Resumo em Inglês:

In this paper, the influence of the optimization for flow field size on the proton exchange membrane fuel cell (PEMFC) performance under the inadequate air supply of cathode was studied based on the three-dimensional, steady-state, and constant temperature PEMFC monomer model. Additionally, the effect of the optimization for hybrid factors, including length, width, depth and width-depth, on the PEMFC performance was also investigated. The results showed that the optimization of the flow field size can improve the performance of the PEMFC and ensure that it is close to the level under the normal gas supply.

Resumo em Inglês:

Asphaltenes fractions were extracted and purified from three heavy Brazilian oils. Their mass compositions of C, H, N, Ni and V were obtained from elemental analysis and S and O atomic percentages from EDS. The H/C ratios showed high degree of unsaturation, while the O atomic percentages indicated more pronounced biodegradation effects on two samples. Quantitative data on N, Ni, and V and semi-quantitative data on S were related to oils origins. The structural data of asphaltenes were explored by combining Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The oil with the lower degree of biodegradation contained asphaltenes with a lower level of condensed aromatic rings and longer aliphatic chain substituents. The asphaltenes obtained from the two most biodegraded oils showed similarities of polar groups and the presence of carboxylic functions, as well as lower contents of aliphatic substituents. The quality and quantity of occluded hydrocarbons were assessed after the mild oxidation of the separated asphaltenes fractions. It was suggested that the severe biodegradation which altered these structures may also be responsible to affect their occluded hydrocarbons.

Resumo em Inglês:

Mullite is used to obtain a refractory material, there are several factors that influence the synthesis process of mullite: the preparation of the mixture, the precipitation and the reaction of SiO2 and Al2O3. For the synthesis of mullite, samples of kaolin processing residues were used as precursor material, because it presents SiO2 and Al2O3 in its composition. This work aimed to identify, by X-ray diffraction, and quantify the mineral phases present in samples of kaolin processing residues from the Amazon region calcined at 1300, 1400 and 1500 ºC, using the Rietveld method. The method allowed the refinement of the complex crystalline structures and was applied to the data supply for quantitative analyses with satisfactory results of good accuracy. The results of the quantification of crystalline and non-crystalline phases (with internal standard) in the samples calcined at 1500 ºC presented approximate values of mullite (62%), cristobalite (32%) and non-crystalline phases (6%), for both samples, indicating that the refinement model applied is optimal. These results obtained from the quantification of the phases by the method of Rietveld are presenting coherent and satisfactory values, in comparison with the theoretical ones by the phase diagram Al2O3 and SiO2.

Resumo em Inglês:

This work studied the obtaining of methyl biodiesel and ethyl biodiesel using alkaline transesterification from macroalgae Fucus vesiculosos oil (FVO). FVO has 86.59% of its composition in unsaturated fatty acids, with a greater quantity of linoleic acid and oleic acid, a chemical composition near the soybean oil, the most used raw material for the production of biodiesel. Linoleic acid (47.88%), and oleic acid (34.66%) are the fatty acids present in the greatest amount in FVO, and unsaturated fatty acids correspond to 86.59% the composition of FVO, a composition of fatty acids close to that of soybean oil, which is the oil most produced and used for the production of biodiesel. To obtain methyl biodiesel (MBFVO) and ethyl biodiesel (EBFVO) the molar ratio oil: alcohol 1: 3 and 1% alkaline catalyst, NaOH, was used. The yield of the transesterification reaction was evaluated by varying the reaction time between 30 and 60 minutes and the highest yields were obtained after 60 minutes of reaction. In order to check the quality of the obtained biodiesel, the properties acidity index, iodine value, water content, specific mass at 20 ºC, oxidative stability, cold filter plugging point and kinematic viscosity were evaluated. The oxidative stability had an induction period below the recommended, but it can be corrected with the addition of antioxidants to the biodiesel. All other physical and chemical properties had values within the stipulated by the regulatory agencies, indicating that the macroalgae Fucus vesiculosus can be a raw material in potential for production of biodiesel.

Resumo em Inglês:

In this work, the chemical modification of pristine polypropylene was carried out through sulfonation reactions with concentrated sulfuric acid (PPS1) and fuming sulfuric acid (PPS2), for production of heterogeneous catalysts used in esterification reactions. Fourier transform infrared spectroscopy, elemental analysis, degree of substitution and ion exchange capacity showed that both sulfonation agents were effective to promote the functionalization of polypropylene, with the fuming sulfuric acid capable of promoting a greater chemical modification. The materials catalytic activity in esterification reaction of oleic acid with methanol was evaluated at 100 ºC, methanol: oleic acid molar ratio of 78:1 and with 5 wt% of catalyst (referred to oleic acid weight). It was observed that reaction catalyzed by PPS1 converted 68.02% of oleic acid to methyl oleate in 3 hours of reaction, while PPS2 reached 86.47% conversion in five hours, showing even greater catalytic efficiency than the commercial ion exchange resin, Amberlyst 15. Therefore, the conditions employed for the sulfonation of polypropylene were satisfactory to produce materials with acid characteristics necessary to catalyze the esterification reaction of oleic acid with methanol.

