Latest ArticlesCarbocations such as tropylium and trityl cation, can be stable enough to be isolated and used without inert conditions. They can act as Lewis acids to lower the LUMO of electrophile, thus promoting reactions with nucleophiles. Additionally, the interaction between carbocations and alcohols can form Brønsted acids with enhanced acidity. Furthermore, electrophoto activation of TAC+ (trisaminocyclopropenium ion) delivers the excited radical dication TAC•2+*, which is a strong oxidant and capable of oxidizing a range of challenging substrates. Moreover, Pr-DMQA+ is disclosed as a versatile photoredox catalyst as its excited state can be quenched through both oxidation and reduction. This review summarizes recent advance in carbocation-catalyzed reactions. These developed methods provide an environmentally friendly pathway for the synthesis of valuable compounds and will inspire chemists to discover more interesting transformations promoted by carbocations.
The issue about how outstanding scientists obtained innovative findings has drawn the interest of researchers in science, policy and scientometrics. Here, we attempt to address this question by using computational methods to measure the cognitive content and concepts of K. Barry Sharpless' research and estimate the knowledge flow of his click chemistry to other fields. First, we traced Sharpless' conceptual journey over time through topic modeling approach, mapping and clustering of the epistemic network from distant reading his publications. We find that connectivity and functions, the core features of click chemistry, are embodied in his constant search for simplicity. What makes simplicity possible is his continuous work with collaborators on reactivity and reaction mechanisms. Moreover, citation and link analysis show that click chemistry had a much richer impact on other research fields than what is generally acknowledged, and drew solutions to significant and practical questions back to chemistry from biology. Together with these findings, we propose that the click chemistry philosophy follows the way that values nature's principle. Chemistry has a clear-cut epistemic domain in modeling Nature. Thus, click chemistry as a concept on doing science beyond a connective technology goes across the boundaries between disciplines and impacts many other fields.
Dynamic manipulation of enzymatic activity is a challenging task for applications in chemical and pharmaceutical industries due to the difficult modification and variable conformation of various enzymes. Here, we report a new strategy for reversible dynamic modulation of enzymatic activity by near-infrared light-induced photothermal conversion based on polyphenol-functionalized liquid metal nanodroplets (LM). The metal-phenolic nanocoating not only provides colloidal stability of LM nanodroplets but also generates nanointerfaces for the assembly of various enzymes on the LM nanodroplets. Upon near infrared (NIR) irradiation, the localized microenvironmental heating through photothermal effect of the LM nanodroplets allows tailoring the enzymatic activity without affecting the bulk temperature. A library of functional enzymes, including proteinase K, glucoamylase, glucose oxidase, and Bst DNA polymerase, is integrated to perform a reversible control and enhanced activities even after five times of cycles, demonstrating great potential in bacterial fermentation, bacteriostasis, and target gene amplification.
A series of DL-serine covalently modified multinuclear lanthanide implanted arsenotungstates K2[{Ln(H2O)7}2{As4W44O137(OH)18(H2O)2(DL-Ser)2}{Ln2(H2O)5(DL-Ser)}2]·65H2O (DL-Ser = DL-serine, Ln = La (1), Ce (2), Pr (3)) are obtained. Crystal structure analysis shows that these compounds are isomorphic and contain the basic [{As4W44O137(OH)18(H2O)2(DL-Ser)2}{Ln2(H2O)5(DL-Ser)}2]8– polyoxoanion constituted by two {As2W19O59(OH)8(H2O)}6‒ subunits, a [W6O23(OH)2(DL-Ser)2]14‒ fragment, and two embedded [Ln2(H2O)5(DL-Ser)]5+ groups, which further build into one dimensional linear chainlike structure via two peripheral Ln3+ ions. Most remarkably, these compounds exhibit rapid photochromic behaviors, which changed color quickly from white (1), yellow (2), green (3) to blue (1), brown (2) and glaucous (3) in ten minutes under UV irradiation, and that the colors gradually recovered in the dark for approximately 22 h.
The horizontal flow anaerobic digester indicated that high ammonia (2923 mg/L) and SO42- (3653 mg/L) would influence the performance of methane production with food waste as substrates. Therefore, bottle anaerobic digestion reactors were carried out to investigate the effect of ammonia/sulfate concentrations on the methane production. Experimental results manifested that the anaerobic digesters with an ammonia concentration of 3500 mg/L or sulfate of 1600 mg/L showed the best performance of methane production, with an average methane yield of 0.32 and 0.33 L (g VS)-1 d-1, respectively. Specifically, a higher ammonia (6500 mg/L) or sulfate (1600-3500 mg/L) level hindered the bioconversion of C from liquid to gas phase (2.68% or 1.73% CH4-Gas, respectively), while insignificantly for the hydrolyzation of C and N from solid to liquid phase. Similar to sulfate, high ammonia nitrogen seriously inhibited the methanation process, leading to a significant carbon accumulation in the anaerobic reactor, especially for propionic acid. The predominant archaea Methanosarcina at genus level indicated that aceticlastic methanogenesis was the major methanogenic pathway. Meanwhile, high ammonia level suppressed the activity of Methanosarcina, while modest sulfate improved H2-consuming methanogens activity. A large fraction of unclassified bacteria within the Firmicutes (43.78%-63.17%) and Bacteroidetes (24.20%-33.30%) phylum played an important role in substrates hydrolysis.
