Shaping calcite crystals by customized self-assembling pseudopeptide foldamers

Abstract

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.