Fig. 19.

The top panel shows self-assembly starting at the folded monomer (left) and proceeding to soluble peptide assemblies of increasing mass (right). Soluble peptide oligomers with identical mass (that is, number of monomer units n) can assume different conformations, such as globular (bottom row) or β-strand conformations (top row) with different collision cross-sections. Successively mass-extracting a specific aggregation state from the solution-phase distribution and subsequent determination of its collision cross-section revealed the self-assembly pathway that occurred in solution (see arrow). The bottom panels show plots of measured collision cross sections as a function of the oligomer number n. YGGFL self-assembled isotropically with cross-sections that increased as n 2/3 (line) V = volume. NNQQNY followed an isotropic assembly up to the octamer. Fibril-like β-sheet conformations emerged at the nonamer and became prevalent at the nonadecamer. Figure adapted from Ref. [132].