The freshness of seafood can be judged by detecting the concentration of triethylamine (TEA). In this work, 2D CuO porous nanosheets (CuO PNs) were prepared by a graphene oxide template method and their particle sizes were regulated by changing the calcination temperature. Their structure, morphology and gas sensing performances were investigated by various characterization methods. The response (Rg/Ra) of the gas sensor based on CuO PNs calcined at 700 ℃ was as high as 440-100 ppm TEA at the operating temperature of 40 ℃. The detection limit was as low as 0.25 ppm. In addition, the gas sensor has good selectivity and stability. The excellent TEA sensitivity is mainly resulted from the appropriate particle size and loose porous framework. This work not only paves the way to explore the novel low temperature TEA gas sensors, but also provides deep insight on improving the structure and properties of gas sensitive materials by controlling the calcination temperature.
Developing the high activity, low cost and robust large-current-density-based electrocatalysts is of great significance for the industrial electrolytic water splitting. However, the current range of most reported materials is small, which makes it difficult for them to play their roles in practical applications. Here, a self-supported amorphous FexNi1-xMoO4/IF treated with ammonium fluoride (AF0.1-FNMO/IF) is synthesized by one-step hydrothermal method. With the help of NH4F, AF0.1-FNMO/IF exhibits a vertically cross-linked nanosheet with spherical structure. Electrochemical measurement shows that AF0.1-FNMO/IF affords a large current density ordeal and only need low overpotentials of 289 and 345 mV to reach a current response of 500 mA/cm2 for oxygen evolution reaction and hydrogen evolution reaction, respectively, together with long-time stability (both at 500, 1000 and 2000 mA/cm2) in 1.0 mol/L KOH solution. Using it as bifunctional catalyst for overall water splitting, the current densities of 100, 500, 1000 and 1500 mA/cm2 are achieved at a cell voltage of 1.71, 1.88, 1.94 and 1.97 V with excellent durability, which is much better than that of most published electrodes. The work provides valuable insight for designing higher activity nickel iron-based molybdate catalysts with large current density.
Exosome and inclusive cargoes have manifested significant function in different biological events. In particular, glycopeptides in exosome are closely associated with occurrence and development of various diseases. Developing advanced tools is highly desired to enrich glycopeptides from exosomes, and enrich exosomes from complex biological samples as well. In this work, integration of L-cysteine and titania onto the surface of magnetic nanoparticles is designed to realize the coefficient affinity towards exosomes and inclusive glycopeptides. Benefiting from the synergistic affinity, we separate exosomes from human urine concentrate directly, which was proved by the detection of three typical antigen markers of exosomes. Furthermore, hardly any exosomes remained on materials after ultrasonication, which confirmed the good capture performance of Fe3O4@TiO2@L-Cys and high release effect of direct lysis. Moreover, 146 glycopeptides corresponding to 77 glycoproteins were successfully identified from captured exosomes. These satisfactory results will inspire more efforts to be devoted to this field and will be extremely helpful to in-depth information excavation of biological markers, especially disease-related ones, through exosomes and inclusive glycopeptides.
Defect-rich, highly porous two-dimensional carbon nanosheets (CNS) have attracted tremendous research interests in catalysis and environmental purification and other fields, because of their unique micromorphology, chemical stability and high specific surface area. Herein, in this work, we report a new solution to synthesize an ultrathin two-dimensional CNS with rich defects and abundant pores via two-step etching the Ti3AlC2 with the help of I2 and NaOH. The CNS thickness, specific surface area and pore volume could be all tunable by adding the amount of I2. And the highest specific surface area and pore volume of the synthesized 2D CNS can be achieved 1134.4 m2/g and 0.80 cm3/g, with a thickness of only 0.64 nm and a yield of 35.9%. When employed as the anodes for lithium-ion batteries, the synthesized CNS anodes exhibit good cycling and rate capabilities. This work provides a novel and facile strategy for synthesizing highly porous and defective 2D carbon materials with good lithium storage properties.
The polysulfide shuttle limits the development of lithium-sulfur (Li-S) batteries with high energy density and long lifespan. Herein, nitrogen doped hollow carbon nanospheres (NHCS) derived from polymerization of dopamine on SiO2 nanospheres are employed to modify the commercial polypropylene/polyethylene/polypropylene tri-layer separators (PP/PE/PP@NHCS). The abundant nitrogen heteroatoms in NHCS exhibit strong chemical adsorption toward polysulfides, which can effectively suppress the lithium polysulfides shuttle and further enhance the utilization of active sulfur. Lithium-sulfur batteries employing the PP/PE/PP@NHCS deliver an initial discharge capacity of 1355 mAh/g and retain high capacity of 921 mAh/g after 100 cycles at 0.2 C. At a high rate of 2 C, the lithium-sulfur batteries exhibit capacity of 461 mAh/g after 1000 cycles with a capacity fading rate of 0.049% per cycle. This work demonstrates that the NHCS coated PP/PE/PP separator is promising for future commercial applications of lithium-sulfur batteries with improved electrochemical performances.
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