Modulation of DNA mediated hole transport by novel substituents on DNA

虽然DNA介导的空穴传输机制一直存在争议，但从含有拴系氧化剂的双链DNA的远程鸟嘌呤(G)氧化可以明显看出，G自由基阳离子(空穴)通过DNA_<TT>-堆叠进行距离迁移。由于GG和GGG的电离势比单一G低，这些堆积的G位起到热力学下沉的作用，最终产生(哌啶不稳定位)。从原理上讲，空穴从空穴施主到空穴受体的迁移与被水和/或氧气捕获的空穴竞争。因此，空穴转移的整体效率主要取决于空穴迁移和空穴捕获的速率。当空穴捕获速率远低于空穴迁移速率时，可以实现空穴在施主和受主之间的平衡。虽然可以通过改变空穴施主和受主之间的势能差来减弱空穴的迁移速率，但通过改变空穴俘获速率来调节空穴的传输效率还没有得到证实。我们报道了一种新型的空穴捕获核苷N_2-环丙基-2‘-脱氧鸟苷1(DCPG)，它在N_2上带有环丙基，作为自由基捕获器。光激发核黄素对dCPG的单电子氧化导致均解环丙烷开环，形成N_2-(3-羟基丙酰基)dG_2。利用含有dCPG的双链，我们证明dCPG在其自身的位置有效地终止了DNA介导的空穴传输。

While the mechanism of DNA mediated hole transport is a subject of controversy, it is now evident from remote guanine (G) oxidation of duplex DNAs containing a tethered oxidant that G radical cation (hole) migrates distance through DNA _<TT>-stack. Due to lower ionization potentials of GG and GGG than single G, these stacked G sites function as a thermodynamic sink of holes eventually producing, (piperidine labile sites. In principle, hole migration from hole donor to acceptor competes with hole trapping by water and/or oxygen. Therefore, overall efficiency of hole transfer is primarily determined by the rates of hole migration and hole trapping. When the rate of hole trapping is much slower than hole migration rate, equilibration of hole between donor and acceptor can be achieved. While the rate of hole migration can be attenuated by changing the potential energy gap between hole donor and acceptor, the modulation of hole transport efficiency by changing the rate of hole trapping has never been demonstrated. We report a novel hole-trapping nucleoside N2-cyclopropyl2'-deoxyguanosine 1 (dCPG), which possesses a cyclopropyl group on N2 as a radical-trapping device. One electron oxidation of dCPG by photoexcited riboflavine induces homolytic cyclopropane ring opening as evidenced by the formation of N2-(3-hydroxypropanoyl)dG 2. With the use of dCPG -containing duplex, we have demonstrated that dCPG efficiently terminates DNA mediated hole transport at its own site.