IMR Press / FBE / Volume 5 / Issue 2 / DOI: 10.2741/E645

Frontiers in Bioscience-Elite (FBE) is published by IMR Press from Volume 13 Issue 2 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Article

The carbonate ion in hydroxyapatite: Recent X-ray and infrared results

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1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada

*Author to whom correspondence should be addressed.

Academic Editor: Roger J. Narayan

Front. Biosci. (Elite Ed) 2013, 5(2), 643–652; https://doi.org/10.2741/E645
Published: 1 January 2013
(This article belongs to the Special Issue Nanostructured biomaterials)
Abstract

The location and orientation of the carbonate ion in the channel (A) and phosphate (B) positions of hydroxyapatite (CHAP) have been investigated by single- crystal X-ray structure and Fourier transform infrared (FTIR) spectroscopy, using crystals synthesized at high pressure. The type A carbonate ion is oriented in the apatite channel with two oxygen atoms close to the c-axis and the B carbonate ion is located near a sloping face of the substituted phosphate tetrahedron. Close comparison of FTIR and X-ray structure results shows that a Na-bearing CHAP containing approximately equal amounts of A and B carbonate ions is a realistic model for the overall crystal structure of biological apatite. However, the absence of distinct OH stretch and OH libration bands indicates that the hydroxyl content of biological apatite is disordered in respect to its orientation and precise location both in the channel and elsewhere in the structure.

Keywords
Apatite structure
Carbonate hydroxyapatite
X-ray structure
Infrared spectroscopy
Biomineralisation
CO2 sequestration
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