Can far-IR action spectroscopy combined with BOMD simulations be conformation selective?

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Structural characterization of peptides is crucial for understanding their function.
• Far-infrared (far-IR) spectroscopy offers unique insights into molecular conformations.
• Distinguishing between different peptide turns, such as gamma-turns and beta-turns, remains challenging.

Purpose of the Study:

• To structurally characterize Ac-Phe-Pro-NH2 peptide conformers in the far-IR spectral domain (<800 cm(-1)).
• To identify unique spectral signatures for gamma-turn (C7 interaction) and beta-turn (C10 interaction) conformers.
• To validate the use of combined spectroscopy and simulations for far-IR conformational analysis.

Main Methods:

• Conformation-selective far-IR/UV double resonance spectroscopy.
• Born-Oppenheimer molecular dynamics (BOMD) simulations.
• Analysis of far-IR spectra in the 400-550 cm(-1) region.

Main Results:

• Two distinct conformers, a gamma-turn and a beta-turn, were identified experimentally.
• Simulated BOMD far-IR spectra showed excellent agreement with experimental data.
• The 400-550 cm(-1) spectral region was found to be highly selective for distinguishing conformer-specific hydrogen bond signatures.

Conclusions:

• The combination of far-IR spectroscopy and BOMD simulations effectively characterizes peptide conformations.
• Specific far-IR spectral features in the 400-550 cm(-1) range allow for the differentiation of gamma-turns and beta-turns.
• This approach provides a powerful tool for analyzing peptide structures in the far-IR domain.