Resumo em Inglês:

A new spectrophotometric method was developed for the determination of taurine using 7,7,8,8-tetracyanoquinodimethane (TCNQ). The method was based on the formation of charge transfer (CT) complex of this drug as n-electron donor with the π-acceptor TCNQ. TCNQ was found to react with taurine to produce a kind of yellow complex. The spectrum obtained for taurine/TCNQ system showed the maximum absorption band at a wavelength of 420 nm. The formation of such complex was also confirmed by both infrared and 1H NMR measurements. Different variables affecting the reaction were studies and optimized. Beer’s law was obeyed in a concentration limit of 1~9 µg mL-1 for taurine. R.S.D. was less than 1.5%, and average recovery was over 100.3%. The stoichiometry of the complex was found to be 1:1 ratio by Job’s and straight line methods between the donor and the acceptor. The thermodynamic standard reaction quantities of the complex between the donor and the acceptor were estimated. The developed method could be applied successfully for the determination of the studied compound in the pharmaceutical dosage form with a good precision and accuracy compared to official and reported method as revealed by t- and F-tests.

Resumo em Inglês:

Biodiesel contains unsaturated methyl esters making it susceptible to oxidation reaction. Among the factors that cause oxidative instability is the contamination by transition metal ions that in small quantities catalyze the oxidation reaction. The objective of this work was to evaluate the relative protection factor of rosemary extract, in biodiesel, in the presence of transition metal ions. Chromatographic analysis and characterization of biodiesel were performed as well as the quantification of total phenolic compounds and extract activity. The ions Cr3+, Co2+ and Fe2+, at a concentration of 3.95 x 10-3 mol L-1, were added to the biodiesel with and without rosemary extract. The samples were submitted to the Rancimat test and to infrared region analyses. The infrared region spectra of the samples with Cr3+ are in accordance with the least catalytic power of this ion under the biodiesel oxidation. Samples with Co2+ ions, without extract, presented bands of aldehydes, and samples with Fe2+ ions show the formation of peroxide radicals, without rosemary extract at 48h. The antioxidant effect of the extract in biodiesel is observed by the reduction of the induction period of the samples. The relative protection factor proved to be a good tool to evaluate its efficiency.

Resumo em Inglês:

This work describes the chemical composition of MeOH seeds and flowers extracts of Tapirira guianensis, a known tree that occurs in the Brazilian Atlantic forest. The CH2Cl2 soluble fraction of seeds extract was submitted to chromatographic procedures to obtain a mixture of new alkenyl dihydrobenzofuranoids which were identified as 2-[(10’Z)-dodec-10’-enyl]-dihydro-1-benzofuran-5-ol, 2-[(10’Z)-tridec-10’-enyl]-dihydro-1-benzofuran-5-ol e 2-[(10’Z)-pentadec-10’-enyl]-dihydro-1-benzofuran-5-ol (1 - 3) besides β-sitosterol. From the EtOAc soluble fraction of flowers MeOH extract quercetin, quercitrin and gallic acid were obtained by chromatographic techniques. The fatty acid composition of oils from leaves and seeds were also determinate and the leaves’ oil is composed by 63.94% of saturated and 36.04% of unsaturated fatty acids while in the seeds the oil present 42.13% of saturated and 57.87% of unsaturated. All compounds and derivatives were identified by their spectrometric data analysis. The brine shrimp test of the extracts showed the seed CH2Cl2 and the EtOAc and BuOH soluble fractions of the flowers were actives and, the alkyl phenols are the responsible for this moderate activity. The antioxidant tests of the extracts indicated EtOAc soluble fraction of MeOH extract of flowers showed better results possibly due the presence of flavonoids and gallic acid.

