Polaronic semiconductor behavior of long-range charge transfer in DNA oligomers in solution: controlling barriers to long-distance radical cation migration in DNA with thymine analogs.

A series of anthraquinone-linked DNA oligonucleotides was prepared and the efficiency of long-distance radical cation migration was measured. In one set of oligonucleotides, two GG steps are separated by either a TATA or an ATAT bridge. In these two compounds, the efficiency of radical cation migration from GG to GG differs by more than an order of magnitude. Replacement of the thymines in the TATA or ATAT bridges with 3-methyl-2-pyridone (t, a thymine analog) results in the much more efficient radical cation migration across the bridge in both cases. This is attributed to a decrease in the oxidation potential of t to a value below that of A. In contrast, replacement of the thymines in the TATA or ATAT bridges with difluorotoluene (f, a thymine analog with high oxidation potential) does not measurably affect radical cation migration. These findings are readily accommodated by the phonon-assisted polaron-hopping mechanism for long-distance charge transfer in duplex DNA and indicate that DNA in solution behaves as a polaronic semiconductor.

制备了一系列蒽醌连接的DNA寡核苷酸，并测量了长距离自由基阳离子迁移的效率。在一组寡核苷酸中，两个GG碱基对由TATA或ATAT桥隔开。在这两种化合物中，自由基阳离子从GG到GG的迁移效率相差一个数量级以上。用3 - 甲基 - 2 - 吡啶酮（t，一种胸腺嘧啶类似物）取代TATA或ATAT桥中的胸腺嘧啶，在两种情况下都导致跨桥的自由基阳离子迁移效率大大提高。这归因于t的氧化电位降低到低于A的值。相比之下，用二氟甲苯（f，一种具有高氧化电位的胸腺嘧啶类似物）取代TATA或ATAT桥中的胸腺嘧啶，对自由基阳离子迁移没有可测量的影响。这些发现很容易被双链DNA中长距离电荷转移的声子辅助极化子跳跃机制所解释，并表明溶液中的DNA表现为极化子半导体。