Radiation Damage to Proteins–An E.S.R. Study of a Single Crystal of Glycyl-glycine at Low Temperatures

Summary

The electron paramagnetic spectra from a single crystal of glycyl-glycine have been analysed in the temperature range between 77 and 300 k, after the crystal had been irradiated at 77 k and then gradually heated. At 77 k a decarboxylation product remains stabilized within the crystal lattice, as well as, most probably, the product of a deamination process. At about 140 k, the finally stable radical appears, although the decarboxylation product dissappears, simultaneously. The finally stable radical is due to a hydrogen abstraction at the carbon-6 position. Two other radical species also arise, one of which is reported to originate from a hydrogen abstraction from the carbon-1 position, whereas the other is thought to stem from a fragmentation process at the peptide nitrogen. Both these radicals convert, upon further heating, into the finally stable radical. The entire spectrum also contains some other resonances, which are interpreted to originate from odd σ-electron systems.