Shaping calcite crystals by customized self-assembling pseudopeptide foldamers

Two pseudopeptide foldamers with similar backbones, one containing a d-4-carboxy-5-methyl-oxazolidin-2-one moiety (1) and the other a d-proline moiety (2), self-assembled in a 9:1 water-ethanol mixture. Molecule 1 formed fibres that generated a highly viscous sol or a gel by increasing its concentration; molecule 2 assembled in nanoparticles that aggregated in bigger particles by increasing its concentration. This behaviour was conserved in the presence of 10 mM CaCl2. Both foldamers, which exposed carboxylate groups, were able to modify the shape of single crystals of calcite. The presence of molecule 1 favoured the formation of rhombohedral calcite showing additional crystalline faces, while molecule 2 induced the formation of cavities and curvatures. Thus, pseudopeptide foldamers diversely act as crystal growth modifiers according to minor structural changes that mutate their self-assembly. This result is of general interest for the design of new molecules affecting the crystallization process and has implications in understanding how biological molecules control the growth of mineral phases.