Resumo em Inglês:

The Zika virus is a flavivirus spread by the Aedes aegypti mosquito, which also transmits dengue and chikungunya. Current forms of control include elimination of mosquito breeding sites, use of insecticides, repellents and other means. The present study developed new adsorbent materials based on silica and biomaterials capable of releasing an Aedes aegypti mosquito repellent. The materials synthesized were characterized by Fourier-Transform Infrared, thermogravimetric analysis, Scanning Electron Microscopy and Brunauer, Emmett and Teller analysis and tested with citronella, an essential oil widely recognized as a natural insect repellent. The materials presented type IV isotherms, with type H1 hysteresis, characteristic of mesoporous materials, with pore diameters of between 50 Å and 80 Å. Materials based on silica-chitosan-glutaraldehyde dried in an oven (SCGO) and silica-chitosan-glutaraldehyde dried under a vacuum (SCGV) were found to produce more controlled release of citronella essential oil. The bioassay test was performed using a horizontal double-choice olfactometer. The adsorbent SCGO remained stable for the four hours of the bioassay, while the commercial repellent became ineffective after two hours of release. The production of a prototype in the form of bracelets, stickers releasing a volatile repellent is therefore proposed as a method for the control of the mosquito in urban areas.

Resumo em Inglês:

Glycosylation reaction is an important class of reactions in organic chemistry, and the development of the method contributes to the synthesis of many biologically active compounds containing various glycoside bonds. Is arguably the most important, albeit challenging, reaction in the field of carbohydrate chemistry. Examples of the products of glycosylation reactions are glycoproteins, glycolipids, glycosaminoglycans, oligosaccharides, and polysaccharides. Glycosylation types are classified according to the identity of the atom which binds the carbohydrate chain, i.e. C-linked, N-linked, O-linked or S-linked. In this short review, recent reports of the main glycosylation methods, basic mechanisms, factors influencing the stereoselectivity and their applications in the synthesis of bioactive molecules are described.

Resumo em Inglês:

The increased emissions of reactive nitrogen gases from anthropogenic sources to the atmosphere has been pointed out as responsible for triggering a series of environmental problems at the local, regional, and global scale. Among the many consequences associated with the excess of reactive nitrogen in the environment is the increase of atmospheric aerosol formation. In this way, the present review article aims to provide an overview of the main aerosol formation reactions from the reactive nitrogen gases, their growth processes, and removal from the atmosphere. The paper also addresses the implications of increasing the atmospheric aerosol load, including effects on the planet’s radiative forcing, cloud formation and precipitation, macronutrient dispersion, visibility and human health. The possible relationship between the long-term exposure to these pollutants and COVID-19 fatality is also discussed. The need for more information related to reactive nitrogen gases and atmospheric aerosols is urgent since they act on fundamental processes on planet Earth and their quantity and composition have been abruptly changed over the last hundred years. Therefore, further investigations on this topic should be stimulated and better integrated in order to guide normative decisions and the delineation of possible solutions.

Resumo em Inglês:

Cysteine proteases are an important class of enzymes involved in several essential biological processes. For this reason, these enzymes are important therapeutic targets, and therefore can be used in enzymatic assays for the search of hits. The most widely used methods in the search of enzyme inhibitors are spectrophotometric, however they have relatively high operational costs. For this reason, simpler, and cheaper methods can be useful in the search for enzyme inhibitors. In this work, a simple and low-cost semi-quantitative method was optimized and validated using papain and skimmed powdered milk (casein) as a substrate. The ideal condition for the method was the one that used powdered milk, 0.250%, papain solution, 9.4 mg mL-1 and incubation time, 18 h. The method validation was performed using the inhibitor E64 and herb extracts, in different concentrations. After carrying out the experiments and statistical analyses, a high reproducibility can be observed, with relative standard deviations below 2.1%. Plant extracts were used to test the method and the results indicated that these extracts are promising for the search of cysteine protease inhibitors. The method developed here has simplicity and reproducibility and has great application, as preliminary study, in the search for inhibitors of cysteine proteases.

Resumo em Inglês:

The brewing waste, also known as trub, is an abundant by-product of the brewing industry. Such material presents high levels of phenolic compounds, which promote antioxidant, antimicrobial and antifungal effects, turning the trub economically attractive. In this study, the trub’s phenolic compounds were extracted by ultrasound-assisted extraction technology. Such experiments were conducted according to a central composite rotatable design (CCRD), with the evaluated parameters being ethanol concentration, solid-liquid ratio and extraction temperature. Response surface methodology (RSM) described the effect of process’ variables through second order polynomial models, adjusted appropriately for such analysis, and optimized the operating conditions, aiming to obtain the maximum extraction of phenolic compounds through the proposed technique. The extraction’s optimal conditions for the evaluated variables were ethanol concentration of 58%, solid-liquid ratio of 1 g per 32 mL, and extraction temperature of 36 ºC, during a 30 minute process. Considering such experimental conditions, the total amount of phenolic compounds was equal to 7.23 mg of gallic acid g-1 trub, indicating that a great concentration of phenolic compounds can be extracted from this material through the proposed technique. Thus, this indicates that trub might be a promising by-product that can be used in different industrial fields.