Resumo em Inglês:

The surface intermediates formed on the Mg-La catalyst (molar ratio 1:1) were studied through temperature-programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy coupled to mass spectrometry (DRIFTS-MS) using methanol (MeOH) and ethyl acetate (EA) as probe molecules. TPD results showed that the products formed from adsorbed MeOH were hydrogen and formaldehyde, whereas EA produced hydrogen, ethanol, and acetone. DRIFTS-MS of a MeOH and EA mixture results showed that methanol adsorbs as methoxy species on the catalyst surface, and EA adsorbs through the oxygen of carbonyl groups forming ethoxy and acetate species. The reaction of the adsorbed intermediate species resulted in the formation of methane, CO2 gas phase, ethanol, and methyl acetate. Also, methanol adsorbed preferentially on the basic site and EA in a dissociative form. Surface intermediates identification allowed to confirm that the Eley-Rideal type mechanism was predominant on the catalyst surface studied.

Resumo em Inglês:

The volatile compounds present in cachaça can derive from the raw material used in the production of the beverage, from the fermentative process, from distillation or aging. The aim of the research was to evaluate the volatile compounds, in the cachaças from stills produced with different sugarcane varieties, under the organic and conventional managements. The varieties RB867515, RB962869 and RB85553 were cultivated in three distinct ways, planting without fertilization (OUTF); organic planting (ORGN) and conventional planting (CONV). The results showed that for the total esters, higher alcohols and coefficient of congeners present in the cachaça, the varieties and managements are dependent, unlike volatile acidity, total aldehydes, methyl alcohol and furfural. Therefore, the quality, origin and lineage of the sugarcane variety used for the production of cachaça were confirmed to influence the chemical concentrations of the volatile compounds of the beverage, modifying its chemical profile. It is worth reinforcing that none of the volatiles presented concentration above that allowed by the Brazilian legislation.

Resumo em Inglês:

The lipase from Rhizomucor miehei (RML) has been immobilized on chitosan-based hybrid (sodium alginate or carrageenan) matrices activated with glycidol (GLY), epichlorohydrin (EPI) or glutaraldehyde (GLU) groups. Then, the properties of the different biocatalysts have been evaluated and compared with the soluble RML. Thermal stability (at pH 7.0 and 60 °C) was significantly increased when compared to the soluble enzyme: 154-fold for chitosan 5.0% - GLU, 80-fold for chitosan 2.5% - carrageenan 2.5% - GLY and 93-fold for chitosan 2.5% - alginate 2.5% - EPI. The best biocatalyst preparation, which was 154-fold more stable than the soluble enzyme, was obtained when RML was immobilized on chitosan activated with glutaraldehyde 5.0% v/v. According to the results, it was concluded that RML immobilization on chitosan-based hybrid matrices using different chemistries greatly produced biocatalysts with different properties.

Resumo em Inglês:

The analysis of volatiles is an alternative in the routine of quality control of fruits, since the volatile metabolites can change in the presence of microorganisms. A well-established method for extracting volatiles is the solid phase microextraction (SPME). This work aims to define some parameters (fiber coating, conditioning time and fiber exposure time) for an effective extraction. Whole papaya was inserted into a hermetically closed glass bottle and the system was left in conditioning for the volatiles accumulation. Then, extraction by SPME and subsequent desorption in a gas chromatograph was performed. Two fibers were evaluated: a 100 µm polydimethylsiloxane (PDMS) and a 65 µm polydimethylsiloxane/divinylbenzene (PDMS/DVB). The PDMS/DVB fiber extracted the highest number of volatiles. Central composite design (CCD) was performed to assess the effect of papaya conditioning time and the fiber exposure time on the response: number of detectable peaks. Both variables studied and their interactions were significant for the response. ANOVA showed that the quadratic terms and the lack of fit were not significant (p <0.05). A conditioning time of 10 min and exposure time of 30 min was sufficient for the detection of more than 100 compounds.

