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Selected AbstractsUnconventional Spin Crossover in Dinuclear and Trinuclear Iron(III) Complexes with Cyanido and Metallacyanido BridgesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2009alitro Abstract A nonsymmetrical triamine, 1,6-diamino-4-azahexane, was Schiff-condensed with (X-substituted) o -salicylaldehyde to yield pentadentate ligands X-L5: salpet and MeBu-salpet. These ligands form mononuclear, dinuclear, and trinuclear FeIII complexes, whose structures were determined by single-crystal X-ray analysis. Of the mononuclear complexes, [FeIII(salpet)Cl] and [FeIII(MeBu-salpet)Cl] are high spin (S = 5/2), whereas [FeIII(salpet)CN]·MeOH is low spin (S = 1/2). The dinuclear and trinuclear complexes show a kind ofthermally induced spin crossover. The dinuclear complex [L5FeIII(CN)FeIIIL5](ClO4)·2H2O (L5 = salpet) is a mixed-spin assembly: the C -coordinated FeIII center is low spin (L) and the N -coordinated FeIII center is high spin (H) at low temperature; an antiferromagnetic interaction occurs between them. This LH reference state is mixed with the LL one. Upon heating, the system shows an increasing content of the HH state. Also, the dinuclear complex [L5FeIII(CN)FeIIIL5](BPh4)·2MeCN (L5 = MeBu-salpet) exhibits a spin transition between LH and HH spin pairs. The mixed-valence trinuclear complex [L5FeIII{FeII(CN)5(NO)}FeIIIL5]·0.5MeOH·3.75H2O (L5 = salpet) shows spin crossover with a residual high-spin fraction at liquid He temperature owing to the LL + LH ground state. The metallacyanido-bridged complex [L5FeIII{Ni(CN)4}FeIIIL5]·2MeOH (L5 = MeBu-salpet) contains a high-spin pair, HH, over the whole temperature interval with a ferromagnetic exchange interaction. A theoretical model was outlined that allows simultaneous fitting of all available experimental data (magnetic susceptibility, magnetization, high-spin mole fraction obtained from the Mössbauer spectra) on a common set of parameters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Contrasting paleofluid systems in the continental basement: a fluid inclusion and stable isotope study of hydrothermal vein mineralization, Schwarzwald district, GermanyGEOFLUIDS (ELECTRONIC), Issue 2 2007B. BAATARTSOGT Abstract An integrated fluid inclusion and stable isotope study was carried out on hydrothermal veins (Sb-bearing quartz veins, metal-bearing fluorite,barite,quartz veins) from the Schwarzwald district, Germany. A total number of 106 Variscan (quartz veins related to Variscan orogenic processes) and post-Variscan deposits were studied by microthermometry, Raman spectroscopy, and stable isotope analysis. The fluid inclusions in Variscan quartz veins are of the H2O,NaCl,(KCl) type, have low salinities (0,10 wt.% eqv. NaCl) and high Th values (150,350°C). Oxygen isotope data for quartz range from +2.8, to +12.2, and calculated ,18OH2O values of the fluid are between ,12.5, and +4.4,. The ,D values of water extracted from fluid inclusions vary between ,49, and +4,. The geological framework, fluid inclusion and stable isotope characteristics of the Variscan veins suggest an origin from regional metamorphic devolatilization processes. By contrast, the fluid inclusions in post-Variscan fluorite, calcite, barite, quartz, and sphalerite belong to the H2O,NaCl,CaCl2 type, have high salinities (22,25 wt.% eqv. NaCl) and lower Th values of 90,200°C. A low-salinity fluid (0,15 wt.% eqv. NaCl) was observed in late-stage fluorite, calcite, and quartz, which was trapped at similar temperatures. The ,18O values of quartz range between +11.1, and +20.9,, which translates into calculated ,18OH2O values between ,11.0, and +4.4,. This range is consistent with ,18OH2O values of fluid inclusion water extracted from fluorite (,11.6, to +1.1,). The ,D values of directly measured fluid inclusion water range between ,29, and ,1,, ,26, and ,15,, and ,63, and +9, for fluorite, quartz, and calcite, respectively. Calculations using the fluid inclusion and isotope data point to formation of the fluorite,barite,quartz veins under near-hydrostatic conditions. The ,18OH2O and ,D data, particularly the observed wide range in ,D, indicate that the mineralization formed through large-scale mixing of a basement-derived saline NaCl,CaCl2 brine with meteoric water. Our comprehensive study provides evidence for two fundamentally different fluid systems in the crystalline basement. The Variscan fluid regime is dominated by fluids generated through metamorphic devolatilization and fluid expulsion driven by compressional nappe tectonics. The