By merging C–O and C–F bond cleavage in cross-electrophile coupling, we developed a method for efficient synthesis of gem-difluoroalkenes with an alkoxy-substituent on the homoallylic position using ...easily accessible acetals as coupling partners with α-trifluoromethyl alkenes. Remarkably, this Ni-catalyzed allylic defluorinative cross-coupling reaction demonstrates high tolerance of a wide range of sensitive functional groups and proves to be applicable in late-stage functionalization of structurally complex compounds.
Herein, we report a method for efficient synthesis of gem-difluorobishomoallylic alcohols starting from trifluoromethyl-substituted alkenes and epoxides via a titanocene-catalyzed reductive domino ...reaction, which consists of a Ti(III)-mediated radical-type ring opening and the following allylic defluorinative cross-coupling reaction via sequential radical addition and β-F elimination. Notably, complete regioselectivity and high tolerance of functionalities can be achieved in this reaction. Furthermore, diverse 6-fluoro-3,4-dihydro-2H-pyrans have been prepared through derivatization of the cross-coupling products in one single step.
Herein we successfully applied Katritzky salts as the alkyl electrophile in the reductive allylic defluorinative cross-coupling reaction with α-trifluoromethyl alkenes. The merger of C–F and C–N bond ...cleavage via the synergistic effect of nickel and zinc allows the efficient synthesis of diverse gem-difluoroalkenes with a good tolerance for various functional groups.
By merging C–F and C–C bond activation in the cross-electrophile coupling, we developed an efficient cyanide-free synthesis of diverse functional-group-rich cyano-substituted gem-difluoroalkenes ...using cyclobutanone oxime esters and trifluoromethyl alkenes as precursors. Notably, this Ni-catalyzed reaction is bestowed with broad substrate scope, low catalyst loading, complete regioselectivities, and high tolerance of a wide range of sensitive functional groups. Preliminary mechanistic studies indicate that an iminyl radical-initiated C–C bond cleavage is involved in the reaction pathway.
Background The causes of chronic cough in China and its relations with geography, seasonality, age, and sex are largely uncertain. Methods A prospective, multicenter survey was conducted to evaluate ...patients with chronic cough across five regions in China by using a modified diagnostic algorithm. The effects of geography, seasonality, age, and sex on spectrum of chronic cough were also investigated. Results The current study evaluated 704 adult patients, including 315 men (44.7%) and 389 women (55.3%). The causes of chronic cough were determined in 640 subjects (90.9%). Common causes included cough variant asthma (CVA) (32.6%), upper airway cough syndrome (UACS) (18.6%), eosinophilic bronchitis (EB) (17.2%), and atopic cough (AC) (13.2%). Collectively, these four causes accounted for 75.2% to 87.6% across five different regions without significant difference ( P > .05), although there was variation on single causes. Gastroesophageal reflux-related cough was identified in 4.6% of causes. Seasonality, sex, and age were not associated with the spectrum of chronic cough (all P > .05). Conclusion CVA, UACS, EB, and AC were common causes of chronic cough in China. Geography, seasonality, age, and sex were not associated with the spectrum of chronic cough.
•Ba2MgSi2O7:M (M = Bi3+, Sm3+, Sm3+/Bi3+) are is preparedby the solid-statereaction method in air.•Ba2MgSi2O7:Bi3+ shows blue-white emission with a 316 nm excitation wavelength.•a2MgSi2O7:Sm3+, ...Bi3+can emita adjustable-color light with a 316 nm excitation wavelength.•4. Ba2MgSi2O7:Sm3+ and Ba2MgSi2O7:Sm3+, Bi3+ under excited at 402 nm emits orange-red light.
Ba2MgSi2O7:M (M = Bi3+, Sm3+, Sm3+/Bi3+) phosphors are synthesized in air by the high-temperature solid-state reaction method. All samples are confirmed to be a pure phase. With a 316 nm excitation wavelength, Ba2MgSi2O7:Bi3+ shows blue-white emission including a broad emission band in the range of 340 - 750 nm, and Ba2MgSi2O7:Sm3+, Bi3+ emits a adjustable-color light with the change of the ratio of Sm3+ to Bi3+ ions. Under excited at 402 nm, Ba2MgSi2O7:Sm3+ and Ba2MgSi2O7:Sm3+, Bi3+ emit orange-red light with emission spectrum region from 545 nm to 750 nm, which contain four emission bands peaking at ∼560, 598, 646 and 704 nm due to the 4G5/2 → 6H5/2, 6H7/2, 6H9/2, and 6H11/2 transitions of Sm3+ ion, respectively. Ba2MgSi2O7:Sm3+, Bi3+ under excitation at 316 nm can show a white-color emission by changing the ratio between Sm3+ and Bi3+ ions. Lifetimes of samples decrease with increasing doped ion (Sm3+ or Bi3+) concentration. We explain the luminous mechanism of samples by the schematic energy level diagrams of Bi3+ and Sm3+ ions in Ba2MgSi2O7:Sm3+, Bi3+.
