19 research outputs found
Active Coordinatively Unsaturated Manganese Monoxide-Containing Mesoporous Carbon Catalyst in Wet Peroxide Oxidation
A novel heterogeneous coordinatively unsaturated manganese
monoxide-containing
mesoporous carbon catalyst (C-MnO) is reported here. The catalysts
exhibit high catalytic activity in wet oxidation of phenol (almost
complete mineralization with an initial concentration of 50 mg/L at
atmospheric pressure) and stability (reused 20 times without obvious
activity loss or metal leaching), and they take more advantages than
most developed heterogeneous Fenton catalysts. The one-pot surfactant
self-assembly approach is used for the synthesis of the mesoporous
C-MnO catalysts. Small-angle X-ray diffraction (XRD), N<sub>2</sub> sorption, and transmission electron microscopy results reveal that
the catalysts have the ordered two-dimensional hexagonal mesostructure,
large surface areas (530â552 m<sup>2</sup>/g), uniform pore
sizes (3.3â5.4 nm), and large pore volumes (0.34â0.44
cm<sup>3</sup>/g); MnO nanoparticles (<12 nm) are well dispersed
inside carbon mesopore systems with high crystallinity. The wide-angle
XRD pattern reveals the presence of cubic rock salt structure MnO,
and the Mn K-edge X-ray absorption fine structure spectra confirms
the low chemical valence and the coordination unsaturated state of
Mn. The high activity and stability of C-MnO catalysts might be related
to the mesostructure, carbon pore wall, and, more importantly, the
confined undercoordinative MnO nanoparticles
Effect of Microelectrode Structure on Electrocatalysis at Nucleic Acid-Modified Sensors
The electrochemical detection of nucleic acids using an electrocatalytic reporter system and nanostructured microelectrodes is a powerful approach to ultrasensitive biosensing. In this report we systematically study for the first time the behavior of an electrocatalytic reporter system at nucleic acid-modified electrodes with varying structures and sizes. [RuÂ(NH<sub>3</sub>)<sub>6</sub>]<sup>3+</sup> is used as a primary electron acceptor that is electrostatically attracted to nucleic acid-modified electrodes, and [FeÂ(CN)<sub>6</sub>]<sup>3â</sup> is introduced into the redox system as a secondary electron acceptor to regenerate Ru<sup>3+</sup> after electrochemical reduction. We found that the electrode structure has strong impact on mass transport and electron-transfer kinetics, with structures of specific dimensions yielding much higher electrochemical signals and catalytic efficiencies. The electrocatalytic signals obtained when gold sensors were electrodeposited in both circular and linear apertures were studied, and the smallest structures plated in linear apertures were found to exhibit the best performance with high current densities and turnover rates. This study provides important information for optimal assay performance and insights for the future design and fabrication of high performance biomolecular assays
Enantioselective Construction of Cyclopenta[<i>b</i>]indole Scaffolds via the Catalytic Asymmetric [3 + 2] Cycloaddition of 2âIndolylmethanols with <i>p</i>âHydroxystyrenes
The catalytic asymmetric
[3 + 2] cycloaddition of 2-indolylmethanols
to <i>p</i>-hydroxystyrenes was established in the presence
of a chiral phosphoramide, and this reaction provided chiral cyclopentaÂ[<i>b</i>]Âindole scaffolds in generally high yields and with good
enantioselectivities (up to 98% yield, 99:1 er). The control experiments
demonstrated that the dual hydrogen-bonding activation mode of the
chiral catalyst toward the two substrates played an important role
in the reaction. In addition, the large-scale reaction indicated that
this catalytic asymmetric [3 + 2] cycloaddition could be scaled up
for the synthesis of chiral cyclopentaÂ[<i>b</i>]Âindole derivatives
Activation of Aryl Chlorides in Water under Phase-Transfer Agent-Free and Ligand-Free Suzuki Coupling by Heterogeneous Palladium Supported on Hybrid Mesoporous Carbon
In this study, heterogeneous palladium
catalysts supported on ordered
mesoporous cobalt oxideâcarbon nanocomposites were applied
to the water-mediated Suzuki coupling reaction of chlorobenzene and
phenylboronic acid and exhibited a high yield of biphenyl (49%) under
mild reaction conditions free of phase-transfer agents and ligands.
