Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral

• DOI: 10.2138/am.2014.4627
• Publication Date: 2014-01-02T17:39:22Z
• Authors: J. D. Pasteris; C. H. Yoder; B. Wopenka
• Keywords: Hydroxylapatite; Thermogravimetric analysis

Despite numerous analytical studies, the exact nature of mineral component bone is not yet totally defined, even though it recognized as a type carbonated hydroxylapatite. The present study addresses hydration state through Raman spectroscopic and thermogravimetric analysis 56 samples apatite containing from 1 to 17 wt% CO3, synthesized in H2O or D2O. Focus on relation between concentration molecular water (as distinguished hydroxyl ions) carbonate apatite. spectra confirm presence part crystalline structure all aqueously precipitated apatites. TGA results quantitatively document that, regardless structure, hydroxylapatites contain ~3 structurally incorporated addition multiple adsorbed water. We spectroscopically confirmed that natural also contains based independent analyses by means spectral stripping (subtracting spectrum collagen bone) chemical (chemically removing content prior analysis). Taken together, above data support model which molecules densely populate channels abundance vacancies. hypothesize keep stable when 80% sites are vacant (typical bone), hinder ions substituting for channels, help regulate access (e.g., ion exchange, entry small molecules). Our show "flawed hydroxylapatite," but instead definable mineralogical entity, combined hydrated-hydroxylated calcium phosphate phase form Ca10-x[(PO4)6-x(CO3)x](OH)2-x·nH2O, where n ~ 1.5. Water therefore an accidental, rather essential, other synthetic low-temperature phases.