Showing papers in "Journal of the Brazilian Chemical Society in 2008"
TL;DR: In this article, the Hartree-Fock model was used to translate the classical concepts of molecular structure, chemical structure and chemical bond into a quantum-mechanical language.
Abstract: In this paper we briefly review the basic requirements that must be satisfied by any wave function representing many-electron systems. Following that, we examine the conditions under which the classical concepts of molecular structure, chemical structure and chemical bond can be translated into a quantum-mechanical language. Essential to this aim is the utilization of an independent particle model (IPM) for a many-electron system. In spite of the great popularity of the Hartree-Fock (HF) model only Valence-Bond (VB) type wave functions with optimized, singly occupied and non necessarily orthogonal atomic-like orbitals, can provide a quantum-mechanical translation of the classical concepts of chemical structure and chemical bond, although the HF model can still be useful for translating the concept of molecular structure. Finally, a quantum-dynamical-type of analysis allows us to conclude that, from the quantum mechanical point of view, the chemical bond is a consequence of interference effects. From the energetic point of view, the interference effect responsible for the bond formation manifests itself as a reduction of the kinetic energy of the electrons as the bond is formed.
358 citations
TL;DR: MKTOP is a free-software capable of automatic atom type recognition and construction of molecular topologies for GROMACS, being a useful tool for its users.
Abstract: Molecular mechanics methods are widely-used for simulations of biomolecules. A molecular topology file containing all atom types, which depend on the chemical environment, must be constructed. MKTOP is a free-software capable of automatic atom type recognition and construction of molecular topologies for GROMACS, being a useful tool for its users.
134 citations
TL;DR: In this article, a set of 1-alkyl ether and 3-methylimidazolium ionic liquids 2-4 ([CxOyMIm]+[Anion]- or [CxMIm]-[Anions]], where MIm = 3-Methylimidine, CxOY = 1-alkyl ether, C7O3 = -(CH2)2O(CH 2)2 OCH3 (A), C3O1 = -((CH2))2OCH3(B), C10
Abstract: A set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium ionic liquids 2-4 ([CxOyMIm]+[Anion]- or [CxMIm]+[Anion]-, where MIm = 3-methylimidazolium; CxOy = 1-alkyl ether, C7O3 = -(CH2)2O(CH2)2O(CH2)2OCH3 (A), C3O1 = -(CH2)2OCH3 (B); Cx = 1-alkyl, C10 = C10H21 (C), C4 = C4H9 (D); and [Anion]- = H3CSO3- (2), BF4- (3) or PF6- (4)) was prepared and characterized. The cation-anion hydrogen bonding strength showed to be mainly anion dependent and decreased in the order H3CSO3- > BF4- > PF6-. All methanesulfonate ionic liquids 2 possessed a strongly deshielded H2 imidazolium ring proton. 1-Alkyl ether functionalized ionic liquids showed higher densities in comparison to their 1-alkyl equivalents. The salts 2a-b, 3a-d and 4a-b are room-temperature ionic liquids. All 1-alkyl ether functionalized ionic liquids (except 4b) are completely amorphous. The widest liquid ranges were obtained with the tetrafluoroborate ionic liquids due to their late solidification and excellent thermal stability. These data provide important information for the understanding of their application scope and the preparation of task-specific ionic liquids.
79 citations
TL;DR: The results seem to indicate that apoptotic cell demise appears to be induced in KB and DU-145 cells, and the presence of nitro and hydroxyl groups could be important in the activity of these compounds.
