Elucidating the role of charge density on the growth of CaCO3 crystals underneath Calix[4]arene monolayers

The amphiphilic 5,11,17,23-tetrakis-(1,1,3,3-tetramethylbutyl)-25,26,27,28-tetra(2-hydroxyethoxy)calix[4]arene (1) forms stable monolayers at the air-water interface. The growth of CaCO3 crystals underneath monolayers of 1 is strongly inhibited, in contrast to the corresponding carboxylic acid derivative 5,11,17,23-tetrakis-(1,1,3,3-tetramethylbutyl)-25,26,27,28-tetra(carboxymethoxy)calix[4]arene (2), the monolayers of which lead to growth of preferentially oriented calcite single crystals. The growth morphology of CaCO3 crystals is correlated with the phase behaviour and surface potential of the monolayers. The investigations demonstrate that the average charge density is the dominant factor for heterogeneous nucleation of CaCO3 crystals at the calixarene monolayer/solution interface.