Ultrafast deactivation of an excited cytosine-guanine base pair in DNA
Ultrafast deactivation of an excited cytosine-guanine base pair in DNA
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DOI：
10.1021/ja069176c
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发表时间：
2007-05-30
影响因子：
15
通讯作者：
Robb, Michael A.
中科院分区：
文献类型：
--
作者：
Groenhof, Gerrit;Schaefer, Lars V.;Robb, Michael A.
多构型从头计算和QM/MM分子动力学模拟的光激发的胞嘧啶鸟嘌呤碱基对在气相和嵌入在DNA中提供详细的结构和动力学的见解超快无辐射失活机制。光子吸收促进质子从鸟嘌呤转移到胞嘧啶。这种质子转移之后是一个有效的无辐射衰减的激发态通过一个扩展的锥形交叉缝。圆锥相交的优化表明，它有一个不寻常的拓扑结构，因为只有一个退化提升坐标。这是真空中和DNA中衰变的主要机制特征。无辐射衰变发生沿着一个扩展的超线几乎平行于质子转移坐标，表明质子转移本身并不直接负责失活。接缝从最小能量质子转移路径沿着基底的骨架变形移位。因此，衰变可以发生在沿着单质子转移坐标的任何地方，这是沃森-克里克碱基对的激发态寿命非常短的原因。在真空中，衰变发生在一个完整的质子转移之后，而在DNA中，衰变也可以发生得更早。这种效应的起因在于DNA中电荷转移态偶极的时间静电稳定。
Multiconfigurational ab initio calculations and QM/MM molecular dynamics simulations of a photoexcited cytosine-guanine base pair in both gas phase and embedded in the DNA provide detailed structural and dynamical insights into the ultrafast radiationless deactivation mechanism. Photon absorption promotes transfer of a proton from the guanine to the cytosine. This proton transfer is followed by an efficient radiationless decay of the excited state via an extended conical intersection seam. The optimization of the conical intersection revealed that it has an unusual topology, in that there is only one degeneracy-lifting coordinate. This is the central mechanistic feature for the decay both in vacuo and in the DNA. Radiationless decay occurs along an extended hyperline nearly parallel to the proton-transfer coordinate, indicating the proton transfer itself is not directly responsible for the deactivation. The seam is displaced from the minimum energy proton-transfer path along a skeletal deformation of the bases. Decay can thus occur anywhere along the single proton-transfer coordinate, accounting for the remarkably short excited-state lifetime of the Watson-Crick base pair. In vacuo, decay occurs after a complete proton transfer, whereas in DNA, decay can also occur much earlier. The origin of this effect lies in the temporal electrostatic stabilization of dipole in the charge-transfer state in DNA.