Charge build-up during decay of DNA-incorporated (123/125)I: consequences for labeled molecular structures

To further elucidate the mechanisms behind the strong biological effectiveness of DNA-incorporated Auger electron emitters (123)I and (125)I, which are mostly attributed to the shower of low-energy electrons released during the decay. A second, frequently mentioned cause can be seen in the charges accumulated during the Auger cascade on the decaying nuclide and its subsequent intra-molecular redistribution leading to a Coulomb explosion.

To assess the size of the charge and the dimensions of DNA damage thus determined, the first Auger cascade was simulated by Monte Carlo methods. The consequences of intra-molecular charge transfer in terms of structural molecular alterations were estimated by density functional theory (DFT) calculations and folding with the results of the Monte Carlo studies.

Charge distributions of (123)I and (125)I were found to be very similar with values between + 1 and + 15 and a mean value of + 6.4. The molecules could tolerate charges up to + 5 (base), + 2 (nucleoside) and + 7 (nucleotide) without being destroyed.

The strong molecular DNA damage after (123)I and (125)I decay depends very much on the size of the DNA molecule involved in the calculation. In general, not every decay can be expected to lead to a Coulomb explosion.