Volume 78, Issue 8

Chemical and physical processes in biological systems take place in an aqueous environment, and understanding of the properties of solutions is of major importance for advancements in science. Similarly, this holds true for many technologies, where solutions and liquids are in contact with various materials. All this makes the chemistry and physics of solutions one of the most important topics of physical chemistry. The advancements in this area of science are reviewed every second year through the series of world conferences under the title International Conference on Solution Chemistry (ICSC). The 29th International Conference on Solution Chemistry sponsored by IUPAC was held in Portorož, Slovenia, 20-25 August 2005. The conference was organized by the faculty of chemistry and chemical technology at the University of Ljubljana, Slovenia. The ICSC has been held biannually since 1967 and under the present name since 1988. The meetings, which have been held in locations ranging from Debrecen (Hungary) to Vaals (Netherlands) and from Fukuoka (Japan) to Vichy (France), are organized by a 10-member international steering committee. The present chairperson of the committee is Prof. Ingmar Persson from the University of Uppsala in Sweden. Altogether, the 29th ICSC hosted almost 300 participants from 36 countries, including approximately 50 Ph.D. students who took advantage of the conference's reduced fees for students, and more than 40 accompanying family members. The theme of the conference was "the chemistry of solutions", but sessions were also held on supramolecular assemblies and nanostructures, interfaces, biophysical and pharmaceutical problems, aquatic chemistry, ionic liquids, and others. An array of eminent scientists from around the world gave plenary presentations and keynote lectures, and a broad spectrum of the research is reflected in the selection of papers presented in this issue. The first contribution entitled "Reactive intermediates in aqueous ozone decomposition: A mechanistic approach", by Fábián István (University of Debrecen, Debrecen, Hungary) provides a detailed account of recent developments in mechanistic interpretation of aqueous ozone decomposition. Experimental complications with collecting reliable kinetic information for this system are illustrated via selected examples. It is also demonstrated how a complex kinetic model can be validated by studying the system under the specific experimental conditions. Ion-pairing is a classic topic of electrochemistry, and powerful tools such as the spectroscopic techniques UV/vis, NMR, and Raman are often used for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Recent developments in this area of research are reviewed by Glenn Hefter (Murdoch University, Perth, Australia). In the paper entitled "When spectroscopy fails: The measurement of ion pairing", data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve non-contact ion pairs. The next contribution, "Ionic liquids: A most promising research field in solution chemistry and thermodynamics", written by Andreas Heintz and Christiane Wertz (University of Rostock, Rostock, Germany), reviews current research in the field of room-temperature ionic liquids. This topic had a special place at the conference - the round-table discussion about theory and application of these systems, sponsored by Merck KGaA Darmstadt and chaired by Prof. A. Heintz. In the present paper, several selected examples of the most promising chemical and technical applications of ionic liquids are presented, underlining the importance of thermophysical properties of ionic liquids and their role in catalytic and separation processes. Solvation steric effect plays a decisive role in reaction thermodynamics and kinetics of the metal ions. This topic is analyzed by Shin-Ichi Ishiguro and his coworkers from Kyushu University in Fukuoka, Japan in a study entitled "Solvent conformation and ion solvation: From molecular to ionic liquids". The authors discuss their recent results on solvation steric effects in view of structure and thermodynamics, particularly, the conformational change of solvents and their effect on the metal-ion complexation. Electrolyte solutions play major roles in nature and in technological processes, yet the understanding of their properties and interaction with other materials is far from being complete. On the contrary, the ion specific effects, experimentally determined more than 100 years ago, are still largely unexplained. Toward this end, the paper "Specific ion effects in liquids, in biological systems, and at interfaces" by Werner Kunz (University of Regensburg, Regensburg, Germany) reviews the present knowledge of ion effects in solutions, at interfaces, and in complex colloidal systems. Some important experiments and theoretical approaches are discussed, and references of most important papers are provided. V. Vlachy and M. Bešter-Rogač Conference Editors

