bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and application of very high temperature mass spectrometry. Vapor pressure determinations over liquid refractories
Authors: Hastie J. W. , Bonnell D. W. , Schenck P. K.
Published: October 2007

Existing thermodynamic and vaporization data for liquid refractories are based either on estimates or on data extrapolated from studies on the solids obtained at much lower temperatures. Previously, we have shown that pulsed laser heating, coupled with time-dependent mass spectrometry of the free-expansion vapor plume, can be used for semi-quantitative measurements of vaporization thermochemistry. The present work extends this approach with the development of (a) more direct, and more accurate, methods for determining the system temperature and pressure; (b) improved experimental and theoretical determinations of key parameters such as ionization cross sections; and (c) improved characterization of the gas dynamic expansion and thermal equilibration processes. Example material systems considered include C, SiC, Al2O3, ZrO2—7%Y2O3, and Y2O3 at temperatures and total pressures typically in the range of 3000 to 5000 K and 0.01 to 10 bar, respectively (1 bar = 105 Nm-2).
Femtochemistry. Past, present, and future
Authors: Zewail Ahmed H.
Published: October 2007

This review highlights, with a historical perspective, the development of the field, with focus on the evolution since its birth in 1987, the scope of applications in present-time research, and some future developments in femtochemistry and the sibling field, femtobiology.
Recent advances in spin chemistry
Authors: Buchachenko Anatoly L.
Published: October 2007

The great success in controlling chemical reactivity by spin manipulation was achieved in the last decade, and many remarkable spin and magnetic phenomena have been discovered. Among those discoveries, the most chemically important highlights are magnetic isotope effect, spin catalysis, and single-spin tunneling spectroscopy. This paper summarizes recent advances in these new and hot areas of modern chemistry.
Influence of chloride, water, and organic solvents on the physical properties of ionic liquids
Authors: Seddon Kenneth R. , Stark Annegret , Torres María-José
Published: October 2007

We report here the first systematic study of the effect of impurities and additives (e.g., water, chloride, and cosolvents) on the physical properties of room-temperature ionic liquids. Remarkably, it was discovered that the viscosity of mixtures was dependent mainly on the mole fraction of added molecular solvents and only to a lesser extent upon their identity, allowing viscosity changes during the course of a reaction to be entirely predictable. While the addition of such molecular solvents decreases the viscosity and density, chloride impurities, arising from the preparation of the ionic liquids, increase viscosity dramatically. The commonly used methods of preparation were validated with respect to chloride impurity.
Reactive intermediates. Some chemistry of quinone methides
Authors: Chiang Y. , Kresge A. J. , Zhu Y.
Published: October 2007

Quinone methides were produced in aqueous solution by photochemical dehydration of o-hydroxybenzyl alcohols (o-HOC6H4CHROH; R = H, C6H5, 4-CH3OC6H4), and flash photolytic techniques were used to examine their rehydration back to starting substrate as well as their interaction with bromide and thiocyanate ions. These reactions are acid-catalyzed and show inverse isotope effects (kH+/kD+ < 1), indicating that they occur through preequilibrium protonation of the quinone methide on its carbonyl carbon atom followed by rate-determining capture of the benzyl carbocations so formed by H2O, Br-, or SCN-. With some quinone methides (R = C6H5 and 4-CH3OC6H4) this acid catalysis could be saturated, and analysis of the data obtained in the region of saturation for the example with R = 4-CH3OC6H4 produced both the equilibrium constant for the substrate protonation step and the rate constant for the rate-determining step. Energy relationships comparing the quinone methides with their benzyl alcohol precursors are derived.
Comparative chemistry of unsaturated compounds of Group 14 elements
Authors: Kira Mitsuo
Published: October 2007

Structures and reactions of a stable dialkylsilylene and various cyclic and acyclic disilenes, which we have recently synthesized, are discussed in detail. The stable silylene was found to be well protected sterically from dimerization but least perturbed electronically as evidenced by UV­vis and NMR spectroscopy. Persilylated acyclic and cyclic disilenes have shown interesting features in the Si=Si bond distances, electronic spectra, and reactions, due to the remarkable electronic and steric effects of trialkylsilyl substituents. Detailed theoretical calculations for the addition of water to disilene has shown that the intramolecular anti-addition pathway is rationalized using the orbital symmetry rule. The reactions of disilenes with haloalkanes were judged to proceed via the rate-determining halogen abstraction of disilenes from haloalkanes. The biradical character of disilenes may be related to the small π bond energy.
Dendrimers as reactive modules for the synthesis of new structure-controlled, higher-complexity megamers
Authors: Tomalia Donald A. , Uppuluri Srinivas , Swanson Douglas R. , Li Jing
Published: October 2007

Dendrimers are macromolecular, nanoscale objects that are widely recognized as precise, mathematically defined, covalent core-shell assemblies. As such, they are composed of quantized numbers of atoms, monomers, and terminal functional groups relative to the respective shell levels (generations) surrounding their cores. Dendrimers have been referred to as molecular-level analogs of atoms. This perspective arises from their potential to function as precise macromolecular tectons (modules), suitable for the synthesis of structure-controlled complexity beyond dendrimers. We have termed this major new class of generic structures "megamers". Our group has now synthesized such "megamer complexity" in the form of both covalent and supra-macromolecular dendri-catenanes, dendri-macrocycles, dendri-clefts, and dendri-clusters. The covalent dendri-cluster subset of megamers has been coined "core-shell tecto(dendrimers)". New mathematically defined, covalent bonding rules for tecto(dendrimer) formation are consistent with sterically induced stoichiometry (SIS) predictions and have been verified experimentally.
In situ speciation measurements. Using diffusive gradients in thin films (DGT) to determine inorganically and organically complexed metals
Authors: Zhang Hao , Davison William
Published: October 2007

