Radiosensitization of microorganisms by radical anions. I. Medium effects
Schubert, J.; Stegeman, H.; Swildens, M.
International Journal of Radiation Biology and Related Studies in Physics Chemistry and Medicine 40(2): 131-141
1981
ISSN/ISBN: 0020-7616 PMID: 6792101 Document Number: 180765
Irradiation of Streptococcus faecalis in a neutral, N2O/Br- system leads to practically complete killing with extraordinarily low doses of irradiation, namely a D10 [10% lethal dose] of 13 Gy [Gray] compared to 470 Gy in N2, 250 Gy in N2O and 160 Gy in O2. Irradiation and chemical investigations demonstrated that the apparent radiosensitization in neutral, N2O/Br- is due mainly to bromine, Br2 and HOBr rather than Br3- or the radical anion, Br2-. Addition of unirradiated bacteria to a previously irradiated neutral solution of N2O/Br- reduces survival. The medium effects are eliminated by radiation chemical and/or chemical reactions which destroy bromine, such as occur in basic solutions, in N2/Br- or O2/Br- systems because of back reactions of Br2 with .**GRAPHIC**. in the former and of Br2 with H2O2 and O2- in the latter. Neither are medium effects produced in N2O/Br- systems at pH > 9. In N2/Br- the D10 = 82 Gy compared to 160 Gy in O2 which indicates that for S. faecalis Br2- is intrinsically a more effective radiosensitizing agent than O2.