Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the ...exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost‐effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo‐ and organometal‐catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles.
A myriad of biologically and pharmaceutically active molecules featuring a heterocyclic segment with a CCF3 stereogenic center are springing up, and some of them have been employed at the clinic stage. This review article describes recent progress on the manufacture of heterocycles possessing a CF3 group at the stereogenic carbon center, prepared from catalytic asymmetric reactions.
•Assess the causal relation among oil price, geopolitical risk, and green bond index.•Use Granger-causality in quantile from December 2013 to January 2019 in the U.S.•Find unidirectional causality ...from geopolitical risk to oil price at the extreme tails.•Support bi-directional lower-tail causality from oil price to green bond index.•Present causality from geopolitical risk to green bond index in the lower quantiles.
This research explores the causal relation among oil price, geopolitical risks, and green bond index in the United States from December 2013 to January 2019. Unlike the conventional linear model specification used in earlier works, we evaluate causal relations based on Granger-causality in quantile analysis. Our empirical results reveal unidirectional Granger-causality from geopolitical risk to oil price at the extreme quantiles. We also observe a significant bi-directional causality from oil price to green bond index for the lower quantiles. Findings also reveal causality from geopolitical risk to green bond index in the lower quantiles of the distribution. Therefore, knowledge of these causal relationships can help policy makers to evaluate and implement effective policies to prevent sudden and substantial oil price shocks and geopolitical risk.
Extracellular vesicles (EVs), a class of heterogeneous membrane vesicles, are generally divided into exosomes and microvesicles on basis of their origination from the endosomal membrane or the plasma ...membrane, respectively. EV-mediated bidirectional communication among various cell types supports cancer cell growth and metastasis. EVs derived from different cell types and status have been shown to have distinct RNA profiles, comprising messenger RNAs and non-coding RNAs (ncRNAs). Recently, ncRNAs have attracted great interests in the field of EV-RNA research, and growing numbers of ncRNAs ranging from microRNAs to long ncRNAs have been investigated to reveal their specific functions and underlying mechanisms in the tumor microenvironment and premetastatic niches. Emerging evidence has indicated that EV-RNAs are essential functional cargoes in modulating hallmarks of cancers and in reciprocal crosstalk within tumor cells and between tumor and stromal cells over short and long distance, thereby regulating the initiation, development and progression of cancers. In this review, we discuss current findings regarding EV biogenesis, release and interaction with target cells as well as EV-RNA sorting, and highlight biological roles and molecular mechanisms of EV-ncRNAs in cancer biology.
This paper presents a review of the deterioration of concrete under seawater attack with particular interests in field exposure. The research reported in the literature has shown that salinity of ...seawater in different areas varies considerably but the type of ions and their proportion are similar. Because of this variation, laboratory studies should use specific artificial seawater to simulate on field environments. The phase changes induced by chloride, magnesium and sulfate ions contained in seawater are reviewed. The interaction between hydrates and chloride ion can lead to the formation Friedel's and Kuzel's salts. Magnesium ion can replace the calcium in Portlandite, and lowers the alkalinity of pore solution and eventually destabilizes C-S-H gel. The expansive ettringite is inhibited at the presence of chloride ions. At the tidal zone, the phase change mainly occurs on the surface of concrete, which weakens the structure and leads to spalling and delamination under the physical attack of the wave. Based on the existing deterioration mechanisms, the protocols to enhance the durability performance of marine concrete are also reviewed, such as using supplementary cementitious materials (SCMs) to mitigate rate of chloride penetration and, more promisingly, to use alternative binder systems. This paper also proposes a concept of designing a more durable concrete cover system by enhancing the chemical stability of cement hydrates, rapid self-healing and intelligent alkalinity control.
