2-aminopurine (2AP) is a responsive fluorescent base analogue that is used widely as a probe of the local molecular environment in DNA. The ability of 2AP to report changes in local conformation and base-stacking interactions arises from the efficient quenching of its fluorescence by the natural DNA bases. However, the mechanism of this inter-base quenching remains imperfectly understood. Two previous studies of the collisional quenching of 2AP by the natural bases, in different buffer solutions, showed that dynamic quenching efficiency depends on the identity of the natural base, but disagreed on the relative quenching efficiencies of the bases. We report a comprehensive investigation of inter-base quenching of 2AP by the natural nucleoside monophosphates (NMPs), replicating the buffer conditions used in the previous studies. Using time-resolved fluorescence measurements to distinguish between dynamic and static quenching, we find that the dynamic quenching rate constants of the different bases show a consistent trend across both buffers, and this is in line with a charge-transfer mechanism. Time-resolved measurements also provide insight into static quenching, revealing formation of 2AP-NMP ground-state complexes in which 2AP displays a very short fluorescence lifetime, comparable to that seen in oligonucleotides. In these complexes, the dependence of the rate of quenching on the partner base also supports a charge-transfer mechanism.

中文翻译：

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通过溶液中的天然DNA核苷酸动态和静态淬灭2-氨基嘌呤荧光。

2-氨基嘌呤（2AP）是一种响应性荧光碱基类似物，被广泛用作DNA局部分子环境的探针。2AP报告局部构象和碱基堆积相互作用变化的能力来自天然DNA碱基对荧光的有效淬灭。但是，这种碱间猝灭的机理仍未得到很好的理解。先前关于天然碱在不同缓冲溶液中对2AP的碰撞猝灭的两项研究表明，动态猝灭效率取决于天然碱的特性，但对碱的相对猝灭效率却不同。我们报告了由天然核苷一磷酸（NMPs）对2AP碱基间淬灭的全面研究，复制了先前研究中使用的缓冲条件。使用时间分辨的荧光测量值来区分动态和静态猝灭，我们发现不同碱基的动态猝灭速率常数在两种缓冲液中均显示出一致的趋势，这与电荷转移机制相符。时间分辨的测量还提供了对静态猝灭的见解，揭示了2AP-NMP基态复合物的形成，其中2AP显示的荧光寿命很短，与寡核苷酸相当。在这些配合物中，猝灭速率对配偶基的依赖性也支持电荷转移机制。这符合电荷转移机制。时间分辨的测量还提供了对静态猝灭的见解，揭示了2AP-NMP基态复合物的形成，其中2AP显示的荧光寿命很短，与寡核苷酸相当。在这些配合物中，猝灭速率对配偶基的依赖性也支持电荷转移机制。这符合电荷转移机制。时间分辨的测量还提供了对静态猝灭的见解，揭示了2AP-NMP基态复合物的形成，其中2AP显示的荧光寿命很短，与寡核苷酸相当。在这些配合物中，猝灭速率对配偶基的依赖性也支持电荷转移机制。