School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, 24098 Kiel (Germany).
Angew Chem Int Ed Engl. 2015 Dec 1;54(49):14719-22. doi: 10.1002/anie.201506940. Epub 2015 Oct 13.
Ultrafast deactivation pathways bestow photostability on nucleobases and hence preserve the structural integrity of DNA following absorption of ultraviolet (UV) radiation. One controversial recovery mechanism proposed to account for this photostability involves electron-driven proton transfer (EDPT) in Watson-Crick base pairs. The first direct observation is reported of the EDPT process after UV excitation of individual guanine-cytosine (G⋅C) Watson-Crick base pairs by ultrafast time-resolved UV/visible and mid-infrared spectroscopy. The formation of an intermediate biradical species (G[-H]⋅C[+H]) with a lifetime of 2.9 ps was tracked. The majority of these biradicals return to the original G⋅C Watson-Crick pairs, but up to 10% of the initially excited molecules instead form a stable photoproduct G*⋅C* that has undergone double hydrogen-atom transfer. The observation of these sequential EDPT mechanisms across intermolecular hydrogen bonds confirms an important and long debated pathway for the deactivation of photoexcited base pairs, with possible implications for the UV photochemistry of DNA.
超快失活途径赋予碱基光稳定性，从而在吸收紫外线 (UV) 辐射后保持 DNA 的结构完整性。一种有争议的恢复机制被提出，以解释这种光稳定性，涉及 Watson-Crick 碱基对中的电子驱动质子转移 (EDPT)。通过超快时间分辨的 UV/可见和中红外光谱，首次直接观察到单个鸟嘌呤-胞嘧啶 (G⋅C) Watson-Crick 碱基对在 UV 激发后 EDPT 过程。跟踪了具有 2.9 ps 寿命的中间体双自由基物种 (G[-H]⋅C[+H]) 的形成。这些双自由基中的大多数会回到原始的 G⋅C Watson-Crick 对，但最初激发的分子中高达 10%会形成经历双氢原子转移的稳定光产物 G*⋅C*。这些跨分子氢键的连续 EDPT 机制的观察证实了一种对于光激发碱基对失活的重要且长期存在争议的途径，这可能对 DNA 的 UV 光化学有影响。
