ESR and ENDOR studies on the structure of primary oxidation products in irradiated α-amino acids

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Abstract
Combining the ESR and ENDOR techniques, the primary oxidation products responsible for the complex ESR spectra of irradiatedsingle crystals of α‐glycine and α‐aminoisobutyric acid have been identified as deprotonated cations formed from loss of one electron and one of the amino protons. For both the α‐amino acids, the species preserves the geometry of the main frame of the undamaged molecule except for the amino proton, which is supposed to be transferred to the neighboring CO2 group through the shortest hydrogen bond. Although the chemical structure of the species is H2NCH2CO2 for glycine and H2NC(CH3)2CO2 for α‐aminoisobutyric acid, the unpaired electron is delocalized over the main molecular frame and occupies the in‐plane orbitals. The electronic nature of the species may be represented, say for glycine, by the superposition of [H2N+=CH2]CO2 ⋅−, [H2N⋅⋅⋅CH2]CO2, H2Ṅ+—CH2CO2 −, and H2N–CH2–C〈O O⋅. The species exhibits a characteristic negative g shift because of the contribution from the first electronic structure. The similarity of the g shift suggests that the oxidation product in α‐alanine possess essentially the same structure.

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