Covalent organic frameworks (COFs), which are built upon dynamic covalent chemistry (DCC) with various organic building blocks, possess predesignable, highly ordered and crystalline porous ...structures. These features endow COFs with great potential in the development of function‐tailored materials, particularly in catalytic organic synthesis. Start from selective oxidation reactions early introduced by Ferdi, Thomas and their co‐workers, and then Wang and co‐workers performed Suzuki‐Miyaura reaction through integrating palladium into COFs, increasing numbers of works were established to explore their potentials in the 4.5catalysis of organic reactions. As heterogeneous organic catalysts, COFs bring benefits and solve problems, but also create new obstacles. Hence, we would like to establish a comprehensive system to review some pioneering works in this area. This will help us get a better view so that we can discuss the key and challenging issues we are currently confronted with.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A
bstract
The lifetimes of bottom and charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as weak
W
...-annihilation and Pauli interference. Spectator effects originating from dimension-7 four-quark operators are derived. Hadronic matrix elements of four-quark operators are parameterized in a model-independent way. Using the dimension-6 bag parameters recently determined from HQET sum rules and the vacuum insertion approximation for meson matrix elements of dimension-7 operators, the calculated
B
meson lifetime ratios
τ
(
B
+
)/
τ
(
B
d
0
) = 1.074
− 0.016
+ 0.017
and
τ
(
B
s
0
)/
τ
(
B
d
0
) = 0.9962 ± 0.0024 are in excellent agreement with experiment. Likewise, based on the quark model evaluation of baryon matrix elements, the resulting baryon lifetime ratios
τ
(Ξ
b
−
)/
τ
(Λ
b
0
),
τ
(Ξ
b
−
)/
τ
(
Ξ
b
0
),
τ
(Ω
b
−
)/
τ
(
Ξ
b
−
) and the Λ
b
−
B
0
lifetime ratio
τ
(Λ
b
0
)/
τ
(
B
d
0
) = 0.953 also agree well with the data. Contrary to the bottom hadron sector where the HQE in 1/
m
b
works well, the HQE to 1/
m
c
3
fails to give a satisfactory description of the lifetimes of both charmed mesons and charmed baryons. This calls for the subleading 1/
m
Q
corrections to spectator effects. The relevant dimension-7 spectator effects are in the right direction for explaining the large lifetime ratio of
τ
(Ξ
c
+
)/
τ
(Λ
c
+
). However, the destructive 1/
m
c
corrections to Γ(Ω
c
0
) are too large to justify the validity of the HQE, namely, the predicted Pauli interference and semileptonic rates for Ω
c
0
become negative. Demanding these rates to be positive for a sensible HQE, we find the lifetime pattern
τ
(Ξ
c
+
) >
τ
(
Ω
c
0
) >
τ
(Λ
c
+
) >
τ
(Ξ
c
0
), contrary to the current hierarchy
τ
(Ξ
c
+
) >
τ
(Λ
c
+
) >
τ
(Ξ
c
0
) >
τ
(
Ω
c
0
). We conclude that the Ω
c
0
, which is naively expected to be shortest-lived in the charmed baryon system owing to the large constructive Pauli interference, could live longer than the Λ
c
+
due to the suppression from 1/
m
c
corrections arising from dimension-7 four-quark operators. The new charmed baryon lifetime pattern needs to be tested in forthcoming experiments.
