Resumo em Português:

Metal-organic frameworks (MOFs) are promising nanomaterials with unprecedented capacity to store small molecules. Titanium cooperated with NH2-UiO-66 were prepared via post synthesis modifications approach and their structures and properties were characterized by X-raydiffraction,Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption isotherms, and scanning electron microscopy. The resultant titanium cooperated with NH2-UiO-66 showed excellent performance for CO2 adsorption via the formation of oxo-bridged hetero-Zr-Ti clusters. This result clearly demonstrates that the smaller Ti ions exchanged with the Zr ions of NH2-UiO-66 may decrease the pore sizes within the framework to be closer to the ideal pore sizes for CO2 adsorption.

Resumo em Inglês:

Human serum albumin (HSA) plays an important role in the transport of a wide variety of substances, including compounds with pharmacological properties. The dansylglycine (DanG) is a fluorescent amino acid derivative specific for the site II of HSA. This work aimed to elucidate the induction of chirality in the DanG due to its bonding to the HSA. Theoretical electronic circular dichroism spectra (ECDs) were simulated using the Density Functional Theory (DFT) and the implicit Solvation Model based on Density (SMD). The DanG-HSA complexation resulted in the appearance of a positive ECD spectrum centered at 346 nm. Focusing on the dihedral angles between the -N(CH3)2 group bounded to the naphthalene ring, the potential energy surface (PES) of the DanG was obtained. Analysis of the various conformations obtained revealed that the calculated dihedral angle (150º) is in agreed with the experimental ECD spectrum. In addition, we observed that the nitrogen atom of the -N(CH3)2 group presented the greatest contribution to the HOMO-LUMO transition that gives rise to the n→π* electronic transition involved in the generation of the ECD signal. Molecular docking analysis of the complexation between DanG and HSA revealed a conformation with a dihedral angle similar to that obtained by DFT.

Resumo em Inglês:

The production of methyl esters via transesterification reaction of triacylglycerides of macaúba and palm kernel oils, with subsequent atmospheric distillation and separation of six fractions of the produced biodiesel, corresponding to 60% of its initial volume, is reported. The composition in esters of the produced biodiesel, its fractions and remaining residue of the distillation was determined by gas chromatography. This analytical procedure has allowed to monitor the content in esters for each distilled fraction. The fractions richer in C8:0, C10:0, C12:0, C14:0 is intended to be used as an aviation fuel, in blends with the Jet-A1 biokerosene. The residues from the distillation with higher molecular weights than those corresponding to esters C16:0, C18:0 and C18:1 are destined to other combustion engines as any conventional biodiesel. For the biodiesel obtained from the macaúba kernel, this distillation led to an enrichment from 45.86% to up to 74.35% in the C12:0 ester. For the palm kernel biodiesel, the corresponding enrichment was from 66.76% up to 82.96%. Through this simple distillation, it was thus possible to effectively enrich, in C8:0 to C14:0 esters, the initial crude biofuel, with an efficiency of 30% for the macaúba and 11.5% for the palmiste biodiesel.

Resumo em Inglês:

The present work evaluated the influence of phenolic mediators (five dihydroxybenzenes and gallic acid) on the decolorization kinetics of phenol red, chromotrope 2R, and methylene blue by Fenton systems. The reactions were performed with H2O2, iron salts as catalysts, and the absence or presence of phenolic mediators. Based on the decolorization data from previous study of our group, the 1st and 2nd order kinetic models were analyzed, as well as the alternative BMG model. It was found that the mediators accelerated the reactions, based in 1st and 2nd order kinetic models. Reactions containing Fe2+ fitted better to the BMG model, while reactions containing Fe3+ fitted better to the 2nd order kinetic model, independent of mediators. Based on the three evaluated kinetic models, pro-oxidant properties were observed for the mediators in Fenton systems.

Resumo em Inglês:

In the present work, leaves of Pentacalia desiderabilis (Asteraceae) were subjected to extraction using aqueous 1-butyl-3-methylimidazolium bromide (BMImBr) in the microwave assisted extraction (MAE). The obtained extract was partitioned using CH2Cl2 and antifungal activity against Cladosporium cladosporioides and C. sphaerospermum of the organic phase was evaluated. Sequentially, this material was subjected to several chromatographic procedures to afford four quinoid derivatives identified as jacaranone (1), methyl-jacaranone (2), quinolacetic acid (3), and methyl 1-hydroxy-4-oxo-cyclohexaneacetate (4), being the first occurrence of compounds 2 - 4 in P. desiderabilis. Isolated quinoid derivatives were submitted to bioautography assay and the obtained results indicated that compounds 1 - 3 are active against Cladosporium cladosporioides (0.78, 12.5 and 12.5 µg, respectively) and C. sphaerospermum (3.13, 12.5 and 12.5 µg, respectively).

