A.P. Lee

In situ Raman spectroscopic studies of the teeth of the chiton Acanthopleura hirtosa

Abstract In situ Raman spectroscopy, in combination with energy dispersive spectroscopy, has been used for the first time to determine the identities and locations, at the micron level, of mineral phases present in single chiton teeth that have been extensively mineralized. At the later stages of development the major lateral teeth of the chiton Acanthopleura hirtosa show characteristic spectroscopic evidence for the presence of lepidocrocite (γ-FeOOH), magnetite (Fe3O4), and an apatitic calcium phosphate. Goethite (α-FeOOH) and ferrihydrite (5 Fe2O3·9 H2O), which have been detected previously in teeth at the early stages of mineralization, were not detected in this mature tooth. The spatial distribution of these phases was determined, providing evidence for the presence of a discrete layer of lepidocrocite between the magnetite and apatite regions, illustrating the complexity of the biomineralization process. The technique of laser Raman microscopy is shown to be ideal for the examination of small biomineralized structures in situ, such as chiton teeth.

Apatite Mineralization in Teeth of the Chiton Acanthopleura echinata

Abstract. Raman spectroscopy has been used to demonstrate, for the first time, that calcium mineralization in the core of the major lateral teeth of the chiton Acanthopleura echinata takes place as an ordered process, with crystalline carbonated apatite being the first mineral deposited. Deposition begins at the top of the tooth core, under the so-called tab region, progresses down the interior surface of the tab and lepidocrocite layer, and then extends outwards to the anterior surface. Mineralization is not initiated until the lepidocrocite layer has isolated the core of the tooth from the magnetite cap. The last region to be infiltrated is the anterior basal region of the tooth cusp, immediately above the junction zone. The junction zone is also a region of high ion density, as determined by energy dispersive spectroscopy (EDS) analysis, but we show here for the first time that it is free of mineral deposits, acting instead as a transfer and storage region.

A new biomineral identified in the cores of teeth from the chiton Plaxiphora albida

The hydrated iron(III) oxide limonite is reported for the first time as a biomineral. In situ laser Raman spectra of the tooth cores from major lateral teeth of the chiton Plaxiphora albida are compared with those of synthetic and mineral iron phosphates and iron oxides. Raman spectra measured on iron phosphate and iron oxide standard materials are shown to be easily distinguishable from one another. The central tooth cores of mature P. albida teeth do not show any evidence for the presence of a separate iron phosphate mineral. Rather, in each tooth a narrow band of the hydrated iron(III) oxide limonite is shown to separate the magnetite of the tooth surface from a central core region comprising both lepidocrocite and limonite. The high concentration of phosphorus in P. albida tooth cores, previously observed by energy dispersive spectroscopy, is not associated with a separate iron phosphate mineral, indicating that this element may be adsorbed onto the surface of the iron oxide minerals present. The failure to detect a separate iron(III) phosphate is discussed with reference to other chiton species that display high levels of iron and phosphorus in the cores of their mature major lateral teeth.

Biomineralization-controlled microarchitecture in the radula teeth of chitons and limpets

The biomineralization-controlled microarchitecture in the radula teeth of chitons and limpets was discussed. Studies of teeth at different stages shows that Si region was mineralized after the mineralization of iron and at a slower rate. Raman spectroscopy confirmed the presence of goethite in a late mineralized tooth. The studies illustrated the distinct advantages of vibrational and Raman spectroscopy in the identification and mapping of phase distributions in tissue mineralization.

Marine teeth (and mammal teeth)

Under the competitive pressures within complex ecosystems, the teeth of marine organisms have developed through evolutionary time to enable the organisms to feed successfully in their particular ecological niche. The diets of organisms vary, in part, due to differences in the susceptibility of their food and to differences in their feeding ability. Such teeth exhibit a diverse range of composition, microarchitecture, and overall morphology as revealed by recent studies of mineralized tissues (Mann et al. 1989, Simkiss and Wilbur 1989, Weiner and Lowenstam 1989, Frankel and Blakemore 1991).While many species of marine organisms have teeth constructed predominantly from the polysaccharide chitin (β-1-4-linked polymer of 2-acetamido-2-deoxy-D-glucose, often found partially deacetylated), those whose teeth have been modified by the inclusion of inorganic components (biominerals) reveal many of the strategies that have been studied extensively in recent years. Such studies are proving inspirational to materials scientists in their quest for inorganic and composite materials of desired composition, form, and function. An ecological approach provides a particularly helpful perspective to understand the diversity of teeth in marine organisms.