Free Radical Fprmation in Amino Acids Exposed to Hydrogen Atoms

Electron spin .resonance spectroscopy has been used to identify free radicals formed in powdered amino acids by the exposure to thermal hydrogen atoms at 77°K. The low temperature ESR spectra of the radicals produced at 77°K are different from the spectra at room temperature. The primary radicals are those produced by the abstraction of H atoms from the common part of amino acids (in the zwitter-ion compounds) or from some position of the amino acid residue (in neutral compounds). In most amino acids a reversible change of the radical conformation was observed. The irreversible change of the isoleucine resonance pattern is attributed to the change of the unpaired electron from the sp3 to the p orbital. Different conformations of radicals at room temperature when they are produced at 77° and at 300°K are interpreted by the difference in the crystal lattice arrangement in the vicinity of the radical