An X-ray radial distribution study of amorphous calcium phosphate

Betts, F.; Posner, Aaron S.

doi:10.1016/0025-5408(74)90087-7

Cited by 143 publications

(103 citation statements)

References 15 publications

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“…Heavy solid curves: s ACP ¼ 0.15, light solid curves: s ACP ¼ 0.4. 41 demonstrated that ACP consisted of subunits already containing some of the structural features of AP and proposed these subunits-later termed Posner's clusters-to be Ca 9 (PO 4 ) 6 . They assigned peaks in the radial distribution functions derived from X-ray data to the atom pairs P-O (1.5 Å), O-O and Ca-O (2.3 Å), and Ca-Ca, Ca-P and P-P (3-6 Å).…”

Section: Resultsmentioning

confidence: 99%

Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate

et al. 2013

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Despite its importance in many industrial, geological and biological processes, the mechanism of crystallization from supersaturated solutions remains a matter of debate. Recent discoveries show that in many solution systems nanometre-sized structural units are already present before nucleation. Still little is known about the structure and role of these so-called pre-nucleation clusters. Here we present a combination of in situ investigations, which show that for the crystallization of calcium phosphate these nanometre-sized units are in fact calcium triphosphate complexes. Under conditions in which apatite forms from an amorphous calcium phosphate precursor, these complexes aggregate and take up an extra calcium ion to form amorphous calcium phosphate, which is a fractal of Ca 2 (HPO 4 ) 3 2 À clusters. The calcium triphosphate complex also forms the basis of the crystal structure of octacalcium phosphate and apatite. Finally, we demonstrate how the existence of these complexes lowers the energy barrier to nucleation and unites classical and non-classical nucleation theories.

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Section: Resultsmentioning

confidence: 99%

Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate

et al. 2013

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“…Amorphous TCP (Ca/P = 1.5) is formed in alkaline conditions with a structure built by agglomeration of the so-called Posner clusters (Betts andPosner 1974, Blumenthal andPosner 1973): Ca 9 (PO 4 ) 6 units of 0.8-1 nm diameter, where interstitial water can be removed irreversibly by drying (Kojima et al 1994). This is an arrangement also present in the unit cell of apatites, OCP and β-TCP.…”

Section: Introductionmentioning

confidence: 99%

Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters

et al. 2016

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There are abundant examples of nanoclusters and inorganic microcrystals in biology.Their study under physiologically relevant conditions remains challenging due to their instability, the requirements of sample preparation and other intrinsic limitations of the techniques used. Advantages of using neutron diffraction and contrast matching to characterize biomaterials are highlighted in this article. We have applied these methods and complementary techniques to search for long-range order within nanoclusters of calcium phosphate sequestered by bovine phosphopeptides, derived from osteopontin or casein. Hydrated and dried samples with different nanocluster radii were analyzed and compared to samples of known calcium phosphate phases. The absence of a distinct diffraction pattern from the nanoclusters is consistent with the presence of amorphous calcium phosphate structure.

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“…In proportions of magnesium. The fourth, Ti, was one model of its structure it is described as being prepared at the Van 't Hoff Laboratorium, formed from Ca 9(P04 )6 clusters; a similar cluster Utrecht, and, in addition to physical and chemical can be identified in the unit cell of apatites [7,8].…”

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confidence: 99%

Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

Holt

Kemenade²,

Harries

et al. 1988

Journal of Crystal Growth

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Amorphous calcium-magnesium phosphates were prepared by precipitation from moderately supersaturated aqueous solutions at pH 7. Chemical analysis of the samples by ion chromatography showed that up to about 50% of the phosphate ions were protonated, the proportion increasing with the magnesium to calcium ion activity ratio in the solution. When left it contact with the supernatant, the amorphous precipitates matured to form the crystalline calcium phosphate brushite (CaHPO 4.2H20). The amorphous phases were characterized by X-ray absorption spectroscopy and by Fourier transform infrared spectroscopy and their properties compared with those of a basic amorphous tricalcium phosphate precipitated at pH 10. The X-ray absorption spectra near the K edge of calcium were very similar for all samples but there were differences in the infrared spectra between the basic and the more acidic salts. In the phosphate stretching region, the main band of the more acidic materials occurred at higher wavenumber and was broader. Also there was a broad band of medium intensity at about 890 cm 1 whereas there was virtually no absorption band in this region in the spectrum of the amorphous tricalcium phosphate. The acidic amorphous calcium phosphates may be useful as model compounds in describing some complex biological calcium phosphates that form near neutral pH.

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An X-ray radial distribution study of amorphous calcium phosphate

Cited by 143 publications

References 15 publications

Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate

Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate

Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters

Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

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