30 research outputs found
Surfactant-Free Solvothermal Synthesis of 3D Flowerlike Iron Alkoxide (Fe-EG) Micro/Nanostructures: Structure, Formation Mechanism, and Fenton Oxidation of Azo Dyes
A three-dimensional
(3D) flowerlike iron alkoxide (Fe-EG) micro/nanostructure
has been fabricated for the first time via a facile surfactant-free
solvothermal method using CH<sub>3</sub>COONa·3H<sub>2</sub>O
as the alkali source and systematically characterized. The green-colored
3D flowerlike Fe-EG micro/nanostructure is a polymeric ferrous glycolate
with the chemical formula [Fe<sub>2</sub>(OCH<sub>2</sub>CH<sub>2</sub>O)<sub>2</sub>(HOCH<sub>2</sub>CH<sub>2</sub>OH)<sub>2</sub>]<sub><i>n</i></sub>. Upon quasi-in situ monitoring of the morphology
and composition of the samples collected at various reaction times,
a coordination/ligand substitution/reduction/polymerization mechanism
for Fe-EG is tentatively proposed. The Fe-EG micro/nanostructure exhibited
âŒ99.7% Acid Orange 7 (AO7) degradation efficiency in 40 min
with H<sub>2</sub>O<sub>2</sub> as the oxidant at pH<sub>0</sub> =
6.0. It is believed that the high dispersion of a large amount of
Fe<sup>3+</sup> on the surface of in situ-formed 3D flowerlike amorphous
FeOOH with a large surface area and rich porous structure by the moderate
interfacial hydrolysis process of Fe-EG benefits the adsorption of
dye molecules and the formation of hydroxyl radicals
DFT Studies on Copper-Catalyzed Arylation of Aromatic CâH Bonds
Cu-catalyzed arylation of aromatic CâH bonds with
phenyl
iodide has been investigated with the aid of density functional theory
calculations at the B3LYP level. Both the neutral and anionic catalytic
cycles have been examined by considering the neutral (phen)ÂCuâOMe
and anionic [MeOâCuâOMe]<sup>â</sup> complexes,
respectively, as the active species. Various heterocycle and polyfluorobenzene
substrates were studied. The relationship between the overall reaction
barrier and the acidity of the cleaved CâH bond was studied
in both the neutral and anionic catalytic cycles. Comparing the overall
reaction barriers based on the neutral and anionic catalytic cycles,
we were able to understand that some substrates prefer the anionic
mechanism while others prefer the neutral mechanism. We also examined
how different ligands influence the overall barriers in the neutral
catalytic cycles by employing <i>N</i>,<i>N</i>âČ-dimethylethylenediamine (DMEDA) and <i>N</i>-methylpyrrolidine-2-carboxamide
as the ligands
Novel Morphology-Controlled Hierarchical Core@Shell Structural Organo-Layered Double Hydroxides Magnetic Nanovehicles for Drug Release
Novel hierarchical core@shell structured
salicylate (SA) intercalated ZnAl-LDH (layered double hydroxides)
magnetic nanovehicles were obtained via a special double-drop coprecipitation
strategy assembling organo-ZnAl-LDH nanocrystals onto the surface
of Fe<sub>3</sub>O<sub>4</sub> submicrospheres (âŒ480 nm) from
cheap aspirin and Zn- and Al-nitrates in alkaline solutions. The obtained
Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-<i>r</i> nanovehicles
exhibit varied morphologies with hexagonal LDH <i>ab</i>-face horizontal, vertical, and vertical/slant/horizontal to the
surfaces of Fe<sub>3</sub>O<sub>4</sub> upon proper mass ratio (<i>r</i>) of Zn-salt to Fe<sub>3</sub>O<sub>4</sub> from 1.93 to
7.71 in a low supersaturation system and possess moderate drug loadings
and strong superparamagnetism. An <i>in vitro</i> release
study reveals that under âno MFâ mode (without external
magnetic field) the SA release exhibits the higher accumulated release
amount and smaller half-life (<i>t</i><sub>0.5</sub>) for
Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-3.85 (41.2%, 1.63 min) and Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-7.71 (51.1%, 1.66 min) probably owing
to their mainly vertical LDH orientations, while the dramatically
reduced SA release (10.0%) and greatly elongated <i>t</i><sub>0.5</sub> (25.6 min) for Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-1.93
may be due to its relatively stronger hostâguest interaction
and compact horizontally oriented LDH shell stack. Under âMF
onâ mode, all the magnetic samples show a detectable reduced
SA release owing to the particleâparticle interactions among
the magnetic nanovehicles. The kinetic fittings show that the release
processes of all the samples involve the bulk and surface diffusion.
