Berlin Y A, Burin A L, Ratner M A
Contribution from the Department of Chemistry, Center for Nanofabrication and Molecular Self-Assembly, and Materials Research Center, Northwestern University, 2145 N Sheridan Road, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2001 Jan 17;123(2):260-8. doi: 10.1021/ja001496n.
The efficiency of charge migration through stacked Watson-Crick base pairs is analyzed for coherent hole motion interrupted by localization on guanine (G) bases. Our analysis rests on recent experiments, which demonstrate the competition of hole hopping transitions between nearest neighbor G bases and a chemical reaction of the cation G(+) with water. In addition, it has been assumed that the presence of units with several adjacent stacked G bases on the same strand leads to the additional vibronic relaxation process (G(+)G...G) --> (GG...G)(+). The latter may also compete with the hole transfer from (G(+)G...G) to a single G site, depending on the relative positions of energy levels for G(+) and (G(+)G...G). A hopping model is proposed to take the competition of these three rate steps into account. It is shown that the model includes two important limits. One corresponds to the situation where the charge relaxation inside a multiple guanine unit is faster than hopping. In this case hopping is terminated by several adjacent G bases located on the same strand, as has been observed for the GGG triple. In the opposite, slow relaxation limit the GG...G unit allows a hole to migrate further in accord with experiments on strand cleavage exploiting GG pairs. We demonstrate that for base pair sequences with only the GGG triple, the fast relaxation limit of our model yields practically the same sequence- and distance dependencies as measurements, without invoking adjustable parameters. For sequences with a certain number of repeating adenine:thymine pairs between neighboring G bases, our analysis predicts that the hole transfer efficiency varies in inverse proportion to the sequence length for short sequences, with change to slow exponential decay for longer sequences. Calculations performed within the slow relaxation limit enable us to specify parameters that provide a reasonable fit of our numerical results to the hole migration efficiency deduced from experiments with sequences containing GG pairs. The relation of the results obtained to other theoretical and experimental studies of charge transfer in DNA is discussed. We propose experiments to gain a deeper insight into complicated kinetics of charge-transfer hopping in DNA.
针对因鸟嘌呤（G）碱基上的局域化而中断的相干空穴运动，分析了通过堆叠的沃森 - 克里克碱基对进行电荷迁移的效率。我们的分析基于最近的实验，这些实验证明了最近邻G碱基之间的空穴跳跃跃迁与阳离子G(+)与水的化学反应之间的竞争。此外，还假设在同一条链上存在具有几个相邻堆叠G碱基的单元会导致额外的电子 - 振动弛豫过程（G(+)G...G）→（GG...G)(+)。后者也可能与空穴从（G(+)G...G）转移到单个G位点竞争，这取决于G(+)和（G(+)G...G）的能级相对位置。提出了一个跳跃模型来考虑这三个速率步骤的竞争。结果表明，该模型包括两个重要极限。一个对应于多个鸟嘌呤单元内的电荷弛豫比跳跃快的情况。在这种情况下，跳跃会被位于同一条链上的几个相邻G碱基终止，就像GGG三联体所观察到的那样。在相反的、弛豫缓慢的极限情况下，GG...G单元允许空穴进一步迁移，这与利用GG对进行链断裂的实验结果一致。我们证明，对于仅具有GGG三联体的碱基对序列，我们模型的快速弛豫极限产生的序列和距离依赖性实际上与测量结果相同，无需调用可调参数。对于相邻G碱基之间有一定数量重复腺嘌呤：胸腺嘧啶对的序列，我们的分析预测，对于短序列，空穴转移效率与序列长度成反比变化，对于长序列则变为缓慢的指数衰减。在缓慢弛豫极限内进行的计算使我们能够确定参数，从而使我们的数值结果与从含有GG对序列的实验中推导出的空穴迁移效率合理拟合。讨论了所得结果与DNA中电荷转移的其他理论和实验研究的关系。我们提出了一些实验，以更深入地了解DNA中电荷转移跳跃的复杂动力学。
