Since contributions in these wavelength ranges may originate from Raman-active modes in the histidine rings, further simulations were performed with all imidazole rings of the peptide's side chains carrying an additional proton (Fig. ). In fact, the pH of the experimental peptide solution is close to the pKa of histidine. Reduced peaks are indeed obtained after protonation of all histidine residues, although at the present stage we cannot exclude other reasons for the deviation of some of the calculated spectral patterns from the experi-ment, such as interaction of the solvent (e.g. with the imidazole rings or other side chains, dependence on the DFT-level, etc.).