12 research outputs found
Temporary Silicon Tether Strategy for Palladium-Catalyzed C-H Activation Reactions
A palladium-catalyzed intramolecular ortho CâH arylation of phenols has been developed. This methodology features the employment of a removable silicon tether strategy, allowing both TBDPS and a newly developed Br-TBDPS protecting groups to serve as efficient aryl group donors for arylation of phenols. Along this line, this removable silicon tether strategy was further applied to the intramolecular arylation of bisaryloxysilanes for the preparation of unsymmetrical ortho-biphenols, ortho-binaphthols, and mixed ortho-phenol-naphthols.
We have also developed a silanol-directed, palladium-catalyzed CâH alkenylation of phenols. Thus, employment of silanol as a traceless directing group is very convenient as it can easily be installed and removed under mild conditions. This alkenylation method is general, as it tolerates a variety of differently substituted phenols and diverse electron-deficient alkenes. The synthetic usefulness of this novel transformation was demonstrated in the efficient synthesis of benzofuranone derivative. Furthermore, the application of this method to the olefination of estrone showcased the viability of this method for the late-stage modification of bioactive molecules for drug discovery. Mechanistic studies supported an electrophilic pathway for the CâH activation step.
We have also shown that silanol can direct palladium-catalyzed CâH oxygenation of phenols en route to catechols. This protocol is highly site selective and general, as it allows for efficient oxygenation of phenols regardless of their electronic properties. Mechanistic studies indicated that this CâH oxygenation reaction undergoes ortho CâH acetoxylation first, the product of which is then converted into the cyclic silyl-protected catechol via a transesterification/cyclization sequence mediated by the in situ generated acetic acid
Synthesis of Catechols from Phenols via Pd-Catalyzed Silanol-Directed CâH Oxygenation
A silanol-directed, Pd-catalyzed CâH oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product
Mitochondria-Directed Fluorescent Probe for the Detection of Hydrogen Peroxide near Mitochondrial DNA
It
is important to detect hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) near mitochondrial DNA (mtDNA) because mtDNA is more prone
to oxidative attack than nuclear DNA (nDNA). In this study, a mitochondria-targeted
fluorescence probe, <b>pep3-NP1</b>, has been designed and synthesized.
The probe contains a DNA-binding peptide, a H<sub>2</sub>O<sub>2</sub> fluorescence reporter, and a positively charged red emissive styryl
dye to facilitate accumulation in mitochondria. Due to groove binding
of the peptide with DNA, the styryl dye of <b>pep3-NP1</b> intercalated
into the bases of DNA, leading to an increase in red fluorescence
intensity (centered at 646 nm) and quantum yield. In this case, <b>pep3-NP1</b> was a turn-on probe for labeling DNA. Subcellular
locations of <b>pep3-NP1</b> and MitoTracker suggested that <b>pep3-NP1</b> mostly accumulated in the mitochondria of live cells.
Namely, as an intracellular DNA marker, <b>pep3-NP1</b> bound
to mtDNA. In the presence of H<sub>2</sub>O<sub>2</sub>, <b>pep3-NP1</b> emitted green fluorescence (centered at 555 nm). Thus, the ratio
of green with red fluorescence of <b>pep3-NP1</b> was suitable
to reflect the change of the H<sub>2</sub>O<sub>2</sub> level near
mtDNA in living cells. The detecting limit for H<sub>2</sub>O<sub>2</sub> was estimated at 2.9 and 5.0 ÎŒM in vitro and in cultured
cells, respectively. The development of <b>pep3-NP1</b> could
help in studies to protect mtDNA from oxidative stress
Solution-Processed CuS NPs as an Inorganic Hole-Selective Contact Material for Inverted Planar Perovskite Solar Cells
Organicâinorganic
hybrid perovskite solar cells (PSCs) have
drawn worldwide intense research in recent years. Herein, we have
first applied another p-type inorganic hole-selective contact material,
CuS nanoparticles (CuS NPs), in an inverted planar heterojunction
(PHJ) perovskite solar cell. The CuS NP-modification of indium tin
oxide (ITO) has successfully tuned the surface work function from
4.9 to 5.1 eV but not affect the surface roughness and transmittance,
which can effectively reduce the interfacial carrier injection barrier
and facilitate high hole extraction efficiency between the perovskite
and ITO layers. After optimization, the maximum power conversion efficiency
(PCE) has been over 16% with low <i>J</i>â<i>V</i> hysteresis and excellent stability. Therefore, the low-cost
solution-processed and stable CuS NPs would be an alternative interfacial
modification material for industrial production in perovskite solar
cells
CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%
Although
inorganic hole-transport materials usually possess high chemical stability,
hole mobility, and low cost, the efficiency of most of inorganic hole
conductor-based perovskite solar cells is still much lower than that
of the traditional organic hole conductor-based cells. Here, we have
successfully fabricated high quality CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films on top of a CuSCN layer by utilizing a one-step fast
deposition-crystallization method, which have lower surface roughness
and smaller interface contact resistance between the perovskite layer
and the selective contacts in comparison with the films prepared by
a conventional two-step sequential deposition process. The average
efficiency of the CuSCN-based inverted planar CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> solar cells has been improved to 15.6% with
a highest PCE of 16.6%, which is comparable to that of the traditional
organic hole conductor-based cells, and may promote wider application
of the inexpensive inorganic materials in perovskite solar cells
Amphiphilic PEGylated Lanthanide-Doped Upconversion Nanoparticles for Significantly Passive Accumulation in the Peritoneal Metastatic Carcinomatosis Models Following Intraperitoneal Administration
Inorganic nanoparticles have emerged
as attractive materials for
cancer research, because of their exceptional physical properties
and multifunctional engineering. However, inorganic nanoparticle accumulation
in the tumors located in the abdominal cavity after intravenous (IV)
administration is confined because of the peritoneumâplasma
barrier. To improve this situation, we developed lanthanide-doped
upconversion nanoparticles (UCNPs), coated by amphiphilic polyethylene
glycol (P-PEG), serving as a representative of inorganic nanoparticles.