Abstract: Eugenol (4-allyl-2-methoxyphenol) (1) has been reported to possess antioxidant and anticancer properties. In an attempt to enhance intrinsic activity of this natural compound, some derivatives were synthesized. Eugenol was extracted from cloves oil and further, the eugenol analogues (2-6) were obtained through acetylation and nitration reactions. Eugenol (1) and its analogues (2-6) were examined by in vitro model of cancer using two human cancer cell lines: DU-145 (androgen-insensitive prostate cancer cells) and KB (oral squamous carcinoma cells). Cell viability, by tetrazolium salts assay, was measured. Lactic dehydrogenase (LDH) release was also investigated to evaluate the presence of cell toxicity as a result of cell disruption, subsequent to membrane rupture. In the examined cancer cells, all compounds showed cell-growth inhibition activity. The obtained results demonstrate that the compounds 5-allyl-3-nitrobenzene-1,2-diol (3) and 4-allyl-2-methoxy-5-nitrophenyl acetate (5) were significantly (p < 0,001) more active than eugenol, with IC50 values in DU-145 cells of 19.02 x 10-6 and 21.5 × 10-6 mol L-1, respectively, and in KB cells of 18.11 × 10-6 and 21.26 × 10-6 mol L-1, respectively, suggesting that the presence of nitro and hydroxyl groups could be important in the activity of these compounds. In addition, our results seem to indicate that apoptotic cell demise appears to be induced in KB and DU-145 cells. In fact, in our experimental conditions, no statistically significant increase in LDH release was observed in cancer cells treated with eugenol and its analogues.
71 citations
TL;DR: In this paper, an SPE-based method (styrene-divinylbenzene copolymer - SDVB) was developed for the simultaneous determination of twelve pesticides in water by HPLC/DAD.
Abstract: Aiming to evaluate the contamination of groundwater by pesticides in cotton growing areas, an SPE-based method (styrene-divinylbenzene copolymer - SDVB) was developed for the simultaneous determination of twelve pesticides in water by HPLC/DAD. The method was validated and average recoveries ranged from 73 to 113%, with a relative standard deviation of 2 to 16%. Detection limits ranged from 0.06 to 0.57 µg L-1. The method was applied to groundwater samples (110) from cotton fields located in "Primavera do Leste", Mato Grosso state, Brazil. Eight pesticides (acetamiprid, aldicarb, carbendazin, carbofuran, diuron, imidacloprid, methomyl and teflubenzuron) were found in the analyzed groundwater samples and 18% of them contained at least one of the pesticides (with concentrations ranging from 0.78 to 68.79 µg L-1). In some cases, detected concentrations exceeded the target levels set by the European Union. These findings confirm the vulnerability of shallow groundwater in the aforementioned areas to pesticide contamination.
63 citations
TL;DR: In this paper, the results of the quantitative determination of fatty acid methyl esters of vegetable oils, (soybean, flaxseed, and palm oils) by eight basic and acid catalysis esterification methods were compared.
Abstract: The results of the quantitative determination of fatty acid methyl esters of vegetable oils, (soybean, flaxseed, and palm oils) by eight basic and acid catalysis esterification methods were compared. The selected methods were described by Metcalfe, 1966 (MET, ref. 17); Bannon, 1982 (BAN, ref. 18); Joseph and Ackman, 1992 (JAC, ref. 3); Hartman and Lago, 1973 (HLA, ref. 19); Jham, 1982 (JHA, ref. 20); ISO 5509, 1978 (ISO, ref. 21); Bannon, 1982 (BBA, ref. 15) and Schuchardt and Lopes, 1988 (SLO, ref. 22). Despite the large variation in the determination of unsaturated fatty acids, all the methods were efficient in the analysis of saturated fatty acids. The results obtained show that fatty acid analysis may be affected by oil composition and that JAC, ISO, and BBA methods are more efficient. ISO, and BBA are recommended for low acidity samples due to their low reagent toxicity and cost. The JAC method is recommended only for high acidity samples, as the ISO and BBA methods are carried out in basic medium and cannot analyze the free fatty acids.
60 citations
TL;DR: In this paper, the authors discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr on the mediated process, and calculate the parameters of removal efficiency and energy consumption for electrochemical incineration of OA.
Abstract: Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated.
54 citations
TL;DR: The Brazil nut (Bertholletia excelsa) was studied for its composition in fatty acids, tocopherols, sterols and phospholipids as mentioned in this paper.
Abstract: The oil of the Brazil nut (Bertholletia excelsa) was studied for its composition in fatty acids, tocopherols, sterols and phospholipids. The fatty acids composition of phospholipids was also studied. These results were compared to those of sunflower, walnut, almond, soya and olive oils. Its high content of unsaturated fatty acids, of β-tocopherol and of β-sitosterol gave to the Brazil nut interesting antioxidant and anti-cholesterol properties. The composition of fatty acids in phospholipid is very different from the composition of the oil. Linolenic acid, which is not present in the oil, is present at a high level in phosphatidylethanolamine.
