Volume 81, Issue 9

<div>The 13th International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP-13) was held at Trinity College, Dublin, Ireland, 27-31 July 2008. The symposium was sponsored by IUPAC, and arrangements were carried out by Trinity College, Dublin and University College, Dublin.<br /><br />About 80 delegates attended the symposium from 27 different countries. The meeting comprised 8 invited speakers, 30 oral presentations, and 21 poster presentations.<br /><br />The ISSP was first organized in 1984, is held in even-numbered years, and was an outcrop of the solubility data project where a team of experts provides critical compilations of solubility data of importance in various technologies.</a> <br /><br />Each symposium has a well-defined focus which incorporates experimental methods, data analysis, modeling, and predictive methods and general applications of solubility phenomena.<br /><br />Previous symposia have focused on several themes related to solubility. These have included solubility phenomena related to atmospheric and environmental chemistry, solubility phenomena in physiology, medicine and pharmacology, solubility phenomena in salt industries, thermodynamic and kinetic aspects of solubility equilibria, and solubility phenomena related to waste processing, to name a few.<br /><br />This issue of <i>Pure and Applied Chemistry</i> contains seven contributions from the invited lectures presented at the symposium: Modification of molecular organization of polymers by gas sorption: Thermodynamic aspects and industrial applications (J. P. Grolier, France); Solubility and related properties in hydrometallurgy (E. Königsberger, Australia); Thermodynamics of trivalent actinides and neodymium in NaCl, MgCl<sub>2</sub>, and CaCl<sub>2</sub> solutions: Solubility, hydrolysis and ternary Ca-M(III)-OH complexes (V. Neck, Germany); A more realistic approach to speciation based on the stability constants database (L. Pettit, UK); Surface complexation and proton-promoted dissolution in aqueous apatite systems (S. Sjöberg, Sweden); Solubility and critical phenomena in reactive liquid-liquid systems (A. Toikka, Russia); and Dispersion of antimony from oxidizing ore deposits (P. Williams, Australia).<br /><br />The conference program, as reflected both by the invited lectures as well as the oral communications and poster presentations, covered a variety of research areas such as: thermodynamics of species relative to nuclear waste storage, gas polymer interactions with reference to the petrochemical industry, hydrometallurgy, geochemistry, environmental aspects of solubility, as well as critical phenomena and the interpretation of a variety of phase diagrams.<br /><br /><i>Reginald P. T. Tomkins</i><br />Conference Editor<br /></div>

<div>Extending a long history of successful conferences, the XXIInd IUPAC Symposium on Photochemistry was held in Göteborg, Sweden, from 28 July to 1 August 2008. It was attended by participants from 51 countries. The Symposium featured 7 plenary lectures, 12 invited lectures, 96 selected oral presentations, and 414 posters given by attendees. One of the highlights was the presentation of the Porter Medal to Prof. Michael R. Wasielewski of Northwestern University, USA. The title of his lecture was "Photodriven charge and spin dynamics in molecules and materials: From photosynthesis to spintronics."<br /><br />A featured theme of the Symposium was solar energy conversion in the context of global climate change and the energy crisis. However, a large variety of subjects were covered, including spectroscopy of single molecules and of nanostructures, molecular photochemistry in solution and in microhetero - geneous media, photochemistry of pharmaceuticals, fluorescent markers and sensors, photochemically based molecular logic, supramolecular units mimicking photosynthetic antennas and reaction centers, photopolymerizations and photochemistry in solid state, theoretical considerations and calculations of excited states, and spectroscopic studies of biological photosensors and biomedically important materials. Many of the topics were of both fundamental scientific interest and practical and technological importance. The next Symposium will be held in Ferrara, Italy in 2010.<br /><br />This issue of <i>Pure and Applied Chemistry</i> contains a collection of papers based on plenary and invited lectures given at the Symposium and kindly supplied by the speakers. They cover a variety of modern photochemical topics and appear in the order of their presentation at the Symposium. They help illustrate the vital place of modern photochemistry in promoting the health and welfare of humanity, and indeed of all life on the planet.</a> <br /><br /><i>Devens Gust</i><br />Conference Editor<br /></div>