Resumo em Inglês:

The classification of chemical substances is a concept little explored in Chemistry teaching literature and in Chemistry textbooks at higher and secondary levels. The aim of this paper is to discuss theoretically the importance and contributions of this concept for teaching and learning Chemistry. The History of Chemistry reveals that the chemical criteria for classifying materials came up with the modern concepts of chemical element and chemical reaction, which gave rise to the notion of chemical similarity. Later, such similarity was related to molecular structure through functional groups. The classes of substances are related throughout chemical reactions, during which substances of given classes are transformed into substances of other classes, constituting a wide network. The classification of chemical substances can contribute to the intellectual development of Chemistry students, in order to study it, it becomes necessary to understand its theoretical foundation, as well as its characteristics of objectivity, completeness, simplicity and prediction. In this sense, one can contribute to the stimulation of perception, attention and abstraction that are typical of the chemical ways of thinking and communicating necessary for learning the chemical concepts linked to classification.

Resumo em Inglês:

The flipped classroom is one of the types of rotation model strategies that aim of increasing interaction and personalized contact time between students and teachers in the classroom setting. In this study, we investigated the application of the flipped classroom strategy in two classes of the different semesters in the discipline of Organic Chemistry. The teacher applied this strategy in different ways in order to verify how the flipped classroom can contribute to the teaching and learning process in the content of Nuclear Magnetic Resonance (NMR). The research, of qualitative nature, is a case study being carried out in six steps with the participation of twenty-five students and one teacher. The instruments used for data collection were an investigative questionnaire (applied to students) and a structured interview (carried out with the teacher). The results show that the students had control over their learning, presenting a favorable position for the application of the strategy. In addition, the teacher reported that it was possible to deepen the content of NMR with his students, teaching the class in a different way than he was used to, focusing on doubts (individual and collective), as well as comments regarding the materials produced by him.

Resumo em Inglês:

Teaching laboratory of qualitative analytical chemistry is still a controversial issue in chemistry courses. However, important researchers and educators in chemistry recognized and highlighted the importance that the contents of this discipline represent in the formation of chemists, once it can provide handling and understanding of microscopic phenomena based on the observation of their macroscopic effects, once such reactions and phenomena are the basis of important instrumental methods of analysis. Thus, a proposal based on a bottom-up approach has been developed, starting with the observation of different reactions of cations in laboratory, followed by a search for the reaction responsible for each resulting phenomenon observed during the experimental step. Then these reactions are related with the separation procedures of each group of cations. Eventually the separation of these groups can also be performed depending on the time available. The proposal has been applied in teaching laboratory of qualitative analytical chemistry at Instituto de Química de São Carlos/USP since 2015, where the discipline is offered duirng 4 hours/week, and a positive feedback regarding the evolution of the methodology and its acceptance by students. Good results were also obtained concerning the appropriation of the contents by the students, using the proposal.

Resumo em Inglês:

The growing predominance of nanoscience and nanotechnology makes it increasingly important that these topics become an integral part of all scientific education. For this reason, in the present work, an interdisciplinary experiment of nanotechnology is introduced. As silver nanoparticles (AgNPs) are the most applied nanomaterial in consumer products, the current understanding of their stability is needed. Silver nanoparticles were synthesized using chitosan as a capping agent and a size distribution of 9.7 nm was determined by transmission electron microscopy. After preparation, the AgNPs colloid was divided into two parts. One part was stored in dark at 4.0 ± 1.0 ºC and it was removed out from the fridge only to be analyzed by UV-vis. The second part was used to study the colloid stability in the presence of Hg2+, and also in the combination of mercury with the ions Cu2+, Fe2+, Ni2+, Sn2+, and Zn2+. The UV-vis analysis indicated that the AgNPs were oxidized in the presence of these ions, but in different intensities, which can be explained by using the electrochemistry approach. This work may be relevant for graduate-level or upper-level undergraduate experimental course preparation as the procedure is simple and easily reproducible in a typical chemistry laboratory.

Resumo em Inglês:

Saltpeter demanded for a long-time strategic attention in view of its importance in the form of gunpowder by the governments of many nations. The sources of this mineral in Brazil were almost always associated to the soil in caves, which was extracted because of a limited amount of that precious salt. The first references pointed out that saltpeter was first discovered in the São Francisco basin in regions of the south of the Captaincy of Bahia and in the north of Minas Gerais. Some historical documents show that the Serra do Baldim was the object of intensive mining activities of saltpeter from its caves and the product became the focus of conflicts and left scars on the walls of some limestone caverns.

Resumo em Inglês:

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.