5-卤代嘧啶碱基分子激发态光化学反应动力学的理论与实验研究

Substituted bases have attracted considerable attention due to their enhanced photochemical reactivities. Compared with intensive reports for photophysical process including internal conversion and intersystem crossing of thiopyrimidines, studies on the dynamics of excited states of halopyrimidines are limited at present due to their complicated photochemical reactions. In the proposal, we select 5-halopyrimidine and 5-halo-thiopyrimidine as prototypical systems to investigate their photochemical reaction dynamics. By using time-resolved FTIR and transient absorption spectroscopy, the crucial reaction intermediates and elementary reaction products are detected, which unravels sophisticated photochemical reaction pathways and provides direct experimental evidences for reaction mechanisms. Combined with experimental results, the CASPT2//CASSCF quantum chemistry calculations propose the key role of crossing of potential energy surfaces in reaction pathways, and elaborate the substituting effect on photochemical reactivities and reaction mechanisms, revealing the dynamics of excited states and reaction mechanisms of 5-halopyrimidine and 5-halo-thioprimidine and thus providing important chemical insights to understand the DNA/RNA photodamage and various photochemical applications at the molecular and quantum state specific level.

取代碱基分子由于其增强的光化学活性，吸引了分子生物学及药物学等相关领域的广泛关注。但以往的研究主要集中在硫代碱基，侧重于内转换、系间窜越等光物理过程的研究，而对另一类重要的卤代碱基分子的研究较少，主要是因为卤代碱基光激发后涉及复杂的光化学反应。本项目选取典型的卤代碱基：5-卤代嘧啶碱基和5-卤代-硫代嘧啶碱基为研究对象，采用对研究核酸分子的光化学反应有独特优势的时间分辨红外（TR-FTIR）光谱技术，并结合紫外-可见瞬态吸收光谱等互为补充的时间分辨光谱技术，通过对其光化学反应的关键反应中间体和基元产物的光谱测量，阐明这些碱基分子复杂的光化学反应途径，给出揭示机理的直接实验证据。实验结果结合CASPT2//CASSCF量化计算，确定势能面交叉的关键作用，探讨取代效应对反应活性和反应机理的影响，揭示此类取代碱基的激发态动力学和反应机理，为取代碱基丰富的光化学应用提供关键的动力学微观机理的指导。

取代碱基分子由于其增强的光化学活性，吸引了分子生物学及药物学等相关领域的广泛关注。但以往的研究主要集中在硫代碱基，侧重于内转换、系间窜越等光物理过程的研究，而对另一类重要的卤代碱基分子的研究较少，主要是因为卤代碱基光激发后涉及复杂的光化学反应。本项目选取了典型的卤代碱基：5-卤代嘧啶碱基和5-卤代-硫代嘧啶碱基为研究对象，利用纳秒、飞秒紫外-可见瞬态吸收光谱、时间分辨红外光谱、条纹相机等技术，测量了光物理和光化学反应中的重要激发态和中间体，阐明了这些碱基分子的光物理和光化学反应途径，给出了揭示机理的直接实验证据。实验结果结合高水平的CASPT2//CASSCF量化计算，确定了势能面交叉点的关键作用，并探讨了取代效应对反应活性和反应机理的影响，揭示了此类取代碱基的激发态动力学和反应机理。