The possibilities of using diffusive gradients in thin films (DGT) and anodic stripping voltammetry (ASV) to perform speciation measurements in natural waters are discussed. Both techniques measure labile species, but different approaches have been used to discriminate organic (Corg) and inorganic (Cinorg) metal complexes. In DGT, metals are bound to a resin after passing through a hydrogel that serves as a well-defined diffusion layer. DGT devices with different hydrogels that impede the diffusion of humic substances by different amounts were deployed in solutions of copper and humic substances. Devices with a gel composition that greatly restricted the diffusion of humic substances, but only retarded the diffusion of Cu ions slightly, could be used directly to determine Cinorg. By using different, more open pored gels, which allowed some passage of humic substances, it was possible to determine both Corg and Cinorg. The two separate measurements of Cinorg obtained using the two DGT approaches agreed well. At the high concentrations of Cu used there was good agreement with the predicted distribution from the speciation code WHAM. At the lowest Cu concentration, the proportion of Cinorg estimated using DGT was higher than with WHAM. Possibilities of errors in the DGT or modeling approaches are discussed.
Affinity electrochemical biosensors for pollution control
Authors: Mascini M.
Published: October 2007

Disposable, electrochemical DNA-based biosensors have been exploited for the determination of low-molecular-weight compounds with affinity for nucleic acids. The application is related to the molecular interaction between the surface-linked DNA obtained from calf thymus and the target pollutants or drugs, in order to develop a simple device for rapid screening of genotoxic or similar compounds. The determination of such compounds was measured by their effect on the oxidation signal of the guanine peak of the DNA immobilized on the electrode surface and investigated by chronopotentiometric or square-wave voltammetric analysis. The DNA biosensor is able to detect known intercalating and groove-binding compounds such as daunomycin, polychlorinated biphenyls (PCBs), aflatoxin B1, and aromatic amines. Applicability to river and waste water samples is discussed and reported.
Devices for ion-sensing and pX measurements
Authors: Thomas J. D. R.
Published: October 2007

Thirty years of ion-selective electrode (ISE) researches at the University of Wales, Cardiff are outlined. They summarize developments of PVC membrane ISEs, first for calcium and then of other systems, including the improved calcium dioctyl-phenyl-phosphate sensor for calcium and those of ion-exchangers, polyalkoxylates, and cyclic and acyclic polyethers for various anions and cations. Electrodes based on polyalkoxylates have interesting properties toward the polyethers themselves. Some ISE failure causes are discussed. Attention is given to applications, including analysis of wash liquors and nonionic surfactants, biomedical roles, and studies of sulfate-reducing bacteria activity. Coated-wire ISEs and ion-selective field effect transistors (ISFETs) are mentioned, as are other modes of ISE deployment. The review concludes with some fundamental features of PVC electrode membranes as determined by radiotracer, applied potential, and potentiostatic approaches.
Speciation dynamics and bioavailability of metals. Exploration of the case of two uptake routes
Authors: van Leeuwen Herman P. , Pinheiro José Paulo
Published: October 2007

The steady-state biouptake of metals from complex media is outlined for the case of two different uptake routes. The analysis comprises the limiting situations of inert and labile complexes, and distinguishes between bioinactive and bioactive (lipophilic) complexes. Depending on the dynamic features, fluxes of the different species may be either coupled or uncoupled. The role of the lipophilic ligands may be important in the overall uptake process. Some specific cases are discussed.
Detecting and circumventing sources of inaccuracy in flow analysis
Authors: Zagatto Elias A. G. , Rocha Fábio R. P. , Martelli Patrícia B. , Reis Boaventura F.
Published: October 2007

Mechanized procedures for chemical analyses are susceptible to systematic errors usually difficult to trace. This holds also for flow analysis that although accepted worldwide may sometimes yield inaccurate results. The present work focused on the development of a simple system able to detect and circumvent sources of inaccuracy. The versatility inherent in the multicommuted flow analyzers was exploited for real-time characterization of the source of inaccuracy and overcoming the problem for every assayed sample. Specific situations where the analytical results are more susceptible to inaccuracy are emphasized.
Green chemistry. Sustaining a high-technology civilization
Authors: Ghosh Anindya , Gupta Sayam S. , Bartos Michael J. , Hangun Yelda , Vuocolo Leonard D. , Steinhoff Bradley A. , Noser Christopher A. , Horner David , Mayer Sherry , Inderhees Kevin , Horwitz Colin P. , Spatz Jonathan , Ryabov Alexander D. , Mondal Sujit , Collins Terrence J.
Published: October 2007

