Calcium binding mode of {gamma}-carboxyglutamic acids in conantokins

Conantokin-T (con-T) and conantokin-G (con-G) are two highlyhomologous peptide toxins found in Conus venom. The former isa 21-residue peptide with four gif" ALT="{gamma}" BORDER="0">-carboxyglutamic acid (Gla) residues(at positions 3, 4, 10 and 14), while the latter is a 17-residuepeptide with five gif" ALT="{gamma}" BORDER="0">-carboxyglutamic acid residues (at positions3, 4, 7, 10 and 14). Despite the apparent similarity in numberand relative positions of the gif" ALT="{gamma}" BORDER="0">-carboxyglutamic acid residues,¹¹³Cd-NMR studies indicated a distinct metal binding behaviorfor con-G and con-T. There appears to be four binding sitesin con-G in contrast to one metal binding site in con-T. Toelucidate the mode of calcium binding by the gif" ALT="{gamma}" BORDER="0">-carboxyglutamicacid residues in these conantokins, we designed various analogouspeptides with their gif" ALT="{gamma}" BORDER="0">-carboxyglutamic acid replaced by otheramino acid residues. ¹¹³Cd-NMR experiments on conantokin analoguesreveal that the major difference in the number of metal bindingsites between con-G and con-T is due to the residue at position7. We also performed molecular simulations to calculate therelative binding free energies of several potential bindingsites. Based on our theoretical and experimental results, wepropose a `four-site' binding model for conantokin-G and a `single-site'binding model for conantokin-T.     

Laminar and turbulent mass transfer simulations in a parallel plate reactor

Laminar and turbulent mass transfer in a parallel plate reactor at high Schmidt number obtained from numerical simulation is compared with literature data. In a first step, the fluid flow is determined numerically in the reactor by solving the Navier–Stokes equations. For turbulent flow, a low Reynolds number k—gif" alt="ohgr" align="BASELINE" BORDER="0"> model is used to calculate the turbulent viscosity. Using the obtained flow field and turbulent viscosity, the current density distribution is calculated for different flow velocities by solving the equations describing the transport of multiple ions due to diffusion, convection and migration. For the laminar case, a very good agreement with literature data is obtained. For turbulent flow, different numerical models for turbulent mass transfer are proposed in the literature. A detailed study of the behaviour close to the wall of these different turbulence models is presented, together with a comparison of the calculated results with literature correlations. This allows identification of the benefits and disadvantages of each of the turbulence models for the numerical calculation of mass transfer at high Schmidt numbers in a parallel plate reactor.     

Molecular modelling of Staphylococcal {delta}-toxin ion channels by restrained molecular dynamics

gif" ALT="{delta}" BORDER="0">-Toxin is a 26-residue channel-forming peptide from Staphylococcusaureus which forms an amphipathic gif" ALT="{alpha}" BORDER="0">-helix in a membrane environment.Channel formation in planar bilayers suggests that an averageof six gif" ALT="{delta}" BORDER="0">-toxin helices self-assemble to form transbilayer pores.Molecular models for channels formed by gif" ALT="{delta}" BORDER="0">-toxin and by a syntheticanalogue have been generated using a simulated annealing protocolapplied via restrained molecular dynamics. These models areanalysed in terms of the predicted geometric and energetic propertiesof the transbilayer pores. Pore radius calculations of the modelsdemonstrate that rings of channel-lining residues contributea series of constrictions along the pore. Electrostatic propertiesof the pores are determined both by pore-lining charged sidechains and by the aligned helix dipoles of the parallel helixbundle. Molecular dynamics simulations (100 ps) of gif" ALT="{delta}" BORDER="0">-toxin modelscontaining intra-pore water were performed. Analysis of theresultant dynamics trajectories further supports the proposalthat alternative conformations of pore-constricting side chainsmay be responsible for the observed conductance heterogeneityof gif" ALT="{delta}" BORDER="0">-toxin ion channels.     

Hydroformylation of functional alkenes with heterodonor phosphine rhodium catalysts: substrate or ligand directed regioselectivity?

The catalytic activity and selectivity of heterodonor phosphine rhodium catalysts prepared in situ were tested in the hydroformylation of functional alkenes (ethyl acrylate, methyl methacrylate, styrene, 4-vinyl-1-cyclohexene, dicyclopentadiene and cis-1,2,3,6-tetrahydrophthalic anhydride). Systematic variation of the heterodonor atom in the ortho position of the ligand showed that the heterodonor atom has a significant influence on the activities and selectivities of the reaction. However, the activity seems to depend mainly on the modifying ligand, and the regioselectivity mainly on the substrate (i.e., the structure and functionality of the alkene). Nevertheless, regioselective control is only obtained through synergy between the substrate and the catalyst. Clear regiocontrol was observed in the hydroformylation of gif" alt="agr" align="BASELINE" BORDER="0">,gif" alt="beta" align="MIDDLE" BORDER="0">-unsaturated esters and styrene with an in situ formed o-(thiomethylphenyl)diphenylphosphine rhodium catalyst.     

