4 research outputs found
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Activity of Antimicrobial Peptide Aggregates Decreases with Increased Cell Membrane Embedding Free Energy Cost
Antimicrobial
peptides (AMPs) are a promising alternative to antibiotics
for mitigating bacterial infections, in light of increasing bacterial
resistance to antibiotics. However, predicting, understanding, and
controlling the antibacterial activity of AMPs remain a significant
challenge. While peptide intramolecular interactions are known to
modulate AMP antimicrobial activity, peptide intermolecular interactions
remain elusive in their impact on peptide bioactivity. Herein, we
test the relationship between AMP intermolecular interactions and
antibacterial efficacy by controlling AMP intermolecular hydrophobic
and hydrogen bonding interactions. Molecular dynamics simulations
and Gibbs free energy calculations in concert with experimental assays
show that increasing intermolecular interactions via interpeptide
aggregation increases the energy cost for the peptide to embed into
the bacterial cell membrane, which in turn decreases the AMP antibacterial
activity. Our findings provide a route for predicting and controlling
the antibacterial activity of AMPs against Gram-negative bacteria
via reductions of intermolecular AMP interactions
Competitive Binding in Mixed Surfactant Systems for Single-Walled Carbon Nanotube Separation
The
separation of single-walled carbon nanotubes (SWNTs) by chirality
is of great interest to enable the next generation of optical and
optoelectronic devices. Many separation schemes employ the surfactant
sodium dodecyl sulfate (SDS), with or without a bile salt surfactant
such as sodium cholate (SC). In this study, we observe and explain
the effect of these mixed surfactant systems on the hydrogel-based
selective adsorption separation method. We find that sodium cholate
outcompetes SDS more effectively on smaller diameter tubes and quantify
this difference as the sodium cholate concentration is increased and
(6,5) separation is diminished. These changes in separation efficiency
with surfactant composition are understood using a theoretical model
developed previously and predict that surfactant mixtures alter the
charge per unit length of specific (<i>n</i>,<i>m</i>) SWNTs, altering the separation. This understanding of the chiral
dependence of the surfactant binding will not only enable a greater
understanding of surfactant coverage on the SWNT but also pave the
path to further control the SWNT separation processes that depend
on these surfactants
Lipid Exchange Envelope Penetration (LEEP) of Nanoparticles for Plant Engineering: A Universal Localization Mechanism
Nanoparticles offer clear advantages
for both passive and active penetration into biologically important
membranes. However, the uptake and localization mechanism of nanoparticles
within living plants, plant cells, and organelles has yet to be elucidated. Here, we examine the subcellular uptake and kinetic
trapping of a wide range of nanoparticles for the first time, using
the plant chloroplast as a model system, but validated in vivo in
living plants. Confocal visible and near-infrared fluorescent microscopy
and single particle tracking of gold-cysteine-AF405 (GNP-Cys-AF405),
streptavidin-quantum dot (SA-QD), dextran and polyÂ(acrylic acid) nanoceria,
and various polymer-wrapped single-walled carbon nanotubes (SWCNTs),
including lipid-PEG-SWCNT, chitosan-SWCNT and 30-base (dAdT) sequence
of ssDNA (AT)<sub>15</sub> wrapped SWCNTs (hereafter referred to as
ssÂ(AT)<sub>15</sub>-SWCNT), are used to demonstrate that particle
size and the magnitude, but not the sign, of the zeta potential are
key in determining whether a particle is spontaneously and kinetically
trapped within the organelle, despite the negative zeta potential
of the envelope. We develop a mathematical model of this lipid exchange
envelope and penetration (LEEP) mechanism, which agrees well with
observations of this size and zeta potential dependence. The theory
predicts a critical particle size below which the mechanism fails
at all zeta potentials, explaining why nanoparticles are critical
for this process. LEEP constitutes a powerful particulate transport
and localization mechanism for nanoparticles within the plant system
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A Nanobionic Light-Emitting Plant
The engineering of
living plants for visible light emission and
sustainable illumination is compelling because plants possess independent
energy generation and storage mechanisms and autonomous self-repair.
Herein, we demonstrate a plant nanobionic approach that enables exceptional
luminosity and lifetime utilizing four chemically interacting nanoparticles,
including firefly luciferase conjugated silica (SNP-Luc), d-luciferin releasing polyÂ(lactic-<i>co</i>-glycolic acid)
(PLGA-LH<sub>2</sub>), coenzyme A functionalized chitosan (CS-CoA)
and semiconductor nanocrystal phosphors for longer wavelength modulation.
An in vitro kinetic model incorporating the release rates of the nanoparticles
is developed to maximize the chemiluminescent lifetimes to exceed
21.5 h. In watercress (<i>Nasturtium officinale)</i> and
other species, the nanoparticles circumvent limitations such as luciferin
toxicity above 400 ÎĽM and colocalization of enzymatic reactions
near high adenosine triphosphate (ATP) production. Pressurized bath
infusion of nanoparticles (PBIN) is introduced to deliver a mixture
of nanoparticles to the entire living plant, well described using
a nanofluidic mathematical model. We rationally design nanoparticle
size and charge to control localization within distinct tissues compartments
with 10 nm nanoparticles localizing within the leaf mesophyll and
stomata guard cells, and those larger than 100 nm segregated in the
leaf mesophyll. The results are mature watercress plants that emit
greater than 1.44 Ă— 10<sup>12</sup> photons/sec or 50% of 1 ÎĽW
commercial luminescent diodes and modulate “off” and
“on” states by chemical addition of dehydroluciferin
and coenzyme A, respectively. We show that CdSe nanocrystals can shift
the chemiluminescent emission to 760 nm enabling near-infrared (nIR)
signaling. These results advance the viability of nanobionic plants
as self-powered photonics, direct and indirect light sources