Department of Chemistry, University of York, Heslington, YO10 5DD, UK.
Phys Chem Chem Phys. 2022 Nov 23;24(45):27836-27846. doi: 10.1039/d2cp03831e.
The photostability of synthetic (unnatural) nucleobases is important in establishing the integrity of new genetic alphabets, and critical for developing healthy semisynthetic organisms. Here, we report the first study to explore the photostability and electronic decay pathways of the synthetic nucleobase, Z (6-amino-5-nitro-2(1)-pyridone), combining UV laser photodissociation and collisional dissociation measurements to characterise the decay pathways across the region from 3.1-4.9 eV. Photoexcitation across this region produced the / 138 ion as the dominant photofragment, mirroring the dominant fragment produced upon higher-energy collisional excitation. Analysis of the ion-yield production curve profile for the / 138 ion indicates that it is produced following ultrafast excited state decay with boil off of the OH functional group of Z from the hot electronic ground state. Electronic structure calculations provide physical insight into why this is the dominant fragmentation pathway, since a node in the electron density along the C-OH bond is found for all tautomers of Z. While the dominant decay pathway for Z is consistent with ultrafast excited state decay, we also identify several minor dissociative photochemistry decay pathways, associated with intrinsic photoinstability. The results presented here can be used to guide the development of more photostable synthetic nucleobases.
合成（非天然）核碱基的光稳定性对于建立新遗传字母表的完整性非常重要，对于开发健康的半合成生物也至关重要。在这里，我们报告了第一项研究，该研究探索了合成核碱基 Z（6-氨基-5-硝基-2（1）-吡啶酮）的光稳定性和电子衰减途径，结合紫外激光光解和碰撞解离测量来描述从 3.1-4.9 eV 的区域的衰减途径。在该区域进行光激发产生了/ 138 离子作为主要光碎片，与在更高能量碰撞激发下产生的主要碎片相呼应。/ 138 离子的离子产率产生曲线轮廓分析表明，它是在 OH 官能团从热电子基态快速蒸发的超快激发态衰变之后产生的。电子结构计算为为什么这是主要的断裂途径提供了物理上的洞察力，因为在 Z 的所有互变异构体中都发现了 C-OH 键上电子密度的节点。虽然 Z 的主要衰变途径与超快激发态衰变一致，但我们也确定了几种与固有光不稳定性相关的次要光分解光化学衰变途径。这里提出的结果可用于指导更耐光的合成核碱基的开发。
