The effects of lattice water on free radical yields in X-irradiated crystalline pyrimidines and purines: a low-temperature electron paramagnetic resonance investigation.

The hydration layer of DNA increases the target size of DNA with respect to the formation of direct-type damage by ionizing radiation. The mechanisms that give rise to this increase are being investigated by EPR spectroscopy. To determine these mechanisms, it is necessary to distinguish between the change in sample mass and changes in packing/conformation brought about by the change in the level of hydration.

Electron paramagnetic resonance investigation of X-irradiated poly(U), poly(A) and poly(A):poly(U): influence of hydration, packing and conformation on radical yield at 4 K.

Powders and films of variably hydrated poly(U), poly(A) and poly(A):poly(U) were X-irradiated at 4 K. Spectra and free radical yields were acquired at 4 K using Q-band EPR spectroscopy. Evidence for electron transfer from the hydration layer to the RNA bases, supporting in part the damage transfer hypothesis of Gregoli et al.

Combination is the dominant free radical process initiated in DNA by ionizing radiation: an overview based on solid-state EPR studies.

An overview of the early processes initiated in DNA by ionizing radiation is given from the perspective of studies done by solid-state EPR with the focus on radical combination. Comparisons with free radical formation and trapping in crystalline pyrimidines (1-methylcytosine, thymine, 1-methylthymine, 1-methyluracil, and cytosine monohydrate) provide insight into the processes occurring in DNA. Between 25 and 50% of low LET ionizations in fully hydrated DNA at 4 K lead to trapped free radicals, the remaining unobserved radicals are assumed to have combined.

The influence of packing on free radical yields in crystalline nucleic acids: the pyrimidine bases.

The total free radical yield has been measured for crystals of five pyrimidine derivatives: thymine (T), 1-methylthymine (1MeT), 1-methyluracil (1MeU), 1-methylcytosine (1MeC) and cytosine monohydrate (C:HOH). Q-band EPR measurements were made on samples X-irradiated between 4 and 12 K. The G values in units of 10(-7) mol/J are 1MeC < 0.

Hydration effects on free radical yields in DNA X-irradiated at 4 K.

Variably hydrated sodium DNA was X-irradiated and observed at 4 K using Q-band EPR spectroscopy. The free radical yield, G, was measured as a function of the mass ratio of water:DNA, gamma. Both humidified and dehumidified samples showed large scatter when G was plotted against gamma in the range gamma < 1.