Resumo em Inglês:

Density, viscosity and calorific values are important physical properties to affect the utilization of biofuel. In this work, mixtures of farnesane and a “jet fuel”, QAv-1, were used to study the variation of density and kinematic viscosity as a function of the volumetric fraction of farnesane and temperature. Experimental measurements were carried out for nineteen farnesane blends and pure farnesane and QAv-1, at four temperatures in the range of 293 - 323 K. Variation of high heating (HHV) and low heating (LHV) values were also determined for different blends of farnesane/QAv-1. Several empirical correlations were used to predict the density, the kinematic viscosity, HHV and LHV values. By using some of these empirical correlations, the estimated values of those three properties studied are in excellent agreement with the experimental data, with low absolute average prediction error.

Resumo em Inglês:

In the present paper, a preconcentration procedure based in the coprecipitation of copper by silver dichromate (Ag2CrO4) and consecutive determination by flame atomic absorption spectrometry (FAAS) was proposed. The experimental factors were optimized from application of the Doehlert matrix and the conditions set: chromate concentration 5.8 × 10-4 mol L-1, silver concentration 1.1 × 10-3 mol L-1, pH 7.3 and disperser concentration HNO3 0.38 mol L-1. Under these conditions, analytical parameters of the procedure were obtained, with the quantification limits of 0.76 µg L-1, precision (based in the relative standard deviation, RSD %) with values lower than 2.7%, and preconcentration factor of 28. The accuracy of the procedure was given by addition/recovery test in water samples groundwater and mineral, and by comparison with results obtained by ICP-MS. The procedure developed presented be simple, sensitive and low cost, thus can be applied in the preconcentration and determination of copper in several water samples.

Resumo em Inglês:

The need to increase the product’s shelf life and the growing concern to minimize the use of synthetic products encouraged the researchers to evaluate the antioxidant activity and quantify phenolic compounds as chlorogenic acid, caffeic acid, rutin, quercetin and apigenin through the use of HPLC, in 29 accesses of Capsicum baccatum. Capsicum baccatum var. pendulum is one species of the Capsicum genus widely consumed in Brazil. It is the second largest pepper produced in the world. However, its chemical composition and mainly its extract antioxidant activity have been poorly reported in literature. In order to deepen the study of the access properties relating the antioxidant activity versus content of phenolic compounds. It is suggested that the BRS, 1643a, 1611 and 1613, accession could be used as natural antioxidants in the food industry.

Resumo em Inglês:

Density functional theory (DFT) methods are used to study on TATP derivatives at DFT-B3LYP/6-311++G (d, p) level to improve TATP’s performance. The derivatives are 3,6,9-trimethyl-3,6,9-tris(trifluoromethyl)-1,2,4,5,7,8-hexaoxonane (TATP3F), 3,6,9-trimethyl-3,6,9-tris(nitromethyl)-1,2,4,5,7,8-hexaoxonane (TATPNO2) and (3,6,9-trimethyl-1,2,4,5,7,8-hexaoxonane-3,6,9-triyl)trimethanamine (TATPNH2). Stability and detonation performance of TATP derivatives were investigated. Detonation performance was estimated using density, heat of formation and EXPLO 5 software. Stability was evaluated by geometrical geometry and electronic structure. The simulation results reveal that TATPNO2 has a best oxygen balance, detonation performance (Q=5424 kJ kg-1, P=23.7 Gpa, D=7699 m s-1) and insensitivity. Since TATPNO2 is more excellent than TATP and traditional explosive TNT in detonation performance, it is a candidate of novel high energy density materials.

Resumo em Inglês:

The present study evaluated the concentrations of Total Suspended Particles (TSP) and associated metals in three distinct regions of Ribeirão Preto city (Center City, Campus and Airport) in the dry and rainy seasons. There were no significant differences (p < 0.05) in TSP and metals concentrations between the sampling sites, except for Cu, Cr and Zn. Seasonal variation was observed for TSP and the following associated metals: As, Be, Cu, Mn, Ni, Pb, Sn and V, being the highest concentrations observed in the dry period. The TSP concentrations did not exceed the air quality standards in São Paulo state, but these can cause harm to the population health, especially in the dry season. Cadmium was the only element that exceeded the WHO air quality guidelines in two consecutive samplings in the Center City and the Airport during the dry season. In this way, preventive measures should be taken through public policies to improve local air quality control and reduce the health risks to the population.

