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. 2022 Mar 30;24(13):7815-7825. doi: 10.1039/d1cp05741c.
We present experimental evidence for soft X-ray induced intramolecular hydrogen transfer in the protonated synthetic tri-oligonucleotide (UAG) in the gas-phase (U: fluorouracil). The trinucleotide cations were stored in a cryogenic ion trap and exposed to monochromatic synchrotron radiation. Photoionization and photofragmentation product ion yields were recorded as a function of photon energy. Predominanly glycosidic bond cleavage leading to formation of nucleobase-related fragments is observed. In most cases, glycosidic bond cleavage is accompanied by single or double hydrogen transfer. The combination of absorption-site-sensitive soft X-ray spectroscopy with fragment specific mass spectrometry allows to directly relate X-ray absorption site and fragmentation site. We observe pronounced resonant features in the competition between single and double hydrogen transfer towards nucleobases. A direct comparison of experimental data with time-dependent density functional theory calculations, using short range corrected hybrid functionals, reveal that these hydrogen transfer processes are universal and not limited to population of particular excited states localized at the nucleobases. Instead, hydrogen transfer can occur upon X-ray absorption in any nucleobase and in the DNA backbone. Resonances seem to occur because of site-selective suppression of hydrogen transfer channels. Furthermore, non-covalent interactions of the optimized ground state geometries were investigated to identify intramolecular hydrogen bonds along which hydrogen transfer is most likely.
我们提供了软 X 射线诱导气相中质子化合成三寡核苷酸（UAG）（U：氟尿嘧啶）中分子内氢转移的实验证据。三核苷酸阳离子被储存在低温离子阱中，并暴露于单色同步辐射下。记录了光致电离和光碎裂产物离子产率作为光子能量的函数。主要观察到糖苷键断裂导致核碱基相关片段的形成。在大多数情况下，糖苷键断裂伴随着单或双氢转移。吸收位敏感的软 X 射线光谱与碎片特异性质谱的结合允许直接将 X 射线吸收位和碎裂位相关联。我们在单氢转移和双氢转移到核碱基之间的竞争中观察到明显的共振特征。用短程校正的杂化泛函进行实验数据与含时密度泛函理论计算的直接比较表明，这些氢转移过程是普遍的，不限于局域在核碱基上的特定激发态的布居。相反，氢转移可以在任何核碱基和 DNA 骨架中通过 X 射线吸收发生。共振似乎是由于氢转移通道的选择性抑制而发生的。此外，还研究了优化基态几何形状的非共价相互作用，以确定最有可能发生氢转移的分子内氢键。