Thermodynamically consistent models based on accurately measured data are required for reliable predictions of equilibria and thermodynamic properties for a wide variety of multicomponent, multiphase systems and reactions relevant to hydrometallurgy. Recent developments in our laboratory concerning the measurement and modeling of physicochemical properties of electrolyte solutions over wide ranges of conditions are reviewed. Particular emphasis is on applications to the refining of alumina via the Bayer process, in which various solubility phenomena involving solid, aqueous, and gaseous phases are of critical importance to product yield and purity as well as to economical and environmental sustainability. Appropriately designed models and software allow these aspects to be tackled by thermodynamic process simulations of alumina refinery circuits.

The solubilities of brandholzite, [Mg(H 2 O) 6 ][Sb(OH) 6 ] 2 , and bottinoite, [Ni(H 2 O) 6 ][Sb(OH) 6 ] 2 , at 25 °C in water have been measured. Solubilities are 1.95(4) × 10 -3 and 3.42(11) × 10 -4 mol dm -3 , respectively. The incongruent dissolution of romeite, Ca 2 Sb 2 O 7 , and bindheimite, Pb 2 Sb 2 O 7 , at 25 °C in 0.100 mol dm -3 aqueous HNO 3 was also investigated. Equilibrium dissolved Sb concentrations were 3.3 ± 1.0 × 10 -7 and 7.7 ± 2.1 × 10 -8 mol dm -3 , respectively. These values have been used to re-evaluate the geochemical mobility of Sb in the supergene environment. It is concluded that the element is geochemically immobile in solution and in soils. This was in part validated by an orientation soil geochemical survey over the Bayley Park prospect near Armidale, New South Wales, Australia. Anomalous soil Sb levels are confined to within 100 m of known stibnite mineralization.

Known data on the solubility of Am(OH) 3 (s) and the hydrolysis of Am(III) and Cm(III), additional information from an extensive solubility study with Nd(OH) 3 (s) in NaCl, MgCl 2 , and CaCl 2 media of various ionic strengths and spectroscopic (time-resolved laser fluorescence spectroscopy, TRLFS) data for Cm(III) in alkaline CaCl 2 solutions are used to evaluate a comprehensive set of standard-state equilibrium constants and ion interaction parameters for the specific ion interaction theory (SIT) and Pitzer equations at 25 °C. The thermodynamic model takes into account the analogous solubility and hydrolysis behavior of trivalent actinides and Nd(III) and covers the entire pH range in dilute to concentrated NaCl, MgCl 2 , and CaCl 2 solutions. In alkali chloride/hydroxide solutions, the formation of the tetrahydroxide complex M(OH) 4 – requires OH – concentration above 3 mol l –1 , whereas in alkaline CaCl 2 solutions (at pH c < 12) M(III) complexes with four and six hydroxide ligands are formed. Similar as the recently detected ternary Ca–M(IV)–OH complexes Ca 3 [Zr(OH) 6 ] 4+ and Ca 4 [Th(OH) 8 ] 4+ , these complexes are stabilized by the association of Ca 2+ ions. The solubility and hydrolysis of Am(III), Cm(III), and Nd(III) in both Ca-free and -containing solutions is consistently described with a model including the ternary Ca–M(III)–OH complexes Ca[M(OH) 3 ] 2+ , Ca 2 [M(OH) 4 ] 3+ , and Ca 3 [M(OH) 6 ] 3+ .

The dissolution of hydroxyapatite (HAP) and fluorapatite (FAP) has been studied (25 °C, 0.1 M NaCl medium) within the pH ranges 2–11 (FAP) and 4–10 (HAP). A range of techniques has been utilized to achieve understanding in how these two abundant minerals may interact with their natural surroundings (e.g., body fluids and soil environments). Synthetic crystalline HAP and FAP were prepared, and both minerals were found to undergo a phase transformation generated during a dialysis step of the synthetic routes. Surface-deficient layers with the nonstoichiometric compositions Ca 8.4 (HPO 4 ) 1.6 (PO 4 ) 4.4 (OH) 0.4 and Ca 9 (HPO 4 ) 2 (PO 4 ) 4 F 2 were identified. The equilibrium analysis of experimental solubility data of the two apatite systems was based upon potentiometric titration data, batch experiments, and zeta-potential measurements in combination with information provided by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis required, besides the two solubility equilibria, the formation of surface protonation/deprotonation reactions, re-adsorption processes involving phosphate and fluoride ions as well as an ion exchange reaction (≡F + H 2 O ⇋ ≡OH + H + + F – ) to fully describe the dissolution characteristics of the two apatite systems. The resulting model also agrees with observations from XPS and solubility data, claiming the formation of CaF 2 (s) in the most acidic pH range of the FAP system. In addition, calculated isoelectric points (pH iep ) are in agreement with values from surface charge measurements showing pH iep (HAP) = 8.1 and pH iep (FAP) = 5.7.

