Lewis Frederick D, Liu Jianqin, Zuo Xiaobing, Hayes Ryan T, Wasielewski Michael R
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2003 Apr 23;125(16):4850-61. doi: 10.1021/ja029390a.
The dynamics of single-step hole transport processes have been investigated in a number of DNA conjugates possessing a stilbenedicarboxamide electron acceptor, a guanine primary donor, and several secondary donors. Rate constants for both forward and return hole transport between the primary and secondary donor are obtained from kinetic modeling of the nanosecond transient absorption decay profiles of the stilbene anion radical. The kinetic model requires that the hole be localized on either the primary or the secondary donor and not delocalized over both the primary and the secondary donor. Rate constants for hole transport are found to be dependent upon the identity of the secondary donor, the intervening bases, and the location of the secondary donor in the same strand as the primary donor or in the complementary strand. Rate constants for hole transport are much slower than those for the superexchange process used to inject the hole on the primary donor. This difference is attributed to the larger solvent reorganization energy for charge transport versus charge separation. The hole transport rate constants obtained in these experiments are consistent with experimental data for single-step hole transport from other transient absorption studies. Their relevance to long-distance hole migration over tens of base pairs remains to be determined. The forward and return hole transport rate constants provide equilibrium constants and free energies for hole transport equilibria. Secondary GG and GGG donors are found to form very shallow hole traps, whereas the nucleobase deazaguanine forms a relatively deep hole trap. This conclusion is in accord with selected strand cleavage data and thus appears to be representative of the behavior of holes in duplex DNA. Our results are discussed in the context of current theoretical models of hole transport in DNA.
在许多含有二苯乙烯二甲酰胺电子受体、鸟嘌呤初级供体和几个次级供体的DNA共轭物中，已经研究了单步空穴传输过程的动力学。通过对二苯乙烯阴离子自由基的纳秒瞬态吸收衰减曲线进行动力学建模，获得了初级供体和次级供体之间正向和反向空穴传输的速率常数。动力学模型要求空穴定位于初级供体或次级供体上，而不是在初级供体和次级供体上离域。发现空穴传输的速率常数取决于次级供体的身份、中间碱基以及次级供体与初级供体在同一条链上还是在互补链上的位置。空穴传输的速率常数比用于在初级供体上注入空穴的超交换过程的速率常数慢得多。这种差异归因于电荷传输与电荷分离相比具有更大的溶剂重组能。这些实验中获得的空穴传输速率常数与其他瞬态吸收研究中关于单步空穴传输的实验数据一致。它们与跨越数十个碱基对的长距离空穴迁移的相关性仍有待确定。正向和反向空穴传输速率常数提供了空穴传输平衡的平衡常数和自由能。发现次级GG和GGG供体形成非常浅的空穴陷阱，而核碱基脱氮鸟嘌呤形成相对较深的空穴陷阱。这一结论与选定的链断裂数据一致，因此似乎代表了双链DNA中空穴的行为。我们的结果在当前DNA中空穴传输的理论模型背景下进行了讨论。