Conspectus Supramolecular self-assembly, which creates the ordered structures as a result of spontaneous organization of building blocks driven by noncovalent interactions (NCIs), is ubiquitous in ...nature. Recently, it has become increasingly clear that nature often builds up complex structures by employing a hierarchical self-assembly (HSA) strategy, in which the components are brought together in a stepwise process via multiple NCIs. Inspired by the dedicated biological structures in nature, HSA has been widely explored to construct well-defined assemblies with increasing complexity. The employment of direct metal–ligand bonds to drive the formation of discrete metallosupramolecular architectures has proven to be a highly efficient strategy to prepare structurally diverse architectures like two-dimensional (2-D) polygons and three-dimensional (3-D) polyhedra with well-defined shapes, sizes, and geometries. Such well-defined organometallic assemblies provide an ideal platform for designing novel artificial supramolecular systems with the increasing complexity though HSA. The presence of a well-defined organometallic scaffold brings an additional dimension to the final nanoscale structures. Moreover, the multilevel dynamic nature of hierarchical self-assemblies brings more structural and functional possibilities of resultant supramolecular systems. This Account will focus on our recent advance on construction of stimuli-responsive functional materials through HSA involving coordination interactions. In our study, a series of functionalized metallacycles were first constructed through coordination-driven self-assembly (CDSA). Then, the secondary noncovalent interaction sites were integrated within the functionalized metallacycle system via either preassembly or postassembly approach. Different segments, such as alkyl chains, dendrimers, cholesteryl moiety, covalent macrocycles, and even polymeric fragments, which could provide hydrophobic and hydrophilic interactions, van der Waals forces, hydrogen bonding, CH−π and π–π interactions, and host–guest interactions, have been utilized to provide the secondary NCIs. Further self-assembly of functionalized metallacycles gives rise to the formation of complex higher-order structures driven by other NCIs by taking advantages of orthogonal property of coordination bonds with other NCIs. By changing the type of additional NCIs embodied in building blocks, different supramolecular architectures, such as the ordered nanostructures, supramolecular polymers and gels, fluorescent materials and sensors, have been successfully prepared with the tailored chemical and physical properties. In particular, the dynamic nature of coordination bonds as well as other NCIs endows final assemblies with stimuli-responsive functions. Collectively, our studies suggest that combining coordination and other NCIs in a well-defined and precise manner is a highly efficient strategy to achieve the complex architectures and functional materials. Therefore, it is very promising to develop the desired functional materials with high precision and fidelity by employing HSA involving coordination interactions.
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IJS, KILJ, NUK, PNG, UL, UM
An iron‐catalyzed coupling reaction of O‐acyloximes and O‐benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6‐ketonitriles, pyrrolines ...and imidazolines via carbon‐centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring‐opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3‐hydrogen transfer, providing insights into iron‐catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen‐containing products.
Functionalized heterocycles and ketonitriles were synthesized by coupling O‐acyloximes and O‐benzoyl amidoximes with silyl enol ethers using an iron catalyst. The three reaction pathways of the iminyl radical to carbon‐centered radicals gave rise to the diversity of products (see scheme).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
The nearly 33 yr long-term radio light curve obtained with the Metsähovi Radio Observatory 14 m telescope at 37 GHz and the recent 12.7 yr
γ
-ray light curve of the blazar S5 0716+714 at ...0.1–300 GeV from the Fermi Large Area Telescope (Fermi-LAT) were analyzed by using the Lomb–Scargle periodogram and the weighted wavelet Z-transform techniques. In the radio light curve, we discovered a possible quasi-periodic oscillation (QPO) signal of about 352 ± 23 days at a confidence level of ∼3
σ
. We recalculated the periodicity and its significance in a chosen time range that has higher variability and denser sampling, and then found that the significance had increased to a confidence level of 99.996% (∼4.1
σ
). This QPO component was further confirmed by fitting a linear autoregressive integrated moving average model to the selected radio light curve. A possible QPO of 960 ± 80 days at a 99.35% level (∼2.7
σ
) was found in the
γ
-ray light curve, which generally agrees with the earlier QPO claims of S5 0716+714. This paper discusses possible mechanisms for this potential year-like QPO. One possibility is a pure geometrical scenario with blobs moving helically inside the jet. Another is a supermassive binary black hole involving a gravitational wave-driven regime. In the latter scenario, we derived a milliparsec separation in the binary system that undergoes coalescence within a century due to the emission of low-frequency gravitational waves.
The exploring of catalysts with high‐efficiency and low‐cost for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key issues for many renewable energy systems ...including fuel cells, metal–air batteries, and water splitting. Despite several decades pursuing, bifunctional oxygen catalysts with high catalytic performance at low‐cost, especially the one that could be easily scaled up for mass production are still missing and highly desired. Herein, a hybrid catalyst with NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers is synthesized by a facile electrospinning method and postcalcination treatment. The hybrid catalyst NiCo@N‐C 2 exhibits outstanding ORR and OER catalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively. The synergetic effects between alloy nanoparticles and the N‐doped carbon fiber are considered as the main contributions for the excellent catalytic activities, which include decreasing the intrinsic and charge transfer resistances, increasing CC, graphitic‐N/pyridinic‐N contents in the hybrid catalyst. This work opens up a new way to fabricate high‐efficient, low‐cost oxygen catalysts with high production.
NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers as a highly active and durable oxygen electrocatalyst at low‐cost are synthesized and reported. The hybrid catalyst with suitable amount of NiCo alloy nanoparticles loading (NiCo@N‐C 2) gives the most outstanding oxygen reduction reaction and oxygen evolution reaction electrocatalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively.
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Developing efficient sensor materials with superior performance for selective, fast and sensitive detection of gases and volatile organic compounds (VOCs) is essential for human health and ...environmental protection, through monitoring indoor and outdoor air pollutions, managing industrial processes, controlling food quality and assisting early diagnosis of diseases. Metal-organic frameworks (MOFs) are a unique type of crystalline and porous solid material constructed from metal nodes (metal ions or clusters) and functional organic ligands. They have been investigated extensively for possible use as high performance sensors for the detection of many different gases and VOCs in recent years, due to their large surface area, tunable pore size, functionalizable sites and intriguing properties, such as electrical conductivity, magnetism, ferroelectricity, luminescence and chromism. The high porosity of MOFs allows them to interact strongly with various analytes, including gases and VOCs, thus resulting in easily measurable responses to different physicochemical parameters. Although much of the recent work on MOF-based luminescent sensors have been summarized in several excellent reviews (up to 2018), a comprehensive overview of these materials for sensing gases and VOCs based on chemiresistive, magnetic, ferroelectric, and colorimertic mechanisms is missing. In this review, we highlight the most recent progress in developing MOF sensing and switching materials with an emphasis on sensing mechanisms based on electricity, magnetism, ferroelectricity and chromism. We provide a comprehensive analysis on the MOF-analyte interactions in these processes, which play a key role in the sensing performance of the MOF-based sensors and switches. We discuss in detail possible applications of MOF-based sensing and switching materials in detecting oxygen, water vapor, toxic industrial gases (such as hydrogen sulfide, ammonia, sulfur dioxide, nitrous oxide, carbon oxides and carbon disulfide) and VOCs (such as aromatic and aliphatic hydrocarbons, ketones, alcohols, aldehydes, chlorinated hydrocarbons and
N
,
N
′-dimethylformamide). Overall, this review serves as a timely source of information and provides insight for the future development of advanced MOF materials as next-generation gas and VOC sensors.
This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.
Charmed baryon physics circa 2021 Cheng, Hai-Yang
Chinese journal of physics (Taipei),
August 2022, 2022-08-00, Volume:
78
Journal Article
Peer reviewed
Open access
This is an update of the two articles (Cheng, 2009; Cheng, 2015) in which charmed baryon physics around 2007 and 2015, respectively, were reviewed. In this review we emphasize the experimental ...progress and the theoretical development since 2015.
•Spin-parity assignments of higher excited charmed baryon states are discussed.•Lifetimes of charmed baryons are studied in heavy quark expansion.•Nonleptonic weak decays and radiative decays of charmed baryons are reviewed.•CP violation in the charmed baryon system is addressed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper considers the initial–boundary value problem of the attraction–repulsion Keller–Segel model describing aggregation of Microglia in the central nervous system in Alzheimer's disease due to ...the interaction of chemoattractant and chemorepellent. If repulsion dominates over attraction, we show the global existence of classical solution in two dimensions and weak solution in three dimensions with large initial data.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Polymers have greatly changed and are still changing the way we live ever since, and the construction of novel polymers as functional materials remains an attractive topic in polymer science and ...related areas. During the past few years, the marriage of discrete supramolecular coordination complexes (SCCs), including two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages, and polymers gave rise to two novel types of metallo-supramolecular polymers,
i.e.
, metallacycle/metallacage-cored star polymers (MSPs) and metallacycle/metallacage-crosslinked polymer networks (MPNs), which has attracted increasing attention and emerged as an exciting new research direction in polymer chemistry. Attributed to their well-defined and diverse topological architectures as well as the unique dynamic features of metallacycles/metallacages as cores or crosslinks, these novel polymers have shown extensive applications. In this review, aiming at providing a practical guide to this emerging area, the introduction of synthetic strategies towards MSPs and MPNs will be presented. In addition, their wide applications in areas such as functional materials, molecular sieving, drug delivery, bacterial killing and bioimaging are also discussed.
The marriage of polymerization and coordination-driven self-assembly has given rise to novel types of metallo-supramolecular polymers with well-defined and diverse topological architectures as well as unique dynamic features.
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