Octacalcium phosphate

Octacalcium phosphate
IUPAC name tetracalcium hydrogen phosphate diphosphate
Other names Octacalcium Phosphate
Identifiers
CAS number	13767-12-9
PubChem	123896
Properties
Molecular formula	Ca8H2(PO4)6.5H2O
Molar mass	446.234023 g/mol
Appearance	white powder
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.^[6] 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 ^[7]

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.^[8]

Ca(C₂H₃O₂)₂ + Na₂H₂P₂O₇ → Ca₄HO₁₂P₃ pH 5 or 6

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. 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. ^[9]

Reactions

Hydrolysis of OCP easily creates hydroxyapatite ^[10]

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. ^ 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. ^ www.pubmed.gov Octacalcium phosphate: Osteoconductivity and crystal chemistry. Suzaki, O. Last accessed 4/09/10
6. ^ Brown, W. E., Lehr, J. R.. Smith, J. P., Frazier, A. W., J. Am. Chem. Soc., 1957, 79 (19), 5318.
7. ^ M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.
8. ^ M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.
9. ^ LeGeros, R. Z., 1985. Calcif Tissue Int 37:194
10. ^ M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.

Sources

• Laurence C. Chow, Edward D. Eanes, "Octacalcium phosphate", Monograph in Oral Science, S. Karger AG, 2001, ISBN 978-3805572286.(Google books)
• Brown, W. E., Lehr, J. R.. Smith, J. P., Frazier, A. W., J. Am. Chem. Soc., 1957, 79 (19), 5318.
• M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.
• LeGeros, R. Z., 1985. Calcif Tissue Int 37:194
• http://pubchem.ncbi.nlm.nih.gov Summary octacalcium phosphate. Last accessed 4/9/10
• www.pubmed.gov Octacalcium phosphate: Osteoconductivity and crystal chemistry. Suzaki, O. Last accessed 4/09/10
• Nelson, D.J.A., McLean, J.D., 1984. Calcif Tissue Int. 36, 219.
• Brown, W.E., Eidelman, N., Tomazic, B., 1987. Adv. Dent. Res., 1; 306
• http://www.ccmr.cornell.edu/facilities/Winners06Sum/dattran.html Cornell Center for Materials Research. Dat T. Tran. Last Accessed 4/09/10