LIGAND ELECTRON NUCLEAR DOUBLE-RESONANCE STUDY OF CU(II)-DOPED ALPHA-GLYCYLGLYCINE SINGLE-CRYSTALS AT 4.2-K

Electron nuclear double resonance (ENDOR) has been used to study Cu(II)-doped α-glycylglycine single crystals at 4.2 K. Analysis of the ENDOR spectra yielded the principal values and directions cosines of the g tensor, the hyperfine coupling, nuclear quadruple coupling tensors, and the asymmetry parameters for two different 14N nuclei. The two 14N nuclei were identified as N1, belonging to the NH2 group, and N2 to the NH group, respectively. In addition, we determined the hyperfine interaction tensors for four protons and assigned these to their respective molecules. Moreover, by comparing the experimentally determined components of the proton hyperfine interaction tensors with the corresponding values calculated theoretically from the X-ray and neutron diffraction data, we were able to identify uniquely the lattice positions of the interacting protons which yielded the observed ENDOR transitions. We calculated theoretical values of the components of the g tensor using a method that depends on the simultaneous diagonalizing of the ligand field, electron-electron repulsion, and the spin-orbit couling interactions. The theoretical and experimental values are in excellent agreement. © 1990 American Chemical Society.