Studies of metal pyrophosphates in vivo and in vitro

• Main Author: Masala, Ombretta
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2003
• Subjects: Biochemistry
• ISBN: 9780355978155; 0355978156

Marine invertebrates accumulate trace metals from the surrounding aquatic environment in the form of phosphate granules. This process has often been associated with the capacity of these aquatic organisms to detoxify metals temporarily or permanently in their body. Granules are usually amorphous to X-ray and electron diffraction and have a spherical shape with diameters ranging from 0.1 to 1 μm. The mechanism of granule formation is thought to involve the binding of the metal in the form of mixed metal calcium pyrophosphate. Amorphous deposits of calcium pyrophosphate act as fraps for foreign metal ions that are exchanged with calcium and then incorporated inside the granules. Specimens of the barnacle Tetmclita squamosa were collected from metal polluted sites of the Hong Kong area and the spherical deposits were isolated and analysed by X-ray powder diffraction, electron microscopy, energy dispersive analysis by X-rays and infr-ared spectroscopy. The granules mainly contained iron, calcium and zinc and the anion was present in part as pyrophosphate. The granules were amorphous to X-ray and electron diffraction and had spherical shape with diameters between 100 and 500 nm. The process of metal incorporation into granules is not frilly understood and few studies have been carried out in order to elucidate the mechanism. To date, a "chemical" approach to understand the formation of spherical granules of calcium pyrophosphate and the incorporation of metal ions into these solids has never been fully undertaken. In order to give an insight on this process, the formation of calcium pyrophosphate in presence of metal ions such as cadmium, manganese and zinc in aqueous solutions has been studied. The materials were characterised by X-ray powder diffraction, electron microscopy, infrared specfroscopy, nuclear magnetic resonance, electron paramagnetic resonance, thermo-gravimetric and elemental analysis. Undoped calcium pyrophosphate precipitated in aqueous solutions as a mixture of hydrated salts in the form of orthorhombic crystal plates or aggregates of needles with lengths of 50 p.m. When calcium pyrophosphate is doped with cadmium(II) ions, Cd(II) is accommodated into calcium pyrophosphate with no remarkable changes of morphology and crystallinity with respect to the parent compound. In contrast, the doping with zinc(II) and manganese(II) ions promoted the formation of spherical particles amorphous to X-ray and electron diffraction and with diameters between 100 - 600 nm. Extended X-ray absorption fine structure at the phosphorus K-edge and zinc K-edge was performed on the zinc-doped calcium pyrophosphate spherical particles to gain information on the structural environment of Zn and P. Zinc was found to be in a tetrahedi'al coordination as ZnO4 which is a very unusual arrangement for this metal in pyrophosphate salts. Amorphous manganese- and zinc-doped calcium pyrophosphate spherical particles were suspended in aqueous solutions containing Cd(II), Fe(II), Mn(II) or Zn(n), and substitution of calcium ions was observed. The displacement of a large amount of calcium resulted in a breakdown of the spherical morphology with formation of aggregates of plates amorphous to X-ray and electron diffraction. Similar changes were observed fn vivo when spherical deposits of calcium pyrophosphate of the snail Helix aspersa were doped with Fe(II), Mn(II) and Zn(II) ions. This similarity suggests that the process by which metals are incorporated into the spherical particles of synthetic metal-doped calcium pyrophosphates may account for the accumulation of the metals into phosphate granules of the snail in vivo.