Volume 80, Issue 6

The 30th International Conference on Solution Chemistry (ICSC 30) was held at Murdoch University, Perth, Western Australia, 16-20 July 2007. Under the proficient chairmanship of Prof. Glenn Hefter, about 100 participants from more than 20 countries from all parts of the world gathered down under not only to discuss science but also to enjoy the relaxed Australian lifestyle and the picturesque scenery surrounding Perth. A representative selection of the many excellent and timely contributions presented at the Conference is collected in this issue of Pure and Applied Chemistry . This continues a tradition of regular publication coverage of this series over many years, http://www.iupac.org/publications/pac/conferences/ family/ICSC/, and thus enriches a record of ongoing progress in theoretical and experimental solution chemistry. Subjects covered by ICSC 30 include computer modeling of solution structure and dynamics (Hofer, Bowron); simulation of nanocolloidal suspensions (Turq); ion solvation and association (Buchner); polyelectrolyte hydration (Vlachy); aqueous mixtures of hydrophilic and -phobic ions (Kumar); spin-state transitions in solution (Linert); prediction of multiphase chemical equilibria with applications to hydrometallurgy (Eriksson); chemical speciation of polynuclear complexes (Torres); synthesis, solubility, and stability of minerals (Williams); ternary mixtures involving ionic liquids (MacFarlane); and structure of biological macromolecules in mixed solvents (Yamaguchi). The Conference Editor wishes to thank all authors for their contributions to this issue. The 31st International Conference on Solution Chemistry will be organized by Prof. Bernd M. Rode, Dr. Bernhard Randolf, and Dr. Thomas Hofer in Innsbruck, Austria, 21-25 August 2009 (http://icsc2009.org/). Erich Königsberger Conference Editor

As a result of recent methodological developments in connection with enhanced computational capacity, theoretical methods have become increasingly valuable and reliable tools for the investigation of solutions. Simulation techniques utilizing a quantum mechanical (QM) approach for the treatment of the chemically most relevant region so-called hybrid quantum mechanical/molecular mechanical (QM/MM) simulations have reached a level of accuracy that often equals or may even surpass experimental methods. The latter is true in particular whenever ultrafast (i.e., picosecond) dynamics prevail, such as in labile hydrates or structure-breaking systems. The recent development of an improved QM/MM framework, the quantum mechanical charge field (QMCF) ansatz, enables a broad spectrum of solute systems to be elucidated. As this novel methodology does not require any solute solvent potential functions, the applicability of the QMCF method is straightforward and universal. This advantage is bought, however, at the price of a substantial increase of the QM subregion, and an attendant increase in computational periods to levels of months, and even a year, despite parallelizing high-performance computing (HPC) clusters. Molecular dynamics (MD) simulations of chemical systems showing increasing complexity have been performed, and demonstrate the superiority of the QMCF ansatz over conventional QM/MM schemes. The systems studied include Pd 2+ , Pt 2+ , and Hg 2 2+ , as well as composite anions such as PO 4 3- and ClO 4 - .

This article presents an overview of the use of the empirical potential structure refinement (EPSR) technique for generating three-dimensional atomistic models of liquids and structurally disordered solids that are consistent with experimental neutron and X-ray scattering data. The extension of this technique through the calculation of extended X-ray absorption fine structure (EXAFS) spectra is outlined, and the benefits of this are demonstrated for a range of systems and in particular for our ability to address structural questions of importance in solution chemistry. The model systems chosen as examples for structural analysis are (i) liquid gallium, (ii) silica glass, and (iii) a 1 m aqueous solution of YCl 3 . The advantages of this analytical approach for addressing chemically specific structural questions in disordered systems are discussed within the context of the experimental alternatives based on the techniques of neutron scattering with isotopic substitution and anomalous X-ray scattering.

A coarse-grain description of nanocolloidal suspensions in the presence of an added salt is presented here. It enables us to simulate trajectories of the nanoparticles from effective functions that depend on average densities of salt ions. In practice, the ion-averaged effective potential is used as input of a Brownian dynamics (BD) simulation. This potential may be derived by various methods, ranging from purely analytical to fully numerical ones. For the description of dynamical properties, this simulation also requires an effective diffusion coefficient that must be calculated or experimentally determined, and that accounts for the effects of microions on the mobility of the nanoparticles. The different versions of our coarse-graining procedure are applied to the case of a maghemite suspension, for which an explicit description of all ions would be very time-consuming.

