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

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, In-111(EC)Cd-111 and Cd-111m, were used for direct comparison of dynamic interaction parameters. Data for the parent In-111-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) x 10(6) s(-1) was observed for the Cd-111m-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, V-zz = 6.7(2) x 10(21) V/m(2) with an asymmetry parameter eta = 0.75(5). (C) 2002 Published by Elsevier Science B.V.