Silica-borax pearl samples impregnated with 0.17 and 0.64% Cr3+ were characterized by specific surface area measurements, UV-Vis spectroscopy, energy-dispersive X-ray fluorescence and laser-scanning confocal microscopy. Pearl stability against oxidizing conditions was tested by adding samples to an aqueous hydrogen peroxide solution. The reaction was examined by UV-Vis spectroscopic measurements of the supernatant and laser-scanning confocal microscopy images of the substrate. Overall, hydrogen peroxide-induced Cr3+ to Cr6+ oxidation across the solid-liquid interface promoted solid matrix cleavage pearl degradation and concomitant formation of multiple scattering centers was observed. A dual-detection scheme was employed in the confocal microscopy measurements allowing us to separate scattering and absorptive contributions to the observed signals. The confocal microscopy images indicate that Cr3+ oxidation induced by hydrogen peroxide solutions occurs throughout the entire pearl sample and indicate that oxidation reactions induce leakage of chromate ion into aqueous solutions.

A reação entre um novo derivado de imidazol, 3,5-bis((1H-imidazol-1-il)metil)anilina (BIm), e o triéster de fosfato dietil 2,4-dinitrofenil fosfato (DEDNPP), que procede por um mecanismo SN2(P), é substancialmente acelerada em presença do surfactante catiônico brometo de cetiltrimetrilamônio (CTAB) e do surfactante aniônico dodecil sulfato de sódio (SDS). Tal efeito micelar atípico ilustra o emprego de efeitos hidrofóbicos dos reagentes para otimizar o efeito catalítico de micelas aquosas. Tal observação é importante e útil no planejamento de modelos miméticos de reações biológicas, já que a melhoria da incorporação dos reagentes aumentará efetivamente a qualidade dos sistemas biomiméticos, sendo que ambos os surfactantes catiônico e aniônico poderão atuar como nanoreatores homogêneos, concentrando os reagentes neutros hidrofóbicos.

The reaction of a new imidazole derivative, 3,5-bis((1H-imidazol-1-yl)methyl)aniline (BIm), and the model triester diethyl 2,4-dinitrophenyl phosphate (DEDNPP), which proceeds via a SN2(P) mechanism, is substantially enhanced in the presence of either cationic cetyltrimethylammonium bromide (CTAB) or anionic sodium dodecyl sulfate (SDS). This unusual micellar effect illustrates the use of the hydrophobic character of the reactants to enhance micellar catalysis. This is an important and useful guideline in planning mimics for biological reactions, because improving incorporation will increase the quality of the biomimetic systems, and both cationic or anionic surfactants will act as homogeneous nanoreactors concentrating the neutral, hydrophobic reactants.

O estudo da sorção e dessorção de Cd(II) na interface de vários sorventes e soluções aquosas mostrou que a capacidade de troca depende do tipo de sorvente, do pH e do sistema tampão. Tampões como succinato e citrato, os quais são bons complexantes de Cd(II) suprimem completamente a incorporação dentro dos diferentes sorventes. Na presença do tampão Tris, a capacidade de troca observada decresce na seguinte ordem, gama-alumina > montmorilonita > caolinita <FONT FACE=Symbol>»</FONT> sílica. A precipitação de Cd(II) torna-se importante na presença de bicarbonato aquoso na faixa de pH 5,5-7. As isotermas observadas para as diferentes argilas mostram saturação em concentração bastante altas de Cd(II). Isto sugere que em águas naturais, a sorção e distribuição de Cd(II) entre as fases geoquímicas dos sedimentos deve seguir uma relação linear. A cinética de dessorção de Cd(II) da superfície da montmorilonita, na presença do íon citrato, mostra que este é um ligante orgânico eficiente para remover o Cd(II) ligado em sítios facilmente acessíveis. O processo ocorre em duas etapas, com liberação inicial de aproximadamente 70% do Cd(II), seguido pela liberação lenta do metal de sítios com acesso controlado pela difusão.

The sorption and desorption of Cd(II) that occurs at the interface between several sorbents and aqueous solutions has been investigated and it is shown that the observed exchange capacity depends on the type of sorbent, the pH and the buffering system. Buffers such as succinate and citrate, which are good complexants of Cd(II) completely supress its incorporation into the different sorbents. In the presence of Tris buffer the observed exchange capacity decreases in the order gamma-alumina > montmorillonite > kaolinite <FONT FACE=Symbol>»</FONT> silica, while precipitation is important in the presence of aqueous bicarbonate in the pH range 5.5-7. The sorption data fit with general purpose isotherms well, and the sorption isotherm shows saturation at rather high concentrations of Cd(II) in both clays. This suggests that under many experimental conditions in natural waters, the sorption and distribution of Cd(II) between geochemical phases of sediments should follow a linear relationship. The kinetics of desorption from montmorillonite, in the presence of citrate ion, is particularly important, showing that this efficient organic ligand removes all the Cd(II) bound to readily accessible sites in a fast step, while removal of Cd(II) from sites with diffusion-restricted access is much slower.

Adopting the perspective of human health risk assessment, an interdisciplinary research group has been investigating since 1998 the quality of mussels and oysters cultivated in coastal zones of Santa Catarina State. Evaluation of physico-chemical parameters considered relevant in measuring the degree of eutrophication showed values compatible with the dynamics of well balanced environmental systems. Concentrations of metallic and semi-metallic elements in seawater and bivalves were found to be similar to or lower than those found in Chile, Greenland and the USA. Further investigations focusing upon sediments will provide new and useful data for the management of sustainable mariculture strategies in Brazil.