The mechanisms governing selective CaCO3 crystal nucleation in living organisms remain unclear. For example, nacreous layers from the inner surfaces of shells are built as brick-and-mortar complexes of plate-like aragonite single crystals and organic layers. Unstable [001] surfaces of calcite columns in prismatic layers are also stabilized by organic molecules. Biogenic calcite crystals show different morphologies compared to geological calcite minerals. Langmuir monolayers are used as structured templates in simulated biomineralization from CaCO3 supersaturated subphases. But pure or mixed Langmuir monolayers do not mimic the nucleation sites of aspartic-rich proteins found within real biominerals. It has previously been shown that there is organic-inorganic lattice relaxation in the cases of BaF2 and hydrocerussite (2PbCO3Pb(OH)2) nucleation under fatty (carboxylate) acid with preferred orientation of crystals, but no lattice match is observed during CaCO3 crystallization under fatty acid Langmuir monolayers. Overall, geometric influences such as structural match between the interfacial lattices and the interactions between monolayer headgroups and aqueous ions do not guarantee any well-defined orientation of CaCO3 crystallization. CaCO3 mineralization on self-assembled monolayers on metal and alloy substrates have achieved higher degrees of orientations, even though molecules in Langmuir monolayers are better ordered than in self-assembled monolayers. Until now, Langmuir monolayer experiments have emphasized only the function of the acidic proteins. To better mimic the real organic template, it is important to include the hydrophobic and polyelectrolyte characteristics of real organic templates in shells. The organic matrix in actual shells contains hydrophobic silk fibroin (which is hydrophobic) and polyelectrolytes. Some acidic proteins reside on the surface of silk fibroins. There is also semi-crystalline β-chitin structure whose function has not been fully understood. To better simulate the biological system, chitosan was added to the aqueous subphase. The crystallization processes were monitored using in-situ Grazing incidence X-ray diffraction (GID). Scanning electron microscopy (SEM) was used to perform morphological studies on grown crystals. Dissolved chitosan causes distinct concentration-dependent changes in orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

Last modified

• 09/17/2018

Creator

• Kyungil Kim

DOI

• https://doi.org/10.21985/N2G44R

Subject

• Physics and Astronomy

Keyword

• SEM
• Biomineralization
• Chitosan
• Calcite
• Langmuir monolayer
• Grazing incidence x-ray diffraction

Date created

• 2008-11-21

Resource type

• Dissertation

Rights statement

• In Copyright