Resumo em Inglês:

Low-cost tungsten monometallic catalysts containing variable amounts of metal (4.5, 7.1 and 8.5%W) were prepared by impregnating alumina with ammonium metatungstate as an inexpensive precursor. The catalysts were characterized using ICP, XPS, XRD, TPR and hydrogen chemisorption. These techniques revealed mainly WO3-Al2O3 (W6+) species on the surface. The effects of the content of W nanoparticles and reaction temperature on activity and selectivity for the partial hydrogenation of 3-hexyne, a non-terminal alkyne, were assessed under moderate conditions of temperature and pressure. The monometallic catalysts prepared were found to be active and stereoselective for the production of (Z )-3-hexene, had the following order: 7.1WN/A > 8.5 WN/A ≥ 4.5 WN/A. Additionally, the performance of the synthesized xWN/A catalysts exhibited high sensitivity to temperature variation. In all cases, the maximum 3-hexyne total conversion and selectivity was achieved at 323 K. The performance of the catalysts was considered to be a consequence of two phenomena: a) the electronic effects, related to the high charge of W (+6), causing an intensive dipole moment in the hydrogen molecule (van der Waals forces) and leading to heterolytic bond rupture; the H+ and H- species generated approach a 3-hexyne adsorbate molecule and cause heterolytic rupture of the C≡C bond into C- = C+; and b) steric effects related to the high concentration of WO3 on 8.5WN/A that block the Al2O3 support. Catalyst deactivation was detected, starting at about 50 min of reaction time. Electrodeficient W6+ species are responsible for the formation of green oil at the surface level, blocking pores and active sites of the catalyst, particularly at low reaction temperatures (293 and 303 K). The resulting best catalyst, 7.1WN/A, has low fabrication cost and high selectivity for (Z )-3-hexene (94%) at 323 K. This selectivity is comparable to that of the classical and more expensive industrial Lindlar catalyst (5 wt% Pd). The alumina supported tungsten catalysts are low-cost potential replacements for the Lindlar industrial catalyst. These catalysts could also be used for preparing bimetallic W-Pd catalysts for selective hydrogenation of terminal and non-terminal alkynes.

Resumo em Português:

We report herein a study on the glycosylation of cyclohexanol with four D-glucosamine-based peracetylated glycosyl chlorides bearing different substituents at C-2 and three glycosylation promoters, silver carbonate, silver triflate and mercury II chloride/mercury II oxide, by the Koenigs-Knorr method. Under the conditions studied, glycosylation was successful only when 3,4,6-tri-O -acetyl-2-deoxy-2-phthalimido-α-D-glucopyranosyl chloride was used as the glycosyl donor, with silver carbonate proving the best promoter. In order to investigate the influence of the nature of the halogen at C-1, we also carried out the glycosylation of cyclohexanol with 3,4,6-tri-O -acetyl-2-deoxy-2-phthalimido-α-D-glucopyranosyl bromide, a more reactive glycosyl donor. As expected, the yield with the bromide derivative was higher with the three promoters and, again, silver carbonate was the most efficient promoter. Finally, to illustrate the well-known efficient procedure for conversion of the phtalimido group at C-2 to the corresponding acetamido group, cyclohexyl 3,4,6-tri-O -acetyl-2-deoxy-2-phtalimido-β-D-glucopyranoside was converted into cyclohexyl 2-deoxy-2-acetamido-β-D-glucopyranoside in two steps, namely, hydrazinolysis of the phtalimido group followed by chemoselective acetylation of the free amino group by treatment with acetic anhydride in methanol, at 77% overall yield.

Resumo em Inglês:

The goal of this study was to investigate the effect of composted pig slurry (PS) on the organic matter concentration and distribution of humic acid (HA), fulvic acid (FA) and humin (HU) fractions. The fractions were quantified following the addition of composted PS to the soil, which was produced with no acidification (T2) or with acidification with H3PO4 (T3); and in soil without compost addition (T1). The HA chemical composition was analyzed by FTIR spectroscopy. The addition of the two composts did not change the soil carbon concentration but affected the distribution of the humic fractions. For the three treatments, the carbon concentration of humic substances increased until 52 days following compost addition, with more pronounced increases with the addition of non-acidified PS compost (14.5 g kg-1) and acidified PS compost (15.1 g kg-1). This increase was reflected in both the FA and HA concentrations. The addition of compost with PS acidification resulted in the formation of larger humic micelles (HA) with higher aromatic content and fewer functional groups than the non-acidified PS compost. These findings, together with a lower proportion of carbohydrate-type structures, indicated the presence of more stable humic micelles in the soil treated with acidified PS compost.

