadays. Due to its importance, the synthesis of molecules containing this nucleus becomes a point of interest for synthetic chemists. In this way, several methodologies have been recently developed to prepare quinoline derivatives with high structural diversity. Such chemical transformations allow the chemical modification of these rings with high selectivity and tolerance to diverse functional groups and these properties have been conveniently used in the preparation of biologically active molecules containing this unit. Herein, we present a review of the main methodologies employed in the selective functionalization of quinolines in the last twenty years. In this context, a brief introduction addressing general synthetic and medicinal aspects related to the functionalization positions of the quinoline ring is presented. Several methodologies used in the functionalization of this moiety are discussed, as well relevant synthetic applications, both in the preparation and functionalization of substances of biological interest.

BIOGEOQUIMICA ESPAÇO-TEMPORAL DA LITEIRA EM AMBIENTE DE FLORESTA NATURAL NA AMAZÔNIA CENTRAL

SPACE-TEMPORAL BIOGEOCHEMISTRY OF THE LITTER IN A NATURAL FOREST ENVIRONMENT IN THE CENTRAL AMAZON. This research was aimed to evaluate the concentration of 15 chemical elements as a reference base for the quality of the litter in a forest in the central region of the Amazon. The sampling of the litter was performed monthly in two topographic positions for one year. For the quantification of the elements, digestion by nitroperchloric solution and reading by ICP OES were performed. The mean of macronutrient contents in the litter in decreasing order were Ca>K>Mg>Na. For micronutrients, the order was Al>Mn>Fe>Sr>Zn>Cu>Ba>Cr>Ni>Co>Cd for the Plateau and Al>Mn>Fe Sr>Zn>Cu>Ba>Cr>Ni>Cd>Co for the Baixio. Among the fractions, calcium had its highest concentration in the woody material, potassium in the reproductive material, while magnesium, sodium, and aluminum showed higher concentrations in the leaf fraction. Also, it was observed that the return of the elements to the soil by litter was greater in the dry period of the region, due to the greater fall in plant material. Calcium differed significantly within the same area, obtaining the highest concentrations compared to the other elements, while aluminum and zinc differed significantly between the areas studied, with a higher return for both elements on the Plateau.

A VISITA DE FRITZ HABER AO BRASIL

FRITZ HABER VISIT TO BRAZIL. Fritz Haber was awarded with the Nobel Prize in Chemistry in 1918 for the ammonia synthesis from its gaseous components. This work was fundamental to stop starvation around the world. On the opposite, his engagement to produce chemical weapons during the First World War is also an important fact in the life of this scientist. This polemic scientist visited Brazil in 1923, carrying out a project to extract gold from the sea. The present work tries to recover the historical fact behind the visit of this scientist to Brazil.

ATIVIDADE INIBITÓRIA DE PESTICIDAS PIRETROIDES SOBRE A GLUTATIONA S-TRANSFERASE

INHIBITORY ACTIVITY OF PYRETHROID PESTICIDES ON GLUTATHIONE S-TRANSFERASE. Glutathione S-transferase (GST) is one of the enzymes used to evaluate the effects caused by environmental contaminants. The aim of this work was to study the effects of four pyrethroid compounds (allethrin, cypermethrin, deltamethrin and fenpropathrin) on the catalytic activity of GST and to estimate the potential for environmental contamination in silico of these insecticides. Spectrophotometric analyses showed that the activity of the GST enzyme was inhibited by the four pesticides, with the values for the inhibition constant (Ki) varying from 0.12 to 20 µmol L-1, with the following order of inhibition from the highest to the lowest Ki value: deltamethrin > cypermethrin > allethrin > fenpropathrin. They presented a competitive and non-competitive inhibition mechanism depending on the compound. The IC50 values (concentration that inhibits 50% of the enzyme activity) showed the insecticide deltamethrin with greater inhibitory capacity, since it reduced the activity of the GST enzyme by half, even though it was in a lower concentration in relation to the other analyzed compounds. The in silico evaluation indicated the possibility of most of the insecticides contaminating the surface waters (rivers and lakes) adhered to the suspended sediment, but did not show any potential for contamination of groundwater through leaching.

AVALIAÇÃO DA CONCENTRAÇÃO TOTAL E DA FRAÇÃO BIOACESSÍVEL DE METAIS EM AMOSTRAS DE CASCA DE UVA DE CULTIVARES TANNAT E CABERNET SAUVIGNON POR MIP OES

