Two-dimensional infrared (2D-IR) spectroscopy is a powerful experimental method for probing the structure and dynamics of proteins in aqueous solution. So far, most experimental studies focus on the amide I vibrations, for which empirical vibrational exciton models provide a means of interpreting such experiments. However, such models are largely lacking for other regions of the vibrational spectrum. To close this gap, we employ an efficient quantum-chemical methodology for the calculation of 2D-IR spectra, which is based on anharmonic theoretical vibrational spectroscopy with localized modes. We apply this approach to explore the potential of 2D-IR spectroscopy in the extended amide III region. Using calculations for a dipeptide model as well as alanine polypeptides, we show that distinct 2D-IR cross-peaks in the extended amide~III region can potentially be used to distinguish \alpha-helix and \beta-strand structures. We propose that the extended amide III region could be a promising target for future 2D-IR experiments.
Additional computational details and description of the computational methodology, additional calculated one-dimensional infrared and 2D-IR spectra for all 50 considered dipeptides, additional calculated 2D-IR spectra for snapshots of polyalanine-15/16.