52 citations
TL;DR: In this paper, the effects of pH and ionic strength (I) on copper (Cu) adsorption and the driving force of the reaction in variable charge soils were evaluated from batch studies.
Abstract: Effects of pH and ionic strength (I) on copper (Cu) adsorption and the driving force of the reaction in variable charge soils were evaluated from batch studies. Experimental results of Cu adsorption fitted Langmuir model. According to adsorption isotherms, Cu affinity (KL) was greater in the subsoil (0.061-0.468 L kg-1) than in the topsoil samples (0.169-0.359 L kg-1). Maximum adsorption (Adsmax) ranged from 1114-2422 mg kg-1 (topsoil) to 1002-1334 mg kg-1 (subsoil). Strong dependence of Cu adsorption on the pH was observed in subsoil samples. Adsorption edges showed sharply increase of Cu adsorption (20-90%) in the 4.0-5.0 pH range. Copper adsorption changed with increase in I and indicated different metal retention mechanisms (outer- and inner-spheres). Adsorption reaction was favorable and spontaneous, as indicated by negative values of the free energy variation (ΔG) and the separation factor KR < 1. Soil-solution interface and Cu adsorption were also thermodynamically described by a theoretical approach.
51 citations
TL;DR: A detailed and comprehensive literature collection about the versatility of ionic liquid in conjunction with palladium for various types of reactions is presented in this article, where a number of carbon-carbon bond forming reactions in organic chemistry are facilitated by catalysis with Palladium compounds.
Abstract: A number of carbon-carbon bond forming reactions in organic chemistry (such as the Heck, Suzuki, Stille, Negishi, Sonogashira coupling etc) are facilitated by catalysis with palladium compounds. An attempt has been made to present a detailed and comprehensive literature collection about the versatility of ionic liquid in conjunction with palladium for various types of reactions.
51 citations
TL;DR: In this article, the authors describe the steps undertaken to find and separate such peaks in the range of 3000 to 4000 cm -1 in the case of three different infrared absorption spectra of the glass surface of hydrolyzed silica optical fibers.
Abstract: A analise espectral so se torna confiavel se o espectro e detalhadamente analisado quanto a todos os picos sobrepostos e ocultos. Neste trabalho sao descritas as etapas para revelar e separar esses picos na faixa de 3000-4000 cm -1 em tres espectros de absorcao de infravermelho colhidos na superficie vitrea de fibras opticas de silica hidrolizada. A revelacao dos picos foi feita com a analise da segunda e quarta derivada dos dados experimentais digitalizados, juntamente com o conhecimento disponivel de espectroscopia de infravermelho da interacao silica-agua na faixa espectral investigada. A separacao de picos foi realizada com ajuste de curva usando quatro modelos distintos. O melhor ajuste foi alcancado com um modelo que descrevia os espectros com uma soma de picos do tipo Gaussiano. Mapas descrevendo os limites de ombro (“shoulder limits”) e de deteccao foram utilizados para validar os detalhes espectrais revelados. Reliable spectral analysis is only achieved if the spectrum is thoroughly investigated in regard to all hidden and overlapped peaks. This paper describes the steps undertaken to find and separate such peaks in the range of 3000 to 4000 cm -1 in the case of three different infrared absorption spectra of the glass surface of hydrolyzed silica optical fibers. Peak finding was done by the analysis of the second and fourth derivatives of the digital data, coupled with the available knowledge of infrared spectroscopy of silica-water interaction in the investigated range. Peak separation was accomplished by curve fitting with four different models. The model with the best fit was described by a sum of pure Gaussian peaks. Shoulder limit and detection limit maps were used to validate the revealed spectral features.
TL;DR: In this article, an array of vertically aligned titanium oxide nanotubes was successfully grown on the surface of a titanium substrate by the anodization technique, and they were characterized by scanning electron microscopy (SEM), powder X-ray diffractometry (XRD), Raman spectroscopy and photoluminescence spectroscopic analysis (PL).