onset of post-Variscan extensional tectonics resulted in replacement of the orogenic fluid regime by fluids which have distinct compositional characteristics and are related to a change in the principal fluid sources and the general fluid flow patterns. This younger system shows remarkably persistent geochemical and isotopic features over a prolonged period of more than 100 Ma. [source] The dynamics of nitrogen movement in an Arctic salt marsh in response to goose herbivory: a parameterized model with alternate stable statesJOURNAL OF ECOLOGY, Issue 4 2003N. A. Walker Summary 1LPBN is a parameterized simulation model of flows of nitrogen (N) in an ecosystem of cyanobacteria, grass and grazers, based on the N dynamics of a grazed Puccinellia lawn in an intertidal marsh on Hudson Bay. This system shows two alternate stable states: (a) lawns that either support a foraging population of lesser snow geese, or are not grazed by geese; and (b) exposed saline sediments that support little or no vegetation. The model represents the flow of N from cyanobacterial fixation, the major N input into the system, to the geese that migrate in autumn; those that do not return represent the major N output from the system. We have modelled N fixation, the transformations of N in the soil, plant growth, lawn regeneration, and goose grazing and grubbing. 2The model simulates steady-state flows of N similar to those observed in the field at zero and at moderate goose density, and it also simulates the transition to the state of zero plant biomass, a consequence of increased grubbing at high goose density. The simulated steady-state flows are found to be more sensitive to changes in the parameters that describe N fixation and goose biology, than to similar changes in the parameters describing plant biology. 3Because the model shows the alternate stable states and the transition between them, with values for the state variables that are consistent with field data, we conclude that N dynamics are crucial in determining the stability of the real salt marsh-goose system. The determining factor is the loss of the input of N from fixation when lawn area is reduced because the rate of goose grubbing exceeds that of plant re-establishment. [source] Metastable persistence of pelitic metamorphic assemblages at the root of a Cretaceous magmatic arc , Fiordland, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009N. R. DACZKO Abstract Four aluminosilicate-bearing, amphibolite facies pelitic schists sampled from the root of the long-lived eastern Gondwana continental magmatic arc now exposed in southwest Fiordland, New Zealand, record remarkably different P,T,t histories. The four samples were collected from within 20 km of each other within the Fanny Bay Group and Deep Cove Gneiss near Dusky Sound. Integrated petrography, mineral chemistry, mineral equilibria modelling and in situ electron microprobe chemical dating of monazite shows that the sample of the Fanny Bay Group south of the Dusky Fault records a Carboniferous history with peak conditions of 4,4.5 kbar at 570,590 °C, while one sample of the Deep Cove Gneiss from Long Island records a Cretaceous history with apparent peak conditions of 7.5 kbar at 650 °C. Two other samples of the Deep Cove Gneiss from Resolution Island record mixed Carboniferous and Cretaceous histories with apparent peak conditions of 7 kbar at 650 °C and 3,7 kbar at 640,720 °C. The metapelitic schists on Resolution Island were intruded by arc magmas including the voluminous high- P Western Fiordland Orthogneiss, yet they lack mineralogical evidence of the Cretaceous high- P (>12 kbar) event. Analysis of water isopleths in a model system shows that the amount of water accommodated in the rock mineral assemblage increases with pressure. With the exhaustion of all free water, and without the addition of external water, these rocks persisted metastably within the deep arc during the high- P event. The emplacement of large volumes of diorite (i.e. the Western Fiordland Orthogneiss) into the root of the Early Cretaceous continental magmatic arc did not lead to regional granulite facies metamorphism of the country rock schists, as large volumes of amphibolite facies rock metamorphosed under medium- P conditions persisted metastably in the deep arc crust. [source] Direct monitoring of molecular recognition processes using fluorescence enhancement at colloid-coated microplatesJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2001Ch. Lobmaier Abstract Direct monitoring of recognition processes at the molecular level is a