Resumo em Inglês:

We presented a theoretical study on the detailed reaction mechanism and kinetics of the HNCS molecule with the OH-. The barrierless minimum energy path and the most favorable entrance channel have been determined by study the thermodynamic and kinetic characters of the channel with low energy barrier. The B3LYP/6-311++G** method was employed for all the geometrical optimizations and a multi-level extrapolation method based on the G3 energies was employed for further energy refinements. In addition, the analysis of the combining interaction between hydroxide ion and HNCS was performed by natural bond orbitals (NBO) analysis. The calculation results indicated that the reaction of OH- with HNCS had four channels, and the channel of H-atom in HNCS direct extraction to OH- (OH-+HNCS→IM1→TS3→IM4→P2(SCN- +H2O)) in singlet state was the main channel with the low potential energy and high equilibrium constant and reaction rate constant. SCN- and H2O were main products.

Resumo em Inglês:

Density functional theory (DFT) periodic calculations were performed to study the geometrical and electronic structures of energetic compound dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) under the pressure ranging from 0 to 400 GPa. The optimized crystal structure by the local density approximation (LDA) with CA-PZ functional matches well with the experimental values under the ambient pressure. When the structural transformations occur under the pressure of 126, 288, and 334 GPa, with the pressure increasing, the lattice constants, unit cell volume, total energy, interatomic distances, bond angles, atomic charges, and bond populations of TKX-50 change gradually. First of all, TKX-50 is rearranged in the crystal and the improvement of the molecular planarity occurs. Next, structural transformation appears with the distortion of the tetrazole rings. Finally, the rotation of molecular conformation occurs. The results of the band gap and density of states show that TKX-50 crystal, with the increase of pressure, undergoes an electronic transition from the semiconductor to the metallic system. These results provide basic information for the high pressure behavior of crystalline TKX-50.

Resumo em Inglês:

Kinetic models of solid thermal decomposition are traditionally used for individual fit of isothermal experimental data. However, this methodology presents unacceptable errors in some regions of the data. To solve this problem, a neural network was adopted in this work. The implemented algorithm uses the rate constants as predetermined weights between the input and intermediate layer and kinetic models as activation functions of neurons in the hidden layer. The contribution of each model in the overall fit of experimental data is calculated as the weights between the intermediate and output layer. In this way, the phenomenon is better described as a sum of kinetic processes. Two rigid polyurethane foam samples: loaded with Al2O3 and no inorganic filler were used in this work. The R3 and D2 models described the thermal decomposition kinetic process for all temperatures for both foams with smaller residual error. However, the network, combining the kinetic models, presented residual errors on average 102 times lower compared to these individual models. The determined activation energy is 12.44 kJ mol-1 higher for the loaded foam. This result corroborates the use of this material as flame retardant, even with the presence of a small amount of charge in its structure.

Resumo em Inglês:

Phytochemical investigation of the leaf extracts from Miconia ferruginata (Melastomataceae) led to the isolation and characterization of the flavonoids 5,6,7-trihydroxy-4'-methoxyflavone, 5-hydroxy-7,4'-dimethoxy-8-methylflavone and 5,7,4'-trihydroxy-6,8-dimetilflavone, triterpenes ursolic acid and oleanolic acid, in addition to the steroids β-sitosterol and stigmasterol. The structures of these compounds were proposed by spectroscopic analysis and comparison with literature data. This paper also describes the insecticidal effects of leaf extracts from M. ferruginata to one of the main pests of maize, the fall armyworm (Spodoptera frugiperda). The ingestion bioassays, the leaf extracts showed an elongation of the larval stage of 16.56 days as compared to the control.

Resumo em Inglês:

The influence of the structural and microstructural characteristics of graphitic precursors on the production of graphite oxide (GO) is investigated in the present work. Six different graphitic precursors were used to produce GO following a modified Hummers method, namely: natural graphite, commercial lubricant graphite, milled graphite, graphite flakes, high-purity graphite and graphite recycled from Li-ion batteries. The products were characterized by X-ray diffraction (XRD), thermogravimetry, solid-state 13C nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). 13C NMR spectra revealed the presence of epoxy, hydroxyl, carbonyl and lactol groups in the synthesized GOs. However, the oxidation degree of each product was found to be dependent on the average crystallite size (Lc) and particle size of the graphitic precursors, with the best GO samples being produced from the milled graphite and the graphite recycled from ion-Li batteries. These results were rationalized in terms of the structural and microstructural differences among the graphitic precursors, as revealed by the XRD patterns and SEM images, evidencing the importance of the correct choice of the precursor aiming the achievement of a well-developed structure for the GO product.

