Liquid-Liquid Extraction of the Eu(III) Cation by BTP Ligands into Ionic Liquids: Interfacial Features and Extraction Mechanisms Investigated by MD Simulations.

What happens at the ionic-liquid (IL)/water interface when the Eu cation is complexed and extracted by bis(dimethyltriazinyl) pyridine "BTP" ligands has been investigated by molecular dynamics and potential of mean force simulations on the interface crossing by key species: neutral BTP, its protonated BTPH form, Eu, and the Eu(BTP) complex. At both the [BMI][TfN]/water and [OMI][TfN]/water interfaces, neither BTP nor Eu(BTP) are found to adsorb. The distribution of Eu(BTP) and Eu(BTP) precursors of Eu(BTP), and of their nitrate adducts, implies the occurrence of a stepwise complexation process in the interfacial domain, however.

Formation of Aqueous Biphasic Systems with an Ionic Liquid Induced by Metallic Salts: Nanoscopic Views from Molecular Dynamics Simulations.

The formation of aqueous biphasic systems (ABSs) based on aqueous ionic liquid (IL)/salt mixtures has been investigated via molecular dynamics simulations (with IL butyl-methyl-imidazolium triflate; salts NaCl, CsCl, SrCl, and EuCl). The analysis of ion distributions, solvation, and mutual interactions during the dynamics reveals the heterogeneity of all solutions due to ion segregation into mutually exclusive IL and salt domains, even in monophasic solutions ("ionic sociology"). Ion segregation and ABS formation are found to increase with (i) the salt content and (ii) the IL content, (iii) in the order Na < Sr < Eu, and (iv) when the IL ion "polarity" is diminished, following experimental trends.

Assembly Mechanism of Zr-Containing and Other TM-Containing Polyoxometalates.

The mechanism by which Zr-substituted and other transition metal-substituted polyoxometalates (POMs) form covalently linked dimers has been analyzed by means of static density functional theory (DFT) calculations with a continuous solvent model as well as Car-Parrinello molecular dynamics (CPMD) simulations with explicit solvent molecules. The study includes different stages of the process: the formation of the active species by alkalination of the solution and formation of intercluster linkages. CPMD simulations show that the Zr-triaqua precursor, [WOZr(HO)], under basic conditions, reacts with hydroxide anions to form Zr-aqua-hydroxo active species, [WOZr(OH)(HO)].

Formation of Long, Multicenter π-[TCNE] Dimers in Solution: Solvation and Stability Assessed through Molecular Dynamics Simulations.

Purely organic radical ions dimerize in solution at low temperature, forming long, multicenter bonds, despite the metastability of the isolated dimers. Here, we present the first computational study of these π-dimers in solution, with explicit consideration of solvent molecules and finite temperature effects. By means of force-field and ab initio molecular dynamics and free energy simulations, the structure and stability of π-[TCNE] (TCNE=tetracyanoethylene) dimers in dichloromethane have been evaluated.

Uranyl extraction by N,N-dialkylamide ligands studied using static and dynamic DFT simulations.

We report DFT static and dynamic studies on uranyl complexes [UO(2)(NO(3))x(H(2)O)(y)L(z)](2-x) involved in the uranyl extraction from water to an "oil" phase (hexane) by an amide ligand L (N,N-dimethylacetamide). Static DFT results "in solution" (continuum SMD models for water and hexane) predict that the stepwise formation of [UO(2)(NO(3))(2)L(2)] from the UO(2)(H(2)O)(5)(2+) species is energetically favourable, and allow us to compare cis/trans isomers of penta- and hexa-coordinated complexes and key intermediates in the two solvents. DFT-MD simulations of [UO(2)(NO(3))(2)L(2)], [UO(2)(NO(3))(2)(H(2)O)L(2)], and [UO(2)(NO(3))(H(2)O)L(2)](+) species in explicit solvent environments (water, hexane, or the water/hexane interface) represented at the MM or full-DFT level reveal a versatile solvent dependent binding mode of nitrates, also evidenced by metadynamics simulations.

Distributed polarizability models for imidazolium-based ionic liquids.

