Track structure in DNA irradiated with heavy ions

Area of Science:

• Radiation chemistry
• Biophysics
• Materials science

Background:

• Understanding DNA damage from heavy-ion radiation is crucial for radiation protection and therapy.
• Previous studies lacked direct experimental data on the spatial distribution of radicals within heavy-ion tracks in DNA.

Purpose of the Study:

• To experimentally determine the spatial properties of trapped radicals in heavy-ion-irradiated solid DNA.
• To characterize the dimensions and radical density within heavy-ion tracks in DNA.

Main Methods:

• Irradiation of hydrated salmon testes DNA with 40Ar ions (100 MeV/nucleon).
• Cryogenic temperature maintenance (77 K) throughout sample handling and measurement.
• Pulsed electron paramagnetic double resonance (PELDOR, also known as DEER) using a refocused echo detection sequence.

Main Results:

• Attribution of the EPR spectrum to DNA base radicals and carbon-centered sugar radicals.
• Measured radical concentration of 13.5 x 10^18 cm^-3 within tracks.
• Determined track radius of 6.79 nm, track cross-section of 144 nm^2, and lineal radical density of 2.6 radicals/nm.

Conclusions:

• The study provides the first direct experimental determination of track characteristics in irradiated DNA.
• The measured lineal radical density aligns with calculated Linear Energy Transfer (LET) values, validating the experimental approach.
• These findings offer critical insights into the nanometer-scale spatial distribution of radiation-induced DNA damage.