Calculation of DNA strand breakage by neutralisation effect after 125I decays in a synthetic oligodeoxynucleotide using charge transfer theory.

The decay of the radioisotope (125)I into (125)Te is typically followed by the emission of two groups of approximately 10 electrons each via Auger processes. In deoxyribonucleic acid (DNA) with (125)I incorporated, these electrons produce various types of damage to DNA, e.g. single strand breaks (SSBs) and double strand breaks (DSBs) through direct actions of physical tracks, or indirect actions of radicals produced in water. Among the direct actions one should consider not only the excitation and ionisation of DNA by Auger electrons, but also the neutralisation of highly charged (125 m)Te ions with electrons from neighbouring molecules. Comparison between experiment and simulation done recently revealed that without including neutralisation effect the simulated yield of SSBs was 50% less than the measured result. In the present work a calculation of DNA strand breakage by the neutralization effect in a 41-mer synthetic oligodeoxynucleotide (oligoDNA) model was done using the charge transfer theory. Calculation based on transfer rate using the newly evaluated electronic coupling of DNA bases showed that the positive charge (hole) transfer rate is of the order of magnitudes of several 10(13) s(-1), implying that a charge higher than 10 units might not build on a (125 m)Te atom. The potential energy accumulated on the decay base is transferred to bases along the DNA chain nearby and destroys those bases and ionises the sugar-phosphate group, leading a DNA SSB with a frequency of 0.2% per eV in average.