Recognition of Actinides by Siderocalin

Plain simulations and enhanced sampling unveil a novel siderocalin (Scn) recognition mode for An–Ent (where An = actinides and Ent = enterobactin) complexes and identify a “seesaw” relationship between actinide affinity to Ent and Scn recognition to an An–Ent complex. Electrostatic interactions predominantly govern competitive binding in both processes. Additionally, hydrolysis-induced negative charge, water expulsion-driven entropy, and Ent’s conformational adaptability collectively enhance high-affinity recognition

Trivalent Uranium Complex As a Catalyst to Promote the Functionalization of Carbon Dioxide and Carbon Disulfide: A Computational Mechanistic Study

We report our recent DFT mechanistic study on the functionalization of CO₂ and CS₂ promoted by a trivalent uranium complex (Tp*)₂UCH₂Ph. In the calculations, the uranium atom is described by a quasi-relativistic 5f-in-core ECP basis set (LPP) developed for the trivalent uranium cation, which was qualified by the calculations with a quasi-relativistic small core ECP basis set (SPP) for uranium. According to our calculations, the functionalization proceeds in a stepwise manner, and the CO₂ or CS₂ does not interact with the central uranium atom to form a stable complex prior to the reaction due to the steric hindrance from the bulky ligands but directly cleaves the U–C (benzyl) bond by forming a C–C covalent bond. The released coordination site of uranium is concomitantly occupied by one chalcogen atom of the incoming molecule and gives an intermediate with the uranium atom interacting with the functionalized CO₂ or CS₂ in an η¹ fasion. This step is followed by a reorientation of the (dithio)­carboxylate side chain of the newly formed PhCH₂CE₂^– (E = O, S) ligand to give the corresponding product. Energetically, the first step is characterized as the rate-determining step with a barrier of 9.5 (CO₂) or 25.0 (CS₂) kcal/mol, and during the reaction, the chalcogen atoms are reduced, while the methylene of the benzyl group is oxidized. Comparison of the results from SPP and LPP calculations indicates that our calculations qualify the use of an LPP treatment of the uranium atom toward a reasonable description of the model systems in the present study

Recognition of Actinides by Siderocalin

Plain simulations and enhanced sampling unveil a novel siderocalin (Scn) recognition mode for An–Ent (where An = actinides and Ent = enterobactin) complexes and identify a “seesaw” relationship between actinide affinity to Ent and Scn recognition to an An–Ent complex. Electrostatic interactions predominantly govern competitive binding in both processes. Additionally, hydrolysis-induced negative charge, water expulsion-driven entropy, and Ent’s conformational adaptability collectively enhance high-affinity recognition

Key Factors Determining Efficiency of Liquid–Liquid Extraction: Implications from Molecular Dynamics Simulations of Biphasic Behaviors of CyMe₄‑BTPhen and Its Am(III) Complexes

CyMe4-BTPhen (2,9-bis­(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline, denoted as L) has been considered as a promising extractant in lanthanide­(III)/actinide­(III) separation. Vast endeavors in its application put forward a compelling need on the understanding of the underlying mechanism in the liquid–liquid extraction. To address the issue of its dynamics in biphasic systems, we carried out molecular dynamics (MD) simulations of L and its complexes with a heavy f-block metal ion, americium­(III) (Am3+) in “oil”/water binary solvents. Two types of organic phases have been considered, differing in the presence of octanol in the bulk n-dodecane or not, and the distribution of the solutes and their interfacial behaviors have been investigated. Two of the key factors that determine the efficiency of a liquid–liquid extraction protocol were delineated and discussed, that is, the appropriate ligand to enhance the lipophilicity of AmL complexes and appropriate way to form ion pairs to minimize the attraction between the complexes and aqueous phase. The simulations showed that the charge states of both ligand and AmL complexes were strongly correlated with their phase behavior, and the migration of neutral species was driven by van der Waals interactions while that of charged species by electrostatic interactions, indicating stronger lipophilicity of the former than the latter. The presence of octanol facilitated the migration of the ligand from the interface to the organic phase via hydrogen bond between its polar head and the ligand or the AmL complexes and constituted a polar core in the organic phase. This work bridged the widely used liquid–liquid extraction technique in chemistry to a fundamental chemical concept, that is, minimization of hydrophilicity and maximization of lipophilicity to facilitate phase transfer from the aqueous phase to the organic phase, and is expected to improve the understanding of dynamics of ligands and their complexes with metal ions and to contribute to the development of efficient protocols for phase transfer of target species

Chelation Behaviors of 3,4,3-LI(1,2-HOPO) with Lanthanides and Actinides Implicated by Molecular Dynamics Simulations

