Extraction of Gd³⁺ and UO₂²⁺ Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study

Abstract

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd) and uranium dioxide (UO) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd and UO is investigated for the first time. Our simulation results demonstrate that the binding of Gd and UO onto the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free energy (ΔG) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔG becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔG). ΔG is significantly favorable for both Gd and UO for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd and UO show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases.

Adsorption of Gadolinium (Gd3+) Ions on the Dibenzo Crown Ether (DBCE) and Dicyclo Hexano Crown Ether (DCHCE) Grafted on the Polystyrene Surface: Insights from All Atom Molecular Dynamics Simulations and Experiments

“…This particular behavior is in good agreement with the previous gas phase theoretical results reported by Boda et al, 11 where the binding distance of 0.24 nm between Gd 3+ and O C of DBCE is reported. The previous simulation studies 27,28 have shown the Gd 3+ binding distance as ∼0.24 nm for both DBCE and DCHCE, where it is considered as a precomplexed structure as Gd 3+ -DBCE and Gd 3+ -DCHCE. However, in the present work, the binding distance between O C -Gd 3+ in water is ∼0.48 nm, which is 2 times higher than that in the gas phase.…”

“…The OPLS force field is used for all the molecules such as DBCE, DCHCE, PS, HNO 3 , Gd 3+ , and NO 3 for the all atom molecular dynamics simulations . The details of all the bonded and nonbonded interactions are presented in the previous work. , We have used the TIP3P water model, and the acidic medium (1 M) is maintained by considering H 3 O + and NO 3 – ions in an aqueous solution. The particle mesh Ewald (PME) is used for calculating the electrostatic interactions with a 1 nm cutoff radius with a grid spacing of 0.1 nm and an interpolation order of 4.…”

“…The column chromatography study by Boda et al on DBCE grafted on the polystyrene surface has shown enhanced adsorption behavior of Gd 3+ ions. The complexation behavior of Gd 3+ with crown ethers has been studied theoretically in the literature. − A recent molecular simulation study from our group , has shown that an increase in the polystyrene chain length on the DBCE and DCHCE increases the binding affinity of Gd 3+ .…”

“…The complexation behavior of Gd 3+ with crown ethers has been studied theoretically in the literature. 23−26 A recent molecular simulation study from our group 27,28 has shown that an increase in the polystyrene chain length on the DBCE and DCHCE increases the binding affinity of Gd 3+ .…”

Molecular Dynamics Study on the Adsorption of UO22+ from an Aqueous Phase: Effect of Grafting Dibenzo Crown Ether and Dicyclohexano Crown Ether on the Polystyrene Surface

“…The detailed information on the force-field is given in earlier works. 22,23 The atomic charges of all molecules are taken from previous work. 22,23 Tables 1 and 2 present the bonded and nonbonded interactions, respectively.…”