Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determinação de metais em meio aquoso

Since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. Many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the pH, the scan rate, and the preparation of the electrodes itself. There are various methos of preparing the electrodes. The goal of this paper is to review some of them. The advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.

Intercalação e funcionalização da brucita com ácidos carboxílicos

Brucite (Mg(OH)2) is a structural model of several natural layered minerals as well as of synthetic layered double hydroxides (LDH). Exchange reaction studies of these compounds are well documented in the literature but surface chemical modifications, especially for brucite, are quite rare. We report the behaviour of brucite in reaction with succinic and benzoic acid in different solvents and temperatures. The compounds were analysed through X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The surfaces of brucite crystals were grafted producing expansions, attributed to the arrangement of the grafted species between the layers.

Ácidos siálicos: da compreensão do seu envolvimento em processos biológicos ao desenvolvimento de fármacos contra o agente etiológico da gripe

Sialic acids are nine-carbon carbohydrates that occur widely in nature and occupy the terminal portions of some glycoproteins and glycolipids of cell membranes. These carbohydrates are closely involved in cell-cell interactions and in processes such as microbial infection, inflammation, etc. Studies on the participation of sialic acids in biological processes have provided comprehension about their role in the infection by the influenza virus, the causal agent of flu. In this article, we present an overview of the importance of sialic acids in the influenza virus infection and how the knowledge of their involvement in this process has allowed the development of selective and efficient drugs against the virus.

Estudo espectroscópico de complexos de Eu3+, Tb3+ E Gd3+ com ligantes derivados de ácidos dicarboxílicos

Complexes of Eu3+, Tb3+ and Gd3+ with dipicolinic acid, chelidamic acid and chelidonic acid have been synthesized in order to study the effect of the substituent groups on the luminescence of the lanthanide complexes. The luminescence of the Eu3+ and Tb3+ complexes was quantified by quantum yield measurements. The complexes of Gd3+ have been used to determine the energies of the triplet states of the ligands. The Tb3+ complex synthesized with dipicolinic acid presented the highest quantum yield due to the energy difference between the triplet state of the dipicolinic acid and the emitting level of the Tb3+ ion.

Titulação potenciométrica aplicada na determinação de ácidos graxos livres de óleos e gorduras comestíveis

Free fatty acids are a measure of evaluating fats and oils, submitted to abusive conditions, besides being a quality characteristic of edible vegetable oils. The official method of determination (AOCS Ca 5a-40, 2004) is based on titration, using phenolphthalein as an indicator. For crude and degummed oils, the titration end point is difficult to be observed due to the high level of pigments, resulting in dark solutions. In this case and others, such as self-life studies, in which sample quantities are limited, potentiometric titration may be a very good alternative.

Efeito dos ácidos hexenurônicos e da lignina no desempenho da ozonólize, em diferentes pHs da reação

The effect of pH on the performance of the ozonolysis stage in pulp production was evaluated for conventional and acid treated brown and oxygen delignified eucalyptus kraft pulps. The objective was to determine separately the effects of lignin and hexenuronic acid on the performance of the ozonolysis stage. The reaction of ozone with hexenuronic acid is less sensitive to pH than the reaction of ozone with lignin. The efficiency and the selectivity of the reaction of ozone with pulp decreases after removal of hexenuronic acids. Increasing up to 7.0 the pH during the ozonolysis is viable in the sequence Z/D(EOP)D, resulting in savings of H2SO4 (8,5 kg/tsa) and NaOH (5 kg/tsa), but is not recommended in the sequence Z/ED(PO).

