Electron Spin Resonance in Gamma-Irradiated Single Crystals of Hydroxylated Organic Compounds

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Abstract
Free radicals produced by gamma irradiation in the single crystals of four hydroxylated organic compounds, monoammonium malate, monoammonium malate monohydrate, ammonium tartrate, and potassium tartrate, have been studied using the methods of electron spin resonance. In all the four molecules, stably trapped radicals were found to be the result of the splitting of a C–H bond adjacent to both the hydroxyl and carboxyl groups. The isotropic parts of the hyperfine couplings of the two methylene protons in monoammonium malate are 8.9 and 34.3 G. These values in the monohydrate are 14.7 and 34.1 G. The isotropic part of the hydroxyl proton hyperfine coupling in the monohydrate is 2.3 G. Strong spin-flip transitions, giving rise to satellite lines having an intensity up to 40% of the main lines for certain orientations of the crystal in the magnetic field, were observed in monoammonium malate and its monohydrate. The proton responsible for these spin-flip transitions was found to be the hydroxyl proton. The isotropic part of the C–H proton hyperfine coupling in both ammonium and potassium tartrates is 2.1 G.