Abstract
The local structures of a series of amorphous calcium phosphate (ACP) phases with increasing carbonate contents (2–14 wt %) were studied by multinuclear 1H, 13C, 23Na, and 31P magic-angle spinning ...
Highlights
Calcium hydroxyapatite (HA; Ca5(PO4)3OH) constitutes the mother structure of bone, dentin, and enamel mineral.[1−3] bone/dentin mineral comprises 3.5−6 wt % of carbonate species[4,5] and merely consists of calcium hydroxycarbonate apatite (HCA)
The chemical composition and structure proposed by Betts and Posner[4] is oversimplified, as it has for long been acknowledged that acidic phosphate (HPO42−) groups account for a significant fraction of the phosphate speciation of amorphous calcium phosphate (ACP),[12−17] except for specimens prepared at very high pH ≳ 10.5.14 the literature is almost devoid on concrete proposals for the structural role of the HPO42− species in bulk ACP.[15]
HPO42− species likely contribute to the 500−600 cm−1 spectral region, where an signal at 550 cm−1 was attributed to such groups in CO32−-bearing ACP,[42] whereas the HPO42− moieties of amorphous calcium hydrogen phosphate (ACHP) produced a band ≈534 cm−1,35 i.e., in the mid of the 525−550 cm−1 range attributed to acidic phosphates in H(C)A.43,45
Summary
Calcium hydroxyapatite (HA; Ca5(PO4)3OH) constitutes the mother structure of bone, dentin, and enamel mineral.[1−3] bone/dentin mineral comprises 3.5−6 wt % of carbonate species[4,5] and merely consists of calcium hydroxycarbonate apatite (HCA). Owing to the immense importance of bone and its mineral component for living vertebrates, the composition, structure and notably so the factors controlling the biomineralization have been intensively investigated for more than six decades. The chemical composition and structure proposed by Betts and Posner[4] is oversimplified, as it has for long been acknowledged that acidic phosphate (HPO42−) groups account for a significant fraction of the phosphate speciation of ACP,[12−17] except for specimens prepared at very high pH ≳ 10.5.14 the literature is almost devoid on concrete proposals for the structural role of the HPO42− species in bulk ACP.[15] Yet, the involvement of acidic phosphates in ACP formation is highlighted in very recent studies, which suggest that the assemblies embryos of osfyhnythderatitcedACCaP2+paanrtdicHlesP1O8−4221−
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