A interação entre ácidos fúlvicos aquáticos (AFA) de região tropical com cloro e formação de trihalometanos foi estudada por fluorescência. As substâncias húmicas aquáticas (SHA) foram extraídas de córrego com coloração escura (localizado em uma área de proteção ambiental perto da cidade de Cubatão-SP, Brasil) utilizando resina XAD 8, de acordo com o procedimento recomendado pela Sociedade Internacional de Substâncias Húmicas. As medidas de fotoluminescência foram feitas em espectrômetro Perkin Elmer utilizando-se amostras de AFA tratadas e sem tratamento com cloro em diferentes tempos de reação (1, 24, 48, 72 e 168 h) e concentrações de cloro (2,5; 5,0; 10,0 e 20,0 mg L -1 ). A intensidade de fluorescência relativa foi significativamente diminuída com o aumento da concentração de cloro e tempo de reação. A redução na intensidade de fluorescência na região de maiores comprimentos de onda foi interpretada como um indicativo da interação entre os grupos aromáticos condensados dos AFA e o cloro.The interactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes were characterized by fluorescence spectroscopy. The aquatic humic substances (AHS) were isolated from a dark-brown stream (located in a environmental protection area near Cubatão city in São Paulo State, Brazil) by means of the collector XAD 8 according the procedure recommended by the International Humic Substances Society. The photoluminescence measurements were made by using a Perkin Elmer spectrometer; AHS, aquatic humic acids (AHA) and AFA samples were assayed. The interactions of AFA and chlorine were characterized by using different reaction times (1, 24, 48, 72 and 168 h) ). The relative fluorescence intensity for AFA was significantly decreased with the increasing of chlorine concentration and reaction time. The reduction of fluorescence intensity in the region of longer wavelength was interpreted as an indicative of interaction between condensed aromatic groups of AFA and chlorine.

No abstract

The detection of the carcinogenic trihalomethanes (THM) in public water supply systems using low-cost equipment has become an essential feature, since these compounds may be generated as by-products of water-treatment processes. Here we report on a sensor array that extends the concept of an “electronic tongue” to detect small amounts of bromoform, bromodichloromethane and dibromochloromethane, with detection limits as low as 0.02 mg L-1. The sensor array was made up of 10 sensing units, in which nanostructured films of conducting and natural polymers were deposited onto gold interdigitated electrodes. The principle of detection was impedance spectroscopy, with measurements carried out in the range between 1 Hz to 1 MHz. Using data at 1 kHz, at which the electrical response varied considerably by changing the analyte, we demonstrated with principal component analysis (PCA) that samples with the 3 brominated trihalomethanes can be distinguished from each other and for various concentrations.

Estudos do comportamento morfológico dos ácidos fúlvicos foram realizados utilizando a técnica de microscopia de força atômica aliada às técnicas de potencial zeta e espectroscopia de fluorescência. Os resultados mostraram que o ácido fúlvico (AFA) de um rio tropical mudou a sua morfologia quando variado o pH da solução aquosa dos AFA. Em pH ácido a morfologia é mais granular formando aglomerados de altura entre 10-55 nm. Em pH alcalino os valores foram de 2,5-4,0 nm, sendo que a morfologia em condições alcalinas é aberta formando estruturas não granulares. Estes resultados sugerem que para pH 3,5 as interações eletrostáticas são fracas e as ligações de hidrogênio são responsáveis pela formação de agregados, enquanto em pH 9,0 as interações eletrostáticas são fortes devido ao aumento da ionização de grupos fenólicos e ocorrem poucas ligações hidrogênio formando estruturas mais abertas. Os resultados de espectroscopia de fluorescência mostraram mudança na estrutura do AFA de rio tropical em pH alcalino em comparação com a estrutura em pH ácido, corroborando com os resultados obtidos pela AFM.Studies of the morphological behavior of fulvic acids were carried out using the Atomic Force Microscopy technique together with zeta Potential techniques and fluorescence spectroscopy. Results showed that the aquatic fulvic acid (AFA) of a Brazilian River changed its morphology when the AFA aqueous solution had its pH changed. In acid pH the morphology is granular forming 10-55 nm high agglomerates. In alkaline pH values were 2.5-4.0 nm, and the morphology forms non granular structures. These results suggest that for pH 3.0 electrostatic interactions are weak and hydrogen bonding is responsible for the aggregates formation; while at pH 9.0 electrostatic interactions are strong due to the increase in phenolic groups ionization and low hydrogen interaction forming open structures. Fluorescence spectroscopy results confirmed the AFM, that is, a change in the AFA in tropical river in alkaline pH compared to the structure in acid pH.

