g TENSOR ANISOTROPY AND ELECTRON-NUCLEUS DIPOLE-DIPOLE INTERACTION IN THE Cu (II) - (L-His)2 COMPLEX IN SOLUTION

Cu(II) complexes with low molecular weight ligands have been suggested to play relevant roles in the biochemistry of copper. Among them the Cu(lI)(L-His)2 species has been recognized as the most abundant in biolo gical fluids. However the binding features of the two L-His molecules have not been yet defined; histamine*. like (one amino nitrogen plus one imidazole nitrogen) and/or glycinelike (one amino nitrogen plus one carboxyl oxygen) binding modes have been alternatively suggested. Different rapidly interchanging species can be present as well. In this report we have combined NMR relaxation rate measurements and ESR lineshape analysis with the aim of delineating the structural and motional features of the title complex in solution.