Crystal structure of octacalcium bis(hydrogenphosphate) tetrakis(phosphate)pentahydrate, Ca8(HP04)2(PO4)4�5H2O

Mathew, M.; Brown, W. E.; Schroeder, L. W.; Dickens, Brian

doi:10.1007/bf01194315

Cited by 192 publications

(100 citation statements)

References 11 publications

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“…However, OCP might be non-stoichiometric and be either Ca-deficient (down to Ca/ P = 1.26) or include excessive calcium (up to Ca/ P = 1.48) in the structure (Suzuki 2010a). It has been proposed that the structure of a non-stoichiometric OCP contains an excess of hydrogen, resulting in a non-stoichiometric chemical formula Ca 16 H 4?x (PO 4 ) 12 (-OH) x Á(10 -x)H 2 O, which resembles the structure of HA even more closely than previously anticipated (Mathew et al 1988). Furthermore, a partially hydrolyzed form of OCP with Ca/P molar ratio of 1.37 might be prepared (Suzuki 2010a;Miyatake et al 2009).…”

Section: Dcpa (Or Dcp)mentioning

confidence: 78%

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

Dorozhkin¹

2017

Morphologie

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Section: Dcpa (Or Dcp)mentioning

confidence: 78%

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

Dorozhkin¹

2017

Morphologie

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“…Since pseudo-OCP gradually changed to actual OCP with maturation in the solution, it was metastable intermediate phase. The OCP crystal structure along the a-axis consists of alternating apatite-like layers and HPO 4 -OH layers (corresponding to the center of hydrated layer in the previous OCP model) [8,24]. We simulated the XRD pattern based on the OCP structure and found that the lack of an HPO 4 -OH layer resulted in the XRD pattern of pseudo-OCP; i.e.…”

Section: Introductionmentioning

confidence: 98%

“…One is solvent-mediated transformation, which is the simple dissolution and growth of materials depending on the difference in solubility. A representative example for calcium phosphate is the hydrolysis of DCPD and subsequent growth of OCP [8]. The other is structural conversion from metastable to stable phases as was revealed in situ using a light scattering technique [9,10].…”

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confidence: 99%

Metastable Intermediate Phase during Phase Transformation of Calcium Phosphates

Onuma¹,

Sugiura²

2015

J Biotechnol Biomater

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Phase transformation of calcium phosphates from amorphous to crystalline phases around neutral pH proceeds via direct structure conversion using non-ionic elementary units. This transformation inevitably forms metastable intermediate-structured phase(s) between the two end phases. In addition to conventional calcium phosphate phases appearing in the transformation, new unknown phases were observed. They did not correspond to simply poor crystalline materials of conventional phases and instead had particular structures. One was pseudo-OCP, which lacked the HPO 4 -OH layers in the conventional OCP structure.Keywords: Phase transformation; Amorphous phase; Intermediate phase; OCP; HAP Calcium phosphates have been energetically investigated for more than half a century because of their important role not only in forming hard tissues such as bone and teeth but also being a frequent cause of calculus and arteriosclerosis [1,2]. One factor hindering a sound understanding of their formation mechanism is that they appear in several forms at room to body temperatures [3,4]. For example, amorphous calcium phosphate (ACP), dicalcium phosphate dihydrate (DCPD), β-tricalcium phosphate (β-TCP), octacalcium phosphate (OCP), and hydroxyapatite (HAP) form in weak acidic to weak basic calcium phosphate solutions. They precipitate and stably exist or transform into other more stable phases depending on the solution conditions. Transformation between each calcium phosphate [5][6][7] is of particular interest because the control of this process results in obtaining a desirable phase that can contribute to the design of calciumphosphate-based biomaterials with novel functions.Two phase-transformation mechanisms have been proposed. One is solvent-mediated transformation, which is the simple dissolution and growth of materials depending on the difference in solubility. A representative example for calcium phosphate is the hydrolysis of DCPD and subsequent growth of OCP [8]. The other is structural conversion from metastable to stable phases as was revealed in situ using a light scattering technique [9,10]. If the concentrations of calcium and phosphate ions in the solution are sufficiently high, ACP first forms in the solution and transforms into other phases such as OCP and HAP. The transformation proceeds via direct conversion of an amorphous structure into crystalline ones. This kinetics is attributed to a common cluster unit present in both the amorphous and crystalline phases [11][12][13][14][15]. Posner's cluster [11] and its symmetric isomers [16] were proposed for this common cluster, and then more complex structures of clusters were found through experimental and computational investigations [17,18]. That the clusters can be decomposed into smaller ion pairs as the minimum unit was also proposed [19], indicating the need for more careful investigation of the elemental unit in the phase transformation of calcium phosphates.Leaving aside the question about the structure of the minimum unit, we note that it is well accepte...

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“…Taking these things into consideration, it is clear that OCP in saiga horn has specific characteristics which can be understood from the theory of crystallization in solution. Because of the structural similarity between OCP and HA (Brown WE, 1966;Mathew M et al, 1988), the ideas proposed to explain are that the mechanism of progressive mineralization in saiga horn are epithelial, epitaxial mineralization (Theseleff I, 1995;Vainio S et al, 1993). We think, there are many points which need mineralization with regard to the mechanism of HA formation.…”

Section: Discussionmentioning

confidence: 99%

Morphological Character of Crystalline Components Present in Saiga Horn

Hashiguchi

Hashimoto

Akao

2001

Okajimas Folia Anatomica Japonica

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Summary: The purpose of this study was to investigate the ultrastructure of saiga-antelope (Saiga tatarica) horn for proposing the mechanism of the initial mineralization. Horn is derived from horny tooth of Cyclostomata. The minerals in saiga horn were identified crystallographically using electron microscopy and X-ray diffraction techniques. Soft X-ray photographs revealed the degree of the mineralization pattern. However, the number of rings did not indicate the age of saiga.Mineral deposites were observed among well banded keratin fibers and composed of powder like crystals. This deposited crystals were found by the X-ray diffraction method to be octacalcium phospate (OCP) by comparing these periodic lattice fringes to JCPDS card data The chemical formula of OCP is Ca8H2(PO4)6 5H2O. Evidences for the presence of OCP in mature hard tissues have never been obtained. This phenomenon described here may be characteristic of saiga horn because we have found no reports on this type of OCP mineralization in any other animal species. It is possible that OCP is the precursor in the initial mineralization step, indicating in a nucleation of mineral on the keratin fibers.

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Crystal structure of octacalcium bis(hydrogenphosphate) tetrakis(phosphate)pentahydrate, Ca8(HP04)2(PO4)4�5H2O

Cited by 192 publications

References 11 publications

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

Metastable Intermediate Phase during Phase Transformation of Calcium Phosphates

Morphological Character of Crystalline Components Present in Saiga Horn

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