CHARACTERIZATION OF LANTHANIDE COMPLEXES WITH A SERIES OF AMIDE-BASEDMACROCYCLES, POTENTIAL MRI CONTRAST AGENTS, USING EU3+ LUMINESCENCE SPECTROSCOPY AND MOLECULAR MECHANICS

Eu3+ luminescence spectroscopy was used to characterize the solution c omplexes of the following ligands: l)-8,15-dioxo-1,4,7,10,13-pentaazac yclopentadecane (edta-dam); l)-9,14-dioxo-1,4,7,10,13-pentaazacyclopen tadecane (edta-dam); l)-9,14-dioxo-1,4,7,10,13-pentaazacyclopentadecan e (dtpa-eam); o-13,16-dioxa-1,4,7,10,19-pentaazacycloheneicosane (dtpa -oam); 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane (bis(dtpa-ea m)), 4,7,10-tetraazacyclododecan-1-yl)acetyl)piperazine (piperazine do 3a-dimer). A single isomeric form of the Eu3+ complex with each ligand is observed. Edta-dam, dtpa-eam, and dtpa-oam form 1:1 stoichiometric metal-ligand complexes while bis(dtpa-eam) and the do3a-dimer form 2: 1 stoichiometric metal-ligand complexes. Formation constants were meas ured for the Eu3+ complexes of dtpa-eam, dtpa-oam, and edta-dam. Relat ive formation constants for the other members of the lanthanide series were measured by competition experiments for dtpa-eam, dtpa-oam, and edta-dam. The number of coordinated water molecules were determined fo r the Eu3+ complex of each ligand. Inter-metal ion energy transfer bet ween the Eu3+ ion and various other coordinated lanthanide ions is obs erved in dinuclear complexes of bis(dtpa-eam) and the piperazine do3a- dimer. Deductions regarding the composition of the first coordination sphere of the Eu3+ ion were made on the basis of molecular mechanics c alculations and the number of coordinated water molecules determined f rom excited-state lifetime measurements in H2O and D2O.