18 research outputs found
Unusual Structural Morphology of Dendrimer/CdS Nanocomposites Revealed by Synchrotron X-ray Scattering
Low-resolution structure of CdS nanoparticles (NPs) grown in the
presence of the third-generation rigid polyphenylenepyridyl dendrimers
(PPPDs) is analyzed by synchrotron small-angle X-ray scattering (SAXS)
and transmission electron microscopy (TEM). The combination of rigidity
of the PPPDs and a high local concentration of chelating nitrogens
strongly interacting with growing CdS NPs yields anisometric particles
instead of conventional spherical ones. The scattering data from the
free PPPDs and from the composite CdS/PPPD NPs are interpreted in
terms of 3-D models revealing a peculiar morphology of the nanocomposite
whereby the PPPDs enclose the CdS NPs like a âflattened ball-in-handsâ.
The sizes of the CdS NPs found by SAXS are in good agreement with
the TEM data. The presented approach to elucidate particle morphology
should open the ways of detailed characterization of the modern composite
materials from the SAXS data
Development of Fe/Fe<sub>3</sub>O<sub>4</sub> CoreâShell Nanocubes as a Promising Magnetic Resonance Imaging Contrast Agent
Here, we report the synthesis, characterization, and properties of Fe/Fe<sub>3</sub>O<sub>4</sub> coreâshell nanocubes prepared via a simple route. It includes NaBH<sub>4</sub> reduction of FeCl<sub>3</sub> in an ethylene glycol solution in the presence of 2-mercaptopropionic acid (surfactant) and trisodium citrate (cosurfactant) followed by surface oxidation with trimethylamine <i>N</i>-oxide. The morphology and structure of Fe/Fe<sub>3</sub>O<sub>4</sub> coreâshell nanocubes were characterized using transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction, X-ray powder diffraction, and X-ray photoelectron spectroscopy. All of the methods confirm a Fe/Fe<sub>3</sub>O<sub>4</sub> coreâshell structure of nanocubes. Magnetic measurements revealed that the Fe/Fe<sub>3</sub>O<sub>4</sub> core/shell nanocubes are superparamagnetic at 300 K with a saturation magnetization of 129 emu/g. The <i>T</i><sub>2</sub> weighted imaging and the <i>T</i><sub>2</sub> relaxation time showed high MRI contrast and sensitivity, making these nanocubes viable candidates as enhanced MRI contrast agents
Structural Study of PtâFe Nanoparticles: New Insights into Pt Bimetallic Nanoparticle Formation with Oxidized Fe Species
A combination of
physicochemical methods allowed us to assess a
structure of comparatively monodisperse 3â4 nm PtâFe<sub><i>x</i></sub>O<sub><i>y</i></sub> nanoparticles
(NPs) synthesized by thermal decomposition of platinum acetylacetonate
in the presence of iron oxide NPs as an iron source. Unlike traditional
PtFe alloys composed of zerovalent Pt and Fe species with the surface
enriched by Pt atoms, the NPs discussed in this work contain Pt(0)
and oxidized Fe species (most probably Fe<sup>3+</sup> or Fe<sup>2+</sup>) as is proven by X-ray photoelectron spectroscopy (XPS). Angular
dependence XPS measurements demonstrated the absence of the coreâshell
structure, although a minor enrichment of the NP surface with Fe species
was observed. High-resolution transmission electron microscopy and
X-ray powder diffraction (XRD) reveal that these PtâFe<sub><i>x</i></sub>O<sub><i>y</i></sub> NPs are not
alloys, but consist of different domains; i.e., they have a âcluster-in-clusterâ
morphology. A comparison of the XPS and XRD data allowed us to conclude
that the NPs also include amorphous iron oxide. These results allow
better understanding of the mechanism of such NP formation and possible
predictions of their catalytic performance
Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2âPropanol
Here,
we report transfer hydrogenation of nitroarenes to aminoarenes
using 2-propanol as a hydrogen source and Ag-containing magnetically
recoverable catalysts based on partially reduced graphene oxide (pRGO)
sheets. X-ray diffraction and X-ray photoelectron spectroscopy data
demonstrated that, during the one-pot catalyst synthesis, formation
of magnetite nanoparticles (NPs) is accompanied by the reduction of
graphene oxide (GO) to pRGO. The formation of Ag<sup>0</sup> NPs on
top of magnetite nanoparticles does not change the pRGO structure.