Melanin is a biological pigment formed by indoles and phenolic compounds. It is widely found in living organisms and has a variety of unique properties. Due to its diverse characteristics and good ...biocompatibility, melanin has become the focus in the fields of biomedicine, agriculture, the food industry, etc. However, due to the wide range of melanin sources, complex polymerization properties, and low solubility of specific solvents, the specific macromolecular structure and polymerization mechanism of melanin remain unclear, which significantly limits the further study and application of melanin. Its synthesis and degradation pathways are also controversial. In addition, new properties and applications of melanin are constantly being discovered. In this review, we focus on the recent advances in the research of melanin in all aspects. Firstly, the classification, source, and degradation of melanin are summarized. Secondly, a detailed description of the structure, characterization, and properties of melanin is followed. The novel biological activity of melanin and its application is described at the end.
Durability is one of the technical bottlenecks restricting fuel cell electric vehicle development. As a result, significant time and resources have been invested in research related to this area ...worldwide. Current durability research mainly focuses on the single cell and stack levels, which is quite different from the usage scenarios of actual vehicles. There is almost no research on developing durability test cycles on the fuel cell system level. This paper proposes a universal model for developing a durability test cycle for fuel cell system based on the China automotive test cycle. Large-scale comparison tests of the fuel cell systems are conducted. After 1000 h test, the output performance degradation of three mass-produced fuel cell system is 14.49%, 9.59%, and 4.21%, respectively. The test results show that the durability test cycle proposed in this paper can effectively accelerate the durability test of the fuel cell system and evaluate the durability performance of the fuel cell system. Moreover, the methodology proposed in this paper could be used in any other test cycles such as NEDC (New European Driving Cycle), WLTC (Worldwide Harmonized Light Vehicles Test Procedure), etc. And it has comprehensive application value and are significant for reducing the cost of durability testing of fuel cell systems and promoting the industrialization of fuel cell electric vehicles.
•Ca3Zn3Te2O12:Bi3+, Ca3Zn3Te2O12:Eu3+, Ca3Zn3Te2O12:Eu3+/Bi3+ are prepared successfully in air.•The green emission of Ca3Zn3Te2O12:Bi3+ phosphor with excitation at 314 nm is observed.•Under ...excitation at 395 nm, the red emission of Ca3Zn3Te2O12:Eu3+ is observed.•The adjustable color light of Ca3Zn3Te2O12:Eu3+, Bi3+ phosphor with excitation at 314 nm is revealed.
Ca3Zn3Te2O12:Bi3+, Ca3Zn3Te2O12:Eu3+, Ca3Zn3Te2O12:Eu3+/Bi3+ are prepared successfully in air. The crystal phase, microscopic image, and optical properties of samples are investigated by the X-ray difractometer, scanning electron microscopy, and edinburgh steady-state FLS 980 spectrograph. The green emission of Ca3Zn3Te2O12:Bi3+ phosphor with excitation at 314 nm is observed and its broad emission spectrum in the range of 360 - 790 nm is attributed to the 3P1 → 1S0 transition of Bi3+ ion. Under excitation at 395 nm, the red emission of Ca3Zn3Te2O12:Eu3+ is found, the chromaticity coordinates are (0.6392, 0.3605), and its PL spectrum is in the rang of 575 - 750 nm because of the 5D0 → 7F0,7F1, 7F2, 7F3, and 7F4 transations of Eu3+ ion. The doping Bi3+ ion can affect the luminescence properties of Ca3Zn3Te2O12:Eu3+ phosphor. The adjustable color light from green to yellow of Ca3Zn3Te2O12:Eu3+, Bi3+ phosphor with excitation at 314 nm is revealed when Eu3+ concentration is changed from 0 to 12 mol%. When the excitation wavelength is 395 nm, Ca3Zn3Te2O12:Eu3+, Bi3+ phosphor only emits red light with emission spectrum in the rang of 575 - 750 nm. The energy level diagrams of Eu3+ and Bi3+ in Ca3Zn3Te2O12:Eu3+, Bi3+ are drawn, which is used to analyze the luminous mechanism of samples.
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Cutting fluids are the most effective method to lower the cutting temperature and decrease the cutting tool wear. At the same time, the cutting fluids influence the corrosion resistance property of ...the machined surface. In this study, chlorinated paraffin (CP), which is a common additive in the cutting fluid, was selected as the research objective to study its corrosion resistance property. The passivation effect of CP with different concentrations on the machined surface of stainless steel was studied. Electrochemical measurements and surface morphology investigation were used to characterize the passivation effect of CP with different concentrations. The test results showed that the corrosion resistance of stainless steel in the cutting fluid was enhanced with the increase in CP additive. This reason is that the charge transfer resistance increases and the corrosion current density decreases with the increase in CP additive. The X-ray photoelectron spectroscopy (XPS) results show that the proportion of metal oxides on the processed surface of the stainless steel sample was increased from 20.4% to 22.0%, 32.9%, 26.6%, and 31.1% after adding 1 mL, 2 mL, 4 mL and 6 mL CP in the cutting fluid with a total volume of 500 mL, respectively. The oxidation reaction between CP and the stainless steel sample resulted in an increase in metal oxides proportion, which prevented the stainless steel sample from corrosion in cutting fluid.
