Relaxation mechanisms of UV-photoexcited DNA and RNA nucleobases
Relaxation mechanisms of UV-photoexcited DNA and RNA nucleobases
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DOI：
10.1073/pnas.1014982107
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发表时间：
2010-12-14
影响因子：
11.1
通讯作者：
Lischka, Hans
中科院分区：
文献类型：
--
作者：
Barbatti, Mario;Aquino, Adelia J. A.;Lischka, Hans
一个全面的努力在光动力学从头计算模拟的超快失活途径的所有五个核碱基腺嘌呤，鸟嘌呤，胞嘧啶，胸腺嘧啶和尿嘧啶的报告。这些模拟是基于一个完整的非绝热表面跳跃的方法，使用扩展的多组态波函数。尽管所有五个核碱基共享基本的内部转换机制，但计算显示了嘌呤和嘧啶碱基的不同分组，这与光动力学的复杂性有关。嘌呤碱基腺嘌呤和鸟嘌呤代表了最简单的光失活机制，其动力学直接沿着非绝热π π * 路径沿着，并且没有障碍地到达与基态的锥形交叉缝。在嘧啶碱基的情况下，由于几个状态的耦合，动力学开始于π π * 能量表面的更平坦的区域。这一事实阻碍了单一反应路径的清晰形成，因此，嘧啶碱基的光动力学要丰富得多，并且还包括n个重要性不同的π * 态，这取决于所考虑的实际核碱基。可能发生局部最小值的捕获，因此，在这些情况下，到基态的失活时间也要长得多。这些研究结果的影响进行了讨论（i）确定结构的可能性，其中单重态/三重态转换可以发生，因为有足够的保留时间在单重态动力学和（ii）有关的灵活性，找到其他失活途径取代嘧啶作为候选人的替代核碱基。
A comprehensive effort in photodynamical ab initio simulations of the ultrafast deactivation pathways for all five nucleobases adenine, guanine, cytosine, thymine, and uracil is reported. These simulations are based on a complete nonadiabatic surface-hopping approach using extended multiconfigurational wave functions. Even though all five nucleobases share the basic internal conversion mechanisms, the calculations show a distinct grouping into purine and pyrimidine bases as concerns the complexity of the photodynamics. The purine bases adenine and guanine represent the most simple photodeactivation mechanism with the dynamics leading along a diabatic pi pi* path directly and without barrier to the conical intersection seam with the ground state. In the case of the pyrimidine bases, the dynamics starts off in much flatter regions of the pi pi* energy surface due to coupling of several states. This fact prohibits a clear formation of a single reaction path. Thus, the photodynamics of the pyrimidine bases is much richer and includes also n pi* states with varying importance, depending on the actual nucleobase considered. Trapping in local minima may occur and, therefore, the deactivation time to the ground state is also much longer in these cases. Implications of these findings are discussed (i) for identifying structural possibilities where singlet/triplet transitions can occur because of sufficient retention time during the singlet dynamics and (ii) concerning the flexibility of finding other deactivation pathways in substituted pyrimidines serving as candidates for alternative nucleobases.