Structures of Th4+ aqueous solutions: insights from AIMD and metadynamics simulations

Solution chemistry of actinide ions is critical to understanding the solvation behaviors and hydrolysis process. Using tetravalent thorium ion Th4+ as a representative example, we investigate the local structures and dynamic behaviors of hydrated Th4+ ions by ab initio molecular dynamics (AIMD) simulations using the recently developed norm-conserving pseudopotentials and basis sets optimized for actinides (J.-B. Lu et al., J. Chem. Theory Comput. 2021, 17, 3360-3371). AIMD simulations reveal two distinct solvation shells, with the first shell comprising 9 water molecules at approximately rTh-O = 2.50 Å and exhibiting a tricapped trigonal prism geometry. These conclusions are confirmed through metadynamics simulations and further structural analysis. AIMD simulations also show the slight effect of temperature and counterions on the structure of the solution. The structured solvation shells of the highly charged Th4+ ion with the specific geometry, distinct from the structure of liquid water, lead to corresponding structural changes in the hydrogen bond network in water. Additionally, beyond the solvent-shared ion pair (SIP) state observed in the unbiased AIMD simulations, the metadynamics simulations reconstruct a two-dimensional free energy surface that clearly indicates the potential stability of the contact ion pair (CIP) state in the system with Cl- as a counterion. The findings in this work provide insights into the solution chemistry of actinides and serve as a reference for studying other actinide solution systems.

Theoretical insights into selective extraction of Am(III) from Cm(III) and Eu(III) with asymmetric N-heterocyclic ligands

Separation of lanthanide (Ln) and minor actinide (MA) elements and mutual separation between minor actinide elements (e.g. Am(III) and Cm(III)) represent a crucial undertaking. However, separating these elements poses a significant challenge owing to their highly similar physicochemical properties. Asymmetric N-heterocyclic ligands such as N-ethyl-6-(1H-pyrazol-3-yl)-N-(p-tolyl)picolinamide (Et-p-Tol-A-PzPy) and N-ethyl-N-(p-tolyl)-1,10-phenanthroline-2-carboxamide (ETPhenAm) have recently received considerable attention in the separation of MAs over Ln from acid solutions. By changing the central skeleton structures of these ligands and introducing substituents with different properties on the side chains, their complexation behavior with Am(III), Cm(III), and Eu(III) may be affected. In this work, we explore four different asymmetric N-containing heterocyclic ligands, namely Et-p-Tol-A-PzPy (L1), N-ethyl-6'-(1H-pyrazol-3-yl)-N-(p-tolyl)-[2,2'-bipyridine]-6-carboxamide (L2), N-ethyl-9-(1H-pyrazol-3-yl)-N-(p-tolyl)-1,10-phenanthroline-2-carboxamide (L3), and ETPhenAm (L4) using density functional theory (DFT). The calculated results demonstrate the potential of ligands L1-L4 for the extraction and separation of Am(III), Cm(III), and Eu(III). Ligand analysis shows that ligand L3 binds more easily to the central metal atom, in line with the stronger extraction capacity of L3. In spite of the higher covalence between the side chain and the central metal atom for complexes with L1-L3, the main chain seems to control the stability of the extraction complexes. The preorganized 1,10-phenanthroline backbone also further enhances the extraction performance of L3 and L4. The difference in coordination ability between the side chain donors of these ligands and metal ions may affect their separation efficiency. This work presents theoretical insights into synthesizing novel ligands for separating trivalent actinides by adjusting N-heterocyclic ligands.

Matrix-Isolation Infrared Spectra and Electronic Structure Calculations for Dinitrogen Complexes with Uranium Trioxide Molecules UO3(η1-NN)1-4

