ENDOR investigations of the structure of glycine radicals in X-irradiated tri-glycine sulphate and of structural changes near the ferroelectric phase transition point

Abstract

A report is given on ENDOR investigations of the structure of radicals in X-irradiated tri-glycine sulphate single crystals at 77 K and 300 K. Two non-equivalent radicals of the type NH₃ ⁺-ĊH-COO^- which originate at sites on the glycine molecules gly II and gly III were identified. Their hyperfine coupling parameeters differ by a maximum of 1 MHz at room temperature. The radicals have non-equivalent β-protons indicating strongly hindered rotation of the amino group. INDO calculations were also performed. The radicals were found to be non-planar. The proton deviates from the nodal plane of the π-orbital by about 10°. The positions of the hydrogen atoms of the amino groups were found to agree with the corresponding hydrogen bonds in the non-irradiated crystals.