Product yields in the reaction of aryl chlorides containing electron-withdrawing
groups attached to their benzene ring can reach approximately 90%.
Thiol-functionalized mesoporous silica, which can trap soluble Pd
species, was used to confirm the negligible leaching in solution and
therefore heterogeneous reaction. This heterogeneous catalyst is stable,
showing unobvious activity loss after 10 catalytic runs. Characterization
by X-ray diffraction, transmission electron microscopy, X-ray photoelectron
spectroscopy, X-ray absorption fine structure analysis, and N<sub>2</sub> sorption techniques revealed intercalated CoO nanoparticles
inside a carbon matrix with uniform mesopore sizes (âŒ3 nm),
high surface area (âŒ504 m<sup>2</sup>/g), and large pore volumes
(âŒ0.38 cm<sup>3</sup>/g). Additionally, very small Pd clusters
consisting of approximately three atoms and PdâO bonds formed
on the interface between CoO and Pd nanoparticles. The unsaturated
coordinative Pd may be responsible for the activation of chlorobenzene
in the absence of any additives or ligands. Uniform mesopores and
the hydrophobic nature of the carbon support may also facilitate the
mass transfer of the reactant molecules and enrichment inside pores.
For comparison, the catalytic activities of Pd catalysts supported
on pristine mesoporous carbon and carbon embedded with nickel oxide
nanoparticles were also tested
Enhancing Doxorubicin Delivery toward Tumor by Hydroxyethyl Starchâ<i>g</i>âPolylactide Partner Nanocarriers
Doxorubicin (DOX),
a kind of wide-spectrum chemotherapeutic drug,
can cause severe side effects in clinical use. To enhance its antitumor
efficacy while reducing the side effects, two kinds of nanoparticles
with desirable compositions and properties were assembled using optimally
synthesized hydroxyethyl starch-grafted-polylactide (HES-<i>g</i>-PLA) copolymers and utilized as partner nanocarriers. The large
empty HES-<i>g</i>-PLA nanoparticles (mean size, <i>ca.</i> 700 nm), at an optimized dose of 400 mg/kg, were used
to block up the reticuloendothelial system in tumor-bearing mice 1.5
h in advance, and the small DOX-loaded HES-<i>g</i>-PLA
nanoparticles (mean size, <i>ca.</i> 130 nm) were subsequently
applied to the mice. When these partner nanocarriers were administered
in this sequential mode, the released DOX had a significantly prolonged
plasma half-life time and much slower clearance rate as well as a
largely enhanced intratumoral accumulation as compared to free DOX. <i>In vivo</i> antitumor studies demonstrated that the DOX-loaded
HES-<i>g</i>-PLA nanoparticles working together with their
partner exhibited remarkably enhanced antitumor efficacy in comparison
to free DOX. In addition, these HES-<i>g</i>-PLA partner
nanocarriers showed negligible damage to the normal organs of the
treated mice. Considering safe and efficient antitumor performance
of DOX-loaded HES-<i>g</i>-PLA nanoparticles, the newly
developed partner nanocarriers in combination with their administration
mode have promising potential in clinical cancer chemotherapy
뱉Amylase- and Redox-Responsive Nanoparticles for Tumor-Targeted Drug Delivery
Paclitaxel (PTX)
is an effective antineoplastic agent and shows potent antitumor activity
against a wide spectrum of cancers. Yet, the wide clinical use of
PTX is limited by its poor aqueous solubility and the side effects
associated with its current therapeutic formulation. To tackle these
obstacles, we report, for the first time, α-amylase- and redox-responsive
nanoparticles based on hydroxyethyl starch (HES) for the tumor-targeted
delivery of PTX. PTX is conjugated onto HES by a redox-sensitive disulfide
bond to form HESâSS-PTX, which was confirmed by results from
NMR, high-performance liquid chromatography-mass spectrometry, and
