Resumo em Inglês:

Brazilian law forbids the addition of cheese whey in milk. However, adulteration with cheese whey is one of the most applied fraud due to its low cost. The detection of this fraud is the quantification of Caseinomacropeptide (CMP). The CMP is a constituent of the whey that can be used as adulteration marker. Thus, an analytical method capable of identifying CMP by Fourier Transform Infrared Spectra (FTIR) was developed using chemometrics methods. Firstly, we attempted to develop an exploratory analysis model by Hierarchical Grouping Analysis (HCA) and Principal Component Analysis (PCA) that indicated similarity between samples of raw milk and semi-skimmed milk. Moreover, in the PCA scores, it was possible to observe a tendency of separation between samples with different concentrations of CMP. Afterwards, multivariate regression models were used for Partial Least Squares (PLS), Partial Least Square with Interval Synergism (siPLS) and Supporting Machines with Least Squares (LS-SVM) to quantify the adulteration in different types of milk by Cheese serum through the CMP. All the models were then compared to each other and the results of the official method with Liquid Chromatography Tandem mass spectrometry (LCMS/MS) analysis used by the Ministry of Livestock and Supply (MAPA). The model LS-SVM, employing the full spectrum, obtained the best result compared to the other models (PLS and siPLS) to quantify the CMP in the milk samples.

Resumo em Inglês:

Two sensors were synthesized for the detection of free cyanide (CN-), based on silver sulfide nanoparticles (Np-Ag2S) supported on Multiwall Carbon Nanotubes (MWCNT) and hierarchical porous carbon (HPC). The Ag2S/HPC400 and Ag2S/MWCNT were characterized by physicochemical techniques such as Raman spectroscopy, X-Ray diffraction (XRD) and Scanning electron microscopy (SEM). These sensors were evaluated against the detection of free cyanide by potentiometry; the stability, reproducibility and linearity of each sensor were determined. A limit of detection of 3.34 µg L-1 and a limit of quantification of 11.05 µg L-1 for Ag2S/HPC400 sensor was obtained; while for the Ag2S/MWCNT sensor a limit of detection and limit of quantification value of 23.17 µg L-1 and 76.46 µg L-1 were obtained, respectively. The results show that the presence of carbonaceous materials with a hierarchical structure improves the limits of quantification and detection of the Ag2S/HPC400 sensor.

Resumo em Inglês:

Hydrochar washed (1.0, 2.5, 5.0 and 10.0 %) and not washed (10.0%) produced by hydrothermal carbonization using vinasse and sugarcane bagasse was applied in sand, ultisol and oxisol columns, and the release of NO3-, Orthophosphate, SO42-, Total Organic Carbon (TOC), H+ were evaluated for 30 days. These results were compared with the release of these parameters from experiments conducted with anthropogenic soils. The results demonstrated that higher amounts of nutrients were released for the experiments conducted with hydrochar not washed. With higher rates of hydrochar washed, higher the amount of nutrients released. TOC and SO42- were released throughout the experiment, which is beneficial from the agricultural point of view. Low values of orthophosphate and nitrate release in the leachates were observed for ultisol and oxisol due to the clay and iron and manganese oxides contents. Principal components analysis confirmed the observations and demonstrated that SO42- and TOC preferentially influence the oxisol, being that nitrate and pH influenced the columns containing Terra Mulata and sand. The results allow to conclude that it is possible to adjust the application rate of hydrochar in soils with lower fertility in order to increase it as observed for anthropogenic soils.

Resumo em Inglês:

Atmospheric processes in an urban scenario are very complex and depend on meteorological parameters, emission, transport and deposition processes and the chemical mechanism. Simple air quality models can be used to understand the main aspects of ozone formation and provide information to adopt pollution control strategies. In this work the detailed simulation of ozone concentrations using the air quality model OZIPR (Ozone Isopleth Package for Research) coupled with the SAPRC (Statewide Air Pollution Research Center) chemical model is presented. First, the methods to determine volatile organic compounds (VOCs) are described as well as the statistical treatment of experimental data: Meteorological parameters (temperature, humidity, pressure, wind speed and direction), concentrations of nitrogen oxides (NOx = NO2 + NO), carbon monoxide (CO) and ozone (O3), which are needed to characterize the problem. Then, the construction and adjust of the model (base case) is detailed using, as an example, data for a typical urban area in the city of Rio de Janeiro. Finally, the limitations and the potential of the model are discussed. Clearly the quality of experimental data, mainly NOx and COVs concentrations and the COVs speciation, are a key information to obtain a correct estimation of O3 levels.

