4 research outputs found
Isolation of Template Effects That Control the Structure and Function of Nonspherical, Biotemplated Pd Nanomaterials
Advances in nanotechnology have indicated that the passivant
and
the inorganic surface play a pivotal role in controlling the structure/function
relationship of materials. Beyond standard materials-based methods,
bioligands have recently demonstrated the production of unique nanomaterial
morphologies for application under ambient conditions for multiple
activities, such as catalysis and biosensing. We have recently demonstrated
that a biotemplate technique could be employed to produce spherical
and linear Pd nanostructures in water using a self-assembling peptide
framework. The materials possessed high catalytic reactivity that
was controlled by the three-dimensional structure of the composite
materials. To investigate the effect of the peptide template on the
reactivity of Pd nanostructures, an in depth analysis of the catalytic
activity of Pd nanostructures fabricated via truncated templates is
presented. The new templates were designed from portions of the original
framework, which demonstrated unique synthetic and functionality control.
Two different reactions, Stille C–C coupling and 4-nitrophenol
reduction, were employed to ascertain the effect of template structure
on the reactivity of synthesized Pd nanomaterials via changes in reagent
diffusion through the bioscaffold. The results indicate that the peptide
framework plays an important role and could be used to tune and optimize
the functionality of the final composite materials for the target
application
Peptide-Modified Dendrimers as Templates for the Production of Highly Reactive Catalytic Nanomaterials
Peptide-driven
nanomaterials synthesis and assembly has become
a significant research thrust due to the capability to generate a
range of multifunctional materials with high spatial precision and
tunable properties. Despite the extensive amount of available literature,
the majority of studies report the use of free peptides to drive synthesis
and assembly. Such strategies are not an entirely accurate representation
of nature, as many materials binding peptides found in biological
systems are sterically constrained to a larger biological motif. Herein
we report the synthesis of catalytic Pd nanomaterials using constrained
peptides covalently attached to the surface of small, water-soluble
dendrimers. Using the R5 peptide conjugated to polyamidoamine dendrimer
as a bioconjugate, Pd nanomaterials were generated that displayed
altered morphologies compared to nanomaterials templated with free
R5. It was discovered that the peptide surface density on the dendrimer
affected the resulting nanoscale morphology. Furthermore, the catalytic
activities of Pd materials templated with R5/dendrimer are higher
as compared to the R5-templated Pd materials for the hydrogenation
of allyl alcohol, with an average increase in turnover frequency of
∼1500 mol product (mol Pd × h)<sup>−1</sup>. Small
angle X-ray scattering analysis and dynamic light scattering indicate
that Pd derived from R5/dendrimer templates remained less aggregated
in solution and displayed more available reactive Pd surface area.
Such morphological changes in solution are attributed to the constrained
peptide binding motifs, which altered the Pd morphology and subsequent
properties. Moreover, the results of this study suggest that constrained
materials binding peptide systems can be employed as a means to alter
morphology and improve resulting properties
Synthesis and Characterization of Thermoresponsive Hydrogels Based on <i>N</i>‑Isopropylacrylamide Crosslinked with 4,4′-Dihydroxybiphenyl Diacrylate
A novel crosslinker [4,4′-dihydroxybiphenyl
diacrylate (44BDA)]
was developed, and a series of temperature-responsive hydrogels were
synthesized through free radical polymerization of <i>N</i>-isopropylacrylamide (NIPAAm) with 44BDA. The temperature-responsive
behavior of the resulting gels was characterized by swelling studies,
and the lower critical solution temperature (LCST) of the hydrogels
was characterized through differential scanning calorimetry. Increased
content of 44BDA led to a decreased swelling ratio and shifted the
LCST to lower temperatures. These novel hydrogels also displayed resiliency
through multiple swelling–deswelling cycles, and their temperature
responsiveness was reversible. The successful synthesis of NIPAAm-based
hydrogels crosslinked with 44BDA has led to a new class of temperature-responsive
hydrogel systems with a variety of potential applications
Electrochemical Activity of Dendrimer-Stabilized Tin Nanoparticles for Lithium Alloying Reactions
The
synthesis and characterization of Sn nanoparticles in organic
solvents using sixth-generation dendrimers modified on their periphery
with hydrophobic groups as stabilizers are reported. Sn<sup>2+</sup>:dendrimer ratios of 147 and 225 were employed for the synthesis,
corresponding to formation of Sn<sub>147</sub> and Sn<sub>225</sub> dendrimer-stabilized nanoparticles (DSNs). Transmission electron
microscopy analysis indicated the presence of ultrasmall Sn nanoparticles
having an average size of 3.0–5.0 nm. X-ray absorption spectroscopy
suggested the presence of Sn nanoparticles with only partially oxidized
surfaces. Cyclic voltammetry studies of the Sn DSNs for Li alloying/dealloying
reactions demonstrated good reversibility. Control experiments carried
out in the absence of DSNs clearly indicated that these ultrasmall
Sn DSNs react directly with Li to form SnLi alloys