Resumo em Inglês:

In this study, new 1,3,4-thiadiazole compounds were synthesised and characterised by FT-IR, 1H-NMR, UV-vis spectroscopy and elemental analysis, Furthermore, the relationship between the electronic and spectral data of the 16 conformers of each compound was investigated by theoretical calculations; the theoretical data were compared with the experimental results. The B3LYP hybrid functional level with a 6-311++g(2d,2p) basis set was used to obtain the ground state geometries, frontier molecular orbital energies, band gap energies and chemical reactivity parameters and to perform a spectral analysis of the compounds. Significant correlations were calculated between the minimum molecular energy and the N-H and C=O vibrational frequencies and the NH proton chemical shifts of the conformers. The charge density on the nitrogen atom and the delocalisation index of the highly polar N-H covalent bond were investigated by quantum theory of atoms in molecules. The effect of conformer structure on the theoretical results and its role in interpreting the experimental data were presented, and it was theoretically shown that the activity degree of the non-aromatic electronegative atoms or groups of atoms in the intramolecular interaction was a very important factor in determining the electronic and spectral properties of each compound.

Resumo em Inglês:

The present work presents combustion simulations of hydroxyl-terminated liquid polybutadiene loaded with ammonium perchlorate and aluminum, using Chemkin software and the “Plug Flow” type reactor. These materials are widely used in solid composite propellant formulations. Through this study, the effect of parameters of axial velocity, equivalence ratio, pressure and temperature during the firing of the propellant were discussed. The objective of this work was to discuss how to define the best parameter value based on the obtained results, and thus generate optimized formulations.

Resumo em Inglês:

A series of cyclic energetic derivatives based on nitroguanidine and 1,1-diamino-2,2-dinitroethene were theoretically designed. The spatial structures, infrared spectrometry, heats of formation, electronic structures, detonation properties, and thermal stabilities of these designed compounds were fully investigated by density functional theory. It is found that all the designed compounds have moderate stabilities (bond dissociation energies range from 11.3 to 99.0 kJ mol-1), high crystal densities (from 1.9589 to 2.00188 g cm-3), high positive heats of formation (from 649.6 to 1060.8 kJ mol-1) and high positive heats of detonation (from 1074.77 to 1332.06 cal g-1) which lead to the excellent detonation properties (detonation velocities range from 8.71 to 9.05 km s-1 while detonation pressures range from 35.47 to 38.55 GPa). Electronic structures such as electrostatic potentials on the surface, electronic densities, highest occupied molecular orbitals, lowest unoccupied molecular orbitals and their energy gaps were also simulated to give a better understanding of chemical and physical properties of these compounds. All the data may shine lights on the explosive searching and synthesis.

Resumo em Inglês:

Phytochemical investigation of the CHCl3 fraction from EtOH extract of Tocoyena hispidula (Rubiaceae) stem resulted in the isolation and identification of D-(+)-mannitol, lupenone, 3-O-acetyloleanolic acid, lapachol, dimethyl chelidonate, morindolide and four mixtures (M1-M4): M1 (palmitate, margarate, linoleate, oleate e stearate of the multiflorenyl, lupeyl, sitosteryl and stigmasteryl), M2 (lupeol, taraxerol, germanicol, β-amyrin and E-fitol), M3 (campesterol, campestanol, stigmasterol, Δ22-stigmastenol, sitosterol and sitostanol) and M4 (7-ketositosterol and 7-ketostigmasterol). Structural identification of the compounds was performed by analysis 1H and 13C NMR spectra and by GC-MS. Extract, fractions, dimethyl chelidonate and morindolide inhibited the growth of Leishmania major promastigotes, being the CHCl3 (IC50 = 26.25 µg mL-1) and EtOAc (IC50 = 29.77 µg mL-1) fractions the more active.

Resumo em Inglês:

For the evaluation of PAH extraction techniques in adipose and liver tissues of marine tetrapod, samples of some species (Pontoporia blainvillei, Chelonia mydas, Thalassarche melanophris, and Balaenoptera brydei) were spiked with PAH standards and extracted using soxhlet system and microwave oven. The results of both extraction techniques for the two different tissues of the four species of tetrapod were within the quality assurance and quality control criteria, that means both extraction techniques produced acceptable recoveries for surrogate and spiked compounds added to the sample tissues. Although both techniques of extraction met quality criteria and were considered suitable for extraction of marine tetrapod tissues, the soxhlet system produced a higher recovery of the spiked compounds and a lower standard deviation between the replicates than the microwave extraction; therefore the soxhlet system was considered the more efficient extraction method for PAH. The evaluation of liver and adipose tissue PAH accumulation, as well as the influence of tissue heterogeneity, was impaired as the concentrations of PAHs in almost all samples were lower than the detection limits of the analytical method.

