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

Abstract

Single crystals of α-glycylglycine, X-irradiated at 77°K, give four-line ESR spectra-the result of the odd electron's interacting with two protons. The main interaction is with the single methylene proton that remains attached to the α-carbon after irradiation. The weaker interaction is with one of the other two methylene protons in the molecule. A seven-atom π system, the result of radiation damage, is postulated to explain the delocalization of the electron. In acetylglycine radicals, a similar situation exists. A synthesis of acetylglycine 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 undeuterated acetylglycine. The difference in line width implies a delocalization of the odd electron resulting in interaction with methyl protons. A small nitrogen hyperfine splitting is detected in the spectra of deuterated acetylglycine. Huckel-type molecular orbital theory accounts for...