What molecule am I?
Hydroxyapatite, sometimes referred to as durapatite, is a calcium phosphate/hydroxide mineral that occurs naturally in “phosphate rock”. It is also present in as much as 70 wt% of human bone.
Although the formula for hydroxyapatite is usually expressed as Ca5(PO4)3OH, it is sometimes given as Ca10(PO4)6OH2 or 3Ca2(PO4)2CaOH2 to indicate that its crystal unit cell consists of two formula weights. In the 3-D image shown above, calcium is represented in green, phosphorus in gray, oxygen in pink, and hydrogen in black.
In addition to natural hydroxyapatite, the commercial substance is frequently synthetic. It was made as long ago as 1873, when British agricultural chemist Robert Warington, Jr., prepared it from calcium nitrate and potassium dihydrogen phosphate. In modern times, it is synthesized via wet chemical precipitation, biomimetic deposition, or electrodeposition. One biosynthetic method that used the bacterium Klebsiella pneumoniae was reported in 2019 by Arivalagan Pugazhendhi, Rathinasamy Subashkumar, and coauthors at institutions in India and Viet Nam.
Natural hydroxyapatite contains impurities, so its main use is as a source of phosphate and subsequently other phosphorus-containing compounds. The much purer synthetic material is used to form artificial teeth and bones or repair natural tissues. Several aspects of hydroxyapatite chemistry and biology are covered in the ScienceDirect page about the molecule.
When you see skeletons hanging about this Halloween week, think of hydroxyapatite!
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.