Chelation Behaviors of 3,4,3-LI(1,2-HOPO) with Lanthanides and Actinides Implicated by Molecular Dynamics Simulations.

The hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (denoted as t -HOPO) is a potential chelator agent for decorporation of in vivo actinides (An), while its coordination modes with actinides and the dynamics of the complexes (An( t -HOPO)) in aqueous phase remain unclear. Here, we report molecular dynamics simulations of the complexes with key actinides (Am 3+ , Cm 3+ , Th 4+ , U 4+ , Np 4+ , Pu 4+ ) to study their coordination and dynamic behaviors. For comparison, the complexation of the ligand with a ferric ion and key lanthanides (Sm 3+ , Eu 3+ , Gd 3+ ) was also studied. The simulations show that the nature of metal ions determines the properties of the complexes. The t -HOPO in the Fe III ( t -HOPO) 1- complex ion formed a compact and rigid cage to encapsulate the ferric ion, which was hexa-coordinated. Ln 3+ /An 3+ cations were ennea-coordinated with eight ligating oxygen atoms from t -HOPO and one from an aqua ligand, and An 4+ cations were deca-coordinated with a second aqua ligand. The t -HOPO shows strong affinity for metal ions (stronger for An 4+ than Ln 3+ /An 3+ ) benefited from its high denticity and its flexible backbone. Meanwhile, the complexes displayed different dynamic flexibilities, with the An IV ( t -HOPO) complexes more significant than the others, and in the An IV ( t -HOPO) complexes, the fluctuation of the t -HOPO ligand was highly correlated with that of the eight ligating O atoms. This is attributed to the more compact conformation of the ligand, which raises backbone tension, and the competition of the aqua ligand against the t -HOPO ligand in coordinating with the tetravalent actinides. This work enriches our understanding on the structures and conformational dynamics of the complexes of actinides with t -HOPO and is expected to benefit the design of HOPO analogues for actinide sequestering.