The IUPAC Stability Constants Database (SC-Database), designed to contain all significant published constants, provides the most complete and accessible route to stability constants in the literature. Collection of new constants is becoming less significant since most are now measured to confirm a mechanism or to identify bonding centers, not to provide data for general use. As a result, constants are often measured less rigorously and are of lower accuracy. What are required now are critical evaluations of existing data, coupled with accurate study of a number of important and superficially simpler systems (e.g., complexes with some inorganic ligands). Calculation of species distribution curves is a major use of stability constants. Ways of reflecting possible errors in the calculated curves are now required. Historically, curves have been drawn as sharp lines, but these could only result from using the exact stability constants with an accurate model for the system. Two techniques for demonstrating the effect of errors are outlined. Constants are dependent on ionic strength and temperature changes. Specific ion interaction theory (SIT) is the most general method of compensating for ionic strength changes up to about 5 molal. Software to correct constants for ionic strength changes, prepared under recent IUPAC projects, is described.

The goal of this work is to consider solubility phenomena in reactive fluid mixtures with liquid-phase splitting. One of the main tasks is to analyze peculiarities of liquid–liquid (LL) systems with equilibrium and nonequilibrium chemical reaction. The special aim is to consider the critical states in these systems. The reactive liquid–liquid equilibrium (LLE) is treated on the base of phase rule. The topology of diagrams of reactive LLE is discussed for some types of binary and ternary systems. Examples are presented of a possible transformation of phase diagrams caused by the shifting of chemical equilibrium and by changes in the shape of the binodal. The transformations resulting in the reactive critical phase formation are considered. Quaternary mixtures are also discussed with the use of experimental data on the solubility in the system with n -propyl acetate synthesis reaction. The mutual crossing of the chemical equilibrium surface and binodal in the composition tetrahedron leads to the origin of the area of simultaneous chemical and LLE with two critical points (reactive critical phases). The shape of the curve of simultaneous chemical and phase equilibrium is also presented in the square of transformed composition variables.

In polymer science, gas–polymer interactions play a central role for the development of new polymeric structures for specific applications. This is typically the case for polymer foaming and for self-assembling of nanoscale structures where the nature of the gas and the thermodynamic conditions are essential to control. An important applied field where gas sorption in polymers has to be documented through intensive investigations concerns the (non)-controlled solubilization of light gases in the polymers serving, for example, in the oil industry for the transport of petroleum fluids. An experimental set-up coupling a vibrating-wire (VW) detector and a pVT technique has been used to simultaneously evaluate the amount of gas entering a polymer under controlled temperature and pressure and the concomitant swelling of the polymer. Scanning transitiometry has been used to determine the interaction energy during gas sorption in different polymers; the technique was also used to determine the thermophysical properties of polymers submitted to gas sorption. The role of the pressurizing fluid has been documented in terms of the influence of pressure, temperature, and nature of the fluid.

