In-Situ IR Spectral Measurement in Organic Matrix-Mediated Hydroxyapatite Formation

Organic template-directed crystallization of hydroxyapatite (HAp) was studied in-situ via Fourier transform IR external reflection spectroscopy. Langmuir monolayer of arachidic acid was formed on a surface of simulated body fluid, which possesses inorganic ion concentrations and a pH value almost equal to those of human blood plasma. Owing to the chemical interactions between inorganic ions and carboxyl groups, heterogeneous nucleation of HAp occurred below the monolayer. The absorbances of the antisymmetric and symmetric methylene stretching bands in the IR spectra varied during the nucleation process, which means that conformational change of hydrocarbon chain occurred. Interfacial interactions between organic templates and induced crystals are often discussed only through static experimental models. However, the organic matrices should also be treated as elastic template and their structural changes due to the formation of HAp crystals should be recognized, when the biomineralization mechanism is discussed.