Calcite nucleation on the surface of PNIPAM–PAAc micelles studied by time resolved in situ PXRD

Jensen, Anders C. S.; Hinge, Mogens; Birkedal, Henrik

doi:10.1039/c5ce00424a

Cited by 10 publications

(15 citation statements)

References 44 publications

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“…[1][2][3][4][5] Calcite, the thermodynamically stable polymorph of calcium carbonate, is often not directly formed from solution, but rather through a series of polymorphs starting with an amorphous precursor known as amorphous calcium carbonate (ACC). [6][7][8][9] The stability of ACC is a key factor in its role as a biomineral precursor and in biogenic ACC stabilizers are often present, most commonly Mg ions. 1 The stabilizing effect of Mg 2+ is frequently attributed to the high dehydration energy of magnesium ions, relative to calcium ions, 10,11 which retards the dehydration of the ACC 8 and hence prevents crystallization.…”

Section: Introductionmentioning

confidence: 99%

“…1 The stabilizing effect of Mg 2+ is frequently attributed to the high dehydration energy of magnesium ions, relative to calcium ions, 10,11 which retards the dehydration of the ACC 8 and hence prevents crystallization. The stability of synthetic ACC has been studied extensively both with 8,12,13 and without 6,7,9,[14][15][16][17] the incorporation of Mg 2+ . In magnesium-free ACC the stability has been suggested to depend on the mobility of water molecules [17][18][19] and NMR studies 14,20 have suggested that several types of water exist in ACC: translationally rigid, restricted mobile and liquid-like H 2 O.…”

Section: Introductionmentioning

confidence: 99%

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Mobility of hydrous species in amorphous calcium/magnesium carbonates

Jensen

Rodríguez

Habraken

et al. 2018

Phys. Chem. Chem. Phys.

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Amorphous calcium carbonate (ACC) is commonly found in many biological materials. As ACC readily crystallizes into calcite, stabilizers, such as anions, cations or macromolecules, often occur to avoid or delay unwanted crystallization. In biogenic ACC, magnesium is commonly present as one of the stabilizing agents. It is generally thought that the presence of mobile water in ACC is responsible for its limited stability and that the strong interaction of Mg2+ with water stabilizes the amorphous structure by retarding dehydration of ACC. To test this hypothesis, we studied the mobility of hydrous species in the model materials ACC, amorphous magnesium carbonate (AMC) and amorphous calcium/magnesium carbonate (ACMC), using quasi elastic neutron scattering (QENS) which is highly sensitive to the dynamics of H atoms. We discovered that hydrous species in the considered amorphous materials consist of water and hydroxide ions, as magnesium ions are incorporated in a ratio of 1 to about 0.6 with OH-. Surprisingly, we found that there is no evidence of translational diffusion of water and hydroxides when calcium is present in the samples, showing that hydrous species are highly static. However, we did observe diffusion of water in AMC with similar dynamics to that found for water in clays. Our results suggest that Mg2+-water interactions alone are not the only reason for the high stability of AMC and ACMC. The stabilizing effect of Mg ions, in addition to Mg-water binding, is likely to be caused by binding to hydroxide in amorphous calcium carbonates. In fact, the incorporation of hydroxides into the amorphous phase results in a mineral composition that is incompatible with any of the known Ca/Mg-carbonate crystal phases, requiring large scale phase separation to reach the composition of even the basic magnesium carbonate minerals artinite and hydromagnesite.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mobility of hydrous species in amorphous calcium/magnesium carbonates

Jensen

Rodríguez

Habraken

et al. 2018

Phys. Chem. Chem. Phys.

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“…We employed in situ X-ray diffraction [22][23][24][25]29,30] to follow the crystallization of apatite as in our previous work on other types of apatite formation [22,24,25]. We performed in situ synchrotron diffraction in a home built stopped flow apparatus with high temperature stability [24] by mixing equal volumes of a calcium chloride solution (0.4 M) with a sodium phosphate solution (0.24 M) loaded with varying quantities of sodium pyrophosphate (0-0.02 M).…”

Section: Methodsmentioning

confidence: 99%

“…In spite of the important roles of pyrophosphate as a mineralization inhibitor in vivo, no quantitative studies of its impact on nanocrystal formation kinetics have been performed to the best of our knowledge. Herein, we use in situ synchrotron powder diffraction [22][23][24][25] to quantify the impact of pyrophosphate on apatite formation from amorphous calcium phosphate (ACP).…”

Section: Introductionmentioning

confidence: 99%

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

Ibsen

Birkedal

2018

Minerals

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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.

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“…PNIPAM-b-PAAc ( Figure 1) was used as the polymer additive. The polymer has an lower critical solubility temperature (LCST) of 32 °C and we have previously shown how this polymer can be used to afford calcite nanocrystals 22 . The PAAc block acts like an anchor binding the polymer to the surface of the calcite crystal.…”

Section: Introductionmentioning

confidence: 99%

Morphology-preserving transformation of minerals mediated by a temperature-responsive polymer membrane: calcite to hydroxyapatite

et al. 2016

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Assemblies of nano crystals with complex morphologies have solicited great scientific interest. Controlling the formation of these self-assembled structures has proved difficult. Here we present a novel transformation reaction for transforming a single crystal of minerals into assemblies of nanocrystals of substances with lower solubility without changing the overall morphology. This study focusses on the transformation of rhombohedral calcite crystals to assemblies of hydroxyapatite nanoscrystals (HAP) using poly-(N-isopropyl-acrylamide)-block- Corresponding Author

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Calcite nucleation on the surface of PNIPAM–PAAc micelles studied by time resolved in situ PXRD

Cited by 10 publications

References 44 publications

Mobility of hydrous species in amorphous calcium/magnesium carbonates

Mobility of hydrous species in amorphous calcium/magnesium carbonates

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

Morphology-preserving transformation of minerals mediated by a temperature-responsive polymer membrane: calcite to hydroxyapatite

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