The kinetics for surface-catalyzed alcohol dehydration reactions often depend on the structure of the alcohol. Studies of structure–activity relations across primary, secondary, and tertiary alcohols ...can provide fundamental information on the nature of active sites on the surface. Here, we investigated the dehydration of 1-butanol, 2-butanol, and tert-butanol over TiO2 anatase catalysts modified with various phosphonic acid (PA) self-assembled monolayers (SAMs). As a response to the presence of PAs, the three C4 alcohol isomers showed different dehydration rates, with 1-butanol dehydration being enhanced to the greatest extent by PA modification. Furthermore, the fluorinated, more polar 4-fluorobenzylphosphonic acid outperformed alkyl PAs across all alcohols. Steady-state kinetic measurements and temperature-programmed desorption studies indicated that PA SAMs significantly lowered the dehydration activation barrier; the extent of reduction in the barrier was sensitive to both the substitution of the alcohol and the charge distribution on the PA in a way that was consistent with stabilization of a carbenium-like transition state. Overall, the effect of PA modifiers on alcohol dehydration rates was found to be determined from a balance between transition state stabilization and active site blocking effects, with the potential to tune activity and selectivity based on the structure and coverage of the SAM.
A full account of the development of a concise and highly stereoselective synthesis of (+)-7,20-diisocyanoadociane (DICA)─a structurally complex isocyanoditerpene with potent antiplasmodial ...activity─is described. The strategy that evolved relies on the rapid construction of unsaturated tricyclic precursors designed to undergo stereocontrolled Birch reductions and a subsequent "bay ring" formation to generate the isocycloamphilectane core. This report is divided into three sections: (1) a description of the initial strategy and the results that focused our efforts on a single route to the DICA core, (2) a discussion of the precise choreography needed to enable a first-generation formal synthesis of (±)-DICA, and (3) the execution of a 13-step second-generation synthesis of (+)-DICA that builds on important lessons learned from the first-generation effort.
DNA nanotechnology provides a versatile and powerful tool to dissect the structure–function relationship of biomolecular machines like the nuclear pore complex (NPC), an enormous protein assembly ...that controls molecular traffic between the nucleus and cytoplasm. To understand how the intrinsically disordered, Phe-Gly-rich nucleoporins (FG-nups) within the NPC establish a selective barrier to macromolecules, we built a DNA-origami NanoTrap. The NanoTrap comprises precisely arranged FG-nups in an NPC-like channel, which sits on a baseplate that captures macromolecules that pass through the FG network. Using this biomimetic construct, we determined that the FG-motif type, grafting density, and spatial arrangement are critical determinants of an effective diffusion barrier. Further, we observed that diffusion barriers formed with cohesive FG interactions dominate in mixed-FG-nup scenarios. Finally, we demonstrated that the nuclear transport receptor, Ntf2, can selectively transport model cargo through NanoTraps composed of FxFG but not GLFG Nups. Our NanoTrap thus recapitulates the NPC’s fundamental biological activities, providing a valuable tool for studying nuclear transport.
2,3,3,3‐Tetrafluoropropene (HFO‐1234yf) is an inexpensive and readily available fluorinated building block, owing to its growing use as a low global warming potential 4th generation refrigerant, but ...there have so far been few reported uses of this fluoroalkene in organic synthesis. Herein, we report our investigations into nucleophilic substitution reactions of HFO‐1234yf with alkoxide and thiolate derivatives. The regiochemistry of these transformations varies with conditions and we propose these reactions proceed through addition–elimination with reversible formation of a carbanion intermediate. The regioselectivity is dictated by hard/soft nucleophile/electrophile control. This is supported by deuterium trapping of the proposed reactive intermediate. The effect of solvent and base choice was examined and the substrate scope for the synthesis of α‐trifluoromethyl enol ethers was expanded.
2,3,3,3‐Tetrafluoropropene is an inexpensive and readily available 4th generation refrigerant. Reaction with alkoxides and thiolates gives α‐CF3 enol ethers and β‐CF3 vinyl sulfides, respectively, with complete regioselectivity.
Organisms that modify the availability of abiotic resources for other species can alter the structure and function of ecological communities through multiple pathways. In Florida Bay, red grouper ...(Epinephelus morio) engineer habitats by excavating sediment and detritus from karst solution holes and are also predators that consume a variety of benthic crustaceans and fish, some of which colonize engineered habitats. The effect of red grouper on these communities is complex as colonizing species interact with red grouper in different ways, including both direct (e.g., predator–prey) and indirect interactions. Here, I present the results of an experiment designed to test the direct effects of red grouper on faunal communities associated with Florida Bay solution holes by excluding red grouper from solution holes for four weeks. Red grouper presence generally had positive effects on the abundance, richness, and diversity of faunal communities associated with engineered habitats. Few strong interactions were observed between red grouper and colonizing species, mainly juvenile coral reef fishes. These results suggest that by acting as both a predator and habitat engineer, red grouper shape unique communities, distinct from those of surrounding areas, and influence the composition of communities associated with manipulated habitats.