By learning how to balance natural resource limitations and pollution prevention with economic growth, green chemistry will become the central science of sustainability. The elimination of persistent pollutants is vital for a sustainable civilization. To achieve this, the most important guiding concept is that the elemental composition of technology should be shifted toward the elemental composition of biochemistry. Oxidation chemistry is currently a prolific producer of persistent pollutants. Many arise from the use of chlorine, hypochlorite, or chlorine dioxide in large-scale oxidation processes. Oxidation chemistry can be greened by replacing these with catalyzed alternatives based on Nature's oxidizing agent, hydrogen peroxide. TAML® (TetraAmidoMacrocyclicLigand) iron catalysts, which were invented at Carnegie Mellon University, are widely patented and are being developed to activate H2O2 for commercial applications. TAML activators are water-soluble, easy to use, function well from neutral to basic pH, are not dominated by nonselective Fenton-like reactivity, are straightforward to synthesize, work effectively in minute concentrations, enable peroxide processes to occur at temperatures well below those of the processes targeted for replacement, and are amenable to modification for capturing novel selectivities. TAML activators are "dial-a-lifetime" catalysts: an activator can be chosen exhibiting a lifetime commensurate with the desired task.
Dry media reactions
Authors: Kidwai M.
Published: October 2007

Dry media reaction under microwaves is an effort toward "green chemistry". Effects of microwaves in dry media organic reactions have shown synthetic utility for the preparation of biodynamic heterocycles.
Using neoteric solvents in oil shale studies
Authors: Koel M. , Ljovin S. , Hollis K. , Rubin J.
Published: October 2007

The liquefaction, gasification, and other chemical modifications of oil shale are challenging goals of chemistry and chemical engineering. The use of new solvent systems, such as supercritical fluids and ionic liquids, represents new avenues in the search of environmentally benign technologies. Supercritical fluid extraction (SFE) with carbon dioxide is particularly effective for the isolation of substances of medium molecular weight and relatively low polarity. At elevated temperatures it is possible to unite the breaking chemical bonds in the kerogen organic matter and convert the former into oil with extraction using supercritical fluids. Quantitative and qualitative information obtained at different temperatures during SFE is providing some insight into the speciation of hydrocarbons in geological samples. Ionic liquids were studied as potential solvents for kerogen extraction. However, these chemical processes are favored at elevated temperatures up to the thermal degradation temperature of kerogen, 400 C. There were observed significant differences in the chemical composition of extracted oil and from the oil from the classical semicoking process of oil shale. An additional application would be a combination of the two methodsthe use of supercritical carbon dioxide to recover nonvolatile organic compounds from room-temperature ionic liquid without using organic solvents.
Organometallic chemistry at the threshold of a new millennium. Retrospect and prospect
Authors: Halpern Jack
Published: October 2007

The evolution of organometallic chemistry during the second half of the 20th century has transformed chemical science and technology to a degree and in ways that have rarely been matched throughout the history of chemistry. These include the discovery of radically new types of chemical compounds; novel structures and bonding modes; unprecedented reactivity patterns; unsuspected roles of organometallic chemistry in biology; powerful new synthetic methodologies; new materials; and whole new classes of catalysts and catalytic processes of extraordinary versatility and selectivity. The impact of these developments, which still are unfolding, has been truly revolutionary. Some milestones in this remarkable chapter of chemical history, as well as challenges and opportunities confronting organometallic chemistry today, will be examined.
Organometallic pentalene complexes
Authors: Cloke F. Geoffrey N.
Published: October 2007

There has been a recent renaissance in the organometallic chemistry of pentalene, following the discovery of the first complexes incorporating pentalene η8-ligated to a single metal center. This short review outlines recent work in the author's laboratory on the preparation of silylated pentalene ligands and the subsequent synthesis of novel, monometallic, and bimetallic pentalene sandwich and half-sandwich complexes of the f- and d-block elements.
New olefin polymerization and copolymerization catalysts. Effect of coordinating functionalities
Authors: Sen Ayusman
Published: October 2007

The coordination of the functionalities that may be present either in the monomer or in the growing polymer chain to the metal center is a key impediment in the development of new transition metal-based catalysts for the insertion polymerization of polar monomers. Several examples are discussed to illustrate this problem. Additionally, it is shown that the reduction of the electrophilicity of the metal center is one way to decrease this interaction.
Racemic catalysis through asymmetric activation
Authors: Mikami Koichi , Korenaga Toshinobu , Matsumoto Yousuke , Ueki Makoto , Terada Masahiro , Matsukawa Satoru
Published: October 2007

"Asymmetric activation" provides a general strategy for the use of racemic catalysts not only with atropos but also tropos ligands without enantiomer resolution.
Novel coordination behavior of unsaturated hydrocarbon ligands on Pd-Pd bonds
Authors: Kurosawa Hideo , Murahashi Tetsuro
Published: October 2007

The dinuclear Pd (I) complexes containing substitutionally labile acetonitrile ligands [Pd2 (CH3CN) 2 (L) 2] (BF4) 2 [L = CH3CN (1) , PPh3 (2) ] were prepared. The complex 1 was demonstrated to serve as a versatile building block for synthesizing sandwich chain complexes made of conjugated polyenes and linear polypalladium chains. The complex 2 reacted with 2 equiv arylacetylenes to give dinuclear organopalladium complexes arising from formal [2s + 2p + 2p] addition with the Pd-Pd s bond participating as one component. The reaction of 2 with 1,3-butadiene afforded a complex regarded as an intermediate lying halfway on the [2s + 4p] reaction coordinate.
Recent advances in asymmetric catalysis. Synthetic applications to biologically active compounds
Authors: Genet Jean Pierre , Marinetti Angela , Ratovelomanana-Vidal Virginie
Published: October 2007

