4.2. Peptide self‐assembly

Peptide self‐assembly was initiated in a solution of water and 1,1,1,3,3,3‐HFIP (95:5, v/v) (pH 3–4 as a consequence of residual TFA from HPLC purification). Self‐assembly was analyzed at a peptide concentration of 0.2 mM quantified according to previously described protocols.^{16, 24, 25} Lyophilized peptides were dissolved in an acetonitrile:water:TFA mixture (60:39.9:0.1, v/v/v) to maintain an unassembled peptide state. Thus, peptides were analyzed under acidic conditions (pH 3–4) due to residual TFA. As such, all peptides had a net charge of +2 from the lysine side chains. Meanwhile, protonation of the glutamic acid side chains resulted in a neutral charge.

Peptide concentrations were determined from these solutions by analytical HPLC analysis and correlation of HPLC peak area to a standard curve constructed for each peptide (see Figures S21–S28 for standard curves). Standard concentration curves were prepared as described previously, and integrated peak areas were correlated to absolute peptide concentration by amino acid analysis (AIBiotech, Richmond, VA). Aliquots of the desired peptide quantity were frozen, lyophilized, and used immediately in self‐assembly studies. Self‐assembly was initiated by dissolving lyophilized peptides in HFIP followed by addition of water to give a peptide concentration of 0.2 mM (final solvent composition of 5% HFIP by volume); solutions were treated by vortex (1 min) and sonication (5 min) to give optically transparent, homogenous solutions. Self‐assembly was characterized using CD, FT‐IR spectroscopy, and TEM imaging as described in the following sections.