PHYSICAL PARAMETERS AND BIOLOGICAL STABILITY OF YTTRIUM(III) DIETHYLENETRIAMINEPENTAACETIC ACID-DERIVATIVE CONJUGATES

The solution equilibria, acid dissociation, and serum stability of a s eries of Y(III) complexes of DTPA ligands functionalized with p-nitrob enzyl, methyl, and trans-cyclohexyl substituents were studied. The the rmodynamic stability of the complexes studied ranged from log K = 21.5 3 to 24.7. Acid dissociation rates were found to decrease as the subst itution on the carbon backbone increased, and significant differences in dissociation rates were observed for the Y(III) complexes of a pair of diasteriomeric cyclohexyl-DTPA ligands. While one diastereomer was found to have the slowest acid dissociation rate of the entire DTPA s eries, it was remarkably labile in both serum stability and in vivo st udies.