Ion solvation and ion association are key features of ion-solvent interactions, and their balance largely determines structure, thermodynamics, and dynamics of electrolyte solutions. Despite being studied for many years with various techniques, these effects are still intriguing because too often results obtained with different methods-each having its individual merits and limitations-cannot be connected properly due to lacking information. In this contribution, we would like to bring dielectric relaxation spectroscopy (DRS) as a further tool for solution studies to the attention of the audience. The principles of DRS and the required instrumentation are briefly introduced. The major focus will be on the kind of results obtained with this technique regarding ion solvation and association and how this information compares with results obtained from other techniques.

A short review of recent theoretical and experimental advances in studies of polyelectrolyte solutions is presented. The focus is on ion-specific effects as revealed in measurements of osmotic pressure and enthalpy of dilution. We review the experimental results for two different polyelectrolyte systems: (i) salts of polyanetholesulfonic acid, and (ii) aliphatic ionenes (polycations) in aqueous solution with various counterions. A theoretical approach based on the extension of Wertheim's integral equation theory [ J. Stat. Phys. 35 , 19 (1984)] is used to analyze the experimental data. Preliminary results, based on the all-atom simulation of model 3,3 ionene oligomers, are discussed in the light of polyelectrolyte hydration.

Ions of both hydrophilic and -phobic nature play a pivotal role in biological systems and during synthesis of many organic molecules. However, the interaction of a hydrophilic ion with a hydrophobic one is not a simple physical process and is useful in understanding the rate enhancement in organic transformations and thermal stability of DNA and RNA. During the talk, an attempt was made to present some of the experimental work on aqueous mixtures of these ions carried out at National Chemical Laboratory, Pune, and give a theoretical interpretation of the binary, ternary, and quaternary interactions operating in these systems. The contribution of these interaction terms to the excess free energy of mixing, Δ m G E , will be analyzed.

Thermal induced spin transitions between low- and high-spin states of Fe(II) complexes are commonly observed in the solid state. Cooperative effects, such as abrupt and two-step spin crossover, are typical for these objects and arise from intermolecular interactions described by several formalisms. These phenomena appear as deviations from the linearity of the respective van't Hoff plots. In solutions, molecular interactions manifest themselves in isoequilibrium relationships (IERs) as well as in a few cases of specific deviations of van't Hoff plots from linearity. The nature of these phenomena will be discussed on the basis of a statistical-thermodynamic model of spin crossover.

The integrated thermochemical databank system FactSage enables the user to calculate equilibria and thermodynamic properties for a wide variety of multicomponent, multiphase systems and reactions. The Gibbs energy models and databases for condensed, gaseous, and aqueous solutions presently implemented in FactSage are of interest to chemical and physical metallurgy, chemical and corrosion engineering, inorganic and solution chemistry, geochemistry, environmental science, etc. Models for the aqueous phase include the Pitzer and Helgeson formalisms, but data and subroutines for concentrated aqueous solutions have also been provided by OLI Systems. ChemApp is a programmer's library for thermochemistry that also incorporates the Gibbs energy minimizer of FactSage. Applications of ChemApp include, for example, the handling of repetitive complex equilibrium calculations in application-specific programs and its linking to third-party process simulation packages. In this work, user-defined aqueous solution models in FactSage and ChemApp have been applied to the hydrometallurgical processing of aluminum ores in both caustic and acidic leach solutions.

Polynuclear complexes are widely regarded as potential materials in separation, catalysis, gas storage, and molecular recognition. Those complexes including lanthanide (Ln) ions in the heterobimetallic assembly enhance the structural flexibility and increase the thermodynamic stability. Up to now, the studies on these heteropolynuclear complexes have been mostly focused on lanthanide-copper compounds in the solid state. We have expanded the studies to solution chemistry, to know if such polynuclear species can also exist in aqueous solution. In this work, potentiometric titrations (25.0 °C, and I = 0.50 M Me 4 NCl) were carried out for systems containing a Ln ion (La, Ce, Sm), a bridging ligand (oda or ida), and a second metal ion. We found that polynuclear units can be formed with M II (Mn, Fe, Co, Ni, Cu, Zn, Cd, and VO 2+ ) and M III (Fe, Al) ions, and can be predominant in aqueous solution. Species like [Ln 2 M 3 L 6 ] or [Ln 2 M 3 L 6 (OH) n ] n- ( n = 3, 6) can exist in solution, representing the same 2:3:6 stoichiometry found in the solid state. The presence of an amino group in the ida ligand makes the mononuclear complexes with 3 d metal ions more stable, preventing to some extent the formation of polynuclear complexes.

