Direct observation of hole transfer through DNA by hopping between adenine bases and by tunnelling
Direct observation of hole transfer through DNA by hopping between adenine bases and by tunnelling
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DOI：
10.1038/35085542
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发表时间：
2001-07-19
期刊：
影响因子：
64.8
通讯作者：
Wessely, S
中科院分区：
文献类型：
--
作者：
Giese, B;Amaudrut, J;Wessely, S
DNA在氧化应激过程中的功能(1)以及它是否适合作为分子器件的潜在构件(2-4)取决于电子和空穴通过分子的长距离转移，然而关于这一过程的效率的许多相互矛盾的测量已经被报道(5，6)。人们普遍认为，电荷通过多步跳跃反应(7-11)进行长距离传输；这种“G跳跃”(8)包括正电荷在鸟嘌呤(Gs)之间移动，鸟嘌呤(Gs)是具有最低电离电势的DNA碱基。但该机制不能解释当鸟嘌呤位置较远(7，12)时有效电荷转移的持久性，转移速率并不像预期的那样随着转移距离的增加而迅速下降。我们的实验表明，只有当鸟嘌呤之间的距离不超过三个碱基对时，两个鸟嘌呤碱基之间的电荷转移速率才会随着间距的增加而降低；如果存在更多的桥接碱基对，则转移速率仅表现出弱的距离依赖性。我们将通过DNA的电荷转移速率与距离的关系的这种明显变化归因于从短距离的相干超交换电荷转移(隧穿)转移到长距离由热诱导的腺嘌呤碱基之间的电荷跳跃(A-跳跃)所介导的过程。我们的结果证实了这一行为的理论预测(13-17)，强调了对距离对DNA电荷转移的强(8，9)和弱(7，12)影响的看似矛盾的观察很容易被转移机制的改变解释。
The function of DNA during oxidative stress(1) and its suitability as a potential building block for molecular devices(2-4) depend on long-distance transfer of electrons and holes through the molecule, yet many conflicting measurements of the efficiency of this process have been reported(5,6). It is accepted that charges are transported over long distances through a multistep hopping reaction(7-11); this 'G-hopping'(8) involves positive charges moving between guanines (Gs), the DNA bases with the lowest ionization potential. But the mechanism fails to explain the persistence of efficient charge transfer when the guanine sites are distant(7,12), where transfer rates do not, as expected, decrease rapidly with transfer distance. Here we show experimentally that the rate of charge transfer between two guanine bases decreases with increasing separation only if the guanines are separated by no more than three base pairs; if more bridging base pairs are present, the transfer rates exhibit only a weak distance dependence. We attribute this distinct change in the distance dependence of the rate of charge transfer through DNA to a shift from coherent superexchange charge transfer (tunnelling) at short distances to a process mediated by thermally induced hopping of charges between adenine bases (A-hopping) at long distances. Our results confirm theoretical predictions of this behaviour(13-17), emphasizing that seemingly contradictory observations of a strong(8,9) as well as a weak(7,12) influence of distance on DNA charge transfer are readily explained by a change in the transfer mechanism.