Resumo em Inglês:

In this study, a simple, fast, portable, environment-friendly and inexpensive method, CPE-scanometry, is applied for the determination of Phenylalanine (Phe) amino acid. The extraction of analytes from water samples (15 ml) was performed in the presence of Triton X-114 as a non-ionic surfactant in a water bath environment, diluting the extracted surfactant-rich phase with alkali ethanol as a suitable solvent to 0.5 mL and transferring an appropriate volume to a special cell. The individually cylindrical cavities in the sheet of Plexiglas serve as reaction chambers. These cylindrical cavities in the sheet of Plexiglas are fabricated with a laser beam. The cells containing the analyte solution were scanned with a scanner, then the color of each cell was analyzed, by software written in Visual Basic (VB 6), to obtain the red, green and blue values. The influence of operation parameters including pH, concentrations of surfactant and electrolyte on the cloud point extraction of analyte were studied and optimum conditions were established. Under optimum condition, limit of detection (LOD), relative standard deviation (RSD) and linear range for the proposed method are obtained 0.06, 3.42 and 0.2-10.0 mg L-1 respectively. Finally, the proposed method was utilized successfully for the determination of Phenylalanine in some water and waste water samples in recoveries range 94.1–107.7%.

Resumo em Inglês:

Brazilian Forensic Scientists are frequently asked about ballpoint pen manuscripts chronology in documents suspected to be forged. In the recent years, many methods like quantification of 2-PE (2-phenoxyethanol) have been developed on this subject. The validation of these methods only recently has been a concern between scientific forensic community. Researchers studied the behavior of ink on ageing, but few of them concerned about the influence of the paper on the extraction of 2-PE. This study performed the figures of merit evaluation of the quantification of 2-PE using GC/MS, testing the main parameters involved in the reliability of the method (linearity, repeatability, limits of detection and quantification, accuracy and robustness). After, based on a full factorial design with four factors and two repetitions, the authors tested kind of paper, grammage of paper, ink color and three ink ages, to verify the paper influence on the quantity of 2-PE from ink, trough GC/MS analysis. The merit parameters evaluation showed that the method is linear, precise, accurate and robust. The results for the effect of paper showed main effects of the factors and the existence of interactions effects between the kind of paper and paper grammage, and between the kind of paper and other factors.

Resumo em Inglês:

The aim of this investigation was to analyze two samples of pollen collected by Apis mellifera bees in view of their chemical composition, antiradicalar and antimicrobial activities. Palynological analysis showed that the predominant pollen was Fabaceae species (42.3%, sample I and 50.6%, sample II). The characterization by ultra-performance liquid chromatography coupled with a diode array detector and quadrupole time of flight mass spectrometry (UPLC-DAD-QTOF-MS/MS) resulted in the identification of three derivatives of putrescine (di-4-coumaroylputrescine, coumaroyl-feruloyl-putrescine and di-feruloyl-putrescine), two spermidine derivatives (coumaroyl-di-cafeoyl-spermidine and tri-coumaroyl-spermidine and four biflavonoids (2,3-di-hydrohydroxy-amentoflavone, 2,3-dihydro-amentoflavone, amentoflavone and 2,3-dihydro-biapigenin). The two samples showed antiradical and antimicrobial activities, probably due to the presence of these compounds.

Resumo em Inglês:

Superparamagnetic iron oxide nanoparticles are suitable contrast agents for magnetic resonance imaging due to their effect on proton relaxation times, and excellent biocompatibility and biodistribution in tissue. In the present study, a ferrofluid formed by dextran-coated iron oxide nanoparticles was prepared by the coprecipitation method and with subsequent steps of crosslinking and addition of functionalizations on the nanoparticle's surface (amino groups and a fluorophore). The effect of differences in the synthesis route (ratio of dextran to iron salts and temperature of the reaction) on the physico-chemical characteristics of the nanoparticles and their performance as contrast agents for magnetic resonance imaging was investigated. Overall, the nuclear magnetic relaxation times of water protons in aqueous suspensions of the nanoparticles did not show major differences among different batches, with no significant effect due to the addition of the fluorophore or changes in the dextran fraction of up to 50%. Larger reductions in the ratio of dextran to iron salts resulted in particles with slightly larger sizes, higher saturation magnetization and distinct nuclear magnetic relaxation times.

Resumo em Inglês:

Chemical analysis involving gas chromatography coupled to mass spectrometry of the essential oils of red and orange flowers from E. velutina revealed a predominance of phenylpropanoids in both samples. However, qualitative and quantitative differences were found in the compositions. (E)-Asarone (16.22 ± 0.23%) and (E)-caryophyllene (12.22 ± 0.11%) were identified as the major constituents of the essential oil from the red flowers, whereas (E)-caryophyllene (41.72 ± 1.65%) and eugenol (20.99 ± 0.21%) were identified as the major constituents of the oil from the orange flowers. Seventeen fatty acids were characterized in the red and black seeds. The fatty acid composition in the two chromatic variations had a high degree of similarity. Oleic acid (41.56 ± 1.33% and 46.12 ± 1.90% in the red and black seeds, respectively), palmitic acid (15.39 ± 0.16% and 12.33 ± 0.41%) and behenic acid (9.95 ± 0.14% and 12.10 ± 0.42%) were identified as the main fatty acids. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) enabled identifying significant differences in the chemical profile of the essential oils from the red flower and orange flower varieties of E. velutina. In contrast, PCA and HCA analysis revealed no significant differences in the fatty acid profile of the red and black seeds.

