FREE-RADICAL INTERMEDIATES IN REACTION OF HYDROXYL RADICAL WITH AMINO ACIDS

Intermediate radicals formed in the reaction of the hydroxyl radical with some carboxylic acids, amines, and amino acids have been studied by esr spectroscopy using a continuous-flow method. A titanous chloride-hydrogen peroxide system is employed as a source of the hydroxyl radical in most experiments and Fenton's reagent is also used in the case of alanine. Some good esr spectra are obtained for glycine, α-alanine, β-alanine, serine, threonine, valine, leucine, and isoleucine. The structures of the radicals deduced from analysis of the spectra and the hyperfine coupling constants are tabulated. It is found that the hydroxyl radical abstracts hydrogen atom preferentially from the CH bonds distant from the protonated amino group, those adjacent to the methyl group, and those distant from the carboxyl group. This is consistent with the electrophilic character of the hydroxyl radical. Hyperfine coupling data of various protons and 14N nuclei give information concerning steric conformations of the radicals and freedom in the internal rotations.