3 resultados para Ácido glutâmico Teses
em Repositório Institucional da Universidade de Aveiro - Portugal
Resumo:
The introduction of chemicals into the environment by human activities may represent a serious risk to environmental and human health. Environmental risk assessment requires the use of efficient and sensitive tools to determine the impact of contaminants on the ecosystems. The use of zebrafish for the toxicity assessment of pharmaceuticals, drugs, and pollutants, is becoming well accepted due to zebrafish unique advantages for the screening of compounds for hazard identification. The aim of the present work is to apply toxicogenomic approaches to identify novel biomarkers and uncovered potential modes of action of classic and emergent contaminants able to disrupt endocrine systems, such as the Retinoic Acid Receptor, Retinoid X Receptor and the Aryl Hydrocarbon Receptor. This study relies on different nuclear and cytosolic protein receptors and other conditional (ligand- or stress- activated) transcriptional factors that are intimately involved in the regulation of defensome genes and in mechanisms of chemical toxicity. The transcriptomic effects of organic compounds, endogenous compounds, and nanoparticles were analysed during the early stages of zebrafish development. Studying the gene expression profiles of exposed and unexposed organisms to pollutants using microarrays allowed the identification of specific gene markers and to establish a "genetic code" for the tested compounds. Changes in gene expression were observed at toxicant concentrations that did not cause morphological effects. Even at low toxicant concentrations, the observed changes in transcript levels were robust for some target genes. Microarray responses of selected genes were further complemented by the real time quantitative polymerase chain reaction (qRT-PCR) methodology. The combination of bio-informatic, toxicological analyses of differential gene expression profiles, and biochemical and phenotypic responses across the treatments allowed the identification of uncovered potential mechanisms of action. In addition, this work provides an integrated set of tools that can be used to aid management-decision making by improving the predictive capability to measure environmental stress of contaminants in freshwater ecosystems. This study also illustrates the potential of zebrafish embryos for the systematic, large-scale analysis of chemical effects on developing vertebrates.
Resumo:
A reao entre o xido de magnsio (MgO) e o fosfato de monoamnio (MAP), temperatura ambiente, origina os cimentos de fosfato de magnsio, materiais caracterizados pela sua presa rpida e pelas excelentes propriedades mecnicas adquiridas precocemente. As propriedades finais so dependentes, essencialmente, da composio do cimento (razo molar magnsia:fosfato e utilizao de retardantes de presa) mas tambm so influenciadas pela reatividade da magnsia utilizada. Neste trabalho, a reao foi caracterizada atravs do estudo da influncia da razo molar MgO:MAP (variando de 1:1 at 8:1), da presena e teor de aditivos retardantes (cido brico, cido ctrico e tripolifosfato de sdio) e da variao da rea superficial especfica da magnsia (conseguida por calcinao do xido), no tempo de presa, na temperatura mxima atingida e nas fases cristalinas finais formadas. A reao de presa pode ser comparada hidratao do cimento Portland, com a existncia de 4 estgios (reao inicial, induo, acelerao e desacelerao), com a diferena que estes estgios ocorrem a velocidade muito mais alta nos cimentos de fosfato de magnsio. Este estudo foi realizado utilizando a espetroscopia de impedncias, acompanhada pela monitorizao da evoluo de temperatura ao longo do tempo de reao e, por paragem de reao, identificando as fases cristalinas formadas. A investigao do mecanismo de reao foi complementada com a observao da microestrutura dos cimentos formados e permitiu concluir que a origem da magnsia usada no afeta a reao nem as propriedades do cimento final. A metodologia de superfcie de resposta foi utilizada para o estudo e otimizao das caractersticas finais do produto, tendo-se mostrado um mtodo muito eficaz. Para o estudo da variao da rea superficial especfica da magnsia com as condies de calcinao (temperatura e tempo de patamar) usou-se o planeamento fatorial de experincias tendo sido obtido um modelo matemtico que relaciona a resposta da rea superficial especfica da magnsia com as condies de calcinao. As propriedades finais dos cimentos (resistncia mecnica compresso e absoro de gua) foram estudadas utilizando o planeamento simplex de experincias, que permitiu encontrar modelos que relacionam a propriedade em estudo com os valores das variveis (razo molar MgO:MAP, rea superficial especfica da magnsia e quantidade de cido brico). Estes modelos podem ser usados para formular composies e produzir cimentos com propriedades finais especficas.
Resumo:
The development of mining activities over thousands of years in the region of Aljustrel is nowadays visible as a vast area of ore tailings, slag and host rocks of sulphides mineralization. The generation of acidic waters by the alteration of pyritic minerals - Acid Mine Drainage (AMD) - causes a significant impact on the river system both in the south of the village (Rib . gua Forte) and in the north of it (Rib . gua Azeda and Barranco do Farrobo), which is reflected in extremely low pH values (< 3) and high concentrations of As, Cd, Cu, Fe, Mn, Pb, Zn and sulphates. This study aimed to assess the environmental impacts extent, integrating geochemical (surface waters and stream sediments) and biological (diatoms) parameters. Three groups of sites were defined, based on sediments and water analysis, which integration with diatom data showed the same association of groups: Group 1- impacted, with acidic pH (1.9-5.1), high metal contents (0.4-1975 mg L-1) and Fe-Mg-sulphate waters, being metals more bioavailable in waters in cationic form (Me2+); mineralogically the sediments were characterized by phyllosilicates and sulphates/oxy-hydroxysulphate phases, easily solubilized, retaining a high amount of metals when precipitated; dominant taxon was Pinnularia aljustrelica (a new species); Group 2- slightly impacted, weak acid to neutral pH (5.0-6.8), metal contents not so high (0.2-25 mg L-1) and Fe-Mg-sulphate to Mg-chloride waters; dominant taxa were Brachysira neglectissima and Achnanthidium minutissimum; Group 3- unimpacted, alkaline pH (7.0-8.4), low metal contents (0-7 mg L-1) with Mg-chloride waters. In this group, metals were associated to the primary phases (e.g. sulphides), not so easily available; the existence of high chloride contents explained the presence of typical taxa of brackish/marine (e.g. Entomoneis paludosa) waters. Taxonomical aspects of the diatoms were studied (discovery of a new species: Pinnularia aljustrelica Luis, Almeida et Ector sp. nov.), as well as morphometric (size decrease of diatoms valves, as well as the appearance of deformed valves of Eunotia exigua in Group 1 and A. minutissimum in Group 2) and physiological (effective to assess the effects of metals/acidity in the photosynthetic efficiency through PAM Fluorometry) aspects. A study was carried out in an artificial river system (microcosm) that aimed to mimic Aljustrels extreme conditions in controlled laboratory conditions. The chronic effects of Fe, SO42- and acidity in field biofilms, inoculated in the artificial rivers, were evaluated as well as their contribution to the communities tolerance to metal toxicity, through acute tests with two metals (Cu and Zn). In general, the effects caused by low pH values and high concentrations of Fe and SO42- were reflected at the community level by the decrease in diversity, the predominance of acidophilic species, the decrease in photosynthetic efficiency and the increase of enzymatic (e.g. catalase, superoxide dismutase) and non-enzymatic activities (e.g. total glutathione and total phytochelatins). However, it was possible to verify that acidity performed a protective effect in the communities, upon Cu and Zn addition. A comparative study between Aljustrel mining area and New Brunswick mining area was carried out, both with similar mining and geological conditions, reflected in similar diatom communities in both mines, but in very different geographic and climatic areas.
