Octacalcium phosphate

Octacalcium phosphate
Names
IUPAC name
octacalcium dihydrogen hexakis(phosphate) pentahydrate
Other names
Octacalcium Phosphate
Identifiers
13767-12-9 Yes
PubChem 123896
Properties
Ca8H2(PO4)6.5H2O
Molar mass 446.234023 g/mol
Appearance white powder
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Octacalcium phosphate (sometimes referred to as OCP) is a calcium phosphate with a formula Ca8H2(PO4)6.5H2O.[1] OCP may be a precursor in creation of the tooth enamel, dentine and bones in living organisms.

OCP has been shown to be a precursor of hydroxylapatite (HAP), an inorganic biomineral that is very important in bone growth. Determinations of the crystal structures of OCP and acidic apatite thus appear to be a pre-requisite to an understanding of the formation and chemical properties of skeletal tissues.[2] OCP could one day replace HAP in bone grafts and implants because of the similar apatite structure. OCP is an intermediate complex before the synthesis of HAP. When mixed with boiling water the crystal structure morphs to one that is very similar to apatitic structure of HAP. OCP has similar domains to HAP and has an apatite crystal structure. This makes it ideal to fill in calcium pores in teeth and bones.[3] The morphology of tooth and bone crystallites, as seen in their micrographs, strongly indicates that OCP is involved in the formation of these tissues. There have been studies that have shown the advantages of using OCP in tooth enamel repair to stimulate the regrowth of the enamel because the crystal structure fits into the pores of tooth enamel.[4] Studies have been done with titanium plates and bone implants with a coating of OCP. The implants and plates with coatings of OCP were accepted and integrated more quickly and fully than those without OCP because of the apatite crystal structure of OCP that is similar to the crystal structure of bone.[5] OCP shows very promising signs of replacing HAP in bone and tooth repair and growth in grafts and implants and will likely be used more widespread in the healthcare fields.

Molecular and Crystal Structure

Weissenberg measurements on OCP gave the lattice a = 19.7 A., b = 9.59 A., c =6.87 A., α≅β = 90.7’ and γ = 71.8’. Corresponding hydroxyapatite constant 2a = 18.84 A., a’ = 9.42 A., c = 6.885 k., α = α’ = 90” and γ = 60”, resemble closely those of OCP in the values of b, c and a, which lie in the plane of the OCP plates. The final pattern was apatitic, intermediate in sharpness between those of tooth enamel and bone. Boiling water decomposed OCP into an apatite approaching hydroxyapatite in composition, along with a variable amount of CaHP04. Both thermal and hydrothermal treatments sometimes yielded apatitic single crystal pseudomorphs after OCP, the c-axes being parallel to the c of the original OCP.[2] Due to the small crystal structure of OCP it is often a twinned crystal structure. The average crystal size of OCP is 13.5 ± 0.2 nm [6]

Synthesis

Ca(CH3COO) + Na2HPO4 + NaH2PO4 → Ca4HO12P3 at pH 5

Dropwise addition of calcium acetate solution into a sodium acid phosphate solution at pH 5 or 6, maintained at 60°C for 3 to 4 hours.[6]

Dropwise addition of calcium into phosphate solution or vice versa at pH 4.5 at 70°C for 1 hour. The solutions were either stirred or unstirred during precipitation and during the subsequent digestion periods. The precipitates are filtered, washed several times with distilled water and air-dried.[7]

Reactions

Hydrolysis of OCP easily creates hydroxyapatite [6]

References

  1. ↑ Reacquel Z. LeGeros "Preparation of octacalcium phosphate (OCP): A direct fast method", Journal Calcified Tissue International, Volume 37, Number 2, March 1985, pp.194-197.(abstract)
  2. ↑ 2.0 2.1 Brown, W. E., Lehr, J. R.. Smith, J. P., Frazier, A. W., J. Am. Chem. Soc., 1957, 79 (19), 5318.
  3. ↑ Brown, W.E., Eidelman, N., Tomazic, B., 1987. Adv. Dent. Res., 1; 306
  4. ↑ Nelson, D.J.A., McLean, J.D., 1984. Calcif Tissue Int. 36, 219.
  5. ↑ http://www.pubmed.gov Octacalcium phosphate: Osteoconductivity and crystal chemistry. Suzaki, O. Last accessed 4/09/10
  6. ↑ 6.0 6.1 6.2 M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.
  7. ↑ LeGeros, R. Z., 1985. Calcif Tissue Int 37:194

Sources