New chiral cationic ruthenium complexes have been used for the industrial synthesis of (+) -dihydrojasmonate. A new class of electron-rich C2-symmetric 2,4-disubstituted phosphetanes (CnrPHOS) was developed. Preliminary evaluation of their catalytic properties revealed high efficiency in rhodium and ruthenium-catalyzed asymmetric hydrogenations. A new stereochemical model is presented in which the phosphetane Rh-catalyzed hydrogenation follows an apparent stability-controlled mechanism.
Copper complexes for catalytic, aerobic oxidation of hydrocarbons
Authors: Murahashi Shun-Ichi , Komiya Naruyoshi , Hayashi Yukiko , Kumano Tatsuyuki
Published: October 2007

Catalytic oxidation of hydrocarbons can be performed efficiently upon treatment with tert-butylhydroperoxide or peracetic acid in the presence of a low-valent ruthenium catalyst. Furthermore, aerobic oxidation of hydrocarbons can be performed in the presence of acetaldehyde using ruthenium, iron, and copper catalysts. Copper derived from copper chloride/crown ether or copper chloride/crown ether/alkaline metal salts have proved to be efficient catalysts. Further study revealed that specific copper complexes formed from copper salts and acetonitrile are convenient and highly useful catalysts for the aerobic oxidation of unactivated hydrocarbons.
Asymmetric synthesis with "privileged" ligands
Authors: Bandini Marco , Cozzi Pier Giorgio , Umani-Ronchi Achille
Published: October 2007

Different types of chiral "privileged" ligands 1 and 2 in promoting enantioselective addition of allylating agents to aliphatic and aromatic aldehydes are described. Here, a new concept in the asymmetric allylation reaction is presented. Redox [Cr (Salen) ] mediated addition of allyl halides to carbonyl compounds is described, and mechanistic investigations are discussed. These results open access to the fascinating area of the catalytic redox processes mediated by metallo-Salen complexes.
Reactions of d0 alkylidene and amide complexes with silanes
Authors: Diminnie Jonathan B. , Liu Xiaozhan , Cai Hu , Wu Zhongzhi , Blanton Jaime R. , Chen Tianniu , Tuinman Albert A. , Quisenberry Keith T. , Vallet Catherine E. , Zuhr Ray A. , Beach David B. , Peng Zhihui , Wu Yun-Dong , Concolino Thomas E. , Rheingold Arnold L. , Xue Ziling
Published: October 2007

Reactions of silanes with d0 Ta alkylidene and Group 4 amide complexes were found to involve the initial attack on silicon atoms in the silanes by nucleophilic alkylidene carbon or amide nitrogen atoms. The reaction of (Me3SiCH2) 3Ta (PMe 3) [=CHSiMe3] (1) with H2SiR'Ph (R' = Me, Ph) gave (Me3SiCH2) 3Ta[=C (SiMe 3) SiHR'Ph] (2a-b). Similar reactions of these two silanes and (H2PhSi) 2CH2 with (Me3SiCH2) Ta (PMe3) 2[=CHR]2 (R = SiMe3, 3; CMe3, 4) yielded novel metallasilacyclobutadienes and a metalladisilacyclohexadiene, respectively. In comparison, the reactions between M (NMe2) 4 (M = Ti, Zr, Hf) and silanes were found to give aminosilanes and metal amide hydride species which were perhaps involved in the formation of titanium-silicon-nitride (Ti-Si-N) ternary materials.
Chemistry of 1,2-allenyl/propargyl metal species. A personal account
Authors: Ma Sheng-Ming , Zhang Ai-Bin
Published: October 2007

The Pd (0) -catalyzed coupling reaction of aryl and electron-deficient alkenyl halides with the organozinc reagents formed by the subsequent treatment of 1-phenylalk-1-ynes with n-BuLi and ZnBr2 with or without a catalytic amount of HgCl2 was studied. Both the allene-formation- and the alkyne-formation-type coupling reactions were observed, depending on the structures of organic halides and 1-arylalk-1-ynes.
Asymmetric catalysis with "planar-chiral" heterocycles
Authors: Fu Gregory C.
Published: October 2007

Planar-chiral heterocycles serve as effective enantioselective nucleophilic catalysts and as useful ligands for asymmetric metal-catalyzed processes.
Rare earth metal-based catalysts for the polymerization of nonpolar and polar monomers
Authors: Okuda Jun , Arndt Stefan , Beckerle Klaus , Hultzsch Kai C. , Voth Peter , Spaniol Thomas P.
Published: October 2007

The synthesis of rare earth metal half-sandwich hydrido complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (THF) (µ-H) ] 2 (Ln = Y, Lu) through s-bond metathesis of the easily accessible alkyl complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (CH2 SiMe3) (THF) ] was developed. The dimeric yttrium hydrido complexes are highly fluxional, and a monomer-dimer equilibrium is present. They were tested as single-site, single-component catalysts for the polymerization of ethylene and styrene, as well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly and form isolable mono (insertion) products with styrene. The yttrium n-alkyl complexes [Y (h5:h1-C5Me 4SiMe2NCMe3) (R) (THF) ] [R = (CH2) nCH3, n = 3-9], prepared by the mono (insertion) of a-olefins, initiate polymerization in a relatively controlled manner. Thus, styrene was polymerized by the n-alkyl complex to give atactic polystyrenes with somewhat enriched syndiotacticities.
New P-chirogenic diphosphines and their use in catalytic asymmetric reactions
Authors: Imamoto Tsuneo
Published: October 2007

