Calcium Phosphate Prenucleation Complexes in Water by Means of ab Initio Molecular Dynamics Simulations

The nucleation of calcium phosphates, the main inorganic component of bone and tooth tissues, is thought to proceed by aggregation of prenucleation clusters recently identified as calcium triphosphate complexes. We have performed ab initio molecular dynamics simulations to elucidate their structures and stabilities in aqueous solution. We find the calcium to be seven-coordinated by two water molecules, two bidentate phosphates, and one monodentate phosphate. Free energy results obtained using umbrella sampling simulations show that the complex with a Ca/P ratio of 1:3 is the most energetically favored and more thermodynamically stable than the free ions.