Investigations of the interactions of uranium trioxide (UO₃) with other species are expected to provide a new perspective on its reaction and bonding behaviors. Herein, we present a combined matrix-isolation infrared spectroscopy and theoretical study of the geometries, vibrational frequencies, electronic structures, and bonding patterns for a series of dinitrogen (N₂) complexes with UO₃ moieties UO₃(η¹-NN)_1-4. The complexes are prepared by reactions of laser-ablated uranium atoms with O₂/N₂ mixtures or laser-ablated UO₃ molecules with N₂ in solid argon. UO₃(η¹-NN)_1-4 are classified as "nonclassical" metal-N₂ complexes with increased Δν(N₂) values according to the experimental observations and the computed blue-shifts of N-N stretching frequencies and N-N bond length contractions. Electronic structure analysis suggests that UO₃(η¹-NN)_1-4 are σ-only complexes with a total lack of π-back-donation. The energy decomposition analysis combined with natural orbitals for chemical valence calculations reveal that the bonding between the UO₃ moiety and N₂ ligands in UO₃(η¹-NN)_1-4 arises from the roughly equal electrostatic attractions and orbital mixings. The inspection of orbital interactions from pairwise contributions indicates that the strongest orbital stabilization comes from the σ-donations of the 4σ*- and 5σ-based ligand molecular orbitals (MOs) into the hybrid 7s/6d_x²-y² MO of the U center. The electron polarization induced by electrostatic effects in the N_inner ← N_outer direction provides complementary contributions to the orbital stabilization in UO₃(η¹-NN)_1-4. In addition, the reactions of UO₃ with N₂ ligands and the origination of the nonclassical behavior in UO₃(η¹-NN)_1-4 are discussed.

Cation Complexes of Uranium and Thorium with Cyclooctatetraene: Photochemistry and Decomposition Products

Ion-molecule complexes of uranium or thorium singly-charged positive ions bound to cyclooctatetraene (COT), i.e., M⁺(COT)_1,2, are produced by laser ablation and studied with UV laser photodissociation. The ions are selected by mass and excited at 355 or 532 nm, and the ionized dissociation products are detected using a reflectron time-of-flight mass spectrometer. The abundant fragments M⁺(C₆H₆), M⁺(C₄H₄), and M⁺(C₂H₂) occur for complexes of both metals, whereas the M⁺(C₄H₂), M⁺(C₃H₃), and M⁺(C₅H₅) fragments are prominent for uranium complexes but not for thorium. Additional experiments investigate the dissociation of M⁺(benzene)_1,2 ions which may be intermediates in the fragmentation of the COT ions. The experiments are complemented by computational quantum chemistry to investigate the structures and energetics of fragment ions. Various cation-π and metallacycle structures are indicated for different fragment ions. The metal ion-ligand bond energies for corresponding complex ions are systematically greater for the thorium species. The computed thermochemistry makes it possible to explain the mechanistic details of the photochemical fragmentation processes and to reveal new actinide organometallic structures.

Magnetic coupling induced by the interaction between endohedral metal borofullerenes

Superatom-assembled materials have highly tunable magnetic and electronic properties and parameters of clusters. Here, eight superatom dimers composed of two U@B40 motifs have been studied by the density functional theory. Calculation results show that U@B40 dimers exhibit spin antiferromagnetic coupling, spin ferromagnetic coupling and nonmagnetic, that is, the magnetic coupling is induced by the interaction between the U@B40 superatoms. In addition, the monomers in U@B40 dimers still retain the superatomic orbitals, and some of the super atomic orbitals disappear due to the interaction between monomers. The assembly based on U@B40 induced a decrease in the energy gap. This study provides a basis for a deep understanding of controlling the cluster-assembled materials for tailoring their functionalities.

Porphyrinoid actinide complexes

The diverse coordination modes and electronic features of actinide complexes of porphyrins and related oligopyrrolic systems (referred to as "porpyrinoids") have been the subject of interest since the 1960s. Given their stability and accessibility, most work with actinides has focused on thorium and uranium. This trend is also seen in the case of porphyrinoid-based complexation studies. Nevertheless, the diversity of ligand environments provided by porphyrinoids has led to the stabilization of a number of unique complexes with the early actinides that are often without structural parallel within the broader coordination chemical lexicon. This review summarizes key examples of prophyrinoid actinide complexes reported to date, including the limited number of porphyrinoid systems involving transuranic elements. The emphasis will be on synthesis and structure; however, the electronic features and reactivity pattern of representative systems will be detailed as well. Coverage is through December of 2021.