Enantiomerically pure (S,S) -1,2-bis[(o-alkylphenyl) phenylphosphino]ethanes (o-alkylphenyl = o-methylphenyl, o-ethylphenyl, o-isopropylphenyl, 5',6',7',8'-tetrahydro-naphthyl) , (S,S) -1,2-bis (alkyl-methylphosphino) ethanes (alkyl = t-butyl, 1-adamantyl, 1-methylcyclo-hexyl, 1,1-diethylpropyl, cyclopentyl, cyclohexyl) (abbreviated as BisP*) , and (R,R) -1,1-bis (alkylmethylphosphino) methanes (alkyl = isopropyl, t-butyl, cyclohexyl, phenyl) (abbreviated as MiniPHOS) were prepared from phosphorus trichloride via short routes using phosphine-boranes as intermediates. The crystal structures of cationic rhodium complexes, [Rh ((S,S) -1,2-bis ((phenyl) (5',6',7',8'-tetrahydronaphthyl) phosphino) ethane) (cod)]BF4, [Rh ((S,S) -t-Bu-BisP* (nbd))]BF4, and [Rh ((R,R) -t-Bu-MiniPHOS) 2]PF6, clearly indicate the ideal asymmetric environments. These ligands exhibited an excellent to almost perfect level of enantioselectivity in asymmetric hydrogenations of a-dehydroamino acid derivatives and other catalytic asymmetric reactions.
Names for muonium and hydrogen atoms and their ions(IUPAC Recommendations 2001)
Authors: Koppenol W. H.
Published: October 2007

Muons are short-lived species with an elementary positive or negative charge and a mass 207 times that of the electron. These recommendations concern positive muons, given the short lifetime of negative muons. A positive muon mimics a light hydrogen nucleus, and names are given in analogy to existing names for hydrogen-containing compounds. A particle consisting of a positive muon and an electron (µ+ e -) is named "muonium" and has the symbol Mu. Examples: "muonium chloride," MuCl, is the equivalent of deuterium chloride, 2 HCl or DCl; "muoniomethane", CH 3 Mu, is the product of the muoniation of methane;and NaMu is "sodium muonide."
Nomenclature of structural and compositional characteristics of ordered microporous and mesoporous materials with inorganic hosts(IUPAC Recommendations 2001)
Authors: McCusker L. B. , Liebau F. , Engelhardt G.
Published: October 2007

A system of terms applicable to ordered microporous and mesoporous materials is proposed, and rules for writing a standardized crystal chemical formula for such materials are presented. The recommendations are based both on common usage and on a systematic classification scheme. The nomenclature has been developed to encompass all inorganic materials with ordered, accessible pores with free diameters of less than 50 nm. The crystal chemical formula describes the chemical composition of both the guest species and the host, the structure of the host, the structure of the pore system, and the symmetry of the material. This formula can be simplified or expanded to suit the user's requirements.
Twentieth century developments in photochemistry. Brief historical sketches
Authors: Roth Heinz D.
Published: October 2007

In the 20th century, photochemistry blossomed from a poorly defined to a highly sophisticated science. Early breakthroughs in exploratory photochemistry and the underlying physical principles led to new diverse, yet inter-related areas of research. The alluring goal of asymmetric synthesis with circularly polarized light proved elusive. The discovery of the electron brought a gradual awakening to the idea of electron transfer. Time-resolved spectroscopy developed from ms to fs resolution. The field of photosynthesis progressed from an interest in function and structure of photosynthetic pigments to the isolation and structure elucidation of photosynthetic reaction centers (rhodobacter sphaeroides), to the detailed kinetics of sequential electron-transfer steps in natural and synthetic light-harvesting systems.
Photoactive pyrene-containing receptors for transition-metal ions
Authors: Fages Frédéric , Leroy Stéphanie , Soujanya Tirapattur , Sohna Jean-Ernest Sohna
Published: October 2007

Photoresponsive molecular receptors based on the photophysical properties of the pyrene chromophore were designed to exhibit tunable fluorescence emission upon binding of transition-metal ions.
Looking at the photodynamics of individual fluorescent molecules and proteins
Authors: García-Parajó M. F. , Veerman J.-A. , Kuipers L. , van Hulst N. F.
Published: October 2007

The photodynamics of individual molecules and fluorescent proteins has been investigated in real time. In the case of organic molecules, both the triplet state lifetime and intersystem crossing yield appear to vary in time and space. In the case of autofluorescent proteins, light-driven "on-off" fluorescence emission has been observed, with a behavior that is consistent with the existence of a long-lived dark state.
Molecular photovoltaics that mimic photosynthesis
Authors: Grätzel Michael
Published: October 2007