Titration of aqueous copper(II) sulfate solutions with aqueous NaOH at temperatures ranging from 0 to 25 °C results in a complex Ostwald step rule cascade of basic copper sulfate phases. At 25 °C, the thermodynamically stable phase is brochantite [Cu 4 SO 4 (OH) 6 ], but posnjakite [Cu 4 SO 4 (OH) 6 ·H 2 O] is formed first. At lower temperatures, but above 0 °C, wroewolfeite [Cu 4 SO 4 (OH) 6 ·2H 2 O] forms first. If left in contact with the reaction solution, wroewolfeite is converted to posnjakite and brochantite in turn. However, at 0 °C, synthetic wroewolfeite is stable for periods longer than a week, even in contact with the reaction solution, and a stability constant could be determined for its formation. For the reaction below, lg K = -16.3(1) at 0 °C and I = 0, as determined by solution methods. 0.25Cu 4 SO 4 (OH) 6 ·2H 2 O(s,wroewolfeite) = Cu 2+ (aq) + 0.25SO 4 2- (aq) + 1.5OH - (aq) + 0.5H 2 O(l) Stability relations between minerals of stoichiometry Cu 4 SO 4 (OH) 6 ·2H 2 O ( n = 0, 1, 2) are discussed. High concentrations of Mg 2+ ions (1 M) prevent the isolation of wroewolfeite at any temperature down to 0 °C.

Ionic liquids (ILs) and water are both potentially green solvents that are useful in a variety of extraction processes. This report presents the ternary phase diagrams and tie-line data of trihexyl(tetradecyl)phosphonium dicyanamide [P 6,6,6,14 ][DCA], phosphonium bis(2,4,4-trimethylpentyl)phosphinate [P 6,6,6,14 ][((CH 3 ) 3 C 5 H 8 ) 2 PO 2 ], and 1-ethyl-3-methylimidazolium ethylsulfate [emim][C 2 H 5 SO 4 ] ILs in organic solvents (ethanol, acetonitrile, toluene) and water. [P 6,6,6,14 ][DCA] and [P 6,6,6,14 ][((CH 3 ) 3 C 5 H 8 ) 2 PO 2 ] tended to yield emulsions when combined with water and ethanol, while [emim][C 2 H 5 SO 4 ] combined with toluene and water provided two clear phases of reasonable viscosity. The compositions of the ternary mixtures were determined to obtain the tie-lines. A noticeable difference was observed for the tie-lines of the same IL (e.g., [P 6,6,6,14 ][DCA]) with different organic solvents (ethanol and acetonitrile) and water mixtures. In all cases, the addition of ethanol eventually produced a single phase.

The circular dichroism (CD) spectra of chymotrypsin inhibitor 2 (CI2) have been measured as a function of alcohol mole fraction in aqueous mixtures of methanol, ethanol, trifluoroethanol (TFE), and hexafluoro-iso-propanol (HFIP). Small-angle X-ray and neutron scattering (SAXS and SANS) of CI2 was also measured as a function of ethanol mole fraction in ethanol-water mixtures. The CD spectra have shown that the secondary structure of CI2 changes from β-strand to α-helical structure at alcohol mole fractions characteristic of the individual alcohols in an order of HFIP > TFE > ethanol > methanol in effectiveness, where the structure transition of solvent clusters takes place from the typical tetrahedral-like water to the chain-like alcohol clusters in alcohol-water mixtures previously reported. The radius of gyration of CI2, obtained from the analysis of the SANS data, increased with an increase in ethanol mole fraction up to around 0.2 and then gradually decreased. The SAXS data have shown that the shape of CI2 changes from a sphere to a rod-like one at a 0.1 ethanol mole fraction. A possible role of solvent clusters played in alcohol-induced α-helix formation of CI2 is discussed from a viewpoint of the solvent clusters.

Numerous species of metal ions cause immunosensitization in humans. Possible approaches to determine those occupational and environmental exposures to metals that result in immunological changes include lymphocyte transformation assay, cytokine profiling, and measurement of lymphocyte subpopulations. In two previous papers, we considered lymphocyte transformation assay [1] and cytokine profiling [2]. Here we review the effects of exposures to metals on lymphocyte subpopulations. Specific consideration is given to beryllium, chromium, cobalt, nickel, palladium and platinum, cadmium, gold, mercury, and lead. Analysis of the scientific literature shows that immunosensitizing metals may have influences on the lymphocyte subset composition, but only in a few instances does exposure to metals cause reproducible shifts of lymphocyte subpopulations. If lymphocyte subpopulations are analyzed, each diagnostic step, including indication, sample handling, analytic procedure, and data interpretation, should adhere to good quality assurance and quality control.