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The room-temperature reaction between the Dipp2DAB ligand, SnCl2, and SeCl4 results in the quantitative formation of a dicationic N-heterocyclic “carbenoid”. This represents the first example of a chalcogenium dication that mimics the ubiquitous Arduengo-type carbenes; however, the electronic structure is significantly different.
The analogy between cationic group 10 metal−phosphenium complexes and Fischer carbenes has been formalized through structural and reactivity studies and by energy decomposition analysis (EDA) of the M−P bond. The studied compounds were the three-coordinate, 16-electron species [(NHPMes)M(PPh3)2]OTf (M = Pt (1) and Pd (2); [NHPMes]+ is the N-heterocyclic phosphenium (NHP) cation, [tiebar above startPN(2,4,6-Me3-C6H2)CH2CH2tiebar above endN(2,4,6-Me3-C6H2)]+, OTf = trifluoromethanesulfonate); these were made by reaction of [NHPMes]OTf with M(PPh3)4. The metal−phosphenium bond in both compounds was dominated by metal-to-ligand π-donation. This differed from the M−C bonds in the analogous N-heterocyclic carbene (NHC) complexes, (NHCMes)M(PPh3)2 (M = Pt (6), Pd (7)), which were instead predominantly σ-type. Structural determination of 1 by X-ray crystallography revealed the shortest yet reported Pt−P bond of 2.107(3) Å, consistent with significant double-bond character, and trigonal planar geometries at both the P-atom within the [NHPMes]+ ligand (∑(angles) = 359.99°) and at the Pt-atom (∑(angles) = 360.00°), which indicated that 1 was better described as a Pt(0)−phosphenium rather than as a Pt(II)−phosphide. Reactions of 1 and 2 with excess PMe3 cleanly gave the four-coordinate species [(NHPMes)M(PMe3)3]OTf (M = Pt (3) and Pd (4)), while reaction of 1 with bis(diphenylphosphino)ethane (dppe) gave [(NHPMes)Pt(dppe-κ2P)(dppe-κP)]OTf (5). Hydrolysis of these complexes resulted in metal hydrides and oxidation of the NHP to phosphine oxide via intial nucleophilic attack of water at the P-atom in the coordinated [NHPMes]+ ligand, which was calculated to bear a significantly positive charge in 1.
Background - Widely distributed species with populations adapted to different environmental conditions can provide valuable opportunities for tracing the onset of reproductive incompatibilities and their role in the speciation process. Drosophila montana, a D. virilis group species found in high latitude boreal forests in Nearctic and Palearctic regions around the globe, could be an excellent model system for studying the early stages of speciation, as a wealth of information concerning this species' ecology, mating system, life history, genetics and phylogeography is available. However, reproductive barriers between populations have hereto not been investigated. Results - We report both pre- and postmating barriers to reproduction between flies from European (Finnish) and North American (Canadian) populations of Drosophila montana. Using a series of mate-choice designs, we show that flies from these two populations mate assortatively (i.e., exhibit significant sexual isolation) while emphasizing the importance of experimental design in these kinds of studies. We also assessed potential postmating isolation by quantifying egg and progeny production in intra- and interpopulation crosses and show a significant one-way reduction in progeny production, affecting both male and female offspring equally. Conclusion - We provide evidence that allopatric D. montana populations exhibit reproductive isolation and we discuss the potential mechanisms involved. Our data emphasize the importance of experimental design in studies on premating isolation between recently diverged taxa and suggest that postmating barriers may be due to postcopulatory-prezygotic mechanisms. D. montana populations seem to be evolving multiple barriers to gene flow in allopatry and our study lays the groundwork for future investigations of the genetic and phenotypic mechanisms underlying these barriers.
We propose the use of wireless, energy-harvesting, implanted nanodevice arrays with electrodes for selective stimulation of peripheral nerves in the human body. We calculate the input ultrasound energy and harvested power for single fixed-size nanowire-based nanodevices at different tissue depths and compare these with the current and voltage levels required for peripheral neural stimulation. We model the dimensioning of arrays of nanodevices, embedded in biocompatible tissue patches, to meet these neural stimulation requirements. Selectivity of activation of particular nerve bundles requires that the output voltage and current of the array can be varied to increase or decrease penetration into the neural tissue. This variation can be achieved by changing the energised area of the array and/or by decreasing the incident ultrasound power. However, the array must be implanted horizontally relative to the incident ultrasound as any tilting of the nanodevices will reduce the harvested energy. The proposed approach provides a long-term implant solution for nerve stimulation that allows the patient greater freedom of movement than with embedded tethered electrodes.
This paper proposes the use of astrocytes to realize Boolean logic gates, through manipulation of the threshold of Ca 2 + ion flows between the cells based on the input signals. Through wet-lab experiments that engineer the astrocytes cells with pcDNA3.1-hGPR17 genes as well as chemical compounds, we show that both AND and OR gates can be implemented by controlling Ca 2 + signals that flow through the population. A reinforced learning platform is also presented in the paper to optimize the Ca 2 + activated level and time slot of input signals Tb into the gate. This design platform caters for any size and connectivity of the cell population, by taking into consideration the delay and noise produced from the signalling between the cells. To validate the effectiveness of the reinforced learning platform, a Ca 2 + signalling simulator was used to simulate the signalling between the astrocyte cells. The results from the simulation show that an optimum value for both the Ca 2 + activated level and time slot of input signals Tb is required to achieve up to 90% accuracy for both the AND and OR gates. Our method can be used as the basis for future Neural–Molecular Computing chips, constructed from engineered astrocyte cells, which can form the basis for a new generation of brain implants.