Learning from the concepts used by green plants, we have developed a photovoltaic cell based on molecular light absorbers and mesoporous electrodes. The sensitized nanocrystalline injection solar cell employs organic dyes or transition-metal complexes for spectral sensitization of oxide semiconductors, such as TiO2, ZnO, SnO2, and Nb2O5. Mesoporous films of these materials are contacted with redox electrolytes, amorphous organic hole conductors, or conducting polymers, as well as inorganic semiconductors. Light harvesting occurs efficiently over the whole visible and near-IR range due to the very large internal surface area of the films. Judicious molecular engineering allows the photoinduced charge separation to occur quantitatively within femtoseconds. The certified overall power conversion efficiency of the new solar cell for standard air mass 1.5 solar radiation stands presently between 10 and 11. The lecture will highlight recent progress in the development of solar cells for practical use. Advancement in the understanding of the factors that govern photovoltaic performance, as well as improvement of cell components to increase further its conversion efficiency will be discussed.
Important photochemical processes in the atmosphere
Authors: Moortgat Geert K.
Published: October 2007

Among the many important roles played by ozone in the atmosphere is the role it plays in the generation of OH radicals, which are responsible for initiating the oxidation of a wide variety of atmospheric trace constituents. The OH production occurs dominantly from the formation of the excited O(1D) species in the UV photolysis of ozone, followed by the reaction of O(1D) with H2O vapor. The photochemistry of ozone is very complex, as the relatively weak bonds in ozone allow different states of the O and O2 photoproducts to be accessed. Recent detailed studies have now revealed that different photolysis channels are occurring in the 290­375 nm spectral range, the region of importance for the generation of OH radicals in the lower atmosphere. The measured temperature-dependent quantum yields for the production of O(1D) atoms reflect the importance of the longer "wavelength tail" formation with regard to the enhanced OH production. Other significant atmospheric photolysis processes involving carbonyl compounds are reported. Direct photodissociation rates were measured in the outdoor photoreactor EUPHORE in Valencia and compared with model calculations. For most of the carbonyl compounds the effective quantum yields are significantly below unity.
Photophysics of π-conjugated metal­organic oligomers
Authors: Li Yiting , Whittle C. Ed , Walters Keith A. , Ley Kevin D. , Schanze Kirk S.
Published: October 2007

The optical absorption and photoluminescence properties of PPE-type p-conjugated oligomers that contain a 2,2-bipyridine-5,5¢-diyl metal coordinating unit have been examined. The spectra of the free oligomers are compared with those that contain ­Re(CO)3Cl and ­Ru(bpy)22+ chromophores chelated to the bpy-diyl unit.
Protein dynamics detected by the time-resolved transient grating technique
Authors: Terazima Masahide
Published: October 2007

Dynamics of two proteins [myoglobin and photoactive yellow protein (PYP)] initiated by photoexcitation were studied by the time-resolved transient grating (TG) and photo-acoustic methods. For both proteins, the temporal profiles of the TG signals showed new features that have not been detected before by the transient absorption method. These dynamics were attributed to the volume change, which is caused by the protein dynamics apart from the chromophores.
Singlet and triplet energy splitting in the radical ion pairs generated by photoinduced electron-transfer reactions
Authors: Tero-Kubota Shozo
Published: October 2007

Chemically induced dynamic electron polarization (CIDEP) spectra generated by photoinduced electron-transfer reactions have been studied using continuous-wave time-resolved EPR and FTEPR spectroscopy. It has been suggested that the energy difference (DEST) between the singlet and triplet states of radical ion pairs (RIPs) is dependent on the charge recombination free energy (­DGCR) and reorganization energy (l). The result is interpreted in terms of the spin-selective stabilization or destabilization of RIP states by electronic coupling with the S0 and locally excited triplet states of the donor­acceptor pair at equilibrium distance in the reaction coordinate. It has been verified that a charge transfer-type exchange interaction governs the DEST. Magnitudes as well as the sign of DEST can be predicted at the distance of the solvent-separated RIP based on DGCR and l values.
Coherent control for ultrafast photochemical reactions
Authors: de Vivie-Riedle Regina , Kurtz Lukas , Hofmann Angelika
Published: October 2007

Many photochemical processes involving the breaking and formation of chemical bonds take place on a femtosecond time scale. By means of ultrafast laser pulses it became possible to monitor these events in real time with a temporal resolution in the sub-20 fs regime. Moving beyond the observation to the control of chemical reactions requires additional theoretical and experimental effort. We illustrate with the aid of selected model systems the concepts and possibilities of "passive" and "active" control and their differences.
Molecular and biomolecular optoelectronics
Authors: Willner Itamar , Willner Bilha
Published: October 2007

Reversible electronic transduction of photonic processes occurring on electrodes is the conceptual method to develop molecular and biomolecular optoelectronic systems. Cyclic photochemical activation of molecular or biomolecular monolayer redox-functions provides a general methodology for the amperometric transduction of photonic information that is recorded by the chemical assembly. Alternatively, photoisomerizable monolayers associated with electrodes act as "command interfaces" for controlling the interfacial electron transfer between molecular redox-species or redox-proteins. The systems use a photonic input for the generation of an electronic output and act as information processing assemblies. Programmed arrays of photosensitizer/electron acceptor cross-linked Au-nanoparticle arrays are assembled on indium tin oxide (ITO) for photoelectrochemical applications.
Bracken adaptation mechanisms and xenobiotic chemistry
Authors: Alonso-Amelot Miguel E. , Oliveros Alberto , Calcagno María Pía , Arellano Elida
Published: October 2007

