Browsing by Author "Ferreira, Jorge Amaral"
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- Ab-initio simulations for the Cu-Sb-S systemsPublication . Ferreira, Jorge Amaral; Braga, Maria Helena
- Biomineralization studies on cellulose membrane exposed to biological fluids of Anodonta cygneaPublication . Lopes, Anabela; Lima, Manuel Lopes; Ferreira, Jorge Amaral; Araújo, Sandra; Hinzmann, Mariana F.; Oliveira, José; Rocha, António; Domingues, Bernardo; Bobos, Iuliu; Machado, JorgeThe present work proposes to analyse the results obtained under in vitro conditions where cellulose artificial membranes were incubated with biological fluids from the freshwater bivalve Anodonta cygnea. The membranes were mounted between two half ‘Ussing chambers’ with different composition solutions in order to simulate epithelial surfaces separating organic fluid compartments. The membrane surfaces were submitted to two synthetic calcium and phosphate solutions on opposite sides, at pH 6.0, 7.0 or 9.0 during a period of 6 hours. Additional assays were accomplished mixing these solutions with haemolymph or extrapallial fluid from A. cygnea, only on the calcium side. A selective ion movement, mainly dependent on the membrane pore size and/or cationic affinity, occurred with higher permeability for calcium ions to the opposite phosphate chamber supported by calcium diffusion forces across the cellulose membrane. In general, this promoted a more intense mineral precipitation on the phosphate membrane surface. A strong deposition of calcium phosphate mineral was observed at pH 9.0 as a primary layer with a homogeneous microstructure, being totally absent at pH 6.0. The membrane showed an additional crystal phase at pH 7.0 exhibiting a very particular hexagonal or cuttlebone shape, mainly on the phosphate surface. When organic fluids of A. cygnea were included, these crystal forms presented a high tendency to aggregate under rosaceous shapes, also predominantly in the phosphate side. The cellulose membrane was permeable to small organic molecules that diffused from the calcium towards the phosphate side. In the calcium side, very few similar crystals were observed. The presence of organic matrix from A. cygnea fluids induced a preliminary apatite–brushite crystal polymorphism. So, the present results suggest that cellulose membranes can be used as surrogates of biological epithelia with preferential ionic diffusion from the calcium to the phosphate side where the main mineral precipitation events occurred. Additionally, the organic fluids from freshwater bivalves should be also thoroughly researched in the applied biomedical field, as mineral nucleators and crystal modulators on biosynthetic systems.
- Electron microprobe analysis of cryolitePublication . Guimarães, Fernanda; Silva, Paulo Bravo; Ferreira, Jorge Amaral; Piedade, A. P.; Vieira, M. T. F.A sample of cryolite was studied with a JEOL JXA 8500-F electron microprobe under several operating conditions. A TAP crystal was used to analyse Na and Al and a LDE1 crystal to analyse F. As F and Na are both highly "volatile" elements, special care must be taken during analysis. The measurement order of Na, F and Al is not irrelevant and optimum conditions may also result in different combinations of accelerating voltage, beam current, beam size or counting times. Relevant X-ray signals were recorded in order to investigate the behaviour of the Na Ka and F Ka counts with elapsed time. The incident beam current was also recorded at the same time. In a clear contrast to what has normally been reported in the EPMA analysis of aluminosilicates and silicate glasses, we found that the Na X-ray counts increase with time. This increment of X-rays intensities for sodium in cryolite depends on the operating conditions and is accompanied by a strong migration of fluorine from the beam excitation volume, leading to a decrease in F X-ray counting rates. It was also observed that higher incident beam currents induce higher radiation damage in the mineral. The current instability is consistent with possible electron induced dissociation in the cryolite structure. An analytical protocol was achieved for 6 kV and 15kV accelerating voltage for the correct EPMA analysis of cryolite.
- Electron microprobe analysis of cryolitePublication . Guimarães, Fernanda; Silva, Paulo Bravo; Ferreira, Jorge Amaral; Piedade, A. P.; Vieira, M. T. F.
- Electron microprobe analysis of cryolitePublication . Guimarães, Fernanda; Silva, Paulo Bravo; Ferreira, Jorge Amaral; Piedade, A. P.; Vieira, M. T. F.
- Experimental and first principles study of the Ni-Ti-W systemPublication . Sá, M. Helena; Isomäki, I.; Ferreira, Jorge Amaral; Hämäläinen, M.; Braga, M. Helena
- First principles calculations and experiments to determine the hydrogenation process of Cu-Li-MgPublication . Braga, M. Helena; Sá, M. Helena; Ferreira, Jorge Amaral; Daemen, L. L.
- First principles study of copper sulfides (for applications as photoconductors)Publication . Ferreira, Jorge Amaral; Braga, M. Helena
- Hydrides of Cu and Mg intermetallic systems : characterization and catalytic functionPublication . Braga, Maria Helena; Wolverton, Michael J.; Sá, Maria H. de; Ferreira, Jorge Amaral
- Morphological and chemical characterization of mineral concretions in the freshwater bivalve Anodonta cygnea (Unionidae)Publication . Hinzmann, Mariana F.; Lima, Manuel Lopes; Bobos, Iuliu; Ferreira, Jorge Amaral; Domingues, Bernardo; Machado, JorgeThe freshwater mussel Anodonta cygnea is commonly used as a model organism for biomineralization studies, its peculiar morphofunctional properties also make it an excellent environmental biomonitor. The first detailed on the calcareous concretions from gill and mantle tissue, as well as fluids of the freshwater bivalve A. cygnea, supported by histological, scanning, spectrometry, and spectroscopy analyses. Through these analyses, the morphology, structure, and chemical characterization of these biomineral concretions were accomplished. The concretions represent a high percentage of the dry weight of these organisms. In gill tissue, it can reach up to 50% of dry weight prior to reproductive maturity. Analysis of elemental composition of the tissue concretions showed the presence of calcium and phosphate, as main components, associated with other residual elements like iron, manganese, magnesium, and zinc. Concretions are arranged in concentric alternated layers of organic and inorganic matrix. The shape and size of the concretions vary substantially, from very small, less than 1 µm diameter with very regular round structure, found mainly in the mantle tissue, to more than 50 µm length with irregular globular clusters, found predominantly in the gills. The microstructural organization is of a hydroxyapatite polymorphism in the mantle, in contrast to the gills, which exhibit irregular structure and carbonated hydroxyapatite polymorphism. These differences are supported by higher contents of dinitrogen pentoxide, magnesium, and iron in the mantle concretions, but higher contents of manganese and zinc in the gills. Furthermore, the results indicate that the mineral concretion formation in A. cygnea is a hemocytes reaction to particle or toxic invasions. A second relevant role, concerns the close involvement of these microspherules on the adult and larval shell calcification.