Sappidi Praveenkumar, Namsani Sadanandam, Ali Sk Musharaf, Singh Jayant Kumar
Computational Nano Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology (IIT) Kanpur , Kanpur 208016, India.
Chemical Engineering Division, Bhabha Atomic Research Center , Mumbai 400085, India.
J Phys Chem B. 2018 Jan 25;122(3):1334-1344. doi: 10.1021/acs.jpcb.7b11384. Epub 2018 Jan 16.
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.
进行了原子分子动力学（MD）模拟，以推导对于理解在硝基苯（NB）和辛醇（OCT）溶剂中用二苯并冠醚（DBCE）萃取钆（Gd）和二氧化铀（UO₂）而言重要的热力学性质。首次研究了聚苯乙烯接枝长度对DBCE以及对Gd和UO₂结合行为的影响。我们的模拟结果表明，在有机溶剂OCT和NB中，Gd和UO₂与冠醚氧原子的结合对于聚苯乙烯接枝冠醚是有利的。使用热力学积分（TI）方法计算不同溶剂环境中的金属离子结合自由能（ΔG）。随着聚苯乙烯单体长度的增加，在NB和OCT这两种溶剂中ΔG都变得更有利。通过计算转移自由能（ΔG）来估计金属离子从水相到有机相的转移能力。随着聚苯乙烯长度的增加，通过与DBCE形成离子络合物，Gd和UO₂从水相转移到有机相（即NB和OCT）时，ΔG明显有利。Gd和UO₂的分配系数（log P）值表明，聚苯乙烯接枝DBCE的分离能力提高了5倍。我们通过进一步分析不同相中离子的结构和动力学性质来证实观察到的行为。
