Electron and hole transfer induced by thermal annealing of crystalline DNA x-irradiated at 4 K
Electron and hole transfer induced by thermal annealing of crystalline DNA x-irradiated at 4 K
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DOI：
10.1021/jp000988j
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发表时间：
2000-08-17
影响因子：
3.3
通讯作者：
Bernhard, WA
中科院分区：
文献类型：
--
作者：
Debije, MG;Bernhard, WA
最近的电子和空穴通过DNA的长距离（>2 nm）转移模型表明，这种机制既不是单一的长距离隧穿事件，也不是严格由于跳跃的机制，而是两者的混合。从这里报道的结果，我们认为，任何完整的模型的电子或空穴在DNA中的转移应该包括可逆质子转移的影响。可逆质子转移（主要在鸟嘌呤-胞嘧啶碱基对之间）影响DNA捕获自由基的能力，这反过来又影响空穴和电子的迁移。我们提出的退火特性的电子和空穴被困在结晶寡脱氧核苷酸在4 K照射和逐步退火到室温（RT）。退火曲线对DNA构象、序列或碱基堆叠连续性相对不敏感。DNA双链体的包装是已知的，并且很容易表明电子和/或空穴转移必须是分子间的。发现单独分子之间隧穿所需的距离与DNA双链体内隧穿所需的距离相当。DNA的退火特性与在α-Me-甘露糖苷、5 'dCMP和1-甲基胞嘧啶：5-氟尿嘧啶晶体中发现的退火特性有很大不同。这种差异归因于其中可逆质子转移是电子/空穴转移的限速步骤的机制。因此，可逆质子转移是电子/空穴转移的“门”（通过隧穿）。由于可逆的质子转移是热激活的，因此提出这种转移的能量学是确定DNA的热退火曲线的主导因素。在4K辐照下退火样品产生的控制电子/空穴迁移的竞争反应适用于RT下的电子/空穴迁移。这方面的证据来自观察，在许多DNA晶体中，自由基种类和自由基产率非常相似的晶体辐照在RT相比，那些在4 K辐照，然后退火到RT。通过DNA的迁移是其中通过隧穿发生短转移（类似于小于或等于1 nm）的迁移，并且隧穿通过可逆质子转移门控。
Recent models for long range (>2 nm) transfer of electrons and holes through DNA suggest a mechanism that is neither a single long distance tunneling event nor a mechanism strictly due to hopping, but a mixture of the two. From results reported here we argue that any complete model of electron or hole transfer in DNA should include the effects of reversible proton transfer. Reversible proton transfer (primarily between guanine-cytosine base pairs) influences the ability of DNA to trap free radicals, which in turn affects the migration of holes and electrons. We present the annealing characteristics of electrons and holes trapped in crystalline oligodeoxynucleotides irradiated at 4 K and annealed stepwise to room temperature (RT). The annealing profiles are relatively insensitive to DNA conformation, sequence, or base stacking continuity. The packing of the DNA duplexes is known, and it is readily shown that electron and/or hole transfer must be intermolecular. The distances required for tunneling between separate molecules are found to be comparable to the distances required for tunneling within a DNA duplex. The annealing characteristics of DNA are considerably different than those found in crystals of alpha-Me-mannoside, 5'dCMP, and 1-Methylcytosine:5-Fluorouracil. This difference is ascribed to a mechanism wherein reversible proton transfer is a rate-limiting step for electron/hole transfer. Reversible proton transfer is, thereby, a "gate" for electron/hole transfer (via tunneling). Because reversible proton transfer is thermally activated, it is proposed that the energetics of this transfer is a dominant factor in determining the thermal annealing profile of DNA. The competing reactions that govern electron/hole migration created by annealing samples irradiated at 4 K; are applicable to electron/hole migration at RT. Evidence for this comes from the observation that, in a number of DNA crystals, the free radical species and radical yields are very similar to crystals irradiated at RT compared to those irradiated at 4 K followed by annealing to RT. The proposed mechanism for electron and hole migration through DNA is one where short transfers (similar to less than or equal to 1 nm) occur by tunneling, and tunneling is gated by reversible proton-transfer.