Amide I Raman optical activity of polypeptides: fragment approximation

Area of Science:

• Spectroscopy
• Computational Chemistry
• Biophysics

Background:

• Vibrational optical activity (VOA) is crucial for determining chiral molecule configurations in condensed phases.
• Vibrational circular dichroism and Raman optical activity (ROA) are key VOA techniques for biomolecular studies.
• Fragment approximation methods have been used to describe amide I VOA in polypeptides.

Purpose of the Study:

• To develop a fragment approximation theory for numerical simulations of Raman and ROA spectra of amide I vibrations in polypeptides.
• To validate the developed theory by comparing simulated spectra with ab initio calculations and experimental data.

Main Methods:

• Density functional theory (DFT) calculations of polarizability, magnetic dipole-, and electric quadrupole-ROA tensors for alanine dipeptide and pentapeptide analogs.
• Application of the developed fragment approximation theory to simulate ROA spectra.
• Comparison of simulated spectra with DFT results and previously reported experimental data for alanine-based polypeptides.

Main Results:

• The fragment approximation theory was successfully developed for simulating ROA spectra of polypeptides.
• Simulated spectra using the fragment approximation showed excellent agreement with DFT calculations.
• Simulated ROA spectra for alanine-based alpha-helix and polyproline II structures closely matched experimental results.

Conclusions:

• The developed fragment approximation method is valid and useful for numerical simulation of ROA spectra of polypeptides in solution.
• This approach enhances the capability to study the structures and dynamics of biomolecules using ROA spectroscopy.