Electron Spin Resonance Study of Amino Acid Radicals Produced by Fenton’s Reagent

Abstract

Abstract Free-radical intermediates in the reaction of the hydroxyl radical with amino acids and structurally related compounds such as alcohols, amine, and carboxylic acids have been studied by ESR spectroscopy using a continuous-flow method. The hydroxyl radical is generated by a ferrous ion-hydrogen peroxide system (Fenton’s reagent). ESR spectra with fairly good signal-to-noise ratios are obtained for the first time in a Fenton’s reagent system from glycine, valine, leucine, glutamic acid, lysine, methionine, tyrosine, ethylamine, acetic acid, pro-pionic acid, n-butyric acid, and succinic acid. Structures, g-values, and hyperfine coupling constants of these radicals are tabulated. The analysis of ESR spectra shows that the same radical species are produced mainly in a Fenton’s reagent system as in a titanous chloride-hydrogen peroxide system. This is consistent with the existence of the hydroxyl radical in both systems. The observed ratio of C2–H to C1–H proton hyperfine coupling constants gives information concerning steric conformations, freedom in the internal rotations, and s-character of the intermediate radicals.