Anion Solvation Research Articles

Size Effects on the Solvation of Anions at the Aqueous Liquid−Vapor Interface

The presence of certain anions at the aqueous liquid−vapor interface is often attributed to polarization effects. This work shows that the size of the ion also plays an important role in driving monovalent inorganic ions to the surface. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were performed to investigate the liquid−vapor interface for neat water and ionic solutions at 298 K. The total ion concentration is about 1.2 M, but the solutions contained a mixture of anions of varying size all having the same fixed charge and Lennard-Jones well depth (i.e., the same polarizability). Results show that as the size of the anion increases so does the propensity for interfacial solvation. The largest anions are consistently found closer to the interface than smaller anions. We also find that large anions, which may prefer a surface location on their own, can be excluded from the interfacial region by inclusion of even larger anions in a mixture.

Mass spectrometric method of field evaporation of ions from solutions as a potential possibility of the experimental determination of changes in the enthalpy of solvation of ions and ion clusters in electrolyte solutions

Let us consider field evaporation of ions from solutions (FEIS). An electrolyte solution is continuously fed though a metal capillary into a continuously evacuated high-vacuum chamber of a mass spectrometer. A high electric potential of a few kilovolts is applied to the capillary. At a definite solution flow rate ( 10 –4 –10 –7 cm 3 /s), ions and ion clusters are emitted from the outlet (vacuum) end of the capillary. This process is accompanied by intense electrospraying to form charged droplets. The emitted ions and ion clusters are subjected to mass spectral analysis. The sign of the charge of the ions and ion clusters is the same as the sign of the electric potential applied to the capillary. This offers a unique possibility to separately study the solvation of cations and anions in electrolyte solutions. Our experiments showed that FEIS mass spectra are well reproduced and are strongly dependent on the temperature of the solution. According to [1‐5], dealing with the FEIS mechanism, these facts indicate that a strong electric field promotes the evaporation of ions and ion clusters from a solution [1, 2, 6], rather than extracts ions with an arbitrary number of solvent molecules.

Mutual Solubilities of Water and Hydrophobic Ionic Liquids

The ionic nature of ionic liquids (ILs) results in a unique combination of intrinsic properties that produces increasing interest in the research of these fluids as environmentally friendly "neoteric" solvents. One of the main research fields is their exploitation as solvents for liquid-liquid extractions, but although ILs cannot vaporize leading to air pollution, they present non-negligible miscibility with water that may be the cause of some environmental aquatic risks. It is thus important to know the mutual solubilities between ILs and water before their industrial applications. In this work, the mutual solubilities of hydrophobic yet hygroscopic imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based ILs in combination with the anions bis(trifluoromethylsulfonyl)imide, hexafluorophosphate, and tricyanomethane with water were measured between 288.15 and 318.15 K. The effect of the ILs structural combinations, as well as the influence of several factors, namely cation side alkyl chain length, the number of cation substitutions, the cation family, and the anion identity in these mutual solubilities are analyzed and discussed. The hydrophobicity of the anions increases in the order [C(CN)(3)] < [PF(6)] < [Tf(2)N] while the hydrophobicity of the cations increases from [C(n)mim] < [C(n)mpy] < or = [C(n)mpyr] < [C(n)mpip] and with the alkyl chain length increase. From experimental measurements of the temperature dependence of ionic liquid solubilities in water, the thermodynamic molar functions of solution, such as Gibbs energy, enthalpy, and entropy at infinite dilution were determined, showing that the solubility of these ILs in water is entropically driven and that the anion solvation at the IL-rich phase controls their solubilities in water. The COSMO-RS, a predictive method based on unimolecular quantum chemistry calculations, was also evaluated for the description of the water-IL binary systems studied, where it showed to be capable of providing an acceptable qualitative agreement with the experimental data.

