Copper-catalyzed amidation of benzoic acids using tetraalkylthiuram disulfides as amine sources

A facile method for the copper-catalyzed synthesis of N-substituted benzamides was explored. In the presence of CuBr and di-tert-butyl peroxide, various N-substituted benzamides were prepared through amidation of benzoic acid by using commercially available and cheap tetraalkylthiuram disulfides as amine sources. With this protocol, a series of 14 N-substituted benzamides were furnished in good to excellent yields. The broad substrate scope and good to excellent yield show its practical synthetic value in organic synthesis.     

Selective electrochemical CO bond cleavage of β-O-4 lignin model compounds mediated by iodide ion

The electrochemically oxidative cleavage of lignin β-O-4 model compounds mediated by iodide ion has been studied. The results indicate that electrolytic conditions play a predominant role in determining the distribution of cleavage products. The preparative-scale electrolysis proceeds in a simple undivided cell, employing a catalytic amount of NaI as the redox mediator and supporting electrolyte in methanol. Under these conditions, the C_βO bond is selectively cleaved with 2,2-dimethoxy-2-arylacetaldehyde being the main product. In some cases, the reaction gives a good yield of cleavaged products. The results further demonstrate that the indirect electrolysis mediated by halide is a versatile approach for chemical transformation.     

Iodine-catalyzed C3-formylation of indoles using hexamethylenetetramine and air

An efficient iodine-catalyzed chemoselective 3-formylation of free (N–H) and N-substituted indoles was achieved by using hexamethylenetetramine (HMTA) in the presence of activated carbon under air atmosphere. This new method could provide 3-formylindoles in moderate to excellent yields with fairly short reaction times. Moreover, this catalytic formylation of indoles procedure can be applied to gram-scale synthesis.     

Bienzyme-based visual and spectrophotometric aptamer assay for quantitation of nanomolar levels of mercury(II)

The article describes a bienzyme visual system for aptamer-based assay of Hg(II) at nanomolar levels. The detection scheme is based on the finding that Hg(II) ions captured by aptamer-functionalized magnetic beads are capable of inhibiting the enzymatic activity of uricase and thus affect the formation of H₂O₂ and the blue product, i.e., oxidized tetramethylbenzidine. This strategy allows for a visual detection of Hg(II) at nanomolar levels without additional amplification procedure. Measuring the absorbance at 650 nm, the logarithmic calibration plot is linear in the concentration range of 0.5–50 nM and the limit of detection (LOD) is 0.15 nM. This is as low as the LOD obtained by atomic fluorescence spectrometry (AFS). The ions K⁺, Mg²⁺, Na⁺, Ca²⁺, Cu²⁺, Zn²⁺, Fe³⁺, Al³⁺, Co²⁺, AsO₂ ^?, Ni²⁺, Cd²⁺ and Pb²⁺ do not have a significant effect on color formation. The method was applied to the analysis of (spiked) river water, lake water, mineral water, tap water and certified reference water samples, and the results agreed well with those obtained by AFS or certified values, with recoveries ranging from 97% to 109%. The relative standard deviation for five parallel detections at a 10 nM Hg(II) level is 5.2%.

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Graphical abstract A bienzyme-based visual aptasensor was fabricated for label-free detection of nanomolar Hg²⁺ in water samples without any amplification or enrichment procedure.

     

A fluorescence based immunoassay for galectin-4 using gold nanoclusters and a composite consisting of glucose oxidase and a metal-organic framework

The authors describe a fluorescence immunoassay for galectin-4, a candidate biomarker for various cancers. Glucose oxidase was encapsulated into a zeolitic imidazolate framework to give a composite (GOx/ZIF-8 composite) that acts as a signal-transduction tag via a biomimetic mineralization process. After modification of the composite with streptavidin, it binds biotinylated antibody against galectin-4. In the immunoassay, the response to galectin-4 results from the enzymatic oxidation of glucose. This reaction produces hydrogen peroxide (H₂O₂) that reacts with iron(II) ions to generate hydroxy radical (?OH), which leads to the quenching of the fluorescence of gold nanoclusters (AuNCs). Accordingly, the fluorescence quenching of AuNCs depends on the concentration of target galectin-4. The GOx/ZIF-8 composite has a high loading capacity for GOx at uncompromised enzymatic activity. The fluorescence of AuNCs is sensitively quenched by ?OH radicals. Galectin-4 can be detected by this method in concentrations as low as 10 pg·mL^?1. It is expected that this kind of enzyme/MOF composite-based immunoassay has a wide scope in that it may be adapted to other low-abundance proteins and biomarkers.

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Graphical abstract Schematic of a fluorescence immunoassay for galectin-4, a candidate biomarker for various cancers. It is based on a composite consisting of glucose oxidase and a metal-organic framework (GOx/ZIF-8 composite) as well as gold nanoclusters (AuNC)-iron(II) system.

