Synthesis and photooxidation of oligodeoxynucleotides containing 5-dimethylaminocytosine as an efficient hole-trapping site in the positive-charge transfer through DNA duplexes

Abstract

We have designed and synthesized DNA duplexes containing 5-dimethylaminocytosine (^DMAC) to investigate the effects of C(5)-substituted cytosine bases on the transfer and trapping of positive charge (holes) in DNA duplexes. Fluorescence quenching experiments revealed that a ^DMAC base is more readily one-electron oxidized into a radical cation intermediate as compared with other natural nucleobases. Upon photoirradiation of the duplexes containing ^DMAC, the photosensitizer-injected hole migrated through the DNA bases and was trapped efficiently at the ^DMAC sites, where an enhanced oxidative strand cleavage occurred by hot piperidine treatment. The ^DMAC radical cation formed by hole transfer may undergo specific hydration and subsequent addition of molecular oxygen, thereby leading to its decomposition followed by a predominant strand cleavage at the ^DMAC site. This remarkable property suggests that the modified cytosine ^DMAC can function as an efficient hole-trapping site in the positive-charge transfer in DNA duplexes.