Electron spin resonance of DNA irradiated with a heavy-ion beam ([16]O[8+]): evidence for damage to the deoxyribose phosphate backbone.
The free radicals produced from the irradiation of hydrated DNA with a heavy-ion beam have been investigated by ESR spectroscopy. The dominant free radical species formed after 60 MeV/nucleon (16)O(8+) ion-beam irradiations at low temperatures (77 K) are the same as those previously identified from studies using low-LET radiation, pyrimidine electron-gain radicals and purine electron-loss radicals; however, greater relative amounts of neutral carbon-centered radicals are found with the higher-LET radiation, and a new phosphorus-centered radical is identified. The fraction of neutral carbon radicals is also found to increase along the ion-beam track with the highest amounts found in the Bragg peak. The neutral carbon-centered radicals likely arise in part from the sugar moiety. The G values found for total trapped radicals at 77 K are significantly smaller for the (16)O(8+) ion beam than those found for low-LET radiation. The new phosphorus-centered radical species is identified by its large 31P parallel hyperfine coupling of about 780 G as a phosphoryl radical. This species is produced linearly with dose and is not found in significant amounts in DNA irradiated with low-LET radiation. The phosphoryl radical must be produced by the fragmentation of a P-O bond and suggests the possibility of a direct strand break. The yield of phosphoryl species is small (about 0.1% of all radicals); however, it clearly indicates that new mechanisms of damage which are not significant for low-LET radiation must be considered for high-LET radiation.
Becker
D
D
Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA.
Razskazovskii
Y
Y
Callaghan
M U
MU
Sevilla
M D
MD
D000818:Animals; D002244:Carbon / Q000737:chemistry; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects*; D004249:DNA Damage; D003855:Deoxyribose / Q000737:chemistry / Q000528:radiation effects; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry / Q000528:radiation effects; D066298:In Vitro Techniques; D007477:Ions; D018499:Linear Energy Transfer; D008297:Male; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D011854:Radiochemistry
D005609:Free Radicals; D007477:Ions; D010758:Phosphorus; D003855:Deoxyribose; D002244:Carbon; D004247:DNA; D010100:Oxygen