Ligand hyperfine interaction in Cu2+ complexes in amino acid crystals: L-alanine-d4 and α-glycine-d2

At 77°K EPR spectra of Cu2+ impurity complexes in L-alanine-d4 and α-glycine-d2 crystals exhibited well-defined ligand hyperfine structures, indicating that the ligand amino group has a − NH2 structure in place of the zwitterionic −NH3+. This implies that the interstitial accommodation of a divalent Cu2+ ion necessitates removal of two protons from the ligand molecules. The proton hyperfine couplings were small and anisotropic, indicating the presence of a rearrangement motion in the ligand amino protons. The proton tensors were determined in L-alanine-d4 crystals, while in α-glycine-d2 the spectra were so complicated that only estimated values were obtained.