Abstract: An array of vertically aligned titanium oxide nanotubes was successfully grown on the surface of a titanium substrate by the anodization technique. The nanotubes were characterized by scanning electron microscopy (SEM), powder X-ray diffractometry (XRD), Raman spectroscopy and photoluminescence spectroscopy (PL). The results indicate that the size of the titanium oxide nanotube is greatly dependent on the applied voltage, and its photoluminescence properties are strongly influenced by the crystal structure. In addition, it is shown that quantum size effects are present in the optical properties of TiO2 nanotubes.
TL;DR: In this paper, samples of honey produced in three different regional climates in the southwest Bahia, Brazil (semi-arid, Atlantic and Transitional Forest Zones) were characterized on the basis of their mineral and trace elements, ash content and electrical conductivity.
Abstract: In this study, samples of honey produced in three different regional climates in the southwest Bahia, Brazil (semi-arid, Atlantic and Transitional Forest Zones) were characterized on the basis of their mineral and trace elements, ash content and electrical conductivity. The metals were determined by atomic absorption spectrophotometry. The cluster and principal component analysis (PCA) methods were applied to the chemical concentration data in order to study the chemistry variables capable of promoting a characterization of the honey produced in each area. Cluster analysis and PCA distinguishes the different groups of honey samples corresponding to each region of the three geographical origins. The high correlation between electrical conductivity and Cu observed in honey samples from transitional forest zones suggested a coupling to the nutrient cycle, and can be attributed to use of copper compounds in coffee production, a major activity developed in all transitional forest zones.
TL;DR: The transmetalation between boron and zinc is of great importance for application in organic synthesis, since it allows the formation of new carbon-carbon bonds between organometallic units and electrophiles as mentioned in this paper.
Abstract: The transmetalation between boron and zinc is of great importance for application in organic synthesis, since it allows the formation of new carbon-carbon bonds between organometallic units and electrophiles. The direct arylation of aldehydes or more scarcely ketones, in a catalytic, enantioselective manner using chiral catalysts has been described recently. The enantiomerically enriched diarylmethanols obtained in these reactions are valuable precursors for important bioactive molecules. This review provides a synopsis of this ever-growing field and highlights some of the challenges that still remain.
TL;DR: In this paper, a double emulsion/solvent evaporation technique was used to extract microparticulas containing a watersoluble model drug, metformin hydrochloride (MH).
Abstract: Microparticulas de poli(3-hidroxibutirato-co-3-hidroxivalerato) (PHBV) contendo um farmaco modelo hidrofilico, o cloridrato de metformina (MH), foram obtidas pela tecnica de emulsao multipla/evaporacao do solvente. Diversas formulacoes foram preparadas, com o objetivo de investigar a influencia de cada composicao sobre a eficiencia de encapsulacao (EE). O resultado mais elevado de EE (9,76%) foi verificado quando da simultânea alcalinizacao e adicao de NaCl na fase aquosa externa da formulacao. O estudo por MEV das microparticulas revelou morfologia esferica e superficie rugosa. As intensidades de difracao cristalina para as microparticulas contendo o MH foram menores do que aquelas observadas para a mistura fisica. Os resultados obtidos por IVTF sugerem que nenhuma ligacao quimica foi formada entre o polimero e o farmaco. A avaliacao por analise termica indica o surgimento de interacoes favoraveis entre MH e PHBV. O estudo de liberacao in vitro demonstrou a influencia do PHBV no perfil de dissolucao do MH. Poly(3-hydroxybutirate-co-3-hydroxyvalerate) (PHBV) microparticles containing a watersoluble model drug, metformin hydrochloride (MH), were obtained by a double emulsion/solvent evaporation technique. Several formulations were prepared in order to investigate the influence of each composition on the encapsulation efficiency (EE). The highest value of EE (9.76%) was obtained using simultaneously pH alkalinization and NaCl addition in the external water phase of the formulation. SEM study revealed a spherical morphology and a rough surface. The crystalline diffraction intensities for the MH-loaded microparticles were lower than that verified for the physical mixture. FTIR results suggested that no chemical bond between the polymer and the drug was formed. Also thermal analyses indicated a favorable interaction between MH and PHBV. In vitro drug release demonstrated the influence of the PHBV on the dissolution profile of MH.
