Dissociation kinetics of acyclic and macrocyclic polyaminopolycarboxylate complexes of yttrium

Dissociation kinetics of Y-III complexes of a linear as well as two macrocy clic polyaminopolycarboxylates, ethylenediamine diacetic acid (EDDA), 1,7-d inza-4,10,13-trioxacyclopentadecane-N,N'-diacetic acid (K21DA) and 1,10-dia za-4,7,13,16-tetraoxacyclooctadecane-N,N'-diacetic acid (K22DA) have been s tudied at a constant ionic strength (0.1 M) under varying [H+] and temperat ures. Cu-II ion acts as the scavanger of the free ligand. Dissociation rate of Y-III-K21DA is insensitive to Cu-II and acetate (used as buffer anion) concentrations. Kinetic stability of the three complexes follow the order : Y-III-K22DA > Y-III-R21DA > Y-III-EDDA. Enthalpies of activation for K21DA and K22DA complexes of Y-III are also evaluated. Thermodynamic stability c onstant (log K) for Y-III-K22DA complex is 10.81 +/- 0.01.