Abstract

Vibrational energy transport in a short 310-helical peptide is studied by time-resolved femtosecond infrared spectroscopy. The C−D vibrations of decadeuterated leucine incorporated in the helical chain are excited, and the subsequent flow of vibrational energy through the helix is monitored by employing C═O probes at various distances from the heat source as local thermometers. The C−D modes are not resonant to the C═O modes, neither directly nor through any Fermi resonance, thereby suppressing resonant energy transfer directly along the C═O oscillators of the peptide backbone. In contrast to our previous work (J. Phys. Chem. B 2008, 112, 9091), we no longer find any substantial difference in the vibrational energy transport efficiency after high- or low-energy excitation. That is, the heat diffusion constant of (2.0 ± 0.5) Å2 ps−1 is the same as that after depositing vibrational energy through the ultrafast internal conversion of a covalently bound chromophore.