The SA release from Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-1.93 is mainly
determined by the interparticle diffusion among the horizontally oriented
LDH shell nanocrystals while those of Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-3.85
and Fe<sub>3</sub>O<sub>4</sub>@SA-LDH-7.71 mainly involve the interlayer
intraparticle diffusion between LDHs layers due to their largely vertical
LDH shell nanocrystals
DFT Studies on Copper-Catalyzed Hydrocarboxylation of Alkynes Using CO<sub>2</sub> and Hydrosilanes
In
this paper, DFT calculations have been carried out to study
the reaction mechanism of copper-catalyzed hydrocarboxylation of alkynes
using CO<sub>2</sub> and hydrosilanes. In addition to hydrocarboxylation
of alkynes, possible competitive reactions such as hydrosilylation
of alkynes, hydrosilylation of CO<sub>2</sub>, and silacarboxylation
of alkynes have also been investigated and compared. Through these
DFT calculations, we are able to understand the reason only hydrocarboxylation
of alkynes has been observed experimentally
Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?
Two
radicals can form a bond without an energetic barrier. However,
the radical coupling mechanism in ruthenium-catalyzed water oxidation
has been found to be associated with substantial activation energies.
Here we have investigated the coupling reaction of [Ruî»OÂ(bda)ÂL<sub>2</sub>]<sup>+</sup> catalysts with different axial L ligands. The
interaction between the two oxo radical moieties at the RuÂ(V) state
was found to have a favorable interaction in the transition state
in comparison to the prereactive complex. To further understand the
existence of the activation energy, the activation energy has been
decomposed into distortion energy and interaction energy. No correlation
between the experimental rates and the calculated coupling barriers
of different axial L was found, showing that more aspects such as
solvation, supramolecular properties, and solvent dynamics likely
play important roles in the equilibrium between the free Ru<sup>V</sup>î»O monomer and the [Ru<sup>V</sup>î»O···Oî»Ru<sup>V</sup>] dimer. On the basis of our findings, we give general guidelines
for the design of catalysts that operate by the radical coupling mechanism
DFT Studies on Gold-Catalyzed Cycloisomerization of 1,5-Enynes
Gold-catalyzed cycloisomerization of 1,5-enynes has been
investigated
with the aid of density functional theory calculations at the B3LYP
level of theory. We have examined how substituents influence the reaction
paths in the cycloisomerization of 1,5-enynes catalyzed by both AuCl
and [AuL]<sup>+</sup> (L = phosphine)
Analyzing the pathways enriched in genes associated with nicotine dependence in the context of human proteinâprotein interaction network
<p>Nicotine dependence is the primary addictive stage of cigarette smoking. Although a lot of studies have been performed to explore the molecular mechanism underlying nicotine dependence, our understanding on this disorder is still far from complete. Over the past decades, an increasing number of candidate genes involved in nicotine dependence have been identified by different technical approaches, including the genetic association analysis. In this study, we performed a comprehensive collection of candidate genes reported to be genetically associated with nicotine dependence. Then, the biochemical pathways enriched in these genes were identified by considering the geneâs propensity to be related to nicotine dependence. One of the most widely used pathway enrichment analysis approach, over-representation analysis, ignores the function non-equivalence of genes in candidate gene set and may have low discriminative power in identifying some dysfunctional pathways. To overcome such drawbacks, we constructed a comprehensive human proteinâprotein interaction network, and then assigned a function weighting score to each candidate gene based on their network topological features. Evaluation indicated the function weighting score scheme was consistent with available evidence. Finally, the function weighting scores of the candidate genes were incorporated into pathway analysis to identify the dysfunctional pathways involved in nicotine dependence, and the interactions between pathways was detected by pathway crosstalk analysis. Compared to conventional over-representation-based pathway analysis tool, the modified method exhibited improved discriminative power and detected some novel pathways potentially underlying nicotine dependence. In summary, we conducted a comprehensive collection of genes associated with nicotine dependence and then detected the biochemical pathways enriched in these genes using a modified pathway enrichment analysis approach with function weighting score of candidate genes integrated. Our results may provide insight into the molecular mechanism underlying nicotine dependence.</p
The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway
Many
Ru water oxidation catalysts have been documented in the literature.
However, only a few can catalyze the OâO bond formation via
the radical coupling pathway, while most go through the water nucleophilic
attack pathway. Understanding the electronic effect on the reaction
pathway is of importance in design of active water oxidation catalysts.
