Luiz Henrique Viana

Voltammetric determination of tert-butylhydroquinone in biodiesel using a carbon paste electrode in the presence of surfactant

This paper reports an electroanalytical method developed for determining the antioxidant tert-butylhydroquinone (TBHQ) in biodiesel, based on the enhancement effect of cetyltrimethylammonium bromide (CTAB). In pH 6.5 Britton-Robinson buffer, a poorly defined oxidation peak was observed for TBHQ at a carbon paste electrode (CPE). In the presence of low concentrations of CTAB, however, the oxidation peak current was markedly increased. Several parameters were studied and optimized for the development of this methodology, and under optimal conditions the oxidation peak current was proportional to TBHQ concentration in the range of (1.05-10.15) x 10(-6) mol L(-1), with limits of detection and quantification of 7.11 x 10(-8) mol L(-1) and 2.37 x 10(-7) mol L(-1), respectively, by linear sweep voltammetry (LSV). The method was applied to TBHQ determination in soybean biodiesel samples. The results were satisfactory in comparison with those obtained using high-performance liquid chromatography (HPLC).

Carbon-nanotube-modified screen-printed electrodes, a cationic surfactant, and a peak deconvolution procedure: alternatives to provide satisfactory simultaneous determination of three synthetic antioxidants in complex samples

The development of electroanalytical methods for determining three or more analytes simultaneously in a complex sample is highly desirable. Unfortunately, this is not an easy task in electrochemical studies of organic compounds, and alternative methods to achieve this goal have been increasingly sought in recent years. To this end, the present investigation employed a combination of screen-printed electrodes (SPEs), cetyltrimethylammonium bromide (CTAB), and a peak deconvolution procedure as an alternative approach to improve the sensitivity and selectivity in the simultaneous determination of three antioxidants in samples of biodiesel and cosmetic oils. The use of CTAB also prevents the occurrence of SPE fouling by matrix constituents, being essential in the simultaneous detection of the antioxidants tert-butylhydroquinone (TBHQ), propyl gallate (PG), and butylhydroxyanisole (BHA). Under optimized conditions, the limit of detection proved satisfactory, with relative standard deviations of 0.99% for TBHQ, 2.1% for PG, and 0.61% for BHA, indicating that the method has satisfactory repeatability. The approach was successfully applied to determine the target antioxidants in biodiesel samples at different concentrations after simple, rapid dilution, yielding recovery rates of 98–106% for TBHQ, 98–103% for PG, and 92–101% for BHA. In the analysis of cosmetic oils, a deconvolution procedure was applied to achieve separation of the oxidation peak potentials, with recovery rates of 94% for PG and 101% for BHA using the standard addition method. The results were satisfactory compared with those obtained using high-performance liquid chromatography.

Perfil lipídico da polpa e amêndoa da guarirova

The oils of fruits are being studied for its potential in the food industry and also to increase the consumption of mono and polyunsaturated fatty acids. This study aimed to determine the physio-chemical constants, chemical composition and identify and quantify the major fatty acids present in the lipid fraction of pulp and kernel of the fruits of guarirova, species Syagrus oleracea (Mart.) Becc. It was performed the physicochemical characterization of oils, fatty acid composition and nutritional quality indexes. Almond oil has the highest concentration of saturated fatty acids (89,2%), represented mainly by lauric acid (48,34%). The pulp showed monounsaturated (24,84%) and polyunsaturated fatty acids (33,25%), with higher percentage of omega-6 (31,94%) and omega-9 (19,15%) and lower omega-3 (1,31%).

Processo químico industrial de extração de óleo vegetal: um experimento de química geral

In this study we describe an experimental procedure based on a chemical industrial process of soya-bean oil extraction applied in general chemistry for undergraduate students. The experiment was planned according to the Science, Technology and Society (STS) approach to teach basic chemical concepts and provide grounding in the management of environmental care. The use of real life chemistry problems seems to salient the relevance of chemistry to our students and enhances their motivation to learn both the practical and theoretical components of the discipline.