Quantum chemical calculations are used to derive distributed polarizability models sufficiently accurate and compact to be used in classical molecular dynamics simulations of imidazolium-based room temperature ionic liquids. Two distributed polarizability models are fitted to reproduce the induction energy of three imidazolium cations (1,3-dimethyl-, 1-ethyl-3-methyl-, and 1-butyl-3-methylimidazolium) and four anions (tetrafluoroborate, hexafluorophosphate, nitrate, and thiocyanate) polarized by a point charge located successively on a grid of surrounding points. The first model includes charge-flow polarizabilities between first-neighbor atoms and isotropic dipolar polarizability on all atoms (except H), while the second model includes anisotropic dipolar polarizabilities on all atoms (except H).

Nature of Zr-monosubstituted monomeric and dimeric polyoxometalates in water solution at different pH conditions: static density functional theory calculations and dynamic simulations.

Static density functional theory (DFT) calculations with a continuous solvent model as well as classical and Car-Parrinello molecular dynamics (MD) simulations with explicit solvent molecules were performed to study the nature of Zr-monosubstituted monomeric and dimeric polyoxometalates (POMs) in water at different pHs. We have analyzed Zr-aqua, -hydroxo, and -aqua-hydroxo species derived from Linqvist- and Keggin-type anions. Both DFT and Car-Parrinello MD methods suggest that the Zr center tends to have coordination number greater than 6 and can bind up to 3 water molecules.

Structure of a uranyl peroxo complex in aqueous solution from first-principles molecular dynamics simulations.

Static ab initio and density-functional computations, as well as Car-Parrinello molecular dynamics simulations in aqueous solution are reported for [UO2(OH)(κ(2)-O2)(H2O)2](-) and [UO2(OH)2(κ(1)-O2H)(H2O)](-). Whereas the κ(1)-hydroperoxo isomer is found to be more stable than the κ(2)-peroxo form in the gas phase, the order of stability is reversed in explicit bulk solution. Based on free energies from thermodynamic integration (BLYP functional), the peroxo form is favoured by ca.

Speciation of La(III) chloride complexes in water and acetonitrile: a density functional study.

Car-Parrinello molecular dynamics (CMPD) simulations and static computations are reported at the BLYP level of density functional theory (DFT) for mixed [LaCl(x)(H(2)O)(y)(MeCN)(z)](3-x) complexes in aqueous and nonaqueous solution (acetonitrile). Both methodologies predict coordination numbers (i.e.

Bromide complexation by the Eu(III) lanthanide cation in dry and humid ionic liquids: a molecular dynamics PMF study.

We report a molecular dynamics study on the EuBr(n)(3-n) complexes (n=0 to 6) formed upon complexation of Br(-) by Eu(3+) in the [BMI][PF(6)], [BMI][Tf(2)N] and [MeBu(3)N][Tf(2)N] ionic liquids (ILs), to compare the effect of the IL anion (PF(6)(-) versus Tf(2)N(-)), the IL cation (BMI(+) versus MeBu(3)N(+)) and the "IL humidity" on their solvation and stability. In "dry" solutions all complexes remain stable and the first coordination shell of Eu(3+) is purely anionic (Br(-) and IL anions), surrounded by IL cations (BMI(+) or MeBu(3)N(+) ions). Long range "onion type" solvation features (up to 20 Å from Eu(3+)), with alternating cation-rich and anion-rich solvent shells, are observed around the different complexes.

Perrhenate complexation by uranyl in traditional solvents and in ionic liquids: a joint molecular dynamics/spectroscopic study.

The complexation of perrhenate (ReO(4)(-)) anions by the uranyl (UO(2)(2+)) cation has been investigated by joint molecular dynamics simulations and spectroscopic (UV-vis, TRLFS, and EXAFS) studies in aqueous solution, acetonitrile, and three ionic liquids (ILs), namely, [Bmi][Tf(2)N], [Me(3)BuN][Tf(2)N], and [Bu(3)MeN][Tf(2)N] that are based on the same Tf(2)N(-) anion (bis(trifluoromethylsulfonyl)imide) and either Bmi(+) (1-butyl,3-methylimidazolium), Me(3)BuN(+), or Bu(3)MeN(+) cations. They show that ReO(4)(-) behaves as a weak ligand in aqueous solution and as a strong ligand in acetonitrile and in the ILs. According to MD simulations in aqueous solution, the UO(2)(ReO(4))(2) complex quickly dissociates to form UO(2)(H(2)O)(5)(2+), while in acetonitrile, a stable UO(2)(ReO(4))(5)(3-) species forms from dissociated ions.

