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Interactions of salicylic acid and its derivatives with calcite crystals of different morphologies (Elsevier)

Due to certain specific properties, like biocompatibility, no toxicity, biodegradability and/or ability to dissolve in a controlled manner, calcium carbonate polymorphs have been recently considered as a promising mineral carrier of pharmaceutical substances. Consequently, the understanding of the mechanisms of basic interactions of active pharmaceutical compounds with calcium carbonate surfaces became an important initial step in development of such functional composite materials. In this work a mechanism of adsorption of salicylic acid and its functional derivatives, chosen as a relatively simple model of anti-inflammatory drug compound, onto the calcite crystals of different morphologies was investigated. The improved adsorption of salicylates was achieved by using the substituents known to strongly interact with calcite surfaces, aspartic or glutamic acids. The interactions at the solid/liquid interface have been analysed by performing the crystal growth kinetics measurements of well-defined, scalenohedral and rhombohedral calcite seed crystals, in the presence of appropriate salicylate additives. In addition, the appropriate acustophoretic, spectroscopic and particularly the adsorption measurements have been performed. The N-salicyloil-L-aspartic acid (N-Sal-ASp) and N-salicyloil-L-glutamic acid (N-Sal-Glu) showed a significant crystal growth inhibition in comparison to salicylic acid (SA) and 5- aminosalicylic acid (5-ASA). Based on the kinetic parameters, conclusions on the mechanism of interactions were gained. The results indicated strong interactions of N-Sal-Asp molecules for both types of calcite surfaces, most probably irreversible adsorption, while in the case of SA, 5-ASA and NSal-Glu predominantly electrostatic interactions with calcite surfaces were pointed out. Chemical and conformational properties of used functional derivatives were correlated with different calcite surface structures and the strongest interactions were anticipated for systems scalenohedral calcite / aspartic acid derivative of salicylic acid. Higher affinity for adsorption active sites on scalenohedral surfaces was explained in terms of higher reactivity of calcium ions of {;214}; faces and their better structural matching with carboxylic functional groups.

Calcium carbonate; Salicylic acid derivatives adsorption; Crystal growth kinetics; Drug delivery

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