Electron paramgnetic resonance of x-irradiated tyrosine, thyronine and their iodine-derivatives

Abstract The electron paramagnetic resonance of x-irradiated (∼10 krad.) tyrosine, thyronine and their iodine-derivatives in the form of compressed pellets in vacuum-sealed quartz tubes have been measured between 100 K and 300 K at ∼9 GHz. The EPR spectra of tyrosine, 3–5 diiodo thyronine and thyronine, in the order of decreasing line-width, are spectrally similar singlets with g = 2.004 or 2.005 and hence indicate that the electron spin density is trapped mainly in the ring from which the hydroxyl proton is lost. The samples having iodine on the same ring as the OH group show a rather large anisotropy in g ≊ 2.04 presumably due to the presence of small spin density on the iodine(s). The G r value, i.e. the number of paramagnetic centers produced by 100 eV as deduced from the temperature dependence of the magnetic absorption of the irradiated iodine-derivatives increases with the number of iodines on the molecule. The G r values of tyrosine and thyronine, however, can not be estimated from the magnetic absorptions, since their absorption increases with the temperature indicating the antiferromagnetic exchange between spin densities on the neighboring molecules.