Electron spin resonance studies of fundamental processes in radiation- and photo-chemistry. Part 5.—Dissociative electron capture in amino acids at low temperatures

Abstract

The radiolysis of α-amino acids RCH(NH⁺ ₃)COO^– where R = H, CH₃, CH₂CH₃, CH₂COOH and CH₃SO₃H has been examined by e.s.r. methods. After γ-irradiation at 77°K the predominant e.s.r. spectrum observed at this temperature corresponds to the protonated molecular-anions RCH(NH⁺ ₃)ĊOOH^– formed by electron capture followed by proton transfer. These ions are de-aminated at a higher temperature to yield the radicals RCHCOOH, known from earlier studies to be stable at room temperature. When irradiated in aqueous alkaline glasses at 77°K only trapped electrons, O^– _aq and RCHĊOO^– radicals are observed and it is concluded that the non-protonated species RCH(NH⁺ ₃)ĊOO^2– are insufficiently stable for trapping in this matrix. Single crystal data were analyzed to give the proton hyperfine tensors for the species CH₃CH(NH⁺ ₃)ĊOOH^–, HOSO₂CH₂CH(NH⁺ ₃)ĊOOH^– and HOSO₂CH₂ĊHCOO^–, the latter two species being derived from cysteic acid.