The hydroxypyridinone ligand 3,4,3-LI­(1,2-HOPO) (denoted as t-HOPO) is a potential chelator agent for decorporation of in vivo actinides (An), while its coordination modes with actinides and the dynamics of the complexes (An­(t-HOPO)) in aqueous phase remain unclear. Here, we report molecular dynamics simulations of the complexes with key actinides (Am3+, Cm3+, Th4+, U4+, Np4+, Pu4+) to study their coordination and dynamic behaviors. For comparison, the complexation of the ligand with a ferric ion and key lanthanides (Sm3+, Eu3+, Gd3+) was also studied. The simulations show that the nature of metal ions determines the properties of the complexes. The t-HOPO in the FeIII(t-HOPO)1– complex ion formed a compact and rigid cage to encapsulate the ferric ion, which was hexa-coordinated. Ln3+/An3+ cations were ennea-coordinated with eight ligating oxygen atoms from t-HOPO and one from an aqua ligand, and An4+ cations were deca-coordinated with a second aqua ligand. The t-HOPO shows strong affinity for metal ions (stronger for An4+ than Ln3+/An3+) benefited from its high denticity and its flexible backbone. Meanwhile, the complexes displayed different dynamic flexibilities, with the AnIV(t-HOPO) complexes more significant than the others, and in the AnIV(t-HOPO) complexes, the fluctuation of the t-HOPO ligand was highly correlated with that of the eight ligating O atoms. This is attributed to the more compact conformation of the ligand, which raises backbone tension, and the competition of the aqua ligand against the t-HOPO ligand in coordinating with the tetravalent actinides. This work enriches our understanding on the structures and conformational dynamics of the complexes of actinides with t-HOPO and is expected to benefit the design of HOPO analogues for actinide sequestering

Dual-Phase Structure through Selective Etching of the Double A‑Element MAX Phase in Lewis Acidic Molten Salts

Two-dimensional (2D) MXene materials with innovative properties and versatile applications have gained immense popularity among scientists. The green and environmentally friendly Lewis acid salt etching route has opened up immense possibilities for the advancement of 2D MXene materials. In this study, we precisely etched the Al element from the double A-element MAX phases Ti2(SnyAl1–y)C by employing Lewis molten salt guided by redox potentials. This approach led to the discovery of a novel Ti2SnyCClx dual-phase structure consisting of Ti2SnC and Ti2CClx. We then established that the etching of the MAX phase via Lewis acid salt is facilitated by the oxidation of M-site elements, with the MX sublayer acting as an electron transmission conduit to enable the oxidation of A-site elements. This work is dedicated to unraveling the underlying mechanisms governing the etching processes using Lewis molten salt, thereby contributing to a more profound comprehension of these innovative etching routes

Dual-Phase Structure through Selective Etching of the Double A‑Element MAX Phase in Lewis Acidic Molten Salts

Two-dimensional (2D) MXene materials with innovative properties and versatile applications have gained immense popularity among scientists. The green and environmentally friendly Lewis acid salt etching route has opened up immense possibilities for the advancement of 2D MXene materials. In this study, we precisely etched the Al element from the double A-element MAX phases Ti2(SnyAl1–y)C by employing Lewis molten salt guided by redox potentials. This approach led to the discovery of a novel Ti2SnyCClx dual-phase structure consisting of Ti2SnC and Ti2CClx. We then established that the etching of the MAX phase via Lewis acid salt is facilitated by the oxidation of M-site elements, with the MX sublayer acting as an electron transmission conduit to enable the oxidation of A-site elements. This work is dedicated to unraveling the underlying mechanisms governing the etching processes using Lewis molten salt, thereby contributing to a more profound comprehension of these innovative etching routes

Biphasic Behaviors of Nd³⁺ Bound with Cyanex272, Cyanex301, and Cyanex302: A Molecular Dynamics Simulation Study

By means of molecular dynamics simulations, this work addresses the conformational flexibility and migration of trivalent neodymium (Nd3+) coordinated with three or six titled (thio)­phosphinic ligands and shows that the fluxionality of the complexes enables them to adapt to the solvent environment during the migration. Cyanex272 forms a more compact complex than the other two types of ligands and screens more significantly the interaction between the water solvent and the metal ion in the complex, which weakens the detainment of the aqueous environment. This results in faster motion of the Nd­(C272)3 complex both in its translation and rotation than the other complexes when migrating to the organic phase and wins over the other two ligands in transporting the metal ions from the aqueous phase to the organic phase. Depending on the solvent environment, these complexes may take two types of conformations to balance the forces from the environment benefited from their fluxionality. The migration of the M:L = 1:6 complexes, Nd­[H­(C272)2]3 and Nd­[H­(C301)2]3, was also investigated. The rich presence of the alkyl groups in the complexes screens the influence of the aqueous environment and benefits the transportation of metal ions to the interface. This work is expected to contribute to the community of inorganic chemistry interested in the coordination chemistry of metal ions and their behaviors in the condensed phase