Electron spin resonance study of electron transfer rates in DNA:: Determination of the tunneling constant β for single-step excess electron transfer
Electron spin resonance study of electron transfer rates in DNA:: Determination of the tunneling constant β for single-step excess electron transfer
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DOI：
10.1021/jp993550w
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发表时间：
2000-02-10
影响因子：
3.3
通讯作者：
Sevilla, MD
中科院分区：
文献类型：
--
作者：
Messer, A;Carpenter, K;Sevilla, MD
本文报道了在低温下，在一种含水的草状介质中，由辐射产生电子并将其捕获在DNA上的系统中的电子转移的研究。电子从DNA阴离子自由基转移到随机间隔的嵌入剂之后，通过电子自旋共振光谱观察嵌入剂电子加合物电子自旋共振（ESR）信号中的积聚和DNA阴离子信号在77 K下随时间的损失。研究了插层剂米托蒽醌、溴化乙锭。1，10-菲咯啉和5-硝基-1，10-菲咯啉测试电荷和电子亲合性的影响。实验的时间火焰，几分钟到几周，允许使用大的插层剂间距（低负载），在该间距下随机插层是最可能的。发现嵌入剂捕获的电子分数随着ln（t）增加，如单步隧穿过程所预期的。嵌入剂基于随机分布的电子捕获表达式的拟合结果表明，随机模型适合于取决于嵌入剂的每10-20个DNA碱基对约1个的加载。在77 K下1 min时，电子转移距离从4个碱基对（乙锭）到10个碱基对（米托蒽醌）。采用的低温允许观察单步隧穿自由竞争机制，如跳跃。发现的隧穿常数β的值为0.8-1.2埃（-1），并不表明通过DNA碱基堆的隧穿为过量电子通过DNA的转移提供了特别容易的途径。我们发现，转移距离和速率相关的嵌入剂的电子亲合势计算的密度泛函理论。
An investigation of electron transfer in DNA at low temperatures in an aqueous grassy medium is reported for a system in which electrons are generated by radiation and trapped on DNA. The transfer of the electron from the DNA anion radical to randomly interspaced intercalators is followed by electron spin resonance spectroscopic observation of the buildup in the intercalator electron adduct electron spin resonance (ESR) signal and the loss of the DNA anion signal with time at 77 K. The intercalators investigated, mitoxantrone, ethidium bromide. 1,10-phenanthroline, and 5-nitro-1,10-phenanthroline, test the effect of charge and electron affinity. The time flame of the experiment, minutes to weeks, allowed the use of large intercalator spacings (low loadings) at which random intercalation is most likely. The fraction of the electron captured by the intercalator was found to increase with ln(t) as expected for a single-step tunneling process. Fits of results to expressions for electron capture by intercalators based on a random distribution suggest that the random model is appropriate up to loadings of about 1 per 10-20 DNA base pairs depending on the intercalator. The distances of electron-transfer range from 4 base pairs (ethidium) to 10 base pairs (mitoxantrene) after 1 min at 77 K. The low temperatures employed allow for the observation of single-step tunneling free from competing mechanisms such as hopping. The values of the tunneling constant beta found, 0.8-1.2 Angstrom(-1), do not suggest that tunneling through the DNA base stack provides a particularly facile route for transfer of excess electrons through DNA. We find that the transfer distances and rates correlate with intercalator electron affinities calculated by density functional theory.