The Bolivian Altiplano is part of the inner arc Polymetallic Belt of the Andes, and is a Cretaceous-Cenozoic intermontane basin located between the Andean arc of the Western Cordillera and the Paleozoic fold belt of the Eastern Cordillera. Reconnaissance geological mapping shows that epithermal mineralisation in the NE Altiplano is related to silicic magmatism located on NW-trending Altiplano growth faults and intersections with NE and E-W lineaments. Magmatism was episodic and occurred during the Miocene arc broadening episode, which correlates with increased plate convergence rates. Most magmatism is mid Miocene (19-10 Ma), and formed flow-dome-sill-stock complexes. The upper (9-7.5 Ma) and late (6.5-4 Ma) Miocene episodes, in contrast, generally formed ash-flow calderas and strato-volcanoes. The three episodes are mainly dacites and rhyolites of the high-K calc-alkaline suite, with some shoshonites, and can only be distinguished isotopically, with progressively stronger crustal contamination in the younger episodes. Sr-Nd-O isotopes and trace elements show that the magmas evolved by variable fractionation and assimilation from subduction-related, mantle-derived magmas which were isotopically enriched by bulk contamination with Precambrian gneisses. Mapping, petrography and XRD show that the epithermal deposits have large areas of pervasive phyllic alteration with a propylitic halo. Tourmaline alteration occurs in the cores of Sn-bearing deposits. Argillic and silicic alteration in some deposits are subsurface features of hot spring systems. Mineralisation (Au-Ag-Cu-Pb-Zn) is disseminated and in sheeted veins and veinlets which have a NE-trend, related to the regional tectonic stress. Dating and O-H isotopes show that the mineralisation is genetically related to the dacitic magmatism and formed from a dominantly magmatic fluid, with meteoric mixing in the upper levels. Differences between the Polymetallic Belt and the Copper Belt are mainly a function of erosion level. Polymetallic deposits of the Eastern Cordillera contain important Sn and form the main part of the Tin Belt. Minor Sn also occurs in Altiplano deposits hosted by Paleozoic marine sediments, but not in those in Tertiary red beds. Tin was probably derived from the Paleozoic sediments, and is not related to deep subduction.

No description available.

Currently, many polymeric biomaterials do not possess the most desirable surface properties for direct bone bonding due to the lack of suitable surface functionalities. The incorporation of negatively charged groups has been shown to enhance calcium phosphate formation in vitro and bone bonding ability in vivo. However, there are some conflicting literature reports that highlight the complicated nature of the mineralisation process as well as the sometimes apparent contradictory effect of the negatively charged groups. Surface modification using well-defined polymers offer a more precise control of the chain structures. The aims of this study were to synthesise well-defined polymers containing phosphate and carboxylic acid groups, and perform various surface modification techniques. The influence of the polymer structure on mineralisation was examined using a series of specially synthesised phosphate-containing polymers. The mineralisation ability of the fabricated surfaces was also tested. Soluble poly(monoacryloxyethyl phosphate) (PMAEP) and poly(2-(methacryloyloxy)ethyl phosphate) (PMOEP) were synthesised using reversible addition fragmentation chain transfer (RAFT)-mediated polymerisation. The polymerisation conversions were monitored by in situ Raman spectroscopy. Subsequently 31P NMR investigation revealed the presence of large amounts of diene impurities as well as free orthophosphoric acids in both the MAEP and MOEP monomers. Elemental analyses of the polymers showed loss of phosphate groups due to hydrolysis during the polymerisation. Both gel and soluble PMAEP polymers were found to contain large amounts of carboxyl groups indicating hydrolysis at the C-O-C ester linkages. Block copolymers consisting of PMAEP or PMOEP and poly(2-(acetoacetoxy) ethyl methacrylate) PAAEMA were successfully prepared for the purpose of immobilisation of these polymers onto aminated slides. Well-defined fluorinated polymers, (poly(pentafluorostyrene) (PFS), poly(tetrafluoropropyl acrylate) (TFPA) and poly(tetrafluoropropyl methacrylate) (TFPMA)) were synthesised by RAFT-mediated polymerisation. It was found that the Mn values of PFS at higher conversions were significantly lower than those calculated from the theory, although the PDI's were low (&lt1.1). One possible explanation for this is that it may be a result of the self-initiation of FS which created more chains than the added RAFT agents. Both TFPA and TFPMA showed well-controlled RAFT polymerisations. Chain extension of the fluorinated polymers with tert-butyl acrylate (tBA) followed by hydrolysis of the tBA groups produced the amphiphilic block copolymers containing carboxylic acid groups. Block copolymers consisting of PAAEMA segments were further reacted with glycine and L-phenylalanyl glycine. Three types of surface modifications were carried out: Layer-by-Layer (LbL) assemblies of the soluble phosphate- and carboxylic acid-containing homopolymers, coupling reactions of block copolymers consisting of phosphate and keto groups onto aminated slides, and adsorption of fluorinated homo and block copolymers containing carboxylic acid groups onto PTFE. For LbL assemblies XPS analyses revealed that the thickness of the poly(acrylic acid) (PAA) layer was found to be strongly dependent on the pH at deposition. AFM images showed that the PMAEP LbL had a patchy morphology which was due to the carboxylate groups that were not deprotonated at low pH. Successful coupling of the block copolymers consisting of phosphate and keto groups onto aminated slides was evident in the XPS results. The conformation of attached P(MOEP-b-AAEMA) was investigated by ToF-SIMS. Adsorption of the fluorinated polymers onto the PTFE film was examined using different solvents. PFS showed the best adsorption onto PTFE. The block copolymers consisting of PFS and PtBA or PAA were successfully adsorbed onto PTFE. Contact angle measurements showed that the adsorbed block copolymers reorganised quickly to form a hydrophilic surface during the investigation. In vitro mineralisation of various phosphate-containing polymers and the fabricated surfaces were studied using the simulated body fluid (SBF) technique. The SEM/EDX investigation showed that either brushite or monetite, with a tile-like morphology, was formed on both soluble and gel PMAEP polymers after seven days in SBF. The PMOEP gel formed a similar layer as well as a secondary growth of hydroxyapatite (HAP) that exhibited a typical globular morphology. Fourier transform infrared (FTIR) spectroscopy of the PMOEP film prepared from soluble PMOEP showed large amounts of carbonated HAP formation after seven days in SBF. Carbonated HAP is the phase that most closely resembles that found in biological systems. Both the LbL surfaces and the block copolymer-attached aminated slides showed only patchy mineralisation even after 14 days in SBF. This indicates that ionic interactions of the negatively charged phosphates or carboxylates and protonated amines prevented chelation of calcium ions, which is believed to be the first step in mineralisation. The P(FS-b-AA) adsorbed PTFE film also showed only small amounts of mineral formation after 14 days in SBF. These results highlight the many features controlling the mineralisation outcomes.

