Tetrakis-acridinyl peptide: Distance dependence of photoinduced electron transfer in deoxyribonucleic acid assemblies

The distance dependence of photoinduced electron transfer in deoxyribonucleic acid (DNA) duplex was investigated using the “TAP cassette” systems of the general formula (AT)6AnXA9−n (X denote guanine (G) or cytosine (C)). The tetrakis-9-acridinyl peptide (TAP) binds tightly with (AT)6 duplex region showing strong fluorescence that was not quenched by the AnXA9−n single-stranded region. Quenching was observed after duplex formation with the complementary T9−nXTn strand (G-C pairing), showing clear dependence on the distance between the TAP and a guanine. An extremely low β value of 0.22 was obtained in our electron transfer (ET) system that suggests exceptional good mediation of ET process. Experiments with G-mismatches showed negligible quenching for systems with guanine separated by more than one AT base pair that indicated rather inefficient ET process for duplexes containing disrupted π-electronic system.