The 14th International Symposium on Carotenoids was held in Edinburgh, Scotland, UK 17-22 July 2005, under the chairmanship of Dr. George Britton. The International Symposium on Carotenoids is the official symposium for the International Carotenoid Society (http://carotenoidsociety.org), which supported the symposium as did IUPAC. Financial support was gratefully received from DSM Nutritional Products, BASF Ag, Cognis Deutschland, Fuji Chemical Company Ltd., Inexa Industria Extractora CA, Valensa International, Nu Skin International Inc., Cargill Inc., The Alcon Foundation Inc., Kemin Health, Access Business Group, and LycoRed Natural Products Industries Ltd. The first International Symposium took place in Trondheim, Norway in 1966, and such meetings have continued at three-year intervals since then. Over that period of almost 40 years, the carotenoids field has expanded tremendously and diversified into many fields of study, especially human nutrition and health. There have also been continued advances in our understanding of the roles of carotenoids in photosynthesis and photochemistry, the regulation of their formation, de novo chemical synthesis, and the analytical techniques available for detailed structural analyses. The commercial importance of carotenoids has also significantly increased over the years; the current market was estimated to be around $887 million for 2004 and is expected to rise at an average annual growth rate of 2.9 % to just over $1 billion. These areas were fully reflected in the 220 invited lectures, oral communications, and poster sessions. The seven articles that appear in this issue embody the themes of the symposium, namely: - Carotenoids and Health: a series of themed sessions focusing on protection against disease, the eye, molecular and cellular processes, and nutrition - Carotenoid Oxidation and Breakdown Products and Metabolites - Carotenoids in Photosynthesis - Carotenoid Biosynthesis - Commercial Production and Applications - Carotenoids and Nature: ecology, etc. - Molecular Interactions of Carotenoids Finally, we would like to thank everyone who contributed to a most successful symposium, including the local organizing committee, and look forward to the next meeting in 2008, which will be held in Okinawa, Japan and will be chaired by Prof. Hideki Hashimoto. Richard J. Cogdell Peter M. Bramley Conference Editors

Food colorants may be classified into synthetic, nature-identical, inorganic, and natural colorants. Natural colorants for food are made from renewable sources. Most often, the colorants are extracted from plant material, but other sources such as insects, algae, cyanobacteria, and fungi are used as well. Natural colorants are usually extracted and concentrated using either water or lower alcohols for water-soluble pigments and organic solvents for lipophilic pigments. Legislation restricts which colorants are allowed, what sources may be used for that particular colorant, what solvents may be used to extract it, and the purity of the pigment. Colorants are formulated to make them more suitable for a variety of foods and drinks (e.g., lipophilic pigments for use in beverages) and to increase their stability. The natural colorants allowed in the EU and the USA are presented. Many of these colorants are also allowed in most parts of the world. A few colorants that are not allowed in the EU and the USA, but are important food colorants in other parts of the world, are also presented.

Carotenoid oxidation products have various structures, among which epoxides and apo- or seco-carotenoids are the two main families. Although both these compound types are widely found in the natural world, the sensitivity of carotenoids to oxidation means they can also be an unwanted presence in in vitro assays. On the other hand, carotenoid oxidation products have also provided chemists with useful chemical tools for the structural identification of carotenoids, and in the natural world they are important biological mediators for plants and animals. In vitro, carotenoid oxidation products have been found to exert various effects which are either potentially beneficial or, on the contrary, detrimental to human health. However, to date, few carotenoid oxidation products have been found in humans. In order to isolate and characterize carotenoid oxidation products and identify their mechanism of formation, we set up two chemical oxidation systems. Lycopene was oxidized with potassium permanganate in a biphasic system to produce the fullest possible range of apo-lycopenals and some diapocarotene-dials. Biomimetic chemical systems of a heminic enzyme center were shown to oxidize lycopene and β-carotene into different families of molecules. Analysis by high-performance liquid chromatography coupled with a diode array-UV/vis detector and a mass spectrometry detector (HPLC-DAD-MS) was used to gain insight into the possible mechanisms of formation of the carotenoid oxidation products formed by these biomimetic systems.