valuable tool for studying reaction kinetics to assess affinity constants (e.g. drugs to receptors) and for designing rapid single step immunoassays. Methods currently used to gain information about binding processes predominantly depend on surface plasmon resonance. These systems use excitation with coherent light in attenuated total reflection geometry to obtain discrimination between surface-bound and free molecules in solution. Therefore labeling of the compounds is not necessary, but due to the complexity of the measuring setup the method is rather costly. In this contribution we present a simple method for performing kinetic single step biorecognition assays with fluorophore labeled compounds using the fluorescence enhancement properties of surface bound silver colloids. Silver colloids are bound to standard microplates via silanization of the plastic surface. Fluorophores close to this colloid coated surface show a significant gain in fluorescence compared to fluorophores farther away in the bulk solution. Therefore discrimination between surface bound and free fluorophores is possible and the binding of, for example, fluorophore labeled antibodies to antigens immobilized on the colloid surface results in increasing fluorescence intensity. Utilization of standard microplates makes this method fully compatible with conventional microplate processing and reading devices. Neither excitation with coherent laser light nor ATR geometry is required, the measurement is performed in a standard fluorescence microplate reader in front face geometry with a xenon flash lamp as excitation source. Methods for the preparation of colloid-coated microplates and fluorescence-enhanced biorecognition assays are presented. Additionally the dependence of the system performance on the structure and properties of the metal colloid coated surface is described. A two-component biorecognition model system shows a detection limit in the subnanomolar range. The ease of colloid-surface preparation and the high sensitivity makes fluorescence enhancement at colloid-coated microplates a valuable tool for studying reaction kinetics and performing rapid single-step immunoassays. Copyright © 2001 John Wiley & Sons, Ltd. [source] Prediction of the location of stationary steady-state zone positions in counterflow isotachophoresis performed under constant voltage in a vortex-stabilized annular columnJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2007Schurie L. M. Harrison Abstract A theoretical model is presented and an analytical expression derived to predict the locations of stationary steady-state zone positions in ITP as a function of current for a straight channel under a constant applied voltage. Stationary zones may form in the presence of a countercurrent flow whose average velocity falls between that of a pure leader zone and of a pure trailer zone. A comparison of model predictions with experimental data from an anionic system shows that the model is able to predict the location of protein zones with reasonable accuracy once the ITP stack has formed. This result implies that an ITP stack can be precisely directed by the operator to specific positions in a channel whence portions of the stack can be removed or redirected for further processing or analysis. [source] Labour Flows as Determinants of the Wage,Price Spiral: An Empirical Analysis for The NetherlandsLABOUR, Issue 2 2001Lourens Broersma This study presents an empirical analysis of the influence of labour market flows on wage and price formation. A system of wage, price and employment equations after Nickell (Oxford Bulletin of Economics and Statistics 49: 103,128, 1987) is estimated, including labour flows as indicators of labour market tightness in the wage equation. An impulse response analysis using this system shows how changes in the flow of layoffs (flow from employment to unemployment) may be the basis of short-run Phillips curve effects in The Netherlands [source] Thorough analysis of the Oseen system in 2D exterior domainsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 15 2009Konieczny Abstract We construct Lp -estimates for the inhomogeneous Oseen system studied in a two-dimensional exterior domain , with inhomogeneous slip boundary conditions. The kernel of the paper is a result for the half space ,. Analysis of this model system shows us a parabolic character of the studied problem, resulting as an appearance of the wake region behind the obstacle. Main tools are given by the Fourier analysis to obtain the maximal regularity estimates. The results imply