Valis Linda, Wang Qiang, Raytchev Milen, Buchvarov Ivan, Wagenknecht Hans-Achim, Fiebig Torsten
Institute for Organic Chemistry, University of Regensburg, D-93040 Regensburg, Germany.
Eugene F. Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467; and.
Proc Natl Acad Sci U S A. 2006 Jul 5;103(27):10192-10195. doi: 10.1073/pnas.0600957103. Epub 2006 Jun 26.
In 1999, Wan et al. [Proc. Natl. Acad. Sci. USA 96, 6014-6019] published a pioneering paper that established the entanglement between DNA base pair motions and the transfer time of the charge carrier. The DNA assemblies contained an ethidium covalently bound via a flexible alkyl chain to the 5' hydroxyl group of the DNA backbone. Although covalently attached, the loose way in which the ethidium was linked to DNA allowed for large degrees of conformational freedom and thus raised some concern with respect to conformational inhomogeneity. In this letter, we report studies on a different set of ethidium DNA conjugates. In contrast to the "Caltech systems," these conjugates contain ethidium tightly incorporated (as a base pair surrogate) into the DNA base stack, opposite to an abasic site analog. Despite the tight binding, we found that charge transfer from the photoexcited ethidium base pair surrogate across two or more base pairs is several orders of magnitude slower than in case of the DNA systems bearing the tethered ethidium. To further broaden the scope of this account, we compared (oxidative) electron hole transfer and (reductive) electron transfer using the same ethidium chromophore as a charge donor in combination with two different charge acceptors. We found that both electron and hole transfer are characterized by similar rates and distance dependencies. The results demonstrate the importance of nuclear motions and conformational flexibility and underline the presence of a base gating mechanism, which appears to be generic to electronic transfer processes through pi-stacked nucleic acids.
1999年，万等人[《美国国家科学院院刊》96, 6014 - 6019]发表了一篇开创性论文，确立了DNA碱基对运动与电荷载流子转移时间之间的纠缠关系。这些DNA组装体包含通过柔性烷基链共价连接到DNA主链5'羟基上的溴化乙锭。尽管是共价连接的，但溴化乙锭与DNA连接的松散方式允许其有很大程度的构象自由度，因此引发了对构象不均匀性的一些担忧。在这封信中，我们报告了对另一组溴化乙锭 - DNA共轭物的研究。与“加州理工学院系统”不同，这些共轭物包含紧密并入（作为碱基对替代物）DNA碱基堆积中的溴化乙锭，与一个无碱基位点类似物相对。尽管结合紧密，但我们发现从光激发的溴化乙锭碱基对替代物跨越两个或更多碱基对的电荷转移比带有连接溴化乙锭的DNA系统慢几个数量级。为了进一步拓宽这个研究范围，我们使用相同的溴化乙锭发色团作为电荷供体，结合两种不同的电荷受体，比较了（氧化）电子空穴转移和（还原）电子转移。我们发现电子转移和空穴转移都具有相似的速率和距离依赖性。结果证明了核运动和构象灵活性的重要性，并强调了碱基门控机制的存在，这似乎是通过π堆积核酸进行电子转移过程的共性。