The fluorescence of a rhodamine X dye covalently linked to the 5' terminus of a 25-mers thymine oligodeoxynucleotide (dT 25 -ROX), adsorbed on the shell of thermoresponsive core-shell polymer particles, was used to probe the polarity, mobility, and distribution of the oligodeoxynucleotides (ODNs) in the shell. The particles have a glassy core of poly(methyl methacrylate) (PMMA) with a 67-nm radius, and a thermoresponsive shell of poly( N -isopropyl acrylamide) (PNIPAM) whose thickness changes from 42 nm at 11 ºC to 5 nm at 45 ºC. The variation in polarity of the shell with temperature was obtained both from the lifetimes and from the solvatochromic shifts of the dye and shows a sharp transition at the volume phase transition temperature ( T VPT ) of the PNIPAM shell. Förster resonance energy transfer (FRET) between dT 25 -ROX and a malachite green (MG)-labeled ODN (dT 25 -MG) was used to obtain the distribution of the ODNs in the thermoresponsive shell. Our results show that at 23 ºC (below T VPT ) the ODNs are distributed inside the shell, sensing an environment similar to water. At this temperature, the PNIPAM shell is composed of hydrated chains with high mobility, as probed by the fluorescence anisotropy of dT 25 -ROX. By increasing the temperature above T VPT , the shell collapses and the chain mobility drastically slows down owing to the anchoring of the ODN to the dense shell of PNIPAM. Furthermore, FRET shows that the ODNs are absorbed on the 5-nm-thick collapsed shell but extend into the water. The polarity probed by the ROX averages the dyes distributed in the interior of the particle shell and in water, with 60 % of the dyes outside the particle shell (i.e., sensing pure water). Another indication that above the T VPT most of the ODNs are oriented with the dye toward the water phase is that the mobility of the dye covalently bound to the ODNs is identical in water and in the collapsed particle shell. The hybridization efficiency between an ODN supported in the particle shell (by adsorbing the ODN below T VPT and subsequently increasing the temperature above T VPT ) and the complementary ODN in solution is identical to that of hybridization in water. This result opens good perspectives toward the use of the core-shell thermoresponsive nanoparticles as supports in DNA bioassays.

Recent experimental and theoretical investigations dealing with model DNA double helices, composed of either adenine–thymine (A–T) or guanine–cytosine (G–C) base pairs, and G quadruplexes shed some light on the excited states populated by photon absorption and their relaxation, energy transfer among bases, and one-photon ionization. These studies revealed that the Franck–Condon excited states of DNA helices cannot be considered as the sum of their monomeric constituents because electronic coupling induces delocalization of the excitation over a few bases. Energy transfer takes place via intraband scattering in less than 100 fs. The fluorescence lifetimes of DNA helices detected by fluorescence upconversion and corresponding mainly to ππ* transitions are longer than that of an equimolar mixture of nucleotides; the only exception was observed for alternating G–C polymers. Moreover, nanosecond flash photolysis experiments showed that organization of bases within single and double helices may lead to a lowering of their ionization potential. Finally, the first determination regarding the time-scale needed for the formation of T dimers, the (6–4) adducts, was determined for the single strand (dT) 20 .

Near-field optical probes have been used to produce a subdiffraction-limited observation area for fluorescence correlation spectroscopy (FCS) experiments on supported membranes. The design of a bent, etched fiber probe that is compatible with biological imaging in an aqueous environment is described. This probe design is used for proof of principle experiments to measure lipid diffusion in a fluid-supported bilayer. A reduction in excitation area of approximately one order of magnitude (relative to a confocal FCS experiment) is obtained with a probe aperture diameter of 140 nm. We also demonstrate a simple approach for modeling the autocorrelation decay due to diffusion within the excitation profile at the near-field scanning optical microscopy (NSOM) probe aperture. The use of probes with smaller apertures is expected to provide an additional order of magnitude reduction in the observation area, thus enabling the study of cellular membranes with higher concentrations of fluorophores than is currently possible with diffraction-limited techniques.

Some of the diarylethene derivatives were found to undergo photoisomerization reactions between two isomers even in the single-crystalline phase. The two isomers have different electronic as well as geometrical structures. The electronic structure change induces the reversible color change of the crystal. Single crystals composed of three different kinds of diarylethenes having similar geometrical structures, bisoxazolylethene, bisthiazolylethene, and bisthienylethene have been prepared. The crystals exhibited multicolor photochromism. The colorless crystals turned yellow, red, and blue upon irradiation with the appropriate wavelength of light. The geometrical structure change of component diarylethene molecules in crystals induces reversible surface morphology as well as shape and size changes of the crystals. The photoinduced geometrical structure changes of the molecules in the densely packed crystals were successfully linked to the macro-scale mechanical motion of the solid crystals and resulted in the net task of launching a tiny silica particle.