The photoprotective function of 15,15'- cis -carotenoids bound to the photosynthetic reaction centers (RCs) of purple bacteria has been studied using carotenoids reconstituted into carotenoidless RCs from Rhodobacter sphaeroides strain R26.1. The triplet-energy level of the carotenoid has been proposed to affect the quenching of the triplet state of special-pair bacteriochlorophyll (P). This was investigated using microsecond flash photolysis to detect the carotenoid triplets as a function of the number of conjugated double bonds, n . The carotenoid triplet signals were extracted by using singular-value decomposition (SVD) of the huge matrices data, and were confirmed for those having n = 8 to 11. This interpretation assumes that the reconstituted carotenoids occupy the same binding site in the RC. We have been able to confirm this assumption using X-ray crystallography to determine the structures of carotenoidless, wild-type carotenoid-containing, and 3,4-dihydro-spheroidene-reconstituted RCs. The X-ray study also emphasized the importance of the methoxy group of the carotenoids for binding to the RCs. Electroabsorption (Stark) spectroscopy was used to investigate the effect of the carotenoid on the electrostatic field around P. This electrostatic field changed by 10 % in the presence of the carotenoid.

Carotenoids and retinoids modulate growth and differentiation of a variety of cell types and are fundamental regulators of development. Endothelial cells play an important role in angiogenesis, which is essential for organogenesis and tissue remodeling, but also inflammatory response or carcinogenesis. Binding to the retinoid (RARs) or rexinoid (RXRs) receptors, all- trans -RA, 13- cis -RA, 9- cis -RA, and synthetic retinoids and rexinoids showed antiangiogenic properties in several models. However, the role of β-carotene in endothelial cell function and angiogenesis is still poorly characterized. Although in our experiments, β-carotene used in nontoxic concentrations (up to 3 μM) had no detectable effect on the proliferation or apoptosis of HUVECs or umbilical-cord-blood-derived endothelial progenitors; β-carotene did not change the tubulogenic activity of cells in an in vitro angiogenesis model, but it potently activated the migration of endothelial and progenitor cells. β-Carotene also promoted the development of microcapillaries in a matrigel plug injected subcutaneously into mice. The analysis of microarray data from endothelial cells revealed that β-carotene modified the expression of genes involved in activation of chemotaxis, cell/cell and cell/matrix adhesion, matrix reorganization, G-protein-regulated intracellular signaling as well as genes involved in the rapid remodeling of the actin cytoskeleton. We conclude that physiological levels of β-carotene stimulate early steps of angiogenic activity of endothelial cells by activation of cellular migration as well as matrix reorganization and reduction of cell adhesion.

UVA exposure causes skin photoaging by singlet oxygen ( 1 O 2 )-mediated induction of matrix metalloproteases (MMPs). We assessed whether β-carotene, a carotenoid known as 1 O 2 quencher and retinoic acid (RA) precursor, interferes with UVA-induced gene regulation and prevents UVA-induced gene regulation in HaCaT human keratinocytes. HaCaT cells accumulated β-carotene in a time- and dose-dependent manner. UVA irradiation massively reduced the cellular β-carotene contents. β-Carotene suppressed UVA induction of MMP-1, MMP-3, and MMP-10 - three major MMPs involved in photoaging. HaCaT cells produced weak retinoid activity from β-carotene, as demonstrated by mild up-regulation of retinoid receptor RARβ and activation of an RARE-dependent reporter gene. Of the 568 UVA-regulated genes, β-carotene reduced the UVA effect for 143, enhanced it for 180, and did not interact with UVA for 245 genes. The pathways regulated β-carotene in interaction with UVA were characterized by genes involved in growth factor signaling, stress response, apoptosis, cell cycle, extracellular matrix (ECM) degradation, tanning, and inflammation. In conclusion, β-carotene at physiological concentrations interacted with UVA effects by multiple mechanisms that included, but were not restricted to, 1 O 2 quenching. With our results, we provide a mechanistic basis for the long-known and clinically established photoprotective effects of β-carotene in human skin.