TL;DR: In this paper, the main compounds with radical scavenging activity in juice and leaves extracts were identified by HPLC-UV/PAD analysis combined with HPLC microfractionation monitored by TLC using β-carotene and DPPH as the detection reagents.
Abstract: The antioxidant activity of sugarcane (Saccharum officinarum L.) juice towards DPPH reagent was determined (EC50) and the main compounds with radical scavenging activity in juice and leaves extracts were identified by HPLC-UV/PAD analysis combined with HPLC microfractionation monitored by TLC using β-carotene and DPPH as the detection reagents. In sugarcane leaves, luteolin-8-C-(rhamnosylglucoside) (1) was the most important compound with radical scavenging activity; in sugarcane juice, the flavones diosmetin-8-C-glucoside (2), vitexin (3) schaftoside (9), isoschaftoside (10) and 4',5'-dimethyl-luteolin-8-C-glucoside (11) were the most relevant compounds. The content of juice flavonoids (0.241 ± 0.001 mg total flavonoids/mL juice), comparable to other food sources of flavonoids, suggest the potential of sugarcane as a dietary source of natural antioxidants. However, the low antioxidant ability of sugarcane juice (EC50 = 100.2 ± 2.6 g L-1) also points to the need for further studies about the dietary intake of sugarcane flavonoids and its effects on human health.
TL;DR: This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes, paving the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels and establishing that potentiometry compares favorably to electrochemical stripping analysis.
Abstract: This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the underlying membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications.
TL;DR: In this paper, the electrode response was very fast, with an elapsed time of about 1.0 s, showing the potentiality to be utilized as an electrochemical sensor for determination of ascorbic acid in commercial samples.
Abstract: . The electrode response was very fast, with an elapsed time of about 1.0 s, showing the potentiality to be utilized as an electrochemical sensor for determination of ascorbic acid in commercial samples.
TL;DR: In this paper, a study of the fragmentation patterns of selected flavonoids was conducted using orthogonal acceleration time-of-flight electrospray ionization mass spectrometry (ESI-oa-ToF MS).
Abstract: The flavonoids present in sugarcane (Saccharum officinarum) extracts were analyzed by liquid chromatography - mass spectrometry (LC-MS), and a study of the fragmentation patterns of selected flavonoids was conducted using orthogonal acceleration time-of-flight electrospray ionization mass spectrometry (ESI-oa-ToF MS). Seven C- and O-glycosylflavones were identified in the extracts, namely, schaftoside, isoschaftoside, luteolin-8-C-(rhamnosylglucoside), vitexin, orientin, tricin-7-O-neohesperidoside and tricin-7-O-glucoside. Of these, five were identified in the absence of direct comparison with their respective standards. The described method also permitted the differentiation of the 6-C and 8-C isomeric flavones, schaftoside and isoschaftoside. The combination of fragmentation data and exact mass measurement showed to be complimentary to the HPLC-UV-MS techniques previously utilized for isomers discrimination in sugarcane studies.
TL;DR: B(HSO4)3 was easily prepared and used as a novel and efficient solid acid catalyst for conversion of epoxides to the corresponding thiocyanohydrins under solvent-free conditions with high isolated yields as mentioned in this paper.
Abstract: B(HSO4)3 was easily prepared and used as a novel and efficient solid acid catalyst for conversion of epoxides to the corresponding thiocyanohydrins under solvent-free conditions with high isolated yields. The salient features of this methodology are cheaper process, easy availability of the catalyst, versatility, and high regioselectivity of the procedure.
TL;DR: In this paper, the authors identify the sources of 38 elements in sediments from the Santos-Cubatao Estuarine System (SE Brazil), at one of the most industrialized areas in Latin America.
