Structural Characteristics of Synthetic Amorphous Calcium Carbonate

Michel, F. Marc; MacDonald, Jason; Feng, Jian; Phillips, Brian L.; Ehm, Lars; Tarabrella, Cathy; Parise, John B.; Reeder, Richard J.

doi:10.1021/cm800324v

Cited by 212 publications

(429 citation statements)

References 35 publications

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“…1). Two diffuse maxima centered at 20 and 45°2θ are common features for the ACC phase and were previously observed (19,20). The variable temperature powder XRD patterns of the synthetic ACC-1, 4, and 5 samples indicate that ACC persists up to 330°C (see Fig.…”

Section: Resultssupporting

confidence: 73%

“…Abiotically, ACC is easily formed by mixing aqueous solutions at or below room temperature. These solutions can be totally inorganic or they can contain small organic species which affect the formation and persistence of ACC (13)(14)(15)(16)(17)(18)(19)(20). Increasing interest in CO 2 sequestration has led to proposals and pilot projects in which large plumes of supercritical carbon dioxide would be introduced into deep saline aquifers (21)(22)(23)(24)(25).…”

mentioning

confidence: 99%

“…Nuclear magnetic resonance, X-ray absorption spectroscopy, and infrared spectroscopy have studied the structure of ACC (3,7,31,32). High-energy X-ray total scattering studies on ACC indicate no structural coherence beyond 1.5 nm distance (20).…”

mentioning

confidence: 99%

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Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate

Radha

Forbes

Killian

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

416

449

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Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC ⇒ anhydrous ACC ∼ biogenic anhydrous ACC ⇒ vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO 2 sequestration. amorphous calcium carbonate (ACC) | calorimetry | crystallization enthalpy | sea urchin larval spicules | synthetic and biogenic ACC

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Section: Resultssupporting

confidence: 73%

mentioning

confidence: 99%

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Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate

Radha

Forbes

Killian

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

416

449

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“…One of the most striking features of the PDF data from the amorphous pyrophosphate phases was the complete loss of structural coherence beyond interatomic separations greater than $8 A, thus validating their designation as amorphous. This level of disorder is comparable with that reported for ACC 41 and markedly contrasts with that observed in the analogous crystalline materials. There was nevertheless evidence of short-range order associated with the P 2 O 7 4À units and their short-range interactions with the M 2+ cations and water molecules.…”

supporting

confidence: 84%

Enhanced stability and local structure in biologically relevant amorphous materials containing pyrophosphate

et al. 2011

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There is increasing evidence that amorphous inorganic materials play a key role in biomineralisation in many organisms, however the inherent instability of synthetic analogues in the absence of the complex in vivo matrix limits their study and clinical exploitation. To address this, we report here an approach that enhances long-term stability to >1 year of biologically relevant amorphous metal phosphates, in the absence of any complex stabilisers, by utilising pyrophosphates (P 2 O 7 4À ); species themselves ubiquitous in vivo. Ambient temperature precipitation reactions were employed to synthesise amorphous Ca 2 P 2 O 7 .nH 2 O and Sr 2 P 2 O 7 .nH 2 O (3.8 < n < 4.2) and their stability and structure were investigated. Pair distribution functions (PDF) derived from synchrotron X-ray data indicated a lack of structural order beyond $8 A in both phases, with this local order found to resemble crystalline analogues. Further studies, including 1 H and 31 P solid state NMR, suggest the unusually high stability of these purely inorganic amorphous phases is partly due to disorder in the P-O-P bond angles within the P 2 O 7 units, which impede crystallization, and to water molecules, which are involved in H-bonds of various strengths within the structures and hamper the formation of an ordered network. In situ high temperature powder X-ray diffraction data indicated that the amorphous nature of both phases surprisingly persisted to $450 C. Further NMR and TGA studies found that above ambient temperature some water molecules reacted with P 2 O 7 anions, leading to the hydrolysis of some P-O-P linkages and the formation of HPO 4 2À anions within the amorphous matrix. The latter anions then recombined into P 2 O 7 ions at higher temperatures prior to crystallization. Together, these findings provide important new materials with unexplored potential for enzyme-assisted resorption and establish factors crucial to isolate further stable amorphous inorganic materials. IntroductionA growing awareness of the existence and potential of amorphous inorganic materials has led to a rapid increase in their study in recent years. Often previously neglected or undetected as a consequence of their lack of long-range structural order and relative instability, amorphous inorganic materials are now more readily evident, partly through the continuing development of techniques sensitive to local order, such as magic angle spinning (MAS) solid state NMR and atomic pair distribution functions. Of particular interest has been the discovery of their prevalence in a diverse range of biological systems, 1-8 where it appears organisms exploit their unique properties in a number of processes.Amorphous calcium carbonate (ACC) is one of the most widely studied amorphous materials in nature, 1,2 with numerous studies on marine creatures, 9 where ACC has been shown to be a transient precursor to hard external shell formation. In effect, the highly unstable and soluble ACC is used as a reactive store of calcium and carbonate ions whose transformation in...

