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A molecularly imprinted electrochemical sensor was designed for the quantitative and efficient detection of melatonin (MT) based on a CuxO/MXene modified screen-printed carbon electrode (MIP/CuxO/MXene/SPCE). Herein, the CuxO/MXene nanocomposite was prepared via a hydrothermal method. The CuxO was uniformly dispersed on the surface and the interlayers of the MXene, forming hybrid heterostructures. The encapsulated CuxO increased the interlayer distance of the MXene matrix to bring more active sites and accelerated the oxidation reaction of melatonin molecules, and thereby the electrochemical response of the sensor was improved. The MIP was constructed by electropolymerization of o-phenylenediamine (o-PD) in the presence of MT on the surface of the CuxO/MXene/SPCE. The morphology and chemical composition of the hybrid film were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy; the electrochemical behaviors of the sensor were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimal conditions, the MIP/CuxO/MXene/SPCE sensor had a wide linear detection range of 5–700 μM and a low detection limit of 0.029 μM (S/N = 3) for MT. The sensor also showed excellent selectivity, reproducibility, and stability. Finally, it was successfully applied for MT detection in human urine with satisfactory recovery. Overall, this study provided a sensitive and efficient strategy for the determination of MT. [ABSTRACT FROM AUTHOR]

Narrow bandgap semiconductor CdS demonstrates promising photocatalytic ability for water splitting under visible light response. However, the inherent photocorrosion and high recombination rate of electron–hole pairs constrain its wide application. Here, highly stable ZnS nanoparticles were coated onto CdS nanorods to form Cd/Zn-based composite photocatalysts. The Cd/Zn-based composite photocatalysts demonstrate enhanced specific area and conductivity, reduced photocorrosion, prolonged lifetime of photogenerated electrons, and countless heterojunction structures. The fabricated Cd/Zn-3 composite photocatalyst demonstrates an optimal thickness of the ZnS coating on CdS, which delivers 7.3 mA cm–2 photocurrent density, 1.1 mmol g–1 h–1 H2 production rate, and remarkable long-term stability under solar light irradiation. [ABSTRACT FROM AUTHOR]

A novel KO'-Bu-promoted three-component coupling reaction of aldehydes and alkynes without a transition-metal catalyst is developed. This tandem protocol represents an extremely concise, practical, and economical synthesis of (E)-1-en-4-yn-3-ols and (Z)-2-en-4-yn-1-ols, which are of versatile utilities in organic synthesis.

The catalytic enantioselective synthesis of all-carbon quaternary stereogenic centers in spirocyclic diketones is described. The synthesis included rearrangement an unprecedented asymmetric vinylogous [alpha]-ketol in which an enantiocontrolled semipinacol-type 1,2-carbon migration is realized using multifunctional cinchona-modified primary amine catalysis.

An efficient method is developed for aza-quaternary pyrrolo[1,2-a]azepine and aza-quaternary indolizine, as the key intermediates for syntheses of stemonamine and cephalotaxine, based on the key intramolecular Schmidt reaction of symmetric azido-diones.

A new Rh-catalyzed/Lewis acid-promoted C-C bond formation with olefins via sp3 C-H activation of aliphatic alcohols, which can be simply performed in good yields without the need to sacrifice any extra functional groups is developed. The experimental results are proposed which involved the Lewis acid-promoted direct C-H bond activation of alcohol by a Rh(I) species.

With the goal of achieving highly efficient palladium-catalyzed cross-coupling reactions under mild reaction conditions, the Pd-PEPPSI complexes C1 and C2 bearing 1,2-di(tert-butyl)acenaphthyl (DtBu-An) backbones were synthesized and characterized, and their use in Suzuki-Miyaura cross-coupling was investigated. The effects of catalyst structure and reaction conditions on the cross-coupling efficiency were evaluated in detail. The significant differences in catalytic activity compared with classical PEPPSI-IPr and PEPPSI-IPrAn precatalysts are discussed, where the axial sterics on the backbone play an important role. At low palladium loadings of 0.05-0.1 mol % and upon the addition of the relatively weak base K3PO4, the palladium complex C1 was found to be highly efficient for the coupling of (hetero)aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in excellent yields. [ABSTRACT FROM AUTHOR]

Electronic coupling across a bridging ligand between a chromophore and a catalyst center has an important influence on biological and synthetic photocatalytic processes. Structural and associated electronic modifications of ligands may improve the efficiency of photocatalytic transformations of organic substrates. Two ruthenium-based supramolecular assemblies based on a chromophore-catalyst dyad containing a Ru-aqua complex and its chloro form as the catalytic components were synthesized and structurally characterized, and their spectroscopic and electrochemical properties were investigated. Under visible light irradiation and in the presence of [Co(NH3)5Cl]Cl2 as a sacrificial electron acceptor, both complexes exhibited good photocatalytic activity toward oxidation of sulfide into the corresponding sulfoxide with high efficiency and >99% product selectivity in neutral aqueous solution. The Ru-aqua complex assembly was more efficient than the chloro complex. Isotopic labeling experiments using 18O-labeled water demonstrated the oxygen atom transfer from the water to the organic substrate, likely through the formation of an active intermediate, Ru(IV)-O. [ABSTRACT FROM AUTHOR]

NH4HF2 has been used for the first time to selectively remove the TBS protecting groups from diol ketone precursors in the synthesis of highly functionalized spiroketals. This method allows the synthesis of [5,6], [6,6], and [6,7] spiroketal skeletons, as well as benzannulated spiroketal with retention of acid-sensitive groups. In this way, spiroketals can be synthesized with diverse substituent groups in the skeleton or on side chains. To demonstrate the utility of this methodology, the diverse transformations of highly functionalized spiroketal 3f were also investigated. [ABSTRACT FROM AUTHOR]

The hollow Co3O4 microspheres were prepared by a gas--liquid diffusion reaction in the presence of ionic liquid [Bmim] [BF4] in combination with calcination at 300 °C. Their structures and morphologies were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. The growth mechanism of hollow Co3O4 microspheres was proposed. The ethanol sensing properties were measured using a WS-30A gas sensor measurement system. The influence of working temperatures, ethanol concentrations, and specific surface areas of Co3O4 microspheres on the ethanol sensing properties was investigated. The hollow Co3O4 microspheres showed excellent sensitivity to ethanol vapor at a lower operating temperature. [ABSTRACT FROM AUTHOR]

Placing metallic nanoparticles inside cavities, rather than in dimers, greatly improves their plasmonic response. Such particle-in-cavity (PIC) hybrid architectures are shown to produce extremely strong field enhancement at the particle−cavity junctions, arising from the cascaded focusing of large optical cross sections into small gaps. These simply constructed PIC structures produce the strongest field enhancement for coupled nanoparticles, up to 90% stronger than for a dimer. The coupling is found to follow a universal power law with particle−surface separation, both for field enhancements and resonant wavelength shifts. Significantly enhanced Raman signals are experimentally observed for molecules adsorbed in such PIC structures, in quantitive agreement with theoretical calculations. PIC architectures may have important implications in many applications, such as reliable single molecule sensing and light harvesting in plasmonic photovoltaic devices. [ABSTRACT FROM AUTHOR]