the solvability for the Navier,Stokes system for small velocity at infinity. Copyright © 2009 John Wiley & Sons, Ltd. [source] Around or across the Carpathians: colonization model of the Danube basin inferred from genetic diversification of stone loach (Barbatula barbatula) populationsMOLECULAR ECOLOGY, Issue 5 2008ALENA, EDIVÁ Abstract Despite increasing information about postglacial recolonization of European freshwater systems, very little is known about pre-Pleistocene history. We used data on the recent distribution and phylogenetic relationships of stone loach mitochondrial lineages to reconstruct the initial colonization pattern of the Danube river system, one of the most important refuges for European freshwater ichthyofauna. Fine-scale phylogeography of the Danubian populations revealed five highly divergent lineages of pre-Pleistocene age and suggested the multiple origin of the Danubian stone loach. The mean sequence divergence among lineages extended from 7.0% to 13.4%, which is the highest intraspecific divergence observed so far within this river system. Based on the phylogeographical patterns, we propose the following hypothesis to relate the evolution and dispersal of the studied species with the evolution of the Danube river system and the Carpathian Mountains: (i) during the warmer period in the Miocene, the areas surrounding the uplifting Alps and Carpathians served as mountainous refuges for cold-water adapted fish and promoted the diversification of its populations, and (ii) from these refuges, colonization of the emerging Danube river system may have taken place following the retreat of the Central Paratethys. Co-existence of highly divergent mtDNA lineages in a single river system shows that range shifts in response to climatic changes during the Quaternary did not cause extensive genetic homogenization in the stone loach populations. However, the wide distribution of some mtDNA lineages indicates that the Pleistocene glaciations promoted the dispersal and mixing of populations through the lowlands. [source] Detailed comparison of the structures and kinematics of simulated and observed barred galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003J. K. O'Neill ABSTRACT We examine the observable properties of simulated barred galaxies, including radial mass profiles, edge-on structure and kinematics, bar lengths and pattern speed evolution for detailed comparison to real systems. We have run several simulations in which bars are created through inherent instabilities in self-consistent simulations of a realistic disc+halo galaxy model with a disc-dominated, flat rotation curve. These simulations were run at high (N= 20 million particles) and low (N= 500 000 particles) resolution to test numerical convergence. We determine the pattern speeds in simulations directly from the phase angle of the bar versus time and the Tremaine,Weinberg method. Fundamental dynamics do not change between the high and low resolution, suggesting that convergence has been reached in this case. We find that the higher resolution is needed to simulate structural and kinematic properties accurately. The edge-on view of the higher-resolution system shows the bending instability and formation of a peanut-shaped bulge clearly. We determined bar lengths by different means to determine that the simulated bar is fast, with a corotation to bar length ratio of under 1.5. Simulated bars in these models form with pattern speeds slower than those observed and slow-down during their evolution. Dynamical friction between the bar and dark halo is responsible for this deceleration, as revealed by the transfer of angular momentum between the disc and the halo. However, even though the pattern speed is reduced at later times, the instantaneous scalelength of the disc has grown sufficiently for the bar motion to agree with many observations. By using a different model and simulation technique than other authors, we are able to compare the robustness of these methods. An animation of the face-on and edge-on views of the 20-million-particle simulation is available at http://www.astro.utoronto.ca/~oneill. [source] Polymerization of styrene with a simple rare earth metal initiatorPOLYMER INTERNATIONAL, Issue 11 2001Toshiyuki Hayakawa Abstract The catalytic activity in the polymerization of styrene has been examined using commercially available simple rare earth metal compounds such as Sm(OiPr)3, Sm(acac)3, Sm(OCOMe)3, SmI2(THF)2 or SmCl3 coupled with Et3Al or methylaluminoxane (MAO). Among these compounds, the Sm(OiPr)3/AlEt3 system