Resumo em Inglês:

A bioactive N,N-diacetylglycine (NNDAG) and new organotin(IV) complexes (OTCs) (1-7) were synthesized. Spectroscopic techniques were employed to characterize NNDAG and OTCs. FTIR was employed to verify N,N protection of glycine by acetyl groups. The disappearance of υ(OH) at 3000-2600 cm-1 showed de-protonation of free ligand. The Δυ 150<200 cm-1 of OTCs 4-7 verified bidentate coordination with tetrahedral geometry. The Δυ of OTCs1 and 3 was <200 cm-1 exhibitingtrans -octahedral geometry while OTC 2 dimer was assigned a unique sinusoidal view. The 1H NMR spectra of OTCs verified their synthesis by de-protonation of NNDAG and no chemical shift was found downfield for carboxylic acid proton. The 13C, 119Sn NMR and Mass spectrometric data also supported FTIR and 1H NMR descriptions. The OTCs 4, 5, 6 and7 (500 ppm) proved twice as active against Escherichia coli as the standard antibiotic enoxacin (1000 ppm). The promising property of the OTCs (4, 5, 6 and7) is clearly due to their tetrahedral. The OTCs 4and 5 exhibited excellent activity against M. minimum and good activity against T. castaneum.LD50 of all the compounds were determined and OTCs4, 5 and 7 were found to be active.

Resumo em Inglês:

Asphaltenes are blamed for various problems in the petroleum industry, especially formation of solid deposits and stabilization of water-in-oil emulsions. Many studies have been conducted to characterize chemical structures of asphaltenes and assess their phase behavior in crude oil or in model-systems of asphaltenes extracted from oil or asphaltic residues from refineries. However, due to the diversity and complexity of these structures, there is still much to be investigated. In this study, asphaltene (sub)fractions were extracted from an asphaltic residue (AR02), characterized by NMR, elemental analysis, X-ray fluorescence and MS-TOF, and compared to asphaltene subfractions obtained from another asphaltic residue (AR01) described in a previous article. The (sub)fractions obtained from the two residues were used to prepare model-systems containing 1 wt% of asphaltenes in toluene and their phase behavior was evaluated by measuring asphaltene precipitation onset using optical microscopy. The results obtained indicated minor differences between the asphaltene fractions obtained from the asphaltic residues of distinct origins, with respect to aromaticity, elemental composition (CHN), presence and content of heteroelements and average molar mass. Regarding stability, minor differences in molecule polarity appear to promote major differences in the phase behavior of each of the asphaltene fractions isolated.

Resumo em Português:

Specimens of Leonotis nepetiflolia were obtained from cultivated and wild environments to verify their influences in chemical composition. Phytochemical analyses were conducted for the ethyl acetate phase obtained by partitioning the crude ethanol extract from the cultivated leaves of L. nepetifolia. In doing so, flavonoid 3',4',5-trimethoxy-6,7-dihidroxyflavone (cirsiliol), a chemotaxonomic marker of the family Lamiaceae, was isolated. The results reveal that all phases and extracts tested exhibited weak to moderate antimicrobial activity against the strains of bacteria tested. The evaluation of in vitrocytotoxic and antitumor activity showed that the ethyl acetate phases obtained from both wild and cultivated leaves exhibit high potential cytotoxic and antitumor (> 78.0% of inhibition) activity. The major component of these phases was identified by high-performance liquid chromatography-diode array detector and nuclear magnetic resonance analyses using both 1D and 2D methods. The results further indicate that the flavonoid cirsiliol is the agent responsible for the activity observed in these phases.

