Anharmonic Theoretical Vibrational Spectroscopy of Polypeptides.

Area of Science:

• Computational chemistry
• Spectroscopy
• Biophysics

Background:

• Quantum-chemical prediction of vibrational spectra for large molecules like polypeptides and proteins is computationally demanding.
• Accurately including anharmonicities is crucial for precise spectral predictions but poses a significant challenge.

Purpose of the Study:

• To develop an efficient and reliable method for calculating anharmonic vibrational spectra of polypeptides.
• To address the challenge of incorporating anharmonicities in the quantum-chemical prediction of vibrational spectra for large biomolecules.

Main Methods:

• Utilized an expansion of the potential energy surface in localized-mode coordinates, rather than normal-mode coordinates.
• Applied the developed approach to compute infrared, Raman, and Raman optical activity spectra for helical alanine polypeptides (up to 20 amino acids).

Main Results:

• The new method enables efficient and reliable calculation of anharmonic vibrational spectra.
• Anharmonicities were found not to significantly alter spectral band shapes.
• Simple scaling methods were insufficient to explain observed shifts in individual spectral bands.

Conclusions:

• The study presents a breakthrough in theoretical vibrational spectroscopy by enabling the quantification of anharmonic contributions.
• This work paves the way for first-principles calculations of multidimensional vibrational spectra for polypeptides and proteins.