Dissecting amide-I vibration in β-peptide helices

Area of Science:

• Computational Chemistry
• Biophysics
• Spectroscopy

Background:

• β-peptides are structural analogs of α-peptides with unique helical structures.
• Amide-I band vibrations are sensitive probes of peptide secondary structure.
• Understanding β-peptide vibrational properties is crucial for predicting their folding and function.

Purpose of the Study:

• To investigate the vibrational properties of amide-I modes in various β-peptide helical conformations.
• To determine the influence of peptide structure and hydrogen bonding on vibrational spectra.
• To establish benchmark data for interpreting β-polypeptide amide-I absorption spectra.

Main Methods:

• Ab initio calculations were employed to study tetramer to heptamer β-peptides.
• Normal modes were decoupled into local modes.
• Intramolecular hydrogen bonding interactions were systematically removed.

Main Results:

• Local mode transition energies are sensitive to β-peptide structure and hydrogen bonding.
• Pure local modes show conformational dependence in 8-helix and 10/12-helix structures.
• Homogeneous 10-, 12-, and 14-helical conformations exhibit minimal dependence in pure local modes.

Conclusions:

• Nearly degenerate pure local-mode transitions can model amide-I vibrations in homogeneous β-helices.
• The findings provide critical insights into the complexity of β-polypeptide amide-I absorption spectra.
• This research serves as a benchmark for future studies on β-peptide vibrational dynamics.