The Ru-bda (bda = 2,2âČ-bipyridine-6,6âČ-dicarboxylate)
catalyst is one example that catalyzes the OâO bond formation
via the radical coupling pathway. Herein, we manipulate the equatorial
backbone ligand, change the doubly charged bda<sup>2â</sup> ligand to a singly charged tpc<sup>â</sup> (2,2âČ:6âČ,2âł-terpyridine-6-carboxylate)
ligand, and study the structureâactivity relationship. Surprisingly,
kinetics measurements revealed that the resulting Ru-tpc catalyst
catalyzes water oxidation via the water nucleophilic attack pathway,
which is different from the Ru-bda catalyst. The OâO bond formation
Gibbs free energy of activation (Î<i>G</i><sup>⧧</sup>) at <i>T</i> = 298.15 K was 20.2 ± 1.7 kcal mol<sup>â1</sup>. The electronic structures of a series of Ru<sup>V</sup>î»O species were studied by density function theory
calculations, revealing that the spin density of O<sub>Ruî»O</sub> of Ru<sup>V</sup>î»O is largely dependent on the surrounding
ligands. Seven coordination configuration significantly enhances the
radical character of Ru<sup>V</sup>î»O
Multi-Level Architecture Optimization of MOF-Templated Co-Based Nanoparticles Embedded in Hollow NâDoped Carbon Polyhedra for Efficient OER and ORR
Emerging
clean energy technologies such as regenerative fuel cells
and rechargeable metalâair batteries have attracted increasing
global interest because of their high efficiency and environmental
benignity, but the lack of highly active bifunctional electrocatalysts
at low cost for both oxygen reduction and evolution reactions (ORR
and OER) greatly hinders their commercial applications. Here, we report
the multilevel architecture optimization of Co-based nanoparticles
(NPs) embedded in hollow N-doped carbon polyhedra for boosting the
ORR and OER, which are fabricated by a two-step pyrolysisâoxidation
strategy with a Co-based MOF (ZIF-67) as precursor. The key for this
strategy lies in the precise and effective control of the oxidation
processes of Co NPs, which enables the synthesis of a series of CoâCo<sub>3</sub>O<sub>4</sub>-based nanoarchitectures that are embedded in
hollow nitrogen-doped carbon polyhedra (HNCP), including coreâshell
Co/Co<sub>3</sub>O<sub>4</sub>, yolk@shell Co@Co<sub>3</sub>O<sub>4</sub>, and hollow Co<sub>3</sub>O<sub>4</sub> NPs. Benefiting from
its abundant oxygen vacancies and tetrahedral Co<sup>2+</sup> and
the potential synergies of CoO<sub><i>x</i></sub> species
and nitrogen-doped carbon as well as the efficient mass transfer of
hollow and yolkâshell structures, the optimal yolk@shell Co<sub>3</sub>O<sub>4</sub>/HNCP-40 exhibits high activity for the OER with
a low overpotential of 333 mV at 10 mA cm<sup>â2</sup> and
a small Tafel slope of 69 mV dec<sup>â1</sup>, which is better
than those of commercial IrO<sub>2</sub> (its overpotential and Tafel
slope are 409 mV at 10 mA cm<sup>â2</sup> and 104 mV dec<sup>â1</sup>, respectively). Meanwhile, the catalyst also exhibits
comparable ORR catalytic activity with a half-wave potential of 0.834
V but better stability and methanol tolerance relative to commercial
Pt/C (20 wt %), making it a potential bifunctional electrocatalyst
for both the OER and ORR. This MOF-templated strategy for multilevel
nanostructures provides insights into the development of highly efficient
and low-cost bifunctional electrocatalysts for the OER/ORR
The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway
Many
Ru water oxidation catalysts have been documented in the literature.
However, only a few can catalyze the OâO bond formation via
the radical coupling pathway, while most go through the water nucleophilic
attack pathway. Understanding the electronic effect on the reaction
pathway is of importance in design of active water oxidation catalysts.
The Ru-bda (bda = 2,2âČ-bipyridine-6,6âČ-dicarboxylate)
catalyst is one example that catalyzes the OâO bond formation
via the radical coupling pathway. Herein, we manipulate the equatorial
backbone ligand, change the doubly charged bda<sup>2â</sup> ligand to a singly charged tpc<sup>â</sup> (2,2âČ:6âČ,2âł-terpyridine-6-carboxylate)
ligand, and study the structureâactivity relationship. Surprisingly,
kinetics measurements revealed that the resulting Ru-tpc catalyst
catalyzes water oxidation via the water nucleophilic attack pathway,
which is different from the Ru-bda catalyst. The OâO bond formation
Gibbs free energy of activation (Î<i>G</i><sup>⧧</sup>) at <i>T</i> = 298.15 K was 20.2 ± 1.7 kcal mol<sup>â1</sup>. The electronic structures of a series of Ru<sup>V</sup>î»O species were studied by density function theory
calculations, revealing that the spin density of O<sub>Ruî»O</sub> of Ru<sup>V</sup>î»O is largely dependent on the surrounding
ligands. Seven coordination configuration significantly enhances the
radical character of Ru<sup>V</sup>î»O