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Enantioselective carbon-hydrogen (C-H) activation reactions by asymmetric metallation could provide new routes for the construction of chiral molecules.sup.1,2. However, current methods are typically limited to the formation of five- or six-membered metallacycles, thereby preventing the asymmetric functionalization of C-H bonds at positions remote to existing functional groups. Here we report enantioselective remote C-H activation using a catalytic amount of a chiral norbornene as a transient mediator, which relays initial ortho-C-H activation to the meta position. This was used in the enantioselective meta-C-H arylation of benzylamines, as well as the arylation and alkylation of homobenzylamines. The enantioselectivities obtained using the chiral transient mediator are comparable across different classes of substrates containing either neutral [sigma]-donor or anionic coordinating groups. This relay strategy could provide an alternative means to remote chiral induction, one of the most challenging problems in asymmetric catalysis.sup.3,4. Remote, enantioselective C-H activation reactions can be achieved by relaying ortho-C-H activation to the meta position, using a chiral norbornene as the mediator., Author(s): Hang Shi [sup.1] , Alastair N. Herron [sup.1] , Ying Shao [sup.1] , Qian Shao [sup.1] , Jin-Quan Yu [sup.1] Author Affiliations: (1) Department of Chemistry, The Scripps Research [...]

Abstract: Depicting the mechanism, the step-by-step path followed by a reaction, has evolved to also indicate the movement of electrons during each step through the use of curly arrows. The [...]

A new sodium chlorite--iodide--acetylacetone chemical oscillatory reaction has been studied by the UV-Vis spectrophotometric method. The initial concentrations of acetylacetone, sodium chlorite, iodide, and sulfuric acid and the pH value have great influence on the oscillation observed at a wavelength of 570 nm for the starch-triiodide complex. There is a pre-oscillatory or induction stage and the amplitude and number of oscillations depend on the initial concentration of the reactants. Equations for the starch-triiodide complex reaction rate change with reaction time and the initial concentrations in the oscillation stage were obtained. The induction time decreases linearly with the initial concentration of acetylacetone or sodium chlorite but increases linearly with the initial concentration of sulfuric acid. The oscillation reaction can be accelerated by increasing the reaction temperature. The apparent activation energies at the induction stage and the oscillation stage were 61.02 and 61.36 kJ/mol, respectively, indicating that the two stages have similar reaction mechanisms. Generating the enol isomer by keto-enol tautomerism is an important step to constrain the time of the induction period. Key words: sodium chlorite, oscillation reaction, UV-Vis spectrophotometry, apparent activation energy, acetylacetone. Nous avons etudie une nouvelle reaction chimique oscillante faisant intervenir le chlorite de sodium--iodure acetylacetone par une methode spectrophotometrique UV-Vis. Les concentrations initiales d'acetylacetone, de chlorite de sodium, d'iodure et d'acide sulfurique et les valeurs du pH ont une importante influence sur l'oscillation observee a une longueur d'onde de 570 nm dans des complexes d'amidon et de triiodure. On observe d'abord un stade pre-oscillatoire, ou une periode d'induction, puis l'amplitude et le nombre d'oscillations depend de la concentration initiale des reactifs. Nous avons etabli les equations decrivant la variation de la vitesse de reaction du complexe amidon-triiodure en fonction du temps de reaction et des concentrations initiales au stade d'oscillation. La periode d'induction decroit de facon lineaire avec la concentration initiale d'acetylacetone ou de chlorite de sodium, mais croit, de facon lineaire aussi, avec la concentration initiale d'acide sulfurique. La reaction oscillante peut etre acceleree en augmentant la temperature. Les energies d'activation apparentes aux stades d'induction et d'oscillation etaient de 61,02 et de 61,36 kJ/mol, respectivement, indiquant que des mecanismes de reaction semblables operent aux deux stades. La generation de l'isomere enolique par tautomerisme ceto-enolique est une etape importante pour reduire la periode d'induction. [Traduit par la Redaction] Mots-cles: chlorite de sodium, reaction oscillante, spectrophotometrie UV-Vis, energie d'activation apparente, acetylacetone., Introduction Chemical oscillations are systems of chemicals that exhibit time-based fluctuations when they are far from equilibrium. Chlorite and chlorine dioxide based chemical oscillations play an important role in 'nonlinear [...]

