Figure 2. Hierarchical vaterite toroid suprastructures showing chiral orientations.

SEM images of vaterite toroids grown in 20 mM L- or D-Asp or in a racemic mixture of Asp (a–c), or in 20 mM L- or D-Glu or in a racemic mixture of Glu (d–f; pseudocoloured). L-enantiomers produce chiral toroids having a counterclockwise (right-handed) spiralling morphology (green arrow, a,d), whereas D-enantiomers produce a clockwise (left-handed) spiralling morphology (yellow arrow, b,e). For both L- and D-Glu, toroids form with a central core region remaining uncovered by platelets and with six peripheral structural subdomains, as indicated by the numbered white curved arrows and dashed lines (d,e). Under racemic conditions, no chirality effect is observed (c,f). Vaterite platelets are coloured green and yellow as induced by L- and D-acidic amino acids, respectively, and achiral vaterite structure is coloured pink. Scale bars, 6 μm (a,b,f) and 8 μm (c–e).