Resumo em Inglês:

The leaf essential oils of Eugenia lutescens Cambess andEugenia langsdorffii O. Berg, collected in the rainy (RS) and dry seasons (DS), were extracted by hydrodistillation and then characterized by a gas chromatography-flame ionization detector and a gas chromatography-mass spectrometer. The potential acaricidal activity and oviposition deterrence of these oils were evaluated against Tetranychus urticae . The oil yields were higher in the RS for E. lutescens, while those forE. langsdorffii were higher in the DS. α-Pinene and β-pinene were determined to be the major constituents of the oils fromE. lutescens, while bicyclogermacrene, spathulenol, and β-caryophyllene predominated in E. langsdorffii . Seasonal variations in the oils were primarily related to chemical diversity, and E. lutescens was more affected than was E. langsdorffii . The E. langsdorffii oil collected in the DS was most toxic to the spider mite, while the oils of E. lutescens and E. langsdorffii collected in the RS drastically reduced its egg quantities. This study successfully determined the periods of greater oil production and acaricidal activity.

Resumo em Espanhol:

We report the single-step derivatization reaction of a biopolymer based onL -lysine with D -biotin analogs:Co -poly(L -lysine)-graft-(ε-N -[X-D-biotinyl]-L -lysine) (PLL-X-Biotin). The valeric acid carboxylate of D -biotin is activated to an NHS ester for direct modification of amine groups in proteins and other macromolecules. NHS esters react by nucleophilic attack of an amine in the carbonyl group, releasing the NHS group, and forming a stable amide linkage. NHS-X-Biotin is the simplest biotinylation reagent commercially available. In contrast withD -biotin, it has a longer spacer arm off the valeric acid side chain allowing better binding potential for avidin or streptavidin probes. Derivatization of poly(L -lysine) (PLL) with NHS-X-Biotin led to a copolymer PLL-X-Biotin. UV-Visible, IR-FT and 1H NMR characteristics derived from synthesis are briefly discussed.

Resumo em Português:

Both primary and secondary amines react with 2,4-dinitrochlorobenzene to give derivatives of 1-alkylamino-2,4-dinitrobenzene. These compounds are important intermediates for the synthesis of a diverse range of products. The methodology reported in the present study involves either the room temperature reaction or heating at 70 °C in ethanol in the presence of triethylamine. This transformation occurs via a nucleophilic substitution reaction. The 1-alkylamino-2,4-dinitrobenzene derivatives were obtained in greater than 90% purified yield. The selective reduction of dinitro compounds is an important synthetic strategy for the synthesis of intermediates for dyes, pharmaceuticals and agrochemicals. The use of SnCl2 as a suspension in EtOAc is a promising method for the regio- and chemo-selective reduction of 1-alkylamino-2,4-dinitrobenzenes to 1-alkylamino-2-amino-4-nitrobenzenes. These products are useful intermediates in organic synthesis.

Resumo em Português:

Cathepsins represent a class of enzymes that has the primary function of randomly degrading proteins in the lysosomes, although are also involved in different pathologies. The aim of this paper was to evaluate the capacity of acridone alkaloids isolated from Swinglea glutinosa (Rutaceae) to inhibit cathepsin L in vitro . The IC50 values found were in the 0.8-57 µM range and the most promising compounds were alkaloids 1 and 2, with IC50 of 0.9 and 0.8 µM, respectively. Enzyme kinetics revealed that they are reversible competitive inhibitors with respect to the substrate Z-FR-MCA. This small series of acridone alkaloids showed low selectivity for both cathepsins, but represent promising lead candidates for the further development of competitive cathepsin L and V inhibitors.

Resumo em Português:

With the increase in life expectancy registered in the past few decades, the prevalence of various medical conditions related to aging has been observed, such as dementia and related neurodegenerative conditions. The number of patients afflicted with these conditions is expected to significantly increase in the coming years. The growing social impact of dementia underlines the need for research aimed at identifying and better understanding this type of condition. Among neurodegenerative diseases, amyloidogenic diseases, in particular Alzheimer's disease (AD), are currently the most common form of dementia. Over the years, several hypotheses have been raised regarding the etiology of AD, such as the cholinergic, glutamatergic, amyloid cascade, oligomeric, metallic and diabetes type 3 hypotheses. Unfortunately, no cure is yet available for this disease, only drugs that aid in controlling the symptoms. This review article conducts a comprehensive approach of the main etiological hypotheses of AD, as well as the treatment prospects associated with each hypothesis.

