Excited State Relaxation of Neutral and Basic 8-Oxoguanine

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• 作者：Zhen Lu ; Ashley A. Beckstead ; Bern Kohler ; Spiridoula Matsika
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：July 2, 2015
• 年：2015
• 卷：119
• 期：26
• 页码：8293-8301
• 全文大小：381K
• ISSN：1520-5207

文摘

8-Oxo-7,8-dihydro-2鈥?deoxyguanosine (8-oxo-dGuo) is one of the most common forms of DNA oxidative damage. Recent studies have shown that 8-oxo-dGuo can repair cyclobutane pyrimidine dimers in double-stranded DNA when photoexcited, making its excited state dynamics of particular interest. The excited state lifetimes of 8-oxo-dGuo and its anion have been previously probed using transient absorption spectroscopy; however, more information is required to understand the decay mechanisms. In this work, excited state potential energy surfaces for the neutral and deprotonated forms of the free base, 8-oxoguanine (8-oxo-G), are explored theoretically using multireference methods while the nucleoside is experimentally studied using steady-state fluorescence spectroscopy. It is determined that the neutral species exhibits ultrafast radiationless decay via easy access to conical intersections. The relatively long lifetime for the anion can be explained by the existence of sizable barriers between the Franck鈥揅ondon region and two S₁/S₀ minimum energy conical intersections. A Strickler鈥揃erg analysis of the experimentally measured fluorescence quantum yields and lifetimes is consistent with emission from 蟺蟺* excited states in line with theoretical predictions.