Calcium Phosphonate Frameworks for Treating Bone Tissue Disorders

Two new examples of uncommon three-dimensional Ca-bearing metal organic frameworks, [Ca­(H2O)3(HPXBP)] (CaP1) and [Ca2(H2O)2(HPXBP)1.5] (CaP2) (PXBP: p-xylylenebisphosphonate), were prepared and their structures characterized by single crystal X-ray diffraction. CaP1 crystallizes in the monoclinic C2/c space group, with three water molecules occupying a half coordination sphere on one side of the Ca atom, while CaP2 crystallizes in the triclinic P1̅ space group, with two crystallographic unique Ca atoms, each coordinated by a single water molecule. In contrast with CaP2, which exhibits very low bioactivity, CaP1 readily precipitates bone-precursor phases (octacalcium phosphate, OCP, and hydroxyapatite) in SBF solutions. Moreover, studies with MG63 osteoblast-like cells indicate that CaP1 is not toxic and stimulates bone mineralization and, thus, holds considerable potential for treating bone diseases, such as osteoporosis.