Latest ArticlesDensity functional theory calculations have been performed to investigate the dipeptide phosphine-catalyzed hydroamination of enones with pyridazinones. The computations reveal that a number of the NH···O hydrogen-bonding interactions with the pyridazinone moiety and the C-H···O hydrogen-bonding interactions with the enone moiety are present in the enantioselectivity-determining Michael addition transition states. The experimentally-observed catalyst-controlled enantiodivergence is mainly attributed to the significant impact of the substituent of the amide moiety of the dipeptide phosphine on the relative strength of the NH···O hydrogen-bonding interactions, which was found to affect the Si face attack transition state, enabling the enantioselectivity switch upon change of chiral dipeptide phosphine catalyst.
Supramolecular assemblies constructed through the encapsulation of conductive polymers (CPs) by macrocyclic molecules have attracted increasing interest in the fields of supramolecular chemistry and electrochemistry. In this work, an effective strategy was reported to improve the stability and conductivity of CPs by electrochemically constructing different supramolecular assemblies composed of macrocycles and CPs. Typically, we uploaded zinc-based MOF (ZIF-8) onto carbon nanotube film (CNTF) and further electrically deposited macrocycles and CPs to gain the flexible conductive electrodes. Herein, five different supramolecular macrocycles, including α-cyclodextrin (α-CD), sulfato-β-cyclodextrin (SCD), sulfonatocalix[4]arene (SC[4]), cucurbit[6]uril (CB[6]) and cucurbit[7]uril (CB[7]) were utilized and the electrochemical performances of the assembly electrodes increased in an order of α-CD < SCD < SC[4] < CB[6] < CB[7], significantly improving the areal capacitance up to 1533 mF/cm2. This strategy may provide a new way for the application of macrocyclic supramolecules in electrochemical systems.
The analysis of endogenous glycoproteins and glycopeptides in human body fluids is of great importance for screening and discovering disease biomarkers with clinical significance. However, the presence of interfering substances makes the direct quantitative detection of low-abundance glycoproteins and glycopeptides in human body fluids one of the great challenges in analytical chemistry. Magnetic solid phase extraction (MSPE) has the advantages of easy preparation, low cost and good magnetic responsiveness. Magnetic adsorbents are the core of MSPE technology, and magnetic adsorbents based on different functional materials are widely used in the quantitative analysis of glycoproteins and glycopeptides in human body fluids, making it possible to analyze glycoproteins and glycopeptides with low abundance as well as multiple types, which provides a technical platform for screening and evaluating glycoproteins and glycopeptides in body fluids as disease biomarkers. In this paper, we focus on the recent advances in the application of MSPE technology and magnetic adsorbents for the separation and enrichment of glycoproteins and glycopeptides in human body fluids, and the future trends and application prospects in this field are also presented.
We report a Pd-catalyzed halocyclization of unactivated 1, 6-diynes with N-bromosuccinimide (NBS). This approach produces stereo-defined dibromo substituted dihydropyrans, tetrahydropyridines, and 3-methylene cyclohexenes with exocyclic double bond appendages in mostly good yields. Copper salt was found to be a useful Lewis acid in this reaction. Mechanistically, a formal anti-carbopalladation and a bromide radical promoted PdII-PdIII-PdI-PdII catalytic cycles were proposed to be involved in the formation of the dibromo-substituted products. Further functionalization of the dihydropyran derivatives underwent B(C6F5)3-catalyzed ring opening, and reduction afforded dibrominated 1, 3-dienes with excellent stereoselectivity.
The aerobic, selective oxidation of hydrocarbons via C-H bond activation is still a challenge. This work shows the achievement of the room temperature visible light driven photocatalytic activation of benzylic C-H bonds with N-hydroxysuccinimide over BiOBrxI1-x (0 ≤ x ≤ 1) solid solutions, whose valance bands were engineered through varying the ratio of bromide to iodide. The optimal BiOBr0.85I0.15 catalyst exhibited over 98% conversion ratio of ethylbenzene, which was about 3.9 and 8.9 times that of pure BiOBr and BiOI, respectively. The excellent photocatalytic activity of BiOBr0.85I0.15 solid solution can be ascribed to the orbital hybridization of the valence band containing both Br 4p and I 5p orbitals, which could promote photo-induced charge carrier separation and improve the generation of singlet oxygen. This work shed some light on the rational design of photocatalysts for targeted organic transformation.
