Structures, electronic properties, hydration and UV-vis absorption spectra of actinide motexafins [An-Motex]2+ (An = Ac, Cm, Lr) and [UO2-Motex]1+: insights from DFT calculations

Abstract

Molecular and electronic structures and UV-vis spectra of selected actinide(III) motexafins ([An-Motex]2+, An = Ac, Cm, Lr) as well as of uranyl(IV) motexafin ([UO2-Motex]+) were studied by using density functional theory methods combined with relativistic energy-consistent 5f-in-core actinide pseudopotentials. Solvent effects were considered by an explicit treatment of the first water coordination sphere in combination with the COSMO solvation model for bulk hydration effects. It is concluded that the Ac(III), Cm(III), Lr(III), and uranyl(IV) cations are tightly bound to the macrocyclic skeleton, yielding stable structures. By calculating the changes of the Gibbs free energies ΔG for the reactions X-Motex− + Y → X + Y-Motex− (X = La3+, Eu3+, Gd3+, Lu3+; Y = , Am3+, Cm3+), it is found that although in aqueous solution the Motex− ligand prefers Ln3+ (Ln = Eu, Gd, Lu) over An3+ (An = Am, Cm) it rather prefers over Ln3+ (Ln = La, Eu, Gd, Lu). The results suggest that motexafin might be useful for the separation of uranyl in nuclear waste treatments and possibly also for the treatment of uranyl poisoning in vivo. In particular motexafin might be a chelating agent for 225Ac3+ in targeted α-therapy.