Computational Characterization of AcIII-DOTA Complexes in Aqueous Solution.

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complexes of AcIII with H2O, dimethyl sulfoxide (DMSO), OH-, and F- as axial ligands were studied using density functional theory. Formation of the [AcIII(DOTA)(OH)]2- and [AcIII(DOTA)(F)]2- complexes is predicted to be significantly more favorable than that of [AcIII(DOTA)(H2O)]- and [AcIII(DOTA)(DMSO)]- because of the enhanced relative Gibbs free energies. Further electronic structure analyses demonstrate that the type and nature of the bond between Ac and the ligand donor atom is the main driving force that determines the thermodynamic stability of the complexes. Specifically, the [AcIII(DOTA)]- complex strongly binds to OH- and F- via covalent bonds, while the bonding to H2O and DMSO is ionic and relatively weaker.