Hole Injection and Hole Transfer through DNA: The Hopping Mechanism

Abstract

Hole injection into a guanine of DNA, and hole transfer between the DNA guanines were studied. The reactions were performed in the ground state using a carbohydrate radical cation whose precursor is site-selectively incorporated into the DNA. For the charge injection step the influence of the distance, the energy difference of donor and acceptor, and the bridge were measured. The guanine radical cation , generated in the injection step, triggered long distance charge transfer through DNA, as measured by the water trapping products. It turned out that the guanines are the charge carriers and, if the distance between the guanines is long, adenines also carry the positive charge. Therefore, the positive charge migrates through the DNA over long distances in a multistep hopping process . Trapping of the positive charge at the DNA bases either by nucleophilic attack or by proton transfer to the surrounding water stops the hole transfer through DNA. This can be induced, for example, by mismatches of the G:C base pairs.