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“…The mineral ferrihydrite can be classified as crystalline (this is called six-line ferrihydrite), or as amorphous (this is called two-line ferrihydrite). [4][5][6] The structures of Amorphous Calcium Carbonate (ACC), [7][8][9][10][11][12][13][14][15][16] Amorphous Calcium Phosphate (ACP), 17 and Amorphous Calcium Sulphate (ACS) [18][19][20] are also poorly understood. The properties of ACC clearly depend on how it is prepared, 9,[21][22][23][24] and Gebauer et al 23 refer to 'protovaterite' and 'proto-calcite' forms of ACC, which * To whom correspondence should be addressed although amorphous have NMR and EXAFS spectra that have (broadened) features in common with vaterite, and with calcite, respectively.…”

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confidence: 99%

State between Liquid and Crystal: Locally Crystalline but with the Structure Factor of a Liquid

Mithen

Sear

2016

Crystal Growth & Design

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We are familiar with large highly-ordered single crystals, such as those used in the semiconductor industry. There the crystalline ordering in the silicon crystals extends for billions and more lattice spacings. As a result, X-ray diffraction (XRD) patterns of these crystals have sharp Bragg peaks. We are also familiar with liquids, where the molecules have a local structure that is very different to that in a crystal. In addition, in liquids there is only ordering over a few molecular diameters, and so they do not have Bragg peaks. But there are materials, where the situation is much less clear. Many of these materials are referred to as amorphous.For example, the structure of amorphous silicon is controversial. There is debate 1-3 over whether it possesses some crystalline ordering of the sort variously referred to as paracrystalline order, nanocrystalline order or medium-range crystalline order, or whether it has no crystalline ordering. We do not know if locally, silicon atoms are arranged in the structure of a liquid, or whether they are in tiny crystals only a few silicon atoms across. There are other systems at the borderline between liquid and crystal. The mineral ferrihydrite can be classified as crystalline (this is called six-line ferrihydrite), or as amorphous (this is called two-line ferrihydrite). [4][5][6] The structures of Amorphous Calcium Carbonate (ACC), 7-16 Amorphous Calcium Phosphate (ACP), 17 and Amorphous Calcium Sulphate (ACS) [18][19][20] are also poorly understood. The properties of ACC clearly depend on how it is prepared, 9,21-24 and Gebauer et al. 23 refer to 'protovaterite' and 'proto-calcite' forms of ACC, which * To whom correspondence should be addressed although amorphous have NMR and EXAFS spectra that have (broadened) features in common with vaterite, and with calcite, respectively. Vaterite and calcite are two of the crystal polymorphs of calcium carbonate.Experimental data such as XRD can clearly distinguish between large single crystals and liquids, but as we have known since Scherrer's work a hundred years ago, 25 as the size of crystallites decreases, the width of the Bragg peaks in the structure factor S(k) increases. Finite size effects give a peak width ∆k ≈ k/n, for a crystallite n lattice spacings across. For n 10, the peak is so broad that it is essentially as broad as features in the S(k)'s of liquids, and so XRD is not be able to distinguish between a liquid or glass, and a state made of very small crystallites. In computer simulations we can circumvent the problem this causes in identifying a state, as there we know the exact positions of all molecules, in real space, and so have much more information than is contained in an XRD pattern.Here we use computer simulation to study crystallisation in microscopic detail, in a simple model: the Gaussian Core Model (GCM). 26 In the GCM, molecules interact via the spherically symmetric potential v(r) = ε exp[−r 2 /σ 2 ], where the parameters ε and σ have dimensions of energy and length, respectively. This is a simple mod...

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Structural Characteristics of Synthetic Amorphous Calcium Carbonate

Cited by 212 publications

References 35 publications

Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate

Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate

Enhanced stability and local structure in biologically relevant amorphous materials containing pyrophosphate

State between Liquid and Crystal: Locally Crystalline but with the Structure Factor of a Liquid

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