Preparation of DNA films for studies under vacuum conditions

Experiments were carried out to determine the optimum conditions required for the preparation of uniform films of supercoiled plasmid DNA to be used in irradiation experiments under high vacuum conditions. Investigations reveal that significant damage to the DNA molecules occurs due to the evacuation process when films were formed from DNA samples in ultra high purity water only. A variety of bases were tested for their possible protective capabilities and sodium hydroxide solution was found to be the most effective in maintaining the supercoiled structure of plasmid DNA during the preparation process. Using a transmission electron microscope we also examined the structure of the DNA films which are formed upon evacuation and how the proposed adducts influence the preparation process. It was found that the addition of bases cause the DNA to aggregate, noting that a base is required for the stability of the DNA molecules. The experimental results presented in this paper show that it may not be possible to perform experiments on so-called pure DNA under vacuum with no stabilizers being added to the sample before the evacuation process.