Biomolecular Dynamics, Institute of Physics, Albert Ludwigs University, 79104 Freiburg, Germany.
J Chem Phys. 2010 Jul 21;133(3):034512. doi: 10.1063/1.3462961.
Recent two-dimensional infrared (2D-IR) experiments on a short peptide 3(10)-helix in chloroform solvent [E. H. G. Backus et al., J. Phys. Chem. B 113, 13405 (2009)] revealed an intriguing temperature dependence of the homogeneous line width, which was interpreted in terms of a dynamical transition of the peptide. To explain these findings, extensive molecular dynamics simulations at various temperatures were performed in order to construct the free energy landscape of the system. The study recovers the familiar picture of a glass-forming system, which below the glass transition temperature T(g) is trapped in various energy basins, while it diffuses freely between these basins above T(g). In fact, one finds at T(g) approximately 270 K a sharp rise of the fluctuations of the backbone dihedral angles, which reflects conformational transitions of the peptide. The corresponding C=O frequency fluctuations are found to be a sensitive probe of the peptide conformational dynamics from femtosecond to nanosecond time scales and lead to 2D-IR spectra that qualitatively match the experiment. The calculated homogeneous line width, however, does not show the biphasic temperature dependence observed in experiment.
最近在氯仿溶剂中对短肽 3(10)-螺旋的二维红外（2D-IR）实验[E. H. G. Backus 等人，J. Phys. Chem. B 113, 13405 (2009)]揭示了同相线宽的有趣的温度依赖性，这可以用肽的动力学转变来解释。为了解释这些发现，在不同温度下进行了广泛的分子动力学模拟，以构建系统的自由能景观。该研究恢复了典型的玻璃形成体系的图像，在玻璃化转变温度 T(g)以下，体系被困在各种能量盆地中，而在 T(g)以上，它在这些盆地之间自由扩散。事实上，人们在大约 270 K 的 T(g)处发现了骨架二面角波动的急剧增加，这反映了肽的构象转变。发现相应的 C=O 频率波动是从飞秒到纳秒时间尺度上探测肽构象动力学的灵敏探针，并导致与实验定性匹配的 2D-IR 光谱。然而，计算出的同相线宽并没有显示出实验中观察到的双相温度依赖性。
