Single-handed Double Helix and Spiral Platelet Formed by Racemate of Dissymmetric Cages.

Abstract

Since Pasteur s seminal work, spontaneous deracemization or symmetry breaking has been applied to separate homochiral domains from the erstwhile racemic system. However, the resulting homochirality can only be referred to when the scales of these domains and systems are specified. To clarify this notion, we report on the self-assembly of racemates of dissymmetric cages DC-1 with a cone-shape propeller geometry, forming a centrosymmetric columnar crystalline phase, namely racemic at crystallographic level . Due to their anisotropic geometry, the two enantiomers are packed in a frustrated fashion within this crystalline phase, in which single-handed double helices are observed, i.e. , single-handedness at supramolecular level . The frustrated packing, or layer continuity break-up, in turn facilitates screw dislocation during the crystal growth, forming left- or right-handed spiral platelets, namely symmetry-breaking at morphological level , even though each platelet is composed of DC-1 racemates. We also demonstrated the symmetry correlation between DC-1 molecules, the corresponding crystalline phase and spiral platelets, all exhibiting a C 3 -symmetry. This work might provide new insight into the relationship between racemization, symmetry-breaking and homochirality.