Figure 2: Nanostructure formation in solution and in bulk.

Amide I regions of (a) the solid-state and (b) the solution-phase infrared spectra of M0–M5, and the constituent absorption bands obtained by peak deconvolution. Bulk infrared spectra of M2–M5 as well as solution-phase spectra of M4–M5 exhibited a sharp amide I absorption at 1,625–1,627 cm^–1 (half-height width 14–17 cm⁻¹) accompanied with a secondary absorption at 1,687–1,695 cm⁻¹, consistent with the presence of antiparallel β-sheet structures. (c) Plots of the relative peak area A_1,625/A_I,total of the absorption bands at around 1,625–1,630 cm⁻¹ showed that M2–M5 and D2–D5 in bulk, as well as M4–M5 and D4–D5 in solution were strongly aggregated. (d) AFM images of M1–M5 spin-coated from tetrachloroethane solution onto SiO₂ (left) or HOPG (right) substrates revealed the formation of fibrils for M5 on both substrates (scale bars, 300 nm for M1–M3 and 2 μm for M4–M5). The fibrils exhibited a width of 7.0 (±0.1) nm and a uniform height of 3.5 (±0.8) nm, suggesting they were formed from four to six stacked β-sheet tapes. Fibrils of M4 on both substrates were less defined and 2.1 (±0.9) nm in height, consistent with two to four stacked β-sheet tapes. A second population of thin aggregates (8–10 nm in width, 0.4–0.6 nm in height) was observed on HOPG (but not SiO₂) that were assigned to single β-sheet tapes. M3 gave rise to long flexible fibrils or tapes (0.7–1.2 nm in height, consistent with one to two β-sheet tapes) only on HOPG. In the case of M2, laterally aggregated, short tape-like features (height 0.7 nm) with lengths of several hundred nanometres were observed on HOPG. No defined aggregates but continuous films or drop-like features were observed for M1. See Supplementary Figs 2–6 for details on infrared spectra, peak deconvolution and AFM imaging of M0–M5 and D0–D5.