5 research outputs found
Spin-resolved electron waiting times in a quantum dot spin valve
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
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>
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>
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
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