Probing the γ-turn in a short proline dipeptide chain.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Peptides play crucial roles in biological systems.
• Understanding peptide conformation in the gas phase is essential for deciphering their functions.
• N-acetyl-prolinamide (Ac-Pro-NH2) is a small peptide model system derived from proline.

Purpose of the Study:

• To investigate the gas-phase structure of N-acetyl-prolinamide (Ac-Pro-NH2).
• To characterize the specific conformer adopted by Ac-Pro-NH2 in supersonic expansion.
• To determine the stabilizing interactions and conformational energy barriers within the peptide.

Main Methods:

• Fourier transform microwave spectroscopy (FTMW)
• Laser ablation for supersonic expansion
• Analysis of rotational and nuclear quadrupole coupling constants
• Determination of internal rotation barrier from spectral splittings

Main Results:

• Detection of a single conformer of Ac-Pro-NH2 in the gas phase.
• Characterization of a gamma-turn structure stabilized by a CO···HN intramolecular hydrogen bond.
• Identification of a seven-membered ring formed by the hydrogen bond.
• Quantification of the methyl group internal rotation barrier at 354 cm(-1).

Conclusions:

• The gas-phase structure of Ac-Pro-NH2 is a gamma-turn stabilized by a specific intramolecular hydrogen bond.
• Microwave spectroscopy provides detailed insights into peptide conformation and interactions.
• The determined rotation barrier offers valuable data for computational modeling of peptide dynamics.