As opposed to animals, plants have to cope with the resources, environmental restrictions, herbivores, and pathogens they find in the particular spot where they are bound to grow. Hence, resource sequestration, predation and competition relationships, and adaptation to various sources of other environmental stresses and their seasonal variation must be flexible enough to ensure survival and successful reproduction. Plants express this fitness by a combination of biological traits and chemical arsenals which operate under the reign of a genome of considerable plasticity. For the great majority of plants it is either the biological characters or the chemical composition that are explored independently to understand their fitness. But only in a few instances is the combination of these two avenues examined jointly. The extensive studies on the ecology, chemistry, and toxicology of bracken (Pteridium aquilinum) make this fern one of the few examples where a reasonable explanation for its extraordinary success is beginning to emerge by the combined perception of these two most important aspects of plant life. It is the purpose of this article to briefly review how the sum of biological and chemical traits cooperates to make of bracken one of the five most pernicious weeds in the world today.
Pheromones and kairomones for control of pest insects. Some current results from a Swedish research program
Authors: Norin Torbjörn
Published: October 2007

Some recent results from a research program dealing with the isolation, identification, and synthesis of biologically active compounds for applications in agriculture and forestry will be reported. The solid-phase micro extraction (SPME) technique has been successfully used for identification of the main sex pheromone components of Cydia and Bonagota species (Lepidoptera, Tortricidae). Synthesis of a series of dodecadienols, tetradecadienols, and their corresponding aldehydes and acetates have been performed to be used for testing inhibitory and synergistic effects on pest insects of these species. Behaviorally active volatile compounds emitted from aphids and aphid-infested plants have been identified by SPME-technique, synthesized, and used in olfactometer tests. Methyl salicylate is shown to act in interplant communication released by plants infested by insects. In the presence of the compound, the colonization density of aphids in crop is reduced. Methyl salicylate is a common multifunctional compound, which is active in several biological systems. The action of this compound as an anti-aphrodisiac will be presented. The compound is transferred at mating from the male pierid butterfly Pieris napi to the female and makes the female unattractive for mating.
Treatment of Tunisian salt lakes using solubility phase diagrams
Authors: Kbir-Ariguib Najia , Chehimi Dalila Ben Hassan , Zayani Lotfi
Published: October 2007

The Tunisian salt lakes are considered as an important materials resource useful for industry and agriculture. They are called sebkhat or chott, and they cover a large part of Tunisian land. Their brines correspond to the quinary system: Na+, K+, Mg2+ / Cl­, SO4
2­­H2O. In the first part of this paper, a short description and abstracted geochemical and economical data about some Tunisian salt lakes are given. In the second part, the fitting equations used for modeling the quinary system are established and applied to the subsystems NaCl­KCl­H2O, NaCl­MgCl2­H2O, KCl­MgCl2­H2O, and to NaCl­Na2SO4­H2 O, KCl­K2SO4­H2 O, Na2SO4­K2SO 4­H2O. The coherence between the calculated and the experimental diagrams is discussed.
Phase diagrams at high temperature and high pressure. Determination and consequent developments
Authors: Cohen-Adad M. Th.
Published: October 2007

This presentation focuses on condensed phases within the broader area of phase diagrams at high temperature and high pressure.
Thermodynamic modeling of crystal deposition in humans
Authors: Königsberger Erich , Königsberger Lan-Chi
Published: October 2007

The prevention and treatment of crystal deposition in the human body are based on the understanding of the physicochemical properties underlying the precipitation of the substances involved. Among these properties, the solubilities of the crystals are very important. Recently, experimentally determined solubility data of substances related to urolithiasis, such as calcium oxalate hydrates, uric acid and urates, cystine, and xanthine, were critically assessed. Unfortunately, reported solubilities of these substances were found to be either scarce or in large disagreement. Consequently, detailed studies were carried out in our laboratory, and the results will be discussed in this communication with emphasis on the thermodynamic consistency of the experimentally determined data. Since proper modeling of the solubilities of these substances in artificial urine solutions serves as a prerequisite for solubility predictions in real urine, the Joint Expert Speciation System (JESS) software package was employed to create a comprehensive computer model including the relevant, low-molecular inorganic and organic components of urine. The results of the simulations lead to some useful suggestions regarding the prevention and treatment of stone disease.
Dissolution and formation of nuclear materials in molten media
Authors: Ogawa T. , Minato K.
Published: October 2007

As innovative means to recover actinides from irradiated fuels, pyrochemical processes are proposed. In the Japan Atomic Energy Research Institute (JAERI), the feasibility of applying molten-salts processes to nitride fuels containing transuranium elements for transmutation is investigated. In the course of study, experiments and analyses have been made on the high-temperature chemistry of M­N­Cl systems, the effects of oxygen impurities, and the implications of the divalent state along with the normal trivalent state of lanthanides and actinides. Thermodynamic calculation and the electrochemical measurements are compared in a few aspects of dissolution and precipitation of nuclear materials in molten halides.
Solid-state solubility and its limits. The alkali halide case
Authors: Oonk H. A. J.
Published: October 2007