shows the highest catalytic activity, especially in the presence of a minor amount of toluene at 60,°C. The random copolymerization of styrene with methyl methacrylate suggests that the present polymerization proceeds with a radical polymerization mechanism. (C5Me5)SmCl3Na(THF) and (C5Me5)SmCl3Li(THF) systems exhibit relatively low catalytic activity, even in the presence of AlEt3. © 2001 Society of Chemical Industry [source] A gene regulation system with four distinct expression levelsTHE JOURNAL OF GENE MEDICINE, Issue 8 2006Christel Krueger Abstract Background The amount of a particular protein, and not just its presence or absence, frequently determines the outcome of a developmental process or disease progression. These dosage effects can be studied by conditionally expressing such proteins at different levels. With typical gene regulation systems like the Tet-On system, intermediate expression levels can be obtained by varying the effector concentration. However, this strategy is limited to situations in which these concentrations can be precisely controlled and, thus, not suited for animal models or gene therapy approaches. Here, we present a Tet transregulator setup that allows establishment of four levels of promoter activity largely independent of effector concentration. Methods A newly introduced transsilencer is combined with a reverse transactivator. As the regulators respond differentially to tetracycline derivatives, four expression levels are obtained by adding different effectors. To facilitate integration of the components, we generated versatile all-in-one vectors. Apart from a cassette expressing the transregulators and a selection marker, these vectors encode a bidirectional, regulated promoter driving expression of GFP and the gene of interest. The features of this stepwise regulation system were analyzed by transient and stable transfections of human cell lines. Results We demonstrate in a variety of experimental settings that coexpression of these transregulators leads to robust stepwise regulation. Depending on the respective effectors, four expression levels are achieved with different responsive promoters, cell lines and target genes. Conclusions This system shows that a promoter can be adjusted to different activities and provides an excellent strategy to investigate protein dosage effects. Copyright © 2006 John Wiley & Sons, Ltd. [source] Pyrazolo[3,4- d]pyrimidine Derivatives as COX-2 Selective Inhibitors: Synthesis and Molecular Modelling StudiesARCHIV DER PHARMAZIE, Issue 6 2009Demetrio Raffa Abstract The pyrazolo[3,4- d]pyrimidine system shows a multitude of interesting pharmacological properties. Owing to the potential anti-inflammatory activity of 5-benzamido-pyrazolo[3,4- d]pyrimidin-4-one derivatives and considering the easy synthesis of this class of compounds, a set of new 5-benzamido-1H -pyrazolo[3,4- d]pyrimidin-4-ones has been prepared in 42-80% yields by reacting 5-aminopyrazole-4(N -benzoyl)carbohydrazide derivatives and the opportune triethylorthoesters. Compounds 8a, b, 10a,d, and 11a, b revealed a superior inhibitory profile against COX-2, when compared to that of reference standards NS398 and indomethacin. Molecular modelling studies confirmed the obtained biological results. [source] Dynamics of the ion cyclotron resonance effect on amino acids adsorbed at the interfacesBIOELECTROMAGNETICS, Issue 1 2006N. Comisso Abstract In this study we show a reproduction of the Zhadin experiment, which consists of the transient increase of the electrolytic current flow across an aqueous solution of L -arginine and L -glutamic acid induced by a proper low frequency alternating magnetic field superimposed to a static magnetic field of higher strength. We have identified the mechanisms that were at the origin of the so-far poor reproducibility of the above effect: the state of polarization of the electrode turned out to be a key parameter. The electrochemical investigation of the system shows that the observed phenomenon involves the transitory activation of the anode due to ion cyclotron frequency effect, followed again by anode passivation due to the adsorption of amino acid and its oxidation products. The likely occurrence of similar ion cyclotron resonance (ICR) phenomena at biological membranes, the implications on ion circulation in living matter, and the consequent biological impact of environmental magnetic fields are eventually discussed. Bioelectromagnetics 27:16,25, 2006. © 2005 Wiley-Liss, Inc. [source] Synthesis of Ultra-high Molecular Weight Polystyrene with a