Resumo em Português:

Since their original discovery in 1914, ionic liquids (IL) have been widely examined and explored in chemistry due to their unique physical and chemical properties. Ionic liquids are collectively known as organic salts and have melting points of 100 °C or under. The molten salts most employed in analytical chemistry, including gas chromatography (GC), consist of an organic cation paired with an organic or inorganic anion. This class of materials exhibits negligible vapor pressure and may have their properties (e.g.thermal stability and selectivity) structurally tuned by imparting different moieties to the cation/anion. Currently, there are an estimated 1018possible combinations of IL. In this context, the prospection of highly selective IL-based stationary phases for gas-liquid chromatography has enabled high peak capacity and efficient separations of many critical pairs in complex samples. In this review, we present and discuss fundamental characteristics of ionic liquids and introduce important solvation models for gas-liquid systems. In addition, recent advances and applications of IL in conventional and multidimensional gas chromatography are outlined.

Resumo em Português:

The microencapsulation of palm oil may be a mechanism for protecting and promoting the controlled release of its bioactive compounds. To optimize the microencapsulation process, it is necessary to accurately quantify the palm oil present both external and internal to the microcapsules. In this study, we developed and validated a spectrophotometric method to determine the microencapsulation efficiency of palm oil by complex coacervation. We used gelatin and gum arabic (1:1) as wall material in a 5% concentration (w/v) and palm oil in the same concentration. The coacervates were obtained at pH 4.0 ± 0.01, decanted for 24 h, frozen (−40 ºC), and lyophilized for 72 h. Morphological analyzes were then performed. We standardized the extraction of the external palm oil through five successive washes with an organic solvent. We then explored the best method for rupturing the microcapsules. After successive extractions with hexane, we determined the amount of palm oil contained in the microcapsules using a spectrophotometer. The proposed method was shown to be of low cost, fast, and easy to implement. In addition, in the validation step, we confirmed the method to be safe and reliable, as it proved to be specific, accurate, precise, and robust.

Resumo em Português:

In this study, we developed a method for the visual detection of biodiesel in petrodiesel-biodiesel (BX) blends through the aminolysis of the methyl or ethyl esters of fatty acids that are found in biodiesel and that are absent from diesel and vegetable oils. This method is based on three reactional stages, which produce a dark red and easily visualized complex in the presence of biodiesel. In the absence of biodiesel, there is no dark red coloring, whereas in the presence of diesel or vegetable oil, there is a light red to yellow coloring. This simple, practical, inexpensive, and effective procedure may be applied by petrol stations to guarantee to consumers and resellers the presence of biodiesel in diesel blends, regardless of the BX blend's initial coloring or of the sulfur found in the diesel. In short, it ensures a safe fuel tank fill-up with BX blend.

Resumo em Português:

This research aims to identify the reasons that lead students to pursue a specific course of chemistry teacher training, i.e., their perspectives on the course and the teaching career, and if they are motivated by trainers to become basic education (BE) teachers. It was concluded that most students did not want to be teachers of BE. They identified through the social context of the course that the teachers focused on the area of chemistry teaching sought to motivate them for this career, whereas the teachers of these specific areas of chemistry encouraged them to seek other career opportunities.

Resumo em Português:

In this paper, we describe the development of low-cost teaching experiments of electrogravimetry for undergraduate students using principles of green chemistry. Copper was electrochemically deposited on brass under an electrical current density of 50 mA cm−2 from acidic solutions containing nitrate anions. Color changes at the brass electrode and of the solution were observed, indicating that the reduction of copper ions had occurred. The deposition efficiency values were between 92.8% and 93.8%, and the electrochemical efficiency values were between 85.6% and 86.5%. There was no significant contribution from parallel reactions. These experimental conditions facilitated the didactic exploration of gravimetric and electrochemical concepts. Following the principles of green chemistry, the experiments produced no toxic substances, all the materials could be recycled, and the energy consumption was the lowest. For this reason, this experiment was considered to be very interesting for didactical purposes.

Resumo em Português:

This study proposes an activity to introduce scientific programming. In particular, the multidisciplinary concepts of scientific programming, quantum mechanics, and spectroscopy are presented in the study of the electronic spectrum of the I2 molecule. We use Python programming language and the IPython command shell, in particular, for their user friendliness and versatility.