Resumo em Inglês:

Biodiesel made from oils is rich in polyunsaturated fatty acids methyl esters, and, consequently, presents high tendency to oxidize. Biodiesel made from fats, on the other hand, is mainly comprised by saturated chains. Although it is highly stable, they easily crystalize at low temperatures. Blends from both can exhibit optimized properties. In this work, oxidative stability, expressed by induction period (IP), and cold filter plugging point (CFPP) of blends from palm, palm kernel, babassu, tallow or lard biodiesels with soy one were measured. Biodiesel samples were prepared by two steps transesterification methodology with KOH catalysis followed by H2SO4. IP increases, as the fat biodiesel content in the blend is higher, as expected. Blends comprised by 60% of fat biodiesel by volume had their IP increased from 1.5 (lard) to 2 times (palm kernel), compared to soy one. At this level, IP was found 8 h or higher, except for palm, which 80% was required. CFPP was observed at 8 °C or lower for the blends containing up to 60% of all the fat biodiesel, except for the palm one, which a 20% content must not be surpassed. Palm kernel 80% biodiesel blend reached the Brazilian specification, that is, IP higher than 12 h and CFPP lower than 5 °C.

Resumo em Inglês:

Chitosan is a biopolymer derived from chitin and the most abundant polysaccharide in nature after cellulose. This biopolymer has been applied in different areas due its biodegradability and biocompatibility properties. Modifications of chitosan structure by cross-linking chemical agents can alter its physical, chemical, and morphological characteristics. The present work aimed at studying the structural characteristics of chitosan/polyvinyl alcohol (PVA) spheres cross-linked with glutaraldehyde submitted to oven-drying and freeze-drying processes. The thermal-treated of spheres and chitosan (control sample) were analyzed by XRD, SEM and FTIR techniques. Multivariate statistical analysis, PCA, was applied to samples IR spectra. According to results, the freeze-dried spheres showed a smaller crystal size (6.032 nm), while the oven-dried spheres presented a smaller crystalline phase (3.49%). MEV images have encompassed the different surfaces of the manufactured spheres as a result of drying methods. Slight chemical changes were observed in the IR spectra from the cross-linked spheres. In addition, PCA has revealed different clusters referred to the structural modifications. Therefore, the increasing of openness and receptivity for chemical reactions, as well as the adsorption capacity, could enable different applications of the chitosan, mainly the adsorption properties to remove residues and for water treatment.

Resumo em Inglês:

The generation of mathematical models through the quantitative relationship between the chemical structure and the biological activity (QSARs) of compounds was used in this investigation. Mathematical models were generated from compounds available in literature that predicting the biological activity against SARS-CoV-2. The data indicate that the parameters that most interfere and allow to validate the equations are: number of hydrogen bonding donors, maximum projection radius and length perpendicular to the minimum area. This allows us to infer that there is synergism between the basic capacity of the cysteine protein action site present in the virus and the geometric conditions for the three-dimensional alignment to potential compounds with anti-SARS-CoV-2 action. The authors highlight that mathematical models assist in chemical research, but do not replace evaluation of the efficacy in vitro, in vivo, pre-clinical and clinical studies, which are essential for dosage, release or authorization to use any medication or supplement.

Resumo em Inglês:

Recently, a new class of materials, the Perovskite Nanocrystals, also known as perovskite quantum dots (PQDs) has emerged. Perovskite nanocrystals are promising in optoelectronics due to their quantum confinement properties, narrow photoluminescence bands with short decay times, optically tunable bandgaps, easy surface passivation and high photoluminescent quantum yields. The intense photoluminescence covering the entire visible region of the spectrum can be easily adjusted through the composition and/or the nanocrystals sizes. This paper presents the state-of-the-art of these materials, since their discovery to current research, including their synthesis methods, properties and applications.

