THERMODYNAMICS, PMR, AND FLUORESCENCE STUDIES FOR THE COMPLEXATION OF TRIVALENT LANTHANIDES, CA-2+, CU-2+, AND ZN-2+ BY DIETHYLENETRIAMINEPENTAACETIC ACID BIS(METHYLAMIDE)

H-1-NMR shift data were measured for the diamagnetic La3+ and Lu3+ complexes with diethylenetriaminepentaacetate-N,N'-bis(methylamide) (DTPA-BMA) at different temperatures. Quartet splitting of the methylene protons of the terminal acetate groups and of the amide groups upon complexation with metal ions is indicative of long-lived metal-nitrogen bonds and short-lived metal-oxygen bonds. The observation of two quartets for the terminal acetates and the splitting of the N-methyl singlet upfield is attributed to the presence of more than one conformation in solution. Thermodynamic data indicate that DTPA-BMA acts as an octadentate ligand toward lanthanide ions and possibly as a hexadentate ligand toward Ca2+, Cu2+, and Zn2+ ions. Fluorescence data for the Eu3+ complex support the octadentate behavior of the ligand toward lanthanides and indicate that the complex contains one coordinated water molecule.