Covalent modification of calcium hydroxyapatite surface by grafting phenyl phosphonate moieties

The reaction between phenyl phosphonic dichloride (C6H5P(O)Cl2) and synthetic calcium hydroxy- and fluorapatite has been investigated. The presence of mono- or polymeric (C6H5PO) fragment bound to hydroxyapatite was evidenced by IR, and solid-state 31P NMR spectroscopy. X-ray powder analysis has shown that the apatitic structure remains unchanged during the reaction. In contrast, no reaction was found using fluorapatite. According to the results found for these two different apatites a mechanism was proposed for the formation of covalent P–O–P bonds as the result of a reaction between the C6H5P(O)Cl2 organic reagent and (HPO4)− and/or OH− ions of the hydroxyapatite.