Complexes of EDTA in aqueous solutions. Structural aspects from a C-13 NMRrelaxation study

C-13 NMR relaxation times T-1 of the carboxylate groups in EDTA and its com plexes with Mg(II), Ca(II), Zn(II) and Al(III) ions in aqueous solutions we re measured at different magnetic field strengths, allowing the determinati on of the contribution of the chemical shift anisotropy mechanism to the to tal relaxation rate and, consequently, the shielding tensor (chemical shift ) anisotropy of these nuclei. A discussion of these values in relation to t he possible structure of these species in solution and a comparison with th e values obtained in the solid state were performed.