Comparison of AGNES (absence of gradients and Nernstian equilibrium stripping) and SSCP (scanned stripping chronopotentiometry) for trace metal speciation analysis

The free metal ion concentrations obtained by SSCP (stripping chronopotentiometry at scanned deposition potential) and by AGNES (absence of gradients and Nernstian equilibrium stripping) techniques have been compared and the usefulness of the combination of both techniques in the same electrochemical cell for trace metal speciation analysis is assessed. The free metal ion concentrations and the stability constants obtained for lead(II) and cadmium(II) complexation by pyridinedicarboxylic acid, by 40 nm radius carboxylated latex nanospheres and by a humic acid extracted from an ombrotrophic peat bog were determined. Whenever possible, the free metal ion concentrations were compared with the theoretical predictions of the code MEDUSA and with the free metal ion concentrations estimated from ion selective electrodes (ISE). SSCP values were in agreement with the ones obtained by AGNES, and both of them agreed reasonably with the ISE values and the theoretical predictions. For the lead(II)-humic acid, it was not possible to obtain the stability constants by SSCP due to the heterogeneity effect. However, using AGNES it is possible to obtain, for these heterogeneous systems, the free bulk metal concentration, which allows us to retrieve the stability constant at bulk conditions.

Application of permeation liquid membrane and scanned stripping chronopotentiometry to metal speciation analysis of colloidal complexes

The potential of permeation liquid membrane (PLM) to obtain dynamic metal speciation information for colloidal complexes is evaluated by measurements of lead(II) and copper(II) complexation by carboxyl modified latex nanospheres of different radii (15, 35, 40 and 65 nm). The results are compared with those obtained by a well characterized technique: stripping chronopotentiometry at scanned deposition potential (SSCP). Under the PLM conditions employed, and for large particles or macromolecular ligands, membrane diffusion is the rate-limiting step. That is, the flux is proportional to the free metal ion concentration with only a small contribution from labile complexes. In the absence of ligand aggregation in the PLM channels, good agreement was obtained between the stability constants determined by PLM and SSCP for both metals.

Metal speciation dynamics in colloidal ligand dispersions. Part 3: Lability features of steady-state systems

A lability criterion is developed for dynamic metal binding by colloidal ligands with convective diffusion as the dominant mode of mass transport. Scanned stripping chronopotentiometric measurements of Pb(II) and Cd(II) binding by carboxylated latex core-shell particles were in good agreement with the predicted values. The dynamic features of metal ion binding by these particles illustrate that the conventional approach of assuming a smeared-out homogeneous ligand distribution overestimates the lability of a colloidal ligand system. Due to the nature of the spatial distribution of the binding sites, the change in lability of a metal species with changing ligand concentration depends on whether the ligand concentration is varied via manipulation of the pH (degree of protonation) or via the particle concentration. In the former case the local ligand density varies, whereas in the latter case it is constant. This feature provides a useful diagnostic tool for the presence of geometrically constrained binding sites.

Metal speciation dynamics in colloidal ligand dispersions. Part 2: electrochemical lability

We investigate the dynamic nature of metal speciation in colloidal dispersions using a recently proposed theory [J.P. Pinheiro, M. Minor, H.P. Van Leeuwen, Langmuir, 21 (2005) 8635] for complexing ligands that are situated on the surface of the particles. The new approach effectively modifies the finite rates of association/dissociation of the colloidal metal complexes, thus invoking consideration of the two basic dynamic criteria: the association/dissociation kinetics of the volume complexation reaction (the ‘‘dynamic’’ criterion), and the interfacial flux of free metal to a macroscopic surface due to dissociation of complex species (the ‘‘lability’’ criterion). We demonstrate that the conventional approach for homogeneous systems that assume a smeared-out ligand distribution, overestimates both the dynamics and the lability of metal complexes when applied to colloidal ligands. It is also shown that the increase of lability with increasing particle radius, as expected for a homogeneous solution, is moderated for spherical microelectrodes and practically eliminated for planar electrodes.

Assessing the atmospheric oscillations effects on the biology of the bullet tuna (Auxis rochei) and its possible linkage with global warming

Dissertação de mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve; Instituto Español de Oceanografia; 2015

Lancefield group C and G streptococci in human infection : molecular typing, virulence and antimicrobial susceptibility

Tese de doutoramento, Ciências e Tecnologias da Saúde (Microbiologia), Universidade de Lisboa, Faculdade de Medicina, 2014

Role of β-adrenergic signaling in ovarian cancer cells biology

Tese de mestrado. Biologia (Biologia Evolutiva e do Desenvolvimento). Universidade de Lisboa, Faculdade de Ciências, 2014

Biology and ecology of the white prawn Palaemon longirostris H. Milne Edwards, 1837 (Crustacea, Decapoda, Palaemonidae) in the Mira River, Portugal

Tese de doutoramento, Biologia (Ecografia), Universidade de Lisboa, Faculdade de Ciências, 2014

Metagenomic systems biology: frameworks for modeling and characterizing the gut microbiome

