4 research outputs found
X‑ray Reflectivity Studies on the Mixed Langmuir–Blodgett Monolayers of Thiol-Capped Gold Nanoparticles, Dipalmitoylphosphatidylcholine, and Sodium Dodecyl Sulfate
Langmuir–Blodgett
monolayers of thiolated gold nanoparticles
mixed with dipalmitoylphosphatidylcholine/sodium dodecyl sulfate (DPPC/SDS)
were investigated by combining the X-ray reflectivity, grazing-incident
scattering, and TEM analyses to reveal the in-depth and in-plane organization
and the 2D morphology of such mixed monolayers. It was found that
the addition of a charged single-tail surfactant to the thiolated
Au nanoparticle monolayer helps to stabilize the Au nanoparticle monolayer
and to strengthen the mechanical property of the mixed monolayer film.
For mixing with lipids, it was found that the thiolated gold nanoparticles
could be pushed on top of the lipid monolayer when the mixed monolayer
is compressed. At a typical comparable total surface area ratio of
gold nanoparticle to lipid, the thiolated gold nanoparticles could
form a uniform domain on top of the DPPC monolayer. When there are
more thiolated gold nanoparticles than that could be supported by
the lipid monolayer, domain overlapping could occur to form bilayer
gold nanoparticle domains at some regions. At low total surface area
ratio of thiolated gold nanoparticle to lipid, the thiolated gold
nanoparticles tend to form a connected threadlike aggregation structure.
Evidently, the morphology of the thiolated gold nanoparticle monolayer
is highly depending on the total surface area ratio of the thiolated
gold nanoparticle to lipid. SDS is found to have a dispersion power
capable of dispersing the originally uniform Au-8C nanoparticle domain
of the mixed Au-8C/DPPC monolayer into a foamlike structure for the
mixed Au-8C/SDS/DPPC monolayer. It is evident that not only the concentration
ratio but also the size and shape of the template formed by the amphiphilic
molecules and their interaction with the thiolated gold nanoparticles
can all have great effects on the organizational structure as well
as morphology of the thiolated gold nanoparticle monolayer
Core Dominated Surface Activity of Core–Shell Nanocatalysts on Methanol Electrooxidation
The activity of core–shell nanoparticles (NCs)
in electrooxidation
of methanol (MOR) was found to be dependent on the crystalline structure
of the core and the lattice strain at the core–shell interface.
Ru-core and Pt-shell NCs delivered 6.1-fold peak MOR current density
at −135 mV than Pt NCs, while the Co-core and Pt-shell NCs
showed a 1.4-fold peak MOR current density at 280 mV. The current
density is improved by the compressive lattice strain of the surface
that is caused by the lattice mismatch between the Pt shell and the
Ru core. For Co-core NCs, the enhancement results from the ligand
effect at surface Pt sites. In addition, the Ru-core NCs maintained
a steady current density of 0.11 mA cm<sup>–2</sup> at 500
mV in a half-cell system for 2 h, which is 100-fold higher than that
of Pt NCs and Co-core NCs. These results provide mechanistic information
for the development of fuel cell catalysts along with reduced Pt utilization
and programmable electrochemical performance
Massive Enhancement of Photoluminescence through Nanofilm Dewetting
Due to the rather low efficiencies of conjugated polymers in solid films, their successful applications are scarce. However, recently several experiments indicated that a proper control of molecular conformations and stresses acting on the polymers may provide constructive ways to boost efficiency. Here, we report an amazingly large enhancement of photoluminescence as a consequence of strong shear forces acting on the polymer chains during nanofilm dewetting. Such sheared chains exhibited an emission probability many times higher than the nonsheared chains within a nondewetted film. This increase in emission probability was accompanied by the emergence of an additional blue-shifted emission peak, suggesting reductions in conjugation length induced by the dewetting-driven mass redistribution. Intriguingly, exciton quenching on narrow-band-gap substrates was also reduced, indicating suppression of vibronic interactions of excitons. Dewetting and related shearing processes resulting in enhanced photoluminescence efficiency are compatible with existing fabrication methods of polymer-based diodes and solar cells
The Penetration Depth for Hanatoxin Partitioning into the Membrane Hydrocarbon Core Measured with Neutron Reflectivity
Hanatoxin (HaTx)
from spider venom works as an inhibitor of Kv2.1
channels, most likely by interacting with the voltage sensor (VS).
However, the way in which this water-soluble peptide modifies the
gating remains poorly understood as the VS is deeply embedded within
the bilayer, although it would change its position depending on the
membrane potential. To determine whether HaTx can indeed bind to the
VS, the depth at which HaTx penetrates into the POPC membranes was
measured with neutron reflectivity. Our results successfully demonstrate
that HaTx penetrates into the membrane hydrocarbon core (∼9
Å from the membrane surface), not lying on the membrane–water
interface as reported for another voltage sensor toxin (VSTx). This
difference in penetration depth suggests that the two toxins fix the
voltage
sensors at different positions with respect to the membrane normal,
thereby explaining their different inhibitory effects on the channels.
In particular, results from MD simulations constrained by our penetration
data clearly demonstrate an appropriate orientation for HaTx to interact
with the membranes, which is in line with the biochemical information
derived from stopped-flow analysis through delineation of the toxin–VS
binding interface