Donor-bridge-acceptor energetics determine the distance dependence of electron tunneling in DNA
Donor-bridge-acceptor energetics determine the distance dependence of electron tunneling in DNA
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DOI：
10.1073/pnas.192432899
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发表时间：
2002-10-01
影响因子：
11.1
通讯作者：
Beratan, DN
中科院分区：
文献类型：
--
作者：
Lewis, FD;Liu, JQ;Beratan, DN
DNA中的电子转移（ET）过程是目前的兴趣，因为它们参与氧化链断裂反应和它们的相关性的分子电子学的发展。DNA中的电子转移有两种机制，一种是单步隧穿过程，另一种是多步电荷跳跃过程。隧穿反应的动力学取决于电子供体和受体之间的距离以及分离供体和受体的分子桥的性质。在蛋白质和烷烃桥的情况下，距离依赖性并不强烈依赖于供体和受体的性质。与此相反，我们在这里表明，DNA ET率的距离衰减显着不同的能量的供体和受体相对于桥。具体地，我们发现，在不改变反应自由能的情况下，相对于核苷酸的光化学氧化的供体和受体能量，桥态的能量增加0.25 eV（1 eV = 1.602 × 10（-19）J），导致ET速率的特征指数距离衰减常数从0.71增加到1.1埃（-1）。这些结果表明，在小的隧道能隙区的DNA ET，距离的依赖性是不普遍的，它强烈的隧道能隙的变化。这些DNA ET反应填补了桥介导的ET过程的一般理论中的大势垒（快速衰减）隧穿制度和（缓慢衰减）跳跃制度之间的“缺失环节”或过渡制度。
Electron transfer (ET) processes in DNA are of current interest because of their involvement in oxidative strand cleavage reactions and their relevance to the development of molecular electronics. Two mechanisms have been identified for ET in DNA, a single-step tunneling process and a multistep charge-hopping process. The dynamics of tunneling reactions depend on both the distance between the electron donor and acceptor and the nature of the molecular bridge separating the donor and acceptor. In the case of protein and alkane bridges, the distance dependence is not strongly dependent on the properties of the donor and acceptor. In contrast, we show here that the distance decay of DNA ET rates varies markedly with the energetics of the donor and acceptor relative to the bridge. Specifically, we find that an increase in the energy of the bridge states by 0.25 eV (1 eV = 1.602 x 10(-19) J) relative to the donor and acceptor energies for photochemical oxidation of nucleotides, without changing the reaction free energy, results in an increase in the characteristic exponential distance decay constant for the ET rates from 0.71 to 1.1 Angstrom(-1). These results show that, in the small tunneling energy gap regime of DNA ET, the distance dependence is not universal; it varies strongly with the tunneling energy gap. These DNA ET reactions fill a "missing link" or transition regime between the large barrier (rapidly decaying) tunneling regime and the (slowly decaying) hopping regime in the general theory of bridge-mediated ET processes.