Electron Transfer through DNA: Site‐Specific Modification of Duplex DNA with Ruthenium Donors and Acceptors

The rate of the electron transfer between two ruthenium centers at the ends of an octanucleotide duplex (metal‐to‐metal distance = 21 Å) was determined to be 1.6(4) × 10 6 s −1 . By using automated DNA synthesis techniques, modified oligonucleotides were prepared with a protected phosphoroamidite of 2′‐amino‐2′‐deoxyuridine. The NH 2 ‐modified oligonucleotides were hybridized with complementary DNA sequences to protect nucleotide bases, and then treated with ruthenium complexes. In this way the ruthenium complex was bound only to the free NH 2 group.