Table The geometry optimization and spectral calculations for the IR, Raman and ROA spectra were all performed using the Gaussian16 (A.03) software. Geometry optimization The geometries of different conformations of the peptide were partially optimized in normal coordinates following the approach by Bouř and Keiderling. With this method the backbone conformation of the peptide is mostly retained, while the modes of spectroscopic interest are fully relaxed. Fully optimizing the structure using DFT calculations would significantly alter the conformation. Because of the conformational sensitivity of these spectroscopic techniques, the meaning of the calculated spectra would otherwise be lost. The geometry optimizations and frequency calculations were performed with the B3PW91 functional and 6-31G(d) basis set. No explicit water molecules were included in these calculations. Rather, the C-PCM implicit solvent model ? was used to account for the presence of water molecules.