Resumo em Inglês:

Hybrid inorganic-organic solar cells are an attractive alternative energy source because of their low-cost production and ability to make use of a large amount of solar radiation available. This work aims to evaluate different solar cells composed of TiO2 and ZnO with P3OT/P3MT copolymer. Layers of semiconductor oxides were deposited on transparent fluorine-doped tin oxide (FTO) by spin coating and adsorption in the polymer solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), were used to characterize the fabricated semiconductors and curves of current density vs. potential (j-V), photochronoamperometry (j-t) and electrochemical impedance spectroscopy (EIS) were used to determine their electrical characteristics. The XRD analyses confirmed the crystalline nature of the oxide materials. SEM micrographs showed the spherical morphology of ZnO and the poorly defined agglomerate morphology of TiO2. The electrochemical measurements proved that the best cell was produced with P3OT/P3MT copolymer and TiO2, owing to its lower charge transfer resistance, with the following photovoltaic parameters: Voc = 0.615 V ± 0.004, jsc = 1.545 mA cm-2 ± 0.240, FF = 0.637 ± 0.003, and η = 0.617% ± 0.117.

Resumo em Inglês:

The n-alkylcyclohexanes are poorly evaluated in biodegradation studies of Brazilian petroleum samples. In this context, this work aimed to use the homologue series of alkylcyclohexanes to assess extend of biodegradation of 26 petroleum samples from five Brazilian sedimentary basins, analyzed by gas chromatography coupled to mass spectrometry. The n-alkylcyclohexanes compounds were detected in all samples, with a distribution similar to the n-alkane profile, in which their abundance decreasing with increasing of the biodegradation extent. Based on this, it was suggested the use of the new parameter H30/DC together with the H30/AC already proposed, calculated by the ratio between C30 hopane to the dodecyl-cyclohexane, to assess biodegradation level according Peter and Moldowan scale (PM scale). In addition, it was observed an increasing in the relative abundance of DBE 2 from class O2, analyzed by ESI(-) FT-ICR MS, mainly due to the formation of monocyclic acids with biodegradation, which correlates with the decrease of n-alkylcyclohexanes, a possible precursor of these acids.

Resumo em Inglês:

In this work, the capability to use pine rosin as a biodegradable coupling agent/compatibilizer is studied. To formulate composites, post-consumer polypropylene and discarded agave fibers (as reinforcing agent) are coupled with pine rosin (in pure or maleated form). Besides, poly(lactic acid) (PLA) with poly(butylene adipate-co-terephthalate) (PBAT) are compatibilized with maleated pine rosins to prepare biodegradable blends. For the coupling agent role, the pure or maleated rosin (Amberyl M-15A) are compared with a commercial polyolefin coupling agent (Epolene E-43), while for the blends, two maleated rosins (Amberyls M-15A and MP-30) are used as compatibilizers. Dynamic and static mechanical tests show considerable increments in moduli and strength for both types of polymeric materials surpassing the role of the Epolene E-43 for the composite materials (v.g. 45.2 vs 16.5 increment in storage modulus, or 61.5 vs 40.3 for Young’s modulus in specific tests). Scanning electron microscopy photographs clearly show the interfacial interaction effect within composites and polymer blends. Fourier transform infrared spectroscopy allowed the observation of the aforementioned interactions at bond level. Blends biodegradation performed by composting for 3 months exceeded 76% of weight loss. The multirole of modified natural maleated gums as coupling agents/compatibilizers is demonstrated.

Resumo em Inglês:

Skin cancer is a frequent neoplasm in Brazil and this, is observed the importance of the development of new sunscreens using simple methodologies capable of reducing production costs. In this context, six symmetric acyclic azines were synthesized and characterized, with reaction yields between 54 and 84%, short reaction times (5 to 10 min), and manual grinding as an energy source. Sunscreens 10 %(m/m) of these compounds were produced for the in vitro determination of the solar protection factor UVB (SPF-UVB), of the the six formulations containing the synthesized azines, four showed higher photoprotective capacity in the UVB region (AZN-BZD, AZN-2OH, AZN-4OH and AZN-CIN), with SPF-UVB equivalent or higher than benzophenone-3 (BZF) and at the octylmethoxycinnamate (OMC), commercial chemical filters. The AZN-VAN and AZN-4DAB formulations presented high photoprotective capacity in the UVA region, resulting in lower SPF-UVB when compared to the other synthesized azines, but were still superior to the BZF and equivalent to the OMC. All the azines synthesized showed superior FPS-UVB to their precursor aldehydes, evidencing the increase of the photoprotective capacity due to the insertion of the azine group.

Resumo em Inglês:

Laboratory bioassays on fumigation, ovicidal and oviposition deterrence activity of the essential oil from Indigofera suffruticosa and its constituents [eugenol, (E)-asarone, dill apiole, (Z)-asarone, thymol, (E)-nerolidol and safrole] against Tetranychus urticae were carried out. Components of Indigofera leaf oil were characterized by gas chromatography (GC) ad mass spectrometry (GC-MS), which revealed the identification of 17 components, representing 97.7 ± 0.6% of the total oil, with a high percentage of phenylpropanoids (89.9 ± 0.5%), among which eugenol (45.6 ± 0.4%) and (E)-asarone (17.4 ± 0.2%) were major constituents. The ovicidal activity and oviposition deterrence tests revealed that the essential oil as well as its main compounds affected the oviposition and hatchability of mite eggs. Eugenol and thymol were the most potent compounds and were approximately 225-fold more potent than the oil. The acaricidal action exerted by sesquiterpenes and phenylpropanoids of the leaf oil is also discussed. The results suggest that the Indigofera oil and selected components associated with ovicidal activity and oviposition deterrence can serve as the basis for a promising agent that could be used in the formulation of a product for use against the T. urticae.