Catalyst System Based on Calixarene-yttrium ComplexCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Chen Yao-Feng Abstract Polymerization of styrene (St) with a new catalyst system composed of calixarene-yttrium complex, magnesium-aluminium alkyls and hexamethyl phosphoramide was studied. Hie catalyst system shows extremely high activity (> 7 × 106 g PSt/mol Y × h) and gives polystyrene with very high viscosity-average molecular weight (>5 × 105). [source] Technologies for value creation: an exploration of remote diagnostics systems in the manufacturing industryINFORMATION SYSTEMS JOURNAL, Issue 3 2008Katrin Jonsson Abstract., With firms increasingly relying on ubiquitous computing to implement major business initiatives, it is becoming ever more necessary to understand the technological aspects of business developments. This paper analyzes the use of remote diagnostics systems in the manufacturing industry and discusses the opportunities and challenges for the early adopters. It pays specific attention to the impact on business aspects such as the value creation process consisting of relationships, roles, and architecture and the value proposal consisting of a business offer and customer value. The study shows how ubiquitous computing allows manufacturers to become remote service providers while customers can either become co-creators of value or passive receivers of created value. Ubiquitous computing also creates possibilities for the manufacturing industry to design new kinds of business offers based on remote presence. Studying remote diagnostics systems shows that ubiquitous computing creates value when deployed in products, and not just in relation to individuals. Moreover, the design of the value-creation process should not be limited to the single supplier or customer organization, as ubiquitous computing applications take no notice of organizational boundaries. [source] Alkali-Dinitramide Salts Part 2: Oxidizers for Special Pyrotechnic ApplicationsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2006Abstract Ammonium dinitramide is planned to be a substitute for commonly used oxidizers in rocket motor compositions. Different teams worldwide have already synthesized alkali salts of dinitramide and several times it was used as an oxidizer for pyrotechnic compositions containing boron as a reducing agent. In this paper the results of a systematic investigation to characterize the pyrotechnic redox systems titanium/potassium dinitramide and titanium/cesium dinitramide are presented and the data are compared. The heats of reaction as well as the burning rates of the redox system titanium/potassium dinitramide are higher than those of the redox system titanium/cesium dinitramide. Both systems show a moderate sensitivity to friction and electrostatic discharges. However the sensitivity of mixtures of both redox systems shows a very high sensitivity to impact. These sensitivities are in the range of pure HMX or pentaerythritol tetranitrate. [source] Condensed polyhedral boranes and analogous organometallic clusters: a molecular orbital and density functional theory study on the cap,cap interactions,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6-7 2003Eluvathingal D. Jemmis Abstract The interactions between the non-bonded atoms on adjacent units were assumed to be one of the major factors that hinder the exploration and advancement of macropolyhedral borane chemistry. In sandwich complexes involving boron as the bridging atom, the interaction between non-bonded atoms tends to be antibonding, but a closer analysis of various condensed systems shows that this cannot be generalized. The overlap populations (OPs) calculated for structures optimized at the B3LYP/6-31g* level [B21H181, (5), B20H16 (6), [Al(C2B4H6)2]1, (7), B12H102, (8), B10H82, (9 and 14), B11H13 (10), B10H14 (11), C2B8H12 (13) and B20H182, (15)] indicate bonding interactions between the caps, except for 7 and 13. This is substantiated by a detailed extended Hückel-based molecular orbital (MO) study using B10H14 as a model system to represent macropolyhedral boranes with higher fusions. An isolobal equivalent structure, [C8H6(Ru(CO)2Me)2] (17), studied at the B3LYP/LANL2DZ level has weak RuRu interactions. An analysis of the nature of the MOs in B10H14 (11) shows that there is no direct head on overlap of the cap orbitals that are antibonding; this is in contradiction to sandwiched molecules (7), where there are two occupied MOs with antibonding interactions. The m + n + o electron pair count (m is the number of cages involved in