Langmuir, 2019, vol 35, 17, pp. 5802-5808
The model peptides A8K and A10K self-assemble in water into ca. 100 nm long ribbon-like aggregates. These structures can be described as ?-sheets laminated into a ribbon structure with a constant elliptical cross-section of 4 by 8 nm, where the longer axis corresponds to a finite number, N ? 15, of laminated sheets, and 4 nm corresponds to a stretched peptide length. The ribbon cross-section is strikingly constant and independent of the peptide concentration. High-contrast transmission electron microscopy shows that the ribbons are twisted with a pitch ? ? 15 nm. The self-assembly is analyzed within a simple model taking into account the interfacial free energy of the hydrophobic ?-sheets and a free energy penalty arising from an increased stretching of hydrogen bonds within the laminated ?-sheets, arising from the twist of the ribbons. The model predicts an optimal value N, in agreement with the experimental observations.