Resumo em Inglês:

Silver nanoparticles (AgNPs) have important antimicrobial activity. These nanoparticles are present in several commercial products, leading to human and environmental exposure. This review presents a critical view of the toxic effects of Ag NPs on in vitro and in vivo biological models. It is noteworthy that the toxicity of AgNPs is dependent on several parameters, such as the preparation mode of the colloidal suspension of the nanoparticles, their state of aggregation, the chemical nature of the nanoparticles, surface size, morphology, dose, cell type, nature of the living organism, among others. In general, low concentrations of AgNPs do not present significant toxicity in in vitro and in vivo assays, however with the increase of the concentration of AgNPs there is a significant increase of nanoparticle toxicity and its accumulation in diverse tissues/organs. It should be emphasized that in living organisms, exposure routes should be taken into account, such as ingestion and inhalation. At high concentrations, inhalation or ingestion of AgNPs can cause adverse effects and even lead to human death. In this context, the importance of further studies of the toxicity of AgNPs in several in vitro and in vivo models is emphasized.

Resumo em Inglês:

The interest in a better quality of life raised the concern about food safety. The administration of veterinary drugs in livestock may lead the occurrence of residues in food that may be harmful to consumers. Processed products are being consumed more and more, which increases concern for the safety of infants and children because they are more susceptible physiologically. Among these products stand out canned baby foods, defined by Ordinance 34/1998 issued by Brazilian Ministry of Health. Eggs and meat-based salty products for infants and children, legally designated as soups, fit into this definition and can not contain residues of hormones, antibiotics, as well as other pharmacologically active substances. Several techniques are used as identification and confirmatory assays of veterinary drug residues in food, although the main used technique is liquid chromatography - tandem mass spectrometry (LC-MS/MS). The aim of this work was to make a comparative assessment between different extraction methods in order to establish the best condition within the tested ones for the identification of macrolide residues in meat-based canned baby food by LC-MS/MS. A simple and effective extraction method, with good recoveries (65-93%) and satisfactory relative standard deviations (0.4-11%), was achieved using QuEChERS procedure for sample preparation.

Resumo em Inglês:

Oral presentation (OP) integrates social practices from the academic community, whereby knowledge about the subjects under study can be disseminated and discussed. On the other hand, systematic work is not verified for learning this genre in undergraduate chemistry teaching. In this perspective, this article aims to report on a classroom activity used in a scientific communication course in order to improve the skills needed for chemistry students to develop OP. The students were asked to prepare an OP by reading original research articles published in the Química Nova journal on the subject of biodiesel. The OPs were analyzed according to the Teachable Dimensions of the Oral Presentation Genre so as to indicate both the actions that make the production of this genre feasible and those that hinder it. The results suggest the relevance of commitment to OP teaching and learning in chemistry courses, which is a complex activity, but fundamental for undergraduate education.

Resumo em Inglês:

The United Nations (UN) has proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements (IYPT 2019). For that reason, it is considered pertinent to highlight the importance of the periodic system in the scientific and technological development of the chemistry; therefore, a discussion of some applications of the periodicity of the elements for designing new materials is carried out. In this work, some periodic trends of both molecules and complex structures of materials are discussed, by selecting different cases of the chemical periodicity applied to improve and design steels with higher wear resistance, prepare refractory materials and synthesize chalcogenides glasses, among others. Finally, the proposed subjects and the regularities argued in this work are considered complementary contexts of exceptional interest to motivate the meaningful learning of the periodic table taking into account the current scientific and technological researches.

Resumo em Inglês:

This paper aims to investigate the presentation of the concept of valence in college-level, general chemistry textbooks published in the USA between the 1890s and the 1940s. The delimited period covers the emergence of theories about atomic structure, electronic distribution and chemical bonding. Transition from the classical concept of valence (as the combining power of a chemical element), which resulted from either the analysis of formulas of compounds or experimental results, into the concept related to the electronic structure of elements, according to which the valence is determined by the number of electrons in the last shell, was observed. In general, valence was presented in textbooks in order to serve as an instrument for the writing of formulas of compounds, and historical approaches to the construction of the concept were not contemplated by the authors.