Vibrational Exciton Models for Biomolecules from Quantum Chemistry

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Vibrational spectroscopy can provide insights into fast processes occurring during protein folding and in disordered or unfolded proteins. Here, we propose the development of efficient computational methods for reliably predicting vibrational spectra of biomolecular systems, in particular for two-dimensional infrared (2D-IR) and vibrational Raman optical activity (ROA) spectroscopy of conformationally flexible polypeptides and proteins. To this end, we will develop vibrational exciton models that are derived directly from quantum-chemical calculations on polypeptides and proteins by employing rigorously-defined localized modes, which provide a direct connection between such calculations and vibrational exciton models. In particular, we propose a new methodology for developing vibrational exciton models that goes beyond the present state-of-the art by combining the following ideas: (1) Instead of relying on calculations for (over-)simplified model systems such as N-methylacetamid and glycine dipeptide, the parameters of our novel vibrational exciton models will be derived from calculations on larger polypeptide models of secondary structure elements. (2) For applying our vibrational exciton models to 2D-IR spectroscopy, we will include the anharmonicities of the localized modes in this parametrization instead of relying on the empirical parameters currently in use. (3) While vibrational exciton models have so far been focussed on IR and 2D-IR spectroscopy, we propose to also develop vibrational exciton models for chiral vibrational spectroscopies, in particular for ROA spectroscopy. (4) We aim at developing general protocols that are applicable for any kind of vibration in molecules with repeating building blocks, whereas the current protocols for parametrizing vibrational exciton models are mostly restricted to the amide I vibrations.In the present project, we will apply the developed protocols to study the structural sensitivity of the extended amide III region in both ROA and 2D-IR spectroscopy. For ROA spectroscopy, this will allow for an interpretation of existing experiments, whereas for 2D-IR spectroscopy it will put us in the position to propose and inspire new experiments looking at the extended amide III region.