No abstract

Foram investigadas as interações entre os pesticidas atrazina, imazaquin, metribuzin e paraquat com o polímero condutor poli-(o-etoxianilina)-POEA, utilizando-se as técnicas de microscopia de força atômica (AFM), espectrofotometria de ultravioleta visível (UV-Vis) e espectroscopia de impedância eletroquímica. Os estudos de microscopia de força atômica em filmes automontados mostraram um aumento na rugosidade do filme polimérico, quando exposto aos pesticidas atrazina, imazaquin e metribuzin e uma diminuição na rugosidade do filme polimérico exposto ao pesticida paraquat. Isso evidencia a existência de interação química, provavelmente, ligação iônica entre o nitrogênio presente na POEA e os grupos presentes nos pesticidas estudados. Os estudos de ultravioleta visível mostraram uma maior interação entre a POEA e o pesticida imazaquin. Por meio de medidas elétricas realizadas (espectroscopia de impedância eletroquímica) com um sensor formado por filme de POEA, foi possível distinguir e determinar o limite de detecção dos pesticidas em solução aquosa, o que corrobora com os estudos por AFM e UV-Vis.Interactions of four aromatic nitrogen-heterocyclic herbicides (atrazine, imazaquin, metribuzin and paraquat) with the conductive polymer poly(o-ethoxyaniline)-POEA, were studied with atomic force microscopy (AFM), UV-visible spectrophotometry (UV-Vis) and electrochemical impedance spectroscopy. AFM profiles of self-assembled (SA) films of POEA revealed that the polymer surface became rougher (on the nanoscale) when exposed to atrazine, imazaquin and metribuzin, but slightly smoother in contact with paraquat. This suggested that specific chemical interactions, possibly electroscopic, have occurred between nitrogen atoms in the polymer chain and the dissimilar groups in the various herbicide molecules, during adsorption of the latter onto the film. The UV-Vis analyses indicated a stronger interaction of POEA in solution with imazaquin, that has a special importance for the intended application. Sensors produced by coating microelectrodes with SA films of POEA were used to perform impedance spectroscopy in aqueous solutions of each herbicide. With the resulting data, it was possible to distinguish and set detection limits for each herbicide in water, corroborating AFM and UV-Vis results.

A polymer with characteristics similar to those of humic acids was obtained by synthesis reactions from oxidative polymerization in an alkaline medium using para-benzoquinone, hydroquinone and 4-aminobenzoic acid as precursors. Samples of natural and synthetic humic acid were used to examine the adsorption behavior of Cu 2? ions on these substrates. The mathematical models described by Langmuir and Freundlich equations were applied, yielding the maximum adsorption intensity values K 0 (Langmuir), maximum adsorption capacity, b (Langmuir) and the adsorbent adsorption capacity, m (Freundlich). Based on solubility studies, pH 3 was selected for the development of the adsorption experiment. The Cu 2? ion presented a favorable adsorption, with RL (equilibrium parameter) responses in Langmuir isotherms falling within the desirable ranges.

<p><em>Brazil has a very large surface area and therefore is not always possible the people to have access to all varieties of fruit. Considering this fact, the consumption of frozen fruit pulp has been increase. The aim of this study was to evaluate the content of total phenolics, flavonoids and antioxidant activity of nine commercial frozen fruit pulps. The antioxidant activity was evaluated by the ability to scavenging the 2.2-diphenyl-1-picryl-hydrazil (DPPH) radical, while the phenolic analysis was performed by spectrophotometry. The pulps showed levels of total phenolic compounds ranged from 14.97 mgEAG.100g^-1 (lemon) to 112.40 mgEAG.100g^-1 (orange). The highest content of flavonoids was observed for the raspberry pulp (35.09 mgEQ.100g^-1). The orange pulp showed higher antioxidant capacity, with sequestration percentage of 108.79%, followed by kiwi, peach and tamarind. The results of this study demonstrated that the frozen fruits pulp are good sources of antioxidant compounds and their use should be encouraged among the population.</em></p><p>DOI: 10.14685/rebrapa.v5i3.143</p><p>&nbsp;</p><p><em><br /></em></p>