The FT-IR measurements were performed in solution by preparing samples of pep1 (10 mM) in D2O. A solution of NaOH dissolved in D2O was added to increase the pH to ~10.5. NaCl (3 M) was added to one of the samples. The solution (20 µL) was placed between two CaF2 plates using a spacer (56 µm). The infrared spectra were recorded (2000 scans, 4 cm -1 resolution) on a Nicolet 6700 FT-IR spectrometer with a deuterated triglycine sulfate (DTGS) detector (Thermo Fisher Scientific, Waltham, MA, United States). The absorbance peaks were determined using the OMNIC analysis software (Nicolet).