Computer simulation of strand break yields in plasmid pBR322:: DNA damage following 125I decay

This paper presents results of I-125 effects on plasmid pBR322 in aqueous solution, simulating the complete transport of Auger and X rays up to the chemical phase. In addition to new sampling algorithms, new electronic cross sections are included. Simulations were carried out both with I-125, bound to plasmid, or free, in its vicinity. The influence of the hydroxyl radical scavenger dimethyl sulfoxyde (DMSO) has also been tested, underlying that, in naked DNA, double strand breaks (caused by the decay of bound I-125 are mainly due to direct hits. The calculated yields of relaxation events (RE) and linearization events (LE) show good agreement with experimental ones: when I-125 is bound to the plasmid pBR322, 0.16 RE and 0.83 LE per decay (without DMSO) are then observed. Then, when 2 mol DMSO is added, RE and LE probabilities become 0.22 and 0.76. The very light differences with those from literature could arise from experimental conditions.