Dirty air threatens the health of billions of city dwellers around the world. China's megacities are among the worst, with concentrations of airborne pollutants 10-100 times higher than those in [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.techfore.2006.11.003 Byline: Totti Konnola (a), Ville Brummer (b), Ahti Salo (b) Keywords: Foresight; Innovation processes; Internet-based consultation; Multi-criteria decision analysis; Portfolio modeling; Path dependence Abstract: Foresight activities have often provided support for objectives such as priority-setting, networking and consensual vision-building. In this paper, we draw upon complementary evolutionary perspectives and discuss these objectives from the viewpoint of diversity which may be vital in contexts characterized by technological discontinuities and high uncertainties. We also argue that although the scanning of weak signals has been widely advocated in such contexts, the solicitation of ideas for prospective innovations may provide more focused, action-oriented, and comparable reflections of future developments. For the analysis of such ideas, we develop a collaborative foresight method RPM Screening which consists of phases for the generation, revision, multi-criteria evaluation, and portfolio analysis of innovation ideas. We also report experiences from a pilot project where this method was employed to enhance the work of the Foresight Forum of the Ministry of Trade and Industry in Finland. Encouraging results from this project and other recent applications suggest that RPM Screening can be helpful in foresight processes and the development of shared research agendas. Author Affiliation: (a) VTT Technical Research Centre of Finland, Kemistintie 3, P.O.Box 1002, Espoo, FIN-02044 VTT, Finland (b) Systems Analysis Laboratory, Helsinki University of Technology, P.O.Box 1100, Helsinki, FIN-02015 TKK, Finland Article History: Received 18 October 2005; Revised 10 May 2006; Accepted 13 November 2006

The roles of steric crowding and halogen substitution on the local mode properties of CH oscillators in 1,1,1-trichloroethane were investigated and these local mode properties were compared with those in less crowded molecules and similarly crowded molecules that contain fewer halogens. Multiple complex Fermi resonances were observed in 1,1,1-trichloroethane and in COT between local mode states and local mode/normal mode combination states.

The dynamics of a series of 1-acylaminoanthraquinones with varying degrees of excited-state intramolecular proton transfer are studied in acetonitrile and dichloromethane. Reorganization of the solvent in response to the significant changes in the intermolecular interactions upon proton transfer is found to play an important role in the reaction dynamics.

Abstract -- A new method is proposed for improving the selectivity of semiconductor sensors based on studies of their noise characteristics. The chemisorption of gases and vapors, as well as [...]

The kinetic characterization of the cleavage of the persulfide intermediate in the group I desulfurase Slr0387 from 'Synechocystis' sp. PCC 6803 by a series of chemical reductants is reported. Thus it seems that the activation of cysteine desulfurases (CDs) by accessory proteins can involve effects on either persulfide formation or its subsequent cleavage (or both).

The absolute rate constant of the reaction C2H + NH3 is determined over the temperature range 295-765 K at a pressure of 10 Torr (He) and over a pressure range 5-30 Torr at 295 K. The high rate constant of the reaction, both at combustion temperatures and at interstellar temperatures, makes it very important in planetary atmospheres and combustion environments.

A study of lobe-forming liquid jets of ethylene glycol emerging from narrow slit-shaped nozzles is reported. It was observed that increase in jet velocity elongates the lobes but does not change their number and also the insights in molecular reactions can be valuable in controlling chemical reactions.

The structure and properties of alkyammonium monolayers self-assembled on a montmorillonite surface as well as their dependence on chain length and packing density are investigated. Alkylammonium monolayers, at ambient temperatures, assembled on montmorillonite adopt a two-dimensional state or a disordered state depending on the cross-sectional area of the molecules.

In this paper variance spectra of chemically active species in a dry convective boundary layer are studied by means of large-eddy simulations (LESs). The aim is to quantify the impact of chemistry on the spatial fluctuations in the concentration fields. The computational domain has a large aspect ratio (width/height = 16) in order to encompass all relevant scales (mesoscale to microscale). Variance spectra are used to calculate a characteristic length scale of the species' concentration variability. By locating the peak in the spectrum, a 'variance dominating length scale' is derived. For a simple first-order reaction, this length scale demonstrates a clear dependence on the reaction rate: an increase in the reaction rate leads to a significant decrease of the length scale of the species. For a chemical cycle composed of a second-order reaction and first-order backreaction, the length scales turn out to depend much less on the reaction rate. The value of the length scales of the species involved appears to lie well in the mesoscale range, rather than the microscale range, demonstrating that concentration fluctuations are driven predominantly by scales much larger than the depth of the boundary layer. External perturbation of the chemical balance can have a direct impact on the variance spectra. For the case where a (hypothetical) passing cloud switches off the chemical backreaction for a while, a dramatic drop in the length scale of the nonabundant species is observed. Once the feedback has been restored, a rapid increase of the length scale is observed. To better understand these results, a spectral model is developed that incorporates turbulent production and dissipation of variance, chemistry, and spectral transfer. The model gives valuable insight into the relative importance of these processes at each scale separately, an d enables one to predict the value of the variance dominating length scale in the limiting cases of very slow and very fast chemistry.

