History of EPR Studies from the H. M. Swartz Laboratories: Part 3—EPR Oximetry

• Published in: Applied magnetic resonance 2022, Vol.53 (1), p.81-103
• Main Author: Swartz, Harold M.
• Format: Article
• Language: English
• Subjects: Atoms and Molecules in Strong Fields; Drugs; E coli; Editorial; Energy transfer; Experiments; Free radicals; Harold M. Swartz: On the Occasion of His 85th Birthday; Ionizing radiation; Laboratories; Laser Matter Interaction; Organic Chemistry; Organisms; Oximetry; Oxygen; Pathophysiology; Physical Chemistry; Physics; Physics and Astronomy; Physiology; Radiation; Radiation damage; Radiation effects; Scavenging; Solid State Physics; Spectroscopy/Spectrometry; Survival; Toxicity
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-021-01454-8

The ‘oxygen effect’ to increase damage from ionizing radiation in biological systems My initial research was to try to use a system developed previously by Smaller and Avery [1] to apply EPR to examine energy transfer from irradiated yeast to potential radiation-protection drugs, which had SH groups as their active component. The experimental system was complicated because, to stabilize the radiation-induced free radicals which were expected to be very short-lived in a liquid environment, the experiment needed to be carried out with deeply frozen organisms, i.e., irradiation and initial EPR studies were done at 77 K. At this temperature, the hydroxyl free radicals produced in water, which ordinarily could contribute to biological damage by diffusing to the sensitive sites (termed the indirect effect), cannot cause damage because they are immobilized. [...]the initial free radicals that are seen in frozen samples of the organisms would be due only to the direct effect on the target molecules. Because the purpose of the radioprotective drugs was to reduce damage and increase survival following exposure to radiation, I wanted to determine if there was a correlation between scavenging of the radicals and better survival. Because of the importance of oxygen in radiation damage (the presence of oxygen sensitizes cells to the effects of radiation), both systems were studied in the presence and absence of oxygen.