Investigation of selected amino acids influence on calcium carbonate precipitation - simple model of biomineralization

Calcium carbonate is the main inorganic component of biominerals found in many invertebrate organisms and is present either as a specific polymorph (calcite or aragonite), hydrated or in amorphous form. The calcite skeletal elements regularly contain small amounts of proteins which are either incorporated or adsorbed on the single crystals of calcite. Previously it has been shown that isolated fragments of proteins extracted from mineralised tissue, or their synthetic macromolecular analogues, exert a significant influence on the morphology and crystal structure of calcium carbonate when precipitated in the appropriate model systems. The aim of this research is to investigate a role of the selected amino acids as a simple models of biomacromolecules supposed to be responsible for specific precipitation of calcium carbonates in biomineralising systems. In addition, possible crystallographic distortions of the calcite lattice will be investigated. For that purpose amino acids having distinct chemical and physical properties were selected: asparagine, aspartic acid and lysine were chosen because of differently charged side chains, while tyrosine and phenylalanine, as well as serine and alanine have different polarity. The results of structural (EPR) and kinetic analyses indicated an overall inhibition of calcite growth in the presence of all amino acids. The inhibition is probably caused by a slower transformation of initially formed vaterite into the calcite. Since the selected amino acids are charged under the applied experimental conditions, some surface interactions are assumed to be responsible for the observed effect.