Interactions of Scalenohedral Calcite Crystals with Acidic Amino Acid Derivatives of Salicylic Acid

The kinetics of scalenohedral calcite crystal growth in the presence of N -salicyloil- l -aspartic (N-Sal-Asp) and N -salicyloil- l -glutamic acid (N-Sal-Glu), as selected models of anti-inflammatory drug-like substances, were analyzed in order to study the molecular interactions of the selected salicylates with scalenohedral {2 1 4} surfaces. The results revealed that the growth is controlled by surface reactions, proceeding at the spiral step. The presence of the additives caused the inhibition of the growth, wherein the N-Sal-Asp interacted more strongly than N-Sal-Glu. The obtained data were supported with the electrokinetic, spectroscopic, and adsorption measurements. The interactions between the selected additives and the scalenohedral calcite crystals were compared with the rhombohedral modification. The stronger interactions of salicylates with scalenohedral surfaces are explained in terms of their higher reactivity and, most likely, better structural matching of their surface calcium ions with the salicylate carboxylic groups. In addition, the spontaneous precipitation of scalenohedral or rhombohedral calcite crystals in the presence of selected salicylates indicated that, under the applied conditions, the salicylate incorporation into the scalenohedral modification was significantly higher and could be related to the enhanced adsorption efficiency and the kinetics of crystal growth. The obtained results can contribute to understanding the basic interactions between the model drug derivatives containing carboxylic functional groups with different mineral surfaces, as well as to the development of biocompatible calcium carbonate drug carriers.