Resumo em Inglês:

The composite electrode material of manganese oxide supported on poly glucose (PGS) was prepared by using KMnO4 as manganese source. In order to study the influence of the support on the structure and properties of the composite electrode materials, the changes of the composition of the composite electrode materials were investigated in different weight ratio of KMnO4/PGS (3:1, 3:3, 3:5, 3:7, 3:9). The characterization results of XRD, Raman special and XPS indicated the composition of manganese oxides was greatly influenced by the content of PGS. When the PGS content is lower, the composition of manganese oxide in hybrid material is single-component oxide (MnOOH or Mn3O4). With the increasing PGS content, a mixture of Mn3O4 and MnCO3 was observed, furthermore proportion of MnCO3 in mixture also increased, and up to higher PGS content (KMnO4/PGS=3:9), single-component MnCO3 was founded on hybrid material. In addition, the change of composition of hybrid materials also led to an obvious difference in electrochemical performance. With the increase of PGS content, the specific capacitance of hybrid materials increases firstly, and reaches the maximum with the weight ratio of KMnO4/PGS equal to 3:3, and then gradually decreases. This was attributed to the higher electrochemical performance of Mn3O4 than that of MnOOH and MnCO3.

Resumo em Inglês:

A fast and simple procedure for simultaneous determination of propyphenazone (PRO), paracetamol (PAR) and caffeine (CAF) was performed using batch injection analysis with multiple pulse amperometric detection (BIA-MPA). Three potentials pulses were selected for the analysis: +0.90 V/50 ms: only PAR was oxidized; +1.20 V/50 ms: oxidation of PAR and PRO without the interference of CAF; +1.60 V/50 ms: oxidation of the three compounds (PAR, PRO and CAF). The sample aliquot (150 µL) was directly injected onto the boron-doped diamond (BDD) electrode immersed in a BIA cell. The analytical characteristics of the proposed method include high analytical frequency (75 injections per hour), good stability (RSD < 3.9%; n = 10), and low detection limits (0.3, 0.2 and 0.1 mg L−1 for PRO, PAR and CAF, respectively). The proposed method yielded similar results to those obtained by liquid chromatography at a 95% confidence level.

Resumo em Inglês:

From the natural product 4-(4'-O-acetyl-α-L-rhamnosyloxy)benzylisothiocyanate (1), isolated from the flowers of Moringa oleifera Lam (Moringaceae), four new semisynthetic derivatives, N-[4-(4'-O-acetyl-α-L-rhamnosyloxy)benzyl]-2-(pyridinil-4-carbonil)hydrazine-1-carbothioamide (3), 4-(4'-O-acetyl-2',3'-dimesyloxy-α-L-rhamnosyloxy)benzylisothiocyanate (4), N-[(4'-O-acetyl-α-L-rhamnosyloxy)benzyl]hydrazinecarbothioamide (5), 4-[4'-O-acetyl-2',3'-O-bis(decanoiloxy)-α-L-rhamnosyloxy]benzylisothiocianate (6), and the known compound 4-(2',3',4'-O-triacetyl-α-L-rhamnosyloxy)benzylisothiocyanate (2), were obtained. All compounds were tested for their cytotoxicity against the tumor cell lines SF-295, HL-60, HCT-116 e PC-3. The natural product 1 and the semisynthetic derivatives 2 and 4 were the most active compounds (IC50 from16.0 to 3.7 µmol L-1) against all tumor cell lines.

Resumo em Inglês:

This work presents a critical overview of the NICA-Donnan model for trace metal thermodynamic speciation with humic substances obtained from natural organic matter in soils, natural waters and anthropogenic sources. A first part covers the theoretical aspects of the model, how to obtain good experimental data and perform the modelling. A second part deals with the developments in the last decade namely the use of the generic parameters, criticism and alternatives to the electrostatic modeling, the understanding of the NICA equation and an analysis of the published data, ending with the needs and opportunities for model development.

Resumo em Inglês:

This article critically reviews the spectrometric, chromatographic and electroanalytical methods applied for the identification and quantification of organic and inorganic compounds containing Se and their applications in food, biological and natural water samples. The main characteristics, advantages and disadvantages of each analytical method are presented, and special attention is paid to sample preparation strategies prior to identification and quantification. Perspectives of research on new analytical procedures with improved speed, sensitivity, selectivity, accuracy, and mainly environmentally friendly, are also reported.

Resumo em Inglês:

Semiconductor nanocrystals with sizes in the quantum confinement regime (2-10 nm) present special physical and chemical properties. Additionally, environment-friendly quantum dots (QDs), as zinc oxide and zinc sulfide, offer many practical usages. Herein the ZnO semiconductor nanocrystals properties will be preferentially explored, such as its luminescence, broad spectrum UV absorber and electronics performances, and therefore its multifunctionality, as well as its advantages compared to some toxics QDs. A review is carefully presented stressing some synthesis approaches for applications reasons toward devices, chemosensors, biological labels, UV-absorbers and photocatalysis. ZnO QDs have been used in combination with organic and other inorganic materials. Hybrid materials have many advantages compared to their individual contents leading to important contributions to science and technology. As a result, an important growth in material fields is noticeable.

