Department of Chemistry , University of California , Riverside , California 92521 , United States.
J Phys Chem B. 2018 Dec 20;122(50):12060-12066. doi: 10.1021/acs.jpcb.8b08345. Epub 2018 Dec 10.
Extracting uranium from seawater remains a formidable challenge because of its extremely low concentration of 3.3 ppb. State-of-the-art polymeric sorbents employ both amidoximate and carboxylate groups on the side chains to achieve optimal U uptake and selectivity, but little is known about the synergistic effect between the two functional groups in binding with uranyl. Herein, we simulated the binding of a model amidoximate-carboxylate bifunctional ligand with uranyl using a combination of theoretical methods. Gas-phase quantum-mechanical calculations showed a chelate binding of a η amidoximate and a monodentate carboxylate to uranyl. Ab initio molecular dynamics (MD) simulations in an explicit water solvation model confirmed the stability of the chelate mode. Classical MD and free-energy simulations in 0.5 M NaCl showed that the carboxylate group binds first to uranyl, leading to a loose intermediate state, and then, the amidoximate group binds, resulting in a more stable and tight chelate state. Binding of the second bifunctional ligand follows a similar process, and the two ligands prefer a trans configuration around the uranyl group. The simulated free energies indicate that the two bifunctional ligands bind with uranyl 55 kJ/mol stronger than the two ligands with only amidoximate groups. This work suggests an important synergy between amidoximate and carboxylate groups in binding uranyl.
从海水中提取铀仍然是一个巨大的挑战，因为其浓度极低，仅有 3.3ppb。最先进的聚合物吸附剂在侧链上同时采用偕胺肟和羧酸盐基团，以实现最佳的铀摄取和选择性，但关于这两种官能团在与铀酰结合时的协同作用知之甚少。在此，我们使用理论方法的组合模拟了模型偕胺肟-羧酸盐双功能配体与铀酰的结合。气相量子力学计算表明，偕胺肟和单齿羧酸盐与铀酰呈螯合结合。在明确定义的水溶剂化模型中的从头算分子动力学（MD）模拟证实了螯合模式的稳定性。在 0.5M NaCl 中的经典 MD 和自由能模拟表明，羧酸盐基团首先与铀酰结合，导致松散的中间状态，然后偕胺肟基团结合，形成更稳定和紧密的螯合状态。第二个双功能配体的结合遵循类似的过程，两个配体在铀酰基团周围优先采用反式构型。模拟的自由能表明，两个双功能配体与铀酰的结合强度比只有偕胺肟基团的两个配体强 55kJ/mol。这项工作表明，偕胺肟和羧酸盐基团在结合铀酰方面存在重要的协同作用。
