De Bettencourt A.M.,University of Évora |
Florencio M.H.,FCUL |
Henriques F.F.,New University of Lisbon |
Portela M.I.,University of Évora |
Vilas-Boas L.F.,Institute Tecnologia Quimica e Biologica ITQB
Microchemical Journal | Year: 2011
Arsenic is a type 1 carcinogen and its toxicity is critically dependent on chemical speciation. However, after decades of research, the biogenesis of at least fifty naturally occurring arsenic species is still not well understood.Here, based on experimental work, it is proposed a set of pathways for the formation of multiple arsenic species that might help to clarify the present situation.These are focused on the thiol protein arsenic bond and on its interaction with reactive metabolites. In fact, arsenic bound to glutathione interacting with sulfur adenosyl methionine (SAM), MethylCB12 and AdoCB12, forms a number of complexes that might be key intermediates in arsenic biochemistry. These include dimethylarsino glutathione (DMAG) m/z 412 [M+H]+, synthesized non-enzymatically from glutathione and cacodylate. Trimethylarsonio glutathione (TMAG) m/z 426 [M]+ synthesized from DMA, GSH and SAM, apparently by a classical Challenger methylcarbonium attack. Tetramethyl arsonium ion m/z 135 [M]+ is formed in a third step, apparently by carbanion methylation. The presence of trimethylarsine oxide (TMAO) m/z 137 [M+H]+ is attributed to the hydrolysis of TMAG or TMA, or to carbanion methylation of dimethylarsinoyl glutathione (m/z 428 [M]+) formed from cacodylate and GSH. Cantoni type attacks of DMAG on SAM were unsuccessful, eventually due to competition of the trivalent S+ atom of SAM for the AsIII atom attack. The presence of dimethylarsonio diglutathione (DMADG m/z 717 [M]+), is suggested to result from a GS- attack on dimethylarsenoyl glutathione (m/z 428 [M+H]+). The presence of dimethylarsenoyladenosine (m/z 372 [M+H]+), trimethylarsenosugar adenine (m/z 370 [M]+), and dimethylthioarsenosugar adenine (m/z 388 [M+H]+), is explained by the synthesis of the pecursor dimethylarsonio-adenosine glutathione DMAAG (m/z 661 [M]+), a likely source of oxo-and trimethylated arsenosugars, as well as of thio-arsenosugars by the cleavage of its S-C bond. The results gathered suggest that cell vacuoles might play a major role in arsenic metabolism, and that the dominance of oxo-As sugars, in algae extracts, may be supported by a mechanism of synthesis independent of DMAAG (m/z 661).They also offer an explanation for the reason why arsenobetaine, and tetramethylarsonium are loosely bound to biotic tissues. Four arsenic species new to science, to the best of our knowledge, and a number of known arsenic compounds were synthesized in this work, identified by HPLC-ESI-MSn and FTICR-ESI-MS, and suggestions regarding their mechanisms of synthesis were advanced. These results provide a framework for arsenic biochemistry which may explain the origin of a significant part of arsenic known metabolites. © 2011 Elsevier B.V.
PubMed | CCMM, FCUL, University of Lisbon and DQB
Type: Historical Article | Journal: Historia, ciencias, saude--Manguinhos | Year: 2014
After the Challenger expedition (1872-1878), other nations started to show interest in oceanographic research and organizing their own expeditions. As of 1885, Prince Albert I of Monaco conducted oceanographic campaigns with the collaboration of some of the best marine biologists and physical oceanographers of the day, inventing new techniques and instruments for the oceanographic work. Prince Alberts scientific activity certainly helped kindle the interest of his friend, Dom Carlos I, king of Portugal, in the study of the oceans and marine life. Both shared the need to use photography to document their studies. This article analyzes the role of scientific photography in oceanography, especially in the expeditions organized by the Portuguese monarch.
Monteiro F.,University of Lisbon |
Sebastiana M.,University of Lisbon |
Figueiredo A.,University of Lisbon |
Sousa L.,FCUL |
And 2 more authors.
Functional and Integrative Genomics | Year: 2012
One of the most remarkable pollination strategy in orchids biology is pollination by sexual deception, in which the modified petal labellum lures pollinators by mimicking the chemical (e.g. sex pheromones), visual (e.g. colour and shape/size) and tactile (e.g. labellum trichomes) cues of the receptive female insect species. The present study aimed to characterize the transcriptional changes occurring after pollination in the labellum of a sexually deceptive orchid (Ophrys fusca Link) in order to identify genes involved on signals responsible for pollinator attraction, the major goal of floral tissues. Novel information on alterations in the orchid petal labellum gene expression occurring after pollination demonstrates a reduction in the expression of alkene biosynthetic genes using O. fusca Link as the species under study. Petal labellum transcriptional analysis revealed downregulation of transcripts involved in both pigment machinery and scent compounds, acting as visual and olfactory cues, respectively, important in sexual mimicry. Regulation of petal labellum senescence was revealed by transcripts related to macromolecules breakdown, protein synthesis and remobilization of nutrients. © 2012 Springer-Verlag.
