The Precipitation of Calcium Carbonate in the Presence of Macromolecules Isolated from Corals

This study investigated the CaCO3 spontaneous precipitation in the presence of soluble organic macromolecules (SOMs) extracted from the skeleton of Mediterranean colonial coral species, symbiotic Cladocora caespitosa (SOM-CCA) and asymbiotic Astroides calycularis (SOM-ACL). This approach was used as a model to explore biomineralization processes in marine organisms. The research was conducted in systems without or with the addition of Mg2+ (Mg/Ca molar ratio was 5:1) and/or SOMs (concentration range was 0.5–4 ppm). In the model system (system without Mg2+ or SOMs), only vaterite spherulites precipitated, while in the system with added Mg2+, only aragonite irregular aggregates were observed. Although the addition of SOMs did not influence the polymorphic composition of the CaCO3 precipitates, it led to noticeable changes in induction time and morphology of CaCO3 crystals, and these effects were stronger in the presence of SOM-ACL. By comparing systems containing both Mg2+ and SOM with the model system as well as with systems where Mg2+ or SOMs were added individually, the dominant role of Mg2+ in the aragonite formation was observed. However, the combined effect of Mg2+ and both SOMs enhanced the inhibition of CaCO3 precipitation. This inhibitory effect was particularly enhanced in the system combining Mg2+ and SOM-ACL.