Microscopic energy absorption of the DNA molecules from Auger electrons of iodine-125.

The microscopic energy distribution along the DNA duplex due to local absorption of Auger electrons of iodine-125 incorporated into the DNA molecule, has been theoretically calculated. Our calculation method [Unak T. Nucl. Instrum. Methods A255, 274 (1987); Unak T Ibid. A255, 281 (1987)] recently presented for spatial energy distribution from low-energy electrons in different chemical systems, has also been used for these calculations. As a result, it has been determined that the maximum range of the highest energy 125I Auger electrons in a linear DNA duplex is about 38 micron, and the total energy absorbed by DNA molecule per decay is about 10.3 keV, which is approximately half of the total energy released by electrons (19.8 keV per decay). This absorbed energy is not uniformly distributed along the DNA duplex. Consequently, it has also been determined that the microscopic energy absorption per DNA base or sugar-phosphate group rapidly decreased with the distance from the 125I nuclide, and reached about 5 eV per DNA base or sugar-phosphate group at a distance of about 2 nm. On the other hand, the results also demonstrated that the local absorption of 125I Auger electrons is able to produce alone at least one double strand break (DSB) on the DNA duplex without the support of the neutralization effects of highly charged tellurium ions.