Ring opening of the cyclobutane in a thymine dimer radical anion

The reactions of hydrated electrons (eaq -) with thymine dimer 2 and thymidine have been investigated by radiolytic methods coupled with product studies, and addressed computationally by means of BB1K-HMDFT calculations. Pulse radiolysis revealed that one-electron reduction of the thymine dimer 2 affords the radical anion of thymidine (5) with t 1/2 < 35 ns. Indeed, the theoretical study suggests that radical anion 3, in which the spin density and charge distribution are located in both thymine rings, undergoes a fast partially ionic splitting of the cyclobutane with a half-life of a few ps. This model fits with the in vivo observation of thymine dimer repair in DNA by photolyase. ?-Radiolysis of thymine dimer 2 demonstrates that the one-electron reduction and the subsequent cleavage of the cyclobutane ring does not proceed by means of a radical chain mechanism, that is, in this model reaction the T- is unable to transfer an electron to the thymine dimer 2. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA,.