Chemical interaction between hydroxyapatite and organic molecules in biomaterials

In this study, we tried to elucidate chemical interactions between hydroxyapatite and organic molecules using an ab initio calculation method, i.e. discrete variational Xamethod. Two cluster models were investigated. One cluster model consisted of hydroxyapatite and methyl acetate; the later corresponds to a simplified molecule of poly-L-lactide that is a typical biodegradable material. Another cluster is the model of hydroxyapatite and glycine that is the simplest molecule in 20 amino acids. Although the glycine molecule has three types of ionization states, two types of interface models, cation model and zwitter ion model were adopted. An overlap population between a Ca ion of hydroxyapatite and COO" in glycine was larger than that between a Ca ion of hydroxyapatite and CO in methyl acetate. Further, in the case of the hydroxyapatite/glycine model, the zwitter ion model had larger chemical interaction than that of the cation model.