2D-layered Mg(OH)2 material adsorbing cellobiose via interfacial chemical coupling and its applications in handling toxic Cd2+ and UO22+ ions

The interfacial chemistry of nanocomposite materials is of overarching importance in the separation and purification science; moreover, its understanding helps to guide synthesis, clarify structure-property relationship and unearth novel applications. However, the composites feature rather complicated local structures and hydrogen bonds are often involved in the interface and the vicinity of active sites. In this regard, density functional theory first-principle calculations associated with experimental study have synergistically examined two-dimensional (2D) magnesium hydroxide material with different layers and their adsorption toward cellobiose. Hydrogen bonds are found responsible for the interfacial coupling, which make it vital to cover the dispersion correction in the calculation. The average adsorption energy ranges from -0.29 to -0.35 eV, falling well within the range of reported hydrogen-bonding strength. On the basis of calculated structural/interfacial properties and experimental findings, the 2D Mg(OH)₂ in terms of three-layer model was unraveled to substitute toxic Cd²⁺ ion and sorb radioactive UO₂²⁺ that is coordinated by water and hydroxyl groups. These reactions are thermodynamically feasible. The ion-exchanging mechanism was proposed for cadmium removal and the outer-sphere adsorption one for uranium extraction.

Constructing the bonding interactions between endohedral metallofullerene superatoms by embedded atomic regulation

We present a possible principle that controls intercluster bonding through embedding different kinds of actinide atoms into the centre of fullerenes, thereby exhibiting different bonding forms. Moreover, these superatoms maintain the robustness of electronic structures.

Guided Ion Beam Studies of the Thorium Monocarbonyl Cation Bond Dissociation Energy and Theoretical Unveiling of Different Isomers of [Th,O,C]+ and Their Rearrangement Mechanism

Threshold collision-induced dissociation (TCID) of the thorium monocarbonyl cation, ThCO⁺, with xenon is performed using a guided ion beam tandem mass spectrometer. The only product observed is Th⁺ resulting from loss of the CO ligand. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of Th⁺-CO at 0 K as 0.94 ± 0.06 eV. Calculated BDEs at the CCSD(T) level of theory with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation are in good agreement with the experimental result. The Feller-Peterson-Dixon composite coupled-cluster methodology was also applied on both ThCO⁺ and ThCO, with contributions up to CCSDT(Q) and a four-component treatment of spin-orbit coupling effects. The final 0 K Th⁺-CO BDE of 0.94 ± 0.04 eV is in excellent agreement with the current experimental result. The ionization energy of ThCO, as well as the atomization energies and heats of formation for both ThCO and ThCO⁺, is reported at this same level of theory. Complete potential energy profiles of both quartet and doublet spin are also constructed to elucidate the mechanism for the formation and interconversion of different isomers of [Th,O,C]⁺. Chemical bonding patterns in low-lying states of ThCO⁺ and potential energy curves for ThCO⁺ dissociation are also investigated.

Enhancing the Am3+/Cm3+ separation ability by weakening the binding affinity of N donor atoms: a comparative theoretical study of N, O combined extractants

Mutual separation of trivalent americium (Am3+) and curium (Cm3+) ions through liquid-liquid extraction is challenging due to the similarity in their chemical properties. Three N, O combined extractants 2,6-pyridinedicarboxylic acid di(N-ethyl-4-fluoroanilide) (Et(pFPh)DPA), diphenyl(2-pyridyl)phosphine oxide (Ph2PyPO), and alkyldiamide amine with 2-ethylhexylalkyl chains (ADAAM(EH)) have been identified to exhibit selectivity for Am3+ over Cm3+. In this work, the structures, bonding nature, and thermodynamic behaviors of a series of representative Am- and Cm-complexes with these ligands have been systematically investigated using density functional theory (DFT) calculations. Based on our calculations, the ONO angle formed by three donor atoms of the ligand in the Am-complex is slightly larger than that in its Cm-analogue. The studied ligands show their preference toward Am3+ by opening their "mouths" slightly wider. According to the Mayer bond order and the quantum theory of atoms in molecules (QTAIM) analyses, the interactions between the O donor atoms of these ligands and Am3+ and Cm3+ ions show some weak partial covalent character, and compared to the Am-O bond, there is relatively more covalency in the Cm-O bond in the corresponding complex. However, opposite results can be found in the Am-N and Cm-N bonding for the first two ligands. Particularly, for the better separation ligand ADAAM(EH), the Am-N and Cm-N interactions are extremely weak and no covalent character exists in the bonding. Nevertheless, the difference between the very weak Am-N and Cm-N interactions still leads to a better performance of ADAAM(EH). Based on the comparison of these ligands, we can find that weakening the binding ability of N atoms in the ligand may increase the difference between the Am-N and Cm-N interactions, thus enhancing the Am3+/Cm3+ separation ability of the ligand. Our study might provide new insights into understanding the selectivity of these three N, O combined ligands toward minor actinides and pave the way for designing efficient Am3+/Cm3+ extraction and separation ligands.

