Vibrational Energy Transport in Peptide Helices after Excitation of C−D Modes in Leu-d₁₀

Vibrational energy transport in a short 3(10)-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 horizontal lineO probes at various distances from the heat source as local thermometers. The C-D modes are not resonant to the C horizontal lineO modes, neither directly nor through any Fermi resonance, thereby suppressing resonant energy transfer directly along the C horizontal lineO 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) A(2) ps(-1) is the same as that after depositing vibrational energy through the ultrafast internal conversion of a covalently bound chromophore.