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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Proton transfer in nucleobases is mediated by water
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Proton transfer in nucleobases is mediated by water

机译：核碱基中的质子转移是由水介导的

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摘要

Water plays a central role in chemistry and biology by mediating the interactions between molecules, altering energy levels of solvated species, modifying potential energy profiles along reaction coordinates, and facilitating efficient proton transport through ion channels and interfaces. This study investigates proton transfer in a model system comprising dry and microhydrated clusters of nucleobases. With mass spectrometry and tunable vacuum ultraviolet synchrotron radiation, we show that water shuts down ionization-induced proton transfer between nucleobases, which is very efficient in dry clusters. Instead, a new pathway opens up in which protonated nucleobases are generated by proton transfer from the ionized water molecule and elimination of a hydroxyl radical. Electronic structure calculations reveal that the shape of the potential energy profile along the proton transfer coordinate depends strongly on the character of the molecular orbital from which the electron is removed; i.e., the proton transfer from water to nucleobases is barrierless when an ionized state localized on water is accessed. The computed energetics of proton transfer is in excellent agreement with the experimental appearance energies. Possible adiabatic passage on the ground electronic state of the ionized system, though energetically accessible at lower energies, is not efficient. Thus, proton transfer is controlled electronically, by the character of the ionized state, rather than statistically, by simple energy considerations.
机译：水通过介导分子之间的相互作用，改变溶剂化物种的能级，改变沿反应坐标的势能分布以及促进质子通过离子通道和界面的有效传输，在化学和生物学中起着核心作用。这项研究调查了模型系统中质子的转移，该系统包含干燥和微水合的核碱基簇。借助质谱和可调谐真空紫外同步辐射，我们表明水可以关闭电离诱导的质子在核碱基之间的转移，这在干燥簇中非常有效。取而代之的是，打开了一条新的途径，其中质子化的核碱基是通过从电离的水分子中转移质子并消除羟基自由基而产生的。电子结构计算表明，沿着质子传递坐标的势能分布图的形状在很大程度上取决于从中除去电子的分子轨道的特性。即质子从水到核碱基的转移是无障碍的，当进入位于水上的电离状态时。质子转移的计算能量与实验出现能极佳地吻合。尽管在较低能量下可通过能量进入，但在电离系统的基态电子状态上可能发生的绝热通道效率不高。因此，质子传递是通过电离状态的特性进行电子控制的，而不是通过简单的能量考虑进行统计控制的。

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