In situ Raman spectroscopic studies of the iron and calcium containing biominerals in chiton teeth

Lee, Alasdair Peter (2000) In situ Raman spectroscopic studies of the iron and calcium containing biominerals in chiton teeth. PhD thesis, Murdoch University.

Abstract

The iron and calcium biominerals of the major lateral teeth of the chitons, Acanthopleura hirtosa, Acanthopleura echinata, Plaxiphora albida, Cryptoplax striata, Ischnochiton australis, and Acanthopleura rehderi, have been characterised in situ at all stages of mineralization, with laser Raman microscopy. Mature teeth do not contain goethite and ferrihydrite, both of which have been isolated in early stage teeth.

Deposition of magnetite in the posterior region of tooth cusp occurs on two fronts simultaneously, from both the anterior and posterior. In contrast, the lepidocrocite region, where present, is formed by aggregation over the whole extent of the interior surface. A thin veneer of ferrihydrite over the posterior surface of the magnetite prevents this region from undergoing oxidation prior to use.

The first evidence for conditions favouring the deposition of hematite over goethite in biological systems is shown. Hematite is uniquely located in micro-domains of teeth at a critical stage of development, at the transition between iron and calcium biomineralisation. The Raman spectrum of biogenically produced hematite is distinctly differently from geological and synthetic material.

Calcium biomineralisation in the major lateral teeth of Acanthopleura echinata takes place as an ordered process from the top of the tooth core under the tab region, down its interior surface and down the lepidocrocite layer, before extending outwards to the anterior surface at the junction zone. Mineralization is not initiated until the lepidocrocite layer has isolated the core from the magnetite cap. The junction zone, previously shown to be a region of high ion density, is shown to be free of mineral deposits.

In contrast to previous work, the cores of P. albida, C. striata, and I. australis, are shown to contain amorphous ferric iron oxide minerals and not the previously described ferric phosphate. Mineral deposition progresses in the same manner as all other chitons studied, from posterior to anterior and from tooth tip towards the base.

Item Type:	Thesis (PhD)
Murdoch Affiliation(s):	Division of Science and Engineering
Notes:	Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s):	Webb, John and Macey, David
URI:	http://researchrepository.murdoch.edu.au/id/eprint/51705

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