Effect of Powdered Shells of the Snail Megalobulimus lopesi on Secondary-Intention Wound Healing in an Animal Model

Topical administration of powdered shells of the land snail Megalobulimus lopesi was evaluated in Wistar rats for their healing activity in an excision wound model. The animals were distributed into three groups—G1 (control): no therapeutic intervention; G2 (vehicle controls): Lanette cream once daily; G3 (experimental animals): treated with powdered shells. Variables investigated were: wound area contraction, angiogenic activity, morphometric data, leukocytic inflammatory infiltrate, and total leukocyte count in peripheral blood. Thermogravimetric analysis and quantification and characterization of powdered shell proteins were also performed. Wound area on days 3, 7, and 14 was smaller in G3, besides presenting wound closure on day 21 for all these animals. Topical administration of the powdered shells also led to an increased number of vessels at the wound site, higher leukocyte counts in peripheral blood, and increased leukocytic inflammatory infiltrate. The results lend support to the southern Brazilian folk use of M. lopesi powdered shells, as shown by the enhanced secondary-intention healing achieved with their topical administration to wounds in rats. Topical administration caused inflammatory response modulation, crucial to accelerating the healing process, the chronification of which increases the risks of wound contamination by opportunistic pathogens.

Design, Synthesis and Anticancer Biological Evaluation of Novel 1,4-Diaryl- 1,2,3-triazole Retinoid Analogues of Tamibarotene (AM80)

We report herein the design and synthesis via click chemistry of twelve novel triazole retinoid analogues of tamibarotene (AM80) and the evaluation of their anticancer activities against six cancer cell lines: HL60, K562, 786, HT29, MCF7 and PC3. Among the synthesized compounds, two were more potent than tamibarotene against solid tumor cells, and one of them had similar potency to tamibarotene against HL60 cells. The bioisosteric exchange between the amide group and the 1,2,3-triazole core in the retinoid agent tamibarotene (AM80) reported in this work is a valid strategy for the generation of useful compounds against cancer.

Otimização de Diferentes Procedimentos de Preparo de Amostras: Aplicação na Extração de Antioxidantes Presentes em Biodiesel

In this work, different procedures were compared for the extraction of synthetic antioxidants such as propyl gallate (PG), tert-Butylhydroquinone (TBHQ), 3-tert-butyl-4-hydroxyanisole (BHA) and 3,5-di-tert-butyl-4 hydroxytoluene (BHT) from biodiesel samples. The efficiency of target procedures was tested using liquid-liquid extraction and solid phase extraction containing different stationary phase. To accomplish this efficiency and determine the antioxidants, a method based on high performance liquid chromatography coupled with diode array detector (HPLC / DAD) was optimized. In liquid-liquid extraction was used acetonitrile and n-hexane, however, only acetonitrile presented selectivity, able to extract just PG and BHA, with recovery between 78.3 and 96.0%. Using solid phase extraction cartridges containing C-18 as stationary phase, only the PG and BHA were extracted, which the recovery was between 52.4 and 99.7%. Moreover, the macroporous poly(divinylbenzene-co-N-vinylpyrrolidone) polymer presented satisfactory results for the extraction of PG and BHA with recovery between 77.3 and 103 %. All these procedures provided elimination of the sample interferences, allowing recovery with coefficients of variation always lower than 1.00%. However, the comparison of liquid-liquid extraction and solid phase extraction techniques proved that there are many difficulties in extracting, with precision and accuracy, the PG, TBHQ, BHA and BHT antioxidants contained simultaneously in complex samples such as biodiesel. These difficulties are increased when the interest is to reduce the costs of analysis by reducing organic solvent extractors and propose extraction techniques with considerable environmental benefits. DOI: http://dx.doi.org/10.17807/orbital.v7i2.672