ENDOR study of an irradiated crystal of L-alanine: Environment of the stable CH3ĊHCO2− radical

The environment of the stable radical in an x-ray irradiated crystal of L-alanine CH3CH(NH3+)CO2− was studied at 77 K with the use of ENDOR technique. The analysis indicated that as the C–N bond ruptured and the stable radical was formed, the α carbon atom Cα shifted by a distance of 1.5 Å. As a result, for several protons in the radical environment the distance between the proton and Cα of the radical was found to be much shorter than the corresponding distance in the undamaged crystal; for example, 2.3 Å compared with 3.9 Å in the case of a methyl proton. The transferred N–H hydrogen was found to participate in exchange with the C–H hydrogens of this CH3ĊHCO2− radical.