Guo Xunmin, Liu Zheyun, Song Qinhua, Wang Lijuan, Zhong Dongping
Department of Physics, Department of Chemistry and Biochemistry, and Programs of Biophysics, Chemical Physics, and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
J Phys Chem B. 2015 Feb 26;119(8):3446-55. doi: 10.1021/jp512413t. Epub 2015 Feb 12.
Many biomimetic chemical systems for repair of UV-damaged DNA showed very low repair efficiency, and the molecular origin is still unknown. Here, we report our systematic characterization of the repair dynamics of a model compound of indole-thymine dimer adduct in three solvents with different polarity. By resolving all elementary steps including three electron-transfer processes and two bond-breaking and bond-formation dynamics with femtosecond resolution, we observed the slow electron injection in 580 ps in water, 4 ns in acetonitrile, and 1.38 ns in dioxane, the fast back electron transfer without repair in 120, 150, and 180 ps, and the slow bond splitting in 550 ps, 1.9 ns, and 4.5 ns, respectively. The dimer bond cleavage is clearly accelerated by the solvent polarity. By comparing with the biological repair machine photolyase with a slow back electron transfer (2.4 ns) and a fast bond cleavage (90 ps), the low repair efficiency in the biomimetic system is mainly determined by the fast back electron transfer and slow bond breakage. We also found that the model system exists in a dynamic heterogeneous C-clamped conformation, leading to a stretched dynamic behavior. In water, we even identified another stacked form with ultrafast cyclic electron transfer, significantly reducing the repair efficiency. Thus, the comparison of the repair efficiency in different solvents is complicated and should be cautious, and only the dynamics by resolving all elementary steps can finally determine the total repair efficiency. Finally, we use the Marcus electron-transfer theory to analyze all electron-transfer reactions and rationalize all observed electron-transfer dynamics.
许多用于修复紫外线损伤DNA的仿生化学系统显示出非常低的修复效率，其分子起源仍然未知。在此，我们报告了我们对吲哚 - 胸腺嘧啶二聚体加合物模型化合物在三种不同极性溶剂中的修复动力学的系统表征。通过以飞秒分辨率解析所有基本步骤，包括三个电子转移过程以及两个键断裂和键形成动力学，我们观察到在水中580皮秒、乙腈中4纳秒和二氧六环中1.38纳秒的慢电子注入，在120、150和180皮秒内无修复的快速反向电子转移，以及分别在550皮秒、1.9纳秒和4.5纳秒的慢键断裂。二聚体键的断裂明显受到溶剂极性的加速。通过与具有慢反向电子转移（2.4纳秒）和快速键断裂（90皮秒）的生物修复机器光解酶进行比较，仿生系统中低修复效率主要由快速反向电子转移和慢键断裂决定。我们还发现模型系统以动态异质C夹构象存在，导致伸展的动态行为。在水中，我们甚至识别出另一种具有超快循环电子转移的堆积形式，显著降低了修复效率。因此，不同溶剂中修复效率的比较很复杂且应谨慎，只有通过解析所有基本步骤的动力学才能最终确定总修复效率。最后，我们使用马库斯电子转移理论分析所有电子转移反应，并合理解释所有观察到的电子转移动力学。