Figueiredo A.,University of Lisbon |
Monteiro F.,University of Lisbon |
Fortes A.M.,University of Lisbon |
Bonow-Rex M.,Julius Kuhn Institute |
And 3 more authors.
Functional and Integrative Genomics | Year: 2012
The oomycete pathogen Plasmopara viticola (Berk. et Curt.) Berl. et de Toni is the causing agent of the destructive downy mildew disease in grapevine. Despite the advances towards elucidation of grapevine resistance mechanisms to downy mildew, increased knowledge of the biological and genetic components of the pathosystem is important to design suitable breeding strategies. Previously, a cDNA microarray approach was used to compare two Vitis vinifera genotypes Regent and Trincadeira (resistant and susceptible to downy mildew, respectively) in field conditions. The same cDNA microarray chip was used to confirm field-based results and to compare both genotypes under greenhouse conditions at 0, 6, and 12 h post-inoculation with P. viticola. Results show that when comparing both cultivars after pathogen inoculation, there is a preferential modulation of several defense, signaling, and metabolism associated transcripts in Regent. Early transcriptional changes are discussed in terms of genetic background and resistance mechanism. This study is the first to directly compare resistant and susceptible cultivars responses as early as 6 hpi with P. viticola, providing several candidate genes potentially related to the expression of resistance traits. © Springer-Verlag 2012.
News Article | February 16, 2017
Galaxies have dramatically grown in size since the early Universe, and elliptical galaxies, in particular, are the largest galaxies in both size and mass. What is the main driver behind the late growth of their outer parts was the question that motivated this study. With disc galaxies, like our Milky Way, it is fairly easy to identify their distinct parts: the central bulge, the disc with its spiral arms, and a halo of stars enveloping the whole. Astronomers can tell, for instance, that the stellar halo is formed mostly by stars from satellite galaxies that merged into them. For elliptical galaxies, however, this is much harder because these galaxies look much like a smooth, featureless cloud of stars. Fernando Buitrago (IA and FCUL) says: "With elliptical galaxies, there is direct evidence of merging of satellite galaxies going on, but it is hard to ascertain that the processes that have been happening for these galaxies to grow their outer envelopes are the same that we see occurring in disc galaxies like our own." Hence, Buitrago and his team set out to investigate the nature of the outskirts of a sample of massive elliptical galaxies when the Universe was half its current age, roughly 6,2 billion years ago. Focusing their research on faint features at great distances from the galactic centre, they could only work with the deepest ever image of the Universe, the Hubble Ultra Deep Field (HUDF). Using the six galaxies that matched their criteria and are recorded in this image, the researchers were able to demonstrate for the first time the existence of extended stellar envelopes in individual massive elliptical galaxies at that period in time. The quality of the information collected in the HUDF, enabled the team to characterise the individual galactic haloes and to place them in the context of the evolutionary history of this type of galaxies. Moreover, Buitrago and his team were able to conclude that, for their sample of massive elliptical galaxies at half the age of the Universe, the outer parts were, like disc galaxies, formed mainly due to the merging of other galaxies. They even attempted to identify in those haloes traces of recent episodes of galactic fusion. The results emerged from the comparison of the sample with mathematical simulations based on the current model of galaxy formation and evolution. The team saw that, in this very case, the simulation and the real data matched very well and that it was possible to infer parallelisms. "In elliptical galaxies, we cannot say 'this is the galactic bulge and this is the halo'," says Buitrago, "All the stars form a huge spheroid, like an immense rugby ball. But when we use a computer simulation, we can track the origin of every part of the simulated galaxy and compare with our real galaxies. Through this method, we identified the process behind the dramatic increase of these galaxies outer parts, and were able to explain how their size evolves." Explore further: A massive galaxy long ago and far away More information: Fernando Buitrago et al. The cosmic assembly of stellar haloes in massive Early-Type Galaxies, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stw3382
Leal S.,FCUL |
Proceedings - 2013 2nd Experiment@ International Conference, exp.at 2013 | Year: 2013
In the last three years, e-lab a real laboratory remotely controlled via the internet, has been an important educational resource in basic and secondary Portuguese schools in subjects like Physics and Chemistry. Since a pilot study performed in late 2009 that e-lab platform is being used in and outside the classroom contributing to increase students' motivation and interest toward scientific subjects. Currently, the e-lab team is interested in performing remote chemistry experiments, which are more difficult to execute in this kind of environment. At this time, the challenge is to create an experiment focused in a chemical equilibrium reaction. © 2013 IEEE.