Abstract: Este trabalho registra pela primeira vez o historico da contaminacao e as fontes de 38 elementos em sedimentos do sistema estuarino de Santos-Cubatao (SE do Brasil), em uma das areas mais industrializadas da America Latina. A composicao de um testemunho de 260 cm de profundidade do estuario do rio Morrao foi determinada por ICP-MS e avaliada por meio de fatores de enriquecimento, analise de componentes principais, matrizes de correlacao e assinaturas geoquimicas. Elementos contaminantes como Cr, Mn, Ni, Zn, Ga, Ag, Cd, Sn, Sb, Pb e Bi foram associados ao Fe, derivados de atividades siderurgicas, enquanto Be, Ca, Sc, Co, Cu, Sr, Y, Zr, Nb, Hf, Ta, Th e U estiveram associados ao P, relacionados ao processo produtivo de fertilizantes. Uma sobreposicao da distribuicao do Fe sedimentar e producao local de aco indicaram que o Fe e um marcador confiavel do historico da contaminacao, permitindo a estimativa de taxas de sedimentacao para 45 anos de atividades industriais. This paper records for the first time the contamination history and identifies the sources of 38 elements in sediments from the Santos-Cubatao Estuarine System (SE Brazil), at one of the most industrialized areas in Latin America. The compositions of samples from a 260 cm long sediment core collected in the Morrao River estuary were determined by ICP-MS. Enrichment factors, principal component analysis, correlation matrixes, and the characterization of geochemical signatures permitted a consistent data evaluation. Contaminant elements such as Cr, Mn, Ni, Zn, Ga, Ag, Cd, Sn, Sb, Pb, and Bi were associated with steel plant-derived Fe concentrations, while Be, Ca, Sc, Co, Cu, Sr, Y, Zr, Nb, Hf, Ta, Th, and U were associated with fertilizer industry-derived P concentrations. An overlap of sedimentary Fe distribution and local steel plant production indicated that Fe is a reliable marker of the contamination history, allowing the estimation of sedimentation rates over a period of 45 years of industrial activities.
TL;DR: In this paper, the influence of several parameters in the synthesis, such as type of hydrogel matrix and polymerization conditions, was studied by using a fractional factorial design.
Abstract: Blends formed by electrochemical polymerization of polypyrrole (PPy) into polyacrylamide (PAAm) hydrogels were used as devices for controlled drug release. The influence of several parameters in the synthesis, such as type of hydrogel matrix and polymerization conditions was studied by using a fractional factorial design. The final goal was to obtain an adequate device for use in controlled release tests, based on electrochemical potential control. For controlled release tests, Safranin was used as model drug and release curves (amount of drug vs. time) have shown that these blends are promising materials for this use. The optimized blends obtained were characterized by cyclic voltammetry and Raman spectroscopy.
TL;DR: In this article, a high speed, solvent-free, and practical synthesis of pyrazolones under microwave irradiation is described, which involves the reaction of b-keto ester with substituted or unsubstituted hydrazine and provides a simple and straightforward one-pot approach for the synthesis of a variety of derivatives with high regioselectivity.
Abstract: Descrevemos uma sintese rapida e pratica de pirazolonas, na ausencia de solvente, sob irradiacao de microondas. Esta metodologia sintetica envolve a reacao de b-cetoesteres com hidrazinas substituidas e nao-substituidas e oferece uma preparacao simples e direta de diferentes pirazolonas com alta regioseletividade. Essas pirazolonas podem existir em diferentes formas tautomericas em solucao e o anel 2-aril-pirazol-3-ona permanece torcido em relacao ao plano da pirazolona no estado cristalino. O mecanismo da reacao e proposto levando em conta a regiosseletividade. Uma das pirazolonas obtidas nesse processo foi usada na preparacao de um derivado espirociclohexanona de significativo potencial biologico. A high speed, solvent-free, and practical synthesis of pyrazolones under microwave irradiation is described. This greener synthetic methodology involves the reaction of b-keto ester with substituted or unsubstituted hydrazine and provides a simple and straightforward one-pot approach for the synthesis of a variety of pyrazolone derivatives with high regioselectivity. These pyrazolones can exist in different tautomeric forms in solution and the aryl ring of 2-aryl pyrazol-3-ones remain twisted with respect to the pyrazole plane in the crystal state. Mechanism of the reaction accounting the regioselectivity has been proposed. One of the pyrazolones obtained via this process was utilized to prepare a spirocyclohexanone derivative of potential biological significance.
