Comparison of PXRD and EPR technique for monitoring distortion of calcite lattice in the presence of selected amino acids

Calcium carbonate is main inorganic component of biomineralization in different invertebrate organisms, either in a form of certain polymorph (calcite, vaterite and aragonite) or hydrated modification.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 mineralized 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. In addition, the formation of specific crystal modification can be influenced by parameters like temperature, pH or initial supersaturation, as well as by the presence of inorganic or organic additives. The aim of this research is to investigate distortions of the calcite lattice due to the influence of amino acids, selected as simple models of biomacromolecules supposed to be responsible for nucleation, growth and transformation of calcium carbonates in biomineralizing systems. For that purpose the amino acids having asparagine (Asn), aspartic acid (Asp) and lysine (Lys) were chosen because of differently charged side chains, while the tyrosine (Tyr) and phenylalanine (Phe), as well as serine (Ser) and alanine (Ala) have different polarity. The results of PXRD and EPR techniques as well as growth kinetic data indicate that amino acids interaction with calcite surface increase in the order: Asp > Tyr > Asn > Lys > Ser > Phe > Ala.