Spectroscopic studies concerning the gamma irradiation of deoxyribonucleic acid.

Infrared spectroscopy has been used to investigate glassy and ice-like water in frozen DNA solutions. Using a solvent comprising HOD in D2O, the O-H stretch band in the infrared is sharp. However, HOD in glassy water regions contributes to a broader feature. The extent of phase separation was assessed by band analysis of these two components. The amount of glassy water was determined and the DNA radiation target was described according to a three zone model. The above technique was extended to investigate phase separation in frozen aqueous DNA solutions containing LiCl or NaCl. Changes in the mass of the glassy water-DNA-salt phase were correlated with an increase in DNA radical yield detected by ESR spectroscopy. Added salt increased the DNA radiation target and a salt hydrate (NaC1.2H2O) was formed on freezing solutions containing NaCl. Hence, NaCl contributes two moles of water, as well as the mass of the salt, to the DNA radiation target. A salt hydrate was not detected in solutions containing LiCl as LiCl enters the DNA glassy water phase. Glassy water formation depended on the ratio of LiCl to DNA base pairs and not solely on LiCl concentration. NMR spectroscopy was used to investigate the release of sodium ions from DNA in aqueous solution. When native (double stranded) DNA was irradiated the Na-23 NMR band narrowed. Line narrowing was examined in conjunction with relationships describing dose yields of single and double strand breaks. Line narrowing was sensitive to single strand breaks but not double strand breaks. A single strand break resulted in the net release of approximately eight sodium ions per DNA base pair from native DNA and seventeen sodium ions per nucleotide from single stranded DNA.