Disruption of Secondary Attraction of the Spruce Beetle, Dendroctonus rufipennis, by Pheromones of Two Sympatric Species

Capture of spruce beetles, Dendroctonus rufipennis, in multiple-funnel traps baited with frontalin and gif" alt="agr" align="BASELINE" BORDER="0">-pinene was reduced by up to 42% in the presence of synthetic (+)-exo- and (+)-endo-brevicomin, aggregation pheromones of the sympatric species Dryocoeles affaber. (±)-endo-Brevicomin was inhibitory to spruce beetles in two experiments and (±)-exo-brevicomin was inhibitory in one experiment, reducing spruce beetle trap catches by up to 87% and 75%, respectively. Spruce beetle trap catches were also reduced by 85% by (±)- or (+)-ipsdienol, but not by (–)-ipsdienol. Ips tridens, a second sympatric species, produces both enantiomers of ipsdienol in its pheromone blend. Responses by D. affaber to its own pheromone were significantly enhanced by addition of the spruce beetle lure. Enantiospecific pheromones of secondary competing species, or less costly racemic substitutes, may be useful for managing spruce beetles using competitive displacement or exclusion. Baiting susceptible hosts with pheromones of secondary species may enhance attack by secondary species, while partially repelling spruce beetles.     

Activation of Ni/A12O3 catalysts through modification of the Al2O3 support

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure gif" alt="gamma" align="MIDDLE" BORDER="0"> to pure gif" alt="theta" align="BASELINE" BORDER="0"> phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a gif" alt="theta" align="BASELINE" BORDER="0">/gif" alt="gamma" align="MIDDLE" BORDER="0"> alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.     

Catalytic Combustion of Model Carbon Particles (CPs) over Pt/β-SiC Catalyst

Platinum catalyst supported on a medium surface area gif" alt="beta" align="MIDDLE" BORDER="0">-SiC was successfully used for the catalytic combustion of model carbon particles and compared to a catalyst supported on a low surface area gif" alt="agr" align="BASELINE" BORDER="0">-SiC. The gif" alt="beta" align="MIDDLE" BORDER="0">-SiC-based catalyst showed no deactivation as a function of cycling tests while a strong deactivation was observed on the gif" alt="agr" align="BASELINE" BORDER="0">-SiC-based catalyst. This deactivation was attributed to the progressive encapsulation of the platinum particles by a layer of silica which built up during the combustion cycle. These results render possible the use of Pt/gif" alt="beta" align="MIDDLE" BORDER="0">-SiC catalyst as a diesel carbon particle catalytic filter with continuous regeneration.     

New sesquiterpenes fromMaytenus species (Celastraceae). Taxonomic and chemotaxonomic considerations concerning chileanMaytenus

Three new dihydro-gif" alt="beta" align="MIDDLE" BORDER="0">-agarofuran sesquiterpenes from two species ofMaytenus were isolated and their structures were elucidated by means of¹H and¹³C NMR studies. The differences and similarities noted in the chemical content of the dihydro-gif" alt="beta" align="MIDDLE" BORDER="0">-agarofuran sesquiterpenes from the fourMaytenus species from Chile are in line with the taxonomic characterization of these species; their geographical distribution is also given.     

β-Phellandrene: kairomone for pine engraver,Ips pini (Say) (Coleoptera: Scolytidae)

The responses ofIps pini (Scolytidae) to multiple-funnel traps baited with the pheromone, ipsdienol, and various monoterpenes were determined in stands of lodgepole pine in southern and central British Columbia.Ips pini was attracted to both ipsdienol and gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene, demonstrating that gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene is a kairomone for this species.Lasconotus complex (Colydiidae) and aCorticeus sp. (Tenebrionidae) were attracted to both ipsdienol and gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene. TheCorticeus sp. exhibited a synergistic response to the combination of ipsdienol and gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene; the responses of the other two species to the combination were additive. The predators,Thanasimus undatulus, Enoclerus sphegeus, andE. lecontei (Cleridae), were attracted to ipsdienol-baited traps, whileMonochamus clamator (Cerambycidae) andDendroctonus ponderosae (Scolytidae) were attracted to gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene. Attraction of all eight species increased with increasing release rates of ipsdienol and/or gif" alt="beta" align="MIDDLE" BORDER="0">-phellandrene.     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.