A CuII‐catalyzed asymmetric 1,3‐dipolar cycloaddition using β‐fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. ...Remarkably, a catalyst loading as low as 0.5 mol % is highly efficient. Accordingly, a wide range of enantioenriched 3‐fluoroalkyl pyrrolidines, as well as Δ2‐pyrroline and pyrrole derivatives, are generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo‐adducts could be converted into the corresponding exo′‐adducts by 1,8‐diazabicyclo5.4.0undec‐7‐ene mediated epimerization at C2 of the pyrrolidine core. The free‐energy profiles from DFT calculations suggest the Michael addition of the 1,3‐dipole to be the rate‐ and enantiodetermining step, and the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.
A familiar ring: The commercially available chiral Cu(OAc)2/(S)‐tol‐BINAP catalyst is effective in the asymmetric 1,3‐dipolar cycloaddition of fluoroalkylated building blocks and azomethine ylides. The reaction is enantio‐ and diastereoselective. Notably, both exo‐ and exo′‐pyrrolidine derivatives can be accessed.
At present, solar energy is widely used as a kind of clean energy. The main solar radiation range under AM 1.5 is about 300 ~ 3000 nm. In this paper, we designed an efficient, ultra-broadband perfect ...solar absorber to have as long absorption bands in this range as possible to help alleviate the energy problem. The simulation calculations and experiments of the solar absorber show that the absorption bandwidth with absorption greater than 90% is greater than 2100 nm. It is worth noting that the perfect absorption bandwidth with absorption greater than 99% has more than 1600 nm. The absorption rate over the whole wavelength range (300 nm–3000 nm) (weighted directly around the sun by solar AM 1.5) is more than 90%. We can effectively control the absorption spectrum by adjusting the structural parameters. In addition, the proposed solar absorber is polarization independent, both the transverse electrical (TE) mode and the transverse magnetic (TM) mode, Absorption remains above 80% when the wide incidence angle is as high as 50°. Our propose design has high broadband absorption and great potential for solar thermal energy harvesting, thermoelectrics, and thermal emitters applications.
We propose an ultra-broadband perfect solar energy absorber based on TiN nanodisk and Ti thin film structure. We find that higher solar energy absorption efficiency can be achieved by adjusting the geometric parameters of nanostructures, and the perfect broadband absorption can be achieved in the range of visible light to near infrared. Display omitted
•The solar energy absorber has a perfect broadband absorption in the visible to near-infrared band.•The absorption properties can be changed by the geometric parameters.•The absorber is insensitive to incident angles, regardless of TM or TE polarization.•The absorber has good thermal stability by Ti film and TiN nanodisk.
•Microwave assisted extraction (MAE) technology was used to extract polysaccharides from Porphyra Haitanensis (PHP) and a suitable and efficient technique for PHP extraction.•Inhibition of PHP on the ...proliferation of SGC-7901 cells may be related to induction of tumor cell apoptosis directly. PHP with high antitumor activity in vivo and in vitro had the potential to be clinically used for cancer prevention and treatment.
Microwave assisted extraction (MAE) technology was used to extract polysaccharides from Porphyra Haitanensis (PHP) with water. Polysaccharide yield was used as index to evaluate the extraction process. Effects of ratio of water to raw material (X1), microwave power (X2) and extraction time (X3) on polysaccharide yield were investigated. Based on single factor experiment, MAE process of PHP was optimized using response surface methodology. Chemical characterization of PHP was investigated based on analysis of chemical compositions, monosaccharide and thermal gravimetric. The antitumor activities of PHP in vivo and in vitro were evaluated. The results indicated that the optimal conditions for MAE of PHP were ratio of water to raw material 28.98(mL/g), microwave power 77.84 W and extraction time 14.14 min. MAE was a suitable and efficient technique for PHP extraction compared with traditional hot water extraction. Analysis of chemical characterization showed that PHP contained 75.36 ± 1.48% of total carbohydrates, 24.63 ± 1.69% of uronic acid residue and no proteins with monosaccharides such as rhamnose, arabinose, xylose, mannose, glucose, and galactose in a molar ratio of 10.25:9.38:1:12.45:9.9:11.55. Thermal gravimetric analysis suggested that PHP was relatively stable below 170℃.
