Figure 6: Topological transitions in the ice microstructure.
(a) The calculated in-ice diffusivity (D, orange diamonds) of ribozyme and the corresponding tortuosity (τ, blue triangles) of the eutectic phase in MgCl2 ices (Supplementary Fig. S5). (b–d) Ices formed from undiluted (b), 12-fold diluted (c) and 50-fold diluted (d) extension reactions were flash-frozen in liquid N2 to preserve the eutectic phase structure and freeze-fractured, as in Figures 2b and 5d; however, the samples then underwent prolonged sublimation before gold deposition and SEM imaging. This preferential sublimation of the ice crystals exposes the three-dimensional ultrastructure of the eutectic phase, revealing the prominent sheets of a contiguous eutectic phase in the undiluted reaction (b). Dilution leads to a decrease in the volume of the eutectic phase, manifested by fusion of adjacent ice crystals and shrinking of contiguous sheets of eutectic phase to a network of tubular channels along the vertices of crystals (c), and eventually to sparsely distributed clusters of filamentous tubes (d).