Otimização das condições de produção de ésteres etílicos a partir de óleo de peixe com elevado teor de ácidos graxos ômega-3

The production of ethyl esters by alcoholysis is an alternative for splitting triacylglycerols due to the possibility of using low temperatures, which results in oxidative protection of the polyunsaturated fatty acids. Ethyl esters produced under mild conditions of temperature could be used as substrate for obtaining structured lipids. The reaction parameters of production of ethyl esters from fish oil with high content of omega-3 fatty acids by alcoholysis were optimized using response surface methodology. An experimental design (2³) (with levels +1 and -1, six axial points with levels -alpha and +alpha and three central points) was applied. The variables investigated were concentration of catalyst, amount of ethyl alcohol and temperature. Ethyl ester conversion was monitored by high performance size exclusion chromatography (HPSEC) and the best result obtained was 95% conversion rate. The optimal conditions were 40 °C, 1% of NaOH and 36% of ethanol.

Anéis aromáticos condensados e relação E4/E6: estudo de ácidos húmicos de gleissolos por RMN de 13C no estado sólido utilizando a técnica CP/MAS desacoplamento defasado

In this work, seven samples of humic acids extracted from gleysoils were investigated. These studies, using NMR CP/MAS 13C techniques, did not show significant correlation between the E4/E6 ratio and the degree of aromaticity. However, dipolar dephasing (DD) measurements of condensed aromatic or substituted carbons showed a negative correlation of 0.94. Also, there was a good correlation between the amount of semiquinone free radicals measured by the EPR technique and condensed aromatic rings measured by NMR CP/MAS 13C with the DD technique. The content of semiquinone free radicals was quantified by EPR spectroscopy and was correlated with the humification (degree of aromaticity) of the humic substances. The results indicated that the E4/E6 ratio identifies the degree of aromatic rings condensation. It was also found that the degree of aromaticity, measured by NMR, as frequently presented in the literature (by conventional CP/MAS), underestimates aromatic rings in condensed structures.

Influência de desproteinizantes ácidos na quantificação da glutationa reduzida eritrocitária por CLAE-UV

Large differences in reduced glutathione (GSH) levels have been found in different investigations, also in healthy people. GSH oxidation in vitro has been associated with sample acidification in the presence of oxihemoglobin. In this work, the influence of different acids on GSH determination utilizing HPLC with UV detection was evaluated. The results showed that metaphosphoric acid and sulfosalicylic acid were inadequate for analysis, because metaphosphoric acid showed to be inefficient for deproteinization and with sulfosalicylic acid loss of GSH was observed. Trichloroacetic acid did not effect GSH quantification, since the deproteinized form was immediately derivatized with 5, 5´-dithio-bis (2-nitrobenzoic) acid. Methods with TCA deproteinization presented linear results from 0.5 to 3.0 mM. The correlation coefficient between aqueous curves and GSH spiked RBC exceeded 0.99. Precision calculations showed CV lower than 10% and bias within ± 10% for concentrations of 0.5; 1.5 and 3.0 mM GSH. The recovery was higher than 94%. Moreover, GSH blood concentrations were independent of hemoglobin concentrations.

Propriedades ácido-base e de complexação de ácidos húmico e fúlvico isolados de vermicomposto

Proton binding properties of humic and fulvic acids were studied by potentiometric titration. Carboxylic groups were the predominant ionizable sites in comparison to phenolic and amine groups. Total acidity of fulvic acid was 12 x 10-3 mol g-1, a number significantly higher than that obtained for humic acid (5.2 x 10-3 mol g-1). Copper ion binding was evaluated at pH 4, 5 and 6 by potentiometric titration with an ion selective electrode for Cu(II). Differential stability constants and complexation capacities were systematically higher for humic acid, despite its lower number of ionizable sites in comparison with fulvic acid.

Terpenos e ácidos graxos de Dipteryx lacunifera Ducke

This paper describes the isolation of the furanocassane-type diterpene, named vinhaticoic acid, along with beta-farnesene and spatulenol from fruit shells of D. lacunifera. Structural determinations were accomplished by chemical derivatization and spectral analysis, including 1D and 2D NMR and X-ray crystallography. The fatty portion was extracted from the fruit kernels, transesterfied and analysed by HRGC/MS. Oleic acid (75.8 ± 4.3%) was the major component. Essential oil extracted from the fruit shells of D. lacunifera was analysed by HRGC/MS and nine sesquiterpenes were identified; beta-farnesene (48.6%) and spatulenol (21.61%) were the major constituents.

