Department of Biology and Chemistry, City University of Hong Kong , Kowloon, Hong Kong.
Synchrotron SOLEIL , L'orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette Cedex, France.
J Am Chem Soc. 2016 Dec 28;138(51):16596-16599. doi: 10.1021/jacs.6b10413. Epub 2016 Dec 19.
Biological entities, such as DNA bases or proteins, possess numerous tautomers and isomers that lie close in energy, making the experimental characterization of a unique tautomer challenging. We apply VUV synchrotron-based experiments combined with state-of-the-art ab initio methodology to determine the adiabatic ionization energies (AIEs) of specific gas-phase cytosine tautomers produced in a molecular beam. The structures and energetics of neutral and cationic cytosine tautomers were determined using explicitly correlated methods. The experimental spectra correspond to well-resolved bands that are attributable to the specific contributions of five neutral tautomers of cytosine prior to ionization. Their AIEs are experimentally determined for the first time with an accuracy of 0.003 eV. This study also serves as an important showcase for other biological entities presenting a dense pattern of isomeric and tautomeric forms in their spectra that can be investigated to understand the charge redistribution in these species upon ionization.
生物实体，如 DNA 碱基或蛋白质，具有许多能量上接近的互变异构体和异构体，使得实验表征独特的互变异构体具有挑战性。我们应用基于真空紫外线同步加速器的实验结合最先进的从头算方法来确定在分子束中产生的特定气相胞嘧啶互变异构体的绝热电离能（AIE）。使用显式相关方法确定中性和阳离子胞嘧啶互变异构体的结构和能量。实验光谱对应于可分辨的谱带，这些谱带归因于电离前胞嘧啶的五个中性互变异构体的特定贡献。它们的 AIE 首次以 0.003 eV 的精度进行了实验确定。这项研究还为其他生物实体提供了一个重要的范例，这些生物实体在其光谱中呈现出密集的异构体和互变异构体形式，这些形式可以进行研究，以了解这些物种在电离时的电荷重分布。