Charge transfer stabilization of an excess electron on a molecular surface

AbstractIn a developed molecular surface model (Jalbout and Adamowicz, Mol Phys, 2006, 19, 3101), we suggested a series of cyclohexane and cyclooctane systems with a hydrogen‐bonded network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The OH groups in this work increased the dipole moment of the complexes in order to form stable dipole bound anions. In this report we consider the dipole‐bound and solvated anions between a set of hypothetical molecular surfaces and NH3BF3. The resulting complexes are stable with respect to vertical electron detachment. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Syntheses and Crystal Structures of Linear and Zig‐zag 1D Coordination Polymers with Schiff‐base N,N′‐Type Ligands

AbstractAssembly of the Schiff‐base ligands 1,4‐bis(3‐pyridyl)2,3‐diaza‐1,3‐butadiene (N3Py) and 1,4‐bis(4‐pyridyl)‐2,3‐diaza‐1,3‐butadiene (N4Py) with different transition metal salts afforded four zig‐zag and two linear one‐dimensional (1D) chain coordination polymers, namely {[Hg(N3Py)Cl2]·CHCl3}n (1), [Hg(N3Py)I2]n (2), [Hg(N4Py)I2]n (3), {[Zn(N3Py)(NO3)2H2O]·H2O}n (4), {[Ag2(N3Py)2]·(CF3SO3)2}n (5) and {[Zn(N4Py)]·(C7H7SO3)2· (C2H5OH)2]n (6). These polymeric structures have been characterized by the single‐crystal X‐ray diffraction, FT‐IR and X‐ray powder diffraction measurements. The crystal packing fashions of these 1D chains have been analyzed, which indicates that the difference of the ligands and counter anions could significantly affect the stacking modes of these 1D chains in the crystal lattice, thus resulting in different hosting behaviors of the solvated molecules and anions. The thermal stability of complexes 1 and 6 was investigated by thermogravimetric measurements. The solid‐state phase purity has been checked by X‐ray powder diffraction measurements.

Integration of ion exchange and non-dispersive solvent extraction processes for the separation and concentration of Cr(VI) from ground waters

The focus of this work has been the study of simultaneous removal and recovery of Cr(VI) from ground waters with a high concentration of the metal (700 mg/l). The main objectives of water cleaning were the decrease of the Cr(VI) concentration down to the limits indicated by the Spanish regulations for discharge into channel waters (0.5 mg/l) and the recovery of the chromate compounds up to 15 g/l. The integration of two technologies: non-dispersive solvent extraction and anion exchange is presented as an environmental compatible solution. The final hybrid process allows the individual shortcomings of each technology to be overcome and leads to an optimum process configuration. Non-dispersive solvent extraction (NDSX) is used mainly for the concentration of the metal in a back-extraction solution and ion exchange (IE) is used for the depuration of the metal in the ground water down to 0.5 mg/l. The integrated process has been carried out on two different scales: laboratory and pilot plant, with satisfactory results being obtained.

A novel neutral receptor for selective recognition of H2PO 4 −

A new urea-based receptor was designed to selectively recognize H2PO4− among other anions (such as F-, Cl-, Br-, I-, OH-, AcO-) in organic solvent (DMSO) through intermolecular hydrogen bonding. Addition of anions to the receptor caused changes in UV–vis spectrum which provided the first indication of its anion binding ability.

Quencher–fluorophore ensemble for detection of pyrophosphate in water

We present a new example of on–off switching using a fluorescent PPi sensor system based on the quencher–fluorophore ensemble, which shows a moderate selectivity for PPi ions among other anions in an aqueous solvent.