Fourier transform infrared spectrometry. The HESâSS-PTX conjugates
assemble into stable and monodispersed nanoparticles (NPs), as characterized
with Dynamic light scattering, transmission electron microscopy, and
atomic force microscopy. In blood, α-amylase will degrade the
HES shell and thus decrease the size of the HESâSS-PTX NPs,
facilitating NP extravasation and penetration into the tumor. A pharmacokinetic
study demonstrated that the HESâSS-PTX NPs have a longer half-life
than that of the commercial PTX formulation (Taxol). As a consequence,
HESâSS-PTX NPs accumulate more in the tumor compared with the
extent of Taxol, as shown in an in vivo imaging study. Under reductive
conditions, the HESâSS-PTX NPs could disassemble quickly as
evidenced by their triggered collapse, burst drug release, and enhanced
cytotoxicity against 4T1 tumor cells in the presence of a reducing
agent. Collectively, the HESâSS-PTX NPs show improved in vivo
antitumor efficacy (63.6 vs 52.4%) and reduced toxicity in 4T1 tumor-bearing
mice compared with those of Taxol. These results highlight the advantages
of HES-based α-amylase- and redox-responsive NPs, showing their
great clinical translation potential for cancer chemotherapy
Redox-Sensitive Hydroxyethyl StarchâDoxorubicin Conjugate for Tumor Targeted Drug Delivery
Doxorubicin (DOX)
is one of the most potent anticancer agents in cancer chemotherapy,
but the clinical use of DOX is restricted by its severe side effects
caused by nonspecific delivery. To alleviate the side effects and
improve the antitumor efficacy of DOX, a novel redox-sensitive hydroxyethyl
starchâdoxorubicin conjugate, HES-SS-DOX, with diameter of
19.9 ± 0.4 nm was successfully prepared for tumor targeted drug
delivery and GSH-mediated intracellular drug release. HES-SS-DOX was
relatively stable under extracellular GSH level (âŒ2 ÎŒM)
but released DOX quickly under intracellular GSH level (2â10
mM). In vitro cell study confirmed the GSH-mediated cytotoxicity of
HES-SS-DOX. HES-SS-DOX exhibited prolonged plasma half-life time and
enhanced tumor accumulation in comparison to free DOX. As a consequence,
HES-SS-DOX exhibited better antitumor efficacy and reduced toxicity
as compared to free DOX in the in vivo antitumor activity study. The
redox-sensitive HES-SS-DOX was proved to be a promising prodrug of
DOX, with clinical potentials, to achieve tumor targeted drug delivery
and timely intracellular drug release for effective and safe cancer
chemotherapy
Point-of-Care Diagnosis on Selenium Nutrition Based on Time-Resolved Fluorometric Glycoaffinity Chromatography
Given the lack of timely evaluation of the well-received
selenium
fortification, a neat lateral-flow chromatographic solution was constructed
here by using the recently identified urinary selenosugar (Sel) as
a strongly indicative marker. As there are no ready-made receptors
for this synthetic standard, phenylboronic acid (PBA) esterification
and Dolichos biflorus agglutinin (DBA)
affinity joined up to pinch and pin down the analyte into a sandwich-type
glycol complex. Pilot lectin screening on homemade glycan microarrays
verified such a new pairing between dual recognizers as PBA-Sel-DBA
with a firm monosaccharide-binding constant. To quell the sample autofluorescence,
europium nanoparticles with efficient long-life afterglow were employed
as conjugating probes under 1 ÎŒs excitation. After systematic
process optimizations, the prepared Sel-dipstick achieved swift and
sensitive fluorometry over the physiological level of the target from
0.1 to 10 ÎŒM with a detection limit down to 0.06 ÎŒM. Further
efforts were made to eliminate matrix effects from both temperature
and pH via an approximate formula. Upon completion, the test strips
managed to quantify the presence of Sel in not just imitated but real
