Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany.
Phys Chem Chem Phys. 2021 May 26;23(20):11900-11906. doi: 10.1039/d1cp01014j.
The conformation and the electronic structure of gas-phase oligonucleotides depends strongly on the protonation site. 5'-d(FUAG) can either be protonated at the A-N1 or at the G-N7 position. We have stored protonated 5'-d(FUAG) cations in a cryogenic ion trap held at about 20 K. To identify the protonation site and the corresponding electronic structure, we have employed soft X-ray absorption spectroscopy at the nitrogen K-edge. The obtained spectra were interpreted by comparison to time-dependent density functional theory calculations using a short-range exchange correlation functional. Despite the fact that guanine has a significantly higher proton affinity than adenine, the agreement between experiment and theory is better for the A-N1 protonated system. Furthermore, an inverse site sensitivity is observed in which the yield of the nucleobase fragments that contain the absorption site appears substantially reduced, which could be explained by non-statistical fragmentation processes, localized on the photoabsorbing nucleobase.
气相寡核苷酸的构象和电子结构强烈依赖于质子化位置。5'-d(FUAG) 可以在 A-N1 或 G-N7 位置被质子化。我们将质子化的 5'-d(FUAG)阳离子储存在保持在约 20 K 的低温离子阱中。为了确定质子化位置和相应的电子结构，我们在氮 K 边缘采用软 X 射线吸收光谱法。通过与使用短程交换相关函数的时间相关密度泛函理论计算进行比较，对获得的光谱进行了解释。尽管鸟嘌呤的质子亲和力明显高于腺嘌呤，但实验与理论之间的一致性对于 A-N1 质子化体系更好。此外，观察到反位置灵敏度，其中包含吸收位置的核碱基片段的产率明显降低，这可以通过非统计碎片过程来解释，该过程定位于光吸收核碱基上。
