Computational Studies of Interactions Between Vanadyl, Uranyl, and Thorium Aqua Ions with Bidentate Eudistomin Ligands of Ascidian-origin
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The nuclear waste generated in nuclear power plants is reprocessed to extract useful actinide elements, especially uranium and plutonium. In recent times, interest has been growing towards N-containing ligands to facilitate extraction. More often than not, these ligands have similarities to biogenic compounds such as eudistomins, which are found in marine animals called Ascidians. Ascidians are tunicates which adopt unusual techniques to deter predation, the three main methods are sequestration of unusual metals, high concentrations of sulphuric acid/sulphate ions in tunicate-cells, and the presence of eudistomins. Studies have shown the presence of sulphate ion/sulfuric acid plays a key role in deterring predation. In a separate study, researchers have found that eudistomins can form metal-complexes with Iron outside of the ascidian’s body. Whether eudistomins play any role in the presence of sulfuric acid/sulphate ion, and/or the sequestration of the metals was never studied. In this study, we have explored the possible interactions of eudistomins as ligands with metal-aqua ions viz., vanadyl, uranyl, and thorium ions. We have designed five model reactions and have calculated the formation energies. The model reactions were designed to resemble what might happen in the body of an ascidian, based on the information obtained from the literature. We have adopted density function theory (DFT) using PBE-D3, BLYP, and B3LYP functionals with the ADF (PBE-D3 and BLYP) and ORCA (BLYP and B3LYP) software packages for our calculations. The formation energies of the complexes were calculated in gas phase and in solvation phase. COSMO (in ADF) and CPCM (in ORCA) were used for solvation effects. ZORA was the relativistic method adopted in this work. From our study, based on the results, we can confirm that with respect to model reactions 1, 4, and 5, the anionic form of the ligand is capable of forming decent interactions with the metal aqua ions. The closeness of the ΔG values obtained with respect to all three aqua ions suggest that ascidians may not have a preference to a specific metal. The adoption of different methodology has resulted in similar results. To conclude this work, we are confident that eudistomins may be used as biogenic N-based ligands in the nuclear reprocessing facilities.