嘌呤和嘧啶高分辨率氧1s X射线光电子能谱中的温度与互变异构效应
Temperature and Tautomeric Effects in High-Resolution Oxygen 1s X-ray Photoelectron Spectroscopy of Purines and Pyrimidines
AI总结：
本文通过第一性原理模拟研究了6种嘌呤和嘧啶衍生物在不同温度下的振动分辨O1s X射线光电子能谱，揭示了羰基氧的化学环境差异、温度依赖性及次黄嘌呤的互变异构效应。
摘要：
嘌呤和嘧啶是生物系统中至关重要的构建模块，在分子物理、生物化学、药理学和化学领域引起了广泛关注。大量光谱技术已被用于表征这些分子，但温度和潜在的互变异构效应会使对底层物理和化学过程的解释变得复杂。本文中，我们开展了第一性原理模拟，分析了6种常见生物分子在不同温度下的振动分辨O1s X射线光电子能谱，其中包括3种嘌呤衍生物（黄嘌呤、咖啡因和次黄嘌呤）和3种嘧啶衍生物（胸腺嘧啶、5F-尿嘧啶和尿嘧啶），并研究了次黄嘌呤在不同温度下的互变异构效应。在Franck-Condon近似下，同时采用时间无关（TI）和时间相关（TD）方法，我们获得了与实验高度吻合的理论光谱。我们对这些均含有羰基氧的体系进行分析，揭示了N-CO-N结构中的氧（O2）与N-CO-C结构中的氧（O1）相比所具有的独特特征，即O2表现出更高的O1s结合能和更大的总振动重组能。我们观察到核心电离态与基态之间的零点振动能差异很小，表明Duschinsky旋转效应较弱。我们一致发现O1s电离导致O*=C键长伸长。TI方法有助于将实验光谱指认到不同原子或互变异构体，其中所有6种分子的原子特异性振动电子谱线轮廓表现出相似性，以0-2跃迁为主导。TD方法通过纳入互变异构体的Boltzmann布居比，能够更全面地探索温度效应以及次黄嘌呤的互变异构效应。我们观察到这些光谱中的振动电子特征具有显著的温度依赖性。
英文摘要：
Purines and pyrimidines, crucial building blocks in biological systems, have attracted significant interest across molecular physics, biochemistry, pharmacology, and chemistry. Extensive spectroscopies have been employed for characterization, while the temperature and potential tautomeric effects can complicate the interpretation of underlying physics and chemistry. Here, we conducted first-principles simulations to analyze the vibrationally-resolved O1s X-ray photoelectron spectra of 6 common biomolecules at different temperatures, comprising 3 purine (xanthine, caffeine, and hypoxanthine) and 3 pyrimidine (thymine, 5F-uracil, and uracil) derivatives, and the tautomeric effect of hypoxanthine at varying temperatures. Using both time-independent (TI) and time-dependent (TD) methods under the Franck-Condon approximation, we obtained theoretical spectra that exhibited excellent agreement with experiments. Our analysis of these systems, all featuring carbonyl oxygens, unveiled distinctive characteristics of oxygen in N-CO-N (O2) compared to that within a N-CO-C structure (O1), showcasing higher O1s binding energy and total vibrational reorganization energy. We observed small differences in the zero-point vibration energies between the core-ionized and ground states, indicating a weak Duschinsky rotation effect. We consistently found that O1s ionization resulted in elongation of the O*=C bond length. The TI method facilitated the assignment of experimental spectra to different atoms or tautomers, where the atom-specific vibronic profiles of all 6 molecules exhibited similarity, with the 0-2 transitions dominating. TD enabled a more comprehensive exploration of the temperature effect, and the tautomeric effect of hypoxanthine by incorporating the Boltzmann population ratios of tautomers. We observed significant temperature dependence in the vibronic features present in these spectra.
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