Resumo em Inglês:

The utilization of atomic absorption spectrometer for metformin (MET) and ranitidine (RAN) chlorohydrates determination in medicines is proposed. The spectral lines of nickel and aluminum at 232.0 and 308.2 nm were selected for MET and RAN absorbance monitoring, respectively. The results were compared to those obtained by molecular absorption spectrometry at ultraviolet range (spectrophotometry) and condutometric titration. The figures of merit obtained were adequate for MET and RAN determination in medicines. The limit of detection (LOD) of 0.01 mg L-1 obtained for MET and RAN, were similar and even lowers than those obtained by spectrophotometry and comparable with those found in the literature. The precision evaluated by relative standard deviation (RSD) was lower than 6%. The analytical application shows that in the analyzed samples the MET and RAN concentrations were in agreement with specified value in the label and the limits required by Brazilian legislation.

Resumo em Inglês:

A passive sampler constructed with a new type of material and used for measurement of ambient nitrogen dioxide is presented. The sampler was constructed with parts of two 50 mL conical centrifuge tubes. The procedure is based on NO2 uptaken on cellulose filter impregnated with triethanolamine. After sampling, the analyte is solubilized and placed to react with Griess-Saltzman solution. The absorbance of the formed complex is determined at 540 nm. A mean relative standard deviation of 9,72% was obtained using samplers exposed in triplicate, and a determination coefficient (R2) of 0,979 was achieved in parallel measurements using the samplers and a commercial NOx monitor. Advantages of the technique include ease of use, the ready availability of components, and excellent sensitivity.

Resumo em Inglês:

A sensitive, simple, rapid and reliable HPLC-DAD method for the analysis of the benzylisoquinoline alkaloids (BIA's) content in Argemone mexicana (Papaveraceae) is presented. This method allows the simultaneous separation and quantitation of berberine (Bn), chelerythrine (C) and sanguinarine (S) in extracts from A. mexicana tissues, reducing time of analysis in comparison to previous reports. Alkaloids were separated on a C18 Hypersil Gold column using an acetonitrile gradient (20 to 70%) in 1% acetic acid in water. Alkaloids were identified based on retention times and UV spectra and quantified at 254 nm. Linearity between 0.5-20 µg mL-1 was observed for Bn, C and S, with limits of detection (LOD) and quantitation (LOQ) of 0.11 and 0.33 for Bn, 0.10 and 0.30 for C and 0.05 and 0.15 for S, respectively. Maximal intra- and inter-day variation values were < 0.49% in all cases, with alkaloids' recoveries higher than 95%. System suitability tests (SST), including resolution (Rs), retention factor (K'), selectivity (α), tailing factor and number of theoretical plates were performed according to the United States Pharmacopeia (USP), fulfilling recommended values. The method proved to be efficient and reproducible when analyzing different tissues of field-collected A. mexicana plants.

Resumo em Inglês:

The knowledge transmission in scientific education demands the formulation of methods capable to insert between student and the study object a nearness, making the student apt to build, from autodidactic posture, solutions that only the professional formation can produce. In this sense, a teaching should develop an effective pedagogy, focusing on knowledge production and its preservation, helping the scientific progress. Guided by these concepts, the educational process can be considered complex and should focus on the quality of the transmitted knowledge, through strategies that ensure the maximum information accessibility. In strictu sensu post-graduation context, some particularities related to the knowledge building and not so only the concepts memorization should have more attention, due to the scientific and teacher training goals. The medicinal chemistry area exhibits the necessity to have a great interlocution with other chemistry disciplines, such as organic chemistry, analytical chemistry and as well as disciplines related to human health. In this sense, the evaluation of learning process becomes, currently, a great challenge for professors that seek to develop the interdisciplinary sense. Considering this reality, in this study, the authors present a classroom experience, where specific competences developed in students of medicinal chemistry discipline was a target of evaluation based on creation of review text. From the results obtained was possible to rethink strategies that can contribute to foster new forms to evaluate the learning process based on competences development.

Resumo em Inglês:

Cachaça (brazilian sugarcane spirit) was applied for the first time as an alternative solvent in undergraduate experiments of organics synthesis, and natural dye extraction. The classical Claisen-Schmidt condensation of benzaldehyde with acetophenone and with acetone were employed to demonstrate the cachaça viability as solvent. Cachaça was also the recrystallization solvent of obtained benzalacetophenone and dibenzalacetone. The natural pigment of urucum (Bixa orellana L.) was obtained using as extractor solvent a 5% NaOH solution in cachaça. Considering that in Brazil cachaça is easily available and cheaper than the 40% mixture of ethanol/water, it can be found in every marketplace and is exported to 54 countries, the cachaça use as solvent is viable and attractive to green chemistry experiments in undergraduate courses, in Brazil and abroad.

Resumo em Inglês:

The quantum mechanics of two electrons atoms, as suggested by E. A. Hylleraas in the period between 1928-1930, is discussed in the present work. Hylleraas introduced explicit correlations in the wavefunction by treating the coordinates between the electrons as an independent variable of the problem, an approach that gives very precise energy values. Solution of the problem is given for one, two, three and six basis functions, as in the original work. The solution is also carried out with 140 basis functions, showing that the energy for two electron atoms can be calculated with seven significant figures. Numerical methods presented here are accessible to undergraduated level students.