Resumo em Inglês:

The foods enrichment with essential elements is an alternative to supply deficiencies of micronutrients and the fortification by rich cultivation is a promising strategy for the elemental enrichment of agricultural origin products, mainly in regions where there is high prevalence. On the other hand, in elemental enrichment procedures, possible antagonistic and / or synergistic relationships in the absorption and translocation of essential elements in agricultural products should be evaluated. Additionally, it is important to highlight the need to know the elements species capable of being absorbed and used in the metabolism of edible plants and mushrooms as well as the species formed after enrichment, being necessary to evaluate mainly if enriched foods present the same chemical characteristics, when compared to those grown under natural conditions. Therefore, in this review, works from the literature are presented involving promising strategies for elemental enrichment of edible plants and mushrooms grown in an appropriate medium, prioritizing the chemical characterization of the enriched food. Cultivation enrichment procedures are an excellent and promising alternative to help reduce elemental deficiencies as well as to maintain the recommended daily intake of these essential micronutrients for human nutrition and health.

Resumo em Inglês:

Plants from Fabaceae family have several secondary metabolites and high biological potential. The subfamily Papilionoideae (Fabaceae) has 28 tribes, of which Dalbergieae comprises 49 genera and 1325 species. Isoflavonoids are chemotaxonomic markers of Papilionoideae and have important biological properties. This review describes the isoflavonoids and biological activities from the tribe Dalbergieae (Fabaceae-Papilionoideae) species, in the period of 1945 to 2019. A total of 240 isoflavonoids were found in 69 species and in 15 genera. Formononetin, biochanin A and medicarpin were the most frequent isoflavonoids in this tribe. Dalbergia, Machaerium, Andira and Pterocarpus genera had a high number of species with occurrence of isoflavonoids. A total of 81 isoflavanoids and 46 species showed biological activities. This suggests that more works are necessary to evaluate the potential of this tribe. The present study contributes to the taxonomic classification of genus or species in the family, subfamily or tribe, once the correlation between secondary metabolites and morphological data is an important tool for the classification, phylogeny and evolution of species. This compilation also contributes to extend and update the researched period on the occurrence of isoflavonoids in species of the tribe Dalbergieae, described in the literature in other bibliographic reviews.

Resumo em Português:

Advances in the use of 3D printing technology have led to the development of new low-cost devices. This technology features high versatility, considering the easy modulation of the materials depending on its objectives and applications. In this sense, we have developed a laboratory-built contact angle measuring device (lab-made). The device was composed by the assembly of 26 3D-printed pieces of different sizes and design printed using acrylonitrile-butadiene-styrene polymer. The device was designed in three main parts. The first part was related to the analysis, with the use of platforms for the sample surfaces positioning. The second part was made to support a micropipette, prepared to add the drop for analysis; and the third for the support of a smartphone, utilized to obtain the images. The device was applied for the measurement of contact angle on different surfaces, demonstrating its versatility and precision of the results. The obtained values are in accordance with others found in the literature. The developed device presented a low-cost (US$ 25.34 per device), easy assembly and operation.

Resumo em Inglês:

The ultrasound-assisted extraction (UAE) is an alternative approach for the total lipid content determination in food samples. The high extraction efficiency, being less time-consuming and with the possibility of using less toxic solvents are the main advantages of UAE. It is, thus, an excellent alternative to be applied as a laboratory experiment for undergraduate students. The UAE procedure was optimized and the extraction parameters, such as extractor solvent, time and frequency of the ultrasound, were evaluated. The accuracy of the UAE procedure was evaluated by comparing the obtained results with those found by the traditional lipids extraction approach. The results showed that the lipids content found in the analyzed samples by using UAE were in agreement with the results obtained by the traditional lipids extraction. Therefore, the optimized UAE procedure was proposed as a laboratory experiment to 15 groups of undergraduate students to introduce the subjects of an alternative approach for total lipids determination in food samples. The results obtained showed that 80% of the student groups found results for total lipid contents in agreement with those found by traditional lipids extraction method. The proposed UAE procedure as a laboratory experiment proved to be simple and easy to be applied to undergraduate students.

