Figure 5.

Radical repair scheme for cyclobutane pyrimidine dimers (CPD) based on previous work.¹¹ Forward electron transfer from the fully reduced flavin results in a radical residing on the CPD. First the C5–C5′ bond splits, followed by either C6–C6′ bond splitting or futile back electron transfer to the CPD state. Following bond splitting, either the radical residing on the pyrimidine can undergo electron return to the flavin, resulting in the completion of the repair process, or the radical can facilitate CPD formation and undergo futile back electron transfer.