INVESTIGATION OF THE METAL CATION-BINDING PROPERTIES OF MACROCYCLIC EDTA-BIS(AMIDE) COMPLEXES BY POTENTIOMETRY AND STOPPED-FLOW SPECTROPHOTOMETRY

The protonation constants of macrocyclic EDTA-bis(amide), EDTA-EAM (1) , EDTA-PAM (2), EDTA-BAM (3), and EDTA-PenAM (4), and the stability co nstants of their Ln(3+) and Cu2+ complexes have been determined by pot entiometric titration at 25.0 +/- 0.1 degrees C and I = 0.10 M (KCl). The dissociation rates of some Ln(3+) complexes have been measured by stopped-flow and conventional spectrophotometry at 25.0 +/- 0.1 degree s C and I = 0.10 M (NaClO4). The first protonation constants of the li gands were lower than that of EDTA, reflecting the strong electron-wit hdrawing ability of the carbonyl group. The stability constants and di ssociation rates of Ln(3+) complexes followed the order Ln(1)(+)[Ln(2) (+)]Ln(3)(+)]Ln(4)(+). An increase in ring size from 13 (2) to 15 (4) by addition of the carbon chain between two amide nitrogens of the lig ands leads to an increase in the thermodynamic and kinetic stability o f the complexes. However, 1 shows a different behavior in the complexe s because of its greater rigidity and basicity. (C) 1997 Academic Pres s.