Secondary Structures in Phe-Containing Isolated Dipeptide Chains: Laser Spectroscopy vs Quantum Chemistry

Area of Science:

• Physical Chemistry
• Biophysics
• Computational Chemistry

Background:

• Understanding protein folding and structure is crucial in molecular biology.
• Phenylalanine (Phe) is a key aromatic amino acid influencing protein conformation.
• Gas-phase studies offer insights into intrinsic molecular properties without solvent effects.

Purpose of the Study:

• To investigate the intrinsic conformational landscape of phenylalanine-containing peptide models (-Gly-Phe- and -Ala-Phe-).
• To correlate experimental spectroscopic data with theoretical calculations for accurate structural assignment.
• To identify fundamental protein structural motifs within small peptide sequences.

Main Methods:

• Gas-phase near-UV and IR/UV double resonance spectroscopy.
• Quantum chemistry calculations (DFT-D, CC2) for conformational analysis.
• Excited-state IR spectroscopy for probing electronic transitions and geometry changes.

Main Results:

• Resolved conformational features of peptide models were obtained via jet-cooled spectroscopy.
• Vibrational spectra were assigned to specific conformations and H-bonding patterns.
• Three important protein structural motifs (β-strands, 27 ribbons, β-turns) were identified.

Conclusions:

• The study provides an unambiguous assignment of observed conformers.
• Theoretical methods accounting for dispersive interactions accurately predict experimental conformational distributions.
• The findings validate the use of Phe as a chromophore in spectroscopic studies of peptides.