Ellen Backus

Publications (2)7.39 Total impact

• Source

  Available from: Alessandro Moretto

  Article: Structural flexibility of a helical peptide regulates vibrational energy transport properties.

  Ellen H G Backus, Phuong H Nguyen, Virgiliu Botan, Alessandro Moretto, Marco Crisma, Claudio Toniolo, Oliver Zerbe, Gerhard Stock, Peter Hamm
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  ABSTRACT: Applying ultrafast vibrational spectroscopy, we find that vibrational energy transport along a helical peptide changes from inefficient but mostly ballistic below approximately 270 K into diffusive and significantly more efficient above. On the basis of molecular dynamics simulations, we attribute this change to the increasing flexibility of the helix above this temperature, similar to the glass transition in proteins. Structural flexibility enhances intramolecular vibrational energy redistribution, thereby refeeding energy into the few vibrational modes that delocalize over large parts of the structure and therefore transport energy efficiently. The paper outlines concepts how one might regulate vibrational energy transport properties in ultrafast photobiological processes, as well as in molecular electronic devices, by engineering the flexibility of their components.
  The Journal of Physical Chemistry B 12/2008; 112(48):15487-92. · 3.70 Impact Factor
• Source

  Available from: Alessandro Moretto

  Article: Energy transport in peptide helices: a comparison between high- and low-energy excitations.

  Ellen H G Backus, Phuong H Nguyen, Virgiliu Botan, Rolf Pfister, Alessandro Moretto, Marco Crisma, Claudio Toniolo, Gerhard Stock, Peter Hamm
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  ABSTRACT: Energy transport in a short helical peptide in chloroform solution is studied by time-resolved femtosecond spectroscopy and accompanying nonequilibrium molecular dynamics (MD) simulations. In particular, the heat transport after excitation of an azobenzene chromophore attached to one terminus of the helix with 3 eV (UV) photons is compared to the excitation of a peptide C=O oscillator with 0.2 eV (IR) photons. The heat in the helix is detected at various distances from the heat source as a function of time by employing vibrational pump-probe spectroscopy. As a result, the carbonyl oscillators at different positions along the helix act as local thermometers. The experiments show that heat transport through the peptide after excitation with low-energy photons is at least 4 times faster than after UV excitation. On the other hand, the heat transport obtained by nonequilibrium MD simulations is largely insensitive to the kind of excitation. The calculations agree well with the experimental results for the low-frequency case; however, they give a factor of 5 too fast energy transport for the high-energy case. Employing instantaneous normal mode calculations of the MD trajectories, a simple harmonic model of heat transport is adopted, which shows that the heat diffusivity decreases significantly at temperatures initially reached by high-energy excitation. This finding suggests that the photoinduced energy gets trapped, if it is deposited in high amounts. The various competing mechanisms, such as vibrational T(1) relaxation, resonant transfer between excitonic states, cascading down relaxation, and low-frequency mode transfer, are discussed in detail.
  The Journal of Physical Chemistry B 08/2008; 112(30):9091-9. · 3.70 Impact Factor