Water versus acetonitrile coordination to uranyl. Effect of chloride ligands.

Optimizations at the BLYP and B3LYP levels are reported for the mixed uranyl chloro/water/acetonitrile complexes [UO(2)Cl(n)(H(2)O)(x)(MeCN)(5-n-x)](2-n) (n = 1-3) and [UO(2)Cl(n)(H(2)O)(x)(MeCN)(4-n-x)](2-n) (n = 2-4), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello molecular dynamics (CPMD) simulations have been performed for [UO(2)Cl(2)(H(2)O)(MeCN)(2)] in the gas phase and in a periodic box of liquid acetonitrile. According to population analyses and dipole moments evaluated from maximally localized Wannier function centers, uranium is less Lewis acidic in the neutral UO(2)Cl(2) than in the UO(2)(2+) moiety.

Insights into uranyl chemistry from molecular dynamics simulations.

First-principles and purely classical molecular dynamics (MD) simulations for complexes of the uranyl ion (UO(2)(2+)) are reviewed. Validation of Car-Parrinello MD simulations for small uranyl complexes in aqueous solution is discussed. Special attention is called to the mechanism of ligand-exchange reactions at the uranyl centre and to effects of solvation and hydration on coordination and structural properties.

Liquid-liquid extraction of pertechnetic acid (TcVII) by tri-n-butyl phosphate: where is the proton? A molecular dynamics investigation.

We report a molecular dynamics study on pertechnetic acid (PTA) extraction from water to an oil phase containing either pure TBP (tri-n-butyl phosphate) or a TBP/n-hexane mixture, with the main aim to understand the state of the acid (associated TcO(4)H vs dissociated TcO(4)(-)H(+)) and its "complexation" by TBP. Experimentally, Tc(VII) is extracted from acidic water to TBP:alkane solutions in 1:3 or 1:4 Tc:TBP ratio, suggesting that three or four TBPs coordinate to TcO(4)H or TcO(4)(-). According to simulations in TBP solution, however, neither TcO(4)H nor TcO(4)(-) species displays specific coordination to TBP.

Water versus acetonitrile coordination to uranyl. Density functional study of cooperative polarization effects in solution.

Optimizations at the BLYP and B3LYP levels are reported for mixed uranyl-water/acetonitrile complexes [UO(2)(H(2)O)(5-n)(MeCN)(n)](2+) (n = 0-5), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello molecular dynamics (CPMD) simulations have been performed for these complexes in the gas phase, and for selected species (n = 0, 1, 3, 5) in a periodic box of liquid acetonitrile. According to structural and energetic data, uranyl has a higher affinity for acetonitrile than for water in the gas phase, in keeping with the higher dipole moment and polarizability of acetonitrile.

Complexation of Cs+, K+ and Na+ by norbadione A triggered by the release of a strong hydrogen bond: nature and stability of the complexes.

Norbadione A (NBA) is a pigment present in edible mushrooms which is presumed to selectively complex Cs(+) cations. Due to a very uncommon complexation mechanism, we used a combination of several experimental techniques, including (1)H-NMR, (133)Cs-NMR, isothermal calorimetric, potentiometric titrations and molecular dynamics MD simulations to determine the nature of the complexed species, as well as their stability constants for the NBA-M(+) systems (M(+) = Cs(+), K(+), Na(+)) in methanol:water 80:20 solutions at 25.0 degrees C.

Effect of counterions on the structure and stability of aqueous uranyl(VI) complexes. A first-principles molecular dynamics study.

The inclusion of NH(4)(+) as counterions in Car-Parrinello molecular dynamics (CPMD) simulations of anionic uranyl(VI) complexes is proposed as a viable approach to modeling "real" aqueous solutions. For [UO(2)F(4)(H(2)O)](2-) in water, it is shown that the inclusion of two NH(4)(+) ions strengthens the bond between uranyl and the water ligand by ca. 2 kcal/mol, improving the accordance with experiment.

Ion aggregation in concentrated aqueous and methanol solutions of polyoxometallates Keggin anions: the effect of counterions investigated by molecular dynamics simulations.

Aqueous solutions of the polyoxometallate alpha-PW(12)O(40)(3-) Keggin anion "PW(3-)" have been simulated by molecular dynamics, comparing two anion concentrations (0.06 and ca. 0.