Resumo em Inglês:

Medicines are employed in undergraduate courses as motivational strategy. The experiment herein developed compares the extraction of paracetamol from generic and brand name drugs. Tablets were used from two commercial sources purchased from local drugstores. Twenty tablets of each drug type were individually weighed to average weight analysis and mass dispersion was statistically analyzed in simulating of quality control. Average weight had variation in accordance with the limit of ±5% specified by Brazilian Pharmacopeia. Tablets of each drug were pulverized and extracted in triplicate with ethyl acetate, and the active ingredient was obtained and identified by melting point and FTIR analyzes. Comparing different student groups at different times, there was change in the mass of paracetamol extracted by a simple extraction, affording mass recovery in the range of 59±17% to 28±1%. However, mass recovery of paracetamol extraction of generic and brand name drugs was similar in each student group. Under Soxhlet extraction condition mass recovery was 80-85%. The procedure developed was adequate to undergraduate laboratory, involves simple infrastructure and execution, tablets are easily obtained, and allows discussion on pharmaceutical equivalence and interchangeability.

Resumo em Inglês:

Research in the area of science teaching has highlighted the importance of using argumentation in the classroom, as well as preparing teachers to undertake and conduct activities of this nature. In order to bring elements that contribute to the progress of discussions about the subject, we investigated implementing and developing two teaching strategies (ludic activities and chemistry experiments) in lessons taught by pre-service teachers in supervised internships and we identified their pro-argumentation actions. The results showed that pre-service teachers not fully achieved the task of promoting argumentation practices in chemistry classes, emphasizing their ease and difficulties throughout the activity.

Resumo em Inglês:

Multicomponent reactions are attractive for the development of bioactive substances, being a one-pot synthesis allows a quick and efficient synthesis, and allows the construction of a diversity of privileged structures. The Debus-Radziszewski reaction, a classic example of a multicomponent reaction for obtaining 2,4,5-tri-substituted imidazole, was used to compose a didactic sequence to be applied in undergraduate courses in the following disciplines: Organic Chemistry, Experimental Chemistry, Pharmaceutical Chemistry and Medicinal Chemistry. Thus, the classes were planned and applied, one theoretical and two experimental, the synthesis of lofin (2,4,5-triphenyl-1H-imidazole) and the characterization of the product. The Debus-Radziszewski reaction for the preparation the lofin, proved to be suitable for practical class of multicomponent reactions, as it uses accessible reagents and equipment, it is easy to do and the students can follow the progress of the reaction visually. In addition, the didactic sequence inserts students in a contextualized and interdisciplinary way in the practical chemistry procedures, employing a classic reaction, but with current perspectives of Organic and Medicinal Chemistry, such as the synthesis of the privileged fragments of bioactive compounds.

Resumo em Inglês:

In recent years, much has been said about the approach of the history of science and science teaching. We know that this approach can be made using historical episodes in science classes. In this sense, this work aims to bring a historical episode to be worked on in general chemistry classes in high school, as well as in general chemistry classes 1 of university courses. Thus, we will first make some considerations about the importance of the history of science for teaching chemistry. Then, we will bring the episode that analyzes some of the works that formed the basis of modern chemical thought. From the historical episode we worked on, we intend to show the complex construction of modern atomic-molecular theory. However, it is important to emphasize that, for didactic purposes, we cut the debate, bringing up only the speeches of three of the main authors of the time. Special attention was paid to Dalton’s work.

Resumo em Inglês:

Much is said and written regarding alchemy all across the world, in what could be called a renaissance of alchemical studies. However, relatively little is done in terms of actual alchemical laboratory work. The aim of the project described herein was to show how crucial the development of technical alchemical practice was along the centuries, in the discovery of an immense number of substances, processes and operations, which were of paramount importance in the establishment of modern chemistry. Alchemy is often derided in many circles. On the contrary, for two thousand years it constituted the basis of humankind’s understanding of the material world and the changes undergone by compounds and materials. Here we present an experimental reconstitution of several alchemical discoveries of great importance, using old descriptions followed by modern characterizations. The results were often startling and demonstrated how ancient wisdom bore fruit in different ways, even in the absence of our present-day means of analysis.