Structure and in vivo anticalcification properties of a polymeric calcium–sodium–phosphocitrate organic–inorganic hybrid

This paper describes the synthesis, characterization and crystal structure of an organic–inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl2·2H2O and Na4(HPC)·3H2O in water, at pH 2. Its structure is polymeric with Ca(PC)2(H2O) “monomers” connected through Na+ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H2O oxygens. CaO(C) distances are in the 2.446(2)–2.586(2) Å range. There is a short distance of 2.477(1) Å between Ca and the ester O from C–O–PO3H2. All –COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from –PO3H2. Na ions are six-coordinate surrounded by –COOH’s. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na–phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H5PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H5PC) giving nearly quantitative (95%) plaque inhibition.