Investigation of the thermal quenching of two emission centers in Sr9MnLi(PO4)7:Eu2+ using time-resolved technique

The thermal stability of the phosphors in phosphor-converted light-emitting diodes (LEDs) plays an important role in the practical application of lighting. Herein, the Mn²⁺-based red-emitting phosphors of pure and Eu²⁺-doped Sr₉MnLi(PO₄)₇ (SMPO) samples were prepared using the high temperature solid-state reaction method. The crystal field environment around the Mn²⁺ ions was analyzed by combining the results of photoluminescence excitation spectroscopy and Tanabe-Sugano diagrams. By comparing the results of X-ray photoelectron spectroscopy, two additional bands centered at about 129.8 eV and 130.7 eV were found in the Eu²⁺-doped sample, which corresponded to the chemical states of P 2p_3/2 and P 2p_1/2. Two different sets of emission spectra were observed for Sr₉MnLi(PO₄)₇:5%Eu²⁺ (SMPO:Eu²⁺) on employing the time-resolved technique. The emission peaks centered at 615 nm and 661 nm were attributed to Mn²⁺ and Eu²⁺ ions, respectively. The thermal quenching behaviors of Eu²⁺ and Mn²⁺ were investigated in the temperature range of 300-620 K and the thermal quenching mechanisms are given in this work. Systematic research on the luminescent properties of Eu²⁺ and Mn²⁺ ions in the SMPO:Eu²⁺ phosphor contributes to the understanding of the thermal stability and aids in the development of Mn²⁺-based red-emitting phosphors.

Molecular oxides of high-valent actinides

The past decade has been very productive in the field of actinide (An) oxides containing high-valent An. Novel gas-phase experimental and an impressive number of theoretical studies have been performed, mostly on pure oxides or oxides extended with other ligands. The review covers the structural properties of molecular An oxides with high (An≥V) oxidation states. The presented compounds include the actinide dioxide cations [AnO2]+ and [AnO2]2+, neutral and ionic AnOx (x = 3–6), oxides with more than one An atom like neutral dimers, trimers and dimers from cation–cation interactions, as well as large U-oxide clusters observed very recently in the gaseous phase.

Stronger Hydration of Eu(III) Impedes Its Competition against Am(III) in Binding with N-donor Extractants

The significance of understanding the interaction between actinide(III)/lanthanide(III) (An(III)/Ln(III)) and N-donor extractants lies in the importance of efficient An³⁺/Ln³⁺ separation in advanced nuclear fuel cycles and the high expectation of the application of N-donor extractants. This work reports a density functional theory study aiming at a plausible explanation of the origin of the selectivity of the ligands in An³⁺/Ln³⁺ separation and an evaluation of the influence of the bridging groups of typical N-donor extractants. Five bis(triazine) N-donor ligands were considered, differing in their denticity dictated by their bridging groups and in the flexibility of these bridging groups. The results showed much stronger hydration of Eu(III) in comparison to Am(III) in the ligand exchange of aqua ligands by N-donor ligands, while there was a moderate difference in their interaction strengths with the N-donor ligands. This implicated that the distinct difficulty in desolvating Eu(III) and Am(III) may govern their selectivity in liquid-liquid extraction. The analysis of the role of the bridging groups of the ligands confirmed the importance of a ligand to be equipped with preorganized binding sites to minimize the perturbation of entropy. We tentatively propose that this conclusion may hold in the explanation of the low selectivity of oxygenated extractants and the high selectivity of extractants with soft donors in An³⁺/Ln³⁺ separation.