The linear and nonlinear optical properties of a new organic dye, trans-4-[p-(N-ethyl-N-ethylamino) styryl]-N-methyl-pyridinium tris(thiocyanato) cadmates (II), are reported in this paper. When pumped with a picosecond laser at the wavelength range of 850-1200 nm, intense upconversion fluorescence can be obtained. The upconversion efficiencies at different pump energies were measured when pumped with a 1064-nm laser beam from a mode-locked Nd:YAG laser. The highest upconversion efficiencies were measured to be 5.8% and 7.6% in dimethyl formamide (DMF) and methanol. The lifetime of the dye in DMF was measured to be 75 ps. The strongest nonlinear absorption was at the wavelength of 940 nm, and the highest upconversion efficiency was at the wavelength of 1030 nm. The difference of the two wavelengths was caused by excited state absorption in the dye at wavelengths shorter than 1000 nm. The dye solution in DMF and methanol show a clear optical power limiting effect. OCIS codes: 140.0140, 140.2050, 190.4180, 190.7220.

The article draws attention to the increasing awareness and activity in the area of supramolecular chemistry worldwide and a need for a comprehensive interactive electronic textbook. A vesion of such a book focusing on the structural features of supramolecular species and assemblies is presented.

Thermodynamic reactions that are not at a constant temperature and pressure are rarely covered in basic thermodynamic chemistry because they require too much explanation. However, a computer program using the formula A + B in equilibrium with C can teach chemistry students that the equilibrium theory is valid and applicable to all reaction mode types without requiring extensive classroom time. Examples for using the computer program are included.

The addition of boron-hydrogen bond to various carbon-carbon and carbon-heteroatom double bond is studied using the Interactive Generation of Organic Reactions 2 program. The resulting reactions indicate that the hydroboration of enamines can give both alpha and beta-adducts. It is also found that the alpha and beta adducts ciuld undergo rearrangement to produce the corresponding B-aminomonoalkylborane.

A simple computer program using the mass-action law and knowledge that partial pressures or concentrations in a chemical reaction cannot be negative can calculate equilibrium constants without using the thermodynamic proof that confuses many students. Equilibriums for competing, catalytic and coupled chemical reactions can be determined by the convergence of numerical computations of one root of a quadratic equation.

We have carried out an ab initio electronic structure calculations of electron transfer couplings between chromophores in the bacterial photosynthetic reaction center. The couplings agree remarkably well with parameters obtained from recent quantum dynamical modeling of experimental data assuming an explicit intermediate mechanism. We also have computed couplings on the M-side of the reaction center and have found that the interaction of the primary donor to the M-side intermediate bacteriochlorophyll is quite small because of destructive interference of the two localized coupling matrix elements. This may explain the slow rate of electron transfer down the M-side of the reaction center.

Simulations of molecular dynamics can help chemistry students visualize abstract ideas in a concrete manner. The mathematics application software Mathematica can be used to produce an animated simulation through its notebook function. The example of silicon-fluorine etching reactions is provided with data files recording atom positions at selected intervals. This technique can both fascinate students and make the concepts more approachable.

Alchemy II, a molecular-modeling computer program, can be used to predict reactions through simulated reactions generated by steric energies calculations of structures based on the minimumization of an operator provided structure. The program was used to predict the reaction of 1,1'-dibromocyclopentylcyclohexane with silver nitrate under Kakis' procedure using H.C. Brown's I-strain theory. The actual experiment supported the simulation-generated predictions.

A microcomputer simulation programme was developed for use with the British Broadcasting Corporation (BBC) Master computer to record reactions between iodide ions and persulphate ions in the presence of thiosulphate ions. It allows pupils to experiment with more temperature and concentration levels and combinations than possible manually.

A new approach for the synthesis of chiral diphosphine and monodentate phosphorus ligands on a spiro scaffold is discussed. These complexes are shown to play a significant role in the transition-metal-catalyzed asymmetric reactions.

The first highly anti-selective direct-type catalytic aldol reactions of amides with aldehydes are disclosed. It is observed that aldol reactions are among the most powerful and efficient methods for carbon-carbon bond formation and continuous efforts are dedicated to the development of catalytic asymmetric aldol reactions.

Simple hydrogelation with poly (vinyl alcohol) (PVA) was used for the development of the first actuator based on multiwalled carbon nanotube (MWNT) hydrogels. The salts of carboxylic MWNTs exhibited excellent actuating properties through simple hydrogelation with PVA.

