Vinylcyclopropanes (VCPs) are commonly used in transition‐metal‐catalyzed cycloadditions, and the utilization of their recently realized reactivities to construct new cyclic architectures is of great ...significance in modern synthetic chemistry. Herein, a palladium‐catalyzed, visible‐light‐driven, asymmetric 5+2 cycloaddition of VCPs with α‐diazoketones is accomplished by switching the reactivity of the Pd‐containing dipolar intermediate from an all‐carbon 1,3‐dipole to an oxo‐1,5‐dipole. Enantioenriched seven‐membered lactones were produced with good reaction efficiencies and selectivities (23 examples, 52–92 % yields with up to 99:1 er and 12.5:1 dr). In addition, computational investigations were performed to rationalize the observed high chemo‐ and periselectivities.
By switching the reactivity of Pd‐containing dipolar intermediates from all‐carbon 1,3‐dipoles to oxo‐1,5‐dipoles, Pd‐catalyzed asymmetric 5+2 cycloadditions of vinylcyclopropanes (VCPs) with photogenerated ketenes are achieved. A variety of chiral seven‐membered lactone‐fused polycyclic molecules are produced with good reaction efficiency and selectivity.
Higher‐order cycloadditions, particularly 8+2 cycloadditions, are a straightforward and efficient strategy for constructing significant medium‐sized architectures. Typically, configuration‐restrained ...conjugated systems are utilized as 8π‐components for higher‐order concerted cycloadditions. However, for this reason, 10‐membered monocyclic skeletons have never been constructed via catalytic asymmetric 8+2 cycloaddition with high peri‐ and stereoselectivity. Here, we accomplished an enantioselective 8+2 dipolar cycloaddition via the merger of visible‐light activation and asymmetric palladium catalysis. This protocol provides a new route to 10‐membered monocyclic architectures bearing chiral quaternary stereocenters with high chemo‐, peri‐, and enantioselectivity. The success of this strategy relied on the facile in situ generation of Pd‐containing 1,8‐dipoles and their enantioselective trapping by ketene dipolarophiles, which were formed in situ via a photo‐Wolff rearrangement.
With the help of visible‐light irradiation and a chiral palladium catalyst, enantioselective 8+2 cycloaddition of vinyl carbomates and α‐diazoketones has been accomplished with high peri‐, chemo‐ and stereoselectivity. This protocol provides an unprecedented and straightforward route to 10‐membered monocyclic products bearing chiral quaternary stereocenters under extremely mild conditions (i.e., room temperature and 6 W blue LEDs).
Our field needs research simultaneously driven by theory and context that is both rigorous and relevant. This commentary has sought to propose a viable road map to explore the interplay between ...context and concept toward theory building in an applied area of research such as ours. This commentary discusses a three-step approach of conceptualizing the context, contextualizing the concept, and cross-fertilizing the context and concept to systematically explore the interaction between context and concept in the interest of theory building. Specific steps at each stage of the process are also discussed.
Galactic outflows are observed everywhere in star-forming disk galaxies and are critical for galaxy formation. Supernovae (SNe) play the key role in driving the outflows, but there is no consensus as ...to how much energy, mass, and metal they can launch out of the disk. We perform 3D, high-resolution hydrodynamic simulations to study SNe-driven outflows from stratified media. Assuming the SN rate scales with gas surface density gas as in the Kennicutt-Schmidt relation, we find that the mass loading factor, m, defined as the mass outflow flux divided by the star formation surface density, decreases with increasing gas as . Approximately gas 50 M pc−2 marks when m 1. About 10%-50% of the energy and 40%-80% of the metals produced by SNe end up in the outflows. The tenuous hot phase (T > 3 × 105 K), which fills 60%-80% of the volume at the midplane, carries the majority of the energy and metals in the outflows. We discuss how various physical processes, including the vertical distribution of SNe, photoelectric heating, external gravitational field, and SN rate, affect the loading efficiencies. The relative scale height of gas and SNe is a very important factor in determining the loading efficiencies.
