The Reactions of the Hydroxymethyl Radical with 1,3-dimethyluracil and 1,3-dimethylthymine

Summary

Hydroxymethyl radicals ·CH₂OH, generated by the radiolysis of methanol (0·5 mol dm⁻³) in N₂O-saturated aqueous solutions, were reacted with 1,3-dimethyluracil or 1,3-dimethylthymine (10⁻³) mol dm⁻³). The products were identified and their G values determined. It has been concluded that in 1,3-dimethyluracil ·CH₂OH attack occurs only at C(6) while in 1,3-dimethylthymine there is partitioning between addition (two-thirds) and H-abstraction from the C(5)-methyl group (one-third). A rate constant for CH₂OH addition to 1,3-dimethyluracil of about 10⁴ dm³ mol⁻¹ s⁻¹ is estimated. Complexities that may arise in the radiolysis of pyrimidines such as 1,3-dimethylthymine, apparently as a consequence of the formation of 5-alkylidenepyrimidines, are discussed. A value of 0·15 has been estimated for the disproportionation/combination ratio for the hydroxymethyl radical self-termination reaction.

• hydroxymethyl radical
• uracil
• thymine
• crosslinking
• DNA model