PHP had obvious effect on inhibiting proliferation, inducing apoptosis of SGC-7901 tumor cells in vitro and antitumor effect on SGC-7901 tumor-bearing mice in vivo. The results suggested that PHP had the potential for clinical use in cancer prevention and treatment.
Green human resource management (HRM) practices can help organizations align their business strategies with the environment. Anchored in the resource‐based view of the firm, this study examines the ...influence of green HRM practices on sustainability using cross‐sectional data obtained from 112 large manufacturing firms in Malaysia. The results show that green recruitment and green training have positive effects on sustainability. However, green analysis and job description, green selection, green performance assessment, and green reward were not found to have any significant influence on sustainability. The model presented in this paper offers useful insights into the positive role of green HRM in the sustainability of manufacturing firms, and as previous studies exploring the link between green HRM and sustainability using empirical data from Malaysian manufacturing firms are scarce, this research is of significant importance for scholars and practitioners. The scope of this study focuses on emerging economies with a limited number of variables that are contextual and specific to the Malaysian economy. Future research could explore the relationship between green HRM and other variables that may contribute to the present framework in other contexts. Future studies may also consider each dimension of green HRM, or indeed other elements of green HRM, in relation to the different aspects of sustainability.
In recent years, the number of sequences of diverse species submitted to GenBank has grown explosively and not infrequently the data contain errors. This problem is extensively recognized but not for ...invalid or incorrectly identified species, sample mixed-up, and contamination. DNA barcoding is a powerful tool for identifying and confirming species and one very important application involves forensics. In this study, we use DNA barcoding to detect erroneous sequences in GenBank by evaluating deep intraspecific and shallow interspecific divergences to discover possible taxonomic problems and other sources of error. We use the mitochondrial DNA gene encoding cytochrome b (Cytb) from turtles to test the utility of barcoding for pinpointing potential errors. This gene is widely used in phylogenetic studies of the speciose group. Intraspecific variation is usually less than 2.0% and in most cases it is less than 1.0%. In comparison, most species differ by more than 10.0% in our dataset. Overlapping intra- and interspecific percentages of variation mainly involve problematic identifications of species and outdated taxonomies. Further, we detect identical problems in Cytb from Insectivora and Chiroptera. Upon applying this strategy to 47,524 mammalian CoxI sequences, we resolve a suite of potentially problematic sequences. Our study reveals that erroneous sequences are not rare in GenBank and that the DNA barcoding can serve to confirm sequencing accuracy and discover problems such as misidentified species, inaccurate taxonomies, contamination, and potential errors in sequencing.
In order to increase the strength and lower the cost, this study experimentally investigated the effects of hooked-end steel fiber, basalt fiber and calcium sulfate on mechanical performance of ...polyvinyl alcohol (PVA) fiber-based engineered cementitious composite (ECC) containing high-volume fly ash. The uniaxial tensile, compression and four-point bending tests were carried out to characterize the mechanical behavior of each mixture. Scanning Electron Microscopy (SEM) image analysis and X-ray CT scan method were used to study the microstructures and distributions of pores. Test results showed that the ultimate strain capacity increases nearly linearly with the growth of stress performance index except the ECC reinforced with calcium sulfate and PVA. Hybridization with basalt fiber and PVA fiber or steel fiber and PVA fiber is more effective for improving mechanical performance within small deformation. ECC reinforced with calcium sulfate and PVA exhibits improved tensile, compressive and flexural strength while maintaining high ductility. The cost performance considering strength/cost and ductility/cost of hybrid mixtures was also discussed.
•Strength performance PVA-ECC containing high-volume fly ash was improved.•Strength of the PVA-ECC was improved while maintaining the inherent high ductility by the addition of calcium sulfate.•The macro and micro effects of the addition of steel fiber, basalt fiber and calcium sulfate into PVA-ECC was discussed.
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