Anion Separation with Metal–Organic Frameworks

AbstractThe application of metal–organic frameworks (MOFs) to anion separations with a special emphasis on anion selectivity is reviewed. The coordination frameworks are classified on the basis of the main interactions to the included anion, from weak and non‐specific van der Waals forces to more specific interactions such as coordination to Lewis acid metal centers or hydrogen bonding. The importance of anion solvation phenomena to the observed anion selectivities is highlighted, and strategies for reversing the Hofmeister bias that favors large, less hydrophilic anions, and for obtaining peak selectivities based on shape recognition are delineated. Functionalization of the anion‐binding sites in MOFs with strong and directional hydrogen‐bonding groups that are complementary to the included anion, combined with organizational rigidity of the coordination framework, appears to be the most promising approach for achieving non‐Hofmeister selectivity.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

AbstractSolvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and CS stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li+, calculated by the changes in intensities of the CS asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the CH stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Synthesis and Catalytic Properties in Olefin Epoxidation of Novel Iron(II) Complexes with Pyridine-Containing Macrocycles Bearing an Aminopropyl Pendant Arm

Three novel iron(II) complexes with pyridine-containing macrocycles bearing an aminopropyl pendant arm were synthesized and characterized. Crystal structures of two of the complexes revealed high-spin iron(II) centers coordinated to the five ligand nitrogen atoms with no coordination of either the solvent molecules or anions, resulting in an unusual square-pyramidal geometry. Related tetradentate ligand CRH formed a low-spin iron(II) complex (meso form was structurally characterized) with a planar arrangement of the four nitrogen atoms from the macrocycle and two axial acetonitrile molecules. Similarly to the corresponding nickel and copper complexes of the pentadentate ligands, the protonation of the amino group on the ligand arm in iron(II) complexes was found to be reversible. Spectral changes and magnetic susceptibility measurements indicated that a change in the geometry and spin state of the metal center is associated with this acid-base process. In the presence of noncoordinating acids (e.g., triflic acid), these complexes, as well as their nonmethylated analogue, can efficiently catalyze the epoxidation of cyclooctene and 1-decene under mild conditions, using hydrogen peroxide as the oxidant. However, in the deprotonated form or in the presence of coordinating acids like HCl, no epoxidation occurs.

Spin Crossover in a Series of Iron(II) Complexes of 2-(2-Alkyl-2H-tetrazol-5-yl)-1,10-phenanthroline: Effects of Alkyl Side Chain, Solvent, and Anion

2-(2H-Tetrazol-5-yl)-1,10-phenanthroline (HL0), its alkyl-substituted derivatives (Ln, where n = 1-8, 10, 12, 14, and 16, denoting the carbon atom number of the alkyl chain) at the 2H position of the tetrazole ring, and their iron(II) complexes (a for [Fe(L0)2], na for [Fe(Ln)2](ClO4)2, and nb for [Fe(Ln)2](BF4)2) were synthesized and characterized. The crystal structures of a, a.CH3OH, 1a.CH3OH, 1b.CH3OH.CH3CN, 2a.H2O, 2b.H2O, 4b.CH3OH, 5a.H2O, 5b.H2O, 6a, 6b, 7a, 7b, and 16a are described, along with thermal analyses. a undergoes an abrupt spin crossover (SCO) at 255 K with a hysteresis loop of 6 K. a.CH3OH, 2a.H2O, and 2b.H2O exhibit irreversible SCO behaviors due to the loss of solvent molecules upon heating. 3a, 3b, 4a, and 5a.H2O show simple spin transitions above 350 K. The desolvated samples of 4b.CH3OH and 5b.H2O undergo two-step spin transitions. 16a exhibits a two-step SCO behavior between 100 and 300 K, corresponding to sequential phase transitions from the low-spin (LS) phase to the intermediate phase and then to the high-spin phase, respectively, proved by crystal structure analysis and 57Fe Mössbauer spectroscopy. 1a.CH3OH, 10a, 10b, 12a, 12b, 14a, 14b, and 16b show gradual and incomplete SCO behaviors after cooling down from 400 K. 1b.CH3OH.CH3CN, 6a, 6b, 7a, 7b, 8a, and 8b remain in the LS state even at 400 K. This proves that the alkyl side chains, together with the solvent molecules and anions, play a crucial role in the complicated SCO behaviors in this system.

