5 research outputs found

    Spin-resolved electron waiting times in a quantum dot spin valve

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    We study the electronic waiting time distributions (WTDs) in a non-interacting quantum dot spin valve by varying spin polarization and the noncollinear angle between the magnetizations of the leads using scattering matrix approach. Since the quantum dot spin valve involves two channels (spin up and down) in both the incoming and outgoing channels, we study three different kinds of WTDs, which are two-channel WTD, spin-resolved single-channel WTD and cross-channel WTD. We analyze the behaviors of WTDs in short times, correlated with the current behaviors for different spin polarizations and noncollinear angles. Cross-channel WTD reflects the correlation between two spin channels and can be used to characterize the spin transfer torque process. We study the influence of the earlier detection on the subsequent detection from the perspective of cross-channel WTD, and define the influence degree quantity as the cumulative absolute difference between cross-channel WTDs and first passage time distributions to quantitatively characterize the spin flip process. The influence degree shows a similar behavior with spin transfer torque and can be a new pathway to characterize spin correlation in spintronics system.Comment: 9 pages, 7 figure

    Aerosolized Antimicrobial Agents Based on Degradable Dextran Nanoparticles Loaded with Silver Carbene Complexes

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    Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH<sub>2</sub>Cl<sub>2</sub> (organic):PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). <i>In vitro</i> efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery

    Group 13 Superacid Adducts of [PCl<sub>2</sub>N]<sub>3</sub>

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    Irrespective of the order of the addition of reagents, the reactions of [PCl<sub>2</sub>N]<sub>3</sub> with MX<sub>3</sub> (MX<sub>3</sub> = AlCl<sub>3</sub>, AlBr<sub>3</sub>, GaCl<sub>3</sub>) in the presence of water or gaseous HX give the air- and light-sensitive superacid adducts [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub>. The reactions are quantitative when HX is used. These reactions illustrate a Lewis acid/Brønsted acid dichotomy in which Lewis acid chemistry can become Brønsted acid chemistry in the presence of adventitious water or HX. The crystal structures of all three [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> adducts show that protonation weakens the two P–N bonds that flank the protonated nitrogen atom. Variable-temperature NMR studies indicate that exchange in solution occurs in [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub>, even at lower temperatures than those for [PCl<sub>2</sub>N]<sub>3</sub>·MX<sub>3</sub>. The fragility of [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> at or near room temperature and in the presence of light suggests that such adducts are not involved directly as intermediates in the high-temperature ring-opening polymerization (ROP) of [PCl<sub>2</sub>N]<sub>3</sub> to give [PCl<sub>2</sub>N]<sub>n</sub>. Attempts to catalyze or initiate the ROP of [PCl<sub>2</sub>N]<sub>3</sub> with the addition of [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> at room temperature or at 70 °C were not successful

    Group 13 Superacid Adducts of [PCl<sub>2</sub>N]<sub>3</sub>

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    Irrespective of the order of the addition of reagents, the reactions of [PCl<sub>2</sub>N]<sub>3</sub> with MX<sub>3</sub> (MX<sub>3</sub> = AlCl<sub>3</sub>, AlBr<sub>3</sub>, GaCl<sub>3</sub>) in the presence of water or gaseous HX give the air- and light-sensitive superacid adducts [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub>. The reactions are quantitative when HX is used. These reactions illustrate a Lewis acid/Brønsted acid dichotomy in which Lewis acid chemistry can become Brønsted acid chemistry in the presence of adventitious water or HX. The crystal structures of all three [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> adducts show that protonation weakens the two P–N bonds that flank the protonated nitrogen atom. Variable-temperature NMR studies indicate that exchange in solution occurs in [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub>, even at lower temperatures than those for [PCl<sub>2</sub>N]<sub>3</sub>·MX<sub>3</sub>. The fragility of [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> at or near room temperature and in the presence of light suggests that such adducts are not involved directly as intermediates in the high-temperature ring-opening polymerization (ROP) of [PCl<sub>2</sub>N]<sub>3</sub> to give [PCl<sub>2</sub>N]<sub>n</sub>. Attempts to catalyze or initiate the ROP of [PCl<sub>2</sub>N]<sub>3</sub> with the addition of [PCl<sub>2</sub>N]<sub>3</sub>·HMX<sub>4</sub> at room temperature or at 70 °C were not successful

    Structure and Conformation of the Medium-Sized Chlorophosphazene Rings

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    Medium-sized cyclic oligomeric phosphazenes [PCl<sub>2</sub>N]<sub><i>m</i></sub> (where <i>m</i> = 5–9) that were prepared from the reaction of PCl<sub>5</sub> and NH<sub>4</sub>Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl<sub>2</sub>N]<sub>3</sub> and [PCl<sub>2</sub>N]<sub>4</sub>. The medium-sized rings [PCl<sub>2</sub>N]<sub><i>m</i></sub> have been characterized by electrospray ionization–mass spectroscopy (ESI-MS), their <sup>31</sup>P chemical shifts have been reassigned, and their T<sub>1</sub> relaxation times have been obtained. Crystallographic data has been recollected for [PCl<sub>2</sub>N]<sub>5</sub>, and the crystal structures of [PCl<sub>2</sub>N]<sub>6</sub>, and [PCl<sub>2</sub>N]<sub>8</sub> are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl<sub>2</sub>N]<sub><i>m</i></sub> (<i>m</i> = 3–5, 6, 8). The crystal structures of [P­(OPh)<sub>2</sub>N]<sub>7</sub> and [P­(OPh)<sub>2</sub>N]<sub>8</sub>, which are derivatives of the respective [PCl<sub>2</sub>N]<sub><i>m</i></sub>, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl<sub>2</sub>N]<sub>8</sub> and [P­(OPh)<sub>2</sub>N]<sub>8</sub> with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding
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