TL;DR: A metodo alternativo por eletroforese capilar de zona (CZE) for determinacao of ciprofloxacina (CPFLX), gatifloxacine (GTFLX) and ofloxacidine (OFLX). as mentioned in this paper, a metodo alternate for eletrolito for determining whether a droga is suitable for use in a farmaceutica environment.
Abstract: Um metodo alternativo por eletroforese capilar de zona (CZE) para determinacao de ciprofloxacina (CPFLX), gatifloxacina (GTFLX), moxifloxacina (MFLX) e ofloxacina (OFLX) foi validado. O sistema de eletrolito utilizado consistiu da mistura de 25 mmol L-1 de TRIS/ HCl e 15 mmol L-1 de tetraborato de sodio em meio aquoso resultando em pH 8,87. A analise foi realizada sob deteccao direta por UV em 282 nm com tempo de analise de 3 min. Os parâmetros analiticos de validacao avaliados foram: linearidade (r > 0,998), seletividade (comparacao entre a inclinacao da curva de calibracao de padronizacao externa e curva de calibracao de adicao de padrao), repetitividade em area para amostras (RSD %: < 3,94% para CPFLX, < 3,87% para GTFLX, 1,30% para MFLX e < 1,88% para OFLX), precisao intermediaria em area para amostras (RSD%: < 3,59% para CPFLX, < 3,09% para GTFLX, 2,67% para MFLX e < 2,25% para OFLX), exatidao (media da faixa de recuperacao: 101,2% para CPFLX, 101,0% para GTFLX, 101,3% para MFLX e 99,9% para OFLX), limite de deteccao (mg L-1: 2,72 para CPFLX, 1,92 para GTFLX, 0,795 para MFLX e 1,05 para OFLX), limite de quantificacao (mg L-1: 9,06 para CPFLX, 6,40 para GTFLX, 2,65 para MFLX e 3,50 para OFLX) e robustez. Devido a simplicidade, seletividade, precisao, exatidao e rapidez, o metodo pode ser uma alternativa interessante para auxiliar o controle da qualidade dessas drogas na industria farmaceutica.
TL;DR: The isolation of sakuranetin, kaempferol 7-methyl ether, and aromadendrin 7- methyl ether from both Trigonas spinipes'nest and the exudate from Eucalyptus, may suggest this species as a botanical origin of the nest constituents of these stingless bee in the Northeast of Brazil.
Abstract: In the Northeast of Brazil the stingless bee Trigona spinipes Fabricius injures the tree bark of cultivated Eucalyptus citriodora specimens in order to make them exudate. The chemical investigation of the ethanol extract of an entire nest of T. spinipes allowed the isolation of the cycloartane triterpene magniferolic acid and 3b-hydroxy-24-methylenecicloartan-26-oic acid, besides the flavonoids 3-methyl quercetin, sakuranetin, kaempferol 7-methyl ether, tricetin and aromadendrin 7-methyl ether as the main compounds. The isolation of sakuranetin, kaempferol 7-methyl ether, and aromadendrin 7-methyl ether from both Trigonas spinipes'nest and the exudate from Eucalyptus, may suggest this species as a botanical origin of the nest constituents of these stingless bee in the Northeast of Brazil. The structural characterization of the isolated compounds was accomplished by spectrometric means and comparison with the literature data.
TL;DR: In this article, the authors evaluated the mineral composition of wheat flour consumed in Brazil, using Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES).
Abstract: In the present paper, the mineral composition of wheat flour consumed in Brazil was evaluated. In the sampling step 54 samples were collected in 15 cities, including principal Brazilian cities such as: Sao Paulo, Rio de Janeiro, Salvador, Porto Alegre, Recife and others. The elements determinate were: calcium, copper, magnesium, manganese, iron, phosphorus, potassium and zinc. The samples were digested using nitric acid and hydrogen peroxide in open system. The analytical technique employed was Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). The method validation (including digestion and determination) was performed using a certified reference material of wheat flour furnished by National Institute of Standards & Technology (NIST). Considering the 54 samples analyzed, the results demonstrated that the macronutrients: calcium, magnesium, potassium and phosphorus have average contents of 0.27, 0.35, 1.71 and 1.92 mg g-1, for concentration ranges of 0.11-1.96, 0.19-0.51, 0.76-3.16 and 0.81-7.15 mg g-1, respectively. The micronutrients: copper, iron, manganese and zinc have average contents of 1.84, 37.8, 8.2 and 9.4 µg g-1, for concentration ranges of 1.00-2.80, 10.5-146.6, 3.9-14.7 and 5.1-13.9 µg g-1, respectively. The results were also evaluated using the multivariate analysis techniques: principal component analysis (PCA) and hierarchical cluster analysis (HCA).
