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 $-{\mathrm{NH}}_3^{+}$ . 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.