How to Find Out Whether a 5-Substituted Uracil Could Be a Potential DNA Radiosensitizer

Incorporated into genomic DNA, 5-substituted uracils could be employed in human cancer radiotherapy if they could be sensitized to dissociate upon reaction with hydrated electrons. Using the B3LYP/6-31++G(d,p) method, we calculate electron affinities and energy profiles related to the dissociation of the respective anions for a series of uracil derivatives. We demonstrate that for a uracil analogue to be an efficient electron acceptor the uracil substituent has to possess significant electron-withdrawing power. On the other hand, in order to ensure effective dissociation of the anion, the chemical bond holding together the substituent and uracil residue should be relatively weak. Our theoretical predictions are in excellent agreement with the results of our negative ion photoelectron spectroscopy experiments. We propose two new potential sensitizers that seem to possess the required properties, although they have never been tested in radiobiological experiments.