Chloride complexation by uranyl in a room temperature ionic liquid. A computational study.

The stepwise addition of 1 to 4 Cl(-) anions to the uranyl cation has been studied via potential of mean force (PMF) calculations in the [BMI][Tf 2N] ionic liquid based on the 1-butyl-3-methylimidazolium cation (BMI(+)) and the bis(trifluoromethylsulfonyl)imide anion (Tf2N(-)). According to these calculations, the four Cl(-) complexation reactions are favored and UO2Cl4(2-) is the most stable chloride complex in [BMI][Tf2N]. The solvation of the different chloro-complexes is found to evolve from purely anionic (ca.

Density functional theory study of uranium(VI) aquo chloro complexes in aqueous solution.

Mixed uranyl aquo chloro complexes of the type [UO2(H2O)xCly]2-y (y = 1, 2, 3, 4; x + y = 4, 5) have been optimized at the BLYP, BP86, and B3LYP levels of density functional theory in vacuo and in a polarizable continuum modeling bulk water (PCM) and have been studied at the BLYP level with Car-Parrinello molecular dynamics (MD) simulations in the gas phase and in explicit aqueous solution. Free binding energies were evaluated from static PCM data and from pointwise thermodynamic integration involving constrained MD simulations in water. The computations reveal significant solvent effects on geometric and energetic parameters.

The effect of a solvent modifier in the cesium extraction by a calix[4]arene: a molecular dynamics study of the oil phase and the oil-water interface.

We report a molecular dynamics (MD) study of the effect of a fluorinated lipophilic alcohol (referred to as "cs3" by Delmau et al, Solvent Extr. Ion Exch., 2005, 23, 23) used as a phase modifier in the solvent extraction of Cs(+) NO(3)(-) by a calix[4]arene.

Solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid: a molecular dynamics study.

We report molecular dynamics studies on the solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid ([BMI][Tf2N] IL). We first consider the potential of mean force for dissociating a single Na+Cl- ion pair, showing that the latter prefers to be undissociated rather than dissociated (by ca. 9 kcal/mol), with a free energy barrier of ca.

Coordination mode of nitrate in uranyl(VI) complexes: a first-principles molecular dynamics study.

According to Car-Parrinello molecular dynamics simulations for [UO(2)(NO(3))(3)](-), [UO(2)(NO(3))(4)](2-), and [UO(2)(OH(2))(4-)(NO(3))](+) complexes in the gas phase and in aqueous solution, the nitrate coordination mode to uranyl depends on the interplay between ligand-metal attractions, interligand repulsions, and solvation. In the trinitrate, the eta(2)-coordination is clearly favored in water and in the gas phase, leading to a coordination number (CN) of 6. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, a change in free energy of +6 kcal/mol is predicted for eta(2)- to eta(1)-transition of one of the three nitrate ligands in the gas phase.

Solvation of uranium hexachloro complexes in room-temperature ionic liquids. A molecular dynamics investigation in two liquids.

We report a molecular dynamics study of the solvation of UCl(6)(-), UCl(6)(2-), and UCl(6)(3-) complexes in the [BMI][Tf(2)N] and [MeBu(3)N][Tf(2)N] ionic liquid cations based on the same anion (bis(trifluoromethylsulfonyl)imide (Tf(2)N-)) and the butyl-3-methyl-imidazolium+ (BMI+) or methyl-tri-n-butyl-ammonium (MeBu(3)N+) cation, respectively. The comparison of two electrostatic models of the complexes (ionic model with -1 charged halides versus quantum mechanically derived charges) yields similar solvation features of a given solute. In the two liquids, the first solvation shell of the complexes is positively charged and evolves from purely cationic in the case of UCl(6)(3-) to a mixture of cations and anions in the case of UCl(6)(-).

Rhodium-catalyzed hydroformylation of 1-hexene in an ionic liquid: a molecular dynamics study of the hexene/[BMI][PF6] interface.

We report a molecular dynamics study of biphasic systems involved in the rhodium-catalyzed hydroformylation of 1-hexene in the 1-butyl-3-methyl-imidazolium hexafluorophosphate ionic liquid ([BMI][PF(6)] IL). We first describe the neat [BMI][PF(6)] interfaces with hexene (the substrate) and heptanal (the linear reaction product) as organic phases. The former interface is molecularly sharp with BMI+ cations preferentially oriented "perpendicular" (i.