Octacalcium phosphate (sometimes referred to as OCP) is a

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

with a formula Ca₈H₂(PO₄)₆⋅5H₂O. OCP may be a precursor to

tooth enamel Tooth enamel is one of the four major Tissue (biology), tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the Crown (tooth), crown. The ...

dentine Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...

, and

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

s. OCP is a precursor of

hydroxylapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...

(HAP), an inorganic biomineral that is important in bone growth. OCP has been suggested as a replacement for HAP in

bone grafts Bone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures that are extremely complex, pose a significant health risk to the patient, or fail to heal properly. Some small or acute fractures can be cured wit ...

Properties

Boiling water decomposes OCP into

hydroxyapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...

and

dicalcium phosphate Dicalcium phosphate is the calcium phosphate with the formula CaHPO4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO42– anion involves the removal of two protons from phosphoric acid, H3PO4. It is al ...

. Both thermal and hydrothermal treatments sometimes yield apatitic single crystal

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by ...

s after OCP, the c-axes being parallel to the c of the original OCP. OCP has the lattice constants ''a'' = 19.7 Å, ''b'' = 9.59 Å, ''c'' =6.87 Å, ''α'' = ''β'' = 90.7° and ''γ = 71.8°, slightly different from those of

. OCP has a strong

crystal twinning Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly ...

tendency. The average crystal size of OCP is 13.5 ± 0.2 nm.

Synthesis

It can be prepared by treating

calcium acetate Calcium acetate is a chemical compound which is a calcium salt of acetic acid. It has the formula Ca(C2H3O2)2. Its standard name is calcium acetate, while calcium ethanoate is the systematic name. An older name is acetate of lime. The anhydrous ...

with sodium acid phosphate solution.

References

Sources

* * * * * * * * {{cite journal , last1=Komlev , first1=Vladimir S. , last2=Barinov , first2=Sergei M. , last3=Bozo , first3=Ilya I. , last4=Deev , first4=Roman V. , last5=Eremin , first5=Ilya I. , last6=Fedotov , first6=Alexander Yu. , last7=Gurin , first7=Alex N. , last8=Khromova , first8=Natalia V. , last9=Kopnin , first9=Pavel B. , last10=Kuvshinova , first10=Ekaterina A. , last11=Mamonov , first11=Vasily E. , last12=Rybko , first12=Vera A. , last13=Sergeeva , first13=Natalia S. , last14=Teterina , first14=Anastasia Yu. , last15=Zorin , first15=Vadim L. , title=Bioceramics Composed of Octacalcium Phosphate Demonstrate Enhanced Biological Behavior , journal=ACS Applied Materials & Interfaces , date=8 October 2014 , volume=6 , issue=19 , pages=16610–16620 , doi=10.1021/am502583p , pmid=25184694 Calcium compounds Phosphates Dental enamel Bones