Influence of electron capture after-effects on the stability of 111In(111Cd)-complexes with organic ligands Original Research Article

The TDPAC technique was applied to verify a hypothesis about the influence of electron capture after-effects on the integrity of radiometal complexes with organic ligands in aqueous solutions. The neutral aqueous solutions of DTPA-complexes with two parent isotopes, 111In(EC)111Cd and 111mCd, were used for direct comparison of dynamic interaction parameters. Data for the parent 111In–DTPA complexes revealed three fractions with essentially different relaxation constants, including an “unperturbed” fraction, which, according to the hypothesis, is due to small fragments of the initial complexes disintegrated as a result of Auger-process and the following Coulomb fragmentation. Only one fraction with a relaxation constant of 3(1)×106 s−1 was observed for the 111mCd–DTPA solution confirming the proposal about the influence of electron capture after-effects. Measurements with the frozen solutions allowed determining the electric field gradient (EFG) at Cd-sites in complexes with DTPA, Vzz=6.7(2)×1021 V/m2 with an asymmetry parameter η=0.75(5).