Prediction of Binding Stability of Pu(IV) and PuO2(VI) by Nitrogen Tridentate Ligands in Aqueous Solution

Plutonium has potential applications in energy production in well-controlled nuclear reactors. Since nuclear power plants have great merit as environmentally friendly energy sources with a recyclable system, a recycling system for extracting Pu from spent fuels using suitable extractants has been proposed. Pu leakage is a potential environmental hazard, hence the need for chemical sensor development. Both extractants and chemical sensors involve metal–ligand interactions and to develop efficient extractants and chemical sensors, structural information about Pu ligands must be obtained by quantum calculations. Herein, six representative nitrogen tridentate ligands were introduced, and their binding stabilities were evaluated. The tridentate L6, which contains tri-pyridine chelate with benzene connectors, showed the highest binding energies for Pu(IV) and PuO₂(VI) in water. Analysis based on the quantum theory of atoms in molecular analysis, including natural population analysis and electron density studies, provided insight into the bonding characteristics for each structure. We propose that differences in ionic bonding characteristics account for the Pu-ligand stability differences. These results form a basis for designing novel extractants and organic Pu sensors.

Evaluation of Influencing Factors in Tetravalent Uranium Complex-Mediated CO2 Functionalization by Density Functional Theory

The functionalization of CO₂ mediated by a series of U(IV) mixed-sandwich compounds, (COT^TIPS2)Cp*UR (R = -CH₃, -CH₂Ph, -CH₂TMS, -CH(TMS)₂, -NHPh, -OPh, -SPh, -SePh; COT^TIPS2 = C₈H₆(SiⁱPr₃-1,4)₂; Cp* = C₅Me₅; TMS = SiMe₃), was investigated by the density functional theory method. A two-step mechanism was revealed, in which the insertion of CO₂ into the U-C bond was identified as the rate-determining step via a transition state featured by a four-membered ring with a free-energy barrier of 18.8 kcal/mol to the reaction of the (COT^TIPS2)Cp*UCH₃ system. The whole reaction was strongly exothermic by 45.0 kcal/mol. Substitution effect was discussed, including the bulkiness of the R group and the nature of the ligating atom, and steric hindrance and electrostatic interactions were found to be responsible for the observed variation in reactivity. The reactivity of U(III) and U(IV) complexes in CO₂ functionalization was also compared and discussed. The results were consistent with experimental studies and complemented with molecular level of understanding on the mechanisms of CO₂ functionalization promoted by tetravalent U complexes.

Redox and structural properties of accessible actinide(ii) metallocalixarenes (Ac to Pu): a relativistic DFT study

The redox properties of actinides play a significant role in manipulating organometallic chemistry and energy/environment science, for being involved in fundamental concepts (oxidation state, bonding and reactivity), nuclear fuel cycles and contamination remediation. Herein, a series of trans-calix[2]pyrrole[2]benzene (H₂L²) actinide complexes (An = Ac–Pu, and oxidation states of +II and +III) have been studied by relativistic density functional theory. Reduction potentials (E⁰) of [AnL²]⁺/[AnL²] were computed within −2.45 and −1.64 V versus Fc⁺/Fc in THF, comparable to experimental values of −2.50 V for [UL^1e]/[UL^1e]⁻ (H₃L^1e = (^Ad,MeArOH)₃mesitylene and Ad = adamantyl) and −2.35 V for [U(Cp^iPr)₂]⁺/[U(Cp^iPr)₂] (Cp^iPr = C₅ⁱPr₅). The E⁰ values show an overall increasing trend from Ac to Pu but a break point at Np being lower than adjacent elements. The arene/actinide mixed reduction mechanism is proposed, showing arenes predominant in Ac–Pa complexes but diverting to metal-centered domination in U–Pu ones. Besides being consistent with previously reported those of An^III/An^II couples, the changing trend of our reduction potentials is corroborated by geometric data, topological analysis of bonds and electronic structures as well as additional calculations on actinide complexes ligated by tris(alkyloxide)arene, silyl-cyclopentadiene and octadentate Schiff-base polypyrrole in terms of electron affinity. The regularity would help to explore synthesis and property of novel actinide(ii) complex.

DFT study reveals the trend of reduction potential of [AnL²]⁺/[AnL²] (An = Ac ∼ Pu), comparable to previously reported ones of An^III/An^II and corroborated by calculations of relevant complexes and structural/bonding properties of [AnL²]^+/0.

