Polyethyleneimine methylphosphonate: towards the design of a new class of macromolecular actinide chelating agents in the case of human exposition

Abstract

The use of uranium and to a minor extent plutonium as fuel for nuclear energy production or as components in military applications is under increasing public pressure. Uranium is weakly radioactive in its natural isotopy but its chemical toxicity, combined with its large scale industrial utilization, makes it a source of concern in terms of health impact for workers and possibly the general population. Plutonium is an artificial element that exhibits both chemical and radiological toxicities. So far, uranium (under its form uranyl, U(vi)) or plutonium (as Pu(iv)) decorporation or protecting strategies based on molecular design have been of limited efficiency to remove the actinide once incorporated after human exposure. In all cases, after human exposure, plutonium and uranium are retained in main target organs (liver, kidneys) as well as skeleton although they exhibit differences in their biodistribution. Polymers could represent an alternative strategy as their tropism for specific target organs has been reported. We recently reported on the complexation properties of methylcarboxylated polyethyleneimine (PEI-MC) with uranyl. In this report we extend our work to methylphosphonated polyethyleneimine (PEI-MP) and to the comparison between actinide oxidation states +IV (thorium) and +VI (uranyl). As a first step, thorium (Th(iv)) was used as a chemical surrogate of plutonium because of the difficulty in handling the latter in the laboratory. For both cations, U(vi) and Th(iv), the uptake curve of PEI-MP was recorded. The functionalized PEI-MP exhibits a maximum loading capacity comprised of between 0.56 and 0.80 mg of uranium (elemental) and 0.15-0.20 mg of thorium (elemental) per milligram of PEI-MP. Complexation sites of U(vi) and Th(iv) under model conditions close to physiological pH were then characterized with a combination of Fourier transform Infra Red (FT-IR) and Extended X-Ray Absorption Fine Structure (EXAFS). Although both cations exhibit different coordination modes, similar structural parameters with phosphonate functions were obtained. For example, the coordination sites are composed of fully monodentate phosphonate functions of the polymer chains. These physical chemical data represent a necessary basic chemistry approach before envisioning further biological evaluations of PEI-MP polymers towards U(vi) and Pu/Th(iv) contamination.

Carboxylate- and Phosphonate-Modified Polyethylenimine: Toward the Design of Actinide Decorporation Agents

“…But the uptake curves of PEI-MC-Th, PEI-MP-Th and DTPA-Th have been reported in previous publications. 46,50 The curves are now compared in Figure 5abc EC50 values (we recall that EC50 is the titration point at 50% response of the ligand, therefore the lower the EC50, the higher the affinity) reported in Table 3 reflect the chelating affinity towards Th(IV). With DTPA, the EC50 value (0.13 ± 0.01 mM) is significantly lower than for PEI-MC (1.16…”

“…49 PEI-MP was also investigated for its capacity to complex U(VI) in pseudo physiological conditions. 50 This forum article is formally divided in two parts. First, we present new results on the structural characterization of the complexation of Pu with polyethyleneimine methylphosphonate (PEI-MP) using the combination of EXAFS spectroscopy (Extended X-Ray Absorption Fine Structure) and ab initio molecular dynamics calculations (AIMD).…”

Polymer sequestrants for biological and environmental applications

“…Further analysis of the PEI‐MP–metal complexes using Fourier transform infrared spectroscopy and extended X‐ray adsorption fine structure spectroscopy confirmed the role of the methyl phosphonate groups in coordination to the heavy metals. Lahrouch et al suggest that macromolecular chelation could be a viable approach to remediate heavy metal exposure in vivo …”

Medical countermeasures against radionuclide contamination: An overview

“…The use of functionalized macromolecules bearing numerous chelating sites per area unit is under investigation. For example, the functionalized methy-carboxylated poly(ethylenimine) (PEI-MC) has an high affinity for U but no animal studies have been performed yet [19]. Also, a mesoporous silica (SAMMS TM ) with ferrocyanide moieties has a greater capacity for Cs loading than Prussian Blue but is not more efficient in vivo [20].…”