How do iodized nucleotides fragment due to photoactivation?

Sammanfattning: Cancer is the second leading cause of death worldwide and affects millions of people every year. Furthermore, the available treatments often lead to severe side effects, thus improving radiation treatment is meaningful. Photoactivation therapy seeks to build in heavy atoms into the DNA of cancer cells, as markers, then activating them to cause secondary radiation that damages the DNA of the targeted cells only. This has been suggested but is not well understood. Hence this study seeks to investigate how a reduced model system of iodine-marked DNA is fragmented due to ionization. Computer simulations with eleven separate starting configurations of the molecule 5-iodocytidine were analyzed, for ionization levels from an average 0.03 up to 0.33 electrons removed per atom (e/N), during 200 femtoseconds (fs). A Python program was written in order to estimate bond sensitivities and identify fragments. While 5-iodocytidine resembles an iodized DNA-base it is still a rather simple model system, far from a double stranded DNA chain, and the simulations were limited to non-targeted ionization and an isolated environment. Results of this thesis include that the sugar ”backbone” of 5-iodocytidine seems to be most sensitive to ionization, fragmenting in several pieces after 150-200 fs at ionization levels of 0.30-0.33 e/N, while the rest of the molecule mostly remained intact. These results appear promising since back bone fragmentation is crucial for disrupting cancer cell growth.