The role of bivalent metals in hydroxyapatite structures as revealed by molecular modeling with the HyperChem software.

Hydroxyapatite, the major component of bone, demonstrates significant reactivity with metals. Knowledge of spatial structure and energy data of the molecule helps understand the binding of metals by hydroxyapatite and elucidate the chemical and physical properties of such complexes. We used HyperChem software (Hypercube Inc.) to analyze the structure of hydroxyapatite when the central calcium atom is replaced by one of the metal ions (Mg, Cu, Zn, Fe, Cr, Mn) marked by us in bone. Our results show that hetero-ionic exchange affects composition and leads to deformation of hydroxyapatite crystals. Replacement was accompanied by changes in bond lengths between oxygen and calcium atoms in the hydroxyapatite molecule and by displacement of groups of atoms surrounding the central calcium atom. The use of molecular modeling as a computational tool enabled a preliminary and theoretical understanding of chemical structure without the need for laboratory tests.