EVALUATION OF THE TOTAL CONCENTRATION AND THE BIOACCESSIBLE FRACTION OF METALS IN SAMPLES OF GRAPE SKINS OF CULTIVARS TANNAT AND CABERNET SAUVIGNON BY MIP OES. This paper describes the evaluation of the total concentration of Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Pb e Zn and the bioaccessible fraction of Ba, Cu, Fe, Mn, Pb and Zn in samples of grape skins from different cultivars (Vitis Viníferas Tannat and Cabernet Sauvignon) by MIP OES. For the determination of total concentration, acid decomposition with a reflux system adapted to the digestion tubes in the oxidizing medium of HNO3 and H2O2 were used. The accuracy of the method was verified by recovery tests, whose values ranged from 80 to 120%, as well as through a comparative method in closed system. Bi, Cd and Cr showed values for total content below the LOD or below the values acceptable for health while Pb is higher than 0.2 mg kg-1, for both cultivars. To evaluate the bioacessible fraction, the gastrointestinal system was simulated using an in vitro procedure, and its performance was assessed considering the bioaccessible fraction (supernatant) and the non-bioaccessible fraction, whose sum should be closed to the total concentration, and the results obtained were between 81 and 120%. Both cultivars showed similar values for the bioaccessible fractions (~13.5 – 53% of the total content).

PREPARATION OF FLUORESCENT POLYSTYRENE MICROSPHERES BY IMPROVING SWELLING PERFORMANCE BASED ON MOLECULAR WEIGHT AND SURFACE CARBOXYL GROUP CONTENT

The fluorescent microspheres are prepared by the swelling-evaporation method. The optimal swelling conditions are obtained by researching related factors, such as types and dosages of swelling agent, dosages of fluorescent substance, swelling time and swelling temperature. Considering that the structure of microspheres can influence the swelling properties, the paper mainly focuses on the effect of molecular weight and surface carboxyl group content of polystyrene microspheres on swelling properties. When the molecular weight of microspheres is 75276 g mol-1, the density of carboxyl group on their surface is 6.94×10-4 mol g-1, and the doping amount of europium complex reaches the maximum of 24.9 mg g-1 with the strongest fluorescence intensity. Meanwhile, the as-prepared fluorescent microspheres have high monodispersity, uniform particles size and high thermal stability (the decomposition temperature is 385 oC), which sets up the good foundation for biomolecule detection. So, this work provides a significant experience for the preparation of fluorescent microspheres.

FIRST REPORT ON CHEMICAL COMPOSITION AND BIOLOGICAL PROPERTIES OF VOLATILE OIL FROM Psidium firmum O. BERG LEAVES

Brazil has the greatest plant diversity in the world. Many species exhibit a wide range of phytochemical compounds which can be exploited in food, agronomic, pharmacological and medicinal plant industries. Therefore, the chemical composition and in vitro bioactivities of volatile oil from Psidium firmum fresh leaves (PfVO) were investigated for the first time. GC-FID and GC-MS analyses revealed 28 compounds in PfVO. The major ones were α-selinene (20.8%), β-caryophyllene (16.5%) and nerolidol (10.4%). Results showed that PfVO affected the growth of Leishmania amazonensis promastigote forms in a dose-dependent manner; its IC50 value was 14.05 µg/mL. PfVO also exhibited antibacterial activity against Salmonella enteritidis, Yersinia enterocolitica, Staphylococcus aureus, Pseudomonas aeruginosa and Listeria monocytogenes; MIC values ranged from 25 µg/mL to 250 µg/mL. Moreover, PfVO promoted normal cell growth inhibition at 61.02 ± 1.97 µg/mL. Antiproliferative activity was observed against human tumor cell lines; IC50 values of MCF-7 cells, HeLa cells and M059J cells were 47.91 µg/mL, 73.78 µg/mL and 41.94 µg/mL, respectively. Results provided strong evidence of the promising potential of PfVO as a nature-based antileishmanial, antibacterial and antiproliferative agent.

DIFICULDADES NO ENSINO E NA APRENDIZAGEM DE QUÍMICA ORGÂNICA DO ENSINO SUPERIOR - ESTUDO DE CASO EM DUAS UNIVERSIDADES FEDERAIS

DIFFICULTIES IN TEACHING AND LEARNING ORGANIC CHEMISTRY IN HIGHER EDUCATION - A CASE STUDY IN TWO FEDERAL UNIVERSITIES. This research investigates difficulties associated to the curricular component Organic Chemistry I based on a study case of Chemistry undergraduate courses (Bachelor and Teachers education) in two Federal Universities in the Brazilian South region. The analytical process integrated official documents of the courses (pedagogic projects, students’ grades), questionnaires, interviews, and researcher’s logbook of classes. Results show that the students’ success in Organic Chemistry I is lower than the sum of failure, unattendance, and temporary cancellation rates altogether in the curricular component offered by the different teachers and institutions studied. A complex scenario is highlighted in relation to factors that affect learning and teaching processes in undergraduate Organic Chemistry courses. The subjects’ responses highlight difficulties related to specific contents, such as conformation and spatial visualization of molecules, stereochemistry, and reaction mechanisms; lack of concepts from High School; and individual habits and characteristics of teachers, students, or both, such as didactics, concentration, and engagement. The results report on the importance of rethinking strategies and methodologies in the context of Organic Chemistry I in Higher Education