Computational study of anion solvation in nitrobenzene

The solvation of anions in nitrobenzene was investigated by the polarizable continuum model (PCM). The PCM was parameterized from structural information obtained by molecular dynamics simulations (MD) of anionic solutions in nitrobenzene. The parameterization was performed against experimental free energies of solvation for 22 anions containing H, C, N, O, F, S, Cl, Br, Se, and I atoms. The calculated Gibbs free energies of solvation present a mean absolute deviation from the experimental data of 2.4 kcal/mol. Hartree–Fock and DFT computations produce equivalent results.

The anionic chain process mechanism for reactions of perchlorofluoroethanes with nucleophiles in solution: a theoretical study

AbstractAnionic chain process mechanism (including reactions (1)–(4)) suggested by the experimental investigations for the reactions of nucleophile (CH3O−) with perchlorofluoroethanes CF2ClCCl3 (1), CF2ClCCl2F (2), and CF3CCl3 (3) in solution is examined by performing calculations using the B3LYP method and the SCIPCM (self‐consistent isodensity polarizable continuum) model for simulating solution effects. The SCIPCM‐B3LYP calculations indicate that anionic species have large solvation energies and solvation energy values for different kinds of anions are quite different, which effects changes in ΔH's for the reactions in solution. Competition between anionic hyperconjugation and solvation leads to negative ΔH values for reactions (2) from 1 and 2 in solution. Reactions (3) and (4) from 1, 2, and 3 in solution are predicted to be exothermic or highly exothermic. Since the ΔH values for reactions (1) and (2) from 1 and 2 in solution are negative or small positive values, the reactions of CH3O− with 1 and 2 in solution proceed via the anionic chain process. For 3 in solution, reactions (1) and (2) are endothermic while reactions (3) and (4) are exothermic or highly exothermic. The reactions of CH3O− with 3 in solution may proceed via the anionic chain process. All these conclusions are in agreement with the experimental indications for reactions of nucleophiles with 1, 2, and 3 in solution. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Facilitated Supported Liquid Membrane Transport of Hg2+ Using Calix[4]arene Derivatives

The transport behavior of Hg2+ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivatives (1 and 2) as carriers and Celgard 2400 and Celgard 2500 as the solid support. The effect of solvent type and anions such as chloride and nitrate ions on the transport of Hg2+ was examined. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene. The transport efficiency on the liquid membrane transport was dependent on the type of solvent, anion, and carrier.

Influence of the Hofmeister Anions on Protein Stability As Studied by Thermal Denaturation and Chemical Shift Perturbation

The influence of external cosolutes on the thermal stability of the B1 domain of protein L (ProtL) has been studied by circular dichroism, fluorescence spectroscopy, and differential scanning calorimetry. The thermal denaturation midpoint is effectively modulated by the addition of a suite of anions and follows the Hofmeister series. The maximum increase in thermostability (corresponding to 14 degrees C) was observed in the presence of 1 M sodium sulfate. After conversion of the experimental data into the change in the virial coefficient, a mechanistic model was used to estimate the relative contributions from excluded volume and preferential anion solvation for each anion. As expected, the excluded volume term stabilizes the native conformation of ProtL for all the cosolutes, but opposite effects on protein stability arise from the anion's solvation depending on their tendency to interact with or to become excluded from the protein surface. This behavior is in agreement with the results of independent NMR experiments: the anions that strongly interact with the protein surface produce significant perturbations in the amide protein chemical shift (delta d23(HN)). A correlation obtained between delta d23(HN) and the temperature coefficients for the different amide protons provides qualitative information about the structural determinants for the interaction between the protein surface and the cosolute.