TL;DR: In this paper, a method for the determination of Na and K in biodiesel, from different vegetable oils, is proposed, combining the advantages of FAES with the simplicity of microemulsion preparation and calibration using aqueous standards.
Abstract: A method for the determination of Na and K in biodiesel, from different vegetable oils, is proposed. The advantages of the FAES were combined with the simplicity of microemulsion preparation and calibration using aqueous standards. Microemulsions were prepared by mixing biodiesel samples with n-propanol and aqueous acid solution, which allowed the use of inorganic aqueous standards for the calibration. Sample introduction through discrete aspiration (DA) or by continuous aspiration (CA) were compared, presenting similar LODs, in the order of 0.1 µg g-1 for both analytes, adequate to the established limits in the Brazilian legislation. The accuracy of the method was checked through recovery tests, with results between 83% and 120%, and through the comparison of the results with those obtained by ICP OES.
TL;DR: In this paper, the electrocatalytic oxidation of hydrazine was studied using an ordinary pyrolytic graphite electrode modified with iron tetrapyridinoporphyrazine complex (FeTPyPz), employing cyclic voltammetry and rotating disk electrode techniques.
Abstract: The electrocatalytic oxidation of hydrazine was studied using an ordinary pyrolytic graphite electrode modified with iron tetrapyridinoporphyrazine complex (FeTPyPz), employing cyclic voltammetry and rotating disk electrode techniques. Analyses of the voltammograms recorded at different potential scan rates and the polarization curves at different electrode rotation rates showed that the reaction of electrooxidation of hydrazine on FeTPyPz occurs via 4-electrons with the formation of N2 as main product. The kinetic parameters suggest that the second electron transfer step is rate controlling. The activity of FeTPyPz depends on its Fe(II)/Fe(I) formal potential and fits well in a volcano plot that includes several iron phthalocyanines, indicating that such formal potential is a good reactivity index for these complexes.
TL;DR: A variety of N-substituted pyrroles have been synthesized by reacting γ-diketones with amines in the presence of indium tribromide, indium trichloride, or Indium trifluoromethanesulfonate under solvent-free conditions as mentioned in this paper.
Abstract: A variety of N-substituted pyrroles have been synthesized by reacting γ-diketones (R1C(O)CH2CH2C(O)R2: R1, R2 = Me, Ph) with amines (RNH2: R=Alkyl, Aryl, TsNH) or diamines (1,6-diaminohexane and 1,2-diaminoethane) in the presence of indium tribromide, indium trichloride or indium trifluoromethanesulfonate at room temperature under solvent-free conditions. The experiment protocol features simple operations, and the products are isolated in high to excellent yields (81-98%).
TL;DR: In this article, the experimental observation of oscillatory dynamics during the electrocatalytic oxidation of methanol on platinum was described and compared with the oscillations observed in the electrooxidation of formic acid, a system whose behavior is more understood and widely supported by in situ spectroscopic data.
Abstract: It is described in this paper the experimental observation of oscillatory dynamics during the electrocatalytic oxidation of methanol on platinum. Besides the previously reported potential oscillations, current oscillations obtained under potentiostatic control are also presented. The existence region of current oscillations is mapped in an applied voltage x resistance bifurcation diagram. Conjointly with electrochemical investigations, in situ FTIR spectroscopy was also employed in the present studies. Although we were not able to follow eventual intermediate coverage changes during the oscillations, those experiments revealled that the mean coverage of adsorbed carbon monoxide remains appreciably high along the oscillations. Results are discussed and compared with the oscillations observed in the electrooxidation of formic acid, a system whose behavior is more understood and widely supported by in situ spectroscopic data.