Fig. 5. Chiral switching by vertical platelet layer-by-layer rotation correlates with increasing size of vaterite helicoids during growth evolution in the presence of l-Asp.

(A to C) SEM images at low (top) and corresponding high (bottom) magnification of clockwise (yellow arrows) vaterite helicoids during their growth evolution extending from the first transitional straight-radiating (0° reference start point) achiral vaterite helicoid as depicted previously in Fig. 4D. As helicoids grow and increase in size, vertical platelets then successionally rotate by 22.5° in the clockwise direction in each layer to reach first 22.5°, then 45°, then 67.5° relative to the start point (small yellow bars). (D) When the vertical platelets in the uppermost layer continue to rotate clockwise to the horizontal position (90° from the reference start point), the helicoid becomes achiral having the horizontal-surrounding platelet orientation (gray double-headed arrow and bar). (E to G) With further clockwise rotational growth (to reach first 112.5°, then 135°, and then 157.5°; green bars), helicoids have a counterclockwise chiral structure (green arrows). (H) Finally with additional growth, a transitional achiral state of the helicoid (180°) again appears (gray double-headed arrow, gray bar), completing a cycle to again form an achiral structure with the same morphology as that of the original straight-radiating platelet orientation (0°) of achiral helicoids (as shown earlier in Fig. 4D), but now having a much larger size attributable to the additional growth by platelet layer additions.