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)ĊOO2– 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.