State Key Laboratory of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, College of Chemistry, Nankai University, Tianjin 300071, China.
Tianjin Key Laboratory of Biosensing and Molecular Recognition, College of Chemistry, Nankai University, Tianjin 300071, China.
Int J Mol Sci. 2023 Oct 20;24(20):15385. doi: 10.3390/ijms242015385.
Nucleoside radicals are key intermediates in the process of DNA damage, and alkali metal ions are a common group of ions in living organisms. However, so far, there has been a significant lack of research on the structural effects of alkali metal ions on nucleoside free radicals. In this study, we report a new method for generating metalized nucleoside radical cations in the gas phase. The radical cations [Ade+M-H] (M = Li, Na) are generated by the 280 nm ultraviolet photodissociation (UVPD) of the precursor ions of lithiated and sodiated ions of 2-iodoadenine in a Fourier transform ion cyclotron resonance (FT ICR) cell. Further infrared multiphoton dissociation (IRMPD) spectra of both radical cations were recorded in the region of 2750-3750 cm. By combining these results with theoretical calculations, the most stable isomers of both radicals can be identified, which share the common characteristics of triple coordination patterns of the metal ions. For both radical species, the lowest-energy isomers undergo hydrogen transfer. Although the sugar ring in the most stable isomer of [Ade+Li-H] is in a (South, syn) conformation similar to that of [Ado+Na], [Ade+Na-H] is distinguished by the unexpected opening of the sugar ring. Their theoretical spectra are in good agreement with experimental spectra. However, due to the flexibility of the structures and the complexity of their potential energy surfaces, the hydrogen transfer pathways still need to be further studied. Considering that the free radicals formed directly after C-I cleavage have some similar spectral characteristics, the existence of these corresponding isomers cannot be ruled out. The findings imply that the structures of nucleoside radicals may be significantly influenced by the attached alkali metal ions. More detailed experiments and theoretical calculations are still crucial.
核苷自由基是 DNA 损伤过程中的关键中间体，而碱金属离子是生物体内常见的一类离子。然而，迄今为止，对于碱金属离子对核苷自由基结构的影响，研究还非常缺乏。在本研究中，我们报告了一种在气相中生成金属化核苷自由基阳离子的新方法。通过在傅里叶变换离子回旋共振（FT ICR）腔中，用 280nm 紫外光解（UVPD）前体离子生成的锂化和钠离子化的 2-碘腺嘌呤的前驱体离子，生成了自由基阳离子[Ade+M-H]（M=Li，Na）。进一步在 2750-3750cm 的区域记录了这两种自由基阳离子的红外多光子解离（IRMPD）光谱。结合这些结果和理论计算，可以确定两种自由基的最稳定异构体，它们具有金属离子的三配位模式的共同特征。对于两种自由基物种，最低能量异构体都经历了氢转移。尽管[Ade+Li-H]的最稳定异构体中的糖环处于类似于[Ado+Na]的（南，顺）构象，但[Ade+Na-H]的糖环却出人意料地打开了。它们的理论光谱与实验光谱吻合较好。然而，由于结构的灵活性和潜在势能面的复杂性，氢转移途径仍需进一步研究。考虑到 C-I 断裂后直接形成的自由基具有一些相似的光谱特征，不能排除这些相应异构体的存在。这些发现表明，核苷自由基的结构可能会受到附着的碱金属离子的显著影响。更多详细的实验和理论计算仍然至关重要。