human urine, with comparable results to those in the references. As
far as we know, this would be the first in-house prototype for user-friendly
and facile diagnosis of Se nutrition with fair accuracy as well as
selectivity. Future endeavors will be invested to model a more traceable
Se-supplementary plan based on the rhythmic feedback of Sel excretion
Aggregation-Free Gold Nanoparticles in Ordered Mesoporous Carbons: Toward Highly Active and Stable Heterogeneous Catalysts
A coordination-assisted
synthetic approach is reported here for the synthesis of highly active
and stable gold nanoparticle catalysts in ordered mesoporous carbon
materials using triblock copolymer F127 as a structure-directing agent,
thiol-containing silane as a coordination agent, HAuCl<sub>4</sub> as a gold source, and phenolic resin as a carbon source. Upon carbonization,
the gold precursor becomes reduced to form monodispersed Au nanoparticles
of ca. 9.0 nm, which are entrapped or confined by the ârigidâ
mesoporous carbonaceous framework. Nanoparticle aggregation is inhibited
even at a high temperature of 600 °C. After removal of the silica
component, the materials possess the ordered mesostructure, high surface
area (âŒ1800 m<sup>2</sup>/g), large pore volume (âŒ1.19
cm<sup>3</sup>/g), and uniform bimodal mesopore size (<2.0 and
4.0 nm). The monodispersed gold nanoparticles are highly exposed because
of the interpenetrated bimodal pores in the carbon framework, which
exhibit excellent catalytic performance. A completely selective conversion
of benzyl alcohol in water to benzoic acid can be achieved at 90 °C
and 1 MPa oxygen. Benzyl alcohol can also be quantitatively converted
to benzoic acid at 60 °C even under an atmospheric pressure,
showing great advantages in green chemistry. The catalysts are stable,
poison resistant, and reusable with little activity loss due to metal
leaching. The silane coupling agent played several functions in this
approach: (1) coordinating with gold species by the thiol group to
benefit formation of monodispersed Au nanoparticles; (2) reacting
with phenolic resins by silanol groups to form relatively ârigidâ
composite framework; (3) pore-forming agent to generate secondary
pores in carbon pore walls, which lead to higher surface area, larger
pore volumes, and higher accessibility to to the gold nanoparticles.
Complete removal of the silica component proves to have little effect
on the catalytic performance of entrapped Au nanoparticles
DNA Framework-Engineered Assembly of Cyanine Dyes for Structural Identification of Nucleic Acids
DNA nanostructures
serve as precise templates for organizing organic
dyes, enabling the creation of programmable artificial photonic systems
with efficient light-harvesting and energy transfer capabilities.
However, regulating the organization of organic dyes on DNA frameworks
remains a great challenge. In this study, we investigated the factors
influencing the self-assembly behavior of cyanine dye K21 on DNA frameworks.
We observed that K21 exhibited diverse assembly modes, including monomers,
H-aggregates, J-aggregates, and excimers, when combined with DNA frameworks.
By manipulating conditions such as the ion concentration, dye concentration,
and structure of DNA frameworks, we successfully achieved precise
control over the assembly modes of K21. Leveraging K21âs microenvironment-sensitive
fluorescence properties on DNA nanostructures, we successfully discriminated
between the chirality and topology structures of physiologically relevant
G-quadruplexes. This study provides valuable insights into the factors
influencing the dynamic assembly behavior of organic dyes on DNA framework
nanostructures, offering new perspectives for constructing functional
supramolecular aggregates and identifying DNA secondary structures