Ring‐opening transformations of donor‐acceptor (D‐A) cyclopropanes enable the rapid assembly of complex molecules. However, the enantioselective formation of chiral quaternary stereocenters using ...substrates bearing two different acceptors remains a challenge. Herein, we describe the first palladium‐catalyzed highly diastereo‐ and enantioselective (3+2) cycloaddition of vinyl cyclopropanes bearing two different electron‐withdrawing groups, a subset of D‐A cyclopropanes. The key to the success of this reaction is the remote stereoinduction through hydrogen bond from chiral ligands, which thereby addressed the aforementioned challenge. A variety of chiral five‐membered heterocycles were produced in good yields and with high stereoselectivity (up to 99 % yields, 99 : 1 er and >19 : 1 dr). In‐depth mechanistic investigations, including control experiments and theoretical calculations, revealed the origin of the stereoselectivity and the importance of H‐bonding in stereocontrol.
Two palladium‐catalyzed asymmetric (3+2) cycloadditions of donor‐acceptor (D‐A) cyclopropenes bearing two different electron‐withdrawing groups were reported. Various chiral five‐membered oxa‐ and aza‐heterocycles were produced, and good yields and high stereoselectivities were obtained. The key to the success of this reaction is the remote stereoinduction through H‐bonding from chiral ligands.
DNA double-strand breaks （DSBs） are highly cytotoxic lesions and pose a major threat to genome stability if not properly repaired. We and others have previously shown that a class of DSB-induced ...small RNAs （diRNAs） is produced from sequences around DSB sites. DiRNAs are associated with Argonaute （Ago） proteins and play an im- portant role in DSB repair, though the mechanism through which they act remains unclear. Here, we report that the role of diRNAs in DSB repair is restricted to repair by homologous recombination （HR） and that it specifically relies on the effector protein Ago2 in mammalian cells. Interestingly, we show that Ago2 forms a complex with RadS1 and that the interaction is enhanced in cells treated with ionizing radiation. We demonstrate that RadS1 accumulation at DSB sites and HR repair depend on catalytic activity and small RNA-binding capability of Ago2. In contrast, DSB resection as well as RPA and Mrell loading is unaffected by Ago2 or Dicer depletion, suggesting that Ago2 very likely functions directly in mediating RadS1 accumulation at DSBs. Taken together, our findings suggest that guided by diRNAs, Ago2 can promote RadS1 recruitment and/or retention at DSBs to facilitate repair by HR.
PS microplastic particle (<5 mm) is an emerging contaminant of concern in aquatic and sediment systems with reported negative impacts on environmental and human health. TCS is a broad-spectrum ...antimicrobial which can affect ecosystems and result in long-term human health risks. The interaction between TCS and PS microplastic, partly determines the behavior and dispersion of TCS in the environment. In this study, the sorption kinetics and isotherms for TCS and PS microplastic were investigated. The influences of temperature, pH, ionic strength and coexisting heavy metals were assessed in batch experiments. The pseudo-second-order model (PSOM) was found to effectively describe the sorption kinetics of TCS on PS. TCS sorption on PS was found to be higher within the pH range of 3.0–6.0, while a decrease occurred at pH > 6.0. This result indicates that TCS0 was the major species contributing to the sorption process through hydrophobic interaction. Temperature did not affect the sorption of TCS on polystyrene, with sorption Kd values of 0.15, 0.16, 0.18 and 0.17 L/g at 288, 298, 308 and 318 K, respectively. Furthermore, the sorption amount of TCS showed no obvious variation with NaCl concentrations varying between 0.001 and 0.1 M. Finally, the coexistence of Cu(II)/Zn(II) had no significant influence on TCS sorption on PS, as Cu(II)/Zn(II) and TCS had different mechanisms of sorption on PS.
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•Triclosan (TCS) sorption on Polystyrene (PS) microplastic was assessed.•The sorption capacity of TCS increased with decreasing particle size of PS.•pH value plays an important role in the sorption of TCS on PS microplastic.•Hydrophobic interaction is the main mechanism of TCS sorption on PS.•Temperature, ionic strength and Cu(II)/Zn(II) had no effect on TCS sorption.