     

Solubility and Solution Thermodynamic Properties of 4-(4-Hydroxyphenyl)-2-butanone (Raspberry Ketone) in Different Pure Solvents

The solubility of 4-(4-hydroxyphenyl)-2-butanone (raspberry ketone) in six pure solvents was experimentally determined at temperatures ranging from 283.15 to 313.15 K under the pressure 0.10 MPa by employing a gravimetrical method. The experimental results indicate that the solubility of raspberry ketone in all studied solvents is temperature dependent, a rise in temperature brings about an increase in solubility. The experimental solubility data of raspberry ketone in six pure solvents (acetone, ethanol, ethyl acetate, n-propyl alcohol, n-butyl alcohol, and distilled water) was correlated by using several commonly used thermodynamic models, including the Apelblat, van’t Hoff and λh equations. The results of the error analysis indicate that the van’t Hoff equation was able to give more accurate and reliable predictions of solubility with root-mean-square deviation less than 0.56%. Furthermore, the changes of dissolution enthalpies (Δ_diss H°), dissolution entropies (Δ_diss S°) and dissolution Gibbs energies (Δ_diss G°) of raspberry ketone in the solvents studied were estimated by the van’t Hoff equation. The positive value of Δ_diss H°, Δ_diss S°, and Δ_diss G° indicated that these dissolution processes of raspberry ketone in the solvents studied were all endothermic and enthalpy-driven.     

Fabrication of urchin‐like Ag/ZnO hierarchical nano/microstructures based on galvanic replacement mechanism and their enhanced photocatalytic properties

Urchin‐like Ag/ZnO hierarchical nano/microstructures have been synthesized through a facile low‐temperature hydrothermal growth method based on galvanic replacement mechanism. The experimental results show that the urchin‐like Ag/ZnO heterostructures are formed through the epitaxial growth of ZnO nanorods on the {111} facets of Ag nanoparticles along their own c‐axis. The photocatalytic properties of the products were evaluated by the degradation of RhB dye solution under ultraviolet irradiation, and the results show that the products exhibit significantly enhanced photocatalytic properties comparing with pure ZnO nanorods. The products with a Ag content of 35.64 atom % prepared with a Ag⁺ concentration in solution of 5 mM exhibit surprisingly high degradation rate (99.5%) for RhB dye solution (4 mg/L) after photocatalytic reaction for only 14 min under ultraviolet irradiation. The Schottky barrier formed at the metal‐semiconductor interfaces improves the segregation of charges and prevents the charge recombination, and thus significantly enhances the photocatalytic activities of the products. On the other hand, the high stability of the urchin‐like Ag/ZnO hierarchical nano/microstructures can effectively prevent the aggregation of nanostructures with simultaneously preserving high photocatalytic properties due to the existence of nanosized unites. Copyright © 2016 John Wiley & Sons, Ltd.     

Acid/base controllable self-complexes that mimic flapping butterfly

A new type of self-complexed bis-crown ether containing two bis(p-phenylene)-34-crown-10 (BPP34C10) ether rings and two secondary ammoniums has been synthesized and characterized. The formation of these bis-self-complexes has been identified by NMR spectroscopy, mass spectrometry and X-ray analysis. The acid/base controlled movement of these bis–crown ethers can mimic a flapping butterfly.     

Self-Optimization of the Active Site of Molybdenum Disulfide by an Irreversible Phase Transition during Photocatalytic Hydrogen Evolution

The metallic 1T-MoS₂ has attracted considerable attention as an effective catalyst for hydrogen evolution reactions (HERs). However, the fundamental mechanism about the catalytic activity of 1T-MoS₂ and the associated phase evolution remain elusive and controversial. Herein, we prepared the most stable 1T-MoS₂ by hydrothermal exfoliation of MoS₂ nanosheets vertically rooted into rigid one-dimensional TiO₂ nanofibers. The 1T-MoS₂ can keep highly stable over one year, presenting an ideal model system for investigating the HER catalytic activities as a function of the phase evolution. Both experimental studies and theoretical calculations suggest that 1T phase can be irreversibly transformed into a more active 1T′ phase as true active sites in photocatalytic HERs, resulting in a “catalytic site self-optimization”. Hydrogen atom adsorption is the major driving force for this phase transition.     

Effects of some nucleating agents on the supercooling of erythritol to be applied as phase change material

Nine nucleating agents, calcium pimelate (CaPi), bicyclic [1, 2, 2]heptane di-carboxylate (HPN-68), a commercially obtained aryl amide nucleating agent (TMB-5), calcium salt of hexahydrophthalic acid (HPN-20E), 1,3:2,4-di-p-methylbenzylidene sorbitol (MDBS) and sodium, potassium, magnesium and calcium salt of benzene-1, 3, 5-tricarboxylic acid (Na₃BTC, K₃BTC, Mg₃BTC₂ and Ca₃BTC₂, respectively), were applied to reduce the supercooling of erythritol, and their effects were investigated by cyclic differential scanning calorimetry (DSC). The results revealed that Na₃BTC and K₃BTC could not induce erythritol to crystallize under the experiment condition. MDBS could only make erythritol to crystallize at a temperature slightly higher than that of pure erythritol, and the effect was unstable. Mg₃BTC₂, Ca₃BTC₂ and HPN-68 could induce erythritol to crystallize at relatively high temperature, but the peak temperature of crystallizing (T _{p, cr}) and the phase change enthalpy of crystallizing (Δ_cr H) decreased greatly as the melting–crystallizing cycles increased. HPN-20E-doped erythritol crystallized at a high temperature with the T _{p, cr} of 69.3 °C at the first cycle, but the T _{p, cr} and Δ_cr H varied greatly during the melting–crystallizing cycles. CaPi and TMB-5 could induce erythritol to crystallize at a stable temperature with the T _{p, cr} of about 69 °C and 64 °C, respectively, and with a stable Δ_cr H of about 204 and 185 J g^?1, respectively, in all melting–crystallizing cycles. Hence, CaPi- and TMB-5-doped erythritol could be used as PCMs and applied in thermal energy storage in which the energy was absorbed at a high temperature and released at a lower but stable temperature.