At the same time, the catalyst structure is further modified during
the transfer hydrogenation, leading to a noticeable increase of sp<sup>2</sup> carbons. These carbons are responsible for the adsorption
of substrate and intermediates, facilitating a hydrogen transfer from
Ag NPs and creating synergy between the components of the catalyst.
The nitroarenes with electron withdrawing and electron donating substituents
allow for excellent yields of aniline derivatives with high regio
and chemoselectivity, indicating that the reaction is not disfavored
by these functionalities. The versatility of the catalyst synthetic
protocol was demonstrated by a synthesis of an Ru-containing graphene
derivative based catalyst, also allowing for efficient transfer hydrogenation.
Easy magnetic separation and stable catalyst performance in the transfer
hydrogenation make this catalyst promising for future applications
Coat Protein-Dependent Behavior of Poly(ethylene glycol) Tails in Iron Oxide Core Virus-like Nanoparticles
Here we explore the formation of
virus-like nanoparticles (VNPs) utilizing 22â24 nm iron oxide
nanoparticles (NPs) as cores and proteins derived from viral capsids
of brome mosaic virus (BMV) or hepatitis B virus (HBV) as shells.
To accomplish that, hydrophobic FeO/Fe<sub>3</sub>O<sub>4</sub> NPs
prepared by thermal decomposition of iron oleate were coated with
polyÂ(maleic acid-<i>alt</i>-octadecene) modified with polyÂ(ethylene
glycol) (PEG) tails of different lengths and grafting densities. MRI
studies show high <i>r</i><sub>2</sub>/<i>r</i><sub>1</sub> relaxivity ratios of these NPs that are practically
independent of the polymer coating type. The versatility and flexibility
of the viral capsid protein are on display as they readily form shells
that exceed their native size. The location of the long PEG tails
upon shell formation was investigated by electron microscopy and small-angle
X-ray scattering. PEG tails were located differently in the BMV and
HBV VNPs, with the BMV VNPs preferentially entrapping the tails in
the interior and the HBV VNPs allowing the tails to extend through
the capsid, which highlights the differences between intersubunit
interactions in these two icosahedral viruses. The robustness of the
assembly reaction and the protruding PEG tails, potentially useful
in modulating the immune response, make the systems introduced here
a promising platform for biomedical applications
Insights into Sustainable Glucose Oxidation Using Magnetically Recoverable Biocatalysts
Here,
we developed magnetically recoverable biocatalysts for enzymatic
oxidation of d-glucose to d-gluconic acid with high
product yields. The catalyst support is based on nanoparticle clusters
(NPCs) composed of magnetite particles and coated with the amino terminated
silica layer to facilitate further functionalization. It involves
the attachment of the glutaraldehyde linker followed by the covalent
attachment of glucose oxidase (GOx) via its amino groups. It was established
that the NPCs with a diameter of âŒ430 nm attach 33% more GOx
molecules than NPCs with a diameter of âŒ285 nm, although the
surface area of the former is lower than that of the latter. At the
same time, the biocatalyst based on the smaller NPCs shows higher
relative activity of 94% than that (87%) of the biocatalyst based
on the larger NPCs, both at 50 °C and pH 7 (optimal reaction
conditions). This surprising result has been explained by a combination
of two major factors such as GOx crowding on the support surface which
should prevent denaturation (similar to the enzyme behavior in cells)
and the enzyme mobility which should be preserved upon immobilization.
Apparently, for the biocatalyst based on 285 nm NPCs, the lower GOx
crowding is compensated by its higher mobility. The high stability
of these GOx based biocatalysts in 10 consecutive reactions as well
as facile magnetic recovery combined with excellent catalytic activity
in âtolerantâ pH range make this biocatalyst design
promising for other types of enzymatic catalysts
Functionalization of Monodisperse Iron Oxide NPs and Their Properties as Magnetically Recoverable Catalysts
Here we report the functionalization of monodisperse
iron oxide
nanoparticles (NPs) with commercially available functional acids containing
multiple double bonds such as linolenic (LLA) and linoleic (LEA) acids
or pyridine moieties such as 6-methylpyridine-2-carboxylic acid, isonicotinic
acid, 3-hydroxypicolinic acid, and 6-(1-piperidinyl)Âpyridine-3-carboxlic
acid (PPCA). Both double bonds and pyridine groups can be reacted
with noble metal compounds to form catalytically active species in
the exterior of magnetic NPs, thus making them promising magnetically
recoverable catalysts. We determined that both LLA and LEA stabilize
magnetic iron oxide NPs, allowing the formation of Ï-complexes
with bisÂ(acetonitrile)ÂdichloropalladiumÂ(II) in the NP shells. In both
cases, this leads to the formation of NP aggregates because of interparticle
complexation. In the case of pyridine-containing ligands, only PPCA
with two N-containing rings is able to provide NP stabilization and
functionalization whereas other pyridine-containing acids did now
allow sufficient steric stabilization. The interaction of PPCA-based
particles with Pd acetate also leads to aggregation because of interparticle
interactions, but the aggregates that are formed are much smaller.
