253 research outputs found
Substrate-Dependent Mechanisms for the Gold(I)-Catalyzed Cycloisomerization of Silyl-Tethered Enynes: A Computational Study
The
gold(I)-catalyzed alkenyl-, allyl-, and arylsilylation reactions
of silyl-tethered enynes discovered by Murakami et al. provide efficient
methods for the facile constructions of 1-silaindene derivatives.
A comprehensive mechanistic DFT study of these reactions was carried
out to better understand the experimental outcomes, and divergent
and substrate-dependent mechanisms for the formations of 1-silaindene
derivatives were uncovered based on the computational results. From
cationic gold(I) π-alkyne complexes, the <i>endo</i>-dig cyclization pathway may lead possibly to both C<sub>2</sub>-
and C<sub>3</sub>-group-substituted (group = alkenyl, allyl, or aryl)
1-silaindene products, and the regioselectivity will be finally determined
by the 1,2-group migration of the gold carbenoid intermediate. On
the other hand, the <i>exo</i>-dig cyclization pathway leads
only to C<sub>3</sub>-group-substituted (group = alkenyl, allyl, or
aryl) 1-silaindene, in which a notable promoting effect of the bistriflimide
counterion on the rearrangement of the silyl cation intermediate was
disclosed. The results reported herein provide insights into aspects
of regioselective cyclization, silyl-involved skeletal rearrangements,
chemoselective 1,2-migration in gold carbenoids, and the dramatic
counterion effect in the reactions concerned
PDE1A polymorphism contributes to the susceptibility of nephrolithiasis
We here provide evidence
for a monogenic cause of nephrolithiasis, or kidney stones, based on an
association of a polymorphism in the <i>PDE1A</i>
gene. This variant was detected through whole-exome analysis of ten members of
an affected family, as well as a case–control study of a validation cohort
including over 2000 patients at our hospital
Noninnocent Counterion Effect on the Rearrangements of Cationic Intermediates in a Gold(I)-Catalyzed Alkenylsilylation Reaction
A mechanistic DFT study of the gold(I)-catalyzed alkenylsilylation reaction of a silyl-tethered 1,6-enyne system is reported. A novel pathway involving bistriflimide counterion-assisted rearrangements of carbocation and silyl cation intermediates corroborates the experimental observations. The results suggest the important role of the counterion in modulating the reactivity of cationic intermediates in gold catalysis
Mechanistic Understanding of the Aryl-Dependent Ring Formations in Rh(III)-Catalyzed C–H Activation/Cycloaddition of Benzamides and Methylenecyclopropanes by DFT Calculations
The divergence between Rh(III)-catalyzed
C–H activation/cycloaddition of phenyl- and 2-furanyl-containing
benzamides with methylenecyclopropanes (MCP) was studied by DFT calculations.
Calculations found that the C–H activation via a CMD mechanism
is the most difficult step of the reaction involving phenyl. In contrast,
the C–H activation of the 2-furanyl-containing substrate is
kinetically easier but the formed five-membered rhodacycle is relatively
unstable, making the following MCP insertion more difficult. Thus,
different KIE data was obtained in experiments. The MCP insertion
forms a seven-membered-ring rhodacycle intermediate, from which the
chemoselectivity of the whole reaction is determined by the competitive
pivalate migration (path I) and β-C elimination (path II). While
the β-C elimination is lower in energy when a furanylene is
contained in the intermediate, a reversed preference of pivalate migration
was predicted for the phenylene counterpart. Structural analysis suggested
that the unfavorable β-C elimination in the phenylene case should
be attributed to the obviously increased ring strain in the corresponding
transition state, instead of the difference in electronic properties
between the aryl groups. This accounts for why aryl-dependent chemoselectivity
was observed. In addition, the results indicated that for both paths
I and II the generation of a Rh(V)–nitrenoid intermediate from
pivalate migration is crucial for the final C–N bond formation.
This explains why no reaction occurred when the N–OPiv moiety
was replaced with an N–OMe group, as no Rh(V) intermediate
could be formed in this system
Selective Metallization Induced by Laser Activation: Fabricating Metallized Patterns on Polymer via Metal Oxide Composite
Recently,
metallization on polymer substrates has been given more
attention due to its outstanding properties of both plastics and metals.
In this study, the metal oxide composite of copper–chromium
oxide (CuO·Cr<sub>2</sub>O<sub>3</sub>) was incorporated into
the polymer matrix to design a good laser direct structuring (LDS)
material, and the well-defined copper pattern (thickness =10 μm)
was successfully fabricated through selective metallization based
on 1064 nm near-infrared pulsed laser activation and electroless copper
plating. We also prepared polymer composites incorporated with CuO
and Cr<sub>2</sub>O<sub>3</sub>; however, these two polymer composites
both had very poor capacity of selective metallization, which has
no practical value for LDS technology. In our work, the key reasons
causing the above results were systematically studied and elucidated
using XPS, UV–vis–IR, optical microscopy, SEM, contact
angle, ATR FTIR, and so on. The results showed that 54.0% Cu<sup>2+</sup> in the polymer composite of CuO·Cr<sub>2</sub>O<sub>3</sub> (the amount =5 wt %) is reduced to Cu<sup>0</sup> (elemental copper)
after laser activation (irradiation); however, this value is only
26.8% for the polymer composite of CuO (the amount =5 wt %). It was
confirmed that to achieve a successful selective metallization after
laser activation, not only was the new formed Cu<sup>0</sup> (the
catalytic seeds) the crucial factor, but the number of generated Cu<sup>0</sup> catalytic seeds was also important. These two factors codetermined
the final results of the selective metallization. The CuO·Cr<sub>2</sub>O<sub>3</sub> is very suitable for applications of fabricating
metallic patterns (e.g., metal decoration, circuit) on the inherent
pure black or bright black polymer materials via LDS technology, which
has a prospect of large-scale industrial applications
Specifications of equivalent circuit of the Battery/Supercapacitor HESS in Boost mode.
<p>Specifications of equivalent circuit of the Battery/Supercapacitor HESS in Boost mode.</p
Equivalent circuit of the Battery/Supercapacitor HESS in Boost mode.
<p>Equivalent circuit of the Battery/Supercapacitor HESS in Boost mode.</p
Adaptive fractional order sliding mode control for Boost converter in the Battery/Supercapacitor HESS - Fig 3
<p><b>Simulation results of the FASMC and ASMC strategy for the Battery/supercapacitor HESS:</b> (a) The turn-on voltage of the FASMC; (b) The inductor current of the FASMC; (c)The turn-on voltage of the ASMC; (d) The inductor current of the ASMC.</p
Simulated output voltage responses due to the different λ by AFSMC.
<p>Simulated output voltage responses due to the different λ by AFSMC.</p
Prevalence of hypertension according to different category.
<p>Prevalence of hypertension according to different category.</p
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