Techn. University, Diss., 2003--Clausthal.

PHOSPHO1 is a skeletal specific phosphatase whose activity towards the lipid metabolites, phosphocholine (PCho) and phosphoethanolamine (PEth), results in the generation of inorganic phosphate (Pi) within matrix vesicles (MV). PHOSPHO1 activity is essential for the initiation of biomineralisation. The genetic ablation of Phospho1 results in severe hypomineralisation of the skeleton and dentition. Neutral sphingomyelinase 2 (nSMase2, encoded by the Smpd3 gene) catalyses the breakdown of the membrane lipid sphingomyelin to generate ceramide and PCho. Similar hypomineralisation of the skeleton is noted in the Smpd3-/- mouse. This observation led to the hypothesis that nSMase2 and PHOSPHO1 work in tandem for the generation of Pi within MV. Despite knowledge of the phenotype associated with the absence of Phospho1 or Smpd3, little is known about the expression profiles of these genes during the initiation of extracellular matrix (ECM) mineralisation, or the regulation of these genes. This thesis characterised the expression of Phospho1, Smpd3 and other key genes associated with ECM mineralisation in in vitro models of mineralisation under exogenous phosphatase substrate-free conditions. Additionally, building on preliminary work in osteocytes, the regulation of Phospho1 and Smpd3 by parathyroid hormone (PTH) was investigated both in vitro and in vivo. Characterisation of MC3T3 osteoblast-like cell cultures, primary calvarial osteoblast and embryonic metatarsal organ cultures similarly revealed simultaneous and striking increases in the expression of PHOSPHO1 and nSMase2 prior to the onset of ECM mineralisation. In Phospho1-/- cell and organ cultures, ECM mineralisation was markedly diminished, and nSMase2 expression was notably reduced. The parathyroid hormone (PTH) regulation of Phospho1 and Smpd3 in osteocytes was confirmed in MC3T3 osteoblast-like cell cultures. Phospho1 and Smpd3 mRNA expression was strongly and rapidly (within 15 minutes) inhibited by PTH. Experiments with cycloheximide revealed that this was a direct effect not requiring protein synthesis. Further experimentation utilising the adenylyl cylase agonist, Forskolin and the PKA inhibitor, PKI (5-24), identified the cAMP-PKA signalling pathway as the mediator of the effects of PTH on Phospho1 and Smpd3 expression. In contrast, however, primary calvarial osteoblasts, human subchondral bone osteoblasts and murine embryonic metatarsal cultures all displayed an upregulation of Phospho1 expression in response to a 24 h exposure to PTH. Although informative, these findings highlighted the need to investigate the PTH regulation of Phospho1 in vivo. The administration of PTH (80 μg/kg) enhanced the expression of Phospho1 and Smpd3 within 6 h and after 14 and 28-day intermittent exposure in the distal femur of male wild-type mice. The expression of the transcription factors, Runx2 and Trps1, which have been implicated in the regulation Phospho1 were similarly upregulated by these PTH exposures. I hypothesised that the upregulation of Phospho1 could provide a novel mechanism explaining the osteoanabolic effects of intermittent PTH (iPTH). Bone microarchitecture in response to iPTH was assessed in the tibiae of WT and Phospho1-/- mice by micro computed tomography. The absence of Phospho1 limited the anabolic effects of PTH in cortical bone but not in the metaphyseal trabecular bone. The work described within this thesis provides further evidence of the cooperative functions of nSMase2 and PHOSPHO1 in the initiation of skeletal mineralisation. The potent regulation of these enzymes in vivo by PTH offers an additional explanation of the anabolic effects of iPTH and forms part of an emerging body of evidence seeking to understand the regulation of these enzymes.

No description available.

No description available.

No description available.

Zugl.: Clausthal, Techn. Univ., Diss., 2008

No description available.