Nevertheless, the catalytic properties in the selective hydrogenation
of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol were the
best for the catalyst based on LLA, demonstrating that the NP aggregates
in all cases are penetrable for DMEC. Easy magnetic separation of
this catalyst from the reaction solution makes it promising as a magnetically
recoverable catalyst
Oriented Attachment Is a Major Control Mechanism To Form Nail-like Mn-Doped ZnO Nanocrystals
Here, we present
a controlled synthesis of Mn-doped ZnO nanoparticles
(NPs) with predominantly nail-like shapes, whose formation occurs
via tip-to-base-oriented attachment of initially formed nanopyramids,
followed by leveling of sharp edges that lead to smooth single-crystalline
ânailsâ. This shape is prevalent in noncoordinating
solvents such as octadecene and octadecane. Yet, the double bond in
the former promotes oriented attachment. By contrast, Mn-doped ZnO
NP synthesis in a weakly coordinating solvent, benzyl ether, results
in dendritic structures because of random attachment of initial NPs.
Mn-doped ZnO NPs possess a hexagonal wurtzite structure, and in the
majority of cases, the NP surface is enriched with Mn, indicating
a migration of Mn<sup>2+</sup> ions to the NP surface during the NP
formation. When the NP formation is carried out without the addition
of octadecyl alcohol, which serves as a surfactant and a reaction
initiator, large, concave pyramid dimers are formed whose attachment
takes place via basal planes. UVâvis and photoluminescence
spectra of these NPs confirm the utility of controlling the NP shape
to tune electro-optical properties
Viruslike Nanoparticles with Maghemite Cores Allow for Enhanced MRI Contrast Agents
Here, for the first time, we demonstrate
formation of virus-like
nanoparticles (VNPs) utilizing gold-coated iron oxide nanoparticles
as cores and capsid protein of brome mosaic virus (BMV) or hepatitis
B virus (HBV) as shells. Further, utilizing cryo-electron microscopy
and single particle methods, we are able to show that the BMV coat
on VNPs assembles into a structure very close to that of a native
virion. This is a consequence of an optimal iron oxide NP size (âŒ11
nm) fitting the virus cavity and an ultrathin gold layer on the maghemite
cores, which allows for utilization of SH-(CH<sub>2</sub>)<sub>11</sub>-(CH<sub>2</sub>-CH<sub>2</sub>-O)<sub>4</sub>-OCH<sub>2</sub>-COOH
as capping molecules to provide sufficient stability, charge density,
and small form factor. MRI studies show unique relaxivity ratios that
diminish only slightly with gold coating. A virus protein coating
of a magnetic core mimicking the wild-type virus makes these VNPs
a versatile platform for biomedical applications
Multifunctional Nanohybrids by Self-Assembly of Monodisperse Iron Oxide Nanoparticles and Nanolamellar MoS<sub>2</sub> Plates
Here, we report the synthesis, characterization,
and properties
of novel nanohybrids formed by self-assembly of negatively charged
MoS<sub>2</sub> nanoplates and positively charged iron oxide nanoparticles
(NPs) of two different sizes, 5.1 and 11.6 nm. Iron oxide NPs were
functionalized with an amphiphilic random copolymer, quaternized polyÂ(2-(diÂmethylÂamino)Âethyl
metacrylate-<i>co</i>-stearyl metaÂcrylate), synthesized
for the first time using atom transfer radical polymerization. The
influence of the MoS<sub>2</sub> fraction and the iron oxide NP size
on the structure of the nanohybrids has been studied. Surprisingly,
larger NPs retained a larger fraction of the copolymer, thus requiring
more MoS<sub>2</sub> nanoplates for charge compensation. The nanohybrid
based on 11.6 nm NPs was studied in oxidation of sulfide ions. This
reaction could be used for removing the dangerous pollutant from wastewater
and in the production of hydrogen from water using solar energy. We
demonstrated a higher catalytic activity of the NP/MoS<sub>2</sub> nanohybrid than that of merely dispersed MoS<sub>2</sub> in catalytic
oxidation of sulfide ions and facile magnetic recovery of the catalyst
after the reaction