Effect of amino acid on calcium phosphate phase transformation: attenuated total reflectance-infrared spectroscopy and chemometrics

The effects of amino acids on calcium phosphate phase transformation were investigated by using attenuated total reflection (ATR)-infrared (IR) spectroscopy. A self-setting apatite cement, which consisted of tetracalcium phosphate and dicalcium phosphate, was transformed into hydroxyapatite (HAp) by kneading with a phosphoric acid solution. Phosphate buffer (0.2 M, pH 6.8) or aqueous solutions of 0.1 w/v% amino acids (alanine, asparagine, serine, and o-phospho-l-serine) were used as the kneading solutions. The kneaded samples were analyzed by ATR-IR spectroscopy. The amount of HAp produced was determined by the multivariate curve resolution alternative least-squares method based on the ATR-IR spectra. The phase transformations to HAp were fitted to several solid-state kinetic models. The results indicate that o-phospho-l-serine inhibits the crystal growth of HAp. A simulation model of HAp surface interaction was developed by using the molecular dynamics method. The total energy of the HAp surface with amino acids was sufficient to explain the o-phospho-l-serine inhibition model. The inhibition is attributed to the specific adsorption of o-phospho-l-serine on the surface of HAp seed crystals.