Electron spin resonance study of. gamma. -irradiated frozen aqueous solutions containing dipeptides. Mechanisms of radical reaction
The ..gamma.. irradiation at 77 K of frozen aqueous solutions of over 14 peptides was investigated by ESR (electron spin resonance) spectroscopy. The investigation was composed of three parts. The first part consists of a study of simple dipeptides of glycine and alanine, i.e., Gly-Ala, Ala-Gly, and Ala-Ala. Detailed analyses were made of the radicals produced by the irradiation, their relative concentrations, and their stability as a function of temperature. The results show evidence for anion formation, primary deamination, and decarboxylation initially. This is followed by abstraction from the parent compound to form the ..cap alpha..-carbon radical at the C-terminal residue. In the case of Ala-Ala there is evidence for hole stabilization at low temperature. In the case of Gly-Ala some secondary deamination is noted. In the second part the analysis of the final spectra for 11 dipeptides are reported. The final radicals were all found to be a result of abstraction from the ..cap alpha.. carbon of the C-terminal residue to produce the radical NH/sub 3//sup +/CHRCONHCR'CO/sub 2//sup -/. Radicals with R' = H or CH/sub 2/R'' produced a hyperfine coupling due to one proton of 18 to 19 G. Since 15 of the 20 common amino acid residues have a structure with R' = H or CH/sub 2/R'', the dominant final radical in proteins should produce a doublet spectrum. In the final portion, three dipeptides with aromatic side groups were studied in frozen H/sub 2/O solutions. It was found that electron attachment to the aromatic ring effectively competed with deamination of the primary amine group. The electron attachment to the aromatic ring was followed by protonation at a carbon site on the ring. The results for Gly-His were typical. Here we found a spectrum indicative of 25% protonation, 30% deamination, and 45% decarboxylation. For Gly-Tyr, phenoxyl radical formation was found to dominate decarboxylation as a decomposition pathway for the hole. 10 figures, 2 tables.
- Research Organization:
- Oakland Univ., Rochester, MI
- OSTI ID:
- 5548837
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 83:22; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400600* -- Radiation Chemistry
ALANINES
AMINES
AMINO ACIDS
ANIONS
AQUEOUS SOLUTIONS
AROMATICS
CARBON
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COUPLING
DEAMINATION
DECARBOXYLATION
DECOMPOSITION
DISPERSIONS
ELECTROMAGNETIC RADIATION
ELECTRON ATTACHMENT
ELECTRON SPIN RESONANCE
ELEMENTS
FREEZING
GAMMA RADIATION
GLYCINE
HYDROGEN COMPOUNDS
HYPERFINE STRUCTURE
IONIZING RADIATIONS
IONS
LOW TEMPERATURE
MAGNETIC RESONANCE
MIXTURES
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PEPTIDES
PHENOXY RADICALS
PROTEINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADICALS
RADIOLYSIS
RESONANCE
SOLUTIONS
WATER