Following intraperitoneal (IP) administration into the peritoneal
metastatic carcinomatosis models, UCNPs coated by P-PEG (P-PEG-UCNPs)
passively accumulated in the cancerous tissues at a larger amount
than that in the main normal organs. On the basis of spatial proximity,
P-PEG-UCNPs administrated via the IP route exhibited higher passive
accumulation in the tumors in the abdominal cavity compared to that
via the IV route. It is suggested that IP administration could be
a promising strategy for inorganic nanoparticles to be efficaciously
applied in peritoneal cancer research
Water-Soluble and Highly Luminescent Europium(III) Complexes with Favorable Photostability and Sensitive pH Response Behavior
Two highly luminescent and water-soluble EuÂ(III) complexes, <b>Eu1</b> and <b>Eu2</b>, based on novel carboxyl-functionalized
1,5-naphthyridine derivatives 8-hydroxy-1,5-naphthyridine-2-carboxylic
acid (<b>H</b><sub><b>2</b></sub><b>L1</b>) and
7-cyano-8-hydroxy-1,5-naphthyridine-2-carboxylic acid (<b>H</b><sub><b>2</b></sub><b>L2</b>), respectively, are designed
and synthesized. The crystal structure of <b>Eu2</b> indicates
that the central EuÂ(III) ion is nine-coordinated by three tridentate
ligands (O^N^O). Both <b>Eu1</b> and <b>Eu2</b> show strong
luminescence in aqueous solution with quantum yields (lifetimes) of
28% (1.1 ms) and 14% (0.76 ms), respectively. The chelates display
unique UV-light stability in solution and remain highly emissive after
100 min of strong UV irradiation (âŒ300 W·m<sup>â2</sup> at 345 nm). Moreover, they exhibit reversible luminescence intensity
changes with varied pH values, and the response mechanism is investigated.
âTurn-onâ of the EuÂ(III) emission upon increasing pH
is realized by ligand structure change from keto to enol anion form,
resulting in red-shifted absorption band and suppressed quenching
from solvents and NâH vibration upon deprotonating. The results
show that these novel EuÂ(III) complexes are quite intriguing for potential
application as bioimaging agents and pH probes
Quantum Yields over 80% Achieved in Luminescent Europium Complexes by Employing Diphenylphosphoryl Tridentate Ligands
Four tridentate europiumÂ(III)
complexes containing a diphenylphosphoryl group are prepared with
strong bonding between the ligands and centered ion, convinced by
crystal structures. Compared to their parent bidentate complexes,
the tridentate complexes display improved and exceptionally high photoluminescence
quantum yields (PLQYs) in powder (all over 80%, best 91%), as well
as in a CH<sub>2</sub>Cl<sub>2</sub> solution and polyÂ(methyl methacrylate)
films, benefiting from compact, stable, and saturated coordination
Solid-State, Polymer-Based Fiber Solar Cells with Carbon Nanotube Electrodes
Most previous fiber-shaped solar cells were based on photoelectrochemical systems involving liquid electrolytes, which had issues such as device encapsulation and stability. Here, we deposited classical semiconducting polymer-based bulk heterojunction layers onto stainless steel wires to form primary electrodes and adopted carbon nanotube thin films or densified yarns to replace conventional metal counter electrodes. The polymer-based fiber cells with nanotube film or yarn electrodes showed power conversion efficiencies in the range 1.4% to 2.3%, with stable performance upon rotation and large-angle bending and during long-time storage without further encapsulation. Our fiber solar cells consisting of a polymeric active layer sandwiched between steel and carbon electrodes have potential in the manufacturing of low-cost, liquid-free, and flexible fiber-based photovoltaics
Simple and High Efficiency Phosphorescence Organic Light-Emitting Diodes with Codeposited Copper(I) Emitter
Phosphorescent
copperÂ(I) complexes show great promise as emitters in organic light-emitting
diodes (OLEDs). However, most copperÂ(I) complexes are neither soluble
nor stable toward sublimation and, hence, not amenable to the typical
methods to fabricate OLEDs. In this work, a compound 3-(carbazol-9-yl)-5-((3-carbazol-9-yl)Âphenyl)Âpyridine
(CPPyC) was designed as both a good ligand and host matrix. Codeposition
of CPPyC and copper iodide (CuI) gives luminescent films with photoluminescent
quantum yields (PLQY) as high as 100%. A dimeric copperÂ(I) complex
Cu<sub>2</sub>I<sub>2</sub>(CPPyC)<sub>4</sub> is formed in the thin
film, characterized by X-ray absorption spectroscopy. A series of
simple, highly efficient green-emitting OLEDs were demonstrated by
using the codeposited film as an emissive layer. A device comprised
of only CPPyC and CuI gave an external quantum efficiency (EQE) of
12.6% (42.3 cd/A) at 100 cd/m<sup>2</sup>, while a device with tailored
hole and electron transporting layers gave an efficiency of 15.7%
(51.6 cd/A) at the same brightness