There are approximately 40-50 carotenoids in commonly consumed fruits and vegetables in a typical U.S. diet. These can be divided into carotenoid epoxides, mono- and dihydroxycarotenoids, hydrocarbon carotenoids, and carotenol acyl esters. However, among these, only a selected group of carotenoids are routinely found in human plasma, breast milk, major organs, and ocular tissues. In addition, several carotenoid metabolites have also been isolated and characterized from human plasma, tissues, and ocular tissues. The proposed metabolic transformation of carotenoids in humans will be discussed. Dietary carotenoids and their metabolites have been implicated in the prevention of cancer, cardiovascular disease, and age-related macular degeneration (AMD). An approach for the development of a nutritional supplement that is based on the distribution of carotenoids and their metabolites in humans will be discussed.

This paper provides a detailed account of recent developments in the mechanistic interpretation of aqueous ozone decomposition. Experimental complications with collecting reliable kinetic information for this system are illustrated via a few examples. Classical and comprehensive data treatment methods are compared, and an advanced kinetic model is presented on the basis of simultaneous evaluation of about 60 kinetic traces recorded at 260, 430, and 600 nm. These are the wavelengths of the absorbance maxima of O 3 , O 3 - , and CO 3 - , respectively. The model is used to explore specific features of the initiation sequence, the role of reactive intermediates, and the carbonate ion inhibition. It is also demonstrated how a complex kinetic model can be validated by studying the system under specific experimental conditions.

Spectroscopic techniques such as UV/vis, NMR, and Raman are powerful tools for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Specifically, spectroscopic measurements do not in general produce thermodynamically meaningful association constants for non-contact ion pairs, where the ions are separated by one or more solvent molecules. Such systems can only be properly quantified by techniques such as dielectric or ultrasonic relaxation, which can detect all ion-pair types (or equilibria), or by traditional thermodynamic methods, which detect the overall level of association. Various types of quantitative data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve solvent-separated ion pairs. The implications for ion association equilibria in general are briefly discussed.

Modern room-temperature ionic liquids (RTILs) consisting of large and asymmetric organic cations and small inorganic anions exhibit a special class of recently developed liquids unifying the property of the liquid state and strong Coulomb interactions acting as the prevailing intermolecular interactions in the liquid state. Several selected examples of the most promising chemical and technical applications of ILs are presented, which underline the importance of thermophysical properties of ILs and their role of being particular solvents in catalytic and separation processes as well as in special fields of electrochemistry.

Metal ions are solvated in solution, and, in a sterically congested organic solvent, those solvent molecules that are simultaneously bound to the metal ion will be subject to consequential steric interactions through space. The molecular structure of a solvent, particularly that of any functional groups in the vicinity of the coordinating atom to the metal ion, plays a key role in the solvation steric effect. Weak solvation steric effects lead to a distorted octahedral structure for six-coordinate transition-metal(II) ions, whereas strong steric effects lead to a decreased solvation number. In particular cases, the conformation of a solvent may undergo a change in response to coordination to the metal ion. Solvation steric effects play a decisive role in reaction thermodynamics and kinetics of the metal ion. Here, we show our recent results on solvation steric effects in terms of structure and thermodynamics, particularly, the conformational change of solvent and its effect on the metal-ion complexation.

A short review is given of current knowledge of ion effects in solutions, at interfaces, and in complex colloidal systems. Further to some key experiments, recent and new theoretical approaches are discussed and references of most important papers are given. Finally, an example of a dissipative, self-organizing system involving electrolyte solutions is mentioned.