•Strain response of additively manufactured piezoelectric PVDF actuators are reported.•The EPAM PVDF measured strain is up to 5.2 times greater than that of a PZT actuator.•Measured EPAM PVDF ...response is orders of magnitude larger than commercial PVDF.•Sample performance varies, and so refinement of the EPAM process is required.
Polyvinyldene fluoride (PVDF) polymer piezoelectric actuators were manufactured using an electric poling-assisted additive manufacturing (EPAM) process and tested for actuation strain in the thickness direction. A heterodyne interferometer was used to measure the strain developed by the actuators as a function of applied voltage. Results were compared to a commercially available ceramic lead–zirconium–titanate (PZT) actuator. The EPAM PVDF samples exhibit strains up to 8.78mϵ, compared to 1.7mϵ developed by PZT samples at their maximum working voltages in linear ramp testing (860V for EPAM PVDF and 200V for PZT). The response of the EPAM PVDF samples to an applied force was tested to measure the piezoelectric effect, although no actual piezoelectric constants are calculated with this method. Results show that strain measurements of EPAM PVDF samples were up to 5.2 times greater than comparable measurements of PZT samples. However, the degree of piezoelectricity between EPAM PVDF samples varies so quality control is required for the EPAM process to ensure sample performance.
Western honey bee (Apis mellifera L.) populations face declines commonly attributed to pesticide, pathogen, and parasite stress. One way beekeepers combat these stressors is by providing supplemental ...protein diets to honey bee colonies to ensure adequate colony nutrition. However Nosema spp., a microsporidian parasite of the honey bee, is thought to be associated closely with a colony's nutritional intake, thus possibly negating any benefit the bees otherwise would have received from a nutritional supplement. Through three objectives, we examined how adult bees' consumption of wildflower pollen or commercial pollen substitute diets affected Nosema levels in the bees' midguts. For our first objective, we investigated how method of inoculation with Nosema affects infection levels in inoculated bees. Bees were infected with spores of Nosema four days after emergence. On day 15, bees were collected from the cages and Nosema spores were quantified. We found that inoculation through the pollen diet resulted in the highest Nosema levels in inoculated bees. In our second and third objectives, we provided the test diets to caged, newly emerged bees for a period of 15 days. Bees consuming pollen and a sucrose solution had more Nosema in their midguts than did bees consuming the sucrose solution alone (control). The overall volume of diet consumed by the bees did not correlate with the level of Nosema in their midguts. The level of Nosema was higher in bees fed certain commercial pollen substitute diets than in bees fed wildflower pollen. Our study illustrates how providing nutritional supplements to adult honey bees can impact the intensity of Nosema in their midguts.
We investigate a digital back-propagation simplification method to enable computationally-efficient digital nonlinearity compensation for a coherently-detected 112 Gb/s polarization multiplexed ...quadrature phase shifted keying transmission over a 1,600 km link (20 x 80 km) with no inline compensation. Through numerical simulation, we report up to 80% reduction in required back-propagation steps to perform nonlinear compensation, in comparison to the standard back-propagation algorithm. This method takes into account the correlation between adjacent symbols at a given instant using a weighted-average approach, and optimization of the position of nonlinear compensator stage to enable practical digital back-propagation.
Resolving stock structure is crucial for fisheries conservation to ensure that the spatial implementation of management is commensurate with that of biological population units. To address this in ...the economically important European lobster (Homarus gammarus), genetic structure was explored across the species' range using a small panel of single nucleotide polymorphisms (SNPs) previously isolated from restriction‐site‐associated DNA sequencing; these SNPs were selected to maximize differentiation at a range of both broad and fine scales. After quality control and filtering, 1,278 lobsters from 38 sampling sites were genotyped at 79 SNPs. The results revealed a pronounced phylogeographic break between the Atlantic and Mediterranean basins, while structure within the Mediterranean was also apparent, partitioned between lobsters from the central Mediterranean and the Aegean Sea. In addition, a genetic cline across the north‐east Atlantic was revealed using both putatively neutral and outlier SNPs, but the precise driver(s) of this clinal pattern—isolation by distance, secondary contact, selection across an environmental gradient, or a combination of these factors—remains undetermined. Putatively neutral markers differentiated lobsters from Oosterschelde, an estuary on the Dutch coast, a finding likely explained by past bottlenecks and limited gene flow with adjacent North Sea populations. Building on the findings of our spatial genetic analysis, we were able to test the accuracy of assigning lobsters at various spatial scales, including to basin of origin (Atlantic or Mediterranean), region of origin and sampling location. The predictive model assembled using 79 SNPs correctly assigned 99.7% of lobsters not used to build the model to their basin of origin, but accuracy decreased to region of origin and again to sampling location. These results are of direct relevance to managers of lobster fisheries and hatcheries, and provide the basis for a genetic tool for tracing the origin of European lobsters in the food supply chain.
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