Resumo em Inglês:

Natural products continue to inspire scientists on the search for biological active structures. Recent advances in synthetic biology allow modifying genes to extend structural diversity present on natural products by changing important functional groups guided through genetic information. In this context, polyketides synthases (PKS) represent a class of enzymes from where the first applications and well succeed modifications were achieved. During the last two decades PKSs have been extensively studied, sequenced and deposited in data banks available to scientific community around the world. This newly wide information associated to different methodologies accessible to modify the PKSs genetic circuits including genetic insertion, gene deletion and gene replacement leads to discovery of new natural products. In this review, the recent advances in combinatorial biosynthesis, as well as modern techniques in synthetic biology to promote structural diversity on natural products will be discussed.

Resumo em Inglês:

The objectives of this study were twofold: to assess two chromatographic methods for the analysis of greenhouse gases (GHG) and carbon monoxide, and to propose and evaluate a low-cost and reusable alternative system for their sampling and storage, using 10 different container configurations (flasks and bags). To that end, standard samples containing the gases of interest (CO2, CH4 and CO) and different types of real samples were tested. Finally, procedures for the sampling, storage and analysis of CO2 and CH4 were evaluated and optimized. Two chromatographic methods were applied, using different analysis conditions and columns. Gas chromatography analysis of sample stability and container reusability demonstrated that borosilicate flasks with butyl rubber and PTFE/silicone septa are ideal for storing samples, allowing up to 5 successive sampling cycles with no significant loss of recovery. For larger volume samples, multilayer foil bags are the most stable for the compounds analyzed. The tests conducted with real and synthetic gas samples under optimized chromatography conditions using both methods indicated satisfactory performance for CO2 and CH4 quantification. However, CO analysis in the column with a polystyrene-divinylbenzene stationary phase (Method 1) produced an artifact due to the presence of oxygen in the samples, restricting its quantification.

Resumo em Inglês:

The possibility of detecting some organic compounds directly in a petroleum/water interface was described. Aqueous phase was composed by 1 x 10-3 mol L-1 NaCl solution and the oil phase was carried out using crude oil forming an oil/water interface. Carbon based screen-printed electrodes was used in conjunction with square-wave voltammetry technique, constituting the main tools of this technical note. Petroleum was contaminated with phenol, naphthalene and cyclohexane. The oxidation potentials for these three molecules were 0,72, 0,81 and 0,87 V vs. Ag, respectively. Phenol was chosen to study the stability of currents during the process. After 15 minutes, the currents of this process were stable. Although the formation of a passivation film, the qualitative detection of the molecules was possible. Finally, the main advantage of this methodology is the possibility of detecting contaminants in oil without the necessity of complicated pre-treatment steps.

Resumo em Inglês:

In the present article it is described the validation of a simple, precise, accurate, rapid and low-cost UV spectrophotometric method for the quantification of acetylsalicylic acid in pharmaceutical formulations. The method was validated by linearity, specificity, range, accuracy, precision, robustness, and limits of detection and quantification. The method was linear in the range between 24 – 36 µg mL-1, presenting a good correlation coefficient (r = 0.9994) and adequate limits of quantification (6.57 µg mL-1) and detection (1.99 µg mL-1). Precision analysis showed low coefficient of variation (< 2.0%) and a good average recovery percentual (99.42% - reference and 95.94% - generic). The results and the statistical treated proved that the method may be considered a precise, accurate and low cost analytical alternative for laboratory routine and experimental activity. The method was applied for acetylsalicylic acid determination in two different pharmaceuticals formulations. The results of these analyzes are in accordance with the values declared by the manufacturer, at a 95% confidence level. This experimental activity is a simple and might be used as an practice activities on teaching laboratories improve the student learning.

Resumo em Inglês:

At the turn of the nineteenth century, a frantic search took place in Minas Gerais for minerals that could prove to be of economic value and thus compensate for the decline in the production of gold and diamonds, the mainstay of the economy in the preceding century. This article addresses the search for new mineral wealth, involving the work of many different explorers and their multidisciplinary research, and particularly the unsuccessful efforts directed to finding and obtaining lead and silver in sizable amounts as two such possible replacements.

Resumo em Inglês:

This paper presents a historical case study regarding the development of the concept of valence in late nineteenth and early twentieth centuries. The case study focuses on Edward Frankland’s contribution to the process which lead to the convergence of two theories about the combination of the elements: the theory of types and the theory of radicals. Results show how such process involved many other scientists from various countries and how the concept of valence related to studies on bonding, periodicity and chemical structure. Changes in the nomenclature and notation were also observed. In the beginning of the twentieth century, the empirical concept of valence received theoretical explanations under the light of the then new theories on electronic structure of atoms. Thus, this case study exemplifies the complexity of the process of development of a scientific concept and, in particular, shows the multiplicity of connections of the concept of valence in the body of chemical knowledge.