Fig. 2: Amorphous precursors host the nucleation of β-hematin.

a, b, d, e Negative staining electron micrographs of amorphous particles and crystals in hematin solutions. c Electron diffraction pattern of the particle in (b) reveals an amorphous signature and lack of order. f Electron diffraction pattern of the particle in (e) exhibit two peaks at 1.24 nm⁻¹ from the image center, highlighted in red circles, which corresponds to crystal lattice spacing of about 8 Å, superimposed on an amorphous pattern. Red arrows in (d and e) indicate crystals, identified from their elongated shapes with sharp parallel edges and, in (e), from its diffraction pattern in (f). In (a, b, and d) yellow arrows point at amorphous particles that do not hold crystals, identified from irregular shapes and diffraction patterns in (c), for particle in (b), and Supplementary Fig. S4f, for particle in (a). In (d and e), orange arrows identify particles that host, in (e), or initiate, in (d), crystals. g Schematic of crystal nucleation hosted by a disordered precursor. h, i Time-resolved AFM monitoring of the evolution of an amorphous particle supported on a large β-hematin crystal. h Evolution of the particle shape at the times indicated on the images. i The height profiles along dashed lines in panel (h); for images at 30, 60, 120, and 360 min see Supplementary Fig. S5.