Release of phosphate and phosphonate from phenylphosphonate-modified zirconium phosphate in biomimetic solutions

In this study, the release of phosphorus oxyacid species from organically modified layered zirconium phosphate was investigated. Zirconium phosphate was modified by partially incorporating phenylphosphonate by heating a mixture of phosphoric acid and phenylphosphonic acid under reflux. Characterization by powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis confirmed that approximately 50 % of the phosphate groups in the zirconium phosphate framework were successfully replaced by phenyl groups. Upon immersion in Tris-hydrochloric acid buffer for 168 h, both inorganic phosphate and phenylphosphonate were released. In contrast, in phosphate-buffered saline, phenylphosphonate was eluted while inorganic phosphate from the solution was incorporated into the material. These results suggest that zirconium phosphate modified with phenylphosphonate can serve as a potential material for imparting phosphorus oxyacid-based drug-releasing functionality to zirconia-based dental materials.