To shed more light on the observation that the ability to penetrate membranes modulates the transition from antiparallel to parallel β-sheets, we chose two strategies to unclutter the spectra from the water absorption: i) we devised a global fitting method to remove the broad overlapping H2O absorption from the spectra in Figure , and ii) we recorded the experiments in D2O. The reasons for using these two complementary strategies are as follows. While removing the water absorption (i) requires post-processing of the spectra, it enables analyzing the amide I and amide II bands, which together provide insights into orientational changes of peptides in SEIRA spectroscopy. Instead, the use of D2O (ii) is a popular approach in vibrational spectroscopy to avoid such post-processing, because the water absorption at ~1640 cm -1 is shifted to ~1210 cm -1 via the vibrational isotope effect, while the amide I remains largely unaffected. However, it has been reported that kinetics of (mis)folding can be affected considerably in D2O due to changes in H-bonding strengths. Furthermore, the amide II also experiences a considerable shift by ~100 cm -1 and orientational analysis is impeded.