| Research Abstract |
The purpose of the present study is to elucidate the biomineralization mechanisms that are presumably different from those in inorganic processes. Biomineralization was simulated in the laboratory, by selecting polymerized 10,12-Pentacosadiynoic acid(p-PDA)LB films as organic template and calcium carbonate as biominerals. It was found by electron diffraction study that carboxyl groups are regularly (pseudo-hexagonally) arranged on the p-PDA film. When the silica substrates covered with the p-PDA film were soaked in a solution supersaturated with CaCO_3, calcite crystals were precipitated on the substrates. the crystal orientation of the calcite was analyzed by using electron back-scattering diffraction (EBSD) technique in a field-emission type high-resolution SEM. This new technique revealed the orientation relationship between the polymerized direction of PDA and crystal orientation of calcite accurately. One of the a-axes of calcite was strictly oriented parallel to the polymerized d
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irection, which was identified by the surface cracking of the film, of PDA. the c-axis of calcite was necessarily perpendicular to the polymerized direction but their direction (standing angle from the substrate) was varied. Other CaCO_3 polymorphs, aragonite and vaterite, are rarely formed on the film but no epitaxial relations were observed.
Besides these experiments, the effects of rare-earth elements in solution on the morphology of calcium carbonate crystals were also investigated. Very small amount of La^<3+> ion changed the shape of calcite drastically, but did not change that of vaterite at all. La^<3+> also acted as an inhibitor against the precipitation of calcite from supersaturated solution. These two effects must be related intimately during calcite precipitation and crystal growth. Furthermore, the EBSD technique was applied to several biominerals in nature. Especially the relationship between the structure and crystal orientations of constituting calcite crystals in coccolith (scale of coccolith algae) was successfully determined. Less
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