Formation of Pyrene Dimer Radical Cation in DNA Reflecting DNA Dynamics in the Time Range of 1 μs to 1 ms

Abstract

Doubly pyrene (Py)-conjugated oligodeoxynucleotides (ODNs) were synthesized and used for measurement of the formation rates of Py dimer radical cation (Py₂^•+) upon one-electron oxidation during the pulse radiolyses. Formation of Py radical cation (Py^•+) in the time scale of less than 5 μs was monitored at 470 nm after an electron pulse during pulse radiolysis of D₂O solution of doubly Py-conjugated ODN in the presence of K₂S₂O₈. Concomitant with the decay of Py^•+, formation of Py₂^•+ with an absorption peak at 1500 nm (charge resonance band) was observed in the time range of ∼100 μs. The formation rate of Py₂^•+ in DNA reflected the dynamics of DNA which allows the interaction between Py^•+ and Py, since transiently formed DNA structure is trapped by the attractive charge resonance (CR) interaction to give Py₂^•+. The formation rate of Py₂^•+ with a characteristic CR absorption band in the near-infrared (near-IR) region was demonstrated to be useful to obtain the structural and dynamical information of transiently formed DNA in the time range of 1 μs to 1 ms.