Efficient photosensitized pyrimidine dimer splitting by a reduced flavin requires the deprotonated flavin

Photorepair of cyclobutane pyrimidine dimers by 8‐oxopurine nucleosides

“…The instability of 8‐oxopurine nucleosides at higher pH precluded investigation of repair at pH > 9. Despite that limitation, the pH dependence observed further supports a reductive mechanism for thymine dimer repair by OG and agrees with previous work showing that flavins in an anionic form repair thymine dimer more efficiently . The difference in activity between OG and RU may also imply that the purine redox potential is not the only factor determining the thymine dimer repair efficiency.…”

“…[23] This reductive electron transfer mechanism has also been well characterized for photolyase and for related model systems. [9,26,[28][29][30][31][32][33][34][35][36][37] Mechanistic considerations aside, the absolute repair yield of thymine dimer in these systems is extremely low, only about 1% after 7 h of irradiation. As anticipated, the bimolecular reaction is much less efficient than the case where OG was installed in proximity to the CPD in double-stranded oligonucleotides.…”

“…A key aspect that may be inhibiting repair by photoinduced electron transfer is the separation of charge that occurs when a neutral base such as OG donates an electron to form CPD •– and OG •+ . We postulated that electron transfer would be more facile if the nucleobase carried a negative charge in its resting state, as does FADH – in photolyase . This might be possible by raising the pH to deprotonate the base, or by selecting a different purine with a lower p K a , such as uric acid.…”

“…We postulated that electron transfer would be more facile if the nucleobase carried a negative charge in its resting state, as does FADHin photolyase. [9] This might be possible by raising the pH to deprotonate the base, or by selecting a different purine with a lower pK a , such as uric acid. Although the synthesis of the ribonucleoside 9-ribosyluric acid (RU) is straightforward, [10] the conversion of RU to a phosphoramidite and incorporation into an oligomer are not.…”

Photo-CIDNP study of the splitting of the dinucleotidecis, syn-thymine dimer with reduced flavin as a sensitizer: Evidence for a thymine radical anion intermediate

“…In addition, the flavin-spectrum was recorded at neutral pH, which was chosen asa compromise between the optimum quantum yŸ and the optimum CIDNP intensity. The quantum yield of splitting is somewhat larger at higher pH [24], whereas the CIDNP signal arising from a monomer radical anion has its maximum around pH 3, asa result of cancellation at higher pH [10].…”