Development and investigation of a novel oxidative pyrimidine dimer splitting model

Described is the development of a novel pyrimidine dimer splitting system d esigned for the continued investigation of the mechanisms and intermediates involved in pyrimidine dimer repair. This system consists of the cationic photopolymerization initiator, N-ethoxyisoquinolinium hexafluorophosphate a nd the pyrimidine dimers cis,syn- and trans,syn-N,N'-dimethylthymine dimer, Irradiation of the initiator at wavelengths above 300 nm generated a radic al cation formed by homolytic N-O bond cleavage, This reactive species is t hought to oxidize a dimer, which resulted in splitting, Additional studies performed demonstrate that splitting cannot be attributed to photoinduced e lectron transfer reactions involving dimer and excited state initiator or d imer and the excited state of initiator decomposition products. The results suggest that splitting is due to a one-electron oxidation of dimer by the radical cation of isoquinoline. This splitting mechanism is different from previous oxidative pyrimidine diner splitting pathways in that electron tra nsfer occurs without concomitant generation of a sensitizer-derived radical anion, which alters the nature of the back electron transfer step. The con centration dependence of the quantum yields of splitting reflected the diff erences in reactivity of the stereoisomeric dimers, This novel system may f acilitate spectroscopic studies aimed at detection of dimer-derived interme diates in the splitting reaction.