Direct observation of hole transfer through double-helical DNA over 100 A.
Direct observation of hole transfer through double-helical DNA over 100 A.
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DOI：
10.1073/pnas.0402756101
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发表时间：
2004-09
影响因子：
11.1
通讯作者：
T. Takada;K. Kawai;M. Fujitsuka;T. Majima
中科院分区：
文献类型：
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作者：
T. Takada;K. Kawai;M. Fujitsuka;T. Majima
DNA中光诱导电子转移及随后的空穴转移的机理已被广泛研究，但迄今为止，我们还没有看到任何关于长距离空穴转移过程的可靠报道。在这篇文章中，我们展示了双螺旋DNA中的长距离空穴传输超过100 A的时间分辨瞬态吸收测量的直接观察结果。在DNA的5'端分别偶联了电子受体分子萘酰亚胺（NI）和电子供体分子吩噻嗪（PTZ），观察了DNA的空穴转移过程。通过腺嘌呤跳跃过程的位点选择性电荷注入G是通过用355 nm的激光闪光激发NI来完成的。在400 nm附近的瞬态吸收，这是分配给NI自由基阴离子，观察后立即照射的激光闪光，表明NI和最近的G之间的电荷分离发生。然后，在520 nm处出现了PTZ自由基阳离子（PTZ（*+））的瞬态吸收，这是由于空穴通过DNA转移到PTZ位点。通过对NI-A（6）-（GA）（n）-PTZ和NI-A（6）-（GT）（n）-PTZ（n = 2，3，4，6，8，12）（碱基序列与NI修饰的DNA对应）的PTZ（*+）瞬态吸收时间曲线的监测，直接观察到了发生在微秒至毫秒时间尺度内的从G到PTZ的长距离空穴转移过程。通过假设碱基对之间的平均距离为3.4 A，对于n = 12个序列，总距离达到100 A。我们的结果清楚地显示了100 A以上的长距离空穴传输的直接观测。
Mechanism of photo-induced electron transfer and the subsequent hole transfer in DNA has been studied extensively, but so far we are not aware of any reliable report of the observation of the long-distance hole-transfer process. In this article, we demonstrate the results of direct observation for the long-distance hole transfer in double-helical DNA over 100 A with time-resolved transient absorption measurements. DNA conjugated with naphthalimide (NI) and phenothiazine (PTZ) (which worked as electron-acceptor and donor molecules, respectively) at both 5' ends was synthesized to observe the hole-transfer process. Site-selective charge injection into G by means of the adenine-hopping process was accomplished by excitation of NI with a 355-nm laser flash. Transient absorption around 400 nm, which was assigned to the NI radical anion, was observed immediately after the irradiation of a laser flash, indicating that the charge separation between NI and the nearest G occurred. Then, the transient absorption of the PTZ radical cation (PTZ(*+)) at 520 nm was emerged, which was attributed to the hole transfer through DNA to the PTZ site. By monitoring the time profiles of the transient absorption of PTZ(*+) for NI-A(6)-(GA)(n)-PTZ and NI-A(6)-(GT)(n)-PTZ (n = 2, 3, 4, 6, 8, 12) (base sequences correspond to those for DNA modified with NI), the long-distance hole-transfer process from G to PTZ, which occurred in the time scale of microsecond to millisecond, was observed directly. By assuming an average distance of 3.4 A between base-pairs, total distance reaches 100 A for n = 12 sequences. Our results clearly show the direct observation of the long-distance hole transfer over 100 A.