Efecto de la suplementación con ácidos grasos de cadena media sobre la evolución de peso en lechones con poco peso al nacimiento

La evolución de peso en los períodos de lactación y transición de 583 lechones fue estudiada mediante un análisis estadístico, evaluando el efecto de la suplementación con ácidos grasos de cadena media (AGCM) en lechones con poco peso al nacimiento. 188 de los 375 lechones que nacieron con un peso al nacimiento (PN) <1250 g recibieron 3mL de AGCM cada 24 h durante los primeros 3 días de vida; su peso medio al destete (día 28) fue inferior respecto al grupo control (lechones no suplementados) (-114,17 g). No obstante, 106 de los 180 lechones nacidos con un PN <1000 g fueron suplementados, y su peso medio al destete y a finales de transición (día 63) fue superior respecto al grupo control (destete: +315,16 g; día 63: +775,47 g). Finalmente, los lechones suplementados con PN<800 g tuvieron los peores resultados: su diferencia de peso medio al destete fue de -177,58 g respecto al grupo control. Por lo tanto, en esta prueba fueron estudiados los lechones con un PN entre 800 y 999 g porque el grupo suplementado al destete tuvo una diferencia de peso medio considerable respecto al grupo control:+511,58 g. Asimismo, considerando una probabilidad de error inferior a 0,05, no hubieron diferencias significativas en las diferentes categorías de PN analizadas. De todas maneras, es importante destacar el alto grado de significación en la suplementación con AGCM en lechones con PN entre 800 y 999g (P=0,059). Por otra parte, el PN del grupo suplementado con PN<1000 g fue inferior que el del grupo no suplementado con PN<1000 g; esta diferencia de PN fue significativa (P=0,004) y como consecuencia el grado de significación en la suplementación con AGCM en lechones con PN entre 800 y 999 g fue inferior al esperado. Además, en esta prueba se incluyeron algunos resultados generales y también un análisis simple de supervivencia, aunque no era el objetivo principal

Lipídios estruturados obtidos a partir da mistura de gordura de frango, sua estearina e triacilgliceróis de cadeia média: I- Composição em ácidos graxos e em triacilgliceróis

The purpose of this study is to analyze the interactions that occur in binary and ternary fat blends between medium and long chain triacylglycerols and their structured lipids obtained by chemical interesterification through the analysis of their physico-chemical properties. The synthesized structured triacylglycerols presented from 14.8 to 58.4% medium chain fatty acids, from 15.7 to 37.2% saturated fatty acids, from 19.2 to 47.5% monounsaturated fatty acids, and from 6.7 to 15.2% essential fatty acids. Chemical interesterification modified the behavior of binary and ternary mixtures and new types of triacylglycerol groups were formed.

Síntese de padrões cromatográficos e estabelecimento de método para dosagem da composição de ésteres de ácidos graxos presentes no biodiesel a partir do óleo de babaçu

Several alkyl esters were synthesized, purified, characterized by ¹H NMR and employed as standards for establishing chromatographic methods to monitor their formation in the synthesis of biodiesel. The efficiency of the chromatographic methods was confirmed with the products of enzymatic transesterification of babassu oil with different alcohols (C2 to C4), using Lipozyme as catalyst.

Perfil de ácidos graxos e avaliação da alteração em óleos de fritura

The present study had the purpose of evaluating the profile of fatty acids and the total alteration of cottonseed, sunflower and palm oils brought about during discontinued frying processes of cassava frozen chips. An increase in the percentage of saturated fatty acids and a decrease in polyunsaturated fatty acids was observed, regardless of the type of oil used. With regard to the oil's global alteration, the results showed that palm oil, the most saturated one, underwent less alteration. However, none of the oils presented total polar compound values above the limits prescribed.