Tsoulou, E., Kalfas, C. A. and Sideris, E. G. Conformational Properties of DNA after Exposure to Gamma Rays and Neutrons. Radiat. Res. 163, 90–97 (2005). DNA aqueous solutions were irradiated with 0–40 Gy of 60 Co γ rays and 0–1.5 Gy of (Pu-Be) neutrons. Thermal transition spectrophotometry (TTS) was used to trace the changes in the DNA conformation at the above doses. Previous results using the perturbed angular correlation (PAC) method were used to complement to the current analysis. The TTS and PAC methods are two different approaches to the study of the effects of radiation on DNA. Both showed that neutrons are more effective than γ rays in inducing DNA damage. The TTS method showed that neutrons are 11 ± 5 times more efficient than γ rays, while the PAC method had shown this value to be 34 ± 4. From the current study we deduced that the radiation damage to DNA is not a spontaneous effect but rather is an ensemble of damaging events that occur asynchronously. Any single method selected for the study of such damages can concentrate on only a part of the damage, leading to over- or underestimation of the relative effectiveness of the neutrons.

Tsoulou, E., Kalfas, C. A. and Sideris, E. G. Changes in DNA Flexibility after Irradiation with γ Rays and Neutrons Studied with the Perturbed Angular Correlation Method. Radiat. Res. 159, 33–39 (2003). Neutron and γ irradiation of buffered solutions of calf thymus DNA resulted in changes in the dynamics of the macromolecule. In the low-dose region (0.8–10 cGy of 239 Pu-Be neutrons and 0.34–3 Gy of 60 Co γ rays), the flexibility of DNA decreased as indicated by slower rotation of the molecules. Neutrons appeared to be approximately 35 times more effective than 60 Co γ rays. The rotational correlation time, τ C , was measured using the perturbed angular correlation (PAC) method. Its variation appears to follow a linear-exponential behavior. An attempt is made to formulate this behavior as a function of the energy deposited on the macromolecule (radiation dose), the average threshold energy (dose) required to form new lesions, and the available population of intact DNA sites.

Tsoulou, E., Kalfas, C. A. and Sideris E. G. Probing Irradiated DNA with the Perturbed Angular Correlation Method. Radiat. Res. 156, 181–185 (2001). The technique of perturbed angular correlations of γ rays has been used to study the effects of radiation on DNA molecules. The samples are buffered solutions of calf thymus DNA exposed to various doses (0–80 Gy) of γ rays. Indium-111 is used as a probe. Rotational correlation times, τ c , a parameter measuring the flexibility of a macromolecule, are obtained that show a dependence on radiation dose.

Georgakilas, A.G., Haveles, K.S., Sophianopoulou, V., Sakelliou, L., Zarris, G. and Sideris, E.G. Alpha-Particle-Induced Changes in the Stability and Size of DNA. The effect of α-particle radiation on the thermal stability and size of calf thymus DNA molecules in deoxygenated aqueous solutions was investigated by thermal transition spectrophotometry, pulsed-field gel electrophoresis, and standard agarose gel electrophoresis. The thermal transition of DNA from helix to coil was studied through analysis of the UV A 260 absorbance. The results obtained for α particles of mean LET of 128 keV μm −1 reveal a dual dose response: a tendency for thermal stability of the DNA helix at “low” doses, followed by an increasing instability at higher doses. The same phenomenon was observed for the mean molecular weight of DNA molecules exposed to α particles. The results reported here for α particles in the low-dose region of 0–16 Gy are consistent with our previous hypothesis of inter- and intramolecular interactions of a covalent character in γ-irradiated DNA molecules in the dose region of 0–4 Gy.

The effects of γ radiation on the stability and size of mammalian DNA were studied by using thermal transition spectrophotometry and pulsed-field and standard agarose gel electrophoresis. The experiments were performed using deproteinized calf thymus DNA in buffered deaerated aqueous solutions. A dual dose response was observed: a tendency for increased helix stability at "low" doses (0-4 Gy) accompanied by a high tendency of the DNA molecules to interact, forming larger molecules, followed by a gradual increase of degradation and helix instability at higher doses. The results reported here for the low-dose region are consistent with the hypothesis of inter- and intramolecular interactions of covalent character (crosslinking) in irradiated DNA molecules.

Hordeum vulgare var. Himalaya seeds were irradiated with gamma rays and hydrated in protium or deuterium water. The frequency of radiation-induced chromosome aberrations was lower in the deuterated material. The reduced frequency of chromosome aberrations was coupled with a delay of the early stages, an inhibition of the late stages of mitotic division, and an increase in the melting temperature (Tm) of the deoxyribonucleic acid. The decrease in the radiation-induced damage, in the presence of deuterium water, is attributed to the immobilization of the broken ends of the chromosomes due to the delay of the mitosis and the increased stability of the deoxyribonucleic acid molecule, both of them favoring the reconstitution of the broken ends.