Binding of stereognostically designed ligands to trivalent, pentavalent, and hexavalent f-block elements

摘要

Stability constants were determined for the complexes formed from two stereognostically designed lig-ands and the f-block elements Nd(III), Np(V), and Pu(VI). The ligands investigated were tris[3-(2-carboxyphenoxy)- propyl]amine (NPB) and tris-N,N',N"-[2-(2-carboxy-4-ethyl-phenoxy)ethyl]-1,4,7-triazacyclononane (EETAC). A stereo-gnostically blind ligand, nitrilotriacetic acid (NTA), was also investigated for comparison. The results suggest that there is no significant stereognostic effect for complexation of NPB or EETAC to Np(V). On the other hand, a modest stereognostic effect is seen for the NPB ligand when complexed to Pu(VI), leading to an approximately 8-fold increase in the binding strength. A more significant effect is observed for the EETAC system in which a 250-fold increase in binding is observed for Pu(VI) vs. Nd(III).