E.S.R. of Spin-trapped Radicals in γ-irradiated Polycrystalline Amino Acids,N-acetyl Amino Acids and Dipeptides

Abstract

The radicals produced in several polycrystalline amino acids, N-acetyl amino acids and dipeptides by gamma-radiolysis at room temperature were investigated by spin-trapping. After irradiation in the solid state, the samples were dissolved in aqueous solutions f t-nitrosobutane and the trapped radicals identified by e.s.r. For alpha-amino acids, deamination radicals were found, and in some cases H-abstraction radicals were also observed. No decarboxylation radicals could be detected. For N-acetyl amino acids, except for N-acetylglycine, the major radical was the decarboxylation radical. For N-acetyglycine the H-abstraction radical from the glycine residue was observed. For dipeptides of the x-glycine, the radical formed by removal of H from the alpha-carbon of the carboxyl-terminal residue was always spin-trapped. Some primary deamination radicals and minor amounts of decarboxylation radicals could also be observed. For dipeptides of the type x-alanine, glycine-x and alanine-x, the decarboxylation radical was always the major spin-trapped radical. Some primary and secondary deamination radicals were also detected.

An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution

“…This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0 β-protons of the trapped radical species. The hyperfine couplings extracted by simulation of the spectra are in good agreement with previous reports in which the deaminated L-his radical was either formed from γ-irradiation of histidine in the solid (Minegishi et al, 1980) or solution state (Rustgi et al, 1977) followed by spin trapping in solution with MNP (Table 1). This 18-line signal was not obtained by dissolving the non-irradiated L-his powder in a solution containing the spin-trap MNP ( Fig.…”

“…The irradiation products of numerous amino acids have been investigated previously by EPR in the solid state (Aydin, 2010;Dicle et al, 2015;Karabulut and Yıldırım, 2015), but here the reactivities of the radicals following dissolution were also evaluated by means of spin-trapping EPR experiments (Davies, 2016). While studies involving the spin trapping of radicals formed in the solid state have been previously reported for several organic compounds, including amino acids (Kuwabara et al, 1981;Lagercrantz and Forschult, 1968;Makino and Riesz, 1982;Minegishi et al, 1980;Talbi et al, 2004) we are not aware of previous reports of the regeneration and trapping of amino acid radicals in solution upon addition of the trapping agent many minutes after dissolution of an irradiated powder.…”

Electron spin resonance of spin trapped radicals in γ-irradiated polycrystalline dipeptides. Chromatographic separation of radicals

“…The hfcc of spin adduct I1 and I11 are shown in Table 1. The spin adduct 111 could not be found in a previous work (14).…”

“…The solids are y-irradiated and subsequently dissolved in aqueous MNP solutions. By this method, free radicals produced by yirradiation of polycrystalline amino acids, N-acetyl amino acids, and dipeptides have been analyzed (14). However, when the esr spectra overlap, only major components in the spectra obtained by spin trapping have been analyzed.…”

“…It has been demonstrated previously that spin trapping with MNP can be applied to the study of the effect of ionizing radiation on polycrystalline solids (13)(14)(15)(16). The solids are y-irradiated and subsequently dissolved in aqueous MNP solutions.…”