DFT Investigations of the Magnetic Properties of Actinide Complexes

Over the past 25 years, magnetic actinide complexes have been the object of considerable attention, not only at the experimental level, but also at the theoretical one. Such systems are of great interest, owing to the well-known larger spin–orbit coupling for actinide ions, and could exhibit slow relaxation of the magnetization, arising from a large anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Furthermore, more diffuse 5f orbitals than lanthanide 4f ones (more covalency) could lead to stronger magnetic super-exchange. On the other hand, the extraordinary experimental challenges of actinide complexes chemistry, because of their rarity and toxicity, afford computational chemistry a particularly valuable role. However, for such a purpose, the use of a multiconfigurational post-Hartree-Fock approach is required, but such an approach is computationally demanding for polymetallic systems—notably for actinide ones—and usually simplified models are considered instead of the actual systems. Thus, Density Functional Theory (DFT) appears as an alternative tool to compute magnetic exchange coupling and to explore the electronic structure and magnetic properties of actinide-containing molecules, especially when the considered systems are very large. In this paper, relevant achievements regarding DFT investigations of the magnetic properties of actinide complexes are surveyed, with particular emphasis on some representative examples that illustrate the subject, including actinides in Single Molecular Magnets (SMMs) and systems featuring metal-metal super-exchange coupling interactions. Examples are drawn from studies that are either entirely computational or are combined experimental/computational investigations in which the latter play a significant role.

Theoretical investigation of U(i) arene complexes: is the elusive monovalent oxidation state accessible?

With the goal to extend the uranium oxidation state, relativistic DFT unravels an energetically favored U(i) complex of a heterocalix[4]arene.

Elucidating cation–cation interactions in neptunyl dications using multi-reference ab initio theory

Understanding the binding mechanism in neptunyl clusters formed due to cation–cation interactions is of crucial importance in nuclear waste reprocessing and related areas of research.

Binding for endohedral-metallofullerene superatoms induced by magnetic coupling

To design new materials based on artificial superatoms, clarifying their involved interaction is particularly important. In this study, we discuss first-principle calculations to show that the interaction between endohedral metallofullerenes (EMFs) of U@C28 can lead to different chemical and physical adsorption structures. Especially, these structures are derived from different magnetic coupling resonances, and they can transform by changing the distance between U@C28 superatoms. These findings will promote the future development for bottom-up assembling of new functional materials and even devices.

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

The purpose of this review is to provide an overview of uranium speciation using vibrational spectroscopy methods including Raman and IR. Uranium is a naturally occurring, radioactive element that is utilized in the nuclear energy and national security sectors. Fundamental uranium chemistry is also an active area of investigation due to ongoing questions regarding the participation of 5f orbitals in bonding, variation in oxidation states and coordination environments, and unique chemical and physical properties. Importantly, uranium speciation affects fate and transportation in the environment, influences bioavailability and toxicity to human health, controls separation processes for nuclear waste, and impacts isotopic partitioning and geochronological dating. This review article provides a thorough discussion of the vibrational modes for U(IV), U(V), and U(VI) and applications of infrared absorption and Raman scattering spectroscopies in the identification and detection of both naturally occurring and synthetic uranium species in solid and solution states. The vibrational frequencies of the uranyl moiety, including both symmetric and asymmetric stretches are sensitive to the coordinating ligands and used to identify individual species in water, organic solvents, and ionic liquids or on the surface of materials. Additionally, vibrational spectroscopy allows for the in situ detection and real-time monitoring of chemical reactions involving uranium. Finally, techniques to enhance uranium species signals with vibrational modes are discussed to expand the application of vibrational spectroscopy to biological, environmental, inorganic, and materials scientists and engineers.

Computational chemical analysis of Eu(iii) and Am(iii) complexes with pnictogen-donor ligands using DFT calculations

We demonstrated density functional calculations of Eu(iii) and Am(iii) complexes with pnictogen-donor (X) ligands, (CH3)2X-CH2-CH2-X(CH3)2 (X = N, P, As and Sb). We investigated the optimized structures of the complexes and the Gibbs energy differences in the complex formation reactions. The results indicated that the N- and P-donor ligands exhibit Am(iii) ion selectivity over Eu(iii) ions; especially, the P-donor ligand showed the highest selectivity. The tendency of the Am(iii)/Eu(iii) selectivity by the pnictogen-donor ligands was found to be comparable to that of the soft acid classification in the hard and soft acids and bases rule. Mulliken's spin population analysis indicated that the bonding properties between the metal ion and the pnictogen atoms correlated with the Am(iii)/Eu(iii) selectivity. In particular, the participation of f-orbital electrons of the metal ion in the covalency was indicated to play an important role in the selectivity.

