Influence of Condensed Phosphates on the Physical Chemistry of Calcium Phosphate Solids

This is not the first summary of the contributions toward understanding calcium phosphate spheres found in biology; however, it describes new options for the possible role of condensed phosphates (pyrophosphate and polyphosphates) in the formation, stability, and sometimes the crystallization of these spheres. The first section will briefly review the inorganic conditions required for mineral nucleation and growth and the industrial use of condensed phosphates as inhibitors of crystal formation. The capacity of condensed phosphates to stabilize spherical, x-ray amorphous, Ca- and P-rich granules in biology will be reviewed, and some biological examples provided. Condensed phosphates spontaneously hydrolyze into inorganic phosphate ions in aqueous environments, but the rate is affected by many factors. One accelerator of condensed phosphate hydrolytic degradation is active phosphatase enzymes; these enzymes introduce the potential for biological control of calcium phosphate crystal nucleation by reducing the nucleation-inhibiting effect of condensed phosphates, while simultaneously increasing the Pi concentration – and therefore phosphate crystal supersaturation. The relationship of these condensed phosphate hydrolysis factors on sample preparation and sample observation and the role phosphatase enzymes for biological phosphate mineral formation will be briefly reviewed for some prokaryotes and eukaryotes in which amorphous and/or crystalline Ca- and P-rich solids have been identified.