Arias A.,FCUL |
Bettencourt Da Silva R.J.N.,FCUL |
Camoes M.F.G.F.C.,FCUL |
Talanta | Year: 2013
Abstract: The knowledge of the mass of particulate matter in air, its chemical composition and emission sources is of relevance for taking decisions concerning air quality management in urban areas. The interpretation of these data is a function of the quality of the measurement results expressed by their uncertainties. This study aimed at developing models of the performance of the determination of anions in the water-soluble fraction of atmospheric aerosols, capable of determining, separately, the contribution of aerosols sampling, extraction of water-soluble fraction of atmospheric aerosols and quantification, by ion chromatography, of anions in the extract. The sampling procedure was assessed from the dispersion of results of duplicate parallel sampling after subtracting the analytical component of this dispersion. These models are used to evaluate the adequacy of the measurement procedure for the determination of urban aerosol composition and to support strategies for reducing measurement uncertainty or cost of analysis. The method performance was studied for the following ranges considering extract dilution up to five times: 0.23-8 μg m-3 for chloride and nitrate, and 0.093-3.25 μg m-3 for sulphate. Measurements are fit for the analysis of urban aerosols since the relative expanded measurement uncertainty is smaller than a maximum value of 40%. The percentage contribution of the uncertainty components varies with the analyte and its mass concentration, the major components being 24-93% for the extraction, 43-59% for sampling, 0.2-28% for the interpolation of the sample signal in the calibration curve and 4-8% for air volume measurement. The typical composition of analysed air is: (1.12±0.26) μg m-3, (1.02±0.30) μg m-3 and (0.76±0.22) μg m -3 of chloride, nitrate and sulphate in the water soluble fraction of aerosol, respectively, for a confidence level of approximately 95% considering a coverage factor of 2. © 2012 Elsevier B.V.
Aslanian D.,French Research Institute for Exploitation of the Sea |
Geophysical Journal International | Year: 2010
Torsvik et al. recently presented a revised model for the opening of the South Atlantic Ocean. According to these authors, this new plate tectonic model is internally consistent and consistent with globally balanced plate motion solutions and takes into account realistic intraplate deformation. However, this model shows a number of kinematic and geological problems that we underline here, together with some comparisons with the new kinematic model recently proposed by Moulin et al. © 2010 The Authors Journal compilation © 2010 RAS.
Salgueiro P.A.S.,Laboratorio Of Policia Cientifica |
Borges C.M.F.,FCUL |
Bettencourt da Silva R.J.N.,FCUL
Journal of Chromatography A | Year: 2012
The most popular procedures for the detection of residues of accelerants in fire debris are the ones published by the American Society for Testing and Materials (ASTM E1412-07 and E1618-10). The most critical stages of these tests are the conservation of fire debris from the sampling to the laboratory, the extraction of residues of accelerants from the debris to the activated charcoal strips (ACS) and from those to the final solvent, as well as the analysis of sample extract by gas chromatography-mass spectrometry (GC-MS) and the interpretation of the instrumental signal. This work proposes a strategy for checking the quality of the sample conservation, the accelerant residues transference to final solvent and GC-MS analysis, using internal standard additions. It is used internal standards ranging from a highly volatile compound for checking debris conservation to low volatile compound for checking GC-MS repeatability. The developed quality control (QC) parameters are not affected by GC-MS sensitivity variation and, specifically, the GC-MS performance control is not affected by ACS adsorption saturation that may mask test performance deviations. The proposed QC procedure proved to be adequate to check GC-MS repeatability, ACS extraction and sample conservation since: (1) standard additions are affected by negligible uncertainty and (2) observed dispersion of QC parameters are fit for its intended use. © 2012 Elsevier B.V.
PubMed | FCUL
Type: | Journal: Talanta | Year: 2013
The knowledge of the mass of particulate matter in air, its chemical composition and emission sources is of relevance for taking decisions concerning air quality management in urban areas. The interpretation of these data is a function of the quality of the measurement results expressed by their uncertainties. This study aimed at developing models of the performance of the determination of anions in the water-soluble fraction of atmospheric aerosols, capable of determining, separately, the contribution of aerosols sampling, extraction of water-soluble fraction of atmospheric aerosols and quantification, by ion chromatography, of anions in the extract. The sampling procedure was assessed from the dispersion of results of duplicate parallel sampling after subtracting the analytical component of this dispersion. These models are used to evaluate the adequacy of the measurement procedure for the determination of urban aerosol composition and to support strategies for reducing measurement uncertainty or cost of analysis. The method performance was studied for the following ranges considering extract dilution up to five times: 0.23-8 g m(-3) for chloride and nitrate, and 0.093-3.25 g m(-3) for sulphate. Measurements are fit for the analysis of urban aerosols since the relative expanded measurement uncertainty is smaller than a maximum value of 40%. The percentage contribution of the uncertainty components varies with the analyte and its mass concentration, the major components being 24-93% for the extraction, 43-59% for sampling, 0.2-28% for the interpolation of the sample signal in the calibration curve and 4-8% for air volume measurement. The typical composition of analysed air is: (1.120.26) g m(-3), (1.020.30) g m(-3) and (0.760.22) g m(-3) of chloride, nitrate and sulphate in the water soluble fraction of aerosol, respectively, for a confidence level of approximately 95% considering a coverage factor of 2.