Resumo em Inglês:

The transition metal oxide, such as iron oxide and Fe2O3/Al2O3 is cheap and industrialized that are widely used to catalyze the reaction of chlorine and oxygen with hydrogen in mixture gas to remove hydrogen from tail chlorine at low temperature. The reaction gas was prepared by the same composition with industrial tail chlorine, namely Cl2 (65% ~ 80%), O2 (8% ~ 10%), N2 (6% ~16%) and H2 (1.5% ~ 4%). In this experiment, the fixed bed reactor and iron oxide or Fe2O3/Al2O3 were used as the reaction device and catalysts, respectively. The optimum conversion rate of hydrogen was 84.11% when the reaction temperature was at 70 °C with 3%wt. Fe2O3/Al2O3 and the calcination temperature was 500 °C. The results showed that the catalytic performance of Fe2O3/Al2O3 is superior to Fe2O3. The selectivity of the reaction of hydrogen and chloride was higher than that of hydrogen and oxygen. We also characterized the catalysts with XRD, XPS, SEM and N2 adsorption-desorption and the results showed that the iron oxide was dispersive uniformly on the support surface.

Resumo em Inglês:

TiO2 has been used as a white pigment and studied since the first decades of the XX century for the undesirable chalking of outdoor paintings exposed to sunlight. Since the first report of Honda and Fujishima (1972) of the water splitting by the harvesting of sunlight on a n-type single crystal TiO2 electrode, the engagement of researchers with the field has grown steadily. TiO2-photocatalysis has joined the group of advanced oxidation processes for potential new water and wastewater treatments but, despite of its high chemical and photochemical stability and the great oxidizing power of its photogenerated holes, photons in UVA spectral region are needed to accomplish the high band gap, limiting the yield of sun-driven environmental applications. Nevertheless, this shortcoming has not restricted benchtop research and small and medium scale applications also relying on artificial UV sources, especially nowadays that highly-efficient UVA-LEDs are available. Herein, we review the fundamental aspects and the practical attributions of the trapping model in the charge transfer kinetics of photogenerated holes in nanoparticulate TiO2. Regarding to new practical uses, we focus our attention on some ingenious applications of this photocatalyst in the field of analytical chemistry, covering also subjects never reviewed before.

Resumo em Inglês:

Failing classes is one of the main causes students are held back in universities, which in turn has several academic, social and economic impacts. This study aims to identify factors associated with students flunking General Chemistry, as well as to propose institutional interventions that can remedy these setbacks. The methodology used was based on a conceptual model of nontraditional undergraduate students, evaluating student academic outlook and relating that with institutional data on subject pass rate. Results showed it was possible to correlate variables that influence pass rates in General Chemistry, highlighting the following: busy schedule, study method, high class load per semester, deficiencies in basic chemistry and math, and socioeconomic factors. Results in this work help identify challenges that can aid in developing strategies to eradicate or minimize failing in General Chemistry in higher education institutions in Brazil.

Resumo em Inglês:

Metallic oxides are used in cosmetic shadows formulations in order to highlight the area around the eyes, with different colors. Due to the close proximity to the eye mucosa, these products are a potential source of metal intoxication in human body. Based in this fact, several analytical methods to quantify metals in cosmetic shadows have been proposed in the literature. This paper, propose a contextual experiment to investigated the presence of Al3+, Fe3+ and Cu2+ using UV-VIS spectrophotometric and complexation reactions in solvent mixtures to generate cromophore species. These experiments have the potential to insert a contextual discussion in chemistry and pharmaceutical graduation courses, making a meaningful experimentation in the formative attribute of these courses.

Resumo em Inglês:

Walther Hermann Nernst is known to have established the basis for the third law of thermodynamics and also as one of the founders of the modern physical chemistry. For his work in chemical thermodynamics, he was awarded the Nobel Prize in chemistry, in 1920. An important fact about this scientist life, not always realized, was his stay in Brazil, in 1914, for a short period. He went to the city of São Paulo, where he gave a conference at the Faculdade São Bento. He talked about thermodynamics to a very selected audience. The work presented here explores this visit to Brazil, the importance the newspaper gave to this important visitor, and the community present at his lecture. His impression of Brazil was certainly positive, since one of his daughter immigrates to Brazil in 1939. It is hoped the material will add relevant information to the history of chemistry in Brazil.