The peptide KI4Kwas synthesized on a CEM Liberty microwave synthesizer by using the standard Fmoc solid phase synthesis strategy. The Rink amide resin was used in order to allow the C-terminus to be amidated and then the N-terminus was capped with acetic anhydride before cleavage from the resin. The detailed information for the synthesis and purification procedures have been described in our previous work.^[1] The purity of the final products was ascertained bymatrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF) and reversed-phase high-performance liquid chromatograph (RP-HPLC) analyses, indicating high purities (98%).

The peptide fluffy powder was dissolved in Milli-Q water and acetonitrile mixture to create solutions with the concentration of 16 mM. The suspension was sonicated for about 10 min and then the resulting homogenous solutions were incubated for 7 days at room temperature before further characterization.

AFM measurements were performed on a commercial NanoscopeIVaMultiMode AFM (Digital Instruments, Santa Barbara, CA) in the tapping mode. Samples for this characterization were prepared by dropping about 10-μL aged peptide solution onto the freshly cleaved mica surface and allowed to adsorb for about 30 s. The mica surface was then gently rinsed with water and dried by nitrogen gas. The scan rate was set to 1.50 Hz with the scan angle of 0°. All images were flattened by using a first-order line fit (the flatten function in AFM software) to correct for piezo-derived differences between scan lines.

The SANS experiments were performed on LOQ, ISIS Neutron Facility, Rutherford Appleton Laboratory (Oxford, UK). Samples for this experiment were prepared by directly dissolving the peptide powder in D₂O/CD₃CN mixture. The resulting homogenous solutions were incubated for 7 days and then transferred into the 2.0-mm path length disc-shaped silica cells for further characterization. Neutron incident wavelengths were from 2.2 Å to 10.0 Å at 25 Hz. The 64-cm² detector with 5-mm resolution was placed at a distance of 4.05 m from the samples, giving a wave vector (q) range of 0.006 Å^{− 1} to 0.24 Å^{− 1}. Data were corrected for wavelength dependence of the incident spectrum, the measured sample transmission, and also relative detector efficiencies prior to subtraction of the solvent background (D₂O or D₂O/CD₃CN mixture). Absolute scaling was obtained by making a comparison with the scattering from a partially deuterated polystyrene standard. The data were then fitted by using the SansView 2.1.1 program provided by RAL.