Electron spin resonance of 17O [oxygen isotope]-labeled protein-peroxide radicals: zein and edestin

Hyperfine structure due to 17 O has been measured in irradiated zein and edestin after exposure to gaseous oxygen with 17 O concentrated to 24%. The observations prove that the free radicals produced by ionizing irradiation under vacuum at 300 K are converted by the oxygen to protein-peroxide free radicals X—O (1) —O (2) , with the unpaired electron density in a π-type orbital predominantly on the peroxide group. From the observed couplings, the 2 p π spin densities on zein-peroxide are found to be 0.29 and 0.45 for O (1) and O (2) , respectively; those on edestin-peroxide are 0.26 and 0.48 for O (1) and O (2) , respectively. oxygenated free radicals electron spin resonance spectra 17O hyperfine structure