The group of binary common-ion alkali halide systems correspond to an excellent vehicle for discussing and demonstrating the influence of mismatch in sizebetween the building units of the host crystal and the units of the gueston the formation of mixed crystals and the limits of solid-state solubility. The numerical values of just four constants are needed to formulate a uniform thermodynamic description of the mixed crystalline state of the group of systems. In terms of deviation from ideal mixing behavior, in terms of the excess Gibbs energy, two constants are needed to relate the magnitude of the function to mismatch in size. One constant is to account for the asymmetry of the function, and one to express the dependence on temperature. The values of the constants have been assessed with the help of data available for 13 systems showing complete miscibility. The uniform description allows one to calculate, for every system of the group, the solubilities of the components in one another at any temperature.
Blends containing core-shell impact modifiers Part 1. Structure and tensile deformation mechanisms (IUPAC Technical Report)
Authors: Bucknall C. B.
Published: October 2007

Two impact modifiers, based respectively on polybutadiene (PB) and poly(butyl acrylate-co-styrene) (PBA), are compared in blends with four glassy polymers: polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC). Dynamic mechanical tests show glass transitions at about -80 °C in PB and -15 °C in PBA. Both modifiers have grafted PMMA shells, which are seen in the transmission electron microscope (TEM) to be about 10 nm thick. The two-stage PB particles have 200-nm-diameter polybutadiene cores, whereas the three-stage PBA particles have 260-nm-diameter PMMA cores, with 20-nm thick PBA rubber inner shells. Under tension, the PB particles cavitate to form single voids on reaching a critical volume strain, and subsequently offer little resistance to dilatation. By contrast, tensile tests performed in situ in the TEM show that the PBA shells form fibrils that are anchored to the rigid core, and act as constraints on further dilatation: the stresses developed in the PBA fibrils can be sufficient to draw fibrils from both the PMMA core and the PSAN matrix. There is evidence that the PMMA shells can debond from the matrix both in cryogenic fracture and in fatigue at 23 °C. Tensile dilatometry shows that the PB particles cavitate at higher strains than the PBA particles, but that the PB particles then cause a rapid volume increase, leading to a low strain at break. By contrast, the PBA particles produce a more controlled dilatation, and higher strains to break. Later papers in this series treat the mechanical and rheological behavior of these blends in more detail.
Blends containing core-shell impact modifiers Part 2. Melt rheology of rubber-toughened plastics (IUPAC Technical Report)
Authors: Kozlowski M. , Bucknall C. B.
Published: October 2007

The influence of impact modifiers composed of an elastomer-based core and a poly(methyl methacrylate) (PMMA) shell on the melt flow properties of different thermoplastics has been studied, using both steady-state and dynamic viscosity measurements. The melt viscosities of the rubber-toughened blends were similar to those of the matrix polymers, over the range of shear rates commonly applied during melt processing. In the case of the matrix polymers, viscosity curves obtained under dynamic conditions coincided with those obtained under steady-state conditions. However, for blends the two curves show a slight divergence at low strain rates, where yielding is observed.
Human exposure to outdoor air pollution (IUPAC Technical Report)
Authors: Hertel Ole , De Leeuw Frank A. A. M. ,   Oleraaschou-Nielsen, Jensen Steen Solvang , Gee David , Herbarth Olf , Pryor Sara , Palmgren Finn , Olsen Erik
Published: October 2007

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Human exposure to outdoor air pollution is believed to cause severe health effects, especially in urban areas where pollution levels often are high, because of the poor dispersion conditions and high density of pollution sources. Many factors influence human health, and a good assessment of human air pollution exposure is, therefore, crucial for a proper determination of possible links between air pollution and health effects. Assessment of human exposure is, however, not straightforward, and this is the background for the present paper, which recommends how to carry out such assessments. Assessment of human exposure to air pollution may be carried out by use of:

categorical classification,

application of biomarkers,

analysis of air pollution data from routine monitoring networks,

personal portable exposure monitors, or

application of mathematical air pollution exposure models.

The categorical classification is a crude indirect method based on indicators of exposure such as type of residence, type of job, presence of indoor sources, etc. Categorical classification is generally inadequate for application in air pollution epidemiology. Biomarkers can be a strong instrument in assessment of health effects and provide information about air pollution exposure and dose. Use of biomarkers is, therefore, particularly useful when applied in combination with exposure assessment through one of the methods 3 to 5. The main focus of this paper is on these three methods for determination of human air pollution exposure. The optimal solution is clearly a combination of methods 2 to 5, but the available resources often set a limit to how far the assessment is carried out, and the choice of strategy will, therefore, often be very important for the outcome of the final study. This paper describes how these approaches may be applied and outlines advantages and disadvantages of the approaches used individually and in combination. Furthermore, some examples of specific applications in Denmark and the Netherlands are given for illustration.
On the discovery of the elements 110-112 (IUPAC Technical Report)
Authors: Karol P. J. , Nakahara H. , Petley B. W. , Vogt E.
Published: October 2007

The IUPAC/IUPAP joint working party on the priority of claims to the discovery of elements 110, 111, and 112 has reviewed the relevant literature pertaining to the several claims. In accordance with the criteria for the discovery of elements, previously established by the 1992 IUPAC/IUPAP Transfermium Working Group, it was determined that the claim by the Hofmann et al. research collaboration for the discovery of element 110 at GSI has fulfilled those criteria. For elements 111 and 112, the collaboration of Hofmann et al. produced high-quality data with plausible interpretations, but confirmation by further results is needed to assign priority of discovery for these elements. The working party was not convinced that claims of other collaborations have satisfied the discovery criteria.