Supernovae (SNe) drive multiphase galactic outflows, impacting galaxy formation; however, cosmological simulations mostly use ad hoc feedback models for outflows, making outflow-related predictions ...from first principles problematic. Recent small-box simulations resolve individual SNe remnants in the interstellar medium (ISM), naturally driving outflows and permitting a determination of the wind loading factors of energy E, mass , and metals . In this Letter, we compile small-box results, and find consensus that the hot outflows are much more powerful than the cool outflows: (i) hot outflows generally dominate the energy flux, and (ii) their specific energy es,h is 10-1000 times higher than cool outflows. Moreover, the properties of hot outflows are remarkably simple: is almost invariant over four orders of magnitude of star formation surface density. Also, we find tentatively that 0.5. If corroborated by more simulation data, these correlations reduce the three hot phase loading factors into one. Finally, this one parameter is closely related to whether the ISM has a "breakout" condition. The narrow range of indicates that hot outflows cannot escape dark matter halos with log . This mass is also where the galaxy mass-metallicity relation reaches its plateau, implying a deep connection between hot outflows and galaxy formation. We argue that hot outflows should be included explicitly in cosmological simulations and (semi-)analytic modeling of galaxy formation.
The importance of information-technology (IT)-enabled interactions in promoting interfirm trust has been documented in literature. However, the currently available findings are limited because the ...role of IT-enabled informal interactions has been overlooked and the categorization of trust is unclear. To obtain detailed knowledge about the relation between IT-enabled interactions and trust, this study categorizes not only the IT-enabled interactions into formal and informal types but also trust into goodwill and competence trust. Moreover, this study explores the moderating role of relationship duration on the aforementioned relationships. Through a survey of 240 firms in China, this study made the following observations: (1) IT-enabled formal and informal interactions can promote both competence and goodwill trust; (2) compared with IT-enabled informal interactions, IT-enabled formal interactions promote competence trust, and a comparable extent of goodwill trust; (3) relationship duration strengthens the positive link between IT-enabled formal interactions and competence trust; however, it has no moderating impact on the link between IT-enabled formal interactions and goodwill trust; (4) relationship duration weakens the impact of IT-enabled informal interactions on goodwill trust; however, it has no significant moderating role on the relation between IT-enabled informal interactions and competence trust. Overall, this study enriches the knowledge regarding the relationship between IT-enabled interactions and interfirm trust.
No reliably specific method for complicated appendicitis has been identified in children younger than five years of age. This study aimed to analyze the independent factors for complicated ...appendicitis in children younger than five years of age, develop and validate a prediction model for the differentiation of simple and complicated appendicitis.
A retrospective study of 382 children younger than five years of age with acute appendicitis from January 2007 to December 2016 was conducted with assessments of demographic data, clinical symptoms and signs, and pre-operative laboratory results. According to intraoperative findings and postoperative pathological results, acute appendicitis was divided into simple and complicated appendicitis. Univariate and multivariate analyses were used to screen out the independent factors of complicated appendicitis, and develop a prediction model for complicated appendicitis. Then 156 such patients from January 2017 to December 2019 were collected as validation sample to validate the prediction model. Test performance of the prediction model was compared with the ALVARADO score and Pediatric Appendicitis Score (PAS).
Of the 382 patients, 244 (63.9%) had complicated appendicitis. Age, white blood cell count, and duration of symptoms were the independent factors for complicated appendicitis in children younger than five years of age. The final predication model for complicated appendicitis included factors above. In validation sample, the prediction model exhibited a high degree of discrimination (area under the curve AUC: 0.830; 95% confidence interval CI: 0.762-0.885) corresponding to a optimal cutoff value of 0.62, and outperformed the PAS (AUC: 0.735; 95% CI: 0.658-0.802), ALVARADO score (AUC: 0.733; 95% CI: 0.657-0.801).
Age, white blood cell count, and duration of symptoms could be used to predict complicated appendicitis in children younger than five years of age with acute appendicitis. The prediction model is a novel but promising method that aids in the differentiation of acute simple and complicated appendicitis.
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