ENDOR Study on the Dynamic Properties of the First Stable Paramagnetic Center in γ-Irradiated l-Alanine Crystals

Dynamic properties of the first stable l-alanine radical, SAR1, induced by γ-irradiation of l-alanine crystals, have been investigated by the electron nuclear double resonance technique (ENDOR). The study focuses on the dynamic properties of the α-proton hyperfine splitting in the temperature range from 180 to 320 K. In this region the motion of the NH3 + and CH3 groups exhibits slow and fast motional dynamics in comparison to the nuclear and electron Larmor frequencies, respectively. Evidence for different conformations of the SAR1 center is presented on the basis of thermodynamic properties of the α-hyperfine splitting. The activation processes causing the broadening of the ENDOR lines are studied. At room temperature the motional dynamics of the SAR1 center are modulated by the dynamics of the charged, neighboring NH3 + group.