Thesis (Ph.D.)--University of Washington, 2014

ß-lactamases in the biochemistry and molecular biology laboratory

β-lactamases are hydrolytic enzymes that inactivate the β-lactam ring of antibiotics such as penicillins and cephalosporins. The major diversity of studies carried out until now have mainly focused on the characterization of β-lactamases recovered among clinical isolates of Gram-positive staphylococci and Gram-negative enterobacteria, amongst others. However, only some studies refer to the detection and development of β-lactamases carriers in healthy humans, sick animals, or even in strains isolated from environmental stocks such as food, water, or soils. Considering this, we proposed a 10-week laboratory programme for the Biochemistry and Molecular Biology laboratory for majors in the health, environmental, and agronomical sciences. During those weeks, students would be dealing with some basic techniques such as DNA extraction, bacterial transformation, polymerase chain reaction (PCR), gel electrophoresis, and the use of several bioinformatics tools. These laboratory exercises would be conducted as a mini research project in which all the classes would be connected with the previous ones. This curriculum was compared in an experiment involving two groups of students from two different majors. The new curriculum, with classes linked together as a mini research project, was taught to a major in Pharmacy and an old curriculum was taught to students from environmental health. The results showed that students who were enrolled in the new curriculum obtained better results in the final exam than the students who were enrolled in the former curriculum. Likewise, these students were found to be more enthusiastic during the laboratory classes than those from the former curriculum.

Effect of temperature and prey in the biology of Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae)

Dissertação de Mestrado, Biotecnologia em Controlo Biológico, 18 de Dezembro de 2013, Universidade dos Açores.

Potential pathogenic fungi assessment through molecular biology in cork industry

Portugal has been the world leader in the cork sector in terms of exports, employing ten thousands of workers. In this working activity, the permanent contact with cork may lead to the exposure to fungi, raising concerns as potential occupational hazards in cork industry. The application of molecular tools is crucial in this setting, since fungal species with faster growth rates may hide other species with clinical relevance, such as species belonging to P. glabrum and A. fumigatus complexes. A study was developed aiming at assessing fungal contamination due to Aspergillus fumigatus complex and Penicillium glabrum complex by molecular methods in three cork industries in the outskirt of Lisbon city.

Analysis of chromium behaviour and speciation during the electrodialytic process

The interest in chromium (Cr) arises from the widespread use of this heavy metal in various industrial processes that cause its release as liquid, solid and gaseous waste into the environment. The impact of Cr on the environment and living organisms primarily depends on its chemical form, since Cr(III) is an essential micronutrient for humans, other animals and plants, and Cr(VI) is highly toxic and a known human carcinogen. This study aimed to evaluate if the electrodialytic process (ED) is an appropriate treatment for Cr removal, through a critical overview of Cr speciation, before and after the ED experiments, to assess possible Cr(III)-Cr(VI) interconversions during the treatment. ED was the treatment technique applied to two types of matrices containing Cr: chromate copper arsenate (CCA) contaminated soil and municipal solid waste incineration (MSWI) fly ash. In order to study Cr remediation, three EDR set-ups were used: a new set-up, the combined cell (2/3C or 3/2C), with three compartments, alternating current between two anodes and different initial experimental conditions, one set-up with three compartments (3C cell) and the other set-up with two compartments (2C cell). The Cr removal rates obtained in this study were between 10-36% for the soil, and 1-13% for the fly ash. The highest Cr removal rates were achieved in the 26 days experiments: 36% for the soil, 13% for the fly ash. Regarding the 13 days experiments, the highest Cr removal rates were attained with the 2/3C set-up: 24% for the soil, 5% for the fly ash. The analysis of Cr(VI) was performed before and after ED experiments to evaluate eventual changes in Cr speciation during the treatment. This analysis was conducted by two methods: USEPA Method 3060A, for the extraction of Cr(VI); and Hach Company Method 8023, for the detection of Cr(VI). Despite the differences in Cr total concentration, both matrices presented a similar speciation, with Cr(III) being the main species found and Cr(VI) less than 3% of Cr total, before and after the treatment. For fly ash, Cr(VI) was initially below the detection limit of the method and remained that way after the treatment. For soil, Cr(VI) decreased after the treatment. Oxidation of Cr(III) to Cr(VI) did not occur during the ED process since there was no increase in Cr(VI) in the matrices after the treatment. Hence, the results of this study indicate that ED is an appropriate technique to remediate matrices containing Cr because it contributes to Cr removal, without causing Cr(III)-Cr(VI) interconversions.

Sympatric speciation in palms on an oceanic island.

The origin of species diversity has challenged biologists for over two centuries. Allopatric speciation, the divergence of species resulting from geographical isolation, is well documented. However, sympatric speciation, divergence without geographical isolation, is highly controversial. Claims of sympatric speciation must demonstrate species sympatry, sister relationships, reproductive isolation, and that an earlier allopatric phase is highly unlikely. Here we provide clear support for sympatric speciation in a case study of two species of palm (Arecaceae) on an oceanic island. A large dated phylogenetic tree shows that the two species of Howea, endemic to the remote Lord Howe Island, are sister taxa and diverged from each other well after the island was formed 6.9 million years ago. During fieldwork, we found a substantial disjunction in flowering time that is correlated with soil preference. In addition, a genome scan indicates that few genetic loci are more divergent between the two species than expected under neutrality, a finding consistent with models of sympatric speciation involving disruptive/divergent selection. This case study of sympatric speciation in plants provides an opportunity for refining theoretical models on the origin of species, and new impetus for exploring putative plant and animal examples on oceanic islands.