Molecular Dynamics Study of Gas−Liquid Aqueous Sodium Halide Interfaces. I. Flexible and Polarizable Molecular Modeling and Interfacial Properties

Gas−liquid interfacial structures of NaCl and NaI aqueous solutions are investigated via molecular dynamics simulations using a flexible and polarizable water model we have developed. The new five-site model of water aims at suitably describing interfacial properties, including vibrational sum frequency spectroscopy where both flexibility and polarization are crucial. The performance of the water model is systematically examined and demonstrated by a number of properties of bulk and interface, including density, vaporization energy, dipole moment, diffusion coefficient, radial distribution function, infrared and Raman spectra of the O−H stretching region, surface potential, and surface excess of ions. The orientational structure of surface water is investigated in detail in connection with the issue of surface solvation of anions. These investigations will be utilized to analyze the sum frequency generation spectra in relation to the orientational structure at the molecular level.

Solvation of monovalent anions in acetonitrile and N, N-dimethylformamide: Parameterization of the IEF-PCM model

The present work reports the parameterization of the polarizable continuum model for predicting the free energies of solvation for monovalent anions in acetonitrile and N, N-dimethylformamide. The parameterization of the model for acetonitrile employed the experimental free energies of solvation for a set of 12 charged solutes, containing H, C, N, O, S, F, Cl, Br, and I atoms. For the N, N-dimethylformamide solutions, experimental solvation free energies for 11 monovalent anions were used. A mean absolute error of 0.7 kcal/mol in the solvation free energies has been achieved for the 12 anions in acetonitrile, whereas the mean absolute error for the 11 anions corresponds to 0.5 kcal/mol in N, N-dimethylformamide. These results indicate that the polarizable continuum model is a suitable methodology for the study of thermodynamic effects in solutions of monovalent anions in both solvents.

A simple and selective method for the separation of Cu radioisotopes from nickel

Separation of copper radioisotopes from a nickel target is normally performed using solvent extraction or anion exchange rather than using cationic exchange. A commonly held opinion is that cationic exchangers have very similar thermodynamic complexation constants for metallic ions with identical charges, therefore making the separation very difficult or impossible. The results presented in this article indicate that the selectivity of Chelex-100 (a cationic ion exchanger) for Cu radioisotope and Ni ions not only depends on the thermodynamic complexation constant in the resin but also markedly varies with the concentration of mobile H+. In our developed method, separation of copper radioisotopes from a nickel target was fulfilled in a column filled with Chelex-100 via controlling the HNO3 concentration of the eluent, and the separation is much more effective, simple and economical in comparison with the common method of anion exchange. For an irradiated nickel target with 650 mg Ni, after separation, the loss of Cu radioisotopes in the nickel portion was reduced from 30% to 0.33% of the total initial radioactivity and the nickel mixed into the radioactive products was reduced from 9.5 to 0.5 mg. This significant improvement will make subsequent labeling much easier and reduce consumption of chelating agents and other chemicals during labeling. If the labeled agent is used in human medical applications, the developed method will significantly decrease the uptake of Ni and chelating agents by patients, therefore reducing both the stress on human body associated with clearing the chemicals from blood and tissue and the risk of various types of acute and chronic disorder due to exposure to Ni.

Solvent effect on reductive bond cleavage of 1-chloro-10-methyltribenzotriquinacene: Change from the concerted to the stepwise mechanism

Electrochemical reduction of 1-chloro-10-methyltribenzotriquinacene in benzonitrile, acetonitrile and N,N-dimethylformamide (DMF) is compared. A two-electron DISP1 mechanism was found in C 6H 5CN at glassy carbon and mercury electrodes with C–Cl bond cleavage as the rate determining step. In CH 3CN and DMF the hydrogen atom abstraction from solvent molecules by a radical formed in bond cleavage results in the one-electron process. In the above-mentioned solvents an analysis of a potential dependence of the transfer coefficient, obtained from convoluted voltammetric curves at mercury electrode, showed the concerted mechanism. A change from the stepwise process in C 6H 5CN to the concerted one in CH 3CN and DMF is explained by acceleration of bond cleavage in the radical anion due to stronger solvation of product chloride anions by CH 3CN and DMF.