Fast time-resolved infrared (TRIR) spectroscopy has been useful for studying the reactions of a wide range of organometallic alkane and noble gas complexes at ambient temperature following irradiation of metal carbonyl precursor complexes. The reactivity of organometallic alkane and xenon complexes decreases both across and down groups V, VI, and VII, and for a given metal/ligand combination the alkane and xenon complexes have similar reactivities. Systematic studies of reactivity have produced long-lived Re complexes which have allowed such complexes to be characterized using NMR spectroscopy. A new approach using liquid propane at low temperature as a solvent to monitor the interaction of such weakly coordinating ligands with transition-metal centers is outlined. TRIR studies monitoring the coordination and activation of methane and ethane in supercritical methane and liquid ethane solvents at room temperature are also reviewed.

The organizational effect induced by noncovalent interactions such as hydrogen-bonding (H-B) and metal ion complexation on photoinduced processes is discussed. These include the intermolecular photodimerization of cinnamates, which is shown to occur under topochemical control within the supramolecular assemblies, and the intramolecular photodimerization of a bis-anthracene receptor where photoregulation of the recognition event is achieved. Progress in using supramolecular interactions toward the preparation of assemblies promoting charge separation and charge transport in all-organic photovoltaic devices rests on the preparation of materials that are adapted to the requirements of solid-state devices.

Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV radiation and are effective antioxidants and scavengers of active oxygen species. In plant leaves, one of the functional roles proposed for anthocyanins is protection of the photosynthetic apparatus from the effects of excess incident visible or UV-B radiation and photooxidative stress. In essence, a photoprotective role requires that the excited singlet states of both complexed and uncomplexed anthocyanins deactivate back to the ground state so quickly that intersystem crossing, photoreaction, and diffusion-controlled quenching processes cannot compete. Studies of the photochemical properties of synthetic analogs of anthocyanins and of several naturally occurring anthocyanins show that this is indeed the case, uncomplexed anthocyanins decaying back to the ground state via fast (subnanosecond) excited-state proton transfer (ESPT) and anthocyanin-copigment complexes by fast (subpicosecond) charge-transfer-mediated internal conversion.

Quantum chemical studies using the accurate CASPT2//CASSCF procedure show that π-stacked interactions in biochromophores such as pyrimidine (Pyr) DNA/RNA nucleobases pairs yield excimer-like situations which behave as precursors of processes like charge transfer (CT) or photoreactivity and are the source of the emissive properties in DNA. Examples are the CT between adjacent DNA nucleobases in a strand of oligonucleotides and the photodimerization taking place in cytosine (C) pairs leading to cyclobutanecytosine (CBC) mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersections (CIs) and other surface crossings between different electronic states.

This report describes the results of a Project whose goals were to "assemble, collate and disseminate information about the scope of the newly-emerging discipline of materials chemistry, leading to an authoritative definition of the subject within the family of chemical sciences" and further, as a corollary, "to recommend to IUPAC how this new discipline might best be represented within the IUPAC structure". The history and current status of the research and teaching, only recently labeled as "materials chemistry", is described. This field has become one of the major growth sectors in pure and applied chemistry and now accounts for a significant fraction of all publications in the chemical sciences, based on measures such as journal citations and submitted papers and journals that are devoted entirely or in part to this subject. Nonetheless, there is still considerable confusion about what does, and does not, fall within the scope of "materials chemistry", and there is no consensus regarding a definition for the subject. After examining existing definitions for "chemistry" and "materials science" and considering prior attempts to define the subject, the following working definition for "materials chemistry" was suggested: "Materials chemistry comprises the application of chemistry to the design, synthesis, characterization, processing, understanding and utilisation of materials, particularly those with useful, or potentially useful, physical properties." In conclusion, the report suggests that IUPAC consider elevating this field from its current Subdivision status to that of "a cross-divisional Committee that would work with all the current IUPAC Divisions to develop and co-sponsor new projects, in the area of chemical education, nomenclature, terminology, health and safety, etc., that will increase the recognition of the current and future importance of this field to the international chemistry community".