Alternative titanium-mediated aldol procedure based on several protected Beta-hydroxy ethyl ketones is surveyed. Eventually, enolization of (S)-1-benzyloxy-2-methyl-3-pentamone with (i-PrO)/TiCl(sub 3)/i-Pr(sub 2)NEt provided a very reactive enolate that afforded the corresponding 2,4-syn-4,5-syn aldol adducts in high yields and diasteromeric ratios with a broad range of aldehydes.

A study was conducted to give an overview of the wide-range of nanoreactors that were constructed from synthetic and biological building blocks using both covalent and covalent approaches. The self-assembled nanoreactors that are discussed can be considered as the simple mimics of a cell and contain a cavity in which there is a possibility of a chemical reaction taking place.

A study was conducted on the ferrion-catalyzed Belousov-Zhabotinsky (BZ) reaction in a batch reactor under anaerobic conditions and was found to evolve through two separate regimes of complex oscillations. The two bifurcation regimes exhibited qualitatively different dependence of compositions of the reaction mixture.

The development of three efficient DNA-templated functional group transformations and their use to transform a single-solution mixture of organic azides into sequence-programmed sulfonyl chloride, chloroformate, isocyanate, and isothiocyanate reactants not linked to DNA is described. The linkage of reagents to DNA is not possible or convenient, these transformations only allow such reagents to contribute to small-molecule syntheses.

The comprehensive bioconversion of a series of aromatic compounds with a benzene ring is reported with picolinic acid, which was performed by simple growing cell reactions using recombinant microbes. The products converted from the respective substrates were found to be aromatic compounds, in which a benzene ring was replaced with picolinic acid.

The trans-metalation process involved in the palladium-catalyzed borylation of aryl halide with diboron was theoretically studied. The purpose was to clarify the electronic process, to characterize what was an important factor in the acceleration of the trans-metalation and to offer predictions for future development of the cross-coupling reaction.

The extent to which oxyanion-solvent interactions, oxyanion-amino acid interactions and the anion-binding pocket sizes of the cognate protein influence the anion selectivity process in transport proteins is investigated. Quantum mechanical calculation and continuum dielectric methods are used for the study.

Resonance Raman spectroscopic techniques and quinone staining are used to identify and study the biogenesis of hydroypropylphosphonic acid epoxidase (HppE). It is found that HppE can act as an oxygenase through a putative high valent iron-oxo or an iron-hydroperoxo intermediate.

Noradamantylchlorocarbene was observed in low-temperature matrices and thus evidence for C-tunneling in its subsequent ring expansion is presented. This is the first direct observation of heavy-atom quantum mechanical tunneling in a singlet chlorocarbene rearrangement.

In kinetic models, gas-phase reactions involving large molecules are often supposed to be in the high pressure limit. Simple formulas are being presented, giving guidance for deciding whether a particular reaction's rate can be accurately approximated.

A study was conducted, using density functional theory and continuum dielectic calculations, to find out the kinetic competition of sulfur and nitrogen nucleophiles L in the substitution reactions of cisplatin derivatives. The calculations from the study reveals the intrinsic kinetic preference of platinum(II) for nitrogen over sulfur ligands.

For studying metal hydrides, Pd-based alloys offer a class of attractive materials, because of its higher solubility and permeability with hydrogen. Pd/Ag is the alloy mostly used for the hydrogen extraction industries.

A polymerase chain reaction (PCR)-less target DNA amplification method, which relies on novel two-component oligonucleotide-modified gold nanoparticles (NPs) and single-component oligonucleotide-modified magnetic microparticles (MMPs), is presented. PCR is a primer-mediated enzymatic DNA amplification method, which has significantly influenced the biological and medical communities.

To achieve a useful conversion of prochiral imines to chiral 2-(2-aryl-2-amino-ethyl)acrylates, carbethoxyallylstannane was employed along with the bis-pi-allylpalladium complex. These are important building blocks for further asymmetric of a wide range of compounds.

The experiment conducted to regenerate phenols from various ethers, with the use of enhanced halide anion nucleophilicity, in the form of ionic liquid [bmin][Br], in conjunction with a proton source is presented. The methods for cleavage of ether are described.

The experiment conducted to develop an excimer-monomer switching molecular beacon, Excimer-Monomer Switching Molecular Beacons (EMS-MBs) that has the advantages of synthetic simplicity, and unambiguous detectability as compared with conventional fluorescence resonance energy transfer molecular beacons is presented. The synthesis of EMB-MBs is discussed.

The reactions of a Mn(II) complex, [Mn(PaPy3)(H2O)CIO4, and Mn(III) complex, [Mn(PaPy3)(Cl)]ClO4 with nitric oxide (NO) is studied. The principle findings and conclusions of the study are presented.