condensation, n is the number of vertices and o is the number of single vertex condensations) of sandwich complexes requires the filling of these two MOs. The negative OP between the carbon atoms in 13 is attributed to the greater electronegativity of carbon and is substantiated by a fragment MO analysis. Copyright © 2003 John Wiley & Sons, Ltd. [source] Subtype-selective targeting of voltage-gated sodium channelsBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2009Steve England Voltage-gated sodium channels are key to the initiation and propagation of action potentials in electrically excitable cells. Molecular characterization has shown there to be nine functional members of the family, with a high degree of sequence homology between the channels. This homology translates into similar biophysical and pharmacological properties. Confidence in some of the channels as drug targets has been boosted by the discovery of human mutations in the genes encoding a number of them, which give rise to clinical conditions commensurate with the changes predicted from the altered channel biophysics. As a result, they have received much attention for their therapeutic potential. Sodium channels represent well-precedented drug targets as antidysrhythmics, anticonvulsants and local anaesthetics provide good clinical efficacy, driven through pharmacology at these channels. However, electrophysiological characterization of clinically useful compounds in recombinant expression systems shows them to be weak, with poor selectivity between channel types. This has led to the search for subtype-selective modulators, which offer the promise of treatments with improved clinical efficacy and better toleration. Despite developments in high-throughput electrophysiology platforms, this has proven very challenging. Structural biology is beginning to offer us a greater understanding of the three-dimensional structure of voltage-gated ion channels, bringing with it the opportunity to do real structure-based drug design in the future. This discipline is still in its infancy, but developments with the expression and purification of prokaryotic sodium channels offer the promise of structure-based drug design in the not too distant future. [source] Electronic Properties and Reactivity of Short-Chain Oligomers of 3,4-Phenylenedioxythiophene (PheDOT)CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Igor F. Perepichka Dr. Abstract The dimer and trimer of 3,4-phenylenedioxythiophene (PheDOT) have been synthesized. Unlike the parent systems based on 3,4-ethylenedioxythiophene (EDOT), these compounds are quite stable under atmospheric conditions. The electronic absorption spectra of di- and tri-PheDOT exhibit a well-resolved vibronic fine structure indicative of self-rigidification of the conjugated structure by noncovalent intramolecular sulfur,oxygen interactions. Comparison of UV-visible data for the PheDOT oligomers with those of the corresponding EDOT oligomers reveals a faster decrease of the HOMO,LUMO gap with chain length for the former. Cyclic voltammetric data show that whereas PheDOT oxidizes at a lower potential than EDOT, the PheDOT dimer and trimer exhibit much higher oxidation potentials than their EDOT-based analogues. A comparative analysis of the electropolymerization of the three PheDOT-based systems shows that although PheDOT is very difficult to polymerize, its dimer and trimer can be readily electropolymerized. This unexpected increase of reactivity with chain extension is discussed with the aid of theoretical calculations. [source] The Mechanism of Formation of Amide-Based Interlocked Compounds: Prediction of a New Rotaxane-Forming MotifCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004David A. Leigh Prof. Abstract Molecular modeling of four different reagent systems shows that the (free) energies of supramolecular interactions in the gas phase and in solution can explain the different reaction products (i.e., various sized macrocycles, catenanes, and linear oligomers) that are formed in classic amide-catenane-forming reactions. Self-assembly of the catenanes requires the formation of ordered intertwined chains and is driven by bifurcated hydrogen bonds, with , stacking only playing a lesser role. The understanding gained from the computational study was used to predict the possibility of a new rotaxane-forming system that does not permit catenane formation. The predictions were confirmed by the successful synthesis and characterization (including X-ray crystallography) of two novel rotaxanes. [source] | |||||||||||||||||||