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Minerals 2018, 8(2), 65; doi:10.3390/min8020065

Pyrophosphate-Inhibition of Apatite Formation Studied by In Situ X-Ray Diffraction

Department of Chemistry and iNANO, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus, Denmark
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Received: 28 August 2017 / Revised: 10 February 2018 / Accepted: 12 February 2018 / Published: 13 February 2018
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Abstract

The pathways to crystals are still under debate, especially for materials relevant to biomineralization, such as calcium phosphate apatite known from bone and teeth. Pyrophosphate is widely used in biology to control apatite formation since it is a potent inhibitor of apatite crystallization. The impacts of pyrophosphate on apatite formation and crystallization kinetics are, however, not fully understood. Therefore, we studied apatite crystallization in water by synchrotron in situ X-ray diffraction. Crystallization was conducted from calcium chloride (0.2 M) and sodium phosphate (0.12 M) at pH 12 where hydrogen phosphate is the dominant phosphate species and at 60 °C to allow the synchrotron measurements to be conducted in a timely fashion. Following the formation of an initial amorphous phase, needle shaped crystals formed that had an octacalcium phosphate-like composition, but were too small to display the full 3D periodic structure of octacalcium phosphate. At later growth stages the crystals became apatitic, as revealed by changes in the lattice constant and calcium content. Pyrophosphate strongly inhibited nucleation of apatite and increased the onset of crystallization from minute to hour time scales. Pyrophosphate also reduced the rate of growth. Furthermore, when the pyrophosphate concentration exceeded ~1% of the calcium concentration, the resultant crystals had reduced size anisotropy suggesting that pyrophosphate interacts in a site-specific manner with the formation of apatite crystals. View Full-Text
Keywords: apatite; in situ X-ray diffraction; crystallization; nucleation; pyrophosphate; biomimetic materials apatite; in situ X-ray diffraction; crystallization; nucleation; pyrophosphate; biomimetic materials
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Ibsen, C.J.S.; Birkedal, H. Pyrophosphate-Inhibition of Apatite Formation Studied by In Situ X-Ray Diffraction. Minerals 2018, 8, 65.

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