Modelling uranyl chemistry in liquid ammonia from density functional theory

We developed a computationally efficient protocol based on Density Functional Theory (DFT) and a continuum solvation model (CSM) to predict reaction free energies of complexation reactions of uranyl in liquid ammonia. Several functionals have been tested against CCSD(T) and different CSMs have been assessed relative to Car-Parrinello Molecular Dynamics (CPMD) simulations in explicit solvent.

On the multi-reference nature of plutonium oxides: PuO22+, PuO2, PuO3 and PuO2(OH)2

Actinide-containing complexes present formidable challenges for electronic structure methods due to the large number of degenerate or quasi-degenerate electronic states arising from partially occupied 5f and 6d shells. Conventional multi-reference methods can treat active spaces that are often at the upper limit of what is required for a proper treatment of species with complex electronic structures, leaving no room for verifying their suitability. In this work we address the issue of properly defining the active spaces in such calculations, and introduce a protocol to determine optimal active spaces based on the use of the Density Matrix Renormalization Group algorithm and concepts of quantum information theory. We apply the protocol to elucidate the electronic structure and bonding mechanism of volatile plutonium oxides (PuO₃ and PuO₂(OH)₂), species associated with nuclear safety issues for which little is known about the electronic structure and energetics. We show how, within a scalar relativistic framework, orbital-pair correlations can be used to guide the definition of optimal active spaces which provide an accurate description of static/non-dynamic electron correlation, as well as to analyse the chemical bonding beyond a simple orbital model. From this bonding analysis we are able to show that the addition of oxo- or hydroxo-groups to the plutonium dioxide species considerably changes the π-bonding mechanism with respect to the bare triatomics, resulting in bent structures with a considerable multi-reference character.

Could new U(ii) complexes be accessible via tuning hybrid heterocalix[4]arene? A theoretical study of redox and structural properties

A relativistic DFT study unravels the possible accessibility of several intriguing divalent uranium complexes by tuning building blocks of hybrid heterocalix[4]arene, which are stabilized by δ(U–Ar) bonds and corroborated by computed U^III/II reduction potentials.

In silico prediction of drug-target interaction networks based on drug chemical structure and protein sequences

Analysis of drug–target interactions (DTIs) is of great importance in developing new drug candidates for known protein targets or discovering new targets for old drugs. However, the experimental approaches for identifying DTIs are expensive, laborious and challenging. In this study, we report a novel computational method for predicting DTIs using the highly discriminative information of drug-target interactions and our newly developed discriminative vector machine (DVM) classifier. More specifically, each target protein sequence is transformed as the position-specific scoring matrix (PSSM), in which the evolutionary information is retained; then the local binary pattern (LBP) operator is used to calculate the LBP histogram descriptor. For a drug molecule, a novel fingerprint representation is utilized to describe its chemical structure information representing existence of certain functional groups or fragments. When applying the proposed method to the four datasets (Enzyme, GPCR, Ion Channel and Nuclear Receptor) for predicting DTIs, we obtained good average accuracies of 93.16%, 89.37%, 91.73% and 92.22%, respectively. Furthermore, we compared the performance of the proposed model with that of the state-of-the-art SVM model and other previous methods. The achieved results demonstrate that our method is effective and robust and can be taken as a useful tool for predicting DTIs.

Computational study of Th(4+) and Np(4+) hydration and hydrolysis of Th(4+) from first principles

The aqueous solvation of Th and Np in the IV oxidation state was examined using cluster models generated by Monte Carlo simulations and density functional theory embedded within the COSMO continuum model to approximate the effect of bulk water. Our results suggest that the coordination number (CN) for both Th(IV) and NP(IV) should be 9, in accordance to some experimental and theoretical results from the literature. The structural values for average oxygen-metal distances are within 0.01 Å compared to experimental data, and also within the experimental error. The calculated ΔG _Sol⁰ are in very good agreement with experimental reported values, with deviations at CN = 9 lower than 1% for both Th(IV) and Np(IV). The hydrolysis constants are also in very good agreement with experimental values. Finally, this [corrected] methodology has the advantage of using a GGA functional (BP86) that not only makes the calculations more affordable computationally than hybrid functional or ab initio molecular dynamics simulations (Car-Parrinello) calculations, but also opens the perspective to use resolution of identity (RI) calculations for more extended systems.