Formation of pyrene dimer radical cation in DNA reflecting DNA dynamics in the time range of 1 micros to 1 ms

Doubly pyrene (Py)-conjugated oligodeoxynucleotides (ODNs) were synthesized and used for measurement of the formation rates of Py dimer radical cation (Py(2)(.+)) upon one-electron oxidation during the pulse radiolyses. Formation of Py radical cation (Py(.+)) in the time scale of less than 5 micros was monitored at 470 nm after an electron pulse during pulse radiolysis of D(2)O solution of doubly Py-conjugated ODN in the presence of K(2)S(2)O(8). Concomitant with the decay of Py(.+), formation of Py(2)(.+) with an absorption peak at 1500 nm (charge resonance band) was observed in the time range of approximately 100 micros. The formation rate of Py(2)(.+) 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 Py(2)(.+). The formation rate of Py(2)(.+) 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 micros to 1 ms.