Zinc metal has aroused increasing interest as anode material of Zn-based batteries for their energy storage application. However, the uneven Zn stripping/plating processes induce severe dendrite growth, leading to low Coulombic efficiency and safety hazards. Herein, a surface-tuned two-dimensional (2D) MXene Ti3C2T scaffold as a robust skeleton is developed to facilitate the uniform Zn stripping/plating. The Ti3C2T with high electrical conductivity and unique structure provides fast ionic-transport paths, promising even Zn2+ stripping/plating processes. With suppressed Zn dendrite growth and uniform nucleation, the proposed 2D Ti3C2T scaffold for Zn metal anode delivers a low voltage hysteresis of 63 mV and long lifespan over 280 h. This surface-tuned engineering strategy demonstrates the potential application of Zn anode with MXene skeleton for next-generation Zn-based batteries.
We report the fabrication of highly ordered Nb2O5 nanochannel film (Nb2O5-NCF) onto niobium foil by an anodization method. After thermal treatment, the obtained Nb2O5-NCF with rich oxygen vacancies exhibits electrochemical N2 reduction reaction (NRR) activity with an NH3 yield rate of 2.52×10−10 mol cm-2 s-1 and a faradaic efficiency of 9.81% at −0.4 V (vs. RHE) in 0.1 mol/L Na2SO4 electrolyte (pH 3.2). During electrocatalytic NRR, the Nb2O5-NCF takes place electrochromism (EC), along with a crystalline phase transformation from pseudo hexagonal phase to hexagonal phase owing to H+ insertion. This results in the reduced NRR activity due to the decrease of oxygen vacancies of hexagonal phase Nb2O5, which can be readily regenerated by low-temperature thermal treatment or applying an anodic potential, showing superior recycling reproducibility.
More and more attentions have been focused on design and synthesis of novel metal-organic framework/graphene oxide (MOF/GO) composites with unique performance. Zirconium-porphyrin MOF (PCN-222) is in-situ synthesis with the existence of GO with −COOH group to artfully fabricate a PCN-222/GO composite. This composite can be employed as functional material to modify the working electrode. Thanks to excellent electrical conductivity of GO, abundant mesoporous channels and numerous Zr(Ⅳ) metal sites of PCN-222, this composite can immobilize a large amount of aptamer through strong π-π stacking interaction and high affinity between phosphate group of aptamer and Zr(Ⅳ) site of PCN-222 simultaneously. Hence, an ultra-sensitive electrochemical aptasensor based on PCN-222/GO composite can quantificationally detect trace chloramphenicol with limit of detection of 7.04 pg/mL (21.79 pmol/L) from 0.01 ng/mL to 50 ng/mL by electrochemical impedance spectroscopy even in real samples. Meanwhile, this fabricated aptasensor reveals good repeatability, outstanding selectivity and preferable long-term storage. This research provides a useful approach to construct MOF/GO composites for fabricating electrochemical aptasensors in the electrochemical detection field.
To prevent polysulfides from dissolution into electrolyte, we propose a novel and simple approach to nitrogen-doped carbon foams which contain hierarchically porous structure and are decorated with zinc nanodots through one-pot carbonization and activation process. These carbon foams, which serve as hosts for sulfur in lithium battery, can provide a conducting network and shorter diffusion length for Li-ions. Specially, the zinc nanodots derived from the carbothermal reaction of ZnCl2 at high temperature can interact with sulfur/polysulfides by strong chemisorption. In addition, the zinc nanodots can also facilitate the conversion reaction between Li2Sx (2 < x < 8) and Li2S/Li2S2. Therefore, Zn@NCFs/S cathode presents high sulfur utility and large capacity.
To achieve an efficient photocatalytic for clean energy production and environmental remediation, the highly active Fe-doped and terephthalaldehyde-modified carbon nitride (Fe-CN/NTE) isotypic heterojunction photocatalyst is constructed via a simple annealing method for degradation of organic pollutants with simultaneous resource recovery. The Fe-CN/NTE catalyst exhibits a 93% removal rate of p-nitrophenol (4-NP) and a 1.72 mmol/g H2 evolution rate in 2 h simultaneously under visible light irradiation, which are higher than those of pristine CN, Fe-CN, and NTE, respectively. Photoelectrochemical tests show that the excellent photocatalytic performance of Fe-CN/NTE comes from the improved migration, transportation, and separation of photoinduced charge carriers and expanded light-harvesting range. Moreover, hydroxyl radical (OH), electron (e−), and hole (h+) are the main active species and the rational mechanism of 4-NP photodegradation was proposed based on scavenger measurements and liquid chromatography-mass spectrometry (LC-MS), respectively. Isotypic heterojunction Fe-CN/NTE photocatalyst possesses excellent stability in the H2 evolution and 4-NP degradation during five-run cycle tests, posing as a promising candidate in practical works for organic pollution and energy challenges.
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