Electron-spin-resonance Study of Radiosterilization of Antibiotics - Ceftazidime

□ Fundamental information on radiosterilization of ceftazidime was obtained by electron spin resonance (ESR) measurement of free radicals produced in 7-ray-irradiated ceftazidime at 4.2-295 K. Three types of free radicals are produced by 7-irradiation. The first one shows septet lines in an ESR spectrum and decays at 230 K: it is assigned as a -CiCHabCOOH radical. The second one shows triplet lines and decays at 293 K: it is assigned as iminoxyl radicals (>C=N—O). The third one shows a broad singlet line and survives even at 295 K. The plausible assignment of this spectrum is discussed. It is concluded that an O—C bond of the 7-irradiated ceftazidime is ruptured, producing the iminoxyl radicals and ⋅ CfCHshCOOH radicals. The yields of free radicals increase linearly with the increasing dose of 7-irradiation up to 10 kGy at 295 K as well as 77 K. Half of the radicals that show a broad singlet line survive at 295 K upon storage of the irradiated ceftazidime for 159 days. It is concluded that the ESR measurement of free radicals gives a good method for discrimination of irradiated antibiotics from non-irradiated ones and an estimation of an irradiation dose.