Electron Spin Resonance of Two Glycine Peptides Irradiated at 77°K

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Abstract
Single crystals of a-glycylglycine, X-irradiated at 77[degree]K, give 4-line ESR [electron spin resonance] spectra[long dash]the result of the odd electron''s interacting with 2 protons. The main interaction is with the single methylene proton that remains attached to the a-carbon after irradiation. The weaker interaction is with 1 of the other 2 methylene protons in the molecule. A 7-atom n system, the result of radiation damage, is postulated to explain the delocalization of the electron. In acetyl-glycine radicals, a similar situation exists. A synthesis of acetylgly- cine was carried out in which methyl hydrogens were replaced by deuterium. Radicals produced in crystals of this compound give significantly sharper ESR absorption spectra than those of undeuter-ated acetylglycine. The difference in line width implies a delocaliza-tion of the odd electron resulting in interaction with methyl protons. A small N2 hyperfine splitting is detected in the spectra of deuterated acetylglycine. Huckel-type molecular orbital theory accounts for the main features of the spin density distribution in these radicals.

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