Biomolecular Dynamics, Institute of Physics, Albert Ludwigs University, 79104 Freiburg, Germany.
J Chem Phys. 2011 Mar 28;134(12):124518. doi: 10.1063/1.3574395.
To measure the transport of vibrational energy along a peptide helix, Hamm and co-workers [J. Phys. Chem. B 112, 9091 (2008)] performed time-resolved vibrational experiments, which showed that the energy transport rate increases by at least a factor of 4, when a localized C=O mode of the peptide instead of an attached chromophore is excited. This finding raises the question if coherent excitonic energy transfer between the C=O modes may be of importance for the overall energy transport in peptides. With this idea in mind, nonequilibrium molecular dynamics simulations as well as quantum-classical calculations are performed, which qualitatively reproduce the experimental findings. Moreover, the latter model (an exciton Hamiltonian whose matrix elements depend on the instantaneous positions of the peptide and solvent atoms) indeed exhibits the signatures of coherent quantum energy transport, at least within the first few picoseconds and at low temperatures. The origin of the observed decoherence, the absence of vibrational self-trapping, and the possibility of quantum interference between various transport paths are discussed in some detail.
为了测量振动能量沿着肽螺旋的传输，Hamm 及其同事[J. Phys. Chem. B 112, 9091 (2008)]进行了时间分辨振动实验，实验表明，当激发肽的局部 C=O 模式而不是附着的发色团时，能量传输速率至少增加了 4 倍。这一发现提出了一个问题，即 C=O 模式之间的相干激子能量转移是否对肽中的整体能量传输很重要。考虑到这一想法，进行了非平衡分子动力学模拟和量子经典计算，这些计算定性地再现了实验结果。此外，后一种模型（激子哈密顿量，其矩阵元取决于肽和溶剂原子的瞬时位置）确实表现出相干量子能量传输的特征，至少在最初的几个皮秒内和低温下是如此。详细讨论了观察到的退相干的起源、振动自陷的缺失以及各种传输路径之间量子干涉的可能性。
